Abedi, K.,
Seraj, H.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J.,
Sahmani, S. Publication Date: 2026
Composites Science and Technology (02663538)274
The viscoelastic damping behavior of carbon nanotube (CNT)/polymer nanocomposites is investigated using a 3D numerical micromechanical model based on the finite element method (FEM) and a complex modulus approach. This model uniquely considers the collective behavior and interactions of multiple, randomly or directionally aligned CNTs within a representative volume element (RVE). To account for the frictional energy dissipation at the interface, a thin, weakened, and lossy interphase is simulated around the CNTs. The computational framework is validated by comparing its predictions for the elastic, viscoelastic creep, and damping properties with existing experimental data. Furthermore, the model is used to perform a sensitivity analysis, exploring the influence of key nanostructural parameters on the effective loss factor of the nanocomposite. The results show that the effective loss factor is significantly enhanced by increasing the CNT volume fraction, a finding directly linked to the greater presence of the lossy interphase. Damping also increases with a thicker interphase and a higher relative loss factor of the interphase. The CNT aspect ratio is shown to have a notable effect, influencing the maximum damping achievable at a specific volume fraction. Finally, for aligned nanofillers, the study reveals a strong dependency of the directional loss factors on the CNT off-axis angle. © 2025 Elsevier Ltd.
Dastgir, N.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J.,
Sahmani, S. Publication Date: 2026
European Journal of Mechanics, A/Solids (09977538)116
This study investigates the vibration-based energy harvesting performance of four widely used beam configurations: unimorph, bimorph, trimorph, and sandwich beams, all subjected to identical boundary conditions. Each beam model consists of the aluminum substrate integrated with the piezocomposite layer consisting of piezoelectric ellipsoidal particles embedded within a PVDF matrix. The effective electromechanical properties of the piezocomposite are estimated using the Mori–Tanaka micromechanical scheme. For this purpose, the Mikata approach is employed to compute the Eshelby tensor enabling the micromechanical model to accommodate various matrix types, including general orthotropic materials. Furthermore, this micromechanics-based method allows for considering piezoelectric fillers of diverse geometries. Next, the vibrational energy harvesting of four cantilever-type beams is evaluated using the finite element simulation in COMSOL Multiphysics. To verify the validity of the present modeling technique, comparison studies with the available literature are performed. Parametric studies are conducted to investigate the influence of volume fraction and aspect ratio of piezoelectric fillers, configuration and detailed geometries of harvesters on the resonant frequency, output voltage, and electrical power generation under base excitation. It is observed that increasing the piezoelectric filler percentage in unimorph and bimorph beams leads to an improvement in their harvesting performance. Also, higher aspect ratios of piezoelectric fillers enhance the output voltage of harvesting systems. © 2025 Elsevier Masson SAS
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S.,
Jamali, J.,
Jang, S. Publication Date: 2026
Colloids and Surfaces A: Physicochemical and Engineering Aspects (18734359)728
Highly sensitive thermoresistive composites offer significant potential for mitigating overheating in electronic devices. While adding nanoparticles can enhance nanocomposite properties, hybrid nanoparticles may further improve piezoresistivity. This study introduces a novel modeling framework that examines the quantum tunneling behavior of carbon nanotube (CNT) and carbon nanoparticle (CNP)-filled nanocomposites using a Monte Carlo conductive network approach. Unlike previous models, this multistep percolation scheme captures synergistic inter-filler spacing effects and dynamically recalculates tunneling resistance based on CNT–CNP interactions. The temperature-sensitive response is modeled through junctions transitioning from hopping conduction to thermally activated tunneling. Additionally, the effect of conduction modes on thermoresistivity is evaluated for different volume fractions of CNTs and CNPs. Results indicate that resistance decreases with rising temperature in CNT nanocomposites, primarily due to thermal activation of hopping conduction. Furthermore, subbands play a key role in piezoresistivity by affecting strain-dependent conductivity changes, an effect more pronounced in nanocomposites with fewer stable conductive pathways, where electron scattering increases as subbands diminish. © 2025 Elsevier B.V.
Sahmani, S.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Zareichian, M. Publication Date: 2026
Computers and Structures (00457949)321
The main intention of the proposed multiscale framework is to employ an isogeometric analysis formulation for the size-dependent nonlinear planar instability analysis of dual-phase nanocomposite shallow curved beams at the microscale. A finite element–based micromechanics model is developed at the representative volume element level to capture the material properties. The homogenized properties obtained from the representative volume element-level finite element analysis are directly incorporated into the isogeometric model. This coupling enables accurate surveying of the small scale-dependent nonlinear in-plane stability characteristics of uniformly laterally loaded dual-phase inhomogeneous shallow curved microbeams reinforced with SiO2 nanoparticles and graphene nanoplatelets, while embracing distinct strain gradient tensors. In this regard, cuboid-shaped representative volume elements are employed. This enables consideration of the interphase between the dual-phase nanofillers and the polymer, as well as the critical role of nanofiller agglomeration, in order to create an accurate multiscale correlation. Additionally, non-uniform rational B-splines are utilized in the relevant discretization process. This process involves distinct microstructural-dependent strain gradient tensors. The numerical results reveal that increasing the SiO2 nanoparticle volume fraction significantly enhances both the upper and lower limit loads by nearly 69.5%. This increase does not markedly affect the axial resultant load or the lateral deflection. Conversely, increasing the SiO2 nanoparticle diameter at a fixed volume fraction notably decreases the load-bearing capacity by about 49.5%. Similarly, a rise in graphene nanoplatelet thickness leads to an approximately 61.1% reduction in the stability limits. The inclusion of the interphase region between the nanofillers and the matrix improves the upper and lower limit loads by around 17.4%, demonstrating its reinforcing influence. Furthermore, aligning nanofillers along the beam's longitudinal direction increases the limit loads by roughly 48.1% compared to the random dispersion case. In contrast, agglomeration has the opposite effect, reducing the load-carrying capacity by about 12.4%. © 2025 Elsevier Ltd
Khorrami a., A.,
Golshani, A.,
Hassani, F.,
Kouhkord, A.,
Ansari, R.,
Sahmani, S. Publication Date: 2026
Renewable Energy (09601481)257
Thermal management remains a critical challenge in photovoltaic/thermal (PV/T) systems, as excessive heat buildup adversely affects electrical efficiency and system longevity. This study introduces a novel optimization framework for enhancing heat transfer in water-based PV/T systems through strategically designed circular baffles. Unlike previous studies that employed simple geometric variations, we develop a comprehensive methodology integrating computational fluid dynamics with Response Surface Methodology and Multi-Objective Particle Swarm Optimization to systematically analyze baffle angle (60°–360°), outer radius (12–22 mm), and Reynolds number (100–800) effects. Our approach reveals that increasing baffle angle to 360° enhances the Nusselt number ratio by 8.2 % through the generation of organized secondary vortices, while elevating Reynolds number to 800 boosts heat transfer by 617 %. The developed surrogate models achieve exceptional predictive accuracy (R2 > 0.96), enabling rapid design optimization. The optimization identifies configurations that balance thermal enhancement with hydraulic penalties, with Run 12 (Re = 450) achieving a Performance Evaluation Criterion of 1.02, representing a 6.4 % thermal improvement with manageable flow resistance. This work provides a validated, systematic framework for optimizing baffled PV/T systems, offering practical design guidelines for enhanced solar energy harvesting. © 2025 Elsevier Ltd
Nikparsa, A.,
Eghbalian, M.,
Ansari, R.,
Sahmani, S.,
Postek, E. Publication Date: 2026
Chemical Physics Letters (00092614)885
18-6-Graphdiyne (18-6-GDY) and C18N6 are low-density carbon-based nanomaterials with notable mechanical adaptability. Using molecular dynamics simulations, this study examines how random hydrogen functionalization affects their anisotropic mechanical behavior under uniaxial tension. Increasing hydrogen coverage from 2.5 % to 10 % degrades mechanical performance in both materials. The X-direction tensile strength of 18-6-GDY decreases from 28.8 to 19.0 GPa, while C18N6 shows a more pronounced reduction. Direction-dependent declines in Young's modulus and toughness highlight the combined influence of nitrogen substitution, hydrogen coverage, and lattice orientation. Copyright © 2024. Published by Elsevier B.V.
Kalashami, E.R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J.,
Sahmani, S. Publication Date: 2026
International Communications in Heat and Mass Transfer (07351933)171
The main purpose of this work is to establish a multiscale finite element modeling approach to evaluate thermal conductivities of polymer composites reinforced by both nanoparticles and microfibers. The hybrid material includes a polyethylene matrix, copper nanoparticles, nanoparticle/polymer interphase, and short glass microfibers. Initially, a nanoscale representative volume element in which nanoparticles are randomly distributed within polyethylene is generated. Then, a microscale representative volume element is constructed in which aligned glass fibers are embedded in the nanoparticle-filled polymer as the host material. The proposed modeling approach is validated against existing literature. Influences of the interphase region and variation in its thickness and thermal conductivity, spherical and cylindrical shape of nanoparticles, aspect ratio and volume fraction of both nano- and micro-scale reinforcements as well as the nanoparticle agglomeration on the longitudinal and transverse thermal conductivities of polymer composites are examined. It is found that the inclusion of copper nanoparticles into the polymer matrix results in an enhancement of thermal conductivities of glass fiber/polyethylene composites. Increasing the nanoparticle aspect ratio improves the hybrid composite thermal properties, whereas agglomeration of nanoparticles reduces thermal performance due to localized inhomogeneity and disrupted conduction pathways. In addition, interphase characteristics are identified as critical factors governing the heat transfer efficiency of nanoparticle/glass fiber/polyethylene composites. The findings provide valuable insights for designing lightweight, thermally efficient materials applicable in electronic packaging, heat exchangers, and thermal interface systems. © 2025 Elsevier Ltd
Gholami, R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2026
Communications in Nonlinear Science and Numerical Simulation (10075704)153
In this paper, the nonlinear postbuckling behavior of high-order shear deformable polymer nanocomposite annular-sector plates containing carbon nanotube (CNT)/silica nanoparticle (SiO2) hybrid nanofillers is investigated. The study employs a hierarchical approach by integrating finite element micromechanical modeling to determine the effective material properties of ternary CNT/SiO2/polymer nanocomposites, along with a geometrically nonlinear plate formulation incorporating von Kármán-type nonlinear strain-displacement relations. The governing equations are derived and numerically solved using the variational differential quadrature (VDQ) scheme to evaluate the critical buckling loads as well as postbuckling equilibrium paths under in-plane compressive loading. Key parameters such as the content, geometry, and dispersion pattern of nanofillers, nanofiller/polymer interphase effects, and boundary constraints are systematically studied. Results reveal that the addition of nanofillers enhances the critical buckling load and postbuckling stability, with higher CNT aspect ratios, smaller SiO2 diameters, and aligned dispersion pattern showing superior performance. Moreover, the destructive effects of nanofiller agglomeration can be mitigated by breaking up the agglomerates, and the formation of robust interphase regions between the nanofillers and polymer further improves load-bearing capacity and stability. Boundary conditions play an important role in affecting the structural response, with fully clamped edges demonstrating the maximum load-bearing capacity and simply supported edges the lowest. © 2025 Elsevier B.V.
Kalashami, E.R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S.,
Jamali, J. Publication Date: 2026
Computational Materials Science (09270256)261
This study numerically investigates mechanical and thermal properties of polypropylene/montmorillonite (MMT) clay nanocomposites, focusing on Young's modulus, thermal expansion coefficient (TEC), and thermal conductivity. A three-phase representative volume element (RVE) with periodic boundary conditions (PBCs), incorporating polypropylene matrix, MMT clay nanoplatelets and an interphase, is employed to conduct micromechanics-based finite element simulations. The interphase, modeled with variable characteristics, represents the interaction zone between the matrix and nanofillers. The MMT clay nanoplatelets are dispersed randomly, aligned and agglomerated within the polypropylene matrix, with their aspect ratio and volume fraction systematically changed to investigate the microstructural influences on the nanocomposite's properties. Uniform dispersing MMT clay nanoplatelets into the polypropylene matrix is found to improve the elastic modulus, TEC and thermal conductivity of resulting nanocomposites. However, the nanofiller agglomeration leads to localized stress concentrations, potentially reducing mechanical properties, and introduces thermal barriers that can lower overall thermal conductivities. Results show that alignment of MMT clay nanoplatelets within the polypropylene matrix can be useful from the structural point of view because the nanocomposite gives higher material performances in the longitudinal direction as compared to other states. Higher aspect ratios, where nanoplatelets are aligned, lead to more improvements in the nanocomposite longitudinal properties. Comparisons reveal a good agreement between present numerical results and existing data in the literature. © 2025 Elsevier B.V.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J.,
Sahmani, S.,
Jang, S. Publication Date: 2026
Composites Part A: Applied Science and Manufacturing (1359835X)202
A ternary carbon nanotube (CNT) carbon black (CB) nanocomposite is analyzed studying the synergistic effect between CNT and CB on electrical conductivity. The assessment of the thermoresistivity and piezoresistivity of the nanocomposite with dispersed nanofillers of different diameters and conductivity ranges is investigated. By considering CBs with CNTs in the developed network model, Monte Carlo simulation results correlate well with experimental data. The effects of barrier height, aspect ratio and transverse mode are investigated. To guarantee the convergence of piezoresistivity, the number of CNTs was selected larger than a threshold amount, and this enforced a modified calculation scheme using parallel rows of series resistors formed through conductors. Results indicate that the electrical resistance decreased with increased temperature with higher temperature coefficient of resistance producing more prominent drops in comparison with the polymer thermal expansion minor effect. On this basis, the center mechanism about improving the electrical properties of the composite were high intrinsic conductivity and large aspect ratio CNTs selected with small concentrations of CB nanoparticles. The results demonstrate that increasing the number of transverse modes enhances thermoresistivity by modifying tunneling resistance. © 2025 Elsevier Ltd.
Hassani, F.,
Golshani, A.,
Kouhkord, A.,
Ansari, R.,
Sahmani, S. Publication Date: 2026
Expert Systems with Applications (09574174)297
An integrated pumping module is a crucial component in lab-on-a-chip (LOC) and organ-on-a-chip (OoC) devices, as it enables fluid transport and control for biomedical assays. In this study, an acoustomicrofluidic pump is proposed as a compact and integrable solution compatible with LOC platforms. The reference structure of the micropump is initially parameterized, and a design is established based on two primary variables: the inclination angle of the sharp-edge structures and the applied peak-to-peak voltage. Merits of performance were considered to be pumping rate and Maximum shear stress, latter of which is proposed as an objective function to assess acoustic micropump bio-compatibility. To analyze the functional behavior of the system, a surrogate model is constructed using a face-centered central composite design (CCD), enabling predictive assessment of the objective functions under different design configurations. It is demonstrated that by decreasing the inclination angle from its maximum to minimum value, the pumping rate increases by more than 79%, and maximum shear stress is decreased by more than 95%. Surrogate predictive model is then utilized within a Particle Swarm Optimization (PSO) algorithm to identify optimal design parameters. The resulting optimized designs exhibit an enhancement in system efficiency more than 68% compared to the reference configuration. This modeling and optimization methodology enables effective tuning of the acoustomicrofluidic pump's performance for adapting the system to application-specific requirements. Potential biomedical uses of the optimized device include on-chip cell lysis and biofilm analysis, along with bio-nanoparticle synthesis, where controlled and efficient microfluidic pumping is essential. © 2025 Elsevier Ltd
Publication Date: 2025
Acta Mechanica (16196937)
This paper develops a finite element method (FEM) to study the dynamic behavior of two-dimensional (2D) micromorphic thermo-hyperelastic solids with finite deformations. For this purpose, a two-point formulation is derived using energy functions including mechanical, thermal and coupling (due to thermal expansion) between thermal and mechanical parts. The vector–matrix representation of this formulation is also given which can be exploited in the coding procedure of numerical methods. FEM, utilizing the Newton–Raphson and Newmark techniques, has been employed to solve nonlinear time-dependent micromorphic thermo-hyperelastic governing equations. Some test problems are solved to demonstrate the accuracy and reliability of the approach. Furthermore, the influences of internal length parameter, thermal expansion and heat flux on the dynamic behavior of the micromorphic thermo-hyperelastic structures are examined. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.
Publication Date: 2025
International Journal of Non-Linear Mechanics (00207462)174
The purpose of this article is to introduce a novel finite element (FE) approach for investigating the large deformations of three-dimensional (3D) micromorphic hyperelastic continua that have an arbitrary geometry. The 3D micromorphic hyperelasticity formulation is initially presented in a general form. To facilitate the procedure of coding, the vector-matrix counterparts of the aforementioned relations are also provided, which can be conveniently employed in numerical methods. Afterwards, an FE approach is implemented to investigate the large deformations of micromorphic hyperelastic structures under static loading. This is achieved via the user element (UEL) subroutine utilized by the commercial ABAQUS software. Problems with complex domains can be solved using this FE approach. Solving some test problems, including bending of a beam, Cook's membrane under bending load, a cracked spherical shell under external pressure point load and a cracked cylindrical shell under stretching load, demonstrates the fast convergence rate, simple implementation, accuracy and efficiency of the method. In addition, the influences of internal length and scale-transition parameters and geometrical properties on the finite deformation of considered micromorphic hyperelastic structures are evaluated. © 2025 Elsevier Ltd
Publication Date: 2025
International Journal for Numerical Methods in Engineering (00295981)126(22)
This article presents a comparative study of the computational characteristics of Finite Element Analysis (FEA) and Isogeometric Analysis (IGA) in studying large elastic deformations and large-amplitude vibrations of shell-type structures. A geometrically nonlinear seven-parameter shell model is employed in a Lagrangian description in which the shell deformation is represented in mid-surface. Using a curvilinear coordinate system suitable for various geometries, the kinematic and kinetic of the problem are established, and Hamilton's principle is applied to derive the governing equations. The strain–displacement relationships and consequently, the remaining variational formulations are expressed in a matrix-vector form, allowing for direct implementation in both FEA and IGA. This efficient formulation enables a fair and consistent comparison between the two methods. Several numerical examples are examined, including the well-known static benchmark problems and their corresponding forced vibration analyses. The primary contribution of this article is the demonstration of the computational efficiency of isogeometric analysis in challenging case studies of geometrically nonlinear shells. Additional novel contributions include deriving a unified formulation for seven-parameter FEA and IGA shell models as well as analyzing the large-amplitude free and forced vibrations of shells. © 2025 John Wiley & Sons Ltd.
Dastgir, N.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Journal of Vibration Engineering and Technologies (25233920)13(5)
Purpose: The engineering design of vibrational energy harvesters consisting of piezocomposites is generally a challenging task because of various parameters involved at micro- and macro-scales. This paper aims to comprehensively evaluate vibration energy harvesting from a clamped-free bimorph beam with two layers of particulate piezocomposites. Methods: In this study, a multi-phase computational approach is employed to address the vibration energy harvesting using clamp-free piezocomposite bimorph beams. Two types of piezocomposites are examined, featuring LaRC-SI polyamide as the matrix and BaTiO₃ and PZT-7A as piezoelectric fillers. Using the micromechanical finite element method, electromechanical properties of the representative volume element (RVE) of the piezocomposites are predicted. The parametric studies are conducted to predict and compare output voltage and power, considering factors such as the volume fraction, geometry and type of piezoelectric filler, the series or parallel configuration of the circuit. The mode shapes and natural frequencies under structural weight are also analyzed. Results and Conclusion: The results reveal that increasing the volume fraction of piezoelectric fillers enhances electromechanical properties, leading to higher voltage and power output. Bimorph beams are shown to extract more electrical outputs compared to unimorph beams of the same piezocomposite characteristics. Additionally, a parallel circuit connection of the piezocomposite layers in a bimorph beam enhances the electrical outputs compared to a series connection. It is found that the output voltage and power are significantly increased as the piezoelectric filler aspect ratio increases. The frequency related to the peak voltage and power increases as the fillers’ geometry deviates more from spherical shape. © Springer Nature Singapore Pte Ltd. 2025.
Alidoust, A.,
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S. Publication Date: 2025
Composites Part A: Applied Science and Manufacturing (1359835X)191
The piezoresistive sensitivity of aligned carbon nanotube (CNT)-elastomeric nanocomposites is investigated using a mapped conductive network model on finite element simulation. The study aims to investigate the sensor's geometrical parameters, including shape and thickness, to enhance sensitivity under compressive load for applications requiring accurate pressure measurements. Substrates with different thicknesses and shapes are compressed to obtain the most efficient sensor structure including square, rectangular, and circular diaphragms. The developed strain field in the sensor as a result of indenter penetrating or uniform compressive pressure leads to the resistance change. The pertained resistivity to each maximum principal strain state is used directly from the conductive network model. The results disclose a good agreement with experimental data denoting improved sensitivity through bending of thinner sensors with square substrate. Results also reveal a decreased sensitivity for the rectangular indented substrates compared square substrates caused by more concentrated strain distribution during square substrate indentation. © 2025 Elsevier Ltd
Publication Date: 2025
Measurement and Control (United Kingdom) (00202940)58(5)pp. 682-695
This article is aimed to propose a simple yet efficient unified numerical strategy for solving both linear and non-linear optimal control problems. To do so, the general form of quadratic performance index function and nonlinear state equations are considered first. Then, the idea of variational differential quadrature method is used to convert the integral/differential equations to the equivalent algebraic form. Since time is the only independent variable is this research, the finite difference method with an equally-spaced discretization scheme would be a more appropriate technique rather than the differential quadrature approach. So, the implemented numerical solution is called now as the variational finite difference method. The method of Lagrange multipliers is then utilized for minimization purpose and, as a result, the final set of nonlinear algebraic equations are obtained. Finally, the quadratic and triadic forms of non-linearity are considered and an explicit formulation is represented for the residual and Jacobian of the Newton-based iterative solution procedure. To demonstrate the accuracy and efficiency of the proposed approach in the quadratic optimal control area, several benchmark problems involving linear time-invariant, linear time-variant and nonlinear examples are successfully solved and the results are confirmed with those existed in the literature. © The Author(s) 2024.
Publication Date: 2025
Journal of Materials Research and Technology (22387854)34pp. 2909-2918
The performance of polymer-based micro-electronic systems can be evolved by introducing hybrid graphene nanoplatelet (GNP) carbon nanotube (CNT) into the polymer matrix. The electrical conductivity of GNP-CNT polymer nanocomposites is investigated using a conductive network model through electron tunneling considering the subbands effect in an electro-magnetic field. The representative volume element is generated by distributing rode-like CNTs and disk-like GNPs using a Monte Carlo approach. When calculating electrical resistance, the tunneling effect accounts for the electron transfer between each linked pair of nanofillers. The modeling approach consists of the resistance change with the displacement of nanofillers due to strain. When taking into account tunneling behavior in the percolation transition zone, the magnetic field improves the subbands and augments electrical conductivity by transmitting charges. The study reveals that the piezoresistivity of the nanocomposite exhibits a 30% increase at 1.5% strain when the number of subbands is reduced from 20 to 15, or when the aspect ratio is changed from 150 to 100. Additionally, a nanocomposite containing CNTs with a diameter of 20 nm shows a significant increase in conductivity, rising from 10−13 to 10−3 S/m with a 1% increase in volume fraction. © 2025 The Authors
Gholami, R.,
Ansari, R.,
Aghdasi p., P.,
Sahmani, S. Publication Date: 2025
Thin-Walled Structures (02638231)210
In this study, the buckling and postbuckling of embedded sandwich moderately thick rectangular plates with functionally graded graphene platelet-reinforced composite porous core and metallic face sheets are studied. The considered plates are subjected to the uni-axial and bi-axial compressive loadings. Based on the Reddy's third-order shear deformation plate theory and the von Kármán large deflection assumptions, the weak form of discrete nonlinear equilibrium equations of considered sandwich porous plates are derived using the principle of minimum total potential energy. Then, by solving the linear part of achieved equations as an eigenvalue problem, the critical buckling loads and associated modeshapes are obtained. Then, to obtain the equilibrium postbuckling path of sandwich FG‐GPLRC porous rectangular plates with different boundary conditions, the obtained critical bucking loads and modeshapes are considered as the initial guess as well as incrementally applying the applied in-plane compressive load rise. Finally, using the pseudo arc-length technique and modified Newton–Raphson scheme, the set of nonlinear algebraic equations is solved and the equilibrium postbuckling path is obtained. A detailed parametric study is conducted to study the effects of various parameters such as the sandwich core thickness-to-metallic face sheet thickness ratio, porosity coefficient/distribution pattern, GPL weight fraction/distribution pattern and boundary conditions on the critical buckling load and postbuckling strength of FG-GPLRC porous plates. © 2025 Elsevier Ltd
Publication Date: 2025
European Physical Journal Plus (21905444)140(1)
Carbon–nitrogen nanostructures are promising candidates for various technologies due to their unique behavior and potential applications, motivating extensive experimental and theoretical research. N-triphenylene-Graphdiyne (N-TPG) is a carbon–nitrogen nanostructure derived by doping nitrogen atoms into the Graphdiyne family. This work investigates the mechanical properties of N-TPG under tensile stress using molecular dynamics simulations. Initially, the tension distribution and failure locations are discussed, followed by an exploration of N-TPG's behavior under different temperature gradients. The study also introduces defect density in the structure to obtain more realistic properties. Finally, the investigation extends to nanoribbons to explore the effect of size. Young's modulus, ultimate stress, ultimate strain, and tensile toughness are reported under tensile stress. Results show that these properties decrease as the temperature increases in both the X and Y directions and as defect density increases. Young's modulus is about 16% larger in the X direction than in the Y direction at 300K, and the ultimate stress decreases by about 18% and 4% in uniaxial directions with increasing nanosheet dimensions. © The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Publication Date: 2025
Applied Mathematical Modelling (0307904X)143
In this paper, a numerical method named as variational differential quadrature-finite element method (VDQ-FEM) is proposed to study the dynamic response of hyperelastic structures with finite deformation in the context of 2D micromorphic theory. Continuum micromorphic hyperelasticity relations are first written in a novel vector-matrix form, which are then discretized using the method of VDQ-FEM. In the next step, the resulting relations are discretized on time domain using Newmark's method in order to study the time response. The presented matricized formulation can be exploited in the coding procedure of numerical techniques. Moreover, VDQ-FEM is capable of addressing problems with irregular domains. Simple implementation, absence of locking problem, fast convergence rate and computational efficiency are the main benefits of proposed numerical approach. Three test problems are solved to show the accuracy and efficiency of developed numerical approach. It is revealed that VDQ-FEM in conjunction with Newmark's method is capable of predicting the dynamic response of micromorphic hyperelastic continua with large deformations in an efficient way. The influences of internal length parameter, density and micro-inertia on the responses of considered micromorphic hyperelastic structures are also analyzed. © 2025 Elsevier Inc.
Publication Date: 2025
Functional Composites and Structures (26316331)7(2)
Highly sensitive thermoresistive composites have great potentials for preventing overheating in electronic devices. Electro-magneto influenced mode numbers have a major effect on the quantum tunneling which has a critical role in electronic applications. A numerical model considering the electrical tunneling effect between carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) is developed to describe the electrical resistance change induced by mechanical deformation. The multistep percolation model scheme is based on separation distances and surged tunneling proposed to temperature change. The temperature-dependent quantum tunneling and fillers’ movement account for various parameters, such as CNT dispersion, temperature coefficient of resistance and physical properties. Comparisons between results for applied magnetic field suggest an improved conductivity for intensified magnetic field. Moreover, thermoresistivity declares a linear decrease with temperature, in which the highest thermo-resistive sensitivity was measured for highly aligned CNTs reporting a TCR of −0.004 °C. © 2025 The Korean Society for Composite Materials and IOP Publishing Limited. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Kalashami, E.R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Journal of Thermoplastic Composite Materials (15307980)
In the pursuit of advanced materials with enhanced thermo-mechanical properties, unidirectional short glass fiber (USGF)-reinforced polyethylene composites incorporating alumina nanoparticles can represent a potentially promising development. This study shows the constructive interplay between the multiscale agents, nanofiller/polymer interphase and the overall composite performance, employing the concept of representative volume element (RVE) and the finite element analysis. First, an RVE is created with spherical alumina nanoparticles dispersed randomly within the polyethylene matrix. Next, a different RVE is formed where USGFs are incorporated into the nanoparticle-filled polymer, which serves as the base material. By analyzing the RVEs via the finite element method (FEM), the elastic moduli and coefficients of thermal expansion (CTEs) of the ternary composites are predicted. The validity of the numerical model is assessed by comparison with previous literature, providing an acceptable agreement. The effects of volume fraction and geometry of alumina nanoscale particles and glass microscale fibers on the thermo-elastic constants are investigated. The findings indicate that dispersing alumina nanoparticles into the polyethylene can improve the thermo-elastic properties of the ternary composites. The elastic modulus and CTE in the transverse direction is significantly improved by reducing the diameter of alumina nanoparticles. It is found that nanofiller/polymer interphase region affects mostly the transverse thermo-elastic properties. © The Author(s) 2025
Publication Date: 2025
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)239(17 Special Issue: Materials, processes, and procedures: looking for a more sustainable world)pp. 6968-6982
Piezoelectric composites have emerged as promising materials for highly durable and flexible energy harvesters and sensors, requiring comprehensive modeling frameworks for accurate performance evaluation. This study investigates the influence of PZT-7A piezoelectric filler characteristics, including aspect ratio (AR), volume fraction, and spatial arrangement on the energy harvesting performance of polyvinylidene fluoride (PVDF) matrix composite cantilevers. The research employs a two-stage computational approach: first, a micromechanical finite element (FE) homogenization method determines the effective electromechanical properties of PZT-7A/PVDF composites; second, these properties are implemented in parallel bimorph piezoelectric vibration energy harvester (PVEH) models to predict voltage and power outputs. The results demonstrate significant dependencies of PVEH performance on filler parameters. For random spherical inclusions at 30% volume fraction under optimal electrical resistance, the maximum power density reaches 30.64 μW/cm2. Additionally, the study examines performance enhancement through structural modification, showing that semi-elliptical hollow patterning increases power density output of the PVEH specifically for PZT-7A as active layers. These findings provide critical insights into the design and optimization of piezoelectric composite-based energy harvesting systems. © IMechE 2025
Mahmoudirad m.m., ,
Saghafi h., ,
Khorrami a., A.,
Ansari, R. Publication Date: 2025
Polymer Composites (02728397)
Laminated composite structures with curved geometries are widely used in various engineering applications due to their lightweight and high-strength properties, but their behavior under low-velocity impact remains a critical area of study. This research experimentally investigates the impact response of curved laminated composites with concave and convex curvatures. Test specimens were designed with three distinct camber heights, and a custom fixture was utilized to conduct impact tests at two initial energy levels, with three repetitions per condition to ensure measurement accuracy. Results indicate that concave specimens exhibit significantly smaller damaged areas compared to convex ones under similar impact energies. Furthermore, increasing camber height leads to a larger damaged area. While delamination and matrix cracking dominate the damage mechanisms across all samples, no fiber breakage is observed in concave specimens. To provide further insights, the study evaluates maximum impact force, maximum displacement, and surface damage using optical imaging of the front and back sides of the specimens. These findings contribute to a deeper understanding of the impact performance of curved composites, informing their design and application in impact-prone environments. Highlights: Experimental analysis of curved composite laminates with low-velocity impact. Optical imaging of front and back surfaces of curvature damage propagation. Identifies distinct failure mechanisms: delamination and matrix cracking. Reveals a correlation between increased camber height and damage zones. © 2025 Society of Plastics Engineers.
Abedi, K.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
International Journal of Structural Stability and Dynamics (02194554)
While some studies have explored the effective properties of piezoelectric composites under off-axis loading conditions, as well as their performance within energy harvesting (EH) systems, there remains a limited amount of numerical research specifically dedicated to evaluating the performance of piezoelectric vibration energy harvesters (PVEHs) based on poly(vinylidene fluoride) (PVDF)/PZT-7A piezoelectric composites. This research introduces a computational micromechanics approach that utilizes finite element modeling (FEM) to analyze the representative volume element (RVE) of off-axis PZT-7A fiber-reinforced PVDF piezoelectric composites. The electromechanical properties of piezoelectric composites under different fiber volume fractions and off-axis angles are predicted. Furthermore, the efficiency of the PVEH is assessed for different uni/bi-morph cantilever configurations, including both parallel and series arrangements, as well as for exponentially tapered cantilevers. The findings indicate that at a constant off-axis angle (χ) below 45°, increasing the piezoelectric fiber volume fraction (vf) improves the output voltage density. However, once the fiber off-axis angle reaches 45° and exceeds it, a reduction in output voltage density is observed. This phenomenon occurs due to the reorientation of the off-axis fibers, which disrupts the structural symmetry, leading to the development of new components within the piezoelectric, dielectric, and mechanical property matrices. These newly generated components introduce opposing effects on the stress and voltage distribution throughout the PVEH. For a composite with a fiber volume fraction of 60% and an electrical resistance of 100kΩ, the maximum voltage density of 1210.8mV/cm2 is attained at χ = 0°. Significantly, the tapered cantilever design, which is 42% lighter than its uniform counterpart, yields approximately 1.1% greater voltage density. This enhancement can be further increased by up to 19% through the optimized selection of the electrical resistance. These results underscore the significant influence of fiber orientation, volume fraction, and device geometry in optimizing the performance of PVEHs. © 2026 World Scientific Publishing Company.
Keramati y., Y.,
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2025
Results in Engineering (25901230)28
The intra-matrix incorporation of boron nitride nanotubes (BNNTs), due to their superior mechanical properties, thermal stability, and electrical characteristics, can serve as an infrastructure for cutting-edge implementations of piezoelectric fiber-reinforced composites (PFRCs). This micromechanical investigation systematically elucidates the role of BNNTs in enhancing the thermo-electro-mechanical properties of hybrid piezoelectric systems. In this context, the effective properties of BNNT-polymer building blocks are extracted by accounting for microstructural interactions, notably the agglomeration behavior of randomly dispersed BNNTs. Subsequently, by introducing and refining the structural relations governing the material system, the responsive nature of appropriate representative volume elements is rigorously evaluated through an extended isofield micromechanical framework, specifically tailored to address the identified requirements. Following validation of the developed model against available literature, a comprehensive evaluation is conducted to assess the effects of BNNT content, agglomeration behavior, and nanotube diameter on the elastic stiffness, thermal expansion, thermal stress, and piezoelectric constants of BNNT-filled PFRC system. Furthermore, the influence of BNNT diameter on the effective properties is systematically evaluated, revealing its critical role in tailoring thermo-electro-mechanical performance. This approach lays a robust foundation for optimization, thereby eliminating the necessity for exhaustive and time-consuming parametric analyses. © 2025 The Author(s)
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2025
Computational Materials Science (09270256)246
Agglomeration of carbon nanotubes (CNTs) refers to their tendency to form clusters, an inevitable phenomenon that markedly influences the performance of composite/nanocomposite materials. Comprehending and managing agglomeration are crucial for tailoring the effective properties of nanocomposites, especially those reinforced with high concentrations of nanofillers. Incorporating this anomaly in numerical simulations can yield significant cost and time savings, while also providing valuable insights into this marvel. This pioneering study explores a promising avenue for a more realistic simulation of CNT-loaded polymer nanocomposites. In the present micromechanics-grounded finite element model, representative volume elements (RVEs) containing CNT agglomerates are ingeniously generated in a three-step stochastic-iterative process. These RVEs are subsequently challenged under commonly encountered engineering scenarios, encompassing elastic, thermoelastic, and viscoelastic aspects. In this case, the precise determination of boundary and loading conditions is accomplished by assessing the constitutive equations associated with each characteristic. Through comparison with available experimental measurements, it has been demonstrated that authoritative prediction of Young's moduli, thermal expansion coefficients, and creep strains necessitates the simulation of building blocks with agglomerated CNTs. © 2024 Elsevier B.V.
Eghbalian, M.,
Hashemi, M.J.,
Nikparsa, A.,
Ansari, R.,
Sahmani, S.,
Postek, E. Publication Date: 2025
Computational Materials Science (09270256)258
After the synthetization of graphene, various carbon allotropes with remarkable applications have emerged in the material science. Net Y, closely related to Net C, is a novel carbon allotrope with exceptional properties. This study employs the molecular dynamics simulation to predict key mechanical characters of Net Y subjected to a uniaxial tension, including the failure strain as well as stress, Young's modulus, and strain energy. A detailed tension distribution analysis is provided to explore its mechanical behavior further. The numerical results reveal that the defect density and temperature gradients significantly influence the mechanical performance of Net Y. The nanosheet exhibits over twice the failure stress and 1.5 times the failure strain along with the X direction than the initial failure stress and strain observed along with the Y direction. Also, it is demonstrated that the ultimate failure stress as well as strain along with the Y direction are more significant due to a substantial failure region in the associated stress–strain path. Furthermore, it is observed that the Young's modulus declines consistently allocated to a higher defect density, decreasing by approximately 17 % via increasing the defect density from 0.5 % to 2 % along with the X direction. Moreover, the quantity of strain energy increases with the number of ribbons, reaching 1.58×10-26eV and 3.99×10-26eV along with the X and Y directions, respectively. The study also emphasizes the importance of defect location and structural stability through the tension distribution analysis. © 2025 Elsevier B.V.
Dastgir, N.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Composites Communications (24522139)59
This study uses a finite element method to investigate electro-mechanical behaviors of bimorph cantilever beams composed of a steel substrate and two layers of a piezocomposite made of PZT-5H fiber/PVDF materials. The properties of the representative volume element of piezocomposites are determined by the numerical simulation based on the micromechanical homogenization method. Then, eigenfrequency and static analyses are performed, followed by a comprehensive dynamic study incorporating time-dependent analysis under sinusoidal harmonic loadings at two different excitation frequencies. A parametric study is performed to evaluate natural frequencies, mode shapes, displacement, strain, stress, electric potential, and electric field of the piezocomposite bimorph harvester for three different fiber volume fractions. The results demonstrate that increasing volume fraction leads to better electro-mechanical properties of piezocomposite bimorph harvesters, with resonance occurring at elevated frequencies. Additionally, an increased volume fraction results in reduced displacement and strain, while simultaneously amplifying the electric field and electric potential under static loadings. Dynamic loading analysis reveals that piezocomposite bimorph beams with a higher volume fraction exhibit higher electric potential and electric field, reaching equilibrium in a shorter duration. A frequency response analysis is conducted on the bimorph beam with varying cross-sections and volume fractions. The trapezoidal beam yields better electrical outputs as compared to the rectangular and triangular beams. The obtained mechanical behaviors by the present simulation are found to be in good agreement with those predicted through other researchers. © 2025 Elsevier Ltd
Saberi, M.,
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Journal of Reinforced Plastics and Composites (07316844)
A numerical micromechanics approach based on the finite element method (FEM) is employed to evaluate the elastic modulus and coefficient of thermal expansion (CTE) of graphene nanoplatelet (GNP)-reinforced aluminum (Al) matrix nanocomposites. The modeling framework integrates representative volume elements (RVEs) with detailed consideration of GNP morphology in the nanocomposite structure. The critical role of GNP waviness and the formation of aluminum carbide (Al4C3) interphase, resulting from the interaction between graphene and the metal matrix, is examined in relation to nanocomposite properties. Variations in the volume fraction, geometry, and alignment of GNPs, along with the interphase thickness and its material properties, are considered to capture the microstructural influence on the elastic modulus and CTE of GNP/Al nanocomposites. The study reveals that the presence and growth of the Al4C3 interphase contribute positively to the mechanical and thermal elastic response of the nanocomposite. Although increasing graphene content, aspect ratio, and alignment enhances the elastic modulus and reduces the CTE, the presence of waviness in graphene nanofillers diminishes these benefits. Model validation is carried out through a comparison between micromechanics-based FEM outcomes and experimental data documented in the literature. © The Author(s) 2025
Mirsabetnazar a., A.,
Ansari, R.,
Ershadi, M.Z.,
Rouhi h., H. Publication Date: 2025
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)239(9)pp. 3155-3165
Presented herein is a numerical investigation into the free and forced vibrational characteristics of circular plates made of functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAMs). The material properties of FG-GOEAM are estimated using genetic programing-assisted micromechanical models considering two graphene content distribution patterns. The effects of graphene content, size and folding degree on the material properties are taken into account by the models. The formulation of the paper is in the context of first-order shear deformation plate theory, and the governing equations of motion are achieved utilizing Hamilton’s principle. In the solution approach, the variational differential quadrature (VDQ) method is employed by which the variational statement of problem is directly derived and discretized using matrix differential and integral operators. Selected numerical results are presented to study the effects of graphene origami (GOri) content, folding degree, and distribution pattern on the free and forced vibration responses of FG-GOEAM circular plates with clamped and hinged boundary conditions. © IMechE 2025.
Mirsabetnazar a., A.,
Ansari, R.,
Ershadi, M.Z.,
Sahmani, S. Publication Date: 2025
International Journal of Structural Stability and Dynamics (02194554)
Auxetic metamaterials, identified by their negative Poisson's ratio, have attracted the scientific community's attention because of their superior mechanical behavior. In this investigation, the free and forced vibrations of annular plates fabricated from functionally graded (FG) graphene origami-enabled auxetic metamaterials are analyzed using a numerical approach. The micromechanical model is developed using a genetic algorithm to approximate the material properties for two distinct patterns of graphene content distribution and variations in the degree to which graphene origami is folded. The governing equations are attained utilizing Hamilton's principle, incorporating the first-order shear deformation theory of plates. Vibrational responses of annular sector plates are studied for the first time, employing the variational differential quadrature approach directly applied to the variational equations to obtain their discrete form. The proposed model demonstrates excellent agreement with reference solutions, showing a maximum deviation of less than 0.17% in dimensionless frequency values, thereby validating its accuracy and effectiveness. Numerical studies are presented to explore the influence of factors such as graphene content, the degree of graphene origami folding, distribution patterns, and boundary conditions on the free and forced vibration responses of annular sector plates. An inverse relationship between the folding degree and material strength is detected. This discrepancy is attributed to the interaction between graphene content and graphene folding degree. At low graphene content, higher degrees of folding reduce the material's strength. However, when graphene content exceeds 3%, an increase in the degree of folding enhances the material's strength, resulting in decreased lateral deflection. © 2026 World Scientific Publishing Company.
Publication Date: 2025
Acta Mechanica (16196937)
In the present article, based on the first-order shear deformation theory (FSDT) and strain gradient theory (SGT), vibrational characteristics of plate-type microstructures made of functionally graded materials (FGMs) with arbitrary shape are numerically investigated. To this end, first, the governing equations are obtained within the frameworks of Mindlin’s SGT and FSDT. The relations are presented in a vector–matrix form so as to use in a numerical approach. Also, the developed SGT-based formulation can be reduced to various simplified theories including MCST and MSGT. Then, the variational differential quadrature (VDQ)-transformed method is applied to the variational statement of problem in the solution procedure. FG microplates under various edge conditions are considered whose free vibration response is analyzed. The developed approach can be used to address the problem for various geometries. Natural frequencies of FG skew, triangular and sector plates are computed, and the effects of thickness-to-length-scale parameter and vibration mode number on the results are studied. It is shown that natural frequencies are considerably decreased by increasing the thickness-to-length-scale parameter ratio. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.
Gholami, R.,
Ansari, R.,
Sahmani, S.,
Hassanzadeh-aghdam, M.K. Publication Date: 2025
Acta Mechanica (16196937)
In this study, with the aid of a unified micromechanics–time-periodic mathematical model, the geometrically nonlinear free oscillation characteristics of higher-order shear deformable ternary short glass fiber (SGF)/carbon nanotube (CNT) nanocomposite annular sector plates are investigated considering the influences of different material and structural parameters. The effective mechanical properties of the nanocomposite are derived using a finite element-based micromechanical modeling, accounting for the contributions of SGFs and CNTs. The nonlinear governing equations are formulated by utilizing von Kármán nonlinearity relations and solved using a multiphase numerical solving strategy that includes the Galerkin scheme, time-periodic discretization (TPD) approach, pseudo-arc-length continuation method, and modified Newton–Raphson technique. The nonlinear frequency responses are obtained, and the effects of CNT and SGF volume fractions, aspect ratios, dispersion patterns, interphase effects, and CNT morphology are comprehensively analyzed. The results indicate that increasing CNT and SGF volume fractions significantly enhances the nonlinear frequencies of the nanocomposite structure, with higher aspect ratios leading to further improvements. It is also concluded that the alignment of both fillers provides the highest dynamic performance for SGF/CNT nanocomposite annular sector plates. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.
Gholami, R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
International Journal of Non-Linear Mechanics (00207462)178
Nonlinear primary resonance behavior of titanium dioxide (TiO2)/graphene nanoplatelet (GNP)/polymer nanocomposite rectangular plates using a geometrically nonlinear higher-order shear deformable plate model is investigated. The material properties of the hybrid nanocomposite, consisting of a polymer matrix reinforced with TiO2 nanoparticles and GNPs are determined through the finite element-based micromechanical modeling. The representative volume elements (RVEs) account for nanofiller geometry, dispersion patterns, and interphase effects to accurately simulate the mechanical properties of the nanocomposite. The nonlinear governing equations of motion are derived using Reddy's third-order shear deformation theory and von Kármán nonlinearity and are discretized via the generalized differential quadrature (GDQ) method. The equations are solved using a multistage numerical procedure combining the Galerkin approach, time periodic discretization (TPD) scheme, and pseudo-arc length continuation technique to obtain nonlinear frequency-response curves under various boundary conditions. The results highlight the pronounced contribution of GNP reinforcement, which significantly enhances the stiffness and nonlinear hardening behavior of the plates, as evidenced by increased linear and nonlinear frequencies and reduced vibration amplitudes. © 2025 Elsevier Ltd
Publication Date: 2025
Waves in Random and Complex Media (discontinued) (17455049)35(5)pp. 9070-9093
This article focuses on studying the nonlinear vibration of functionally graded (FG) curved nanobeams resting on the Pasternak-Winkler elastic foundation based on the nonlocal strain gradient theory along with the first-order shear deformation beam theory (FSDBT) considering von-Kármán hypothesis. The Hamilton principle is applied to extract three nonlinear motion equations and the Galerkin method (GM) is utilized to spatially reduce the differential equations. The analytical approach based on the two-step perturbation method (TSPM) was employed to deal with nonlinear governing equations. To verify the outcomes of the present article, the natural frequencies and frequency ratios are validated with those reported in the literature. Subsequently, the results presented in this paper are of a significant point to describe the nonlinear vibration of FG curved nanobeams in conjunction with different parameters. © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.
Abedi, K.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Mechanics of Advanced Materials and Structures (15210596)
This study investigates the performance enhancement of coupled bending-torsional (BT) vibration energy harvesters (VEHs) by incorporating polyvinylidene fluoride (PVDF)/barium titanate (BaTiO3) piezocomposite layers. A unimorph cantilever beam, subjected to BT vibrations, is analyzed using finite element (FE) modeling to evaluate the impact of BaTiO3 (BTO) fiber orientation and connectivity patterns (0–3 and 1–3) within a PVDF matrix. The influence of fiber orientation on the electromechanical properties of long-fiber piezocomposites (LFPs) and short-fiber piezocomposites (SFPs), as well as their corresponding voltage and power output for BT-piezoelectric vibration energy harvesters (PVEHs), has been numerically investigated. Optimal performance for XZ-piezocomposites with 1–3 connectivity (LFPs) is observed at an off-axis angle of 70˚, yielding average maximum voltages of 7.24 V and power of 26.39 μW across the first two vibration modes. For 0–3 connectivity (SFPs), optimal performance occurs at a 50˚ off-axis angle. Furthermore, increasing the mass ratio enhances the contribution of the second vibration mode, potentially broadening the effective frequency range of the harvester. These findings offer crucial insights for optimizing piezocomposite design in energy harvesting applications, particularly for BT-VEHs. © 2025 Taylor & Francis Group, LLC.
Publication Date: 2025
Materials Chemistry and Physics (02540584)344
Temperature dependence of resistance known as thermoresistivity and sharp enhancement of electrical conductivity known as percolation are unique electrical properties affected by temperature and agglomeration of carbon nanotubes (CNTs), respectively. An investigation of the thermoresistivity of a hybrid agglomerated CNT-graphene nanoplatelet (GNP) polymer strain sensor is conducted, taking into account the tunneling mechanism. Rod-like CNTs and disk-shape GNPs are used to generate the representative volume element for evaluating the piezoresistivity caused by the strain and thermoresistivity induced by temperature. The percolation model predicts the tunneling conductance based on contacts that exist inside conductive channels. It is demonstrated that percolation occurs at a GNP concentration of 1.3 vol% when the GNPs have a lateral size of 1 μm, which represents their largest dimension. The effects of CNT aspect ratio and agglomeration radius, and orientation state on the sensitivity of the piezoresistive strain sensor are analyzed. It is found that the piezoresistivity of the 1 vol% CNT polymer nanocomposite increases by 60 % at 1.5 % strain when the orientation state shifts from randomly oriented to partially aligned or when the aspect ratio changes from 370 to 250. The comparison shows that resistance drops as temperature increases because thermal activation hopping becomes more dominant than the thermal expansion of the matrix. A 1 vol% CNT/polymer nanocomposite with 20 nm diameter CNTs with average length of 1.5 μm experiences a 40 % reduction in resistance over a 110 °C temperature increase. © 2025 Elsevier B.V.
Publication Date: 2025
International Journal for Numerical Methods in Engineering (00295981)126(14)
In this study, the bending, buckling, and free vibration analysis of bi-directional functionally graded porous microbeams with variable thickness are investigated. By utilizing the modified strain gradient theory (MSGT) in conjunction with a sinusoidal shear deformation theory, governing equations are derived using Hamilton's principle within the framework of the non-uniform rational B-spline (NURBS)-based isogeometric analysis (IGA). In addition, the C2-continuity requirement can be easily achieved by increasing the order of the NURBS basis functions. The MLSPs and the material properties of microbeams vary along with both thickness and axial directions based on the rule of mixture scheme. To consider the effects of porosity, two even and uneven distributions are considered. After verifying the accuracy of the presented approach, the influence of the aspect ratio, gradient indices, different boundary conditions, porosity parameters, variable MLSPs, and thickness on the bending, buckling, and free vibration characteristics of microbeams are investigated. © 2025 John Wiley & Sons Ltd.
Gholami, R.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Moradi, A.,
Sahmani, S. Publication Date: 2025
Acta Mechanica (16196937)236(8)pp. 4699-4725
This study establishes a unified framework to investigate the mechanical properties and geometrically nonlinear free vibration of polymer nanocomposite rectangular plates containing carbon nanotubes (CNTs) and silica nanoparticles (SiO2). A micromechanics-based finite element approach is employed to predict the effective mechanical properties of the hybrid nanocomposite, accounting for factors such as volume fraction, nanofiller geometries, interphase characteristics, and clustering effects. The geometrically nonlinear governing equations are derived using Reddy’s third-order shear deformation plate theory, von Kármán-type nonlinear strain–displacement relations, and Hamilton’s principle. In order to solve the governing equations, a multistep numerical methodology is applied, incorporating the generalized differential quadrature scheme, Galerkin approach, time-periodic differential scheme, pseudo-arc-length continuation algorithm, and modified Newton–Raphson method. A comprehensive assessment of nonlinear frequency response curves is performed with consideration of microstructure-level parameters and boundary condition variations. It is concluded that increasing nanofiller content, leveraging elongated CNTs and fine SiO2, and optimizing nanofiller dispersion patterns significantly enhance both linear and nonlinear frequencies, with fully clamped boundary conditions exhibiting the highest frequencies. When the length (width)-to-thickness ratio of a 1 vol.% CNT/5 vol.% SiO2/polymer nanocomposite plate is 12, the non-dimensional linear frequencies incorporating aligned, randomly oriented, and agglomerated nanofillers are 0.6765, 0.5814, and 0.5237, respectively, under simply supported edges, and 1.187, 1.0196, and 0.9179, respectively, under fully clamped edges. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2025.
Kouhkord, A.,
Hassani, F.,
Golshani, A.,
Ansari, R. Publication Date: 2025
Results in Engineering (25901230)27
Bio-nanoparticle synthesis, essential for advanced drug delivery systems, relies on precise control over particle size, composition, and transport behavior. This study highlights micro-acoustofluidic heat and mass transport modeling as a powerful tool for designing controllable nano-drugs, including nanocarriers for respiratory systems and targeted cancer therapies, where precise control over the physical properties of nanoparticles is critical for successfully accomplishing the intended biological task. The intelligent acousto-microfluidic chamber is designed to overcome the unpredictability of heat and mass transport affecting nanoparticle properties, caused by the complex physics of acoustic streaming phenomena, thereby enabling controlled microfluidic nanoparticle synthesis. The study demonstrates how slight adjustments to the voltage settings and the arrangement of sharp edges can profoundly affect the acoustic streaming, thereby facilitating precise micro reaction phenomena. The optimal models were identified, showcasing varying efficiencies in three defined objective functions mixing, temperature fluctuation, and power consumption of proposed microsystem based on the configuration of sharp edge in the baffle and the actuation voltage. Results indicate that increasing voltage to 15 V significantly elevates the objective function by 131%. Systems with higher alpha exhibit greater temperature variations due to less intense vortices. Configurations with lower alpha and smaller curvature radii promote stable mechanical energy consumption (MEC), mitigating pressure drops. However, increasing alpha alongside higher voltage and curvature radius values leads to a substantial 115% increase in Mechanical Energy Consumption MEC. The outcomes and the intelligent framework presented here serve as a guide for creating AI-integrated micro-electro-mechanical devices, aiming controlled heat and mass transfer for precise nanoparticle synthesis. Precision is crucial in advanced biomedical fields requiring reproducible synthesis of smart nanoparticles responsive to biological and physical stimuli, as well as targeted treatments for tumors and respiratory infections. Integrated microfluidic designs enhance nanoparticle reproducibility and therapeutic effectiveness by precisely controlling heat and mass transfer in microfluidic design process. In these contexts, even minor changes in nanoparticle properties due to slight variations in synthesis conditions can significantly influence therapeutic outcomes, addressing current limitations and promoting successful clinical translation. © 2025 The Authors
Abedi, K.,
Ansari, R.,
Haghgoo, M.,
Hassanzadeh-aghdam, M.K. Publication Date: 2025
Applied Physics A: Materials Science and Processing (14320630)131(5)
This study proposes a comprehensive finite element analysis (FEA) of an architected piezoresistive pressure sensor for micro-electromechanical systems (MEMS), focusing on the effects of different diaphragm cut patterns to enhance sensitivity, linearity, and pressure range. Two designs are introduced: Design-1 with straight cuts and Design-2 with arc-shaped cuts. The investigation evaluates stress distribution, deflection, and output voltage across a Wheatstone bridge circuit under varying applied pressures. In Design-1, straight cuts near the diaphragm edges regulate stress distribution, channeling it across the piezoresistors and achieving an 80% increase in sensitivity compared to the baseline design, with a maximum sensitivity of 0.464 mV/V/kPa and nonlinearity error of 1.03%FSS. Parametric studies identify optimal cut dimensions to maximize sensitivity while ensuring linearity and compliance with small deflection theory. Design-2 incorporates arc-shaped cuts that redistribute stress away from the piezoresistors, extending the pressure range to 7 MPa with nonlinearity error of 0.12% (full-scale span) FSS. The strategic placement and geometries of these cuts enable precise control over stress distribution, allowing for tailored performance enhancements in sensitivity or pressure range to meet specific application requirements. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Publication Date: 2025
Advanced Materials Interfaces (21967350)
Graphene-based flexible strain sensors have attracted significant interest for next-generation wearable electronics due to their exceptional electromechanical properties. Their sensitivity can be further enhanced by incorporating metal and metal oxide nanoparticles into the graphene framework. However, existing fabrication approaches are often complex and expensive. We present a laser-assisted, scalable, and cost-effective strategy to construct 3D porous graphene architectures uniformly embedded with iron oxide nanoparticles. The process involves fiber laser irradiation of iron-nitrate-treated laser-induced graphene (LIG), which yields hierarchical nanostructures with a markedly enhanced piezoresistive response. The resulting sensors exhibit an ultrahigh gauge factor (GF = 635), fast response time (40 ms), excellent mechanical durability (over 5000 cycles), and a broad sensing range (up to 11%). Structural characterization confirms the effective and homogeneous integration of iron oxide nanoparticles within the graphene matrix. These results highlight the potential of this laser-fabricated nanocomposite platform for high-performance, flexible sensing systems in wearable and soft robotic applications. © 2025 The Author(s). Advanced Materials Interfaces published by Wiley-VCH GmbH.
Publication Date: 2025
International Journal for Numerical Methods in Engineering (00295981)126(15)
The aim of this paper is to propose a novel finite element (FE) approach for studying the large deformations of structures with arbitrary geometry in the context of micromorphic hyperelasticity. The 3D micromorphic hyperelasticity is first formulated in a general form based on novel constitutive relations within a Lagrangian framework. In order to implement in the coding procedure, the vector–matrix counterparts of presented relations are also given, which can be used in numerical approaches readily. In the next step, a finite element method is developed to compute large deformations in arbitrary-shaped structures under static loading. The correctness and reliability of the approach are illustrated by solving some test problems. Additionally, the effects of Young's modulus, internal length, and scale-transition parameters on the large deformation behavior of considered micromorphic hyperelastic structures are analyzed. © 2025 John Wiley & Sons Ltd.
Haghighi s., S.,
Keramati y., Y.,
Eghbalian, M.,
Ansari, R. Publication Date: 2025
Fibers and Polymers (12299197)26(2)pp. 797-812
The effects of the vacancy-type defects in the graphene sheet (GR) and volume fraction (vf) of the GR on Young’s and shear moduli of polylactic acid (PLA) nanocomposite strengthened by the GR (GR/PLA) are investigated. The molecular dynamic (MD) method is implemented and stress–strain evolutions are extracted to explore elastic constants. The simulations demonstrate that adding the defect-free and defective GR in the PLA leads to a vast improvement in tensile and shear moduli. In every vf of the GR, the defective GR/PLA under tensile loadings compared to the defect-free one can endure smaller stress and deformation at the breaking point. Likewise, the bearable stress of the defective GR/PLA subjected to longitudinal shearing is lower than the maximum stress obtained from the defect-free GR/PLA. In any vf of the GR, as the rate of the defects rises, the defective GR/PLA is capable of withstanding a smaller quantity of ultimate stress. However, the variation of the ultimate deformation of defective nanocomposites with the increase of the defect content does not pursue a determined trend, mainly because it is heavily dependent on the distribution pattern and location of defects. Young’s and shear moduli of the GR/PLA experience a downward trend with increasing the degree of the defect. In a desired defect percentage, the stiffness and rigidity of the nanocomposites become larger by choosing a higher GR’s vf. © The Author(s), under exclusive licence to the Korean Fiber Society 2025.
Publication Date: 2025
Molecular Simulation (08927022)51(12)pp. 808-823
Carbon-nitrogen nanostructures hold outstanding promise for advancing technology across numerous fields. Their unique mechanical properties drive substantial experimental and theoretical research, aiming to unlock their full potential for practical applications. N-Graphdiyne (C18N6) is a carbon-nitrogen nanostructure derived by doping nitrogen atoms into Graphdiyne. This study explores the mechanical properties of C18N6 under tensile stress using molecular dynamics simulations. First, an investigation of C18N6's behaviour under different temperature gradients is presented. Next, defect density is applied to the structure to obtain more realistic properties. Finally, the characterisation extends to nanoribbons to explore the effect of size. Young's modulus, first failure stress and strain, and tensile toughness are reported under tensile stress. Results show that Young's modulus is approximately 14% larger in the Y direction than in the X direction at 300 K, and the failure stress decreases by about 37%, with a 0.05 drop in the value of failure strain due to defect density growth. © 2025 Informa UK Limited, trading as Taylor & Francis Group.
Abedi, K.,
Seraj, H.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2025
Journal of Thermoplastic Composite Materials (15307980)
Unidirectional fiber-reinforced polymer matrix composites (PMCs) have great potential for engineering applications. The effective properties can be further tailored by incorporating a secondary reinforcement into these materials. This study investigates the damping characteristics of PMCs reinforced by both unidirectional glass fibers and hollow glass microspheres (HGMs) using a micromechanics-based finite element method (FEM). To account for the complex nature of the filler/matrix dissipation mechanisms, a thin, lossy interphase layer is considered for both the fibers and HGMs inside the representative volume element (RVE) of the PMCs. The numerical homogenization approach is first validated against analytical, numerical, and experimental data from the literature. Subsequently, a comprehensive parametric study is conducted to examine the influence of microstructural features on the composite’s damping behavior. Specifically, the effects of thickness, stiffness, and damping properties of the interphase, as well as fiber volume fraction (FVF), HGM volume fraction (HVF), and HGM thickness on the directional loss factors are evaluated using the strain energy approach. The findings indicate that while an increase in FVF generally reduces the damping performance of the composite, a weak interfacial bond between the fillers and the matrix can enhance the damping properties of hybrid filler-reinforced PMCs. © The Author(s) 2025
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S.,
Jang, S. Publication Date: 2025
Composites Part B: Engineering (13598368)305
Barium titanate (BT) nanofillers play a crucial role in polymer nanocomposites due to their remarkable intrinsic properties, which markedly improve the effectiveness of energy conversion. However, the synthesis of BT nanofillers in varied structural profiles, such as nanowires, nanoplatelets, and nanoparticles, along with their dispersion within the polymer matrix, exerts a substantial impact on the overall performance of the nanocomposite. Non-uniform nanofiller dispersion is inherently tied to the development of microstructural defects, including poor compatibility between phases, the formation of voids, and nanofiller agglomeration. This study investigates the influence of BT nanofiller shape and microstructural defects on the effective properties of BT/polydimethylsiloxane (PDMS) piezoelectric nanocomposites. Based on a micromechanics-based finite element framework, representative volume elements (RVEs) of the nanocomposite are generated using a morphology-centric computational simulation, and their Young's moduli, piezoelectric coefficients, and thermal expansion coefficients are subsequently predicted. The results indicate that establishing robust interphase regions, driven by enhanced interfacial compatibility, has a direct impact on elevating system functionality. Additionally, the adverse effects of void defects and nanofiller agglomeration on the effective properties are alleviated through void minimization and agglomerate breakdown. © 2025 Elsevier Ltd
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S. Publication Date: 2025
Composite Structures (02638223)370
Integrating graphene nanoplatelets (GNPs) and barium titanate nanowires (BTNs) into the polymer enables the formation of a hybrid system, which drives notable advancements: enhancing the interfacial compatibility of nanofillers with the polymer and alleviating defect-related drawbacks; preserving the structural integrity of wire-shaped nanofillers through the stabilizing role of platelet-shaped nanofillers; extending the functional applicability of polymer nanocomposites, particularly in multi-physics domains; etc. This cutting-edge research is directed towards developing a micromechanics-based finite element framework for investigating the coupled-field interactions in GNP/BTN/polydimethylsiloxane (PDMS) piezoelectric nanocomposites. A multi-step stochastic-iterative computational algorithm is employed to generate representative volume elements (RVEs) of this tri-phase system, addressing the key morphological aspects of nanofillers. This algorithm also covers a variety of nanofiller dispersal scenarios, spanning well-dispersed, agglomerated, and hybrid configurations. Parameter-driven analyses underscore the beneficial effects of augmenting the loading of well-dispersed nanofillers, deploying slim GNPs and elongated BTNs, and maintaining proper alignment. The findings reveal that when nanofillers accumulate and form agglomerates, GNP clusters yield a more considerable impact on the degradation of the elastic modulus and thermal expansion coefficient, whereas BTN clusters predominantly influence the piezoelectric coefficient. In addition, the advantageous role of cluster fragmentation is detected universally. © 2025 Elsevier Ltd
Publication Date: 2025
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)
In the context of strain gradient theory and 3D elasticity, the bending characteristics of circular cylindrical small-scale panels are studied in both linear and nonlinear regimes. It is considered that the panel is made of functionally graded (FG) material whose properties are estimated by power-law functions. An energy-based approach is presented to derive the governing equations including strain gradient effects and geometrical nonlinearity. The formulation is also presented in a novel matrix form which can be readily applied in numerical methods. The VDQ technique is utilized to directly discretize the energy functional using matrix operators. Then, an efficient numerical approach based on differential operators and the pseudo arc-length continuation algorithm is developed for solving the nonlinear bending problem. Numerical examples are given to investigate the effects of geometrical properties, length scale parameter, and material gradient index on the linear/nonlinear static behavior of FG small-scale panels under various boundary conditions. Besides, comparisons are presented between the results of various theories including MCST and MSGT. The results obtained from the linear and nonlinear models are also compared. © The Author(s), under exclusive licence to Shiraz University 2025.
Publication Date: 2025
Composites Part C: Open Access (26666820)17
In this article, an efficient numerical approach is developed to study the primary resonant dynamics of rectangular plates with arbitrary boundary conditions made of functionally graded carbon nanotube-reinforced composites (FG-CNTRCs). The problem is formulated in the context of three-dimensional (3D) elasticity theory. Also, a variational approach based on Hamilton's principle together with the variational differential quadrature (VDQ) method is proposed to obtain the discretized governing equations on space domain. Then, the solution procedure on the time domain is completed using the numerical Galerkin method, time periodic discretization method and pseudo arc-length continuation algorithm in order to find the frequency-response curves. It is considered that CNTs are distributed in the thickness direction based on an FG manner considering different patterns. After testing the convergence and validity of developed approach, numerical results are presented to investigate the influences of geometrical properties, CNT's volume fraction and distribution pattern on the nonlinear forced vibration response of plates. © 2025
Gholami, R.,
Ansari, R.,
Sahmani, S.,
Hassanzadeh-aghdam, M.K. Publication Date: 2025
Polymer Composites (02728397)
This study numerically examines the nonlinear stability characteristics of fuzzy fiber-reinforced composite (FFRC) rectangular plates. A notable feature of these inhomogeneous materials is the uniform alignment and radial growth of carbon nanotubes (CNTs) of identical lengths on the circumferential surface of carbon fibers. To predict the mechanical properties of FFRCs, a micromechanical modeling approach utilizing a unit cell model is developed. This model incorporates essential microstructural factors, such as the volume fractions of carbon fiber and CNT, the thickness, and the stiffness of the interphase region between the nanotube and the polymer matrix. The mechanical properties obtained from the micromechanical model are then applied to investigate the nonlinear bending and postbuckling behavior of FFRC rectangular plates under various boundary conditions. The variational differential quadrature (VDQ) method is used to derive the weak form of the discretized nonlinear governing equations based on Reddy's third-order shear deformation plate theory (TOSDPT). Additionally, the pseudo-arc-length continuation scheme is employed to trace the bending and postbuckling paths. Comprehensive parametric studies are performed to assess the impact of critical parameters, including CNT volume fraction, carbon fiber content, and interfacial region properties, on the nonlinear bending and postbuckling responses of FFRC rectangular plates. © 2025 Society of Plastics Engineers.
Publication Date: 2025
International Journal of Structural Stability and Dynamics (02194554)
This paper investigates the nonlinear vibrational behavior of nanocomposite conical shells reinforced with carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) within a polymer matrix. A hierarchical micromechanical model is first developed to predict the effective properties of the nanocomposite, considering critical microstructure-level structural phenomena. Initially, using the finite element method and a representative volume element (RVE), the effective properties of the polymer containing CNTs and GNPs are determined. To realistically simulate the nanocomposite's microstructure, CNTs and GNPs are dispersed randomly within the polymer matrix through a comprehensive algorithm. Applying a prescribed displacement to the RVE faces and calculating the resulting reaction forces allows for the extraction of the nanocomposite shell's effective properties. Furthermore, using Hamilton's principle and incorporating von Kármán nonlinear strains, the equations of motion are derived. Through the stress function approach and the Galerkin method, these equations are transformed into an ordinary differential equation. The study examines the effects of nanocomposite properties - such as the volume fractions of GNPs and CNTs, the presence or absence of the interphase region, the agglomeration of nanofillers within the RVE, CNT aspect ratio, and GNP thickness - on the vibration behavior of the conical shell for the first time. Results indicate that increasing the volume fraction of CNTs enhances the natural frequency of the shell, whereas accounting for nanofiller agglomeration reduces the strength and stiffness of the shell. © 2026 World Scientific Publishing Company.
Nikparsa, A.,
Ansari, R.,
Eghbalian, M.,
Sahmani, S.,
Postek, E. Publication Date: 2025
Colloids and Surfaces A: Physicochemical and Engineering Aspects (18734359)726
Triphenylene-based graphdiyne (TPG) and nitrogen-doped TPG (NTPG) are recently developed two-dimensional nanomaterials with promising mechanical and electronic potential. The current study presents the first exploration of the hydrogen-functionalized TPG and NTPG nanosheets subjected to a uniaxial tensile loading condition using molecular dynamics simulations. The developed computational approach introduces a novel random functionalization scheme to improve the attributed structural stability. The Tersoff potential is employed to model the intra-layer interactions within the TPG. On the other hand, the interactions at the site of functionalization are described by the Dreiding force field for C and H atoms, supplemented by the Lennard-Jones (LJ) potential. The minimization process is applied via the conjugate-gradient technique, and following that, the system undergoes a canonical ensemble (NVT) simulation at 300 K with a timestep of 0.001 ps. In this step, the Nose–Hoover thermostat algorithm controlled the fluctuation of thermodynamic parameters, and the structure surpassed a stable status. The achieved numerical results demonstrate that hydrogen coverage significant influences on the mechanical behavior, including failure stress and strain, Young's modulus and toughness of TPG as well as NTPG nanosheets. For the both of nanosheets, increasing the hydrogen functionalization from 2.5 % to 10 % results in a consistent decline in mechanical properties. In the X direction, TPG shows a reduction in ultimate stress from 15.08 GPa to 9.47 GPa, while NTPG drops more sharply from 30.87 GPa to 18.38 GPa. A similar trend is observed across the Y direction, with TPG decreasing from 11.42 GPa to 9.29 GPa, and NTPG from 30.35 GPa to 22.69 GPa. © 2025 The Authors
Publication Date: 2025
International Journal of Mechanical Sciences (00207403)305
This article presents an efficient numerical framework for solving problems in hyper-elasto-plasticity under finite deformations. The main novelty of the current study lies in the first-time extension of the Variational Differential Quadrature (VDQ) method to finite-strain elasto-plasticity, addressing challenges such as large nonlinear deformations, path-dependent material behavior, and post-critical instability. The general tensorial equations of 3D hyper-elasto-plasticity are first derived and then reformulated into compact vector-matrix forms suitable for computational purposes. The proposed grid-based VDQ method is locking-free, simple to implement, and shows fast convergence. To evaluate the accuracy and efficiency of the method, several benchmark problems involving solid-shell structures with complex geometries are analyzed. The results demonstrate the capability of the proposed approach to reliably capture large deformation responses in elasto-plastic solids, offering a robust alternative to conventional finite element methods. © 2025
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Sahmani, S.,
Jang, S. Publication Date: 2025
Composites Part A: Applied Science and Manufacturing (1359835X)199
A numerical simulation based on Monte Carlo conductive network path finding method has been developed to investigate thermomagnetic carbon nanotube (CNT)-graphene nanoplatelet (GNP) polymeric conductive composites. The modeling methodology consists of three sequential phases: the initial estimation of resistivity followed by an assessment of the displacement of nanofillers and the resulting alterations in resistance by variations of intrinsic resistance with temperature. The formation of a continuous conductive path through the touching of the conductive fillers causes the resistivity to decrease 10 orders of magnitude in the percolation region. GNP gives a higher percolation threshold than CNT, with a 60% decrease with doubling its aspect ratio from 200. The material displayed a good response to strain, generating a gauge factor of about 3.6 for 0.5 vol% CNT polymer nanocomposite that reduced by 40% with doubling CNT volume fraction. © 2025 Elsevier Ltd
Nickabadi, S.,
Askari sayar, M.,
Alirezaeipour, S.,
Ansari, R. Publication Date: 2025
Mechanics Based Design of Structures and Machines (15397742)53(6)pp. 4435-4464
Auxetic metamaterials have gained attention due to their unique mechanical properties. Integrating origami structures with cellular structures can significantly enhance their energy absorption capacity under mechanical loads. This study develops a novel auxetic structure by combining a curved origami design with the cross-petal auxetic structure. The structure’s behavior under in-plane compressive loading is analyzed using finite element simulations and validated through experimental testing of 3D-printed specimens. The effects of loading rates (quasi-static, low-, medium-, and high-velocity) and geometrical parameters on energy absorption are examined through parametric studies. Structure grading, based on unit cell wall thickness, is also investigated to enhance performance. Finally, the proposed structure’s energy absorption is compared with two common auxetic metamaterials (reentrant and chiral) under various loading conditions. Results indicate deformation becomes more localized with increased loading velocity, with the proposed design achieving a 70% improvement in energy absorption over non-origami designs and a 16% enhancement through grading. The main contribution of this study is the creation of a hybrid structure combining curved origami and cross-petal auxetic designs, achieving a 70% improvement in energy absorption. The dual plateau stress region and graded design further enhance performance, positioning it as an innovative solution for impact protection and soft robotics. The proposed structure exhibits up to 7.56 times higher specific energy absorption under quasi-static loading compared to reentrant and chiral designs, maintaining superior performance at higher loading velocities. © 2025 Taylor & Francis Group, LLC.
Publication Date: 2025
Materials Today Physics (25425293)59
With the rapid expansion of electronic devices and the advent of advanced wireless communication technologies utilizing millimeter-wave (mmWave) frequencies, controlling EMI has become a significant engineering challenge. Conventional EMI shielding materials primarily rely on reflection mechanisms, which often cause secondary interference and signal degradation. Additionally, inherent physical limitations, high weight, and manufacturing complexity of traditional materials have driven the need for advanced materials that predominantly absorb electromagnetic energy while minimizing reflection. Innovative approaches incorporating multilayer architectures, conductive polymer composites, carbon-based nanostructures, and two-dimensional materials such as MXenes have demonstrated promising enhancements in EMI shielding performance. This review comprehensively elucidates the fundamental principles and mechanisms underlying EMI shielding with a focus on the mmWave spectrum. Emphasis is placed on the interplay of electrical, magnetic, and structural properties of materials to achieve superior shielding effectiveness, low reflectivity, and broadband absorption of electromagnetic waves. State-of-the-art fabrication techniques for multilayer structures, porous frameworks, prefabricated conductive networks, and MXene-based composite materials are critically examined. Moreover, environmental stability issues, industrial manufacturing compatibility, and integration challenges with existing electronic systems are systematically evaluated. By synthesizing recent advances and identifying emerging trends in absorption-dominant mmWave EMI shielding materials, this article provides strategic insights and research directions aimed at the development of next-generation lightweight, flexible, and high-performance EMI shielding solutions. © 2025 Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
Publication Date: 2025
Advanced Materials Interfaces (21967350)12(12)
In recent years, graphene has emerged as a promising material for flexible wearable sensors due to its exceptional properties, including flexibility, high surface area, excellent conductivity, and remarkable mechanical strength. This review article provides a comprehensive analysis of graphene synthesis techniques, focusing on both traditional methods and advanced laser-based approaches such as laser reduction, laser ablation, and laser-induced graphene. Additionally, various laser fabrication technologies, surface modification strategies are discussed to enhance graphene's physical and chemical properties and heteroatom doping. The article further explores the diverse applications of graphene in wearable sensors, encompassing mechanical sensors, electrophysiological sensors, and gas and humidity sensors. By examining the advancements in fabrication techniques and sensor applications, this study highlights the potential of graphene-based sensors to improve the performance and predictability of wearable devices significantly. © 2025 The Author(s). Advanced Materials Interfaces published by Wiley-VCH GmbH.
Publication Date: 2025
Nano-Structures and Nano-Objects (2352507X)42
Wearable sensors aid in diagnosing various diseases by using chemical, physical, and biological sensing technologies. They also make it possible to continuously and instantly monitor a patient's physiological state. Recently, the demand for sensors that track people's surroundings, fitness and health has increased. In the meantime, the production of flexible and wearable polymer sensors based on biocompatibility, biodegradability, environmentally friendly features and cost-effectiveness has created a significant evolution in the wearable sensor industry. In this review, the most recent researches conducted in the direction of the construction of wearable sensors in different fields including physical, optical, chemical, biochemical and the working mechanism of these sensors have been reviewed. Assisting researchers in selecting the most appropriate selective and sensitive sensor is a key objective of this review. In addition, the applications of these sensors were classified into different categories and discussed in fields such as health care and remote welfare. In general, improving personal health care and monitoring their performance using wearable electrochemical and biosensor technologies have a significant impact on people's daily lives. © 2025 Elsevier B.V.
Publication Date: 2025
Thin-Walled Structures (02638231)211
In this paper, the isogeometric analysis (IGA) is extended to study the size-dependent behavior of bending, buckling and free vibration of in-plane bi-directional functionally graded porous microplates with variable thickness. In order to capture the effect of size, the modified strain gradient elasticity theory, which has three length scale parameters, is used. Regarding to the third-order shear deformation theory, the equations of motions are derived by using the Hamilton's principle and then are discretized based on the IGA approach. The material properties vary continuously through in-plane directions by employing the rule of mixture and the porosity distribution is considered an even type. The C2-continuity requirement can be easily achieved by increasing the order of the non-uniform rational B-spline (NURBS) basis functions larger than two. The influences of the size effect, aspect ratios, boundary conditions, thickness variations, material gradations, and porosity distributions on the deflections, the fundamental natural frequencies, and the buckling load values of the rectangular, circular and elliptical microplates are studied. The obtained results are compared with the previously published studies to show the performance and efficiency of the present research. © 2025 Elsevier Ltd
Hassani, F.,
Khorrami a., A.,
Golshani, A.,
Kouhkord, A.,
Ansari, R.,
Sahmani, S. Publication Date: 2025
Solar Energy (0038092X)301
The increasing global demand for energy, coupled with the depletion of fossil fuels and the growing awareness of environmental issues, has necessitated the transition towards renewable energy sources. Among the various renewable technologies, solar energy stands out as one of the most abundant and sustainable options. In photovoltaic-thermal (PV/T) systems, excess heat is transferred to a cooling medium, such as air or water, to regulate cell temperature. An intelligent and controllable framework is proposed for designing PV/T thermal systems with high levels of efficiency. The framework begins with creating a parametric design of the PV/T unit. Then, the design of experiment (DoE) block is created. In the present model, the parametric design consisted of three variables and the face-centered central composite scheme was utilized. After deriving a predictive model, linking the design variables and objective functions, the functionality of the system under varying conditions is analyzed. In the next step, a machine learning-based algorithm, i.e. non-dominated sorting differential evolution (NSDE), was utilized to find the optimum model, fulfilling adjusted needs such as higher thermal and/or electrical efficiency. It is noticed, that Nusselt number is highly influenced by changes in Reynolds number. The results revealed that the Nusselt number increases by over 80% as Reynolds number rises from 500 to 2200, demonstrating significant heat transfer enhancement. The optimization framework also led to an improvement in electrical efficiency from approximately 12.4% to 13.2%, achieved without the use of nanofluids or phase change materials. Trade-offs between thermal enhancement and pressure drop were managed through a multi-objective optimization approach, ensuring that net power consumption was minimized. The final optimized configurations reflect a balance between performance gains and energy input requirements, providing a practical and scalable design strategy for high-efficiency PV/T systems. © 2025 International Solar Energy Society
Publication Date: 2025
Thin-Walled Structures (02638231)215
This paper investigates the nonlinear vibration behavior of axially moving porous functionally graded material (FGM) truncated conical shells supported by an elastic foundation using a stress function method. The governing equations of motion are derived from von Kármán nonlinear strain-displacement relations in conjunction with the Hamilton's principle. The equations are simplified using the Galerkin method and transformed into nonlinear ordinary differential equations, which are solved through the method of multiple scales (MMS). The frequency response is analyzed in the primary, subharmonic, and superharmonic resonance regions. The effects of porosity distribution patterns along the thickness, ceramic-to-metal volume fraction, axial velocity, semi-vertex angle of the conical shell, and geometric parameters are analyzed. Results indicate that increasing axial velocity amplifies hardening behavior and reduces fundamental natural frequency. The semi-vertex angle is found to significantly influence the hardening behavior, while the stiffness of Pasternak and Winkler elastic foundations effectively reduces the peak vibration amplitude. Moreover, Pasternak stiffness exhibits a more pronounced impact on the frequency response than Winkler stiffness. © 2025 Elsevier Ltd
Publication Date: 2025
Applied Physics A: Materials Science and Processing (14320630)131(7)
A conductive network model approach is developed based on induced magneto-electric modes to investigate the thermal energy effect on the quantized resistance of a conductive polymer composite with rolled shape conductors. The concept of modes describes the characterization of energy levels in accordance with the thermal energy when the size of the solid is scaled down to a finite size. The focus relates the parameters of micro-scale phenomenon to macro-scale resistance. Along with the resistance dependence on the proportion of the conductor, the effect of the geometry and tunneling resistance on percolation threshold is simulated. The other part of the modeling approach consists of the resistance change and the ensuing conductor displacement computation. Analyses of piezoresistivity that take tunneling behavior in the percolation transition zone into account show good agreement with experimental data. By increasing the mobility of the charges, the magnetic field increases the electrical conductivity and improves electron transport states affected by the applied field. As a result of scaling the sensitivity to lower values, smaller conductors improve the effectiveness of the conductive network in facilitating charge transport. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2025.
Publication Date: 2025
Thin-Walled Structures (02638231)212
This investigation presents a comprehensive analysis of the thermomechanical behavior of functionally graded (FG) cylindrical shells subjected to cooling shock employing a novel solution methodology. Utilizing the first-order shear deformation theory, the variational differential quadrature (VDQ) approach is employed to solve the governing equation, which are derived using Hamilton's principle, then complemented by the Newmark integration technique for the time derivatives. The generalized differential quadrature (GDQ) method is employed to solve the one-dimensional transient heat conduction problem. The study systematically investigates the influences of temperature differences, boundary conditions (BCs), power law indices, and thermal load rapidity time on the vibrations and stress distributions across various surfaces of the cylindrical shell. Numerical results demonstrate that significant temperature variations lead to increased vibrational amplitudes and stress concentrations, highlighting the critical role of BCs and material properties in the dynamic behavior of FG cylindrical shells. © 2025
Mirsabetnazar a., A.,
Ansari, R.,
Ershadi, M.Z.,
Rouhi h., H. Publication Date: 2025
International Journal of Structural Stability and Dynamics (02194554)25(16)
Based on the variational differential quadrature (VDQ) method, the bending and buckling characteristics of circular plates made of functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAMs) are numerically studied in this paper. It is considered that the plate is composed of multiple GOEAM layers with graphene origami (GOri) content that changes in layer-wise patterns. The results from genetic programming-assisted micromechanical models are also employed in order to estimate the material properties. The plate is modeled according to the first-order shear deformation plate theory whose governing equations are obtained using an energy approach in the context of VDQ technique. The governing equations are given in a new vector-matrix form which can be easily utilized in coding process of numerical methods. By means of VDQ matrix differential and integral operators, the governing equations are discretized and solved to calculate the lateral deflection and critical buckling load of plates under various boundary conditions. Selected numerical results are presented to investigate the influences of boundary conditions, GOri content, folding degree and distribution pattern on the buckling and bending behaviors of FG-GOEAM plates. © 2025 World Scientific Publishing Company.
Publication Date: 2024
Iranian Polymer Journal (10261265)33(12)pp. 1677-1688
This study aims to examine how moisture absorption affects the impact behavior of a recently developed sandwich structure designed for use as a water-resistant system in the marine industry. For this purpose, two types of balsa-cored sandwich systems were manufactured, one with conventional glass fiber-epoxy (GE) skins and the other with novel fiber metal laminates (FML) skins. Subsequently, the specimens were exposed to environmental aging through distilled water immersion for 100 days before impact testing. Low-velocity impact behavior was studied using Charpy tests, while high-velocity impact tests were conducted with a light gas gun. The experimental results showed that FML sandwich systems exhibited significantly better impact characteristics compared to GE systems. Before aging, the Charpy impact strength and high-velocity impact absorbed energy of FML systems were 187% and 49% higher than those of GE ones. Another main finding was the impact properties of the FML systems showed a lower decline due to moisture aging compared to the GE systems, for both low- and high-velocity impacts. The reduction of Charpy impact strength and high-velocity impact absorbed energy due to moisture aging in GE systems with sealed edges was about 15%, and 3%, respectively, and for sealed edges FML systems was less than 12% and 1%, respectively. The results also indicated that the high-velocity impact properties of both sandwich systems studied were not significantly affected by moisture aging. In general, the findings suggest that FML skins significantly enhance both the impact resistance and environmental durability in marine balsa-cored sandwich structures. Graphical abstract: (Figure presented.) © Iran Polymer and Petrochemical Institute 2024.
Publication Date: 2024
Applied Physics A: Materials Science and Processing (14320630)130(4)
In this study, we investigate the mechanical properties of armchair phosphorene nanotubes using a combination of density functional theory (DFT) and the finite element method (FEM). Utilizing DFT, we determine the Young’s modulus, flexural rigidity, and Poisson's ratio of armchair phosphorene nanotubes. Subsequently, employing the finite element method based on the analogy of molecular mechanics and structural mechanics, we extract elemental properties for the finite element model. Our analysis reveals that the Young’s modulus of phosphorene nanotubes is intricately linked to the nanotube radius, demonstrating a dependency that converges as the radius increases. Furthermore, an increase in the aspect ratio of phosphorene nanotubes corresponds to an elevation in their Young’s modulus, with a notable exception for small aspect ratios where the impact on elastic properties is minimal. This research significantly advances our understanding of the mechanical behavior of armchair phosphorene nanotubes, offering insights crucial for unlocking their potential in diverse scientific and technological applications. The observed relationships between Young's modulus and nanotube parameters provide valuable considerations for the design and application of nanomaterials, making our findings relevant and influential in both scientific research and industrial endeavors. © The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2024.
Publication Date: 2024
Engineering Computations (02644401)41(1)pp. 68-85
Purpose: In this paper, based on the density functional theory (DFT) and finite element method (FEM), the elastic, buckling and vibrational behaviors of the monolayer bismuthene are studied. Design/methodology/approach: The computed elastic properties based on DFT are used to develop a finite element (FE) model for the monolayer bismuthene in which the Bi-Bi bonds are simulated by beam elements. Furthermore, mass elements are used to model the Bi atoms. The developed FE model is used to compute Young's modulus of monolayer bismuthene. The model is then used to evaluate the buckling force and fundamental natural frequency of the monolayer bismuthene with different geometrical parameters. Findings: Comparing the results of the FEM and DFT, it is shown that the proposed model can predict Young's modulus of the monolayer bismuthene with an acceptable accuracy. It is also shown that the influence of the vertical side length on the fundamental natural frequency of the monolayer bismuthene is not significant. However, vibrational characteristics of the bismuthene are significantly affected by the horizontal side length. Originality/value: DFT and FEM are used to study the elastic, vibrational and buckling properties of the monolayer bismuthene. The developed model can be used to predict Young's modulus of the monolayer bismuthene accurately. Effect of the vertical side length on the fundamental natural frequency is negligible. However, vibrational characteristics are significantly affected by the horizontal side length. © 2023, Emerald Publishing Limited.
Alidoust, A.,
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S. Publication Date: 2024
Composites Part A: Applied Science and Manufacturing (1359835X)180
A flexible pressure sensor utilizing carbon nanotubes (CNTs) is investigated employing a finite element methodology to delve into its electro-mechanical behavior. The responsive nature of the three-dimensional representative volume element, containing impenetrable CNT cylinders within an insulating hyperelastic elastomeric cube, is simulated to capture its sensitivity to pressure. Considering applied pressure and updated percolation pathways, a multi-step approach is employed to assess piezoresistivity. Upon adjusting positions of CNTs within the deformed state using the finite element method, novel pathways are identified using the critical distance criterion for percolation paths that contribute to the resistance network. Simulation results demonstrate good agreement with experimental data for resistivity and piezoresistive sensitivity of different CNT elastomeric nanocomposites. The finite element method helps to analyze influences of nanotube volume fraction, geometrical properties, and orientational configurations on the critical distance percolation onset. Lower CNT contents yield more substantial relative resistance changes due to fewer percolating routes. © 2024 Elsevier Ltd
Keramati y., Y.,
Ansari, R.,
Haghighi s., S.,
Eghbalian, M. Publication Date: 2024
Molecular Simulation (08927022)50(14)pp. 1116-1128
Molecular dynamics (MD) simulations have been performed to determine the reinforcing role of two-dimensional (2D) nanosheets on Young’s and shear moduli of nanosheet-strengthened polylactic acid (PLA). Various volume fractions of nanosheets in addition to different kinds of nanosheets, that is, graphene (GR), silicon carbide nanosheet (SiCNS), and boron-nitride nanosheet (BNNS), are regarded as affecting parameters on the mechanical response. Uniaxial tensile and shear tests are conducted and related stress–strain diagrams are achieved to be used for exploring mechanical properties. It is found that the incorporation of 2D nanosheets into PLA has a noticeable impact on the mechanical behavior of the polymer. In a desired percentage of volume fraction ((Formula presented.)), GR and SiCNS have performed the greatest and least roles in augmenting the mechanical properties of PLA nanocomposites, respectively. Compared to those, the reinforcing effect of the BNNS comes in between. Also, the results show that there is a growing trend in longitudinal and transverse Young’s moduli ((Formula presented.) and (Formula presented.)) and the XY-plane shear modulus ((Formula presented.)) of nanocomposites as the (Formula presented.) of nanosheets increases. © 2024 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2024
Synthetic Metals (03796779)302
Reliable, effective, and environmentally friendly supercapacitors still need development despite the progress made in many nanoscale electrode materials. In this area, composite materials made of organic polymers with high electrical conductivity and metal sulfides with various oxidation states were more attractive. This article describes the design and synthesis of zinc sulfide and polyaniline nanocomposites employing a fast and straightforward electrochemical deposition method and their use as electrode materials for supercapacitors. The structural investigation showed clumped spherical for pAni, hexagonal for pure ZnS, and coexisting hexagonal and spherical phases for ZnS@pAni nanocomposites. The ZnS@pAni nanocomposite demonstrated remarkable electrochemical efficiency and faradaic energy storage capabilities with practical reversibility. Also, an impedance inquiry found that the ZnS@pAni composite has better conductivity and a lower charge transfer resistance than its bulk components. ZnS@pAni//AC was used to create a hybrid asymmetric supercapacitor and displayed a large voltage window up to 2.06 V, 235.24 F g−1 specific capacity, and an ultimate energy density of 144.08 Wh kg−1. Also, when energy density drops to 22 Wh kg−1, substantial power delivery is achieved at 6.3 kW kg−1. Moreover, 88.05% of the capacitance was retained after the device completed 5000 cycles, suggesting good ZnS@pAni//AC asymmetric supercapacitor stability. © 2024 Elsevier B.V.
Alidoust, A.,
Haghgoo, M.,
Ansari, R.,
Jamali, J.,
Hassanzadeh-aghdam, M.K. Publication Date: 2024
Results in Engineering (25901230)24
Strain sensors have attracted great attentions for practical applications such as human-machine interface. It is challenging to model the electrical behavior of elastomeric strain sensors modified with nanomaterials. This study presents a finite element simulation to explore the piezoresistivity of graphene nanoplatelet (GNP)-filled elastomeric nanocomposites. The percolation network model is employed to determine the critical distance necessary for electrical percolation. The finite element percolation network model uses the Euclidian distance between GNPs distributed inside the representative volume element to calculate the resistivity. The influence of various parameters, including GNP alignment direction, aspect ratio, and volume fraction, on the resistivity changes of the nanocomposite is investigated. Results demonstrate that nearly 20% more tunneling distance is allowed for percolation of nanocomposite with 30% larger aspect ratio GNPs. Findings reveal that as the volume fraction of GNPs increases, the critical distance for the electrical percolation decreases significantly. © 2024
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Nanotechnology (09574484)35(32)
In this paper, an analytical model based on the percolation theory has been developed to predict the subbands effect on the effective electrical resistivity of carbon nanotubes (CNT)-based polymer nanocomposites. The CNTs are considered as randomly distributed or aligned channel material in the polymer transmitting electrons through tunneling. The tunneling effect takes into account the electron transmission between each connected pair of CNTs to evaluate electrical resistivity. The modeling approach contains two steps of primary prediction of resistivity and further calculation of CNTs’ displacements and subsequent change of the resistance. A good agreement is found between the analytical model predictions and experimental data when the tunneling behavior was considered in the percolation transition region. The effect of CNT diameter, orientation state, and subbands on the resistivity has been investigated. The results depict that subbands increment is a collateral benefit to the aspect ratio in decreasing the resistivity. The analytical results demonstrate that a random CNT dispersion leads to a decreased piezoresistivity, while an increased strain range depicts a more non-linear behavior. © 2024 IOP Publishing Ltd.
Publication Date: 2024
Polymer Bulletin (14362449)81(5)pp. 4319-4334
In this paper, the creep modulus of polymer/spherical Al2O3 nanoparticle nanocomposites is predicted. An analytical micromechanics model is developed which considers the role of nanoparticle agglomeration and interphase between the nanoparticle and polymer matrix. To show the validity of the micromechanical model, the predictions are compared with the experimental measurements for different nanocomposites. It is found that the creep modulus of the polymer matrix improves by addition of a low content of Al2O3 nanoparticles. However, the nanoparticle agglomeration which may be generated at high content, decreases the creep modulus of nanocomposites. A uniform dispersion of nanoparticles into the polymer matrix is needed to have highest mechanical properties of polymer/Al2O3 nanocomposites. Formation of interphase with higher mechanical properties than the polymer matrix can enhance the nanocomposite creep modulus. By the use of micromechanical model, the effect of elastic modulus and thickness of the interphase between the polymer and nanoparticle on the nanocomposite creep modulus is investigated. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023.
Mirnezhad m., M.,
Ansari, R.,
Falahatgar s.r., S.R.,
Aghdasi p., P. Publication Date: 2024
Scientific Reports (20452322)14(1)
In this paper, the quantum effects of fine scaling on the buckling behavior of carbon nanotubes (CNTs) under axial loading are investigated. Molecular mechanics and quantum mechanics are respectively utilized to study the buckling behavior and to obtain the molecular mechanics coefficients of fine-scale nanotubes. The results of buckling behavior of CNTs with different chiralities with finite and infinite dimensions are given, and a comparison study is presented on them. The differences between finite and infinite nanotubes reflect the quantum effects of fine scaling on the buckling behavior. In addition, the results show that the dimensional changes highly affect the mechanical properties and the buckling behavior of CNTs to certain dimensions. Moreover, dimensional changes have a significant effect on the critical buckling strain. Beside, in addition to the structure dimensions, the arrangement of structural and boundary atoms have a major influence on the buckling behavior. © The Author(s) 2024.
Saberi, M.,
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Alexandria Engineering Journal (11100168)108pp. 344-353
There exists a pressing need for polymeric nanocomposites exhibiting enhanced electrical properties when subjected to external electric fields. Via the development of an efficient model based on the physical-analytical relations, the electrical conductivity and percolation threshold of ternary nanocomposites enriched with the synergy of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) are investigated. In so doing, the electrical conductivity of carbon nano-additives is first computed using a discretizer scheme, and subsequently, by incorporating the basic electrical conduction mechanisms and employing the average polarization theory, insights into the overall electrical behavior of CNT/GNP/polymer networks are elucidated. The formulation of the extended framework is in the form of case assessments covering effects of volume fraction and geometry of carbonaceous nanofillers, contribution of the interphase region, which serves as an electron hopping duct, tunneling distance, and electrical potential barrier height. In connection with validation, satisfactory alignment between the predicted outcomes and experimental results substantiates the efficacy of the proposed approach for both binary and ternary nanocomposites. Moreover, parametric studies reveal the remarkable sensitivity of electrical properties of nanocomposites to the aforementioned factors. These findings are valuable and enlightening for the design and manufacturing of highly conductive systems, resulting in time and financial savings. © 2024 The Authors
Mirsabetnazar a., A.,
Ansari, R.,
Zargar ershadi m., M.,
Rouhi h., H. Publication Date: 2024
Materials Today Communications (23524928)41
The behaviors of annular sector plates made of functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAMs) under the action of buckling and bending loads are investigated herein using a numerical approach. Multiple GOEAM layers with graphene origami (GOri) content are considered for the plate which changes in layer-wise patterns. Moreover, the material properties of the plate are calculated using novel genetic programming-assisted micromechanical models. In order to derive the governing equations, the Mindlin plate theory in conjunction with Hamilton's principle is utilized within the framework of the variational differential quadrature (VDQ) method. The vector-matrix representation of the presented formulation can be beneficial from the viewpoint of implementing numerical approaches. The governing equations are then discretized and solved based on VDQ matrix differential and integral operators so as to obtain the critical buckling load and maximum lateral deflection of plates with different edge conditions. The effects of GOri content, folding degree and distribution pattern on the results are studied. It is revealed that increasing the GOri content leads to the negative Poisson's ratio (NPR) effect which respectively reduces and increases the lateral deflection and the critical buckling load. © 2024
Mirsabetnazar a., A.,
Ansari, R.,
Zargar ershadi m., M.,
Rouhi h., H. Publication Date: 2024
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)46(12)
In this paper, an efficient numerical approach is developed to address the linear bending, free vibration and buckling problems of beams made of functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAMs). It is considered that the beam is composed of multiple GOEAM layers with graphene origami (GOri) content which changes in layer-wise patterns. The material properties of the beam are also computed based on the genetic programming-assisted micromechanical models. The governing equations are derived within the framework of Timoshenko beam theory using Hamilton’s principle and the variational differential quadrature (VDQ) method. The formulation is presented in a novel vector–matrix form, and the VDQ technique is directly applied to the weak form of equations, so that the derivation process of the strong form of the equations is bypassed. The governing equations are solved after discretizing via VDQ matrix operators. Parametric studies are conducted to show the effects of GOri content, folding degree and distribution pattern on the critical buckling load, fundamental frequency and maximum lateral deflection of FG-GOEAM beams subject to various end conditions. © The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.
Haghgoo, M.,
Alidoust, A.,
Ansari, R.,
Jamali, J.,
Hassanzadeh-aghdam, M.K. Publication Date: 2024
Composites Part A: Applied Science and Manufacturing (1359835X)187
Resistivity and piezoresistive sensitivity of Carbon Black (CB) elastomeric nanocomposites are studied using a finite element method with a conductive network model. CB spheres are placed into Representative Volume Elements (RVEs) in random positions to perform simulations and obtain the strained state and new position of particles. Numerical results are implemented into a breadth-first search algorithm tailored to find percolation pathways from one end of the RVE to another based on the shortest distance between CBs in the strained regime. Percolation pathways are used by the conductive network model to determine the critical distance for resistivity. Resistivity diminishes as the critical distance increases attributed to a greater number of electrons penetrating the barriers. Critical distance at which tunneling can occur expands with an increase in barrier potential. Smaller CBs that can more efficiently occupy the gaps lead to a reduction in the critical distance range necessary for percolation to happen. © 2024 Elsevier Ltd
Publication Date: 2024
Bulletin of Materials Science (02504707)47(2)
In this study, semi-infinite two-section nanotubes of different radii are used as nanocontainers to encapsulate spherical fullerenes. In particular, the encapsulation behaviours of C60 and B36N36 fullerenes inside carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) are investigated. In order to determine the van der Waals (vdW) interactions between fullerenes and two-section nanotubes, the continuum approximation along with the classical 6-12 Lennard–Jones (LJ) potential function is employed. The proposed continuum model provides explicit analytical expressions for the evaluations of total potential energy and interaction force. Moreover, the suction energy, a measure of the total increase in the kinetic energy experienced by the core, is derived as a function of geometrical parameters and materials of fullerene and nanotube. For C60-CNT, C60-BNNT, B36N36-CNT and B36N36-BNNT mechanisms, the distributions of vdW interactions as well as the nature of suction energy are studied in detail. It is demonstrated that the weakest and strongest interactions are related to C60-CNT and B36N36-BNNT mechanisms. In addition, the interaction of B36N36-CNT mechanism is found to be stronger than that of C60-BNNT one. It is further found that the length of the first section of the nanotube has a negligible effect on the vdW interactions and suction energy. The results of this study also suggest that for a given type of fullerene, the suction radius of CNTs is smaller than that of BNNTs. By contrast, the optimal radius that gives rise to maximum suction energy is unique for all considered mechanisms. The present theoretical study presents deep insights into the basic concepts of encapsulation behaviour and it could be useful to guide the design of novel nanodevices where the nanocapsule may be utilized as a drug container. © Indian Academy of Sciences 2024.
Saberi, M.,
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Composites Part A: Applied Science and Manufacturing (1359835X)185
Inter-cluster bridging of carbon nanotubes (CNTs) and carbon black (CB) nanoparticles conjoins inactive branches of carbonaceous nanofillers within the matrix and reduces the electron tunneling distance. This mechanism moderately overcomes quantum tunneling and provides percolative polymer networks exhibiting favorable electrical responses. This study focuses on devising an analytical procedure to scrutinize the electrical conductivity and percolation threshold of CNT/CB/polymer nanocomposites. To involve the physics of electrical processes, the modeling approach considers cylindrical CNTs and spherical CB nanoparticles surrounded by a continuum interphase, which serves as an electron hopping duct. This model is extended in a bottom-up micromechanics generalization to a level where it is capable of predicting the effects of a wide range of microstructural properties. The comparison of predictions with those obtained via experimental examinations, while affirming the infrastructure for investigating the electrical behavior of binary systems, convincingly captures the electrical conductivity/percolation threshold of ternary nanocomposites containing CNT/CB nanofillers. © 2024 Elsevier Ltd
Publication Date: 2024
Journal of Molecular Graphics and Modelling (10933263)129
In this paper, the finite element method is utilized to evaluate the behavior of the armchair phosphorene nanotubes under the compressive loading. The energy equations of the molecular and structural mechanics are used to obtain the elemental properties. The critical compressive forces of various armchair phosphorene nanotubes are computed with clamped-clamped and clamped-free boundary conditions. Results show that the stability of armchair phosphorene nanotubes increases with increasing nanotube aspect ratio, particularly under clamped-clamped boundary conditions. Finally, the buckling mode shapes of armchair phosphorene nanotubes under different boundary conditions are compared. Our work offers valuable insights into how these nanotubes respond to mechanical stress, helps determine elemental properties, and investigates the effects of nanotube geometry and different boundary conditions on their stability. This knowledge has broad applications in fields like nanotechnology, materials science, and nanomechanics, advancing the understanding of nanoscale materials and their potential for various practical uses. © 2024 Elsevier Inc.
Publication Date: 2024
Materials Science in Semiconductor Processing (13698001)174
In the current study, the density functional theory is utilized to investigate the elastic, plastic and electronic properties of the 2×2 and 3×3 pristine and transition metal (TM) doped germanene. Different atoms, including V, Co, Fe, Mn, Cr, Ti, Ni and Sc are selected for this purpose. It is shown that doping of the transition metal atoms would result in the reduction of the Young's and bulk moduli of the germanene. In addition, the isotropic behavior of these nanosheets were shown by comparing the Young's moduli of both pristine and doped structures in armchair and zigzag directions. Furthermore, the plastic behavior of these structures were investigated by increasing the applied loading. It was seen that except for the 2×2 Co-doped monolayer, the yield strain of both 2×2 and 3×3 nanosheets were reduced under uniaxial and biaxial loading. In 2×2 doped nanosheets under uniaxial loading, the highest reduction occurs for Ti-doped germanene, and in 3×3 cases, the highest reduction happens for Co, Ni, Fe and Sc-doped germanene. Electron localization function revealed the ionic nature of the boding between TM atoms and germanium while the density of state indicated that doping of transition metals would change the semi-metallic behavior of germanene to metallic except for Ti-doped structure. The findings provide valuable information for potential applications in nanotechnology, guiding the development of new materials with specific characteristics based on the identified impacts of different transition metals. © 2024 Elsevier Ltd
Rahnama, E.K.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2024
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)238(6)pp. 1082-1098
In this article, the effect of graphene nanoadditives on the fatigue limit of unidirectional glass fiber-reinforced polymer (GFRP) composites has been investigated. A micromechanical model based on the crack growth has been used to analyze the fatigue limit response of unidirectional GFRP hybrid composite containing nanoadditives. The influence of different percentages of graphene nanosheets (GNS) and different types of nanofiller dispersion has been investigated by the micromechanical model. The fatigue limit of unidirectional GFRP hybrid composites has been plotted in terms of glass fiber volume fraction, interfacial friction shear stress, interfacial fracture energy and reference length. The fatigue limit of unidirectional composites can be improved by addition of GNS into the polymer matrix of such composite systems. The obtained results on the GNS dispersion type demonstrate that the uniform dispersion of GNS into the polymer matrix increases the fatigue limit of unidirectional GFRP hybrid composites. As the agglomeration density of GNS is low, the fatigue limit of GFRP hybrid composites will be improved more than when the density of agglomeration is high. © IMechE 2023.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Sensors and Actuators A: Physical (09244247)373
The effective electrical resistivity of carbon nanotubes (CNT)-based polymer nanocomposites is studied using an analytical model based on the percolation theory. The CNTs are considered as rod-like conductors that are aligned or randomly dispersed in the polymer to transport electrons by tunneling. When assessing non-zero temperature electrical resistivity, the tunneling effect considers the thermally energized electron transmission that occurs between each coupled pair of CNTs by the electrical transport model. The modeling technique consists of three steps: identifying the percolating network from the primary formation of CNTs, initial prediction of resistivity by equivalent resistor network, computation of the displacements of CNTs for the resistance change. Taking into consideration the behavior of tunneling in the percolation transition zone, a good agreement is obtained between the model results and experimental data. The verified code is used to investigate the sensitivity for different orientation states, aspect ratios and mode numbers. The results reveal lower sensitivity for higher mode numbers as collateral with the influence of increasing randomness. © 2024 Elsevier B.V.
Haghgoo, M.,
Alidoust, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2024
Smart Materials and Structures (09641726)33(5)
A finite element (FE)-percolation model approach is developed to predict the strain-sensitive response of the three-dimensional (3D) representative volume element (RVE) of carbon nanotube (CNT)-elastomeric nanocomposite. In the simulation model, CNTs are modeled as solid, impenetrable cylinders inside a cubic insulating matrix. FE simulation is performed to evaluate the structural response of the RVE under applied strain. The FE model updates the locations of the CNTs in the deformed RVE. The paths are found using a suitable 3D resistance network associated with different percolation paths involved in the critical distance criterion. The percolation model utilizes the paths found to identify the electrical circuit for predicting tunneling conductivity. The simulating algorithm is used to study the influence of tunneling barrier height, nanotube volume fraction, and geometrical aspects. The lowest critical distance criterion is achieved for higher volume fractions and the most heightened sensitivity is obtained for lower CNT aspect ratios. © 2024 IOP Publishing Ltd.
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Mechanics of Advanced Materials and Structures (15210596)31(24)pp. 6109-6125
A micromechanical model implemented with the finite element method (FEM) using the representative volume element (RVE) approach is developed to investigate the creep compliance behavior of carbon nanotube (CNT)-polymer nanocomposites. Effects of the CNT waviness, orientation, volume fraction and aspect ratio on the creep compliance of the nanocomposite are examined. Contribution of the interphase region formed due to the interaction between CNTs and matrix to the nanocomposite creep behavior is considered. The nanocomposite creep behavior is affiliate on the waviness and orientation of CNTs. Increasing the volume fraction and length of CNT and interphase thickness improves the nanocomposite creep performance. © 2023 Taylor & Francis Group, LLC.
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Mechanics of Advanced Materials and Structures (15210596)31(27)pp. 9117-9129
Effects of incorporating carbon nanotubes (CNTs) and short carbon fibers (SCFs) into the polyvinyl chloride (PVC) foam core on the flexural behavior of sandwich beams are investigated. Upper and lower skins are made of laminated composites and an initial debonded interface among the upper skin and core is considered. The mechanical properties of the hybrid CNT/SCF/PVC core are determined employing micromechanical models. To inspect the flexural behavior of sandwich beams at macro-scale, end notched shear (ENS) test is simulated using the finite element method (FEM). The results indicate an increase in flexural stiffness in the presence of CNT and SCF. © 2023 Taylor & Francis Group, LLC.
Publication Date: 2024
Applied Physics A: Materials Science and Processing (14320630)130(4)
First principle calculations are used here to obtain the mechanical properties of the monolayer zigzag phosphorene nanosheet. These properties are used to compute some force constants. A finite element model is proposed to investigate the mechanical properties of the zigzag phosphorene nanosheets which is formed by some beam elements. The properties of the beam elements are functions of the mentioned forced constants. The proposed finite element model is used to study the mechanical properties of the monolayer zigzag phosphorene nanosheet under the tensile and compressive loadings. It is shown that the proposed finite element model can predict the mechanical properties of the zigzag phosphorene nanosheet with good accuracy. The multiscale analysis in this study leverages finite element analysis as a distinctive approach, complementing the nanoscale capabilities of density functional theory and molecular dynamics by overcoming limitations faced by these two methods in representing complex scenarios. Furthermore, finite element analysis demonstrates computational efficiency for larger structures, making it suitable for systems where atomistic simulations may be impractical. © The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature 2024.
Ansari, R.,
Zargar ershadi m., M.,
Laskoukalayeh, H.A.,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2024
International Journal of Structural Stability and Dynamics (02194554)24(9)
The nonlinear vibration response of rectangular plates made of functionally graded porous materials (FGPs) induced by hygrothermal loading is investigated in this article using a numerical approach. The effect of elastic foundation on the vibrations is taken into account according to the Winkler-Pasternak model. Hygroscopic stresses produced due to nonlinear rise in moisture concentration are also considered. The temperature-dependent material properties of plate are computed based on the modified Voigt's rule of mixture and Touloukian experiments for even and uneven distribution patterns of porosity. Within the framework of the first-order shear deformation plate theory and von-Kármán nonlinearity, Hamilton's principle is utilized in order to derive the equations of motions. To achieve the temporal evolution of maximum lateral deflection of hygrothermally-induced plates, the generalized differential quadrature (GDQ) and Newmark integration methods are employed. Selected numerical results are presented to study the influences of temperature distribution, porosity volume fraction, moisture concentration, geometrical parameters, elastic foundation parameters and FG index on the geometrically nonlinear vibrations of FG porous plates with various boundary conditions. © 2024 World Scientific Publishing Company.
Publication Date: 2024
Surface and Interface Analysis (01422421)56(9)pp. 616-627
Current study presents a novel hybrid approach combining finite element modeling and density functional theory calculations to investigate the mechanical properties of monolayer puckered arsenene. The multiscale analysis in this study leverages finite element analysis as a distinctive approach, complementing the nano-scale capabilities of density functional theory and molecular dynamics by overcoming limitations faced by these two methods in representing complex scenarios. Furthermore, finite element analysis demonstrates computational efficiency for larger structures, making it suitable for systems where atomistic simulations may be impractical. This hybrid methodology offers a unique framework for accurately predicting key properties, including elastic modulus and buckling force, by synergistically integrating the strengths of both computational techniques. In addition to demonstrating the effectiveness of our approach in accurately capturing material behavior, our findings shed light on fundamental aspects of nanoscale mechanics, with implications for various applications in nanotechnology, materials science, and structural engineering. By providing a deeper understanding of the mechanical response of 2D materials, our research contributes to advancing the field of nanoscale materials engineering and informs the design of innovative nanostructures with tailored mechanical properties. © 2024 John Wiley & Sons Ltd.
Ansari, R.,
Zargar ershadi m., M.,
Akbardoost laskoukalayeh h., ,
Rouhi h., H. Publication Date: 2024
Mechanics Based Design of Structures and Machines (15397742)52(9)pp. 6841-6857
In the present research, the large-amplitude vibration behavior of rectangular plates subjected to cooling shock is investigated based on a numerical solution approach. It is considered that the plates are made of functionally graded materials as a mixture of stainless steel and low-carbon steel. The thermoelastic properties are also considered temperature-dependent which are estimated based on available experimental data. According to the Mindlin plate theory, the nonlinear governing equations of motion together with corresponding boundary conditions are derived. The temperature profile is also obtained based on a one-dimensional Fourier-type transient heat conduction equation. Moreover, two time-dependent thermal loading scenarios for cooling shock on the plate’s top face are considered. To solve the problem numerically, the well-known generalized differential quadrature technique is used for discretization considering the Chebyshev–Gauss–Lobatto grid. In addition, the governing equations are traced in time by Newmark’s time integration scheme. After showing the validity of developed approach, a parametric study is presented to investigate the stress changes along the thickness and the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material properties on the nonlinear vibrations of plates with various boundary conditions subjected to sudden decrease of temperature. It is concluded that the thermal load rapidity time has a significant role in the vibrational behavior and the stress distribution of the plate. © 2023 Taylor & Francis Group, LLC.
Publication Date: 2024
Archive of Applied Mechanics (14320681)94(4)pp. 801-818
In this paper, the nonlinear large-amplitude vibrations of shallow arch structures made of functionally graded materials (FGMs) under cooling shock have been investigated. It is considered that the FG shallow arch is made of low carbon steel AISI1020 and stainless steel (SUS304), whose material properties change in the thickness direction. Using the kinematic assumptions that are modeled based on the first-order shear deformation theory (FSDT) and the von Kármán’s geometrical nonlinearity; along with the aid of Hamilton’s principle, the shallow arch motion equations are obtained. The material properties vary in the direction of arch’s thickness due to the temperature changes and material distribution. Based on the Voigt rule of mixture and power law distribution, the dependence of material properties on temperature and material distribution is defined. Assuming uncoupled theory of thermoelasticity, first, the one-dimensional heat conduction equation is solved along the thickness of the arch in order to obtain the temperature distribution. Afterward, the equations of motion are solved. For the numerical solution of the heat conduction equation and the nonlinear equations of motion, the iterative hybrid method of generalized differential quadrature and the Newmark time integration scheme has been used in an iterative Newton–Raphson loop. After validating the present formulation, a parametric scrutiny is conducted regarding the influence of various parameters, namely, thermal load rapidity time, FG-index, dimensional parameters on the mid-plane non-dimensional lateral deflection of the arch as well as the changes in stress and material properties. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Publication Date: 2024
Mechanics of Advanced Materials and Structures (15210596)31(8)pp. 1655-1665
The aim of current investigation is to study the dynamic behavior of shells made of unsymmetric laminated composites. Based on the higher-order shell model with twelve parameters, a shell element with four nodes is designed and equipped with the ANS method to circumvent the transverse shear locking. Next, by using the Hamilton’s principle, the mass and the stiffness matrices as well as the load vector are extracted. Additionally, the standard Newmark approach for the numerical time integration is employed. Some problems involving plates and cylindrical and spherical shells are solved to verify the performance of the proposed finite element formulation. © 2023 Taylor & Francis Group, LLC.
Publication Date: 2024
Engineering with Computers (14355663)40(3)pp. 1431-1450
The concentration of the current contribution is on the geometrically nonlinear analysis of laminated composite shells employing the finite element method. For this purpose, the use is made of a higher-order shell model with extensible directors possessing twelve parameters, then the exact Green–Lagrange strains and the three-dimensional second Piola–Kirchhoff stress tensor are extracted based on the base vectors of the shell mid-surface. The principle of virtual work is adopted to derive the weak form of governing equations. A computationally efficient four-node shell element is designed and to remedy the locking problems involving transverse shear, membrane and curvature–thickness ones, the ANS (assumed natural strain) approach and the assumed strain scheme are used. Finally, standard benchmarks are solved for isotropic materials allowing geometric nonlinearity to examine the performance of the proposed shell element and then results of thin and thick layered composite structures are presented. © The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature 2023.
Ansari, R.,
Ershadi, M.Z.,
Mirsabetnazar a., A.,
Oskouie, M.F. Publication Date: 2024
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)46(9)
In this paper, the nonlinear large amplitude vibrations of functionally graded material porous annular sector plates have been investigated. The effects of considering nonlinearity in scrutinizing the large amplitude thermally induced vibrations of the annular sector plates have been studied. Additionally, in this work, the effects of moisture distribution and the presence of material porosity are taken into account. Material and temperature distribution in the thickness direction of the plate cause changes in the hygro-thermo-mechanical material properties in the corresponding direction. To define the dependence of material properties on position and temperature, the power law distribution and the Touloukian formula are employed, respectively. Next, according to the classical theory of thermoelasticity, the one-dimensional heat conduction equation along the thickness direction of the plate is solved and the temperature profile is obtained. Afterward, knowing the temperature distribution, the nonlinear equations of motion, which are derived employing Hamilton’s principle, are solved for each time step. To numerically solve the equations, first, using the generalized differential quadrature method (GDQM), the spatial derivatives are discretized and a differential equation with only the time derivatives is achieved, then the time-dependent differential equation is solved utilizing the Newmark implicit time integration method. Finally, a parametric numerical analysis is conducted to investigate the effects of various parameters on the vibrational behavior of the plate. © The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.
Publication Date: 2024
Mechanics Based Design of Structures and Machines (15397742)52(2)pp. 1042-1059
In this work, the nonlinear vibrations of functionally graded (FG) porous circular plates under hygro-thermal loading is studied utilizing a numerical approach. Hygroscopic stresses generated due to the nonlinear rise in moisture concentration, even and uneven porosity distributions, and temperature dependency of material properties are all taken into account. Modified Voigt’s rule of mixture is applied to obtain the hygro-thermo-mechanical properties of the FG circular plate. All material properties are assumed to be temperature-dependent using the Touloukian formula. In order to obtain the equations of motion, the first-order shear deformation theory, von-Kármán geometrical non-linearity assumption, and hygro-thermal strains are considered concurrently. After deriving the equations of motion using Hamilton’s principle, the differential quadrature method and the Newmark-beta time integration scheme are employed in conjunction with an iterative approach to solve the set of nonlinear governing differential equations of motion. The effects of various parameters including temperature distribution, plate’s thickness, porosity volume fraction, moisture concentration, and FG index are studied on plate’s maximum non-dimensional lateral deflection. © 2022 Taylor & Francis Group, LLC.
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jamali, J. Publication Date: 2024
Journal of Composite Materials (00219983)58(9)pp. 1123-1136
The optimal performance of composites enriched with hollow spheres has been reported in contemporary literature, whereas their thermal properties have received less attention. In this regard, a finite element method (FEM)-based micromechanical model has been developed systematically to investigate the role of intra-matrix embedding of hollow spheres on the thermal conductivity and coefficient of thermal expansion (CTE) of unidirectional fiber-reinforced hybrid composites. In so doing, the concept of representative volume element (RVE) considers microstructures comprising an epoxy matrix, E-glass fiber, and E-glass hollow spheres, assuming perfect bonding (ideal interface) between the components and modified approximate periodic boundary conditions. By computing the longitudinal and transverse temperature gradients generated due to the application of uniform heat flux as well as the geometrical variation in RVE owing to temperature enhancement, thermal conductivity and CTE have been respectively determined. Comprehensive evaluations have been conducted to examine the effects of microstructural-level features, including fiber volume content and orientation, plus volume content and thickness of hollow spheres, on the effective thermal conductivity and CTE of pseudo-porous ternary E-glass/epoxy composites. © The Author(s) 2024.
Nickabadi, S.,
Sayar, M.A.,
Alirezaeipour, S.,
Ansari, R. Publication Date: 2024
Journal of Sandwich Structures and Materials (15307972)26(7)pp. 1129-1164
Auxetic metamaterials, characterized by their negative Poisson’s ratio, offer promising prospects for utilization in absorbing energy during quasi-static compressive loading as well as in applications requiring impact energy absorption. The optimization of auxetic structures’ geometrical parameters can improve their performance. This research aims to optimize the design of an auxetic structure for maximum specific energy absorption and investigate its behavior under quasi-static compressive and high-velocity impact loading. The geometrical parameters of the cross-petal auxetic structure are optimized using genetic algorithm and a neural network surrogate model. The behavior of the optimized auxetic structure is examined in quasi-static compressive loading and compared with that of the basic auxetic structure using finite element simulations. The optimized auxetic structure is then evaluated in high-velocity impact loading as the core of a sandwich panel, with two plates placed in the front and rear. Simulations of projectile impacts at velocities ranging from 100 to 250 m/s reveal the sandwich panel’s behavior. Results indicate a 69.82% increase in specific energy absorption capacity for the optimized auxetic structure as compared to the basic structure in quasi-static compressive loading. In high-velocity impact, the sandwich panel with the optimal auxetic core outperforms the one with the basic core. At velocities more than the minimum perforation velocity, the core contributes about 64%–67% of the total absorbed energy by the sandwich panel. © The Author(s) 2024.
Publication Date: 2024
Smart Materials and Structures (09641726)33(11)
Flexible pressure sensors are needed for future artificial electronic skin applications. Carbon black (CB)-enhanced elastomers are known for their unique conductivity, allowing for special uses in sensor technology. This research analyzes the sensitivity of elastomeric sensors reinforced with CB, under a pre-strained buckle, using a modified percolation network model to enhance performance in sensing applications. The finite element method is employed to analyze the piezoresistive characteristics of the sensors across various thicknesses. The research involves analyzing the strain patterns of buckled piezoresistive sensors when an indenter applies a load, and how this influences the sensors’ resistivity. The mechanical parameter is directly correlated to the sensor sensitivity through the maximum principal strain. The model shows a good agreement with the experimental data. The pressure sensitivity resulting from indenter compressive contact is 0.03 and 0.0061 kPa−1 in the pressure range of 0-1 and 0-5 kPa for wavy and straight 1000 μm buckled sensors, respectively. The results show that the film with 50% taller waves has a 40%-60% narrower pressure sensing ranges. Moreover, results indicate that adding waves to the geometry of the sensor improves the piezoresistive behavior by increasing the relative displacements of edges. Results also reveal more stable performance from fewer waves and a higher working range by thicker sensors. © 2024 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.
Mirnezhad m., M.,
Ansari, R.,
Falahatgar s.r., S.R.,
Aghdasi p., P. Publication Date: 2024
Surface and Interface Analysis (01422421)56(10)pp. 681-712
In this study, we introduce a comprehensive investigation into the buckling behavior of carbon nanotubes (CNTs) using a combined approach of quantum mechanics and molecular mechanics methods. A novel aspect of our research lies in the exploration of the quantum effects of fine scaling on the buckling behavior of finite-length nanotubes across various dimensions and chiralities. Specifically, we analyze the critical buckling strain variations in CNTs with distinct lengths, diameters, and chiralities, revealing pronounced differences influenced by atomic arrangement and the type of structure used in nanotube construction. Our findings elucidate that at smaller dimensions, (Formula presented.) nanotubes exhibit a higher critical buckling strain than other chiralities, while zigzag atomic arrangements demonstrate greater resistance to torsional loading at larger diameters. Additionally, we compare the buckling behavior of nanotubes obtained by wrapping armchair and zigzag nanosheets, highlighting differential resistance trends. This research not only underscores the critical role of quantum effects in determining nanotube buckling but also provides valuable insights into the nuanced influences of atomic arrangement and nanosheet type on the mechanical properties of CNTs. Thus, our work contributes a novel perspective to the field, bridging the gap between quantum mechanics and the mechanical behavior of nanostructures, which has significant implications for the design and application of nanoscale materials. © 2024 John Wiley & Sons, Ltd.
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2024
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)46(6)
Thermoelastic constants seem to be important in designing metal-based composite structures under temperature variations. In the current research, the finite element (FE) model has been utilized as a numerical tool to predict equivalent thermoelastic constants of the aluminum matrix composite (AMC) filled with carbon nanotubes (CNTs). The representative volume element of the model has been constructed such that CNTs are randomly oriented and dispersed into the AMC. As an important microstructural factor involved in the CNT-filled AMC, the interfacial reaction product between the two basic phases which may be generated during the composite fabrication has been taken into account. To understand the effect of critical microstructural factors, the equivalent thermoelastic constant of the CNT-filled AMC has been plotted as a function of the percentage and diameter of the nanotube, as well as the elastic modulus, Poisson’s ratio, thermoelastic property and size of the interfacial region. Since CNTs seldom remain straight inclusions, both straight and wavy configurations of nanotubes have been micromechanically analyzed. When the CNT volume fraction is 5%, the thermoelastic constants of the AMC containing wavy and straight CNTs are 21.8 × 10–6 1/K and 20.6 × 10–6 1/K, respectively. A parametric study has been carried out to understand the role of alignment of CNTs in the AMC thermoelastic constant. It is found when the nanotube content is 5 vol%, the thermoelastic constants of the AMC containing randomly oriented and aligned CNTs are 21.8 × 10–6 1/K and 19.8 × 10–6 1/K, respectively. The FE method has been utilized to estimate the equivalent thermoelastic constants of unidirectionally AMCs reinforced by long and short CNTs with the wavy configuration. Comparisons have been made between the present FE predictions and experiments as well as results of other micromechanics approaches. © The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2024.
Publication Date: 2024
Applied Physics A: Materials Science and Processing (14320630)130(5)
This study employs density functional theory calculations to analyze the structural and mechanical properties of stanene nanosheets (SnNs), including elastic moduli, Poisson’s ratio, and plastic behavior under various loads. Parameters of the Morse potential function governing stanene atom interactions are explored. The nanosheets demonstrate isotropic behavior with minimal discrepancy in Young’s modulus between armchair and zigzag directions. Additionally, a progressive finite element method investigates fracture mechanics, simulating the mechanical response using a modified Morse potential function. The nonlinear stress–strain relationships for both pristine and defective armchair and zigzag stanene nanosheets are elucidated, revealing brittle behavior and slightly higher mechanical properties in armchair stanene. Single-vacancy defects significantly impact mechanical properties of stanene, while Stone–Wales defects have negligible effects. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Publication Date: 2024
Acta Mechanica (16196937)235(4)pp. 1887-1909
A micromechanics procedure performed by the finite element method (FEM) was developed for the sake of examining the synergistic effects of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) hybrids on the elastic and viscoelastic properties of polymer nanocomposites. The representative volume element (RVE) approach was employed owing to its capability to consider various nano-additives with disparate dimensions and evaluate microstructure-level aspects. Constant-strain minimization method and linear viscoelastic model were utilized to predict components of elastic stiffness and creep compliance tensors. The validity of the proposed model was assessed by comparison with the well-established Halpin–Tsai micromechanical model and available experimental measurements, providing an acceptable agreement. Effects of orientation (random or unidirectional dispersion), volume content, and variation in the length and thickness of the carbonaceous nano-additives on the Young’s modulus, Poisson’s ratio, and creep compliance of CNT/GNP/epoxy nanocomposites were investigated. The results explicitly revealed that the CNT and GNP contributions to the mechanical reinforcement and the creep resistance in polymer are strongly associated with their distribution and volume content within the hosting matrix. Moreover, the outcomes imply that increasing the length of CNT, reducing the thickness of GNP lead to increasing Young’s modulus, and decreasing creep compliance (or increasing creep resistance) of CNT/GNP/epoxy nanocomposites. © The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature 2023.
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S. Publication Date: 2024
European Journal of Mechanics, A/Solids (09977538)103
Progressive innovations in the field of nanotechnology demonstrate that through the radial growth of aligned carbon nanotubes (CNTs) on the circumferential surfaces of fibers known as fuzzy fibers, the transverse elastic properties of fiber-reinforced composites are notably improved. The main objective of the present work is to numerically examine the effects of using fuzzy fiber-reinforced composite (FFRC) skins on the flexural behavior of sandwich structures. Based on the considered two-stage analysis, in the first instance, the mechanical properties of FFRC are determined by the simplified unit cell (SUC) micromechanical model. Afterward, by simulating the three-point bending test via the finite element method (FEM), major assessments are accomplished to reflect the effects of microstructure-level features, including fiber and CNT volume fractions, CNT/polymer interphase, and CNT diameter, on the bending stiffness and debonding growth between the FFRC skin and polyvinyl chloride (PVC) foam core. The results reveal the satisfactory influence of employing FFRC skins on improving the flexural behavior of sandwich structures. © 2023 Elsevier Masson SAS
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Kim, J. Publication Date: 2024
Composites Part A: Applied Science and Manufacturing (1359835X)185
The percolation inception of CNT-polymer nanocomposites is studied considering the magneto-electric field effects on CNT subbands. The analytical model predicts the electrical conductivity where CNTs are modeled as slender rods with their geometric orientations as randomly distributed or aligned to transfer electrons at tunneling distance range. The tunneling effect takes into account the electron transmission between every linked pair of CNTs when evaluating electrical resistance. The subsequent CNT displacement computation and the resistance change comprise the other phase of the modeling approach. Piezoresistivity results of the analyses agree well with the experimental data when considering tunneling behavior in the percolation transition zone. The magnetic field enhances the field affected subbands and increases the electrical conductivity by enhancing the mobility of the charges. The results reveal that the efficiency of CNT network in transmitting charges is increased with higher aspect ratio CNTs that scaled the sensitivity to lower values. © 2024 Elsevier Ltd
Ansari, R.,
Ershadi, M.Z.,
Laskoukalayeh, H.A.,
Rouhi h., H. Publication Date: 2024
AIAA Journal (1533385X)62(2)pp. 833-841
Based on the first-order shear deformation theory (FSDT), the large-amplitude vibration behavior of shallow spherical shells made of functionally graded materials (FGMs) due to the rapid decrease of temperature (cooling shock) is investigated. FGM is assumed to be a mixture of stainless steel and low-carbon steel whose properties are considered temperature dependent and are estimated based on the power-law model. According to FSDT and von Kármán assumptions, the governing equations of motion in conjunction with corresponding boundary conditions are obtained using Hamilton’s principle. The temperature distribution is also achieved by means of the 1D Fourier transient heat conduction equation, considering two time-dependent thermal loading scenarios. The considered thermal boundary conditions allow that a temperature difference is created with a time delay for the structure under cooling shock. Also, the results of recent experiments are employed to estimate the temperature-dependent properties of structures. In the solution approach, the generalized differential quadrature method and the Newmark-beta integration scheme are utilized. Selected numerical results are presented to study the effects of thermal load rapidity time, geometry, magnitude of thermal load, and material gradient index on the thermally induced vibrations of spherical shells. Stresses generated in the shell due to the thermally induced vibrations are also investigated. © 2023 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Moradi, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S. Publication Date: 2024
European Journal of Mechanics, A/Solids (09977538)107
Stimuli-responsive shape memory polymer (SMP) nanocomposites, characterized by their shape memory capability and customizable properties, have significantly expanded their range of applications when compared to pristine SMPs. This pioneering paper is centered on describing an efficient numerical approach for evaluating the thermomechanical behavior of ternary acrylate-based SMP nanocomposites containing carbon nanotube (CNT) and graphene nanoplatelet (GNP) hybrids. To this aim, a micromechanical procedure based on thermo-visco-hyperelastic constitutive model, which aids in avoiding employing intricate user-defined material subroutines, is developed through the finite element method (FEM). The parameters required for satisfying the governing equations of the rheological model, including thermal expansion and Prony series coefficients, plus Williams-Landel-Ferry equation and Neo-Hookean strain energy function parameters, are derived from accessible experiments to assign SMP properties. A Python-based script is implemented in a stochastic-iterative process to generate appropriate periodic representative volume elements (RVEs) with various microstructures. Thereupon, thermomechanical shape memory cycles in uniaxial tension are simulated by creating loading, cooling, unloading, and heating steps in the Abaqus solver. Following achieving satisfactory agreement between the presented scheme and experimental measurements, case studies are performed to reflect the influences of dispersion type, volume fraction, and geometry of carbonaceous nanofillers, as well as the contribution of nanofiller/matrix interphase region, upon stress-free/shape-recovery and fixed-strain/stress-recovery thermomechanical cycles. © 2024 Elsevier Masson SAS
Aghdasi p., P.,
Yousefi, S.,
Ansari, R.,
Bagheri tagani m., Publication Date: 2024
Journal of Physics and Chemistry of Solids (00223697)191
This study investigates the impact of doping with carbon (C), fluorine (F), and phosphorus (P) atoms on the structural and mechanical properties of 2 × 2 and 3 × 3 ZnO monolayers using Density Functional Theory (DFT) calculations. Our analysis reveals a notable decrease in both the elastic and bulk moduli of the monolayers upon doping, with the most significant reduction observed in the P-doped structure. For the pristine structure, the elastic modulus is measured at 78.84 N/m for the 2×2 monolayer and 79.46 N/m for the 3×3 monolayer, while the bulk modulus is 62.47 N/m and 63.94 N/m, respectively. Following P doping, the elastic modulus decreases by 56.02 % (34.67 N/m) in the 2 × 2 monolayer and 46.40 % (42.59 N/m) in the 3 × 3 monolayer. Similarly, the bulk modulus experiences substantial decreases of 53.09 % (29.30 N/m) in the 2 × 2 monolayer and 42.96 % (36.47 N/m) in the 3×3 monolayer upon P doping. Additionally, C and F doping result in reductions of 26.10 % and 11.04 % in the elastic modulus of the 2×2 monolayer and 26.27 % and 10.92 % in the 3×3 monolayer, respectively. The corresponding bulk modulus reductions are 14.51 % and 10.79 % in the 2×2 monolayer and 20.12 % and 11.15 % in the 3×3 monolayer, respectively. These findings underscore the considerable influence of various dopants on the mechanical characteristics of ZnO nanosheets, with P doping inducing the most significant reductions in both elastic and bulk moduli, suggesting its efficacy in tuning the mechanical properties of ZnO nanosheets for diverse applications. © 2024 Elsevier Ltd
Nickabadi, S.,
Ansari, R.,
Golmohammadi b., ,
Aghdasi p., P. Publication Date: 2024
Scientific Reports (20452322)14(1)
A three-dimensional finite element model is used to investigate the vibrational properties of double-walled silicon carbide nano-cones with various dimensions. The dependence of the vibrational properties of double-walled silicon carbide nano-cones on their length, apex angles and boundary conditions are evaluated. Current model consists a combination of beam and spring elements that simulates the interatomic interactions of bonding and nonbonding. The Lennard–Jones potential is employed to model the interactions between two non-bonding atoms. The fundamental frequency and mode shape of the double-walled silicon carbide nano-cones are calculated. © The Author(s) 2024.
Publication Date: 2023
Mechanics of Advanced Materials and Structures (15210596)30(24)pp. 5159-5175
A two-stage molecular dynamics (MD)-finite element (FE) modeling method is developed based on the concepts of representative volume element (RVE) and equivalent solid fibers (ESFs) containing functionalized carbon nanotubes (ESFs-fCNTs). First, the influences of nanotubes’ chirality, different percent of functionalization ((Formula presented.)), various functional atoms, and polymers on the tensile and shear properties of the fCNTs inserted into the polymer matrix (fCNTs/polymer) are discovered using MD simulations. Then, using MD information as input data, the effective Young’s modulus of polymeric unit cell strengthened by ESFs-fCNTs (ESFs-fCNTs/polymer) is explored through FE modeling. The ratio of effective Young’s modulus of the unit cell ((Formula presented.)) to Young’s modulus of the polymeric cube ((Formula presented.)) is reported and all findings ((Formula presented.)) are compared to the ESFs-pure CNTs/polymer results as well. It is found that longitudinal Young’s modulus ((Formula presented.)) of nanofillers/polymer RVEs affects remarkably the (Formula presented.) of the ESFs-nanofillers/polymer nanocomposites. The (Formula presented.) decreases by increasing the (Formula presented.) Generally, the reinforcing impact of zigzag nanotubes compared to armchair ones on the (Formula presented.) of polymer RVEs is more considerable. Additionally, FE-based results illustrate that as the volume fraction of ESFs ((Formula presented.)) increases, the (Formula presented.) is enhanced. At a specific (Formula presented.) the reinforcing effect of the ESFs-armchair and zigzag fCNTs is more in favor of polyethylene nanocomposites than that of the polypropylene systems. © 2022 Taylor & Francis Group, LLC.
Publication Date: 2023
International Journal of Mechanics and Materials in Design (15691713)19(1)pp. 187-206
The concentration of the present investigation is on the development of a quadrilateral shell element for the deformation analysis of composite laminates. For this purpose, a higher-order shell model with 12 parameters is adopted along with the three-dimensional state of stress. The principle of virtual work is implemented to derive the stiffness matrix and the load vector for the four-node shell element. In order to verify the performance of the higher-order shell element developed herein for the treatment of laminated composites, some benchmarks are solved and compared with solutions available in the literature. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.
Zargar ershadi m., M.,
Bazdid-vahdati m., M.,
Aghaienezhad f., ,
Ansari, R. Publication Date: 2023
Thin-Walled Structures (02638231)187
In this paper, the effect of growth on the stability of elastic materials is examined through a numerical approach. Growth and resorption are considered to have two main effects from the stability standpoint. Corresponding to the change in mass, the geometry of a system changes, and the critical length of the system can be modified. In addition, the growth of the material may be affected by the stress, yet it may also impose residual stresses. As a result, the material is either stabilized or destabilized by these stresses. As a general framework for the description of elastic properties, the theory of finite elasticity is employed to investigate the growth of elastic materials. Growth is taken into account through matrix multiplication of the deformation gradient. The formalism of incremental deformation is adopted to consider growth effects. Using this formalism, the stability of growing neo-Hookean incompressible cylindrical and spherical shells under external pressure is considered. Firstly, the incremental equilibrium equations and the corresponding boundary conditions for the incompressible growing shells are summarized and afterward employed in order to analyze the behavior of spherical and cylindrical shells subjected to external pressure. The generalized differential quadrature method (GDQ) is utilized to solve the eigenvalue problem that results from a linear bifurcation analysis. It is shown that this numerical method can be efficiently utilized to solve the considered problem. The results are in full agreement with the previously obtained results. In the presence of external radial pressure, an elastic shell will buckle circumferentially to a noncircular cross-section. A change in thickness due to the growth can significantly affect buckling, both in terms of the critical pressure and the buckling pattern. Finally, the effects of the thickness ratio A1/A2, mode number n, and the growth parameter γ are studied on the shell's stability. © 2023
Bazdid-vahdati m., M.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2023
European Physical Journal Plus (21905444)138(1)
This paper presents two hyperelastic models for the micromorphic hyperelasticity which can be efficiently utilized for materials with high dependence on the microdeformation gradient. To this end, two new microdeformation gradient-based strain measures are introduced and used in hyperelastic formulation. The developed formulation for the micromorphic hyperelasticity makes it possible to define hyperelastic functions whose dependency on the microdeformation gradient can be clearly discussed. Also, based on the proposed formulation, any kind of hyperelastic models can be formulated using the defined strain measures. © 2023, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Ansari, R.,
Zargar ershadi m., M.,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2023
Acta Mechanica (16196937)234(10)pp. 5115-5129
In this paper, a novel numerical approach is proposed to study the geometrically nonlinear large-amplitude vibrations of circular plates subjected to hygrothermal loading resting on an elastic foundation. It is considered that the plates are made of functionally graded (FG) porous materials whose hygro-thermo-mechanical properties are estimated based on the modified Voigt's rule of mixture. Hygroscopic stresses produced because of the nonlinear rise in moisture concentration are taken into account. Moreover, two distribution patterns for porosity (even and uneven) are considered. The Touloukian formula is also employed to assess the temperature-dependence of material properties. Based on the first-order shear deformation plate theory in conjunction with von-Kármán geometrical nonlinear relations, the variational form of the governing equations is derived using Hamilton’s principle. In addition, the effect of the elastic foundation is incorporated into the formulation according to the Winkler-Pasternak model. For solving the problem of nonlinear vibrations, the generalized differential quadrature, variational differential quadrature, and Newmark-beta integration methods are utilized. The influences of important parameters such as temperature distribution, porosity volume fraction, moisture concentration, elastic foundation parameters and FG index on the geometrically nonlinear vibrations of FG porous plates with different boundary conditions induced by hygro-thermal loadings are analyzed. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Soleimani m., ,
Gholami, R.,
Alijani a., ,
Ansari, R. Publication Date: 2023
Thin-Walled Structures (02638231)193
In this study, an analytical solution is provided to present the stress and strain analyses of the multi-layered filament-wound composite (MLF-WC) pipes subjected to the cyclic internal pressure and cyclic thermal loading in hygrothermal environment. The MLF-WC pipe is made of anisotropic, homogeneous and linear elastic materials. It is assumed that the material properties are temperature-independent. Also, applied cyclic loadings are independent of the tangential and axial coordinates. Using the three-dimensional anisotropic elasticity, time-dependent analytical expressions are provided for the stresses, strains and displacements. The accuracy of present analytical approach and numerical results is verified by comparison with those given in literature. It is remarked that the developed analytical solution can be used for the dynamic analysis of functionally graded pipes and pressure vessels under the cyclic loadings. Moreover, through the numerical results, it is found that stacking sequence has a considerable effect on the distributions of shear strain and stress. Furthermore, for the MLF-WC pipe under simultaneous cyclic internal pressure and cyclic thermal loading, the mean amplitudes of the cyclic loadings have a significant effect on the sign of axial strain. © 2023 Elsevier Ltd
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S.,
Nankali, M. Publication Date: 2023
Composites Part A: Applied Science and Manufacturing (1359835X)173
An analytical model is developed to predict the piezoresistive sensitivity of nanocomposite strain sensors considering physical properties of carbon nanotubes (CNTs) and carbon blacks (CBs) such as the orientation state, aspect ratio, waviness factor, and agglomeration. A Monte Carlo simulation approach is used to disperse hybrid CNTs/CBs into the matrix. The percolation model is used to introduce the percolation phenomenon into the nanocomposites. Afterward, the piezoresistive property of hybrid nanocomposites is determined using updated fillers’ positions after a stretch in a specific direction of nanocomposites. The nanocomposite resistivity is explored as a function of nanofiller volume fraction. The verification is accomplished by comparing model results with experiments. CNTs with higher aspect ratios and lower waviness factors have a beneficial effect on the electrical properties of hybrid nanocomposites. A good combination of conductive fillers leads to a better piezoresistive response, while a further increase in CB volume fraction cannot be beneficial. © 2023 Elsevier Ltd
Publication Date: 2023
Mechanics Based Design of Structures and Machines (15397742)51(4)pp. 2177-2199
This study presents an analytical solution approach to examine the nonlinear vibration of geometrically imperfect functionally graded porous circular cylindrical shells reinforced with graphene platelets (GPL) surrounded on an elastic foundation. First-order shear deformation theory is employed to formulate the considered problem. Four porosity distributions and four GPLs dispersion patterns are considered which vary through the thickness direction. The effective mechanical properties of considered functionally graded graphene platelet-reinforced porous nanocomposites are characterized via a micromechanical model. Governing equations are derived by Hamilton’s principle and then were transformed into a set of ordinary differential equations using the Galerkin method. Afterward, the nonlinear frequency response curves are obtained with the use of the method of multiple scales. Numerical results are provided to explore the effect of parameters such as initial imperfection, geometry, porous distribution, porosity coefficient, and GPLs’ scheme and weight fraction on the nonlinear frequency-response curve. © 2021 Taylor & Francis Group, LLC.
Publication Date: 2023
JVC/Journal of Vibration and Control (10775463)29(11-12)pp. 2868-2877
The purpose of this article is the comprehensive analysis of free vibration of beam-type liquid micro-pump with a free boundary approach. Besides the liquid loading on the micro-beam, the kinematic compatibility between liquid and micro-beam is modeled according to the free boundaries. Galerkin and separation of variables methods are employed to solve these equations. Based on the nonlinear nature of the equations, the Newmark method is applied to obtain the normal frequencies, mode shapes, and the fluid oscillation of the coupled system. The aim of this model is to achieve the exact results for the small oscillations of micro-beam in the liquid container. Comparing the free and fixed boundary method reveals that for small oscillation of Euler–Bernoulli micro-beam, there is a slight deviation on the natural frequency, which can be negligible. © The Author(s) 2022.
Publication Date: 2023
European Physical Journal Plus (21905444)138(3)
Free vibration of single-layered graphene sheets (SLGSs) subjected to compressive in-plane loads and embedded in a Winkler–Pasternak elastic medium in the pre- and post-buckled configurations is examined herein. To consider both geometric and material nonlinearities and include the size-dependent mechanical behavior of small-scale structures without taking any additional phenomenological parameters into account, the high-order Cauchy-Born (HCB) method, hyperelastic membrane and second gradient elasticity theory are used for providing mathematical formulation. Also, the variational differential quadrature (VDQ) method and Hamilton’s principles are applied to provide a set of discretized governing equations of motion. To evaluate the free vibration of SLGSs in post-buckling domain, first, the post-buckling problem corresponding to the considered system is solved. Then, by assuming a small disturbance about the equilibrium condition, the frequency response of SLGSs is obtained as a function of the applied in-plane load. In numerical results, the effects of various parameters such as geometry, elastic foundation and boundary conditions are highlighted and discussed in detail. © 2023, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2023
Journal of Strain Analysis for Engineering Design (03093247)58(1)pp. 17-25
The nonlocal theory is commonly applied for nanomaterials due to its capability in considering size influences. Available studies have shown that the differential version of this theory is not suitable for some problems such as bending of cantilever nanobeams, and the integral version must be used to avoid obtaining inconsistent results. Therefore, an attempt is made in this paper to propose an efficient variational formulation based on the integral nonlocal model for the analysis of nanobeams. The formulation is developed in a general form so that it can be used for arbitrary kernel functions. The nanobeams are modeled using the Bernoulli-Euler beam theory, and their bending behavior is analyzed. Derivation of governing equations is performed according to an energy-based approach. Also, a numerical approach based on the Rayleigh-Ritz method is developed for the solution of problem. Moreover, the results of integral and differential models are compared. It is revealed that by the proposed numerical solution, the paradox in the behavior of nanocantilever is resolved. © IMechE 2022.
Publication Date: 2023
Journal of Alloys and Compounds (09258388)951
This study investigates the effectiveness of CoS2/PPy nanocomposites as electrode materials for supercapacitors. We performed a simple and effective one-step hydrothermal fabrication of these nanostructures on nickel foam as substrate. After accurate characterization, electrochemical studies were performed using various techniques, such as cyclic voltammetry (CV), galvanostatic discharge (GCD), and electrochemical impedance spectroscopy (EIS). The result shows excellent electrochemical behaviour of the synthesized electrode with a specific capacitance of 605.2 C g−1 at a current density of 1 A g−1. Moreover, considerable capacitance retention (∼90.9% after 5000 cycles) was obtained. Next, an asymmetric supercapacitor was developed using a prepared electrode and activated carbon (AC /Ni foam) as cathode and anode, respectively. The device showed a high specific energy of 88.07 Wh kg−1 with a significant power of 4.95 kW kg−1 at an operating voltage of These unexpected results indicate that the CoS2/PPy nanostructure has the potential to become a promising electrode for energy storage systems. © 2023 Elsevier B.V.
Haghgoo, M.,
Ansari, R.,
Jang, S.,
Hassanzadeh-aghdam, M.K.,
Nankali, M. Publication Date: 2023
Composites Part A: Applied Science and Manufacturing (1359835X)166
The thermo-resistive and piezoresistive responses of carbon nanotube (CNT)/graphene nanoplatelet (GNP) polymer-based nanocomposites are analytically investigated. The 3D representative volume element is generated by the Monte Carlo approach to incorporate the random distribution of nanofillers. The Monte Carlo approach is paired with the percolation model to investigate the percolation behavior of the nanocomposite. The validity of the analytical model is verified by comparing the predicted results with the experimental data. The Poisson's ratio and height of barrier potential influence on the piezoresistivity of nanocomposite are studied. Analytical results determine the aspect ratio and influence of carbon nanotube degree of orientation on thermoresistivity of nanocomposite. The effects of intrinsic and physical properties of GNPs on resistivity change with temperature are investigated. It is found that nanocomposite filled with CNTs presented lower percolation threshold than those filled with GNPs. The results also revealed that the filler alignment caused a higher piezoresistivity. © 2022 Elsevier Ltd
Publication Date: 2023
International Journal of Structural Stability and Dynamics (02194554)23(3)
In this paper, the dynamic buckling of functionally graded (FG) porous shallow arches under hygro-thermal loading is studied through a numerical approach. Even and uneven porosity imperfections, hygroscopic stresses generated due to the nonlinear rise in moisture concentration, and the temperature dependence of material properties are all taken into account. The transient heat conduction equation is solved to derive the temperature profile. Hygro-thermo-mechanical properties of the arch are obtained applying the modified Voigt's rule of mixture. The first-order shear deformation theory, the von-Kármán geometrical nonlinearity assumption, and the hygro-thermal strains are considered concomitantly to derive the equations of motions based on Hamilton's principle. The generalized differential quadrature method (GDQM) and Newmark-beta integration schemes are also employed in conjunction with an iterative approach to solve the set of nonlinear governing differential equations of motion. The Budiansky-Hutchinson stability criterion is utilized to capture the dynamic buckling temperature of the structure. A parametric study is conducted in order to investigate the effects of porosity distribution, FG index, geometrical parameters, hygroscopic loading, and thermal/mechanical boundary conditions on arch's dynamic buckling temperature. © 2023 World Scientific Publishing Company.
Keramati y., Y.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Journal of Intelligent Material Systems and Structures (15308138)34(13)pp. 1548-1560
This research investigates the effect of adding graphene nano-sheets (GNSs) on the elastic and piezoelectric responses of PZT-7A piezoelectric fiber/polyimide hybrid composites. The constructional feature of this hybrid composite is such that unidirectional PZT-7A fibers are embedded into the GNS-filled polyimide material. A nested micromechanical modeling strategy based on the Mori-Tanaka scheme is developed to predict the effective properties of PZT-7A/GNS/polyimide hybrid composites. Parametric studies are performed in order to examine the influences of volume fraction, agglomeration and rolling-up of GNSs, and PZT-7A volume fraction on the piezoelectric hybrid composite coefficients. The results indicate that the elastic and piezoelectric properties of PZT-7A/polyimide composites can be improved by the uniform dispersion of GNSs. However, it is observed that the formation of GNS agglomeration into the polyimide matrix has a serious negative effect on the equivalent properties of piezoelectric hybrid composites. The present predictions are also compared with other results reported in the literature. It is believed that the modeling approach and outcomes of this research may help to design these kinds of novel and highly promising piezoelectric hybrid composites. © The Author(s) 2023.
Publication Date: 2023
Silicon (18769918)15(11)pp. 4795-4809
A molecular dynamics (MD)-finite element (FE) modeling scheme is proposed to study the effective Young’s modulus of polymer nanocomposites reinforced by functionalized silicon carbide nanotubes (fSiCNTs). By evaluating the tensile and shear properties of the polymer matrix strengthened by hydroxyl (O–H)-, fluorine (F)-, and hydrogen (H)-fSiCNTs (O-, F-, and H-fSiCNT/polymer) through MD simulations, FE modeling with the consideration of equivalent solid fibers (ESFs) is conducted and the ratio of effective Young’s modulus of the unit cell (E UC) to Young’s modulus of the polymer matrix (E P) is reported. The influence of the chirality, and chemical functionalization of nanotubes along with the effects of the volume fraction of the ESFs, and polymer materials on the E UC are discovered. The results show that the random dispersion of ESFs containing armchair fSiCNTs (ESFs-armchair fSiCNTs) within the polymers (ESFs-armchair fSiCNTs/polymer) instead of the ESFs-pure armchair fSiCNTs leads to reducing the E UC. In every ESFs volume fraction (ν f), the reinforcement impact of the ESFs-armchair and zigzag fSiCNTs on the polyethylene (PE) is more significant in comparison with the polypropylene (PP). Using the ESFs-zigzag H- and F-fSiCNTs/PP instead of the ESFs-pure zigzag SiCNTs/PP decreases EUC/EP, while at the ESFs’ ν f over 10%, the EUC/EP of the ESFs-zigzag O-fSiCNTs/PP is higher than that of the ESFs-pure zigzag SiCNTs/PP. The ESFs-zigzag H- and F-fSiCNTs/PE as compared to the ESFs-pure zigzag SiCNTs/PE are experienced larger effective elastic moduli, however, only at the ESFs’ ν f of 50%, the reinforcing impact of the ESFs-zigzag O-fSiCNTs within the PE is more considerable than that of the ESFs-pure zigzag SiCNTs. © 2023, The Author(s), under exclusive licence to Springer Nature B.V.
Publication Date: 2023
Micro and Nanostructures (27730123)184
The density functional theory is utilized to investigate elastic and plastic properties of zirconium disulfide (ZrS2) nanosheet subjected to a uniform external electric field up to 4 [Formula presented]. In this respect, firstly, unit cell dimensions, bond lengths and bond angles are obtained by optimizing the unit cell of ZrS2nanosheet, and the most stable configuration is considered for the nanostructure accordingly. Then, by applying uniaxial and biaxial tensions on the nanosheet under a uniform external electric field, Young's and bulk moduli are computed, respectively. Finally, the applied strain is extended to the plastic region to evaluate the effect of external electric field on the first and second critical strains. It is shown that applying external electric field results in increasing Young's modulus of the nanosheet. However, the bulk modulus increases up to 2 [Formula presented] and deceases afterwards. Besides, the first and second critical strains, which are respectively used to show the end of harmonic and inharmonic regions, decrease in the presence of the external electric field while the difference between them is not affected by the external electric field. Investigating the elastic and plastic properties of zirconium disulfide under an external electric field is important for both fundamental research and practical applications. It can help us develop new materials with tunable properties, optimize their performance in various devices, and contribute to the development of cutting-edge technologies © 2023 Elsevier Ltd
Publication Date: 2023
Acta Mechanica (16196937)234(7)pp. 3061-3079
The focus of the current work is on the large deformation analysis of shells made of a transversely isotropic material. For this purpose, a higher-order shell model is adopted and strains are derived and subsequently the stress field of a hyperelastic medium is extracted. Then, by taking advantage of the principle of virtual work, the so-called weak form is obtained. A four-node shell element is developed enriched by remedies for alleviation of locking incorporating transverse shear, membrane and curvature-thickness locking for a compressible anisotropic medium. Finally, some examples are addressed to show the performance of the proposed element as well as anisotropy effects. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Eghbalian, M.,
Ansari, R.,
Bidgoli, M.O.,
Rouhi, S. Publication Date: 2023
Journal of The Institution of Engineers (India): Series D (22502130)104(2)pp. 609-622
The present study focuses on the characterization of directional mechanical properties of the polymer matrix reinforced with waviness carbon nanotubes (CNTs) by the finite element method. Young’s and shear elastic modulus in three dimensions have been investigated for representative volume element including straight and waviness (5,5) and (7,7) CNTs with considering the interfacial interaction. These mechanical properties with the alteration of the different parameters such as the number of curves of a CNT, diameter, and length to diameter ratio (L/ D) have been evaluated. The results show that the number of curves, and overall assuming a CNT in its natural state (more curves), significantly impact the longitudinal and directional elastic modulus of nanocomposites. Most outcomes confirm that the transverse Young's and shear elastic modulus of nanocomposites grow and reduce by adding the number of curves and the L/D ratio of CNTs, correspondingly. In addition, the opposite effect is observed in the longitudinal direction for Young’s modulus. © 2022, The Institution of Engineers (India).
Publication Date: 2023
Engineering Analysis with Boundary Elements (09557997)152pp. 66-82
A novel numerical strategy is developed in this article to study the free vibrations of hyperelastic micromorphic continua under bending load. In the proposed approach, the variational differential quadrature (VDQ) method and the idea of position transformation are used. The 3D micromorphic hyperelasticity is first formulated via vector-matrix relations which can be readily utilized in the coding process of numerical methods. The present numerical approach is able to address problems with irregular domains. To this end, the domain of elements is transformed into a regular one by the technique of mapping of position field based on the finite element shape functions. Being locking-free, simple implementation, computational efficiency and fast convergence rate are other features of the present variational approach. Three numerical examples including rectangular, sector and circular plates under bending load are considered whose free vibration behavior is analyzed. It is shown that the method is capable of predicting the relation between natural frequencies of micromorphic hyperelastic continua with load factor in an efficient way. The effects of internal length scale, scale-transition parameter and mode transition on the results are investigated. © 2023 Elsevier Ltd
Publication Date: 2023
Journal of Strain Analysis for Engineering Design (03093247)58(6)pp. 455-463
Several non-classical elasticity theories are used for considering the size-dependent behavior of structures at small scales. The nonlocal theory is widely used to reflect the softening behavior of material at small scales, and theories like the strain gradient theory are employed to reflect the hardening behavior. In this article, the most general form of integral strain- and stress-driven nonlocal models with two nonlocal parameters is developed which is able to consider both hardening and softening influences simultaneously. To this end, it is considered that the stress field at the entire points of the domain is a function of strain field of the entire points of the domain. The free vibration problem of first-order shear deformable beams is solved herein. The integral form of governing equations and associated boundary conditions are obtained first, and then directly solved in a numerical approach. Through developing an efficient matrix formulation and using differential and integral matrix operators, the discretized governing equations are obtained. The simultaneous effects of strain- and stress-driven nonlocal parameters on the natural frequencies of fully clamped, fully simply-supported, and clamped-free nanobeams are investigated. The results indicate that the paradox related to the behavior of clamped-free nanobeams is resolved using the presented integral nonlocal formulation. Also, it is revealed that it is possible to find some specific values of nonlocal parameters at which the prediction of hybrid nonlocal model coincides with that of classical elasticity theory. © IMechE 2023.
Rasoolpoor m., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Mechanics Based Design of Structures and Machines (15397742)51(1)pp. 260-274
Low velocity impact behavior of multi-walled carbon nanotube (MWCNT)-aluminum (Al) nanocomposite plates are investigated. The rule of mixture is employed to obtain the material properties of the nanocomposites. The microstructural features, including amount, aspect ratio, alignment, waviness, and agglomeration of the MWCNTs are considered. The finite element method is used to investigate the plate dynamic behavior. Addition of the MWCNTs increases the contact force and decreases both the plate center deflection and impact duration. A higher volume fraction, higher aspect ratio, straight shape, and a uniform dispersion of MWCNTs can cause a lesser center deflection of the nanocomposite plates. © 2020 Taylor & Francis Group, LLC.
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Pouyanmehr, R.,
Umer, U.,
Haider abidi, M.,
Alkhalefah, H. Publication Date: 2023
Journal of Composite Materials (00219983)57(21)pp. 3365-3376
Various types of batteries are produced to support years of service for implantable medical devices. Evaluation of internal stresses in nanoparticle-contained electrodes for lithium-ion batteries (LIBs) is a fundamental step toward enhancing their durability. In this research, diffusion induced stresses (DISs) in the bilayer electrode consisted of the carbon nanotube (CNT)-aluminum (Al) nanocomposite active plate bonded to the current collector are investigated. Modeling the DIS is performed by applying the initial stretching on the CNT-Al active plate. Effective properties of CNT-filled Al nanocomposites are calculated using micromechanics models in which the formation of interfacial carbide between the Al and CNT is considered. The role of important microstructural features including amount, length, diameters, curved structure and dispersion type of CNTs, and the thickness and property of interphase in DISs is examined to provide design insights for LIB electrodes. The blending of straight CNTs with a high aspect ratio significantly reduces the tensile stress in the current collector, both compressive and tensile stresses in the nanocomposite active plate and especially the stress drop at the collector/plate interface. Moreover, the DISs can be alleviated by the formation of a stiff and thick interphase between the Al and nanotubes. The CNT-contained electrode with a stretched active plate exhibits lower internal stresses. © The Author(s) 2023.
Pakseresht m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Mechanics Based Design of Structures and Machines (15397742)51(2)pp. 841-854
Titanium-based composites with their desirable and great mechanical properties are in high demand. One of the main problems that arise in this field is the chemical reactions that appear between strengthening the material and the matrix that usually undermines the integrity of the composite. This problem will result in dangerous defects such as debonding or degradation of the properties. In this work, a coating solution is presented; a similar process as discussed in the literature yet analytically different. The coating is commonly used for protecting and preserving the reinforcing material’s surface which is in contact with the matrix. Herein, a titanium metal matrix composite reinforced with carbon-coated SiC particles is discussed. Mori-Tanaka method was utilized to firstly determine the properties of the inclusion which is the carbon-coated SiC particle and then using the results based on the thickness of the coating and volume fraction of inclusions, calculating the overall properties of the composite. An incremental method was employed to then calculate the stress-strain curve of the said material. The results obtained were in good agreement with the experimental data. The negative effect of the carbon coating on the elastic properties of the SiC/titanium composite was observed as the coating layer thickness increased. The same thing was observed in the stress-strain curve in the slope of the elastic zone and work hardening growth in the plastic zone. © 2020 Taylor & Francis Group, LLC.
Publication Date: 2023
Acta Mechanica (16196937)234(10)pp. 4535-4557
This paper presents a size-dependent study on the free vibration behaviour of the functionally graded (FG) porous curved microbeams. Based on the different higher-order shear deformation models and the modified strain gradient theory, the governing equations are derived using Hamilton’s principle. Then, the isogeometric analysis approach is employed to solve these equations. Besides, the material properties and the material length scale parameters (MLSPs) vary along the thickness direction of the FG curved microbeams according to the rule of mixture scheme. Also, two types of porosity distributions across the thickness, including even and uneven, are considered. By increasing the order of the non-uniform rational b-spline (MLSPs) basis functions, the C2-continuity requirement can be easily achieved. To establish the validity of the proposed method, the present results are compared with those from the previous studies. Finally, the effects of the variable MLSPs, porosity parameter, material gradient indices, curvature and different boundary conditions on free vibration response of circular, elliptical and parabolic FG porous microbeams are investigated. The obtained results reveal that the size-dependent effects increase the natural frequency as well as porosity decreases it because of decreasing the stiffness. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Ansari, R.,
Hassani r., R.,
Gholami y., Y.,
Rouhi h., H. Publication Date: 2023
Engineering Analysis with Boundary Elements (09557997)146pp. 306-317
Shell-type structures are frequently used in aerospace, marine and civil engineering. In this paper, a numerical approach called as VDQ-transformed is introduced to analyze the large deformations of hyperelastic shell-type structures based on the Saint Venant–Kirchhoff constitutive model in the context of three-dimensional (3D) nonlinear elasticity. According to the Euler–Lagrange description, the kinetic first Piola-Kirchhoff tensor and kinematic deformation gradient tensor are considered for the stress and strain measures in the formulation. By replacing the tensor form of formulations with matricized ones, the governing equations are written in a novel vector-matrix format which can be readily exploited for programming in numerical approaches. Moreover, discretizing is carried out by the variational differential quadrature (VDQ) method as a point-wise numerical method. To apply the VDQ technique, a transformation is used to map the irregular domain into the regular one. Some well-known benchmark problems for the large deformations of shells are solved to assess the approach. Compact matricized formulation, simple implementation, being locking-free, computational efficiency and fast convergence rate can be mentioned as the main features of the introduced numerical approach. © 2022 Elsevier Ltd
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)45(9)
The micromechanical finite element method (FEM) is used to investigate Young’s modulus, yield strength and coefficient of thermal expansion (CTE) of nano-sized silicon carbide (SiC) particle/aluminum (Al) nano-composites (NCs). For this purpose, a 3-dimensional representative volume element containing randomly dispersed SiC nanoparticles is constructed with the precondition of satisfying the periodicity criterion. The effect of the Al4C3 interfacial product formed due to the chemical interaction between the ceramic nanoparticle and metal matrix is numerically evaluated on the NC properties. The results reveal that the mechanical and thermal expanding properties of Al-based composites are improved by the addition of SiC nanoparticles. The increase of uniformly dispersed SiC percentage leads to an increase in Young’s modulus and yield stress and a decrease in the CTE of the Al NC. It is observed that the Al4C3 interfacial product would be beneficial to improve the effective properties of SiC/Al NCs. The higher the interphase thickness is, the better the NC property improvement. In the presence of an interfacial product, the mechanical and thermal expanding properties can be improved by the reduction in the nanoparticle diameter. The reinforcement ratio of Al4C3 turns to be more effective as the SiC diameter decreases. Predictions of the micromechanical FEM are compared with the results of analytical methods and experimental measurements to verify its accuracy. © 2023, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.
Keramati y., Y.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Umer, U. Publication Date: 2023
Acta Mechanica (16196937)234(12)pp. 6251-6270
One mechanism that is expected to play a key role in the enhanced properties of fiber-reinforced composites is adding nano-scale fillers as the second reinforcing agents in the polymer matrix. In this paper, micromechanical analysis of a hybrid smart nanocomposite in which continuous BaTiO3 fibers are embedded into the graphene nanosheet (GNS)-contained epoxy matrix is performed. The Mori–Tanaka model is used at a multi-step procedure to predict the thermal expansion (TE), elastic stiffness and piezoelectric constants of BaTiO3 fiber/graphene hybrid nanocomposites. The micromechanical model has the ability to describe the non-uniform dispersion of GNSs into the epoxy matrix. Further, the effect of the interfacial interaction between the graphene nanoparticles and polymer is captured in the smart nanocomposite modeling through the inclusion of an equivalent solid interphase. Our results indicate that by adding GNSs into the epoxy resin, all stiffness constants, transverse coefficient of TE and piezoelectric constants e31 and e15 of the hybrid nanocomposite are significantly improved. However, non-uniform dispersion and agglomeration of GNSs can decrease the thermo-mechanical and piezoelectric performances of the BaTiO3 fiber/graphene hybrid nanocomposite. In addition, the dependence of effective properties on the interphase characteristics and alignment of GNSs is tested and discussed in details. Comparison studies are carried out in order to show the validity of the present model. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Publication Date: 2023
Journal of Materials Research and Technology (22387854)25pp. 5352-5371
This paper aims to understand the effect of friction stir butt welding on the microstructure and mechanical performance, measured in terms of hardness characteristics, transverse tensile test, and shear punch, of dissimilar weld of duplex stainless steel (DSS) and low carbon steel (LCS). The dynamic recrystallization, material intermixing, and atomic interdiffusion between DSS and LCS governed the microstructure of the stirred zone. The stirred zone was free from harmful intermetallic phases like the sigma phase. It was identified that three distinct metallurgical regions feature the stirred zone, including (i) dual-phase zone (DPZ) with an unbalanced fine duplex microstructure of austenite and ferrite, (ii) ferrite phase zone (FPZ) with fine-grained ferrite strengthened by an enhanced Ni and Cr content, (iii) martensite zone (MRZ), which was formed due to the formation of thermally unstable austenite at high temperatures due to Cr, Ni, and C interdiffusion between DPZ and FPZ. Furthermore, when LCS was positioned on the advancing side, a higher fraction of martensite was formed in the stirred zone due to the more efficient material mixing. The shear punch test indicated that the shear strength of the stirred zone in the dissimilar welds was ∼130% and ∼16% higher than that in the LCS and DSS base metals, respectively. The contributions of solid solution hardening and grain boundary hardening to the hardness/strength of the stirred zone were elucidated. © 2023 The Authors
Publication Date: 2023
Molecular Simulation (08927022)49(4)pp. 415-426
The tensile properties and fracture mechanism of hydroxyl-functionalized silicon carbide nanotubes (O-fSiCNTs) inserted into polymer matrices are explored and the outcomes are compared to results for the hydroxyl-functionalized carbon nanotubes (O-fCNTs) incorporated in similar matrices. The molecular dynamics (MD) method is used and the simulations are based on the notion of representative volume elements (RVEs). The incorporation of chemisorbed nanotubes in polymers has a profound effect on the enhancement of their mechanical properties. The O-fSiCNTs inside the polyethylene (PE) and polypropylene (PP) (O-fSiCNTs/PE and O-fSiCNTs/PP) possess lower Young’s modulus, maximum stress, and strain energy as compared to the O-fCNTs/PE and O-fCNTs/PP. The zigzag O-fSiCNTs/polymer experiences lower bearable maximum strains in response to imposed loads in comparison with the O-fCNTs/polymer which is opposite to what occurs in the armchair O-fSiCNTs and O-fCNTs/polymer. The more the functionalization degree is, the weaker the structure is and its stiffness, tensile strength, tolerable strain before fracture, and ability to absorption of internal energy decline. Not only are the zigzag O-fSiCNTs/polymer stiffer than the armchair O-fSiCNTs/polymer in every percent of functionalization, but also as compared to the armchair ones, they show a lower decrease in the variation of Young’s modulus with increasing the functionalization percentage. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Journal of Composite Materials (00219983)57(23)pp. 3675-3684
This paper aims to predict the elastic-viscoplastic curves of unidirectional carbon nanotube (CNT)-reinforced polymer nanocomposites under the multi-axial tensions, including bi-axial transverse-transverse, bi-axial longitudinal-transverse and tri-axial longitudinal-transverse-transverse loadings by the use of finite element (FE) modeling. The role of the interphase between the CNT and polymer matrix as well as the debonding at the CNT/interphase interface in the stress-strain curves of nanocomposites is investigated. The polymer matrix and interphase region are characterized as elastic-viscoplastic materials, while the CNT behaves as the elastic material. The present results in uni-axial loading are compared to the available numerical outcomes for indicating the accuracy of the FE modeling. The simulation of multi-axial load conditions is based on the three-dimensional representative volume element (RVE) of the unidirectional CNT-polymer nanocomposite. The effect of interface strength on the elastic-viscoplastic stress-strain curves is examined under bi-axial and tri-axial loadings. © The Author(s) 2023.
Rezazadeh, H.,
Zabihi, A.,
Davodi a.g., ,
Ansari, R.,
Ahmad, H.,
Yao, S. Publication Date: 2023
Results in Physics (22113797)49
In this study, disparate analytical methodologies like the tan method, rational Exp-function method, sech method, extended tan method, and sine–cosine method are implemented to solve the double Sine-Gordon equation (DSG). Subsequently, the dynamical attributes of the obtained results have been underlined and depicted in terms of 3D and 2D graphical illustrations, likewise, different soliton solutions such as kink, bright-dark, and bright are depicted under an appropriate selection of parameters, and the existing criteria of these solitons are also given. A Survey of the literature shows that these methodologies are potent enough to extract exact solutions of differential equations applied in engineering mathematics. © 2023 The Authors
Publication Date: 2023
Composite Structures (02638223)307
The concentration of the present study is on the transient dynamic analysis of composite shells given geometric nonlinearity. For this purpose, use is made of a 12-parameter shell model suited for thick composite structures and then strains and stresses are extracted. The so-called weak form is constructed based on the Hamilton's principle and for gaining the solution to the dynamic problem, the nonlinear finite element method, the total Lagrangian scheme, as well as the composite time integration approach are employed. To overcome the numerical anomalies pertaining to the four-node shell element, transverse shear, membrane and curvatures-thickness locking, appropriate approaches are taken into account. Finally, some problems are solved to evaluate the newly developed shell element and a comparison with the data available in the literature is made. © 2022 Elsevier Ltd
Yademellat, H.,
Ansari, R.,
Darvizeh a., A.,
Torabi, J.,
Zabihi, A. Publication Date: 2023
Mechanics Based Design of Structures and Machines (15397742)51(1)pp. 179-198
This study investigates the size-dependent dynamic pull-in instability of piezoelectrically and electrostatically actuated micro/nanobeams considering the Euler–Bernoulli theory and von-Kármán hypothesis based on the nonlocal strain gradient theory. In this respect, the impacts of flexoelectricity and piezoelectricity are considered using electrical Gibbs-free energy density and the governing equation is acquired with the help of Hamilton's principle for a sandwich beam with elastic core and two piezoelectric layers. In the present model, different nonlinear forces, such as the fringing field, electrostatic, and intermolecular forces are taken into account. Then, the governing equation is converted from partial differential equation into ordinary one by the Galerkin method considering various boundary conditions, subsequently, the homotopy analysis method is applied as an analytical procedure. The results are validated by comparing the linear frequency, nonlinear frequency, and dynamic pull-in voltage with those in the literature. Consequently, the impacts of different parameters including piezoelectric voltage, nonlocal parameter, length scale parameter, initial amplitude, electrostatic force, flexoelectric, and gap to thickness ratio are discussed in detail. © 2020 Taylor & Francis Group, LLC.
Ansari, R.,
Zargar ershadi m., M.,
Mirsabetnazar a., A. Publication Date: 2023
Engineering Analysis with Boundary Elements (09557997)152pp. 225-234
In this paper, thermally induced vibrations of beams made of functionally graded materials (FGMs) subjected to cooling shocks are investigated. It is considered that the beam has been made of a mixture of stainless steel (SUS 304) and low-carbon steel (AISI 1020). To model the displacement field, the third-order beam theory, known as the Reddy beam theory (RBT), is used. Material properties depend on temperature and distribution of materials, and this dependence is modeled through the temperature and the location of materials along the thickness direction. Considering the uncoupled thermoelasticity theory, the temperature distribution is obtained using a one-dimensional Fourier-type transient heat conduction equation, and the equations of motion governing the higher-order beam are derived utilizing Hamilton's principle. Solving the equations is done numerically; the generalized differential quadrature method (GDQM) is employed to approximate the spatial derivatives, and the Newton-Raphson scheme is applied to linearize the equations. In addition, for approximation of the time derivatives, the Newmark method is utilized. Subsequently, the effects of various parameters on the non-dimensional lateral deflection of the higher-order beam considering two different types of thermal loading are investigated. A comprehensive parametric study is conducted to study the effects of important parameters including beam thickness, thermal load rapidity time, the amount of applied load, and the FG parameter. © 2023
Ansari, R.,
Zargar ershadi m., M.,
Akbardoost laskoukalayeh h., ,
Rouhi h., H. Publication Date: 2023
Thin-Walled Structures (02638231)193
A numerical approach is developed in the present article to study the geometrically nonlinear vibrations of annular sector plates made of functionally graded materials (FGMs) due to being exposed to cooling shock. The first-order shear deformation plate theory (FSDT) is used in the modeling of plate, and the governing equations of motion are derived based on Hamilton's principle considering von Kármán nonlinear kinematic relations. It is also considered that the properties of FGMs are dependent on temperature and distribution of materials. According to the uncoupled thermoelasticity theory, the temperature distribution is obtained via 1D Fourier-type transient heat conduction equation. To numerically solve the problem, the generalized differential quadrature (GDQ) method and Newmark-beta integration scheme are utilized. Considering two different types of thermal loading as cooling shock, the effects of various parameters including thermal load rapidity time, geometry, magnitude of thermal load and material properties on the large-amplitude vibrations of annular sector plates are investigated. © 2023
Ansari, R.,
Hassani r., R.,
Gholami y., Y.,
Rouhi h., H. Publication Date: 2023
Structural Engineering and Mechanics (12254568)85(2)pp. 147-161
Based on the ideas of variational differential quadrature (VDQ) and finite element method (FEM), a numerical approach named as VDQFEM is applied herein to study the large deformations of plate-type structures under static loading with arbitrary shape hole made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) in the context of higher-order shear deformation theory (HSDT). The material properties of composite are approximated based upon the modified Halpin-Tsai model and rule of mixture. Furthermore, various FG distribution patterns are considered along the thickness direction of plate for GPLs. Using novel vector/matrix relations, the governing equations are derived through a variational approach. The matricized formulation can be efficiently employed in the coding process of numerical methods. In VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element. As the last step, the assemblage procedure is performed to derive the set of governing equations which is solved via the pseudo arc-length continuation algorithm. Also, since HSDT is used herein, the mixed formulation approach is proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Rectangular and circular plates under various boundary conditions with circular/rectangular/elliptical cutout are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the nonlinear maximum deflection-transverse load amplitude curve are studied. Copyright © 2023 Techno-Press, Ltd.
Haghgoo, M.,
Alidoust, A.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2023
Sensors and Actuators A: Physical (09244247)362
The pressure/resistance sensitivity of the GNP elastomeric nanocomposite is investigated using a finite element percolation model. The simulation model creates an elastomeric RVE, including solid GNP disks, and updates the position and direction of GNPs after the applied pressure. The percolation model predicts the tunneling paths between GNP intersections between the two electrodes. The percolation network between electrodes is promoted through the prevalent contact mechanism between GNPs. The developed numerical model simulates the electrical conductivity and pressure/resistance response in a good correlation with experimental data. Results explain the dominant factors of alignment direction and volume fraction on the resistance response. The resistivity of the nanocomposite reduces significantly with critical distance with a reduced variation rate for lower volume fractions. Results indicate linear pressure/resistance sensitivity under a compressed strain up to 0.16. The results reveal a controllable sensitivity through the appropriate choice of GNP alignment direction, aspect ratio, and volume fraction. © 2023 Elsevier B.V.
Publication Date: 2023
Materials Chemistry and Physics (02540584)309
The current work examines the effect of graphene nanoplatelet (GNP) additives upon the electrical conductivity of short carbon fiber (SCF)-reinforced polymer multifunctional composites. GNPs and SCFs are randomly dispersed into the representative volume element of the composite. A multi-step physics-based approach is developed to determine the effective electrical conductivity of SCF/GNP/polymer composites. Outcomes of the current work are compared with the available experimental data and other numerical results to verify its accuracy. Changes in the volume fraction and geometry of multi-scale reinforcements, interphase characteristics, barrier height, nanofiller tunneling distance and fiber material property are considered to reflect the influence of microstructures on the electrical conducing behavior of SCF/GNP/polymer multifunctional composites. It is found that the electrical conductivity of the multifunctional composite enhances by the increase of volume fraction and aspect ratio of GNP as well as the reduction of its thickness. Moreover, the multifunctional composite shows a higher electrical conductivity with the increase of fiber aspect ratio. The electrical conductivity of the SCF/GNP-reinforced composite depends on the interphase such that its value increases by the increase of interphase thickness. The developed method can be adopted to provide useful guidelines for the design and optimization of multifunctional composites filled by hybrid reinforcements. © 2023 Elsevier B.V.
Mohamadnejad zanjani, S.,
Basti a., A.,
Ansari, R. Publication Date: 2023
Mechanics of Time-Dependent Materials (13852000)27(4)pp. 1123-1138
The forming limit diagram is one of the efficient tools to investigate the plastic deformation ability of sheet metals. The forming limits for rate-dependent ideal-orientation crystalline materials are anticipated for the entire variety of linear and nonlinear strain paths and the stress-based forming limit diagrams are also studied. For the first time, crystal plasticity forming limit strains and stresses on the combination of different strain paths such as two-step linear paths, nonlinear strain paths, and the prestrain for an ideal orientation is examined. While the forming limit is very sensitive to the strain path, the strain path has a minor effect on stress forming limit diagrams. A rate-dependent crystal plasticity method is used in combination with the Marciniak–Kuczyniski (M–K) method to anticipate forming limits in face-centered cubic crystalline material with Goss, Cube, and Brass orientations. The results show that strain paths greatly affect the forming limits. It is further shown that in the case of an ideal orientation, forming limit stress curves are not entirely path independent. © 2022, The Author(s), under exclusive licence to Springer Nature B.V.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Jang, S.,
Nankali, M. Publication Date: 2023
Composites Science and Technology (02663538)243
A 3D Monte Carlo method paired with a percolation model is carried out to predict the electrical resistivity and piezoresistive sensitivity of carbon nanotube (CNT)-polymer piezoresistive sensors. CNTs are randomly dispersed into the insulating layer of a polymer matrix having agglomerated morphologies in some parts. The electrical resistivity of nanocomposite with a defined agglomeration state is determined by considering the tunneling effect between each connected pair of CNTs. The influence of various parameters such as agglomeration radius, percentage, intrinsic properties and geometries of CNTs are investigated. A comparison was made between the analytical results and experimental data. Considering the tunneling behavior in the vicinity of the percolation transition, a good agreement is obtained between the analytical results and experimental data. Monte Carlo simulations indicated that the tunneling resistance with a random distribution of CNTs depends on the level of agglomeration. Results revealed that piezoresistive sensitivity was diminished by larger agglomerations. © 2023 Elsevier Ltd
Zabihi, A.,
Shaayesteh, M.T.,
Rezazadeh, H.,
Ansari, R.,
Raza, N.,
Bekir, A. Publication Date: 2023
Journal of Nonlinear Optical Physics and Materials (17936624)32(3)
In this paper, solitons solutions of higher-order dispersive cubic-quintic Schrödinger equationincluding third-order as well as fourth-order derivatives with respect to time, that describes the dynamics of ultrashort pulses in optical fibers are investigated in detail. In this respect,a solution procedure in the locality of applied mathematics called the hyperbolic function method is appliedusing multi-linear variable separation approach (MLVSA). As an outcome, a bunch of soliton solutions isderived in conjunction with plotting dark and periodic wave solutions. The credibility of the results is examined by setting each solution back into its governing equation. Through portraits, different forms of wave solutions are depicted. Moreover, the restrictions on the parameters are also given for the existence of the obtained solutions. © 2023 World Scientific Publishing Company.
Nesarhosseini s., ,
Ansari, R.,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2023
Acta Mechanica (16196937)234(5)pp. 1957-1971
In this paper, the free vibrations of beam-type structures subjected to rapid heating are analyzed within the framework of micropolar thermoelasticity using a novel numerical approach. The equations of motion are derived based on the micropolar elasticity theory and the Timoshenko beam theory using Hamilton’s principle. The transient 1D Fourier-type heat conduction equation is also used as the heat equation. The matrix representation of relations is given which can be efficiently utilized in numerical approaches. Solution in time domain is done by the Newmark algorithm based on the constant average acceleration technique. The generalized differential quadrature and variational differential quadrature techniques are also applied to discretize in space domain. Important effects including those of thermal shock and geometrical parameters on the thermally induced vibrations of micropolar Timoshenko beams with various boundary conditions are investigated. © 2023, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Ansari, R.,
Hassani r., R.,
Gholami y., Y.,
Rouhi h., H. Publication Date: 2023
International Journal of Structural Stability and Dynamics (02194554)23(10)
Using the ideas of variational differential quadrature (VDQ) technique and position transformation, an efficient numerical approach is developed herein in order to address the free vibration problem of compressible and nearly-incompressible solid bodies with arbitrary deformed shape within the framework of 3D hyperelasticity. The 3D hyperelasticity is first formulated by vector-matrix relations with the purpose of applying in coding process. An energy principle together with the Neo-Hookean strain energy function is also employed in the derivation of governing equations. The proposed numerical method is capable of addressing problems with irregular domains. Simple application, being free from the locking problem, and fast convergence rate are the key features of the approach. Hyperelastic rectangular/ sector plates and cylindrical panel subjected to bending load are selected as test problems whose free vibrations are analyzed. The developed numerical method is found to be capable of yielding accurate solutions to the considered problems. Moreover, the effects of mode transition and geometrical properties are investigated in the numerical examples. © 2023 World Scientific Publishing Company.
Nadimi, N.,
Pouranvari, M.,
Ansari, R.,
Pouranvari, M. Publication Date: 2023
Journal of Materials Research and Technology (22387854)26pp. 5549-5565
The fusion zone (FZ) hardness of resistance spot welds is a crucial factor affecting the performance and durability of the welds. Failure mode transition, tendency to fail in interfacial mode, interfacial failure load, and the impact of liquid metal embrittlement cracks on the weld strength are influenced by the FZ hardness. Therefore, accurately predicting the FZ hardness in resistance spot welds made on automotive steels is essential. A simple thermal model is used to calculate the time required for the temperature to drop from 800 °C to 500 °C (Δt[Formula presented]). With the aid of continuous cooling transformation (CCT) diagrams and experimental confirmation, it is shown that in most automotive steels, the FZ exhibits an almost full martensitic microstructure. Generally, the FZ hardness tends to increase in the order of interstitial-free (IF), drawing quality specially killed (DQSK), high strength low alloy (HSLA), ferrite-martensite dual-phase steels, transformation induced plasticity (TRIP), and quench & partitioning (Q&P) steels. To predict the FZ hardness, data-driven regression-based models have been developed based on carbon content, carbon equivalent concept, and the strengthening mechanisms of the martensite. Among these models, the model based on martensite strengthening mechanisms showed the best performance and robustness in estimating the FZ hardness. The assessment of the strengthening mechanism of the FZ showed that most important factors determining the FZ hardness are dislocation hardening due to carbon atoms, interface hardening due to block boundaries, and solid solution hardening due to substitutional alloying elements, respectively. A simple relation is proposed to estimate the load-bearing capacity of automotive steel spot welds during interfacial failure based on the FZ hardness. © 2023 The Author(s)
Publication Date: 2022
Materials Chemistry and Physics (02540584)283
Herein, the effects of halogen and metal atomic adsorption on the mechanical and structural characteristics of silicene are studied using density functional theory (DFT) calculations. Cl, Br, Au, Ca, Ga, Li, and Na atoms are selected as the adsorption atoms. Moreover, the phonon dispersion and electron localization function are investigated to show the stability of considered nanostructures and to visualize the bonding properties, respectively. It is shown that the adsorption leads to decreasing the elastic and bulk moduli of some structures, while it increases them in some other structures. It is seen that except for Ca-adsorbed nanosheet, both the elastic and bulk moduli of all other structures decrease after adsorption. Furthermore, the isotropic behavior of all the studied nanosheets is indicated. The plastic behavior is also analyzed. It is revealed that the second critical strain of all nanosheets, except for SiBr and SiCl, decreases under uniaxial loading. However, under biaxial loading conditions, the second critical strain of Au-, Ca-, and Ga-adsorbed structures decreases, while in other structures (SiBr, SiCl, SiLi, and SiNa) the adsorption increases the yield strain. © 2022 Elsevier B.V.
Aghdasi p., P.,
Yousefi, S.,
Ansari, R.,
Bagheri tagani m., Publication Date: 2022
Applied Physics A: Materials Science and Processing (14320630)128(8)
In this paper, the elastic and plastic properties of 2 × 2 and 3 × 3 pristine and transition metal (TM) doped silicene nanosheets are studied using the density functional theory (DFT) calculations. Cr, Co, Cu, Mn, Ti, V, Zn and Ni atoms are selected as doping atoms. It is observed that Young’s and bulk moduli of both 2 × 2 and 3 × 3 pristine structures decrease when they are affected by the doping atoms. The highest reduction in the Young’s and bulk moduli of the 2 × 2 nanosheets occurs for the Ni-doped structure, and the same reduction is observed for the Ni- and Cu-doped structures in the 3 × 3 nanosheets. In addition, it is shown that all of the investigated structures have an isotropic behavior, since their Young’s moduli have negligible difference along armchair and zigzag directions. Finally, the loading is further increased to investigate the plastic behavior of nanostructures. The results show that the yield strains of all doped nanosheets decrease under uniaxial and biaxial loadings. The highest reduction in the yield strain of the 2 × 2 nanosheets under biaxial loading is observed for Cu, Zn- and Co-doped nanosheets, and in 3 × 3 nanosheets, the highest reduction happens for the Cu- and Zn-doped nanosheets under the same condition. For the yield strain of the 2 × 2 doped nanosheets under the uniaxial loading, the Cu-doped structure experiences the highest reduction, and the highest reduction for the Mn-doped nanosheet under the same condition is observed in 3 × 3 nanosheets. The findings revealed that how electronic configuration of transition metal atom and its electronegativity difference with silicon atom can control the structural and mechanical properties of the nanosheet. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Publication Date: 2022
Diamond and Related Materials (09259635)125
In this paper, the free vibration of hybrid carbon boron-nitride heteronanotubes (CBNNTs) is analyzed through molecular dynamics (MD) simulations. In the vibration analysis, various CBNNTs (Cx ∣ (BN)y and C-BN models) according to two geometrical arrangements of constituent segments are considered. By introducing vacancy defects in nanotubes, the influence of defects on the vibrational response is studied in terms of the weight percentage and distribution pattern. The highest vibration frequency is reported and CBNNTs' results are compared with those of carbon nanotubes (CNTs) and boron-nitride nanotubes (BNNTs). It is observed that CBNNTs possess natural frequencies which lie between the values for CNTs and BNNTs. The natural frequency is found to be reduced by increasing the defect percentage. At each defect percentage, the defective C-(BN) model I and C1.5 ∣ (BN)1.5 experience almost the same natural frequency in both distribution patterns. Vibration frequencies of defective C-(BN) model II and C4.5 ∣ (BN)4.5 are nearly close together at a defined percentage of defects. Despite the minor differences between natural frequencies in either distribution pattern, regularly defected CNTs tend to have a bit higher frequency than randomly defected CNTs, however, the results are opposite in the regularly and randomly defected BNNTs. Moreover, the C-(BN) model II vibrates at a higher natural frequency than that of the C-(BN) model I. It is found that the vibrational behavior of the C-(BN) model I is mostly affected by the BN segment than the C segment. Further, the natural frequency's drop in the defected C1.5 ∣ (BN)4.5 is found to be more significant than other CBNNTs by rising the defect percentage. C-(BN) model I and defective C-(BN) model I experience higher deformations in comparison with the Cx ∣ (BN)y configurations when vibrating at their natural frequency. © 2022
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Nankali, M. Publication Date: 2022
Acta Materialia (13596454)230
Monte Carlo simulation is paired with a percolation model to analytically investigate the temperature effect and carbon nanotube (CNT) dispersion state on the temperature-dependent piezoresistive conductive network nanocomposite. The charge transport switch from electrical tunneling to elevated temperature quantum tunneling is studied based on a temperature-dependent tunneling model. The percolation network theory searches for the shortest distance of any CNT line segments scattered in the representative volume element to form possible interconnections and tunneling resistance approach evaluates resistivity by recognizing the conductive percolating paths. The effect of different factors such as the height of barrier potential, CNT length, degree of orientation and the cutoff distance on the resistance of the nanocomposite which is mainly caused by the inter-tube tunneling resistance is studied through analytical parametric studies. It is shown that the strain sensitivity of reinforced nanocomposite is increased as a result of the uniform dispersion of short aligned CNTs. © 2022
Roudbari, M.A.,
Jorshari, T.D.,
Lü, C.,
Ansari, R.,
Kouzani, A.Z.,
Amabili, M. Publication Date: 2022
Thin-Walled Structures (02638231)170
Recently, the mechanical behavior of micro-/nano-structures has sparked an ongoing debate, which leads to a fundamental question: what steps can be taken to investigate the mechanical characteristics of these structures, and characterize their performance? From the standpoint of the non-classical behavior of materials, size-dependent theories of micro-/nano-structures can be considered to analyze their mechanical behavior. The application of classical theories in the investigation of small-scale structures can lead to inaccurate results. Many studies have been published in the past few years, in which continuum mechanics models have been used to investigate micro-/nano-structures with different geometry such as rods, tubes, beams, plates, and shells. The mechanical behavior of these systems under different loading – resulting in vibration, wave propagation, bending, and buckling phenomena – is the focus of the review covered in this work. The present objective is to provide a detailed survey of the most significant literature on continuum mechanics models of micro-/nano-structures, and thus orient researchers in their future studies in this field of research. © 2021 Elsevier Ltd
Publication Date: 2022
Applied Mathematics and Mechanics (English Edition) (02534827)43(8)pp. 1219-1232
A new numerical approach is presented to compute the large deformations of shell-type structures made of the Saint Venant-Kirchhoff and Neo-Hookean materials based on the seven-parameter shell theory. A work conjugate pair of the first Piola Kirchhoff stress tensor and deformation gradient tensor is considered for the stress and strain measures in the paper. Through introducing the displacement vector, the deformation gradient, and the stress tensor in the Cartesian coordinate system and by means of the chain rule for taking derivative of tensors, the difficulties in using the curvilinear coordinate system are bypassed. The variational differential quadrature (VDQ) method as a pointwise numerical method is also used to discretize the weak form of the governing equations. Being locking-free, the simple implementation, computational efficiency, and fast convergence rate are the main features of the proposed numerical approach. Some well-known benchmark problems are solved to assess the approach. The results indicate that it is capable of addressing the large deformation problems of elastic and hyperelastic shell-type structures efficiently. © 2022, Shanghai University.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Nankali, M. Publication Date: 2022
Journal of Composite Materials (00219983)56(28)pp. 4339-4361
In this study, the temperature-dependent piezoresistivity of hybrid carbon black (CB)/carbon nanotube (CNT) nanocomposites is studied using a percolation model with a Monte Carlo simulation approach. With this approach, the temperature-dependency of electrical resistivity and the strain sensitivity of the nanocomposite are investigated. In addition, other parameters such as the aspect ratio, dispersion state and dimensions’ effect on piezoresistivity of the compensated stretchable nanocomposite are investigated. By developing a temperature-dependent percolation model, the temperature sensitivity response of nanocomposite is investigated based on defining the temperature coefficient of resistance of CNT and thermal expansion coefficient of polymer. It is found that the dimensional aspects and dispersion state affected the percolation threshold and resistivity. The obtained results also indicated that the piezoresistivity increased with the decrease in the Poisson’s ratio and intrinsic electrical conductivity. Moreover, the predicted results showed high prediction accuracy for temperature-dependence resistivity compared with the existing experimental data. © The Author(s) 2022.
Publication Date: 2022
Continuum Mechanics and Thermodynamics (09351175)34(2)
Presented herein is a numerical variational approach to the two-dimensional (2D) incompressible nonlinear elasticity. The governing equations are derived based upon the minimum total energy principle by considering the displacement and a pressure-like field as the two independent unknowns. The tensor equations are replaced by equations in a novel matrix-vector form. The proposed solution method is based upon the variational differential quadrature (VDQ) method and a transformation procedure. Using the introduced VDQ-based approach, the energy functional is precisely discretized in a direct way. Being locking-free, simple implementation and computational efficiency are the main features of this method. Also, it is free from numerical artifacts and instabilities. Some important problems of 2D incompressible elasticity are addressed to test the method. It is revealed that it can be efficiently utilized to capture the large strains of incompressible solids. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Tian, L.,
Nankali, M. Publication Date: 2022
Composites Part A: Applied Science and Manufacturing (1359835X)163
Carbon nanotubes (CNTs) are incorporated into a stretchable polymer to determine modified thermo-resistive and piezoresistive responses of a nanocomposite under temperature variation and mechanical strain. Monte Carlo simulation is paired with tunneling model to disperse CNTs into the representative volume element and recognize CNT-to-CNT separation distance to predict the resistance change of nanocomposites subjected to strain. The principle of thermo-electrical properties is studied under thermo-mechanical stimulus. Nanotube reorientation model is used to investigate the influence of CNT's tunneling and state of alignment on the piezoresistive behavior of the nanocomposite. Comparisons between modeling results and experimental data suggested a good agreement. The nearly linear dependence of relative resistance change with strain displayed more sensitivity with shorter CNTs and less sensitivity with higher CNT volume fractions. Relative resistance change with temperature was strongly affected by CNTs’ temperature coefficient of resistance and volume fraction. Such change was more pronounced for the anisotropic nanocomposite. © 2022 Elsevier Ltd
Publication Date: 2022
International Journal of Mechanics and Materials in Design (15691713)18(1)pp. 39-61
A 3D Monte Carlo simulation and percolation network model for hybrid nanocomposites reinforced by carbon nanotubes (CNTs) and carbon black (CB) nanoparticles (NPs) is established to investigate the percolation probability and piezoresistivity considering electron tunneling effect. Firstly, a Monte Carlo algorithm is developed to form a representative volume element filled with randomly oriented CNTs and randomly dispersed CB NPs. Later, a percolation like network model is developed to determine the resistivity between each of CNTs and CB NPs, and then the electrical model based on modified location analysis is employed to calculate the corresponding piezoresistive behavior of hybrid CNT–CB polymer nanocomposites under tension. Tunneling resistance variation with the evolution of the conductive network during the inducing strain leads to non-linear and exponential behavior of relative electrical resistance change with strain. Parametric studies are performed to show the effects of CB volume fraction, size and CNT maximum orientation angle on the percolation probability and piezoresistivity of hybrid CNT–CB polymer nanocomposites. Results indicate that the piezoresistive sensitivity is greatly improved in the nanocomposites with the introduction of hybrid CB NPs/short aligned CNTs. Respecting to piezoresistive sensibility, the gauge factor calculated from the change of resistance as a function of applied strain reaches high value for sensitive piezoresistive sensor with lower Poisson’s ratio and larger diameter of CB NPs. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Zabihi, A.,
Akinshilo, A.T.,
Rezazadeh, H.,
Ansari, R.,
Sobamowo, M.G.,
Tunç, C. Publication Date: 2022
Computational Methods For Differential Equations (23453982)10(3)pp. 580-594
In this paper, the transport of flow and heat transfer through parallel plates arranged horizontally against each other is studied. The mechanics of fluid transport and heat transfer are formulated utilizing systems of the coupled higher-order numerical model. This governing transport model is investigated by applying the variation of the parameter’s method. Result obtained from the analytical study is reported graphically. It is observed from the generated result that the velocity profile and thermal profile drop by increasing the squeeze parameter. The drop inflow is due to limitations in velocity as plates are close to each other. Also, thermal transfer due to flow pattern causes decreasing boundary layer thickness at the thermal layer, consequently drop in thermal profile. The analytical obtained result from this study is compared with the study in literature for simplified cases, this shows good agreement. The obtained results may therefore provide useful insight to practical applications including food processing, lubrication, and polymer processing industries amongst other relevant applications. © 2022 by the Author(s).
Aryayi, M.,
Hadavi, M.R.,
Nickabadi, S.,
Ansari, R. Publication Date: 2022
Journal of Failure Analysis and Prevention (18641245)22(3)pp. 1144-1150
Pitting corrosion is a typical damage on structures, which causes stiffness reduction and mass loss. These changes affect the vibrational behavior of corroded structures. In this study, a three-dimensional finite element model is used to investigate the influence of pitting on the natural frequencies of transverse vibration of a clamped-free shaft. The results of the finite element numerical simulation are validated by experimental results and the beams analytical methods. The simulation results show that the increase in the amount of corrosion reduces the natural frequencies, but the trend of this change differs for different modes. In addition, the percentage change in the natural frequencies because of the increase in the length of the corroded region and the change of its location depends on the mode shapes. The results also indicate that the corroded surface is effective in the amount of change of transverse natural frequencies of the shaft. © 2022, ASM International.
Publication Date: 2022
Mechanics Based Design of Structures and Machines (15397742)50(2)pp. 588-608
The main subject of this study is the dynamic and static pull-in analyses of rectangular nanoplates made of functionally graded materials based on the nonlocal strain gradient theory compared with the strain gradient theory, Eringen’s differential method, and classical theory considering disparate boundary conditions (BCs). To this end, the governing equation is derived based on Kirchhoff’s plate theory and then, the Galerkin method is implemented to arrive at an ordinary differential equation of second-order in the time domain. The homotopy analysis method is used as an analytical solution methodology to solve the nonlinear ordinary differential equation which is under different nonlinear forces such as intermolecular, electrostatic and hydrostatic one. Likewise, an efficient technique is exerted for omitting secular terms. Accordingly, the dynamic pull-in voltage is obtained for different non-classical continuum theories, material gradient indices, nonlocal parameters and internal length scale parameters. The dynamic and static pull-in instabilities are also compared in the same situation. Additionally, the effects of the nonlocal parameter and internal length scale parameter on the non-dimensional frequency against the initial amplitude, electrostatic force and hydrostatic actuation are explored in disparate boundary conditions. Communicated by Eleonora Tubaldi. © 2020 Taylor & Francis Group, LLC.
Ansari, R.,
Nesarhosseini s., ,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2022
International Journal of Structural Stability and Dynamics (02194554)22(8)
In this paper, the nonlinear thermally induced vibration in rectangular plates made of porous functionally graded materials (FGMs) due to thermal shock is studied based on a new numerical approach. The shear deformation influences are taken into consideration via Mindlin's plate theory. The properties of the materials are also assumed to be temperature- and position-dependent. Moreover, the influence of elastic foundation is captured by the Winkler-Pasternak model. For deriving the governing equations, Hamilton's principle, transient 1D Fourier-type heat conduction equation and von Kármán hypothesis are utilized. The relations of paper are written in a new matricized format for computational aims. The generalized differential quadarature (GDQ) method and Newmark's direct integration scheme are used for solving the heat equation. Furthermore, solving motion equations is done based on the variational differential quadrature (VDQ) formulation. The effects of important parameters including material porosity and elastic foundation on the thermal shock response of porous FG plates are investigated in the numerical results. © 2022 World Scientific Publishing Company.
Publication Date: 2022
Engineering with Computers (14355663)38pp. 43-54
The numerical investigation is performed on the vibration of the higher order shear deformable carbon nanotube reinforced composite (CNTRC) spherical panels subjected to the initial external pressure. The functionally graded nanocomposite is reinforced with the non-uniform distribution of CNTs. The problem is formulated following the higher order shear deformation shell theory (HSDT) within the variational differential quadrature numerical approach. For this purpose, the direct discretization of Hamilton’s principle is carried out with the aid of differential quadrature operators. Derivation of the variational formulation of nanocomposite spherical panels based on the HSDT and studying the effects of external pressure on the vibration behavior are the main novel aspects of this research. Several numerical examples are provided to survey the impacts of geometrical and material factors on the vibration of pressurized functionally graded CNTRC spherical panels. It is shown that the internal pressure has the most influence on the vibrational behavior of the thicker panel. © 2020, Springer-Verlag London Ltd., part of Springer Nature.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Jamali, J.,
Mohaddes deylami, H. Publication Date: 2022
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)44(8)
A nested micromechanical technique is proposed to predict thermal conductivities of discontinuous silicon carbide (SiC)/graphene nanoplatelet (GNP)-reinforced aluminum matrix multiphase composites (AMMCs). Agglomeration and waviness of GNPs and interfacial thermal resistance (ITR) between the nanofiller and metal matrix are considered to perform a more realistic simulation process. The present predictions are compared with experimental measurements to verify the validity of the micromechanics approach. The effects of volume fraction, waviness, size and nonuniform distribution of GNPs, graphene/metal ITR, volume fraction, length and diameter of discontinuous SiC and SiC/matrix ITR on the AMMC thermal conductivities in the axial and transverse directions are investigated. The results show that heat in discontinuous SiC/metal composites is better transferred by a uniform distribution of GNPs in the metal matrix. The increase in graphene volume fraction leads to an enhancement in the heat transfer capacity for the metal-based multiphase composites. It is found that GNP with higher length and thickness can significantly improve the AMMC thermal conductivities. However, a great decrease in the thermal conductivities is observed by the ITRs and waviness of nano-graphene. Also, formation of GNP agglomeration drastically reduces the AMMC heat transfer capacity. Increasing the length of discontinuous SiC up to a certain value significantly increases the AMMC thermal conductivity in the axial direction, however, it has a negative effect on the transverse thermal conductivity. © 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.
Publication Date: 2022
Journal of Molecular Graphics and Modelling (10933263)111
In the present work, molecular dynamics (MD) simulations are used to investigate the impact behavior of single-walled carbon nanotubes (SWCNTs) with free boundary conditions in two directions, i.e. vertical and horizontal. To consider the effect of consecutive impacts, the number of carbon nanotubes (CNTs) participated in simulations is chosen from two to five in a row. MD results show that adding the number of impacts increases the magnitude of energy loss in both mentioned directions and reduces the maximum impact force in horizontal cases. In addition, by increasing the velocity of striker CNT from 1 km/s to the maximum value which causes any fracture, the effect of initial velocity on the impact properties and also the ultimate initial velocity for each model are investigated. It is demonstrated that the energy loss and the maximum value of impact force increase as the initial velocity of the striker increases. Also, it is found that the impact strength in the vertical direction is higher than that of the horizontal one, while the horizontal CNTs perform better in the absorption of impact energy. Moreover, for all models, the fracture mechanism of CNTs resulting from the impact process is represented and the procedure of failure is explained. © 2021 Elsevier Inc.
Publication Date: 2022
Transport In Porous Media (15731634)142(1-2)pp. 41-62
In this article, the nonlinear hygrothermally induced vibrational behavior of bidirectional functionally graded porous beams is studied through a numerical approach. Two-dimensional material and temperature distributions, even and uneven porosity distributions, temperature-dependent nature of material properties, and hygroscopic effects are all taken into account in studying beam’s lateral deflection. All material properties are assumed to vary along both thickness and axial directions of beam following a modified power-law distribution in terms of volume fractions of the material constituents, which are considered temperature dependent using Touloukian experiments. Beam's upper surface is subjected to a sudden temperature rise, while its lower surface is kept at reference temperature or is thermally adiabatic; meanwhile, left and right boundaries are thermally insulated. Two-dimensional transient heat conduction equation is solved using generalized differential quadrature (GDQ) method for discretizing spatial derivatives, while time derivatives are approximated using Newmark-beta integration method. Nonlinear sinusoidal moisture concentration is assumed through the thickness direction. Governing equations of motion are derived based on Timoshenko beam theory (TBT) and with the assumption of Von-Kármán geometrical nonlinearity, which is solved afterward using an iterative scheme in conjunction with GDQ and Newmark's method. Finally, the effects of porosity volume fractions, porosity cases, thermal boundary conditions, moisture concentration, FG indexes, slenderness ratio, and temperature rise on maximum non-dimensional lateral deflection are investigated considering various boundary conditions. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Rezazadeh, H.,
Sab’u, J.,
Zabihi, A.,
Ansari, R.,
Tunç, C. Publication Date: 2022
Nonlinear Studies (21534373)29(2)pp. 547-559
This article deals with new soliton solutions of the generalized nonlinear Schrödinger equation with variable coefficients by the direct algebraic method. Once the variables of this technique are considered as special values, we could achieve the solitary waves that are unique from those attained by the other methods. It can be inferred that the solution methodology in conjunction with symbolic computing eligible to solve nonlinear partial differential equations precisely. © CSP - Cambridge, UK; I&S - Florida, USA, 2022
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mohaddes deylami, H. Publication Date: 2022
International Journal of Thermal Sciences (12900729)171
This study comprehensively investigates the thermal transport behavior of unidirectional hybrid composites (UHCs) by means of a micromechanical methodology. The constructional feature of the UHC is that the continuous carbon fibers are embedded in the graphene nano-platelets (GNPs)-modified epoxy resin. The influences of volume fraction, length, thickness, and alignment of GNPs, the interfacial thermal resistance (ITR) between the nano-graphene and polymer matrix, as well as the volume fraction, arrangement type, and off-axis angle of carbon fibers on the thermal conductivities of UHCs are extensively analyzed. Further, the micromechanical model is extended to account the effect of GNP agglomeration on the UHC thermal conductivities. The results show that uniformly dispersed GNPs play a dominant role in improving the UHC thermal conductivity along the transverse direction, while the axial thermal conductivity is insignificantly influenced by the nano-graphene particles. Besides, using the GNPs with a higher aspect ratio (length/thickness) is an efficient manner to obtain much better thermal transport performance for the UHCs. It is observed that the formation of GNP agglomeration within the epoxy resin severely decreases the transverse thermal conductivity. The presence of GNP/epoxy ITR is a lowering factor of the thermal conductivity. As compared to the hexagonal and random arrays, the square array of carbon fibers within the GNP-modified epoxy produces the largest transverse thermal conductivity. On the basis of comparative studies, the model predictions agree very well with the experimental data available in the literature. © 2021 Elsevier Masson SAS
Publication Date: 2022
European Physical Journal Plus (21905444)137(6)
In this paper, the isogeometric analysis based on the non-uniform rational B-spline (NURBS) basis functions is used to study of the bending, buckling and free vibration of the multi-directional functionally graded porous plates with variable thickness. The third-order shear deformation theory is used to account for shear deformation effect, which does not require any shear correction factors. The material properties of the plates are estimated by the rule of mixture and the Mori–Tanaka scheme. The C1 required degree of continuity is easily obtained by increasing the order of the NURBS basis functions. The governing equations of motion are extracted by Hamilton’s principle and then discretised by the isogeometric analysis approach. The effect of different length-to-thickness ratios, material gradations, thickness variations, porosity parameters, and the different boundary conditions on the bending, buckling and free vibration of rectangular, circular and elliptical multi-directional functionally graded porous plates are evaluated. The effectiveness of the proposed method is verified by comparing its numerical results with those of other methods reported in the relevant literature. The presented results show that the variable thickness, porosity parameter and material gradations have a significant effect on the mechanical responses of the plates. Decreasing the thickness and increasing the porosity due to reducing the stiffness of the plate decrease the buckling load and frequencies and increase the deformation of the plate. © 2022, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2022
Diamond and Related Materials (09259635)121
Molecular dynamics (MD) simulations are used to investigate the tensile properties and fracture behavior of Hydrogen (H)- and Fluorine (F)-chemisorbed single-walled silicon carbide nanotubes (SWSiCNTs). Stress-strain curves are obtained and Young's modulus, toughness, tensile strength, as well as maximum strain of nanotubes are determined through stress-strain profiles. The results are compared to those of single-walled carbon nanotubes (SWCNTs) and a detailed analysis of the tensile fracture behavior of both nanotubes, i.e., SWSiCNTs and SWCNTs, is made. It is found that the functionalized nanotubes possess lower stress and strain at the breaking point than those of their pure counterparts (SWSiCNTs 0% and SWCNTs 0%). The increase of functionalization weight leads to reduced Young's modulus, toughness, and tensile strength. Concerning fluorination and hydrogenation, the fluorination of nanotubes has less influence on the weakening of Young's modulus in every functionalization degree when the findings of F-functionalized SWSiCNTs and SWCNTs (F-fSWSiCNTs and F-fSWCNTs) are compared to those of pure nanotubes. Fluorinated and hydrogenated armchair SWSiCNTs experience a nearly equal value of toughness in each weight of functionalization. Similar results are seen in the zigzag fSWSiCNTs which means that the absorption ability of strain energy in the zigzag H- and F-fSWSiCNTs is almost the same. As the weight of functionalization increases from the minimum value to the maximum one, the variation of ultimate stress with the degree of functionalization for the H-fSWCNTs and zigzag H-fSWSiCNT undergoes more reduction in comparison with their F-functionalized counterparts. Also, the armchair functionalized nanotubes are proved to be more capable of withstanding a larger fracture strain than that of their zigzag counterparts in each desired weight of functionalization. Regarding the fracture behavior of nanotubes, the rupture propagation tends to happen in a benzene ring that has at least three functional atoms and one of its grafts has been broken before. © 2021
Publication Date: 2022
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)236(7)pp. 3663-3671
In this paper, an investigation into the thermal conductivity of cross-linked functionalized carbon nanotubes under physical adsorption of polyethylene (PE) chains (cfCNTs/PE) is performed using molecular dynamics (MD) simulations. To have a comprehensive study, the covalently attached functional groups with two types of distribution patterns, namely mapped and wrapped configurations, are used. The cfCNT/PE shows a smaller thermal conductivity than that of pure one. Also, the results demonstrate that the thermal conductivity of cfCNTs reduces by the physisorption of PE chains. By rising the weight percentage of physisorbed PE, the thermal conductivity of cfCNT/PE reduces more. Based on the results, for the constant weight percentage of non-covalent PE chains, the thermal conductivity increases as the number of cross-linked PE chains augments. © IMechE 2021.
Publication Date: 2022
Composites Part A: Applied Science and Manufacturing (1359835X)152
Piezoresistivity and electrical conductivity of carbon nanotube (CNT)/graphene nanoplatelet (GNP)-filled polymer nanocomposites are investigated using a 3D Monte Carlo analytical-geometrical model. GNPs and CNTs are considered as randomly distributed solid thin rectangular cube and cylinder, respectively. After establishment of a random CNT/GNP network, electrical conductivity and relative resistance change with strain is calculated. Model considers effect of CNT and GNP deformation on filler separation distance as the dominant factor for percolation tunneling. Comparing model results with experimental data of hybrid nanocomposites showed a good agreement for electrical conductivity and piezoresitivity. Analytical model is developed on the basis of geometrical tunneling percolation theory to consider the effect of several parameters like height of barrier potential, GNP side length, CNT orientation and dimensions on electric behavior of nanocomposites. Results revealed that CNT dispersion state and GNP dimensions have significant effects on the percolation threshold and resistivity change ratio of nanocomposites with strain. © 2021 Elsevier Ltd
Ali, M.M.A.,
Jamali a., A.,
Asgharnia a., ,
Ansari, R.,
Mallipeddi, R. Publication Date: 2022
Neural Computing And Applications (09410643)34(2)pp. 1345-1357
In system control, stability is considered the most important factor as unstable system is impractical or dangerous to use. Lyapunov direct method, one of the most useful tools in the stability analysis of nonlinear systems, enables the design of a controller by determining the region of attraction (ROA). However, the two main challenges posed are—(1) it is hard to determine the scalar function referred to as Lyapunov function, and (2) the optimality of the designed controller is generally questionable. In this paper, multi-objective genetic programming (MOGP)-based framework is proposed to obtain both optimal Lyapunov and control functions at the same time. In other words, MOGP framework is employed to minimize several time-domain performances as well as the ROA radius to find the optimal Lyapunov and control functions. The proposed framework is tested in several nonlinear benchmark systems, and the control performance is compared with state-of-the-art algorithms. © 2021, The Author(s), under exclusive licence to Springer-Verlag London Ltd., part of Springer Nature.
Publication Date: 2022
International Journal for Numerical Methods in Engineering (00295981)123(10)pp. 2309-2337
The integration of generalized differential quadrature techniques and finite element (FE) methods has been developed during the past decade for engineering problems within classical continuum theories. Hence, the main objective of the present study is to propose a novel numerical strategy called the multi-patch variational differential quadrature (VDQ) method to model the structural behavior of plate structures obeying the shear deformation plate theory within the strain gradient elasticity theory. The idea is to divide the two-dimensional solution domain of the plate model into sub-domains, called patches, and then to apply the VDQ method along with the FE mapping technique for each patch. The formulation is presented in a weak form and due to the (Formula presented.) -continuity requirements the corresponding compatibility conditions are applied through the patch interfaces. The Lagrange multiplier technique and the penalty method are implemented to apply the higher-order compatibility conditions and boundary conditions, respectively. To show the efficiency of the proposed method, numerical results are provided for plate structures with both regular and irregular solution domains. The provided numerical examples demonstrate the applicability and accuracy of the method in predicting the bending and vibration behavior of plate structures following the higher-order plate model. © 2022 The Authors. International Journal for Numerical Methods in Engineering published by John Wiley & Sons Ltd.
Publication Date: 2022
International Journal of Structural Stability and Dynamics (02194554)22(6)
This paper uses the higher-order shear deformation theory (HOSDT) to analyze the nonlinear resonance of functionally graded graphene platelet-reinforced porous (FG-GPL-RP) circular cylindrical shell with geometrical imperfections subjected to the harmonic transverse loading. The shell considered is surrounded by the elastic Winkler-Pasternak foundation. Based on Hamilton's principle, the nonlinear governing equations of motion of the imperfect system considered are established using the first-order and various higher-order shear deformation shell theories that contain a unified higher-order displacement field. Four types of porosity and graphene nanoplatelet distribution patterns are considered. The modified Halpin-Tsai scheme and rule of mixture are utilized to calculate the effective properties of FG-GPL-RP materials. Explicit expressions of the nonlinear primary resonance of imperfect FG-GPL-RP cylindrical shells for simply-supported boundary conditions are achieved by the Galerkin technique and method of multiple scales. After verifying the accuracy of the model used and the results obtained, the influences of the geometric parameters, material properties and distribution and imperfection value on the nonlinear primary resonant response of the imperfect FG-GPL-RP circular cylindrical shells are examined in detail. © 2022 World Scientific Publishing Company.
Ansari, R.,
Oskouie, M.F.,
Nesarhosseini s., ,
Rouhi h., H. Publication Date: 2022
Transport In Porous Media (15731634)142(1-2)pp. 63-87
In this paper, the geometrically nonlinear thermally induced vibration response of beams made of porous functionally graded materials (FGMs) under thermal shock is investigated using a novel numerical approach. The material properties are considered to be temperature- and position-dependent. It is also assumed that the beams are embedded in an elastic medium which is considered as Winkler–Pasternak type. Hamilton’s principle, the Timoshenko beam theory and the von Kármán geometrical nonlinear assumptions are used to derive the equations of motion. The matrix representation of relations is given that can be efficiently utilized in numerical approaches. Solution in time domain is done using the Newmark algorithm according to the constant average acceleration technique. In the space domain, the generalized differential quadrature and variational differential quadrature (VDQ) methods are employed for discretization. Using VDQ leads to compact/efficient vector–matrix relations which can be readily utilized in the coding process. The numerical results are presented to analyze the effects of power law index, boundary conditions, material porosity, elastic foundation and length-to-thickness ratio on the nonlinear thermally induced vibrations of FGM porous beams. It is shown that considering the even distribution, the vibration amplitude of beams decreases as the porosity volume fraction gets larger, while it increases for the uneven distribution. Moreover, the time required to reach the steady state of vibrations increases with increasing the power law index of FGM. © 2021, The Author(s), under exclusive licence to Springer Nature B.V.
Publication Date: 2022
Mechanics Based Design of Structures and Machines (15397742)50(10)pp. 3491-3510
The main objective of this study is the phase-field (PF) vibration analysis of cracked functionally graded graphene platelets-reinforced composite (FG GPL-RC) plates considering stationary cracks. Mindlin’s plate model and phase-field approach are used to express the governing equations. The plate is numerically modeled using the variational finite difference (FD) method. Various convergence studies are provided to show the performance of the introduced numerical model. Different cracked patterns are regarded to investigate the linear vibration of cracked nanocomposite plates. The numerical results clearly demonstrate that the phase-field model can be effectively employed to simulate the vibration behavior of cracked nanocomposite plates. © 2020 Taylor & Francis Group, LLC.
Publication Date: 2022
Thin-Walled Structures (02638231)181
In this article, a numerical approach is presented for the large deformation analysis of shell-type structures made of Neo-Hookean and Kirchhoff–St Venant materials within the framework of the seven-parameter shell theory. Work conjugate pair of the second Piola–Kirchhoff stress and Green–Lagrange strain tensors are taken for the macroscopic stress and strain measures in this total Lagrangian formulation. By defining displacement vector, deformation gradient and stress tensor in the Cartesian coordinate system, and using the chain rule for taking derivative of tensors, the complications of using the curvilinear coordinate system are bypassed. The variational differential quadrature (VDQ) technique as an effective numerical solution method is applied to obtain the weak form of governing equations. Being locking-free, simple implementation, computational efficiency and fast convergence rate are the main features of the proposed numerical approach. A number of well-known benchmark problems are solved in order to reveal the accuracy and efficiency of the method. It is shown that this approach is able to predict the large deformations of hyperelastic shell-type structures in an efficient way. © 2022 Elsevier Ltd
Publication Date: 2022
Journal of Molecular Graphics and Modelling (10933263)111
The mechanical characteristics of reinforced polymer nanocomposites with Hydrogen (H)- and Fluorine (F)-functionalized silicon carbide nanotubes (H-and F-fSiCNTs) are investigated herein using molecular dynamics (MD) simulations. The effects of covalent functionalization and chirality of SiCNT, and diverse polymer materials on Young's modulus, maximum stress, and strain to the failure point, as well as strain energy are studied. The results reveal that by increasing the functionalization degree, the maximum stress, maximum strain, elastic modulus, and strain energy decrease. The tensile strength of polymer nanocomposites containing SiCNT is higher than that of pure polymer and polymers containing functionalized silicon carbide nanotubes (fSiCNTs). It is also found that the incorporation of fSiCNT into the polymer matrix (fSiCNT/polymer) gives rise to a considerable improvement in the ultimate strength of nanocomposites compared to the pure polymer. Polymer nanocomposites reinforced by armchair SiCNTs and fSiCNTs withstand higher maximum stresses and possess less longitudinal Young's modulus as compared to the same systems comprising zigzag nanotubes. In every percent of functionalization, the zigzag F-fSiCNT/polymer tends to have a higher Young's modulus as compared to the zigzag H-fSiCNT/polymer. Similarly, the armchair F-fSiCNTs incorporated into the polyethylene (PE) matrix (F-fSiCNTs/PE) are stiffer than the armchair H-fSiCNTs/PE in each weight of functionalization. Moreover, the armchair fSiCNTs/polymer nanocomposites show higher storage of strain energy in comparison with their zigzag counterparts. © 2021
Publication Date: 2022
International Journal of Applied Mechanics (17588251)14(10)
In this paper, the incremental equilibrium equations and corresponding boundary conditions for the isotropic, hyperelastic and incompressible shells are derived and then employed in order to analyze the behavior of spherical and cylindrical shells subjected to external pressure. The generalized differential quadrature (GDQ) method is utilized to solve the eigenvalue problem that results from a linear bifurcation analysis. The results are in full agreement with the previously obtained results and the effects of thickness and mode number are studied on the shell's stability. For the spherical and cylindrical shells of arbitrary thickness which are subjected to external hydrostatic pressure, the symmetrical buckling takes place at a value of α1 which depends on the geometric parameter A1/A2 and the mode number n, where A1 and A2 are the undeformed inner and outer radii, respectively, and α1 is the ratio of the deformed inner radius to the undeformed inner radius. © 2022 World Scientific Publishing Europe Ltd.
Publication Date: 2022
Journal of Physics and Chemistry of Solids (00223697)161
A two-step analytical model based on a percolation network model and electron tunneling theory has been developed to predict the electrical resistivity and percolation threshold of a hybrid nanocomposite system comprising carbon black (CB) and carbon nanotube (CNT). The nanostructure of a tunneling network consisting of CNT and CB agglomerates has been generated to study the effects of various parameters on electrical conductivity. Electron tunneling is the primary mechanism for electrical percolation, which is incorporated into the model by considering the effective tunneling distance of CNTs. Later, a percolation network model is introduced to evaluate the electrical properties of the hybrid nanocomposite. Our results indicate that a high level of alignment leads to a significant decrease of the percolation threshold with an increase in conductivity, while a low CB volume fraction with low intrinsic electrical conductivity degrades the percolation and overall conductivity. Our results also reveal that the addition of CB as a second filler in a hybrid nanocomposite leads to improvements in conductance and percolation threshold. Analytical results show that the current model agrees well with existing experimental data, which reveals that tunneling and percolation are the dominant mechanisms for transition behavior in electrical conductivity. © 2021 Elsevier Ltd
Publication Date: 2022
Sensors and Actuators A: Physical (09244247)336
A novel one-step Monte-Carlo approach considering the orientation effect of carbon nanotubes (CNTs) in synergism with uniformly distributed ellipsoidal graphene nanoplatelets (GNPs) teamed up with percolation model is developed to study the percolation probability and gauge factor of hybrid CNT-GNP piezoresistive conductive network composite. A representative volume element is generated based on the randomly oriented rod-like CNTs and uniformly distributed disk-shape GNPs to examine the piezoresistive sensitivity developed by strain under tension. The model predictions are compared with experimental studies related to electrical conductivity and piezoresistivity of hybrid CNT-GNP nanocomposites and a good agreement is achieved. A parametric investigation of the influences of CNT volume fraction, degree of orientation, GNP diameter and volume fraction is performed on the piezoresistive sensitivity of nanocomposite. High piezoresistive sensitivity is achieved for scattered short aligned CNTs distributed in the matrix with sparse low aspect ratio GNPs. The results also demonstrated that high percolation probability is achievable for nanocomposite with longer CNTs oriented in random directions and perfect dispersion of GNPs with higher surface area. © 2022 Elsevier B.V.
Gholami y., Y.,
Ansari, R.,
Gholami, R.,
Sadeghi f., F. Publication Date: 2022
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)236(14)pp. 8116-8133
In this paper, a size-dependent nanoplate model is developed to describe the free vibration and buckling behaviors of magneto-electro-thermo-elastic (METE) rectangular nanoplates. It is assumed that the METE nanoplate is subjected to external electric voltage, external magnetic potential, and uniform temperature rise. The nonlocal elasticity theory along with the third-order shear deformation plate theory is employed for the size-dependent mathematical modeling of nanoplates. The presented model has two advantages over available models: (1) the need for the correction factor is bypassed and (2) it can be successfully applied to thick nanoplates. The governing equations and the corresponding boundary conditions are derived using the Hamilton’s principle which are then discretized on the space domain based on the generalized differential quadrature (GDQ) method. Afterward, an efficient numerical Galerkin procedure is adopted to reduce the discretized equations into Duffing-type ordinary differential equations. Numerical results are presented to examine the influences of nonlocal parameter, length-to-thickness ratio, temperature rise, external electric potential, external magnetic potential and type of boundary condition on the free vibration, and buckling behaviors of METE nanoplates. It is revealed that frequency and critical buckling load of nanoplates are dependent on magneto-electro-mechanical loadings, whereas they are less dependent on thermal loading. © IMechE 2022.
Ansari, R.,
Hassani r., R.,
Hasrati, E.,
Rouhi h., H. Publication Date: 2022
JVC/Journal of Vibration and Control (10775463)28(21-22)pp. 3019-3041
In this article, the vibrational behavior of conical panels in the nonlinear regime made of functionally graded graphene platelet–reinforced composite having a hole with various shapes is investigated in the context of higher-order shear deformation theory. To achieve this aim, a numerical approach is used based on the variational differential quadrature and finite element methods. The geometrical nonlinearity is captured using the von Karman hypothesis. Also, the modified Halpin–Tsai model and rule of mixture are applied to calculate the material properties of graphene platelet–reinforced composite for various functionally graded distribution patterns of graphene platelets. The governing equations are derived by a variational approach and represented in matrix-vector form for the computational purposes. Moreover, attributable to using higher-order shear deformation theory, a mixed formulation approach is presented to consider the continuity of first-order derivatives on the common boundaries of elements. In the numerical results, the nonlinear free vibration behaviors of functionally graded graphene platelet–reinforced composite conical panels including square/circular/elliptical hole and with crack are studied. The effects of boundary conditions, graphene platelet reinforcement, and other important parameters on the vibrational response of panels are comprehensively analyzed. © The Author(s) 2021.
Publication Date: 2022
Waves in Random and Complex Media (discontinued) (17455049)32(6)pp. 2796-2811
A novel numerical approach is proposed herein to study thermomechanical wave propagation in annular disks made of viscoelastic materials under inner thermal shock based on the Lord–Shulman (L–S) theory and the Kelvin–Voigt model. It is assumed that the temperature change is considerable in comparison with the reference temperature and the original nonlinear form of energy equation is considered accordingly. In the polar coordinate system, the coupled governing equations are obtained in a weak form which is then solved using the variational differential quadrature (VDQ) technique. The influences of viscoelastic character and thermal shock on the propagation of temperature and radial displacement of disk are investigated. In addition, the predictions of thermally linear and nonlinear models are compared. © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2022
Engineering Computations (02644401)39(5)pp. 1922-1946
Purpose: The paper aims to presents a numerical analysis of free vibration of micromorphic structures subjected to various boundary conditions. Design/methodology/approach: To accomplish this objective, first, a two-dimensional (2D) micromorphic formulation is presented and the matrix representation of this formulation is given. Then, two size-dependent quadrilateral and triangular elements are developed within the commercial finite element software ABAQUS. User element subroutine (UEL) is used to implement the micromorphic elements. These non-classical elements are capable of capturing the micro-structure effects by considering the micro-motion of materials. The effects of the side length-to-length scale parameter ratio and boundary conditions on the vibration behavior of 2D micro-structures are discussed in detail. The reliability of the present finite element method (FEM) is confirmed by the convergence studies and the obtained results are validated with the results available in the literature. Also, the results of micromorphic theory (MMT) are compared with those of micropolar and classical elasticity theories. Findings: The study found that the size effect becomes very significant when the side length of micro-structures is close to the length scale parameter. Originality/value: The study is to analyze the free vibrations of 2D micro-structures based on MMT; to develop a 2D formulation for micromorphic continua within ABAQUS; to propose quadrilateral and triangular micromorphic elements using UEL and to investigate size effects on the vibrational behavior of micro-structures with various geometries. © 2021, Emerald Publishing Limited.
Publication Date: 2022
Acta Mechanica (16196937)233(9)pp. 3663-3677
Based on the micromorphic theory (MMT), the vibrational behavior of annular sector plates with different angles and subjected to various boundary conditions (BCs) is studied. To this end, the linear formulation of three-dimensional (3D) MMT is first presented and the matrix representation of this formulation is given. Then, a 3D size-dependent 8-node brick element is developed by the user element (UEL) subroutine within the commercial finite element software Abaqus to investigate the effects of microstructures on the vibration response of micromorphic structures. The effects of thickness-to-length scale parameter ratio and sector angle on the vibration behavior of the micromorphic annular sector plates are studied. Also, the results obtained by MMT are compared to those of the classical elasticity theory. © 2022, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Ansari, R.,
Oskouie, M.F.,
Nesarhosseini s., ,
Rouhi h., H. Publication Date: 2022
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)44(2)
In this work, a numerical study is presented for the free vibration behavior of piezoelectric Bernoulli–Euler nanoscale beams considering flexoelectric and nonlocal effects. Strain-driven nonlocal formulations of Eringen’s theory in both differential and integral forms are used to capture nonlocal influences. By Hamilton’s principle, the equation of motion and boundary conditions are obtained which are numerically solved. In the solution method, the finite difference and generalized differential quadrature (GDQ) methods are applied for discretizing the differential and integral equations, respectively. Also, matrix differential and integral operators are proposed. After investigating the convergence and validation of the approach, the influences of nonlocality, flexoelectric coefficient and slenderness ratio on the linear free vibrations of nanobeams subject to different end conditions are studied in the numerical results. It is revealed that the paradox related to the results of differential formulation for nanocantilevers is resolved by the proposed integral formulation. © 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.
Publication Date: 2021
Mechanics of Advanced Materials and Structures (15210596)28(24)pp. 2531-2550
Reinforced by nanowires (NWs), carbon nanotubes (CNTs) and NW encapsulated CNT (NW@CNT), tensile behavior of various types of Cu-Zr based metallic glass (MG) nanocomposites are studied using molecular dynamics (MD) simulations. It is observed that pure two-toms alloy MG and the one reinforced with bigger CNT demonstrates higher tensile properties than other types of MGs. Further, it is observed that the ultimate strength of reinforced MGs with individual CNTs is slightly higher than that of NW@CNT reinforced analogous. In this case, it is noticed that reinforced three-atoms Cu-Zr MG nanocomposites including Ti atoms demonstrate the highest ultimate strength and strain. © 2020 Taylor & Francis Group, LLC.
Publication Date: 2021
Mechanics of Advanced Materials and Structures (15210596)28(4)pp. 331-342
A new mixed micromechanics method for a comprehensive analysis of the coefficient of thermal expansion (CTE) of carbon nanotube (CNT)/polymer nanocomposites with fully random microstructures is established. Comparisons between the model results and experiment clearly prove that for a more realistic prediction, considering random orientation and random distribution of CNTs, interphase region created due to the non-bonded van der Waals interactions between the CNT and polymer, non-straight shape and transversely isotropic behavior of CNT is essential in the modeling. The effects of interphase characteristics, geometrical properties and type of random distribution of CNTs on the nanocomposite CTEs are examined. © 2019 Taylor & Francis Group, LLC.
Goli m., ,
Mozvashi s.m., ,
Aghdasi p., P.,
Yousefi, S.,
Ansari, R. Publication Date: 2021
Superlattices and Microstructures (10963677)152
The density functional theory (DFT) was used to investigate the mechanical properties of the pristine, hydrogenated, and fluorinated germanene sheets, including Young's and bulk moduli, and plastic properties. Young's and bulk moduli were calculated through the second derivation of the total energy versus strain. The electronic properties, namely the planar electron difference density and partial DOS were considered to evaluate the bonding characteristics of the structures. The results show that the adsorption decreases the electron accumulation between Ge atoms, which leads to weaker covalent bonds and reduced Young's and bulk moduli. Furthermore, it is observed that the yield strain of fully fluorinated germanene remains unchanged under uniaxial loading in comparison with the pristine structure. However, the yield strain of the hydrogenated germanene is increased under biaxial loadings. Our results show that germanene has a good mechanical tenability using surface functionalization. © 2021
Publication Date: 2021
Arabian Journal for Science and Engineering (21914281)46(8)pp. 7143-7151
The influence of agglomeration of SiC nanoparticles on the bulk thermal conducting behavior of aluminum (Al)-based nanocomposites is examined using a micromechanics-based hierarchical technique. The interfacial thermal resistance (ITR) between the ceramic nano-scale particles and the metallic matrix is included in the analysis. The predictions of the micromechanical model considering the agglomeration and ITR are in very good agreement with the available experimental results. The agglomeration of ceramic nanoparticles greatly reduces the thermal conducting coefficient of the Al-based nanocomposites. When the nanoparticle volume fraction is 10%, the thermal conductivity decreases from 132 to 115 W/mK with the formation of nanoparticle agglomeration. The uniform distribution of nanoparticles and the elimination of ITR can lead to a substantial enhancement in the nanocomposite thermal conductivity. When the volume fraction is 10%, the thermal conductivity increases from 115 to 188 W/mK by uniform dispersing the nanoparticles and removing the SiC/Al ITR. Moreover, the effects of amount, and diameter of nano-scale particles as well as the constituent material properties on the bulk thermal conductivity of the SiC nanoparticle-filled Al nanocomposites are examined. When the SiC diameter increases from 35 nm to 3.5 µm, the thermal conductivity of the Al-based composite increases from 132 to 173 W/mK. © 2021, King Fahd University of Petroleum & Minerals.
Ajori, S.,
Boroushak s.h., S.H.,
Hassani r., R.,
Ansari, R. Publication Date: 2021
Computational Materials Science (09270256)191
There are many two-dimensional (2D) structures of carbon allotropes which have been at the center of theoretical and experimental studies in recent years. α-, α2-, β- and γ-graphyne as the graphene allotropes with mixed sp1 and sp3 bonds are under study in the present work utilizing the molecular dynamics (MD) simulations. These thermodynamically stable forms of 2D carbon structure can also be rolled-up to generate novel nanotubes (NTs). Hence, the armchair (-A) and zigzag (-Z) NTs of the aforementioned one-atom-thick planar structures and their buckling behavior (critical force and strain) are considered. It is observed that γ-A- and γ-Z-graphyne NTs have the highest critical forces through the chosen range of aspect ratios (length/radius), whereas the α-graphyne NTs have the lowest critical forces. Also, α2- and β-graphyne NTs have the highest and lowest critical strains, respectively. Furthermore, the possible multi-walled (MW) NTs are simulated. In agreement with results of the single-walled (SW) NTs, the buckling analysis of MWNTs shows that γ-graphyne and α-graphyne MWNTs have the highest and the lowest mechanical stability under compression, correspondingly. In addition, the results of the critical strain for MWNTs are comparable with those of SWNTs. © 2021 Elsevier B.V.
Publication Date: 2021
European Journal of Mechanics, A/Solids (09977538)85
Carbon nanostructures as one of the efficient candidates have been employed to reinforce various types of nanocomposites. Accordingly, the current study employs the recently proposed three-dimensional graphene network, i.e. Hexagonal Graphene Network (HGN), Triangular Graphene Network (TGN) and Quadrilateral Graphene Network (QGN), as the reinforcements for highly applicable metallic glass (MG) nanocomposites with various compositions to study the tensile characteristics such as Young's modulus (YM), Ultimate Strength (Sut) and ultimate strain (US) using molecular dynamics (MD) simulations. Considering pure MGs, two-elements MG with higher Cu percentage demonstrate superior tensile behavior compared to other MGs. Moreover, the increase in the number of elements in MG composition slightly deteriorates tensile characteristics. It is observed that reinforcements considerably improve the tensile characteristics which are considerably pronounced for HGN reinforced MG nanocomposites (MGNCs). Further, it is demonstrated that US is more sensitive to the reinforcement of MGs compared to Young's modulus and ultimate strength. In addition, it is observed that the effect of MG types on the tensile characteristics becomes relatively insignificant in large deformations as C–C bond plays the dominant role to resist axial force in comparison with the weak vdW interaction between the elements of MG and the nanofiller. Further, necking is observed for two-elements MGs which indicate their more ductile behavior than other types. Finally, for the applications that correspond to big axial force, large and small deformations, Al-based three-elements, Ti–Ni based four-elements and Ti-based three-elements MGNCs with HGN reinforcement is proposed, respectively. © 2020
Oskouie, M.F.,
Hassanzadeh-aghdam, M.K.,
Ansari, R. Publication Date: 2021
Engineering with Computers (14355663)37(1)pp. 713-730
In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied. © 2019, Springer-Verlag London Ltd., part of Springer Nature.
Rasoolpoor m., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2021
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)43(2)
The hybridization of carbon fibers (CFs) with carbon nanotubes (CNTs) is a new way of improving the mechanical and physical performances of composite materials. The aim of this work is to evaluate the low velocity impact response of polymer-based hybrid composite plates reinforced by the chopped CFs and CNTs using finite element method (FEM). A nested micromechanical FEM considering interphase region created by the non-bonded van der Waals interactions between the CNTs and polymer is developed for predicting the mechanical properties of hybrid composites. The predictions of the proposed numerical model are compared with the results of experiment and other numerical methods. It is demonstrated that adding a small amount of CNTs into the chopped CF-reinforced polymer composites can increase the contact force and decrease the center deflection of hybrid composite plates. The influences of volume fractions of CF and CNT, thickness and elastic modulus of interphase region, diameter and initial velocity of projectile, dimensions and boundary conditions of plate on the dynamic response of hybrid composite structures are discussed. © 2021, The Brazilian Society of Mechanical Sciences and Engineering.
Ansari, R.,
Hassani r., R.,
Hasrati, E.,
Rouhi h., H. Publication Date: 2021
European Physical Journal Plus (21905444)136(6)
Presented herein is a novel numerical approach for the vibrational analysis of conical panels with arbitrary-shaped holes made of functionally graded graphene platelet-reinforced composite (FG-GPLRC) within the framework of higher-order shear deformation theory (HSDT). The developed approach can be called variational differential quadrature finite element method (VDQFEM) as it is based on the ideas of VDQ and finite element methods. The governing equations are obtained by means of Hamilton’s principle. Also, the relations of paper are presented in a new matrix–vector form which can be efficiently utilized in the coding process of numerical techniques. By VDQFEM, the space domain of structure is first transformed into a number of finite elements. Then, the VDQ discretization technique is implemented within each element to derive the mass and stiffness matrices. Finally, the assemblage procedure is followed for obtaining total mass and stiffness matrices. Due to using HSDT, a novel mixed formulation approach is also proposed to accommodate the continuity of first-order derivatives on the common boundaries of elements. Conical panels with square/circular/elliptical cutout and with crack are selected to generate the numerical results. In the numerical examples, the effects of geometrical properties and reinforcement with GPL on the resonant frequencies of panels subject to various boundary conditions are investigated. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Journal of Mechanics (18118216)37pp. 72-99
In this paper, a three-dimensional (3D) size-dependent formulation is developed for the free vibrations of functionally graded quadrilateral nanoplates subjected to thermal environment. The plate model is constructed within the frameworks of the Gurtin-Murdoch surface and the 3D elasticity theories. In this way, the effect of surface free energy and all the components of stress and strain tensors are considered without any initial assumption on them as there is no need to assume the variation of transverse normal stress inside the bulk material in advance. The variational differential quadrature approach and the mapping technique are applied to derive a discretized weak form of the governing equations. The present solution method bypasses the transformation and discretization of the higher order derivatives appearing in the equations of the strong form. The effects of surface stress, thermal environment, material gradient index and geometrical properties on the size-dependent vibrational behavior of quadrilateral nanoplates are investigated. It is observed that the thermal load intensifies the effect of surface free energy on the natural frequency of the nanoplates. The present model is exact in the extent of the continuum models and can be employed for structures with any thickness-span ratios. © 2020 The Author(s) 2020.
Ansari, R.,
Hassani r., R.,
Gholami y., Y.,
Rouhi h., H. Publication Date: 2021
European Physical Journal Plus (21905444)136(7)
Based on the ideas of variational differential quadrature (VDQ) method and position transformation, an efficient numerical variational strategy is proposed in this paper to analyze the large deformations of hyperelastic structures in the context of three-dimensional (3D) compressible and incompressible nonlinear elasticity theories. Based on the minimum total potential energy principle together with the Neo-Hookean model, the governing equations are derived. The relations of paper are presented in novel vector–matrix format. Replacing the tensor form of formulations with matricized ones is a novelty of present work since the matricized formulations can be readily employed for the programming in numerical approaches. Discretizing is also carried out via VDQ operators. For applying the VDQ technique, the irregular domain of elements is transformed into a regular one by the method of mapping of position field based on the finite element shape functions. This feature enables the proposed VDQ-transformed approach to solve problems with irregular domains. Moreover, the developed formulation is simple, compact and easy to implement. Considering structures with various shapes, several illustrative convergence and comparative investigations are given to assess the performance of the approach in both compressible and incompressible regimes. Good accuracy and computational efficiency can be reported as the features of developed VDQ-based approach. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Pakseresht m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2021
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)43(1)
Designing material requires the establishment of structure–property relationships for multiscaled nanoparticle/microparticle-reinforced polymer hybrid nanocomposites. This fundamental task is the first step in developing a reliable new method. In the present study, two micromechanical analytical models are proposed to develop an efficient homogenization scheme, in the case of calculating elastic properties for a multiscaled hybrid nanocomposite consisting of silica nanoparticles and glass microparticles embedded in the epoxy matrix. In the small scale, we consider homogenous interphase surrounding the nanoparticle which the first model takes into consideration. In the small scale, considering the thickness of this interphase as variable and characteristic length scale, the influence of nanoparticle size on the overall elastic properties is calculated. In the large scale, an interface model of homogenization is proposed; this model too calculates the elastic properties of the overall nanocomposite as a function of inclusion size in microsize representative volume elements. In the large scale, the existence of surface stress and strains is a result of “sticking” behavior of the matrix to the inclusion surfaces. By combining these two models, we can determine the effective elastic properties of a hybrid nanocomposite as a function of nanoparticle size, microscale inclusion size, interphase thickness, and volume fractions. The model predictions are in good agreement with the experimental data provided in the literature. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.
Mirnezhad m., M.,
Ansari, R.,
Falahatgar s.r., S.R.,
Aghdasi p., P. Publication Date: 2021
Applied Physics A: Materials Science and Processing (14320630)127(4)
In this paper, quantum and molecular mechanics are used to study the quantum effects of fine scaling on the buckling strength of multi-walled carbon nanotubes under axial loading, as well as the effects of changes in length, diameter, chirality, wall number and length-to-diameter ratio of the structure. To this end, the total potential energy of the system is calculated with the consideration of both bond stretching and bond angular variations. The density functional theory along with the generalized gradient approximation function is used to obtain the relevant elastic constants of the nanotubes. An excellent agreement is found between the present numerical results and those found in the literature which confirms the validity as well as the accuracy of the present closed-form solution. The results show that in the effective longitudinal range for quantum effects of fine scaling, any change that leads to a change in the size of the structure has significant effects on the buckling strength of the structure. By increasing the diameter due to the increase in the number of walls or chirality and increasing the length of the structure, the critical buckling strength experiences a decreasing trend and this decrease is highly dependent on the increasing of the diameter due to the increase in the number of walls. In addition, zigzag multi-walled carbon nanotubes are more resistant than armchair multi-walled nanotubes, and the critical buckling strain of multi-walled carbon nanotubes with different chiralities is in the range of zigzag and armchair nanotubes. In other words, it can be said that quantum effects of fine scaling cause more buckling strengthening of the structure against external axial loads and with each longitudinal change that reduces the quantum effects of fine scaling, the strength of the structure decreases sharply. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Salmani r., ,
Gholami, R.,
Ansari, R.,
Fakhraie m., Publication Date: 2021
European Physical Journal Plus (21905444)136(1)
The objective of this study is an analytical investigation on the nonlinear postbuckling of functionally graded porous cylindrical shells reinforced with graphene nanoplatelets (GNPs). It is assumed that the GNP and porous distribution patterns vary smoothly through the thickness. Three distribution schemes are considered for GNP and porous media distributions. The effective material properties are calculated via a micromechanical method. By considering the geometric nonlinearity, the energy functional of the considered system under the combined axial and radial compressions is obtained based on the classical sell theory. Then, an analytical solution procedure based on the Ritz method and Airy function is used to obtain the nonlinear postbuckling behavior of considered system with simply supported boundary conditions. Finally, the effect of different parameters such as porous distribution, GNP scheme, porosity coefficient, GNP weight fraction and geometry on the nonlinear buckling loads, and postbuckling behavior is studied. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)43(3)
Strain gradient and nonlocal influences have important roles in the mechanical characteristics of structures as they are scaled down to nanoscopic dimensions. In this research, an attempt is made to capture both effects on the static bending response of nanoscopic Bernoulli–Euler beams by means of a comprehensive model. For this purpose, the strain gradient theory of Mindlin is combined with the integral (original) form of Eringen’s nonlocal theory. Also, the integral nonlocal formulation is written on the basis of both strain-driven and stress-driven versions of nonlocal theory. This mixed nonlocal strain gradient formulation is capable of reducing to the size-independent and combination of integral nonlocal strain gradient family theories by employing simple substitutions. Through constructing finite difference-based differential and integral matrix operators, numerical solution approaches are developed to obtain the deflection of nanobeams under various end conditions. In addition, for the solution of governing equation of strain-driven nonlocal strain gradient theory, an efficient technique is presented that is applied to the variational statement of the problem in a direct approach. Selected numerical results are provided to explore the simultaneous influences of strain gradient terms and nonlocality based on different theories on the static bending response of beams. It is revealed that the developed size-dependent model has the ability of considering strain gradient and nonlocal influences in the most general way. © 2021, The Brazilian Society of Mechanical Sciences and Engineering.
Bakamal a., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)235(8)pp. 1455-1469
This paper presents a finite element analysis of the bending, buckling, and free vibration of the chopped carbon fiber/graphene nanoplatelet reinforced polymer hybrid composite plates. Both rectangular and circular composite plates are considered. The effective material properties of the chopped carbon fiber /graphene nanoplatelet reinforced hybrid composites are predicted using a multistep micromechanical model based on the Halpin–Tsai homogenization scheme. An inclusive microstructural assessment is accomplished by the evaluation of the influences of the volume fraction, length, thickness, and agglomeration of graphene nanoplatelets as well as the volume fraction, aspect ratio, and the alignment of the chopped carbon fibers on the mechanical behaviors of the chopped carbon fiber/graphene nanoplatelet hybrid composite plates. It is found that the bending, buckling, and vibration characteristics of hybrid composite structures are highly affected by the microstructural features. The addition of graphene nanoplatelets improves the stability of the chopped fiber-reinforced hybrid composite structures. The agglomeration of the graphene nanoplatelet into the polymer matrix leads to a degradation in the composite plate mechanical performances. Aligning the chopped carbon fibers significantly decreases the deflections, and increases the critical buckling loads and the natural frequencies of hybrid composite plates. Comparisons are conducted with the numerical results reported in literature that indicate good agreement with our results. © IMechE 2020.
Ansari, R.,
Hassani r., R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2021
International Journal of Structural Stability and Dynamics (02194554)21(5)
Within the framework of a variational mixed formation and higher-order shear deformation theory (HSDT), a numerical approach is developed in this research to investigate the buckling and post buckling behaviors of variously-shaped plates made of functionally graded graphene platelet-reinforced composites (FG-GPLRCs) taking the effect of porosity into account. By the proposed approach, which can be named as VDQ-FEM, thick and moderately thick plate-Type structures with different shapes (e.g. rectangular, skew, or quadrilateral) with arbitrary-shaped cutout (e.g. circular or rectangular) can be studied. Various types for porosity distribution scheme and GPL dispersion pattern including uniform and different functionally graded patterns are considered along the thickness of plate. In the computation of material properties, the closed-cell Gaussian Random field scheme and Halpin-Tsai micromechanical model are utilized. One of the key novelties of proposed approach is developing an efficient way according to the mixed formulation to accommodate the continuity of first-order derivatives on the common boundaries of elements for the used HSDT model. Several numerical examples are given to analyze the influences of porosity coefficient/distribution pattern, GPL weight fraction/dispersion pattern, cutout and boundary conditions on the buckling and postbuckling characteristics of FG-GPLR porous composite plates. © 2021 World Scientific Publishing Company.
Bakamal a., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2021
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)43(2)
In this paper, the effects of adding carbon nanotubes (CNTs) on the bending, buckling and free vibration characteristics of carbon fabric/polymer hybrid nanocomposite plates (HNCPs) are investigated using a computational approach. First, a hierarchical finite element micromechanics approach is proposed to estimate the hybrid composite properties. The formation of interfacial region due to the non-bonded van der Waals interactions among the CNTs and polymer is considered. Then, finite element analysis is carried out to compute the mechanical responses of the CNT/carbon fabric hybrid composite structures. It is found that incorporating the CNTs into the carbon fabric-reinforced polymer materials results in an enhancement of buckling capacity and natural frequencies of the HNCPs. The maximum deflection of the traditional carbon fabric/polymer composite plates is decreased by adding the CNTs. A parametric study is accomplished to evaluate the influences of amount and aspect ratio of CNTs, material properties and thickness of interfacial region as well as the thickness and various shapes of plate on the flexural deformation, buckling and vibration characteristics of the HNCPs. The predictions are compared with those available in the literature to verify the validity of the presented computational model. © 2021, The Brazilian Society of Mechanical Sciences and Engineering.
Saffar a., ,
Darvizeh a., A.,
Ansari, R.,
Kazemi a., ,
Alitavoli, M. Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)235(4)pp. 868-879
In this paper, the failure behavior of fiber–metal laminate patches as a repair system for steel transmission lines has been investigated and the results are compared with those of the other materials commonly used for repairing pipelines such as composite patches. The laboratory test is also employed to experimentally estimate the pipe burst pressure for the tubes made of API A106 Grade B steel. A comparison of the results using different fiber–metal laminates patches and composite is made. As fillers, putties with two different elastic constants are introduced. Also, taking the cohesive behavior of the patch into account in the numerical model, the effect of the patch on the failure pressures is evaluated. The failure parameter in different patch layers for various types of fiber–metal laminates made of GLARE and CARRALL has been investigated. For significant improvement in the failure behavior of fiber–metal laminate patches, carbon fiber layers are used. Also, to prevent corrosion effects between aluminum and carbon fibers, a combination of aluminum, glass fiber reinforced polymer, and carbon fiber reinforced polymer is utilized. Moreover, the damage behavior of steel pipe and aluminum layers in the fiber–metal laminate patch has been numerically described. The results obtained in the present work clearly show the superior advantage of fiber–metal laminate patches over the conventional composite ones. Experimental results lead to the fact that internal pressure corresponding to final layer failure in composite patches and first layer failure in fiber–metal laminate patches should be considered as a reliable estimation to predict the final burst pressure. © IMechE 2020.
Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)235(21)pp. 5709-5717
This paper is intended to study the dynamic oscillatory behavior of chloride ion inside electrically charged open carbon nanocones (CNCs) using the molecular dynamics (MD) simulations. The small and wide ends of nanocone are assumed to be identically and uniformly charged with positive electric charges. In the simulation, the Tersoff-Brenner (TB) and the Lennard-Jones (LJ) potential functions are employed to evaluate the interatomic interactions between carbon atoms and the van der Waals (vdW) interactions between the ion and the nanocone, respectively. The Coulomb potential is also adopted to evaluate the electrostatic interactions between the ion and the electric charges distributed at both ends of nanocone. Numerical results are presented to examine the effects of magnitude of electric charges, initial separation distance and initial velocity on the mechanical oscillatory behavior of system and the obtained results are also compared with the ones related to an uncharged nanocone. It is found that operating frequency as well as escape velocity enhance considerably as a result of electrostatic interactions. It is further found that regardless of the value of electric charges, optimal oscillation frequency is achievable when no initial velocity is imposed on the ion initially located inside of nanocone with an offset of 2 Å from its small end. © IMechE 2021.
Publication Date: 2021
Journal Of Molecular Modeling (16102940)27(12)
The mechanical properties of oxygen-functionalized single-walled carbon nanotubes (CNTs) are studied herein by molecular dynamics (MD) simulations. An analysis of the random distribution of oxygen atoms on CNTs of various functionalization percentages is presented in this study. The influences of the nanotube length, diameter, and the percentage of functionalization on longitudinal Young’s modulus, failure stress, strain, and toughness are investigated. The results show that for both zigzag and armchair chiralities, Young’s modulus decreases by increasing the nanotube diameter and length-to-diameter ratio. Also, the values of all studied properties including Young’s modulus, stress, strain, and toughness are reduced by increasing the functionalization percentage until the nanotube reaches failure. Moreover, the reason for the alteration of the mechanical properties of nanotubes and the behavior of the stress-strain diagram are discussed. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Pouyanmehr, R.,
Pakseresht m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)235(24)pp. 7785-7799
One of the limiting factors in the life of lithium-ion batteries is the diffusion-induced stresses on their electrodes that cause cracking and consequently, failure. Therefore, improving the structure of these electrodes to be able to withstand these stresses is one of the ways that can extend the life of the batteries as well as improve their safety. In this study, the effects of adding graphene nanoplatelets and microparticles into the active plate and current collectors, respectively, on the diffusion induced stresses in both layered and bilayered electrodes are numerically investigated. The micromechanical models are employed to predict the mechanical properties of both graphene nanoplatelet-reinforced Sn-based nanocomposite active plate and silica microparticle-reinforced copper composite current collector. The effect of particle size and volume fraction in the current collector on diffusion induced stresses has been studied. The results show that in electrodes with a higher volume fraction of particles and smaller particle radii, decreased diffusion induced stresses in both the active plate and the current collector are observed. These additions will also result in a significant decrease in the bending of the electrode. © IMechE 2021.
Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)235(12)pp. 2762-2770
In this article, we study the thermal conductivity coefficient of the polypropylene composite reinforced by graphene sheets. A hierarchical approach is used for the investigation, which is started by molecular dynamics simulation to evaluate the thermal conductivity coefficient of graphene sheets and continued by the finite element analysis to evaluate the thermal conductivity coefficient of graphene reinforced polypropylene at different temperatures. It is shown that inclusion of the graphene sheets can lead to increasing the thermal conductivity coefficient of the polypropylene, especially when the nanosheets are directed along the temperature difference. Moreover, the higher volume percentages of the graphene sheets in the polymer matrix enhance the thermal conductivity. © IMechE 2021.
Ansari, R.,
Oskouie, M.F.,
Nesarhosseini s., ,
Rouhi h., H. Publication Date: 2021
Applied Physics A: Materials Science and Processing (14320630)127(7)
A numerical investigation is performed to examine the static bending behavior of piezoelectric nanoscale beams subjected to electrical loading, considering flexoelectricity effects and different kinematic boundary conditions. The nanobeams are modeled by the Bernoulli–Euler beam theory, and the stress-driven integral nonlocal model is used in order to capture size influences. It is also considered that the nanobeams are embedded in an elastic medium. The Winkler and Pasternak elastic foundation models are used for simulating the substrate medium. Based upon Hamilton’s principle and the electrical Gibbs free energy, the governing equations are derived which are then numerically solved via a finite difference-based method. Numerical results are presented to study the influences of nonlocal, flexoelectric and Winkler/Pasternak parameters on the bending response of piezoelectric nanobeams under various end conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
Ansari, R.,
Hassani r., R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2021
Thin-Walled Structures (02638231)163
Based upon the third-order shear deformation theory (TSDT) and a variational mixed formation, the postbuckling response and free vibration around buckled configurations of variously-shaped plates made of functionally graded graphene platelet (FG-GPL)-reinforced nanocomposite are numerically investigated considering the effect of porosity. The proposed numerical strategy is formulated according to the ideas of variational differential quadrature (VDQ) and finite element method (FEM), and can be employed for plates with different shapes (e.g. rectangular, skew or quadrilateral and annular) including arbitrary-shaped hole. The material properties of nanocomposite are approximated based upon the Halpin–Tsai model together with the closed-cell Gaussian Random field scheme for various distribution patterns of porosity and GPLs along the thickness direction. The governing equations are obtained according to Hamilton's principle by novel vector-matrix relations which can be readily used in numerical methods. One of the main novelties of developed numerical approach is proposing an efficient technique according to the mixed formulation to accommodate the continuity of first-order derivatives on the common boundaries of elements for the used TSDT model. A number of numerical examples are given to investigate the influences of porosity coefficient/distribution pattern, GPL weight fraction/dispersion pattern, cutout and edge conditions on the free vibrations of postbuckled FG-GPL-reinforced porous nanocomposite plates. © 2021 Elsevier Ltd
Publication Date: 2021
Applied Mathematical Modelling (0307904X)100pp. 689-727
Introduced in this paper is the complete nonlinear model of the micropolar theory (MPT) for shell-type materials. Considering the three-dimensional kinematic model in a convected curvilinear coordinate system, the Lagrangian description of micromorphic theory (MMT) is formulated first. Due to certain assumptions, i.e. skew-symmetricity of micro-displacement and orthogonality of micro-deformation tensors, the highly nonlinear micropolar continuum theory is obtained. Unlike the conventional knowledge in the literature, it is found that not only MPT is not a simple version of MMT but also the present micropolar formulation can be reduced to the corresponding micromorphic shell elasticity. Also, unlike the Kafadar-Eringen's nonlinear micropolar model which only predicts the large micro-deformations, the developed micropolar theory is able to investigate the physical behavior in case of large elastic macro-deformations, for the first time. The isogeometric analysis (IGA) solution method with standard base functions is used to prevent the locking issues arising in the low-order finite element analysis (FEA) of thin shells. Accordingly, the proposed IGA micropolar shell model possesses 10-DOFs (degrees of freedom) standing for 7 macro-displacements and 3 micro-rotations. Size / inhomogeneity effects of small-scale / micropolar materials are investigated in the benchmark problems of geometrically nonlinear shells. As a result, it is revealed that the paper contributes to literature by developing the nonlinear micropolar shell theory which is able of capturing large macro- and micro-deformations. © 2021 Elsevier Inc.
Ajori, S.,
Haghighi s., S.,
Parsapour h., H.,
Ansari, R. Publication Date: 2021
Journal Of Molecular Modeling (16102940)27(11)
The endohedral functionalization of carbon nanotubes (CNTs) with nanowires (NWs), i.e., NWs@CNTs, has been the center of attention in a lot of research due to the applications of NWs@CNTs in nanoelectronic devices, heterogeneous catalysis, and electromagnetic wave absorption. To this end, based on the classical molecular dynamics (MD) simulations, the effect of four pentagonal structures of encapsulated metallic nanowires (mNWs), namely the eclipsed pentagon (E), the deformed staggered pentagon (Ds), staggered pentagon (S), and staggered pentagonal structure without the monatomic chain passing through the centers of the parallel pentagons (R) configurations on the vibrational behavior of CNTs, is investigated. Also, the effects of geometrical parameters such as length and radius of CNTs on the natural frequencies of simulated models are explored. The results illustrate that by increasing the length, the natural frequency of pure CNTs and mNWs@CNTs decreases. In a similar length, mNWs@CNTs possess lower natural frequencies compared to the pure CNTs. According to the results, the highest and lowest natural frequencies are calculated by inserting the S structure of sodium NW and Ds structure of aluminum NW inside their proper armchair CNT, i.e., Na-S NW@ (9,9) CNT and Al-Ds NW@ (7,7) CNT, respectively. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Hosseini s.m.j., ,
Torabi, J.,
Ansari, R.,
Zabihi, A. Publication Date: 2021
International Journal of Structural Stability and Dynamics (02194554)21(4)
This paper is concerned with studying the size-dependent nonlinear dynamic pull-in instability and vibration of functionally graded Euler-Bernoulli nanobeams (FG-EBNs) with the von Kármán hypothesis based on the nonlocal strain gradient theory (NLSGT). To this end, the partial differential equation (PDE) is developed by Hamilton's principle considering the intermolecular, fringing field and electrostatic nonlinear forces. Then, the Galerkin method (GM) is utilized to acquire the ordinary differential equation (ODE) and the results are obtained with the help of an analytical approach called the homotopy analysis method (HAM). To verify the outcome of this study, the nonlinear and linear frequencies obtained are compared with those of the literature. Consequently, the pull-in voltage of the FG nanobeam is obtained and the variations of nonlinear and linear frequencies are discussed in detail. Also, the effects of initial amplitude, electrostatic force, length scale, nonlocal parameter, material gradient index and boundary condition (BC) on the electromechanical behavior of FG-EBNs are analyzed with the results commented. © 2021 World Scientific Publishing Company.
Ansari, R.,
Hassani r., R.,
Hasrati, E.,
Rouhi h., H. Publication Date: 2021
Acta Mechanica (16196937)232(9)pp. 3417-3439
Based on Reddy’s third-order shear deformation theory and mixed formulation, a new numerical approach in the variational framework is developed to analyze the geometrically nonlinear free vibration behavior of cylindrical panels having cutouts with various shapes (e.g., square, circular, elliptical) under arbitrary boundary conditions. It is also assumed that the panel is made of functionally graded graphene platelet-reinforced composite with various patterns for the distribution of GPLs along the thickness direction whose effective properties are estimated using the modified Halpin–Tsai model in conjunction with the rule of mixture. The proposed approach can be named VDQFEM as it utilizes the VDQ and FE methods. Efficient matrix formulation, being free from the locking problem, computational efficiency and being able to solve problems with concave and polygon domains are the main features of VDQFEM. Selected numerical results are given to investigate the influences of geometrical parameters and weight fraction/distribution pattern of GPLs on the large-amplitude vibration response of panels with various cutouts and boundary conditions. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Austria, part of Springer Nature.
Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)235(8)pp. 1925-1936
A multiscale approach is used here to investigate the impact properties of carbon fibre/carbon nanotube-reinforced polymer. For this purpose, the mechanical properties of the carbon nanotubes (CNTs) are obtained by molecular dynamics simulations. Then, they are included in the polyethene matrix, and the mechanical properties of CNT-reinforced polyethene are computed using a stochastic approach. Considering the CNT-reinforced polyethene as the matrix, the effect of adding the carbon fibres on its mechanical properties is investigated in the next step. Finally, utilizing a stochastic method, the macro-scale mechanical properties of carbon fibre/carbon nanotube-reinforced polymer are computed. Thereafter, the impact test is applied on the models. The finite element method is used to investigate the mechanical and impact properties of representative volume elements. The effects of waviness, volume percentage and aspect ratio of the carbon fibre and CNT on the mechanical properties of the multiscale composite are evaluated. It is shown that reinforcing the polyethene matrix by carbon fibres and CNTs significantly increases its impact resistance. Adding 3% and 5% volume percentages of CNT into 3%-carbon fibre/polyethene and 5%-carbon fibre/polyethene respectively, resulted in 26% and 47% improvement in the impact resistance of the composite. © IMechE 2021.
Aghdasi p., P.,
Ansari, R.,
Rouhi, S.,
Yousefi, S.,
Goli m., ,
Soleimani h.r., Publication Date: 2021
Physica B: Condensed Matter (09214526)600
In this paper, the density functional theory is used to study the elastic and plastic properties of monolayer phosphorene with and without atomic adsorption. Different atoms, including Li, Mg, O, Al, Pt, Pd and Mo are selected for this purpose. It is shown that adsorption of the phosphorene nanosheet by the majority of selected atoms leads to increasing the elastic modulus of armchair phosphorene, whereas that of zigzag phosphorene decreases by the atomic adsorption. Furthermore, adsorbing the armchair phosphorene nanosheet by all of the selected atoms leads to increasing the width of the harmonic region and decreasing the width of the inharmonic region. It is also observed that adsorbing the zigzag phosphorene nanosheet by all of the selected atoms results in decreasing the yield strain. © 2020 Elsevier B.V.
Publication Date: 2021
Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanomaterials, Nanoengineering and Nanosystems (23977922)235(1-2)pp. 30-40
On the basis of fractional viscoelasticity, the size-dependent free-vibration response of viscoelastic carbon nanotubes conveying fluid and resting on viscoelastic foundation is studied in this article. To this end, a nonlocal Timoshenko beam model is developed in the context of fractional calculus. Hamilton’s principle is applied in order to obtain the fractional governing equations including nanoscale effects. The Kelvin–Voigt viscoelastic model is also used for the constitutive equations. The free-vibration problem is solved using two methods. In the first method, which is limited to the simply supported boundary conditions, the Galerkin technique is employed for discretizing the spatial variables and reducing the governing equations to a set of ordinary differential equations on the time domain. Then, the Duffing-type time-dependent equations including fractional derivatives are solved via fractional integrator transfer functions. In the second method, which can be utilized for carbon nanotubes with different types of boundary conditions, the generalized differential quadrature technique is used for discretizing the governing equations on spatial grids, whereas the finite difference technique is used on the time domain. In the results, the influences of nonlocality, geometrical parameters, fractional derivative orders, viscoelastic foundation, and fluid flow velocity on the time responses of carbon nanotubes are analyzed. © IMechE 2020.
Publication Date: 2021
Materials Science and Engineering: B (09215107)271
In this paper, antimonene nanosheets are simulated using finite element modeling. First, the elastic properties of antinomene are obtained using the density functional theory as well as the element properties, which are used to represent Sb-Sb bonds in the structure of antimonene. Then, developed model is used to calculate Young's modulus, critical compressive force and fundamental frequency of the antinomene nanosheet with different geometrical parameters. It is shown that proposed simulation can predict Young's modulus of monolayer antinomene accurately. Also, it is revealed that increasing the horizontal side length increases the stiffness of nanosheet, while increasing the vertical side length has the opposite result. Moreover, critical compressive force of nanosheet increases by increasing vertical side length, whereas increasing the horizontal side length leads to the opposite result. Furthermore, vibrational frequency of the antimonene significantly decreases by increasing horizontal side length, while changes observed by increasing vertical side length are negligible. © 2021 Elsevier B.V.
Publication Date: 2021
International Journal of Non-Linear Mechanics (00207462)135
Studying the large-amplitude forced vibration characteristics of micropolar shell-type structures is the main objective of this paper. In order to obtain the full geometrically nonlinear model of micropolar theory, the micromorphic seven-parameter shell kinematic is first developed. Via a nonlinear micro-motion map, the extracted formulation is fitted for the micropolar continuum. As a result, possessing three stress–strain fields with eighteen independent elastic parameters of a linear material, the proposed micropolar shell theory is able to capture the inhomogeneity and size-effects. On the basis of Hamilton's principle, the variational form of governing equations of motion is determined. The finite element isogeometric solution approach is then utilized to produce the geometry and approximate the displacement field in mid-surface area of shell. This would be helpful for resolving the locking and instability issues of the traditional low-order standard finite element shell models. By discretizing the period of harmonic vibration, a numerical method is also implemented in time domain. To demonstrate the microstructural effects, dynamic behavior of micropolar plate- and shell-type structures are investigated in several parametric studies. Since the classical strain and stress tensors are retained in present micropolar elasticity, both the large macro- and micro-deformations are captured for the first time. © 2021 Elsevier Ltd
Ansari, R.,
Hassani r., R.,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2021
Engineering with Computers (14355663)37(4)pp. 3251-3263
In this article, a new solution approach is developed to numerically compute large deformations of 3D hyperelastic solids based on the compressible nonlinear elasticity. The governing equations are derived by the minimum total potential energy principle, and the Neo-Hookean model is used for the hyperelastic character of material. One of the key novelties of the work is its formulation in which the tensor form of equations is replaced by an efficient matrix–vector form that can be readily utilized in the coding process. Moreover, the variational differential quadrature technique is adopted to arrive at the discretized governing equations in a direct way. Simple implementation, fast convergence rate, and computational efficiency are the main advantages of present approach. Through some examples, the accuracy and effectiveness of the proposed numerical approach are revealed. © 2020, Springer-Verlag London Ltd., part of Springer Nature.
Publication Date: 2021
Journal Of Molecular Modeling (16102940)27(6)
In this article, the density functional theory is applied to characterize the mechanical properties of single-walled nanotubes of group IV of the periodic table. These materials include carbon nanotube, silicon nanotube, germanium nanotube, and stanene nanotube. (10,10) armchair nanotube is selected for the investigation. By establishing a link between potential energy expressions in molecular and structural mechanics, a finite element approach is proposed for modeling nanotubes. In the proposed model, the nanotubes are considered as an assemblage of beam elements. Young’s modulus of the nanotubes is computed by the proposed finite element model. Young’s modulus of carbon, silicon, germanium, and tin nanotubes are obtained as 1029, 159.82, 83.23, and 83.15 GPa, respectively, using the density functional theory. Also, the finite element approach gives the values as 1090, 154.67, 85.2, and 82.6 GPa, respectively. It is shown that the finite element model can predict the results of the density functional theory with good accuracy. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Physica B: Condensed Matter (09214526)610
In this paper, a molecular dynamics approach is used to characterize the mechanical characteristics of oxygen-functionalized single-walled silicon carbide nanotubes. The influences of different parameters including the nanotube length, diameter and functionalization percentage on the mechanical properties of the oxygen-functionalized nanotubes are investigated. The evaluated mechanical properties include elastic modulus, maximum stress, maximum strain and the value of toughness. It is seen that increasing the diameter and length-to-diameter ratio leads to decrease in the modulus of elasticity of zigzag and armchair nanotubes. Besides, Young's modulus, maximum stress, maximum strain and toughness of armchair and zigzag oxygen-functionalized silicon carbide nanotubes decrease by increasing the functionalization percentage. In the last step, the effect of functionalization pattern on the mechanical properties is studied. © 2021
Publication Date: 2021
Springer Tracts in Mechanical Engineering (21959870)pp. 339-363
Due to the failure of classical elasticity to correctly model the behavior of small-scale structures as well as inhomogeneous media, a non-classical three-dimensional (3D) finite element formulation is developed on the basis of the micromorphic theory (MMT). Possessing micro-scale rotation, shear and stretch degrees of freedom (DOFs), MMT is an appropriate candidate to take the size- and microstructural-effects into consideration in mechanical problems. First, a general 3D formulation is proposed for the micromorphic solid continua which includes three stress and strain fields with 18 elastic constants. Then, the relations are written in matricized form which is advantageous for computational aims. Using the matrix-vector MMT formulation, a 3D micromorphic element with 12 DOFs (3 classical and 9 non-classical) is developed. Also, a robust scheme is used to determine the material parameters in terms of two classical constants in such a way that the positive-definiteness of the stored energy would be guaranteed. In the next step, the static deformations of micromorphic beams and plates with various kinds of edge supports are computed to reveal the efficiency of the method. The influences of length scale parameter on the bending responses of micromorphic structures with various geometrical properties are also analyzed. From comparing the results obtained from the classical and micromorphic elasticity theories, it is indicated that MMT results do not completely converge to those of the classical elasticity theory where the size does not matter. This is because of considering the micro-deformation DOFs in MMT and shows the microstructural-effects. © 2021, The Author(s), under exclusive license to Springer Nature Switzerland AG.
Publication Date: 2021
Iranian Journal Of Materials Science And Engineering (17350808)18(2)
Phenomenological methods are more diagnostic tools than a predictor, so multi-crystalline material approaches based on their microstructures have been proposed during the last years. The purpose of this research is to review methods taking into account the effect of microstructures and texture deformation on predicting the behavior of sheet metals. These methods can be categorized into six general groups: Taylor-type models, crystal plasticity finite element methods, strain gradient methods, methods that consider dislocations, self-consistent methods, methods based on fast Fourier transform. This paper attempts to explain and compare these methods that have been used to forecasting forming limits or stress-strain curves. © 2021, Iran University of Science and Technology. All rights reserved.
Publication Date: 2021
Optik (00304026)227
Presented herein is an exact examination on the resonant nonlinear Schrödinger equation (RNLSE) with Kerr law nonlinearity considering inter-modal dispersion and spatio-temporal. To this end, the ordinary differential equation (ODE) is derived from the traveling wave transformation. Then, the new extended direct algebraic method (NEDAM) is utilized in the axial direction to obtain the results of this study. Subsequently, a bunch of optical soliton solutions in conjunction with dark, bright, and dark-bright soliton solutions are plotted. As a result, it is verified the methodology has an effective mathematical gadget to solve nonlinear partial differential equations (NPDEs). © 2020 Elsevier GmbH
Ansari, R.,
Oskouie, M.F.,
Roghani m., ,
Rouhi h., H. Publication Date: 2021
Acta Mechanica (16196937)232(6)pp. 2183-2199
In this paper, a nonlinear formulation for beam-type structures is presented within the framework of two-phase stress-driven (SD) nonlocal theory. Various boundary conditions are considered for the beams, and it is assumed that they are on the Winkler- and Pasternak-type elastic foundations. It is considered that the beams are made of laminated functionally graded-graphene platelet-reinforced composite (FG-GPLRC) whose properties are estimated by means of the Halpin–Tsai model. The Euler–Bernoulli beam theory is also used for the modeling. The governing equations are derived based on the integral form of SD nonlocal theory using a variational approach considering geometrical nonlinearity. The equations of the SD model in differential form in conjunction with associated constitutive boundary conditions are also obtained. Moreover, a numerical approach based upon the generalized differential quadrature (GDQ) method is developed for the solution of the nonlinear bending problem. The influences of volume fraction/distribution pattern of GPLs, nonlocality, elastic foundation, and geometrical parameters on the bending response of beams under different end conditions are investigated. Furthermore, comparisons are given between the linear and nonlinear results. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, AT part of Springer Nature.
Ansari, R.,
Hassani r., R.,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2021
Acta Mechanica (16196937)232(2)pp. 741-760
In this paper, a numerical solution strategy is proposed for studying the large deformations of rectangular plates made of hyperelastic materials in the compressible and nearly incompressible regimes. The plate is considered to be Mindlin-type, and material nonlinearities are captured based on the Neo-Hookean model. Based on the Euler–Lagrange description, the governing equations are derived using the minimum total potential energy principle. The tensor form of equations is replaced by a novel matrix–vector format for the computational aims. In the solution strategy, based on the variational differential quadrature technique, a new numerical approach is proposed by which the discretized governing equations are directly obtained through introducing differential and integral matrix operators. Fast convergence rate, computational efficiency and simple implementation are advantages of this approach. The results are first validated with available data in the literature. Selected numerical results are then presented to investigate the nonlinear bending behavior of hyperelastic plates under various types of boundary conditions in the compressible and nearly incompressible regimes. The results reveal that the developed approach has a good performance to address the large deformation problem of hyperelastic plates in both regimes. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.
Publication Date: 2021
European Journal of Mechanics, A/Solids (09977538)87
Nonlinear plate bending within Mindlin's strain gradient elasticity theory (SGT) is investigated by employing somewhat non-standard finite element methods. The main goal is to compare the bending results provided by the geometrically nonlinear three-dimensional (3D) theory and the geometrically nonlinear Reissner–Mindlin plate theory, i.e., the first-order shear deformation plate theory (FSDT), within the SGT. For the 3D theory, the nonlinear Green–Lagrange strain relations are adopted, while the von Kármán nonlinear strains are employed for the FSDT. The matrix-vector forms of the energy functionals are derived for both models. In order to perform the corresponding finite element discretizations, a quasi-C1-continuous 4-node tetrahedral solid element and a quasi-C1-continuous 6-node triangular plate element are employed for the 3D model and plate model, respectively. The first-order derivatives of the primal problem quantities are employed as additional nodal values to respond to the continuity requirements of class C1. A variety of computational results highlighting the differences between the 3D and FSDT models are given for two different plate geometries: a rectangular plate with a circular hole and an elliptical plate. © 2021 Elsevier Masson SAS
Publication Date: 2021
International Journal of Applied Mechanics (17588251)13(4)
In this work, the nonlinear primary resonance of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) circular cylindrical panels is numerically studied. The FG-CNTRC cylindrical panels under the radial harmonic loading are modeled on the basis of the hyperbolic shear deformation shell theory (HSDST). The von Kármán hypothesis is employed to incorporate geometric nonlinearity into mathematical modeling. After representing the kinetic and strain energies and the external work in matrix forms (in terms of displacement vector), the variational differential quadrature (VDQ) method is utilized to obtain the discretized form of the energy functional on the space domain. Then, the nonlinear governing equations are achieved via Hamilton's principle. In the next step, a multistep numerical solution approach is employed to illustrate the influences of geometrical parameters, subtended angle, CNTs distribution scheme and volume fraction on the primary resonant characteristics of FG-CNTRC cylindrical panels. The results are provided for the panels with clamped and simply-supported boundary conditions (BCs). © 2021 World Scientific Publishing Europe Ltd.
Hosseini s.m.j., ,
Ansari, R.,
Torabi, J.,
Hosseini, K.,
Zabihi, A. Publication Date: 2021
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)45(4)pp. 891-909
The main objective of this investigation is to study the size-dependent dynamic pull-in instability of nanobeams based on the nonlocal strain gradient theory (NLSGT) and Euler–Bernoulli beam model. To this end, the partial differential equation is obtained based on the NLSGT considering the electrostatic, fringing field, and intermolecular nonlinear forces. Then, the Galerkin method and the homotopy analysis method (HAM) were employed to solve the nonlinear governing equation. To validate the proposed results, the non-dimensional natural frequency and pull-in voltage are compared with the previously published results. Likewise, the analytical results of the HAM are compared with those obtained based on the Runge–Kutta numerical method. Besides, the impacts of the NLSGT, strain gradient theory, nonlocal theory, and classical theory on the dynamic behavior of nanobeams are investigated in the same situation. The pull-in voltage is also presented and the effects of electrostatic forces, fringing field, and initial gap are discussed in detail for different boundary conditions. © 2020, Shiraz University.
Nickabadi, S.,
Ansari, R.,
Rouhi, S.,
Aghdasi p., P. Publication Date: 2021
Journal Of Molecular Modeling (16102940)27(6)
In this paper, the structural and mechanical properties of silicene are investigated by the density functional theory calculations. To calculate Young’s, bulk, and shear moduli and Poisson’s ratio of the silicene, the optimized unit cells containing two atoms are proposed and the effect of chirality on the elastic properties of silicene is examined. It is shown that the silicene has an isotropic behavior, while graphene has an anisotropic behavior. The results showed that calculated moduli for the silicene are significantly lower than those of graphene in zigzag and armchair directions, while Poisson’s ratio of silicene is higher than that of graphene. The paper describes one common type of inharmonic interatomic potentials used for constructing nonlinear models of the material using the modified Morse potential function. Using this concept, the effects of chirality on dissociation energy, inflection point, and coefficients of the modified Morse potential function are studied. Comparison of the cutoff distance value in the modified Morse potential showed that inflection point values for the armchair and zigzag graphene are highly direction-dependent, whereas these values have negligible difference for silicene. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Mechanics of Materials (01676636)157
In this article, the effect of adding nanotubes made by elements from group IV of the periodic table with different lengths and volume fractions on the axial elastic modulus of the epoxy matrix is investigated. For this purpose, carbon, silicon, germanium, and tin nanotubes (CNT, SiNT, GeNT and SnNT) are considered as reinforcement. At the nanoscale, the axial Young's modulus is obtained using a finite element method (FEM) based on the molecular structural model in which the beam and solid continuum are used for embedded nanotubes (NTs) and matrix, respectively. It is shown that CNT has the most significant effect on strengthening the epoxy matrix. For example, at a 5% CNT volume fraction with a length of 300Å, the axial elastic moduli of CNT, SiNT, GeNT, and SnNT/epoxy increase by 1.58%, 1.37%, 1.34%, and 1.32%, respectively. © 2021 Elsevier Ltd
Publication Date: 2021
Thin-Walled Structures (02638231)167
The micropolar continuum theory (MPT) is able to describe the influence of micro-structures on the mechanical behavior of materials where the classical theories of elasticity are unable to interpret. In this paper, the free vibration analysis of three-dimensional (3D) micropolar structures with different geometries is presented. To this aim, first, based on the 3D linear elasticity, MPT is formulated. Then a novel size-dependent quadratic tetrahedral element is developed by the user element subroutine (UEL) within commercial finite element software ABAQUS to study the free vibration behavior of micropolar structures with various geometries. The length scale parameter effects on the dimensionless natural frequencies of micropolar structures with various geometries are studied. © 2021 Elsevier Ltd
Ansari, R.,
Nesarhosseini s., ,
Oskouie, M.F.,
Rouhi h., H. Publication Date: 2021
European Physical Journal Plus (21905444)136(8)
Presented herein is a size-dependent Bernoulli–Euler beam model for the buckling analysis of piezoelectric nanobeams under electrical loading with the consideration of flexoelectricity influence. In order to capture size effects, the stress-driven model of nonlocal theory is utilized. Moreover, it is considered that the nanobeams are embedded in an elastic medium. According to a variational approach, the governing equations including nonlocal and flexoelectricity effects are obtained. Also, using the generalized differential quadrature technique, a numerical solution approach is proposed for calculating buckling loads of piezoelectric nanobeams with different boundary conditions. The effects of flexoelectricity, nanoscale and elastic foundation on the buckling behavior of nanobeams are studied through presenting some numerical examples. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Journal Of Molecular Modeling (16102940)27(1)
In the current study, the elastic and plastic properties of the 2 × 2 and 3 × 3 pristine and transition metal (TM)-doped antimonene are studied through DFT calculations. Sc, Ti, V, Cr, Fe, Co, Ni, Cu, and Zn atoms are selected as the doping atoms. It was observed that Young’s and bulk moduli of both 2 × 2 and 3 × 3 pristine structure would decrease while affected by the doping atoms. The highest reduction in the Young’s and bulk moduli of the 2 × 2 nanosheets has occurred in the Cr- and Ti-doped structures, respectively, while the same reduction was observed in the V- and Ti-doped structures in the 3 × 3 nanosheets. In addition, it was shown that all of the investigated structures express isotropic behavior since the obtained Young’s moduli of these nanostructures have negligible difference along armchair and zigzag directions. Finally, the loading is further increased to investigate the plastic behavior of these structures. The results showed that except for 2 × 2 Sc-doped structure under biaxial loading, the yield strain of all doped nanosheets would decrease under uniaxial and biaxial loadings. The highest reduction in the yield strain of the 2 × 2 nanosheets under biaxial loading has been observed in Cu-doped nanosheet while in 3 × 3 nanosheets, the highest reduction has occurred in Cu-, Fe-, and Zn-doped nanosheets under the same condition. As for the yield strain of the doped 2 × 2 nanosheets while affected by the uniaxial loading, Cu- and Zn-doped nanosheets experienced the highest reduction while in 3 × 3 nanosheets, the highest reduction has been observed for Cr-doped nanosheet under the same condition. © 2021, Springer-Verlag GmbH Germany, part of Springer Nature.
Saffar a., ,
Darvizeh a., A.,
Ansari, R.,
Kazemi a., ,
Alitavoli, M. Publication Date: 2021
Journal of Failure Analysis and Prevention (18641245)21(2)pp. 570-581
Pipelines are identified as one of the most important elements in the transmission of energy worldwide, and hence, their maintenance is of great importance. Accordingly, many standards have been developed to maintain these pipelines in services, such as ASME B31G and ASME PCC2. In recent years, composite patches are increasingly utilized to repair damaged areas Therefore, there are many studies carried out on this repair system. However, the behavior of the patches and repaired pipes has rarely been studied under dynamic pressures and water hammer phenomenon conditions. The main objective of this paper is to study the effect of the water hammer phenomenon on the damaged area of the steel pipe. Moreover, the behavior of the composite patch, which was used for repairing, after the passage of the pressure wave is studied. Furthermore, the effect of strain rates on composite patch damage is investigated by a specific VUMAT subroutine in the numerical model. It was found that despite the good resistance of the steel pipe in the damaged area, the composite patch is very vulnerable and fails after the water hammer shock wave. Therefore, it is recommended that for all pipelines where there is a risk of water hammer impact, repaired patches, based on ASME PCC2, should be re-examined and restored. © 2021, ASM International.
Publication Date: 2021
European Physical Journal Plus (21905444)136(7)
A physics-based hierarchical modeling approach considering tunneling resistance through polymer is proposed to predict the percolation threshold and resistivity of carbon nanotube (CNT)/graphene nanoplatelet (GNP)-reinforced polymer hybrid nanocomposites. At first, a method is developed to calculate the resistivity of CNT-polymer nanocomposites. Then, percolation theory model is employed to calculate the percolation threshold of CNT-reinforced nanocomposites. At the end, an analytical model is presented for estimating the resistivity of CNT/GNP hybrid nanocomposites. The effects of barrier height, nanofiller aspect ratio and tunneling distance on the percolation threshold and resistivity of hybrid nanocomposites are extensively investigated. The results show that the percolation threshold depends on many factors such as aspect ratio, electrical conductivity and volume fraction of nanofillers. It is clearly shown that the smaller GNP aspect ratio leads to an increase in percolation threshold and electrical resistivity. The results also indicate the dominant role of nanofiller volume fraction at low tunneling distance. The model results are compared with experimental data in the literature for GNP/CNT hybrid nanocomposites where it is demonstrated that the represented model is able to explain the impact of electrical tunneling on the resistivity of polymer nanocomposites. © 2021, The Author(s), under exclusive licence to Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2021
Molecular Simulation (08927022)47(4)pp. 354-362
Thermal transport issues are one of the major concerns of scientists as the size decreases. To this end, the thermal conductivity of perfect and defective single-walled carbon nanotubes (SWCNTs) functionalized with carbene, which is an important functional group in nanodevices, is investigated. A series of molecular dynamics (MD) simulations are performed and the thermal conductivity is determined by the approach introduced by Muller-Plathe. The results demonstrate that functionalization decreases the thermal conductivity. Also, the thermal conductivity of functionalized SWCNT declines as the weight percentage of functional group increases. Additionally, it is shown that increasing the weight percentage decreases the sensitivity of thermal conductivity. According to the obtained results, simulation temperature does not affect the thermal conductivity of functionalized SWCNTs considerably compared to pure ones. Finally, it is revealed that the presence of vacancy defect reduces the thermal conductivity of functionalized SWCNTs. © 2021 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2021
International Journal of Structural Stability and Dynamics (02194554)21(2)
In this study, the thermal buckling and postbuckling of functionally graded (FG) nanocomposite annular sector plates reinforced by carbon nanotubes (CNTs) are numerically analyzed. The effective material properties of FG nanocomposite are temperature-dependent (TD) and evaluated via the modified micromechanical method and rule of mixture. Based on the higher-order shear deformation theory (HSDT) and using the principle of virtual work and variational differential quadrature (VDQ) approach, the unified weak form of discretized nonlinear governing equilibrium equations is derived. Then, by using the linear part of equations and solving the derived eigenvalue problem, the critical temperature rise and associated mode shapes are obtained, which are used as the initial guess in solving the nonlinear thermal postbuckling problem. The pseudo-arc-length method and an iterative solver are employed to obtain the nonlinear thermal postbuckling equilibrium path of the FG nanocomposite annular sector plates. The influences of geometrical parameters, boundary conditions (BCs), CNT volume fraction, and CNT distribution pattern on the critical temperature rise and thermal postbuckling behavior of the FG nanocomposite annular sector plates are evaluated and discussed. Also, comparisons are made between the results considering the TD and temperature-independent (TID) properties. It is demonstrated that for higher values of sector angle, the effect of sector angle on the critical temperature rise and thermal postbuckling path is negligible. Moreover, by increasing the sector angle, the effect of BCs of straight edges vanishes, and the critical temperature rise and thermal postbuckling curves of for BCs of CSCS and SCSC approach those for CCCC and SSSS ones. © 2021 World Scientific Publishing Company.
Mirnezhad m., M.,
Ansari, R.,
Falahatgar s.r., S.R.,
Aghdasi p., P. Publication Date: 2021
Journal of Molecular Graphics and Modelling (10933263)104
In this paper, quantum and molecular mechanics are used to study the quantum effects of fine scaling on the buckling strength of multi-walled carbon nanotubes (MWCNTs), as well as the effects of changes in length, diameter, chirality, wall number and length-to-diameter ratio of the structure under torsional loading. To this end, the total potential energy of the system is calculated with the consideration of both bond stretching and bond angular variations. The density functional theory (DFT) along with the generalized gradient approximation (GGA) function is used to obtain the relevant elastic constants of the nanotubes. The study shows that the quantum effects of fine scaling cause more buckling strength of the structure against external torsional loadings. Also, with any longitudinal change as well as the changes in the structural arrangement that reduce the quantum effects of fine scaling, the strength of the structure decreases sharply. © 2021 Elsevier Inc.
Publication Date: 2021
Bulletin of Materials Science (02504707)44(1)
This study focuses on the van der Waals (vdW) interactions and oscillatory behaviour of nested spherical fullerenes (carbon onions) in the vicinity of a single-layer graphene (SLG) sheet. The carbon onions are of Ih symmetries and the graphene sheet is modelled as a fully constrained flat surface. Employing the continuum approximation along with the 6–12 Lennard-Jones (LJ) potential function, explicit analytical expressions are determined to calculate the vdW potential energy and interaction force. The equation of motion is solved numerically based on the actual force distribution to attain the displacement and velocity of the carbon onion. Using the conservation of mechanical energy principle, a semi-analytical expression is also derived to accurately evaluate the oscillation frequency. Numerical results are presented to examine the influences of size of carbon onion and initial conditions (initial separation distance and initial velocity) on the operating frequency of carbon onion–SLG sheet oscillators. It is shown that carbon onion executes oscillatory motion above the graphene sheet with frequencies in the gigahertz (GHz) range. It is further observed that smaller structures of carbon onions produce greater frequencies. We comment that the presented results in this study would contribute to the development of new generation of nano-oscillators. © 2021, Indian Academy of Sciences.
Kohansal vajargah, M.,
Ansari, R.,
Oskouie, M.F.,
Bazdid-vahdati m., M. Publication Date: 2021
Applied Mathematics and Mechanics (English Edition) (02534827)42(7)pp. 999-1012
Based on the micropolar theory (MPT), a two-dimensional (2D) element is proposed to describe the free vibration response of structures. In the context of the MPT, a 2D formulation is developed within the ABAQUS finite element software. The user-defined element (UEL) subroutine is used to implement a micropolar element. The micropolar effects on the vibration behavior of 2D structures with arbitrary shapes are studied. The effect of micro-inertia becomes dominant, and by considering the micropolar effects, the frequencies decrease. Also, there is a considerable discrepancy between the predicted micropolar and classical frequencies at small scales, and this difference decreases when the side length-to-length scale ratio becomes large. © 2021, Shanghai University.
Publication Date: 2020
Composites Part A: Applied Science and Manufacturing (1359835X)130
This article investigates electrical conductivity and piezoresistivity of carbon nanotube (CNT)-polymer nanocomposites using an efficient analytical model. The effects of chopped carbon fibers on the electrical conductivity and percolation behavior of multiscale polymer-based nanocomposites containing CNTs are examined at various maximum angular orientations and different polymer matrix barrier heights. The multiscale nanocomposite (MSNC) electrical conductivity and percolation onset are found to be dependent on the carbon fiber and CNT geometry and dispersion. The tunneling effect is discussed as an important mechanism to explain the low percolation threshold and nonlinear electric behavior of MSNC. A comparison between nanocomposites filled with CNTs and MSNC reinforced with CNTs and chopped carbon fibers demonstrates different percolation behaviors. Moreover, the influences of CNT position and orientation changes on the piezoresistivity of polymer nanocomposites are studied. Resistance change ratio as a function of applied strain demonstrates a non-linear behavior due to tunneling resistance change between CNTs. © 2019 Elsevier Ltd
Aghdasi p., P.,
Ansari, R.,
Rouhi, S.,
Yousefi, S. Publication Date: 2020
Journal of Molecular Graphics and Modelling (10933263)101
A finite element model is developed to modeli the arsenene nanosheet. To obtain the element properties, which are used to represent As–As bonds in the structure of the arsenene, first principle calculation is used. The developed model is then used to compute Young's modulus, critical compressive force and the fundamental frequency of the arsenene nanosheet with different geometrical parameters. It is seen that the employed finite element model can be efficiently used to predict surface Young's modulus of the arsenene. Furthermore, larger arsenene nanosheets have larger surface Young's modulus. In the next step, the critical compressive forces of the arsenene nanosheet under different boundary conditions are computed. It is seen that the influence of the boundary conditions has higher impact on the bunking force of the smaller arsenenes nanosheets. Finally, investigating the vibrational characteristics of the arsenene nanosheets revealed that increasing the horizontal side length at a constant vertical side length leads to a reduction in the fundamental natural frequency. © 2020 Elsevier Inc.
Publication Date: 2020
Journal Of Molecular Modeling (16102940)26(8)
Molecular dynamics (MD) simulations are carried out to study the buckling of pure gold nanowires (GNWs) and hybrid GNWs@single-walled carbon nanotubes (SWCNTs). The effects of geometrical parameters and endohedral filling of SWCNTs on the critical buckling force are taken into consideration. Two different types of GNWs, namely multi-shell and pentagonal GNWs, with various structures are considered. The results illustrate that the buckling force of the pure GNWs is less than those of the pure SWCNTs and hybrid structures. Also, GNWs possess higher buckling forces by increasing their cross-section area. It is observed that enclosing the GNWs by SWCNTs improves the mechanical behaviors of both CNTs and GNWs. In hybrid multi-shell GNWs@SWCNTs, by increasing the radius, the effect of encapsulation on the buckling force is more remarkable. It can be seen that the encapsulation of pentagonal GNWs has a slightly more effect on the buckling behavior than the encapsulation of multi-shell GNWs. Moreover, it is found out that by increasing the length, the buckling force decreases. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
International Journal of Mechanics and Materials in Design (15691713)16(2)pp. 387-400
Atomic decoration of nanofillers, e.g. graphene sheets (GRs), is of extreme importance in their adequate dispersion into the matrices and load transfer issues for nanocomposites because of its effectiveness for improving interfacial properties of the final system. Therefore, based on molecular dynamics simulations, the average pull-out force and interaction energy of carbene-functionalized graphene sheets incorporated into various polymer matrices (cfGRs@polymers) are determined in this paper. The effect of covalent functionalization on the parameters related to the interfacial properties is investigated in terms of weight percentage and distribution patterns of attached carbene to the GR, namely regular and random, which are arranged on one side and both sides of the GR (OS- and TS-GR) to construct four models of cfGRs. In general, the cfGR@polymers show higher average pull-out force and interaction energy compared to the pure GR@polymers. The average pull-out force of randomly and regularly OS-cfGR embedded in the polymer matrices, i.e. Aramid, polyethylene (PE) and polypropylene, decreases as the weight of carbene increases. Also, the similar results are obtained for the TS-cfGRs@Aramid and PE in the regular distribution pattern. However, by increasing the degree of functionalization, the average pull-out force of randomly TS-cfGR@polymers increases. © 2019, Springer Nature B.V.
Publication Date: 2020
Thin-Walled Structures (02638231)153
In this paper, the free vibration analysis of fuzzy fiber reinforced (FFRC) nanocomposite truncated conical shell is investigated. The FFRC constructional feature is that the uniformly aligned carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of unidirectional carbon fibers. Using a micromechanical model based on the simplified unit cell (SUC) method, the effective material properties of the FFRC conical shells are evaluated. The thin-walled classical shell theory and Hamilton's principle are used to extract the governing equations, and the Ritz method is used to solve the problem. The model predictions are compared with other numerical results available in the literature and the correctness of the proposed theoretical method is attested. Some novel results, including the vibration results of FFRC conical shell accompanied with different combinations of boundary conditions and different material and geometrical properties are presented. The results reveal that the FFRC conical shell vibration behavior is strongly dependent on the material properties, volume fractions of two reinforcements, geometrical characteristics and boundary conditions. © 2020 Elsevier Ltd
Publication Date: 2020
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)44(3)pp. 571-583
The geometrically nonlinear forced vibration response of magneto-electro-thermo-elastic (METE) rectangular plates is analyzed herein using a numerical approach. The shear deformation effect is taken into account based on the first-order shear deformation plate theory. The geometrical nonlinearity is also considered using the von Kármán hypothesis. Based upon a variational approach, the energy functional of problem is obtained and represented in matrix form. Then, the variational differential quadrature technique is utilized to directly discretize that functional. For the solution in the time domain, the time periodic discretization method is employed. Finally, the pseudo arc-length continuation technique is used to find the frequency-response curves of METE plates under various boundary conditions. The influences of electric voltage, magnetic potential and temperature difference on the primary resonant dynamics of METE plates are investigated. © 2019, Shiraz University.
Publication Date: 2020
Molecular Simulation (08927022)46(5)pp. 388-397
The functionalisation of carbon nanotubes (CNTs) with biomolecules in an aqueous environment has found considerable potential applications in nanobiotechnology. To understand the structural properties under physical adsorption and mechanical characteristics of non-covalently functionalised CNTs with four important biomolecules in aqueous environment, i.e. l-alanine, guanine, thymine and uracil, molecular dynamics (MD) simulations are performed. It is demonstrated that, unlike l-alanine, the main factor of adsorption is Π-Π stacking together with van der Waals (vdW) interactions. Computation of gyration radius reveals that gyration radius increases linearly as the weight percentage of functional biomolecules increases. Also, it is shown that the presence of water molecules leads to more expansion of biomolecules around CNTs. Simulations show that Young’s modulus of the adsorbed CNTs is slightly smaller than that of pure ones. Furthermore, it is demonstrated that the critical buckling force of functionalised CNT is higher than that of pure CNT. Also, for high aspect ratios, the critical strain of functionalised CNTs is found to be lower than that of pure ones and changes linearly by increasing the weight percentage of functional biomolecules. The buckling modes of functionalised CNTs in vacuum and aqueous environments are explored. © 2020, © 2020 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2020
International Journal of Applied Mechanics (17588251)12(2)
This paper studies the characteristics of a micro-beam interacting with an incompressible fluid in a fluid chamber with an opening in its bottom face for fluid flow. The Euler-Bernoulli equation for transverse deformation of an elastic beam is coupled with the fundamental hydrodynamic equation, which is solved by Galerkin and separation of variables method. The 2D fluid flow assumption in Cartesian coordinate has been used. Natural frequencies and mode shapes of wet beam are calculated and compared with the dry beam. The effects of geometrical parameter changes are also computed as a benchmark for the design of the micro-pump. It is observed that fluid coupling causes a decrease for beam's natural frequencies, especially in higher modes. Furthermore, since the results of the dry and wet beam show a small discrepancy in lower modes, the mode related to the dry beam was employed as the trial function in the forced vibration analysis of the coupled system. © 2020 World Scientific Publishing Europe Ltd.
Publication Date: 2020
Waves in Random and Complex Media (discontinued) (17455049)30(3)pp. 562-580
In the context of integral formulation of Eringen’s nonlocal elasticity theory, flexural, axial and shear wave propagations in nano-beams/tubes made of functionally graded materials (FGMs) are analytically studied. The nano-beams/tubes are modeled according to the Timoshenko beam theory whose governing equations are derived via Hamilton’s principle. The nonlocal formulation is developed generally so that it can be adopted for arbitrary kernel functions. For the comparison aim, the differential counterpart of the formulation is also developed. Selected numerical results are presented to compare the predictions of the local model, differential nonlocal model and integral nonlocal model according to various types of the kernel function, made on the wave propagation characteristics of nano-beams/tubes. The small-scale influences on the dispersion curves of flexural, axial and shear waves are also studied for different nonlocal parameter-to-length and thickness-to-nonlocal parameter ratios. In addition, the wave frequencies are obtained for FGM nano-beams/tubes with different material gradient indexes. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2020
Acta Mechanica (16196937)231(10)pp. 4351-4363
A progressive finite element method is proposed herein to investigate the fracture of silicene nanosheets. By treating a silicene nanosheet as a buckled frame structure, its mechanical behavior is simulated using the modified Morse potential function. The interatomic force per atom is calculated for all atoms as a set of inharmonic oscillator networks, which are described by the modified Morse potential function, while the nonlinear behavior is defined by these interatomic forces with an iterative solution procedure as strain increases. The nonlinear stress–strain relationships of the armchair and zigzag silicene nanosheets are also obtained for pristine and defective cases including the tensile strength and ultimate strain. For the silicene with both configurations, i.e., armchair and zigzag, a sudden drop is seen in the stress–strain diagram, showing that both of them represent the brittle behavior. Moreover, it is concluded that the tensile strength and ultimate strain of the armchair silicenes are slightly larger than those of the zigzag one. It is also seen that the mechanical properties of the silicene are significantly affected by the single-vacancy and Stone–Wales defects. The computed results reveal that single-vacancy defects can reduce the ultimate strain of silicene by approximately 7.3% with respect to that of pristine silicene, whereas the effect of Stone–Wales defects is less significant. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.
Publication Date: 2020
Continuum Mechanics and Thermodynamics (09351175)32(4)pp. 1011-1036
A computationally efficient numerical strategy called as variational differential quadrature-finite element method (VDQFEM) is developed herein for the nonlinear analysis of hyperelastic micromorphic continua. To this end, a novel formulation including microstructure effects is proposed in which high-order tensors are written in equivalent matrix or vector forms, and is then discretized in an efficient way. This feature is utilized in the coding process of numerical method. For the solution purpose, the domain is first transformed into a number of finite elements. Thereafter, a variational discretization technique called as VDQ is applied within each element. In order to employ the VDQ method, the irregular domain of the element is transformed into the regular one using the mapping technique. Finally, the assemblage procedure is performed. This approach can be used for the analysis of bodies with arbitrary geometries. By considering several numerical examples, it is revealed that the presented size-dependent formulation and numerical solution approach have a good performance to study the large deformations of hyperelastic micromorphic bodies with complex geometries. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
European Physical Journal Plus (21905444)135(2)
Eringen’s nonlocal theory (ENT) provides an efficient tool to consider the size dependency for the structural analysis of small-scale structures. Recently, it has been indicated that in some cases, inconsistent results may be obtained using the Eringen differential model (EDM) and Eringen integral model (EIM) should be employed. In this regard, the vibration of nanoplates resting on the elastic medium is investigated on the basis of the EIM using variational differential quadrature (VDQ) method. On the basis of the first-order shear deformation theory (FSDT), the EIM and EDM formulations are given. An effective numerical technique is applied in the framework of the energy method to find the natural frequencies. Comprehensive results are reported to compare the EIM and EDM. The results show that using the proposed integral model, the paradox related to cantilever nanoplates is resolved. © 2020, Società Italiana di Fisica (SIF) and Springer-Verlag GmbH Germany, part of Springer Nature.
Kaveh a., A.,
Dadras eslamlou a., ,
Geran malek n., ,
Ansari, R. Publication Date: 2020
Acta Mechanica (16196937)231(6)pp. 2629-2650
In the present paper, a flexible framework is developed for the optimization of composite laminate plates. In this framework, an optimization algorithm is employed to find the optimal stacking sequence design of the FE models by interfacing the Abaqus solver with MATLAB through a Python script. The Python script submits dimension, orientation, and diameter of the cutout combinations to Abaqus/CAE. The performance of the codes is validated by applying them to several problems of previous research. Three distinct types of boundary conditions, namely CCCC, SCSC, and SSSS, with different geometries comprising a square and rectangular plates with and without cutouts, are considered as optimal design problems. Besides that, analyses are performed on new symmetrical composites with 16 and 80 plies. The framework is equipped with the GA for optimizing the fiber orientations and maximizing the buckling capacities. The results are comprehensively discussed, showing a reasonable agreement with the literature. This code can easily be used by scientists and industry professionals as an automated tool for optimizing different finite element models and using any arbitrary optimization algorithm. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.
Pakseresht m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2020
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)234(7)pp. 910-923
In this work, a micromechanical approach consisting of high-fidelity generalized method of cells (HFGMC) and Mori-Tanaka (M-T) model is proposed to calculate the damping properties of aligned carbon nanotube-epoxy nanocomposites. To determine the resultant directional specific damping coefficients, these models, by applying strain energy approach in the global system utilize each constituent’s specific damping coefficients and mechanical properties. The effects of interphase created in the contact region of the two initial phases—carbon nanotube and polymer matrix—are extensively investigated. Comparative studies show that the micromechanical results are in good agreement with experimental data. One major finding is the thickness and mechanical and damping properties of interphase significantly affect the overall specific damping coefficients of the carbon nanotube-polymer nanocomposites. It is found that by increasing the elastic modulus of the interphase, the longitudinal specific damping property continuously increases, while other components of damping, initially increase and then asymptotically decrease. The damping properties of polymer nanocomposites can be increased by increasing the interphase damping capacity. However, the rise of interphase thickness leads to a reduction of nanocomposite damping properties. Also, the influences of carbon nanotube volume fraction and radius are examined on the damping response of polymer nanocomposites. © IMechE 2020.
Publication Date: 2020
Journal of Sandwich Structures and Materials (15307972)22(6)pp. 1709-1742
A sandwich material would be an attractive structural candidate for marine applications as long as it can retain its environmental durability. However, the susceptibility to moisture attacks is still the major drawback of sandwich materials in comparison to the single skin laminates. Hence, this paper aims to study the effect of moisture absorption on the mechanical behavior of a newly developed sandwich structure, which is intended for use as a water-resistant constructive system in marine industries. For this purpose, an eco-sandwich material consisting of fiber metal laminate facesheets bonded to a core of agglomerated cork was successfully designed and manufactured. To investigate the moisture effects on possible mechanical degradation, a certain number of sandwich specimens were immersed in distilled water for a period of 100 days. For comparison, a sandwich structure with the commercial E-glass–epoxy facesheets was also manufactured and exposed to the aforementioned conditioning process. Eventually, the flexural, buckling and impact behaviors of the conditioned specimens were evaluated and compared with those of dry specimens. Results showed that that water immersion exposure effectively contributed to reducing the mechanical properties of sandwich specimens with E-glass–epoxy facesheets compared with those having fiber metal laminate facesheets. Moreover, it was found that the excellent mechanical properties of the fiber metal laminates in combination with the high environmental durability of agglomerated cork offer a synergistic effect yielding a sandwich martial with various advantages in terms of eco-friendly, high environmental resistance, and superior mechanical properties. © The Author(s) 2018.
Publication Date: 2020
Superlattices and Microstructures (10963677)142
The inorganic analogous of graphene has demonstrated many potential applications in novel devices. Thus, understanding the mechanical properties of hexagonal boron-nitride sheets is of great importance. To this end, the molecular dynamics (MD) simulations are employed to impose tensile load on the sheets in order to compute their mechanical properties and fracture propagation. Moreover, since the presence of defects is undeniable, the effects of two important kinds of defects, i.e. vacancy and Stone-Wales, on Young's modulus, ultimate strength, failure strain and fracture patterns corresponding to different chiralities are explored. It is observed that Young's modulus reduces linearly with increasing the defect percentage, whereas the ultimate strength and failure strain vary with defect percentage in a homographic-like trend with specific asymptote for each case. According to the results, the presence of vacancy defects reduces the aforementioned values more considerably compared to Stone-Wales defects, especially in the case of zigzag direction. Finally, it is found out that in the defective sheets, fracture begins at the location of sheet with higher densities of defect and propagates through the defect sites. © 2020 Elsevier Ltd
Publication Date: 2020
European Physical Journal Plus (21905444)135(7)
This paper aims to analyze the problem of ion selectivity and, in particular, sodium and chloride ions, through semi-infinite carbon nanotubes decorated by a functional group at the entry. A continuum approach is adopted to model the Van der Waals and the electrostatic interactions using the 6–12 Lennard–Jones and the Coulomb potentials, respectively. Suction energy imparted to the ion in the form of an increased velocity is determined. Moreover, an acceptance condition is obtained in the absence and the presence of functional group to examine whether the rested core is completely sucked into the nanotube or not. With respect to the proposed formulations, numerical results of suction and acceptance energies along with potential energy and interaction force distribution are presented by varying the functional group charge and nanotube radius. Unlike acceptance energy, suction energy configuration is shown to be independent of electrostatic interactions. Our numerical results also indicate that the ion selectivity can be altered by changing the sign and magnitude of functional group charge. In the presence of functional group, it is observed that the acceptance radius of a counterion always reduces and thus the ion can pass through the nanotube more easily. © 2020, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
Thin-Walled Structures (02638231)151
The finite element phase-field modeling is presented to study the crack propagation in functionally graded (FG) two-dimensional structures. Exploring the influences of the effective parameters of the staggered solver such as load increment and the number of staggered iteration on the phase-field solution and crack propagation analysis of FG structures is the main objective the research undertaken. Based on the concept of FG materials, the material properties are continuously varied along the length and width of the structure according to the Voigt rule of mixture. The finite element phase-field formulation is derived in the variational framework, and the staggered scheme together with the hybrid formulation is implemented to solve the problem and find the crack growth path. Various benchmark problems are modeled and the influences of material distribution pattern, load increment and the number of staggered iteration on the fracture of FG two-dimensional structures are extensively examined. The results revealed that considering large load increment or one staggered iteration considerably overestimate the fracture resistance of FG structures. © 2020 Elsevier Ltd
Rasoolpoor m., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2020
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)234(1)pp. 180-195
The main purpose of this work is to investigate low velocity impact behavior of metal matrix nanocomposite plates reinforced with silicon carbide nanoscale particles. First, a micromechanical model is proposed to predict the effective mechanical properties of metal matrix nanocomposites. Two features of the nanocomposite microstructure affecting the elastic properties, including agglomerated state of silicon carbide nanoparticles and size factor, are taken into account in the micromechanical simulation. Then, finite element method is used to analyze the time histories of contact force and center deflection of silicon carbide nanoparticle-reinforced metal matrix nanocomposite plates. Several detailed parametric studies are accomplished to explore the influence of volume fraction, diameter and dispersion type of silicon carbide nanoparticles, spherical impactor velocity and diameter, plate dimensions, as well as different boundary conditions on the dynamic response of metal matrix nanocomposite plates. The presented approach accuracy is verified with the available open literature results displaying a clear agreement. The results indicate that adding the silicon carbide nanoparticles into the metal matrix materials leads to a reduction in plate center deflection and an increase in contact force between the plate and projectile. Moreover, it is found that the nanoparticle agglomeration dramatically decreases the contact force and increases the center deflection of metal matrix nanocomposite plates. © IMechE 2019.
Pouyanmehr, R.,
Hassanzadeh-aghdam, M.K.,
Ansari, R. Publication Date: 2020
Mechanics of Materials (01676636)145
An analytical method is proposed to evaluate the diffusion-induced stresses (DISs) in a layered electrode consisting of a current collector and two graphene nanosheet (GNS)-reinforced nanocomposite active plates for lithium-ion batteries. The main focus is placed on investigating the dispersion effect of GNSs within the Tin (Sn)-based nanocomposite active plates on the DISs of the layered electrode. Three types of GNS dispersion, including aligned, randomly distributed, and agglomerated state are considered in the analysis. The effective material properties of the Sn-based nanocomposites reinforced by different GNS volume fractions are predicted using the Mori-Tanaka micromechanical model. It is found that the DISs in the nanocomposite electrodes are very sensitive to the GNS dispersion type. Aligning the GNSs within the Sn-based nanocomposite active plates can reduce the peak stresses in both current collector and active plate. So, from the mechanical viewpoint of designing an electrode, alignment of GNSs within the nanocomposite active plates is an optimized condition. However, agglomeration of GNSs may increase the stress in the whole electrode. Also, the effects of amount and dispersion type of GNSs as well as the thickness ratio of current collector to active plate on the DISs and the curvature of the bilayer Sn-based nanocomposite electrode for the lithium-ion batteries are extensively discussed. Addition and alignment of the GNSs within the Sn nanocomposite active plate can significantly decrease the peak curvature of the bilayer electrode. © 2020 Elsevier Ltd
Ajori, S.,
Parsapour h., H.,
Ansari, R.,
Haghighi s., S. Publication Date: 2020
European Physical Journal D (14346060)74(5)
Abstract: The encapsulation of nanowires (NWs) into single-walled carbon nanotubes (SWCNTs) is of great significance due to the specific mechanical, electrical and magnetic properties of confined NWs as well as application of filled CNTs in nanoelectromechanical systems (NEMS). The tensile behavior of NWs encapsulated-SWCNTs (NWs@SWCNTs) is investigated herein using molecular dynamics (MD) simulations. The results illustrated that Young’s moduli of NWs@SWCNTs decrease as the length of nanotube increases. Moreover, pure SWCNTs show higher Young’s moduli as compared to NWs@SWCNTs. It is also found that NWs@SWCNTs possess higher ultimate forces than those of pure SWCNTs. In addition, at a given length, the ultimate forces of pure SWCNTs and NWs@SWCNTs increase by increasing the radii of nanotubes. Graphical abstract: [Figure not available: see fulltext.]. © 2020, EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
Brazilian Journal Of Physics (01039733)50(2)pp. 164-177
In this paper, finite element modeling is used to compute the elastic properties of aluminum matrix reinforced by carbon nanotubes at different temperatures. Different patterns, including longitudinal dispersion along the loading, longitudinal dispersion perpendicular to the loading and random dispersion, are employed to disperse the nanotubes in Al matrix. Besides, the dependence of the mechanical properties of nanotube/Al nanocomposites on the nanotube aspect ratio (the ratio of nanotube length to its diameter) and volume percentage is studied. It is shown that the effect of temperature variation on the elastic properties of nanotube/Al nanocomposites is the same as the pure Al matrix. Investigating the influence of nanotube volume percentage, it is seen that nanocomposites with larger nanotube volume percentages possess higher elastic modulus. © 2020, Sociedade Brasileira de Física.
Publication Date: 2020
Physica Scripta (00318949)95(11)
Presented in this study is an analytical investigation on the size-dependent nonlinear vibration and pull-in instability of circular microplates subjected to the electrostatic, Casimir, and hydrostatic forces. Based on the modified strain gradient theory in conjunction with the Kirchhoff thin plate theory and von Kármán’s nonlinear kinematic relations, the governing equations were derived using the variational principle. The Galerkin technique (GT) and Homotopy analysis method (HAM) are employed to present the analytical solution considering the clamped boundary condition. Different comparative studies are presented to show the accuracy of the model. As the main novelty of this study, the effects of the geometric nonlinearity on the strain gradient dynamic pull-in instability of circular microplates are presented through a wide range of analytical results. It is observed that by increasing the gap distance, the impacts of nonlinear strains on pull-in behavior become more remarkable. © 2020 IOP Publishing Ltd Printed in the UK
Hassanzadeh-aghdam, M.K.,
Hasanzadeh, M.,
Ansari, R. Publication Date: 2020
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)44(2)pp. 299-312
This paper investigates the overall elastoplastic behavior of unidirectional fiber-reinforced polymer composites containing silica (SiO2) nanoparticles under tensile transverse uniaxial loading using a multi-procedure micromechanics-based ensemble volume-averaged method. In the first step, the elastoplastic behavior of a nanocomposite consisting of SiO2 nanoparticles embedded in a polymer matrix is modeled. The formation of the interphase region between the nanoparticles and the polymer is taken into account in the simulation. In the second step, considering the nanocomposite as the matrix and fiber as the reinforcement, the elastoplastic behavior of nanoparticle-fiber-reinforced hybrid composites is obtained. The effects of volume fraction and size of nanoparticles, interphase characteristics and fiber volume fraction on the elastoplastic stress–strain curves are examined. The results clearly highlight the benefits of SiO2 nanoparticles into the fibrous composites from a structural point of view. The elastic modulus and strength of fibrous composites can be significantly enhanced with adding nanoparticles. It is found that the interphase region plays a crucial role in the overall mechanical behavior of the hybrid composites. Moreover, the mechanical properties of hybrid composites are highly improved by decreasing the nanoparticle diameter. Finally, the elastoplastic behavior of nanoparticle-fiber-reinforced hybrid composites under transverse/transverse biaxial tension is provided. Comparisons between the predictions and existing experimental data are conducted to verify the predictive capability of the proposed approach. © 2018, Shiraz University.
Publication Date: 2020
Applied Physics A: Materials Science and Processing (14320630)126(2)
In this paper, the influence of the external electric field on the mechanical properties of the antimonene is investigated. For this purpose, the density functional theory is utilized. Using the uniaxial and biaxial loading, the in-plane Young’s modulus, bulk modulus and Yield’s strain of the antimonene are computed. Also, the variation of an individual bond under the mentioned loading conditions is studied. It is shown that while the in-plane Young’s modulus and bulk modulus of the antimonene are not affected significantly at the presence of the external electric field, the Yield strain after which the nanosheet enters the plastic region significantly decreases noticeably. Besides, the largest tolerated strain by individual bonds is not influenced by the external electric field. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
Journal of Molecular Graphics and Modelling (10933263)98
In this paper, first principles calculations are used to investigate atomic structure and mechanical properties of germanene nanosheet. By applying uniaxial and biaxial tensile strains as well as shear strain, the tensile and shear properties of the germanene nanosheet, including Young's and bulk moduli, Poisson's ratio, and shear moduli are computed. Furthermore, the parameters of the modified Morse potential function are calculated for Ge–Ge interaction in the germanene nanosheet. Also, the mechanical behavior of germanene nanosheet is studied under tensile loading at large strains extended to the plastic range. Based on the simulations, Young's modulus of the armchair and zigzag germanene nanosheet are computed as 52.8 and 49.9N/m, respectively. Besides, the values of Poisson's ratio of the armchair and zigzag germanene nanosheet are obtained as 0.35 and 0.29, respectively. © 2020 Elsevier Inc.
Hosseini, K.,
Ma w.x., ,
Ansari, R.,
Mirzazadeh m., ,
Pouyanmehr, R.,
Samadani f., F. Publication Date: 2020
Physica Scripta (00318949)95(6)
A nonlinear integrable model known as the (4 + 1)-dimensional Boiti-Leon-Manna-Pempinelli (4D-BLMP) equation is studied in the present paper. To this end, by considering the Hirota bilinear form of the model and utilizing the linear superposition method (LSM) along with symbolic computations, a group of rational wave solutions including multiple wave and positive (non-singular) compelexiton solutions is formally derived. The dynamical behavior of the solutions is also analyzed graphically by considering the special values of the involved parameters. The results of the current work reveal the existence of different wave structures to the 4D-BLMP equation and distinguish it from other models that do not possess non-singular compelexiton solutions. © 2020 IOP Publishing Ltd.
Oskouie, M.F.,
Bazdid-vahdati m., M.,
Ansari, R.,
Rouhi h., H. Publication Date: 2020
Continuum Mechanics and Thermodynamics (09351175)32(1)pp. 99-110
The micromorphic theory (MMT) is one of the most general higher-order continuum theories capable of describing the behavior of materials when the microstructure of body is important, in which the micro-deformation degrees of freedom (DOFs) of material particles are taken into account. In this article, a new size-dependent finite element approach is developed for the mechanical analysis of micromorphic continua based on the three-dimensional (3D) elasticity. To this end, the linear MMT is first formulated within the framework of 3D elasticity. Relations are matricized in order to use in the finite element method. Then, a 3D size-dependent element is developed with taking the effects of micro-deformation and micro-rotation DOFs of material particles into account. Micromorphic rectangular plates subject to different sets of boundary conditions are considered as the problem under study whose free vibration is investigated. The effects of thickness-to-length scale parameter and side length-to-thickness ratios on the resonant frequencies of plates are studied in the given results. Also, the results of MMT are compared to those of micropolar theory and classical elasticity. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
Superlattices and Microstructures (10963677)140
In this article, the density functional theory is employed to evaluate the elastic and plastic properties of the monolayer bismuthene. To investigate the influence of the external electric field on the bismuthene mechanical properties, the external electric fields with different magnitudes are applied to it. It is shown that Young's modulus of the bismuthene is not sensitive to small electric fields. However, a large external electric field can change it. Similarly, a sufficiently large external electric field can result in decreasing the yield strain of the monolayer bismuthene. Besides, it is shown that the Bi–Bi bond length is not sensitive to the presence of the external electric field. © 2020 Elsevier Ltd
Publication Date: 2020
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)42(9)
In this study, the tensile properties and fracture analysis of functionalized carbon nanotubes (CNTs) with carbene are investigated employing the molecular dynamics simulations. Tensile parameters, i.e., Young’s modulus, ultimate stress, failure strain, and fracture progress, are determined, and the effects of different attachment types, distribution patterns, the weight percentage of functional groups as well as the presence of defect with various defect weights on the aforementioned values are explored. According to the results, the tensile parameters are highly sensitive to the attachment type of carbene. In general, functionalization reduces the value of tensile parameters, especially when the attachment of carbene to base CNT is perpendicular to the loading direction. Compared to the ultimate stress and the failure strain, Young’s modulus is shown to be less affected by functionalization. It is demonstrated that the presence of defect, regardless of functionalization type and distribution pattern, reduces the tensile parameters. This reduction is more pronounced in the case of ultimate stress. Moreover, it is found that the toughness of CNTs reduces by functionalization and the presence of defects. Finally, it is demonstrated that functionalization with carbene and the presence of defects does not have a noticeable effect on the fracture progress of CNTs. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.
Goli m., ,
Ansari, R.,
Rouhi, S.,
Aghdasi p., P.,
Mozvashi s.m., Publication Date: 2020
Physica E: Low-Dimensional Systems and Nanostructures (13869477)119
The density functional theory is used here to study the influence of adsorption on the elastic and plastic properties of silicene. The hydrogen and fluorine atoms are considered as the adsorption atoms. Furthermore, two different configurations are considered for each adsorption, including semi-adsorption and fully-adsorption. Through investigation on the elastic properties of pristine and adsorbed silicene under uniaxial and biaxial loadings, it is observed that both Young's and bulk moduli of the silicene decrease by the adsorption. It is also presented that the adsorption of silicene by H and F atoms leads to a decrease in its yield strain under the uniaxial loading. However, under the biaxial loading, H and F adsorbed silicenes reach plastic deformation at larger strains, compared with the pristine nanosheet. © 2020 Elsevier B.V.
Pouyanmehr, R.,
Hassanzadeh-aghdam, M.K.,
Mohaddes deylami, H.,
Ansari, R. Publication Date: 2020
Solid State Ionics (01672738)349
Structure integrity of electrodes can be broken by the diffusion induced stresses (DISs) leading to a significant degradation of storage capacity and cycling stability of lithium-ion batteries. In this paper, the effects of adding carbon nanotubes (CNTs) into the Tin (Sn)-based nanocomposite active plate bonded to the current collector on the DISs and curvature of bilayer electrodes are numerically investigated. A physics-based hierarchical modeling approach based on the Mori-Tanaka micromechanical method is developed to estimate the effective properties of CNT-Sn nanocomposite active plate. The predictions of the micromechanics method are in good agreement with the experimental data. It is shown that the CNTs embedded into the active plate have the significant contribution to the mechanical performances of lithium-ion battery electrodes. Adding the CNTs into the nanocomposite active plate can alleviate the overall stress and curvature of the bilayer electrodes. The influences of volume fraction, length, diameter, non-straight shape and agglomeration of CNTs as well as the geometric parameters of the bilayer electrode on the built-in stresses and flexural deformation are extensively discussed. The overall stresses and curvature of the bilayer electrodes can be further decreased by aligning the CNTs into the nanocomposite active plate. The present work can provide a novel angle of view for designing and evaluating the bilayer electrodes containing CNT-metal nanocomposite active plates. © 2020 Elsevier B.V.
Norouzzadeh, A.,
Oskouie, M.F.,
Ansari, R.,
Rouhi h., H. Publication Date: 2020
Engineering Computations (02644401)37(2)pp. 566-590
Purpose: This paper aims to combine Eringen’s micromorphic and nonlocal theories and thus develop a comprehensive size-dependent beam model capable of capturing the effects of micro-rotational/stretch/shear degrees of freedom of material particles and nonlocality simultaneously. Design/methodology/approach: To consider nonlocal influences, both integral (original) and differential versions of Eringen’s nonlocal theory are used. Accordingly, integral nonlocal-micromorphic and differential nonlocal-micromorphic beam models are formulated using matrix-vector relations, which are suitable for implementing in numerical approaches. A finite element (FE) formulation is also provided to solve the obtained equilibrium equations in the variational form. Timoshenko micro-/nano-beams with different boundary conditions are selected as the problem under study whose static bending is addressed. Findings: It was shown that the paradox related to the clamped-free beam is resolved by the present integral nonlocal-micromorphic model. It was also indicated that the nonlocal effect captured by the integral model is more pronounced than that by its differential counterpart. Moreover, it was revealed that by the present approach, the softening and hardening effects, respectively, originated from the nonlocal and micromorphic theories can be considered simultaneously. Originality/value: Developing a hybrid size-dependent Timoshenko beam model including micromorphic and nonlocal effects. Considering the nonlocal effect based on both Eringen’s integral and differential models proposing an FE approach to solve the bending problem, and resolving the paradox related to nanocantilever. © 2019, Emerald Publishing Limited.
Hosseini, K.,
Ansari, R.,
Pouyanmehr, R.,
Samadani f., F.,
Aligoli m., Publication Date: 2020
Analysis and Mathematical Physics (1664235X)10(4)
This paper deals with special kinds of exact solutions called kinky breather-wave and lump solutions. In this respect, kinky breather-wave solutions to the (2 + 1)-dimensional Burgers equations are acquired through the use of the extended homoclinic test technique and the Hirota bilinear method. In a special case, bright-dark lump solutions are extracted from kinky breather-wave solutions by adopting some fundamental assumptions. The dynamical behaviors of kinky breather-wave and lump solutions are analyzed by presenting a series of three dimensional and density graphs. © 2020, Springer Nature Switzerland AG.
Pakseresht m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2020
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)234(6)pp. 1212-1219
In this study, the laminate analogy technique is utilized to calculate the elastic properties of metal matrix nanocomposites filled with graphene nanoplatelets. The graphene nanoscale fillers are the most commonly used form of graphene inclusions, which are mostly considered to be disk-shaped. With the help of the Eshelby tensor, the effects of three different shapes of graphene inclusions on the mechanical response are examined. Combining layers of metal matrix composite lamina reinforced by uniformly dispersed graphene inclusions, which are aligned differently in each layer, the metal matrix nanocomposite is simulated. In each lamina, the Mori–Tanaka micromechanical method is employed to calculate the effective elastic properties. Given the fact that the inclusions are aligned, the change in the principal axis of each laminate from the global axis does not affect the Mori–Tanaka results thus resulting in an equivalent laminate composite. Then, classical laminate theory is implemented to obtain the elastic modulus of the equivalent laminate composite. The results obtained from this analytical model are compared with experimental data and a good agreement can be found between them. Two factors are observed to play a critical role in the final results; (i) the number of layers and (ii) the geometrical features of the graphene inclusions. An equivalent laminate composite with few layers acts as a composite material with anisotropic properties, and the increase of the number of layers will cause the isotropic behavior in the equivalent laminate composite. By increasing the aspect ratio, the effective elastic modulus of the nanocomposite exhibits a near-linear growth. © IMechE 2019.
Publication Date: 2020
Journal of Sandwich Structures and Materials (15307972)22(6)pp. 1812-1837
The main objective of this article is to analyze the buckling of sandwich annular plates with carbon nanotube-reinforced face sheets subjected to in-plane mechanical loading resting on the elastic foundation. It is assumed that the sandwich plate is composed of the homogeneous core layer and two functionally graded carbon nanotube-reinforced composite face sheets. The effective material properties of the functionally graded carbon nanotube-reinforced composite face sheets are estimated using the modified rule of mixture method. The higher-order shear deformation theory along with the variational differential quadrature method is employed to derive the governing equations. To this end, the quadratic form of energy functional of the structure is derived based on higher-order shear deformation theory which is directly discretized using numerical differential and integral operators. The validity of the proposed numerical approach is first shown and the effects of various parameters are then investigated on the buckling of sandwich annular plates. It was found that the elastic foundation coefficients, type of distribution of carbon nanotubes, inner-to-outer radius ratio and core-to-face sheet thickness ratio play important roles in the stability of the structure. Furthermore, the numerical results of the higher- and first-order shear deformation theories are compared. © The Author(s) 2018.
Publication Date: 2020
Composite Structures (02638223)235
In the context of variational differential quadrature finite element method (VDQFEM), the vibration and buckling of functionally graded graphene platelet reinforced composite (FG-GPLRC) plates with cutout are investigated in this study. The modified Halpin-Tsai model is used to compute the effective mechanical properties of nanocomposite plate. The mixed-type formulation of the higher-order shear deformation plate theory (HSDPT) is developed based on the Lagrange multiplier to model the mechanical behavior of FG-GPLRC plates. The variational-based differential quadrature element is developed to numerically solve the problem. Various comparative results are provided to check the validity of the proposed approach. Additionally, multiple numerical results are represented to examine the vibration and buckling behaviors of FG-GPLRC plates. © 2019 Elsevier Ltd
Publication Date: 2020
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)42(9)
This study deals with the mechanical oscillatory behavior of a C60 fullerene tunneling through open carbon nanocones (CNCs) using molecular dynamics simulations. The van der Waals (vdW) interactions between two molecules are modeled by Lennard–Jones (LJ) potential, while the interatomic interactions between carbon atoms are modeled by Tersoff–Brenner (TB) potential. Considering the two nanostructures to be either rigid or flexible, a comparative study is conducted to get an insight into the effects of initial conditions (initial separation distance and initial velocity) and geometrical parameters (length and radii of nanocone) on the oscillatory behavior of C60-open CNC oscillators. It is found out that the fullerene molecule performs a uniform oscillation inside open CNCs in the case of rigid nanostructures, whereas it performs a decaying oscillation inside nanocones with a considerable decrease in amplitude and significant increase in oscillation frequency in the case of flexible nanostructures. It is further shown that the preferred position of system corresponding to rigid nanostructures occurs inside of nanocone and close to its small end. On the contrary, this position related to flexible ones changes during the oscillation and moves toward the wide end of nanocone. This study can be used as a benchmark for the improvement of gigahertz (GHz) oscillators and related potential applications together with future developments in the field by extending to fractal calculus. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.
Ansari, R.,
Hassani r., R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2020
International Journal of Non-Linear Mechanics (00207462)126
In this paper, an efficient numerical strategy is used to study the geometrically nonlinear static bending of functionally graded graphene platelet-reinforced composite (FG-GPLRC) porous plates with arbitrary shape. Porous nanocomposite plates including cutout with various shapes can be modeled by the present approach. Four types of porous distribution scheme and four GPL dispersion patterns are selected, and the material properties are calculated based on the closed-cell Gaussian random field scheme, the Halpin–Tsai micromechanical model together with the rule of mixture. First, the variational statement of governing equations based on the virtual work principle and higher-order shear deformation theory (HSDT) is derived and presented in vector–matrix form for computational aims. Then, using the ideas of variational differential quadrature and finite element methods (VDQ and FEM), a numerical approach called as VDQ-FEM is used to address the considered problem. In VDQ-FEM, the domain of problem is first transformed into a number of finite elements. In the next step, the VDQ discretization technique is implemented within each element. Then, the assemblage procedure is performed to obtain the set of Studying effects of porosity and GPL distributions and porosity coefficient matricized governing equations which is finally solved by means of the pseudo arc-length continuation algorithm. One of the main novelties of the present work in implementing VDQ-FEM is proposing an efficient way based on mixed-formulation to guarantee the continuity condition of first-order derivatives in entire domain for the used HSDT model. A detailed parametric study is conducted to investigate the nonlinear bending of FG-GPLRC porous plates with different shapes. In the numerical results, the effects of porosity coefficient, porosity distribution pattern, GPL distribution pattern and boundary conditions on the nonlinear bending response of plates are analyzed. © 2020 Elsevier Ltd
Gholami y., Y.,
Ansari, R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2020
International Journal of Nonlinear Sciences and Numerical Simulation (15651339)21(6)pp. 523-537
A numerical approach is used herein to study the primary resonant dynamics of functionally graded (FG) cylindrical nanoscale panels taking the strain gradient effects into consideration. The basic relations of the paper are written based upon Mindlin's strain gradient theory (SGT) and three-dimensional (3D) elasticity. Since the formulation is developed using Mindlin's SGT, it is possible to reduce it to simpler size-dependent theories including modified forms of couple stress and strain gradient theories (MCST & MSGT). The governing equations is derived and directly discretized via the variational differential quadrature technique. Then, a numerical solution technique is employed to study the nonlinear resonance response of nanopanels with various edge conditions under a harmonic load. The impacts of length scale parameter, material and geometrical parameters on the frequency-response curves of nanopanels are investigated. In addition, comparisons are provided between the predictions of MSGT, MCST and the classical elasticity theory. © 2020 Walter de Gruyter GmbH, Berlin/Boston 2020.
Zabihi, A.,
Ansari, R.,
Hosseini, K.,
Samadani f., F.,
Torabi, J. Publication Date: 2020
Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences (09320784)75(4)pp. 317-331
Based on the positive and negative second-order strain gradient theories along with Kirchhoff thin plate theory and von Kármán hypothesis, the pull-in instability of rectangular nanoplate is analytically investigated in the present article. For this purpose, governing models are extracted under intermolecular, electrostatic, hydrostatic, and thermal forces. The Galerkin method is formally exerted for converting the governing equation into an ordinary differential equation. Then, the homotopy analysis method is implemented as a well-designed technique to acquire the analytical approximations for analyzing the effects of disparate parameters on the nonlinear pull-in behavior. As an outcome, the impacts of nonlinear forces on nondimensional fundamental frequency, the voltage of pull-in, and softening and hardening effects are examined comparatively. © 2020 De Gruyter. All rights reserved.
Publication Date: 2020
Engineering Fracture Mechanics (00137944)228
In this research, a numerical study is performed on the buckling and vibration of cracked functionally graded (FG) cylindrical panels under external pressure based on the phase-field formulation (PFF). For this purpose, the matrix form of energy functional is first derived on the basis of first-order shear deformation shell theory (FSDST) and phase-field model. To numerically handle the problem, the finite difference differential and integral operators are employed to directly discretize the energy functional. Then, by the use of Hamilton's principle, the discretized governing equations are obtained. The accuracy and efficiency of the developed model are demonstrated through various comparative and convergence studies. In order to analyze the vibration and buckling behavior of cracked FG cylindrical panels, two different crack patterns are considered. In addition, a wide range of numerical results is provided to study the effects of crack's shape, length and inclination angle, boundary conditions (BCs) and geometrical parameters on the buckling pressures and natural frequencies of FG cylindrical panels. © 2020 Elsevier Ltd
Publication Date: 2020
Structural Chemistry (15729001)31(1)pp. 371-384
In this study, the buckling behavior of covalently functionalized single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) with azobenzene is investigated in vacuum and aqueous environments using the classical molecular dynamics (MD) simulations. According to the results, functionalization increases the critical buckling force considerably, whereas it reduces the critical strain. It is observed that the critical buckling force of DWCNTs is not as sensitive as that of its constituent inner and outer functionalized SWCNTs. Also, it is observed that increasing the weight percentage of azobenzene results in increasing the critical buckling force of functionalized CNTs, whereas the critical strain decreases. Further, it is observed that critical buckling force of functionalized CNTs in the aqueous environment increases compared to that of functionalized CNTs in vacuum, while the critical strain does not change significantly. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
Publication Date: 2020
European Physical Journal Plus (21905444)135(2)
Presented in this article is a size-dependent analysis which is aimed to discover the surface stress effects on the large deformation characteristics of small-scaled shell structures. Consideration of surface energies in the micro/nanodimensions, and also in the cases of structures with high ratios of surface to volume like shells, significantly affects the predicted responses. To take the surface stress effects into account, it is assumed that the body is surrounded by thin surface layers at the top and bottom. The first-order shear deformation shell theory with seven parameters is adopted in the Lagrangian configuration system for the bulk part of structure. Also, the effects of surface stresses are captured based on the surface elasticity theory. Because of its unique features, IGA (isogeometric analysis) solution methodology is implemented to solve the governing equations. In this regard, the matrix–vector form of nonlinear relations, including the constitutive equations and energy functionals, is presented to directly utilize IGA for the problem. As case studies and also to show the main contribution of present investigation, i.e., studying the effects of surface energies on the mechanical behavior of geometrically nonlinear shells, the well-known benchmarks in the literature are studied in micro/nanodimensions with the consideration of surface influences. © 2020, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Hosseini, K.,
Ansari, R.,
Zabihi, A.,
Shafaroody a., ,
Mirzazadeh m., Publication Date: 2020
Optik (00304026)209
In the present paper, the (3 + 1)-dimensional resonant nonlinear Schrӧdinger (RNLS) equations arising in optical bullets with different forms of nonlinearities are studied using xxx expa and hyperbolic function techniques. As an outcome, a number of optical solitons along with their physical features to the models are formally extracted. The modulation instability (MI) analysis of the models is also presented through the use of the linear stability scheme. © 2020 Elsevier GmbH
Publication Date: 2020
Thin-Walled Structures (02638231)148
In this study, a semi-analytical technique is employed to analyze the postbuckling of functionally graded graphene platelet reinforced composite (FG-GPLRC) conical shells under compressive meridional loading. The non-uniform distribution of graphene platelets (GPLs) along the shell thickness is considered and the modified Halpin-Tsai micromechanical model is implemented to determine the overall material properties of nanocomposite shell. The mechanical behavior of FG-GPLRC conical shell is modeled on the basis of first-order shear deformation theory (FSDT) and von-Kármán's nonlinear strain-displacement relations. The governing equations are formulated in the variational framework. The semi-analytical solution based on the variational differential quadrature method (VDQM) and Fourier series is developed. To trace the postbuckling path, the pseudo arc-length continuation scheme in conjunction with the load disturbance approach was employed. In order to analyze the influences of geometrical factors, weight fractions and dispersion patterns of GPLs on the postbuckling characteristics of FG-GPLRC conical shells, various numerical results are comparatively reported. © 2020 Elsevier Ltd
Mirnezhad m., M.,
Ansari, R.,
Falahatgar s.r., S.R. Publication Date: 2020
European Physical Journal Plus (21905444)135(11)
The quantum effects of fine scaling on the properties of nanostructures are studied in this paper. After studying the dimensional effects of nanosheets on the structural energy of materials using the density functional theory and determining the effective parameters on the structural energy of materials, the mechanical properties of the nanosheets are computed. The results showed that for carbon structures with lengths less than 20 angstroms, dimensional changes have significant effects on the structural energy. Then, by obtaining the coefficients of the molecular mechanics related to the size of structure, the mechanical properties of nanotubes, such as their Young’s modulus, shear modulus and Poisson’s ratio, are calculated. It is seen that the dimensional changes cause significant changes on Young’s and shear moduli, while Poisson’s ratio is affected the most. For example, Young’s moduli of nanosheets with the zigzag boundary atoms arrangement for two widths of 7.1043 and 36.9423 angstroms are 431.28 and 352.21 GPanm, respectively, which have 23.22 and 0.63 percent difference compared to Young’s modulus of graphene which is 350 GPanm, respectively. In addition, Poisson’s ratio for the mentioned structures is equal to 0.41 and 0.22, respectively, which have a difference of 156.25 and 37.5 percent as compared to Poisson’s ratio of graphene, which is 0.16. Moreover, a comparison study is presented on the mechanical properties of finite elemental structures and their maximum lengths, and the differences caused by dimensional changes are reported. The results show that dimensional changes have a significant effect on the properties of nanostructures with certain sizes. For example, for a zigzag nanotube with the length of 7.10431 angstrom and two diameters of 2.349 and 10.96 angstroms, Young’s moduli of nanotube are 354.95 and 425.89 GPanm, respectively. The difference in the diameters results in the change of Young’s modulus for the amount of 19.99 percent. The results also reveal that in addition to the structural dimensions, the layout of structural atoms and the arrangement of boundary atoms has major influences on the mechanical properties of structure. For example, Poisson’s ratio of nanosheets with the of armchair boundary atoms arrangement the for two widths of 7.3830 and 36.9150 angstroms is equal to 0.56 and 0.30, respectively, and Poisson’s ratio for the same width and zigzag boundary atom arrangement is 0.41 and 0.22, respectively, which has the difference of 36.58 and 36.36, respectively. © 2020, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2020
Materials Chemistry and Physics (02540584)252
The influence of fiber arrangement on thermal expanding behavior of unidirectional fiber-reinforced metal matrix composites (MMCs) is evaluated using a unit cell micromechanical approach. Both regular and random fiber arrangements are considered in the MMC simulation by extending the number of sub-cells of the representative volume element (RVE). Moreover, the unit cell micromechanical model is used to investigate the role of fiber cross-section on the coefficients of thermal expansion (CTEs) of unidirectional MMCs. The validity of the model is verified by comparing the predictions and those available experimental measurements. The effective axial CTEs are not dependent on the MMC microstructure with different types of fiber arrays and cross-sections. However, the results show that besides the volume fraction, shape and the arrangement type of fibers plays a significant role in the effective transverse CTEs of MMCs. The discrepancy between the transverse predictions of the model with a random fiber arrangement and those of the model with a regular fiber arrangement increases with the rise of difference between the constituent material properties. Also, the effects of different statistical distributions of the random fiber arrangement, the number of RVE sub-cells and fiber orientation on the MMC thermal expanding response are examined. © 2020 Elsevier B.V.
Torabi, J.,
Ansari, R.,
Bazdid-vahdati m., M.,
Darvizeh m., M. Publication Date: 2020
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)44(3)pp. 631-645
By introducing the C2 continuous hexahedral element, the free vibration finite element analysis of the nanobeam and nanoplate structures is reported based on the second strain gradient (SSG) theory and three-dimensional elasticity model. The SSG elasticity presents the powerful higher-order continuum theory which can be efficiently used to capture the size-effect on the nano-objects. The finite element discretization procedure is performed within Hamilton’s principle where the quadratic matrix version of the strain and kinetic energies are derived on the basis of the three-dimensional SSG elasticity model. In the proposed C2 continuous hexahedral element, the values of the displacement field and the associated higher-order derivatives are considered as the nodal values to satisfy the continuity conditions. As the case studies, the free vibration of the nanobeams and rectangular nanoplates is investigated. Different results are outlined to show the efficiency and convergence of the present model. The influences of the involved parameters on the natural frequencies of nanobeams and plates are also investigated. It is realized that with the increase in the thickness-to-lattice parameter ratio, the difference of the results related to the SSG theory and classical theory decreases. © 2019, Shiraz University.
Publication Date: 2020
Continuum Mechanics and Thermodynamics (09351175)32(3)pp. 729-748
Nowadays, the eye-catching characteristics of boron nitride nanotubes, in particular, the capability of sensing nano-objects, have opened up new prospects to develop the bio-/nano-sensing technologies. This research deals with physically affected single-walled boron nitride nanotubes (SWBNNT) as nano-sensors for sensing attached nanoscale objects. Three different boundary conditions including simply supported at both ends, clamped-free and clamped-clamped are considered to illustrate the vibrational behaviour of SWBNNTs as nano-sensor. The Rayleigh and Timoshenko beam theories are employed to model the SWBNNT. Also, the nonlocal strain gradient model is utilized to capture the size-dependent effects. One of the major factors in the scrutiny of mass nano-sensors is pertinent to the variation in frequency shift magnitudes against the number and mass weight values of attached nanoparticles. Herein, the effects of the nonlocal and material length scale parameters, the number and location of nano-objects, the rotary inertia and mass weight magnitudes of attached nanoparticles, the aspect ratio of SWBNNT, electrical potential and different boundary conditions on the variation in frequency shift and resonant frequency are analysed. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Yousefi, S.,
Ansari, R.,
Aghdasi p., P.,
Mozvashi s.m., Publication Date: 2020
Physica E: Low-Dimensional Systems and Nanostructures (13869477)124
In the current study, the density functional theory is utilized to investigate the elastic and plastic properties of the 2×2 and 3×3 pristine and transition metal (TM) doped arsenene. Different atoms, including Co, Cr, Fe, Mn, Ni, Sc, Ti and V are selected for this purpose. It is shown that doping of the transition metal atoms would result in the reduction of Young's and bulk moduli of the pristine structure. In addition, the isotropic behavior of these nanosheets was shown by comparing the Young's moduli of both pristine and doped structures in armchair and zigzag directions. Furthermore, the plastic behavior of these structures was investigated by increasing the applied loading. It was seen that the yield strain of both 2×2 and 3×3 nanosheets was reduced under uniaxial loading. However, under the biaxial loading, the yield strain of 2×2 Co, Ni and Ti doped structures was increased while other 2×2 and 3×3 nanosheets experienced the opposite result. © 2020 Elsevier B.V.
Publication Date: 2020
Superlattices and Microstructures (10963677)139
Density functional theory is used here to study the influence of the adsorption on the elastic and plastic properties of the arsenene. The Al, Ga, Li and Se atoms are considered as the adsorption atoms. Investigation of Young's modulus of the pristine and adsorbed arsenene in longitudinal and transverse directions showed the anisotropic behavior of these structures. Moreover, the results showed that except for Li-adsorbed structure, longitudinal Young's modulus of other adsorbed structures are increased while the transverse Young's modulus is reduced while affected by adsorption. Besides, it was represented that except for Al-adsorbed structure, the bulk modulus of the arsenene reduces by other atomic adsorptions. Furthermore, the yield strain of Se-adsorbed structure under longitudinal uniaxial loading as well as the Ga- and Li-adsorbed structures under transverse uniaxial loading increases while other structures experience the opposite result. Finally, it was seen that despite Al- and Se-adsorbed structures, adsorbing Ga and Li atoms leads to increasing the yield strain of the structure under biaxial loading. © 2020 Elsevier Ltd
Publication Date: 2020
Solid State Communications (00381098)311
The influences of four different types of atoms (H, F, Cl and Br) on the elastic and plastic properties of antimonene nanosheet are investigated in this paper using the density functional theory. For this purpose, the SIESTA software is used. It is concluded that Young's modulus of the antimonene nanosheet under the uniaxial strain and bulk modulus under the biaxial strain significantly decreases by the adsorption. Moreover, it is shown that due to the negligible difference in the Young's moduli of these structures they have isotropic behavior. Furthermore, the influence of the adsorption on the plastic properties of the antimonene nanosheet is studied by extending the loading until the indication of the plastic behavior. It is shown that the yield strain of the antimonene nanosheet under the uniaxial strain decreases by the adsorption. However, interestingly, it is observed that the adsorption of named atoms increase the plastic strain under the biaxial loading. © 2020
Publication Date: 2020
Scientia Iranica (23453605)27(1 B)pp. 252-261
In this paper, the buckling behavior of rods made of carbon ber/carbon nanotube-reinforced polyimide (CF/CNT-RP) under the action of axial load is investigated based on a multi-scale nite element method. A dual-step procedure is rst adopted to couple the micro- and nano-scale effects in order to obtain the equivalent elastic properties of CF/CNT-RP for various volume fractions of CF and CNT. The interphase effect between CNTs and the polymer matrix is taken into consideration. Further, the dispersion of CF/CNT into the polymer matrix is assumed to be random. Then, rods with square and circular cross-sections are considered whose stability characteristics are analyzed. The nite element modeling is performed using two models including a 3D brick model and a 2D beam model. Selected numerical results are given to study the effects of volume fraction of CNT/CF, interphase, and geometrical properties on the axial buckling response of the multiscale composite rods. © 2020 Sharif University of Technology. All rights reserved.
Publication Date: 2020
Mechanics of Advanced Materials and Structures (15210596)27(10)pp. 800-806
Based on the Lord–Shulman (L-S) theory, the thermally nonlinear coupled thermo-viscoelasticity of a layer is analyzed using a numerical approach. Using the Kelvin-Voigt theory of viscoelasticity in conjunction with the L-S theory, the coupled governing equations are first derived in variational form. Then, the variational differential quadrature (VDQ) method is applied to solve the problem numerically. Parametric studies are presented in order to reveal the effects of viscoelastic parameter, intensity of heat flux and relaxation time on the propagation of displacement, temperature and stress waves. Furthermore, the influence of considering nonlinearity in the energy equation is analyzed. © 2019, © 2019 Taylor & Francis Group, LLC.
Publication Date: 2020
Structural Chemistry (15729001)31(3)pp. 909-915
In this study, the buckling behavior of functionalized single- and double-walled boron-nitride nanotubes (SWBNNTs and DWBNNTs) with a monomer of chitosan using molecular dynamics (MD) simulations is explored. The effect of chemical adsorption of chitosan molecule on the critical buckling force and strain is investigated. The results show that the critical buckling force considerably increases as the chitosan is attached to the side wall of boron-nitride nanotube which is more considerable for larger radii of nanotube. Moreover, increasing the number of walls reduces the sensitivity of boron-nitride nanotube to the functionalization compared with similar SWBNNTs. Further, it is shown that critical buckling of functionalized BNNTs increases by rising the weight percentage of chitosan. Considering the critical strain, it is observed that functionalization reduces the critical strain of functionalized BNNTs which is more pronounced in the case of SWBNNTs with bigger radii. Moreover, the buckling mode shape of functionalized BNNTs is presented. © 2019, Springer Science+Business Media, LLC, part of Springer Nature.
Publication Date: 2020
International Journal of Engineering Science (00207225)157
This study provides a multi-step analytical model to investigate the synergistic effects of carbon black nanoparticles and micro-scale carbon fibers on the electrical conductivity of the polymer matrix multi-scale nanocomposites. In the first step, the homogenized electrical conductivity of the nanoparticle-polymer nanocomposites containing the nanoparticle agglomeration is calculated using the percolation like electrical network model. The second step presents the details of Mori-Tanaka micromechanical model to predict the effective electrical conductivity of the multi-scale nanocomposites composed of the micro-fibers embedded in the nanoparticle-enriched polymer as the matrix phase. The influences of different parameters such as the nanoparticle agglomerate diameter to tunneling distance ratio, fiber aspect ratio, intrinsic electrical conductivity, volume fraction, and polymer potential barrier height on the electrical resistivity of the multi-scale nanocomposites are investigated. Based on the comparative studies, the model predictions are in good agreement with the available experimental results. It is found that the electrical resistivity decreases with the addition of multi-scale fillers. The results also suggest that the tunneling distance between the agglomerates plays a dominant role in the electrical conductivity of the multi-scale nanocomposites. © 2020
Publication Date: 2020
European Physical Journal D (14346060)74(12)
Abstract: In the present work, the thermal conductivity of three-dimensional metallic carbon nanostructure (T6) is investigated by employing the molecular dynamics (MD) simulations. In doing so, two different models of T6 nanostructure, i.e. beam- and plate-like, are chosen to study the effects of size and geometry on the thermal conductivity of the system. It is observed that length increase in beam-like T6 leads to a rise in the thermal conductivity. Also, higher cross-section area in equal length causes lower thermal conductivity. In the case of plate-like T6, the width increases of the structure results in a sharp reduction of the thermal conductivity. Furthermore, increasing the height of the structure in the same length and width causes a decrease in the thermal conductivity. Moreover, a beam-like T6 model is doped with different weight percentages of boron and nitrogen to study the effects of doping on the thermal conductivity. It is demonstrated that doping boron and nitrogen atoms in T6 nanostructure decreases the thermal conductivity drastically. Graphical abstract: [Figure not available: see fulltext.] © 2020, EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature.
Ansari, R.,
Hassani r., R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2020
Aerospace Science and Technology (12709638)106
Using the ideas of variational differential quadrature and finite element methods (VDQ and FEM), a novel numerical approach is developed in this paper to investigate the postbuckling behavior of plates with arbitrary shape under the action of thermal load within the framework of higher-order shear deformation theory (HSDT). It is considered that the plates are made of functionally graded carbon nanotube reinforced composite (FG-CNTRC). By the proposed approach, the thermal postbuckling behavior of plates with arbitrary-shaped cutout can be modeled. The rule of mixture is utilized to obtain the effective material properties of nanocomposite which are considered to be temperature-dependent. To implement the proposed method that can be named as VDQFEM, the variational temperature-dependent formulation of problem is first developed. This formulation is presented using novel vector-matrix relations with the aim of utilizing in programming in an efficient way. In the context of VDQFEM, the space domain of plate is first transformed into a number of finite elements. In the next step, the VDQ discretization technique is implemented within each element. Then, the assemblage procedure is performed to derive the set of matricized governing equations which is finally solved by means of the pseudo arc-length continuation algorithm. One of the main novelties of present approach is proposing an efficient way based on mixed-formulation to accommodate the continuity of first-order derivatives on the common boundaries of elements for the used higher-order shear deformable plate model. Quadrilateral plate, skew plate, annular plate, square plate with rectangular hole and rectangular plate with circular hole under different boundary conditions including CCCC, SSSS, CSCS and CCSS (S: simply-supported, C: clamped) are considered in the numerical example. First, validation studies are presented in terms of critical buckling temperature of CNTRC rectangular plates with various CNT distribution patterns. It is shown that the proposed method has the advantages of standard VDQ technique including fast convergence rate, being locking-free and simple implementation. Moreover, it is capable of considering polygon and concave domains. Also, the effects of geometrical properties, volume fraction and distribution pattern of CNTs and temperature-dependency of material properties on the thermal postbuckling of plates are studied. © 2020 Elsevier Masson SAS
Publication Date: 2020
Thin-Walled Structures (02638231)150
In this paper, a size-dependent three-dimensional (3D) nonlinear weak formulation is provided to examine the nonlinear primary resonance problem for functionally graded rectangular small-scale plates. The small-scale factors are taken into formulation by choosing the Mindlin's strain gradeint theory (SGT). According to the variational differential quadrature (VDQ) method, first, the displacement field, nonlinear strain-displacement and constitutive relations as well as the potential and kinetic energies are expressed as the vector and matrix forms. Then, by applying the discretized form of differential operators obtained via the generalized differential quadrature (GDQ) method, the discretized form of aforementioned relations is achieved. Finally, Hamilton's principle is employed to access the weak form of 3D nonlinear governing equations of thick rectangular small-scale plates. The achieved formulation is solved via a multi-step numerical technique to address the size-dependent nonlinear primary resonance of considered system under the harmonic lateral force. In addition to reducing the run time, computational effort and CPU usage, the feature of proposed weak form formulation is that one can employ it in other solution approaches such as finite element method. Also, the use of this formulation provides the possibility of recovering models on the basis of other types of size-dependent theories such as modified strain gradient and modified couple stress theories (MSGT and MCST). In the numerical results, the effects of boundary conditions, small-scale parameter, material index and geometry are examined. © 2020 Elsevier Ltd
Publication Date: 2019
Engineering Structures (18737323)181pp. 653-669
The main objective of this paper is to analyze the free vibration of arbitrary shaped thick functionally graded carbon nanotube-reinforced composite (FG-CNTRC) plates based on the higher-order shear deformation theory (HSDT) using a variational differential quadrature approach. By means of the generalized differential quadrature (GDQ) numerical operators and Hamilton's principle, the discretized equations of motion are obtained. In order to use the GDQ differential and integral operators appropriately, the coordinate transformation is considered through the conventional finite element approach for transforming the irregular domain of the plate into the regular computational one. Employing a unified numerical approach to analyze different shapes of thick FG-CNTRC plates based on HSDT is the main novel aspect of the present study. To imply the accuracy of the present model, a wide range of comparison studies are presented. The results indicate the efficiency of the developed numerical methodology to study the vibration of arbitrary shaped thick FG-CNTRC plates. Several results are also given to investigate the impacts of geometrical parameters and material properties on the vibrational behavior of FG-CNTRC plates. © 2018 Elsevier Ltd
Publication Date: 2019
Bulletin of Materials Science (02504707)42(4)
Fabrication of new types of nanoscale oscillators with enhanced operating frequency has become the focal centre of interest. The aim of this paper is to explore the mechanical oscillatory behaviour of chloride ion tunnelling through carbon nanotubes (CNTs) decorated with identical functional groups at both ends. To this end, our previously proposed analytical expression for total potential energy between an ion and a functionalized CNT is used to derive a new semi-analytical expression for the accurate evaluation of oscillation frequency. With respect to the proposed frequency formula obtained from the conservation of mechanical energy principle, a comprehensive study is conducted to gain an insight into the effects of different parameters such as, sign and magnitude of functional group charge, nanotube length and initial conditions on the operating frequency of chloride ion-electrically charged CNT oscillators. It is revealed that the presence of functional groups, especially ones with the opposite charges to the chloride ion, leads to enhancement of the maximum achievable frequency. It is further observed that optimal frequency is attained when the ion oscillates near the ends of a positively charged nanotube. © 2019, Indian Academy of Sciences.
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Jamali, J.,
Ansari, R. Publication Date: 2019
Composites Part B: Engineering (13598368)175
In this work, a physics-based hierarchical approach is established to evaluate thermal conducting behavior of carbon fiber (CF)-carbon nanotube (CNT)-reinforced polymer hybrid nanocomposites. For this purpose, the Maxwell-Garnett type effective medium (EM) method is appropriately coupled with a unit cell-based micromechanical model. The predictions of the thermal conductivities of fiber-CNT-reinforced polymer hybrid nanocomposites are verified with the available experimental data. Very good agreement is found between the model predictions and experiments. For a more realistic prediction, considering (i) the CNT random orientation, (ii) the CNT random distribution within the polymer, (iii) the CNT non-straight shape and (iv) the CNT/polymer interfacial thermal resistance is essential in the micromechanical analysis. The influences of volume fraction and aspect ratio of CF, volume fraction and dispersion type of CNTs on the hybrid nanocomposite thermal conductivities along the longitudinal and transverse directions are examined. It is found that the CNT dispersion type within the hybrid nanocomposites can significantly affect the overall heat conducting behavior of such new systems. Agglomeration of CNTs leads to a reduction in the thermal conductivity of hybrid nanocomposites along the transverse direction. © 2019 Elsevier Ltd
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)233(19-20)pp. 7041-7061
Presented herein is the elastic/plastic axisymmetric buckling analysis of circular and annular plates resting on elastic foundation under radial loading based on a variational numerical method named as variational differential quadrature. To accomplish this aim, a first-order shear deformable plate model is developed in the context of incremental theory of plasticity (IT) (with the Prandtl-Reuss constitutive equations) and the deformation theory of plasticity (DT) (with the Hencky constitutive equations). It is considered that the material of plates exhibits strain hardening characterized by the Ramberg-Osgood relation. Also, the Winkler and Pasternak models are employed in order to formulate the elastic foundation. To implement the variational differential quadrature method, the matrix formulations of strain rates and constitutive relations are first derived. Then, based upon Hamilton's principle and using the variational differential quadrature derivative and integral operators, the discretized energy functional of the problem is directly obtained. Selected numerical results are presented to study the effects of various parameters including thickness-to-radius ratio, elastic modulus-to-nominal yield stress ratio, power of the Ramberg-Osgood relation and parameters of elastic foundation on the elastic/plastic buckling of circular and annular plates subject to different boundary conditions. Moreover, several comparisons are provided between the results of two plasticity theories, i.e. IT and DT. The effect of transverse shear deformation is also highlighted. © IMechE 2019.
Publication Date: 2019
International Journal for Numerical Methods in Engineering (00295981)118(6)pp. 345-370
A numerical multifield methodology is developed to address the large deformation problems of hyperelastic solids based on the 2D nonlinear elasticity in the compressible and nearly incompressible regimes. The governing equations are derived using the Hu-Washizu principle, considering displacement, displacement gradient, and the first Piola-Kirchhoff stress tensor as independent unknowns. In the formulation, the tensor form of equations is replaced by a novel matrix-vector format for computational purposes. In the solution strategy, based on the variational differential quadrature (VDQ) technique and a transformation procedure, a new numerical approach is proposed by which the discretized governing equations are directly obtained through introducing derivative and integral matrix operators. The present method can be regarded as a viable alternative to mixed finite element methods because it is locking free and does not involve complexities related to considering several DOFs for each element in the finite element exterior calculus. Simple implementation is another advantage of this VDQ-based approach. Some well-known examples are solved to demonstrate the reliability and effectiveness of the approach. The results reveal that it has good performance in the large deformation problems of hyperelastic solids in compressible and nearly incompressible regimes. © 2018 John Wiley & Sons, Ltd.
Zabihi, A.,
Ansari, R.,
Torabi, J.,
Samadani f., F.,
Hosseini, K. Publication Date: 2019
Materials Research Express (20531591)6(9)
This paper is interested in the development of an analytical model for describing the dynamic pull-in instability of circular nanoplates based on the nonlocal strain gradient theory (NSGT). Herein, Kirchhoff's thin plate theory is accommodated with the NSGT theory; hence the governing equation of motion is procured according to Hamilton's principle. For this goal, the Galerkin method (GM) is used to reduce the governing equation in spatial domain considering clamped boundary condition (BC), and then it is discretized via homotopy analysis method (HAM). Finally, the effects of nonlocal and length scale parameters on the non-dimensional fundamental frequency against electrostatic, hydrostatic, and thermal forces are relatively illuminated. © 2019 IOP Publishing Ltd.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Nankali, M. Publication Date: 2019
Composites Part A: Applied Science and Manufacturing (1359835X)126
Electrical conductivity (EC) and percolation threshold of chopped carbon fiber (CF)-carbon nanotube (CNT)-reinforced epoxy multiscale nanocomposites considering tunneling resistivity are studied based on micromechanics. The percolation theory is applied to determine transition from low to high conductivity. Influences of CNT/polymer interphase and CNT waviness are considered to evaluate percolation threshold of CNT-enriched epoxy nanocomposite prior to CF percolation threshold. Multiscale fillers provide benefit of enhanced EC with different percolation thresholds for different fillers. These characteristics of multiscale filler with high aspect ratio of filler facilitate formation of conductive network even at low multiscale filler volume fraction. Variation of EC as a function of tunneling distance, CNT and CF aspect ratios and intrinsic EC for different CNT volume fractions is investigated. The nanocomposite exhibits a percolation threshold at less than 0.2 vol% of CNTs. The percolation threshold is predicted to be reduced when higher volume fractions of CFs are considered. © 2019 Elsevier Ltd
Publication Date: 2019
Computer Methods in Applied Mechanics and Engineering (00457825)344pp. 1124-1143
In the size-dependent continuum theories such as the strain gradient theory, the higher-order derivatives of displacement field appear in the energy functional of the structure which leads to the employment of C1 continuous shape functions within the finite element discretization procedure. Although a wide range of one- and two-dimensional small-scale finite elements were developed to analyze the structural behavior of micro- and nano-structures, a few studies can be found on the development of size-dependent three-dimensional (3D) finite elements. Hence, the main purpose of this work is the introduction of a four-node tetrahedral element to analyze the size-dependent mechanical behavior of micro- and nano-structures based on the three-dimensional strain gradient theory (SGT). In the proposed element, the values of displacement components and their related first-order derivatives are considered as degrees of freedom at each node. To present the governing equations, the matrix form of kinetic and strain energies and the work of external forces are derived based on the 3D elasticity theory and strain gradient model. To show the efficiency of the proposed model, the size-dependent linear vibration analysis of circular and elliptical micro- and nano-plates is presented. Various numerical results including comparative and convergence studies are reported to check the accuracy and performance of the introduced finite element. © 2018 Elsevier B.V.
Publication Date: 2019
Computational Methods For Differential Equations (23453982)7(3)pp. 359-369
During the past years, a wide range of distinct approaches has been exerted to solve the nonlinear fractional differential equations (NLFDEs). In this paper, the invariant subspace method (ISM) in conjunction with the fractional Sumudu’s transform (FST) in the conformable context is formally adopted to deal with a nonlinear conformable time-fractional dispersive equation of the fifth-order. As an outcome, a new exact solution of the model is procured, corroborating the exceptional performance of the hybrid scheme. © 2019 University of Tabriz. All Rights Reserved.
Publication Date: 2019
International Journal for Multiscale Computational Engineering (15431649)17(1)pp. 45-63
This article reports the geometrically nonlinear bending response of polymeric composite annular plates reinforced with graphene platelets (GPLs) under transverse uniform and biharmonic loadings. The considered plates are embedded on a Winkler-Pasternak elastic foundation. By considering a random orientation and a uniform dispersion for the GPL nanofillers, four types of distribution patterns are assumed for the GPLs along the thickness of the plate. The modified Halpin-Tsai (MHT) technique and the rule of mixture are adopted to obtain the effective material properties of GPL-reinforced polymeric nanocomposites (GPL-RPNCs). The discretized governing equations including the geometric nonlinearity are expressed in their weak form using the principle of virtual work, variational differential quadrature (VDQ) method, and Reddy’s plate theory. For the demonstration of the symmetric and asymmetric bending behaviors of GPL-RPNC annular plates and influence of different parameters, the pseudo-arc length algorithm is coupled with the modified Newton-Raphson approach to plot the maximum deflection of considered plate versus the amplitude of applied loading. © 2019 by Begell House, Inc.
Oskouie, M.F.,
Norouzzadeh, A.,
Ansari, R.,
Rouhi h., H. Publication Date: 2019
Applied Mathematics and Mechanics (English Edition) (02534827)40(6)pp. 767-782
A novel size-dependent model is developed herein to study the bending behavior of beam-type micro/nano-structures considering combined effects of nonlocality and micro-rotational degrees of freedom. To accomplish this aim, the micropolar theory is combined with the nonlocal elasticity. To consider the nonlocality, both integral (original) and differential formulations of Eringen's nonlocal theory are considered. The beams are considered to be Timoshenko-type, and the governing equations are derived in the variational form through Hamilton's principle. The relations are written in an appropriate matrix-vector representation that can be readily utilized in numerical approaches. A finite element (FE) approach is also proposed for the solution procedure. Parametric studies are conducted to show the simultaneous nonlocal and micropolar effects on the bending response of small-scale beams under different boundary conditions. © 2019, Shanghai University and Springer-Verlag GmbH Germany, part of Springer Nature.
Ajori, S.,
Parsapour h., H.,
Ansari, R.,
Ameri a., A. Publication Date: 2019
Materials Research Express (20531591)6(9)
The reinforcement of various materials by nanofillers as nanocomposites has recently received the attention of many researchers. In the present research, molecular dynamics simulations are used to investigate the influence of nanowire (NW)/carbon nanotube (CNT) reinforcement on the buckling behavior of metallic glass matrix nanocomposites (MGMNCs). The buckling characteristics of nanocomposites made by adding Cu NWs, CNTs and Cu NW-encapsulated CNTs to metallic glass matrices are studied. The results demonstrate that MG alloys comprising just two elements (Cu and Zr) with higher Cu percentage have higher mechanical stability. Also, it is observed that adding NW leads to a negative effect on the buckling behavior, while adding CNT and NW-encapsulated CNT considerably increases the buckling force and strain of the metallic glass models. Moreover, it is found that the filled CNT is the most effective nanofiller for amending the buckling behavior of metallic glasses. Furthermore, as the size of nanofillers gets larger, the critical force increases and the critical strain decreases. © 2019 IOP Publishing Ltd.
Publication Date: 2019
Materials Research Express (20531591)6(10)
Carbon nanotubes (CNTs) possess unique structural properties which can be modified by several methods such as partial and full atom substitution. In this method also known as doping, novel hybrid tubular structures with desired and new characteristics can be synthesized. To this end, Boron (B) and Nitrogen (N) are selected as dopants and then by using molecular dynamics (MD) simulations the structural behavior of the new heteronanotubes are investigated. Moreover, the buckling behavior of these novel nanotube alongside the pure CNT and BN nanotube (BNNT) are studied. Apparently, the critical forces of the newly formed structures are computed between those of pure CNT and BNNT. Further, a combination of the doped structures and pure ones are used to simulate hybrid double-wall nanotubes and then their buckling response under axial compressive load is studied. Attained results demonstrated that double-walled hybrid structures possess mechanical stabilities lower and higher than pure double-walled CNT and BNNT, respectively. © 2019 IOP Publishing Ltd.
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Darvizeh a., A. Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)233(2)pp. 169-179
In this work, a unit cell-based micromechanical model with a proper representative volume element is proposed to evaluate the coefficients of thermal expansion of carbon nanotube-reinforced polyimide nanocomposites. The model takes an interphase between carbon nanotube and polyimide matrix into account which characterizes the non-bonded van der Waals interaction between two phases. The effects of some important parameters on the coefficients of thermal expansion such as thickness and adhesion exponent of interphase, temperature deviation as well as volume fraction, diameter and waviness of carbon nanotubes are investigated in detail. It is found that the interphase plays a critical role in determining the coefficients of thermal expansion and should be incorporated into the modeling of nanocomposite. According to the obtained results, there exists a specific value for carbon nanotube diameter beyond which further increasing in carbon nanotube diameter does not affect the coefficients of thermal expansion of nanocomposite. Also, the results reveal that the carbon nanotube waviness has a significant influence on the coefficients of thermal expansion of the nanocomposite. The results of the present model are compared with those of finite element method and a very good agreement is pointed out. © IMechE 2016.
Publication Date: 2019
Biomedical Physics and Engineering Express (20571976)5(4)
Currently, cardiovascular diseases related to atherosclerosis are among the universal primary reasons for mortality. Artery stenosis is the narrowing of the artery, due to the formation of atheromatous plaque in the arterial tunica intima, a region of the blood vessel located between the endothelium and the tunica media. In the present paper, the blood flow is modeled in a stenosed artery, and the dynamic behavior of the atherosclerosis phenomenon is studied using computational analyses. To accomplish this aim, 3D finite element method (FEM) for modeling structural sections (including plaque and artery) and computational fluid dynamics (CFD) for modeling fluid part (blood flow) are coupled through a fluid-structure interaction (FSI). It is shown that the results of present FSI analysis are in good agreement with the available data in the literature. The influences of plaque geometry, in particular, plaque angle and percentage of stenosis, are investigated. Also, the effects of Newtonian and non-Newtonian properties of the blood flow and different hyperelastic artery models, including Ogden and Polynomial, are analyzed. The simulations show that with an increasing angle of the plaque, the stress of the artery increases, while the velocity of the blood flow decreases. © 2019 IOP Publishing Ltd.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)233(9)pp. 3259-3276
There is a growing interest in the development of nanomechanical oscillators operating in the gigahertz range and beyond. This paper introduces a novel nano-oscillator based on a chloride ion inside an open carbon nanocone decorated by functional groups at both small and wide ends. Assuming that the carbon atoms and the electric charges of functional groups are evenly distributed over the surface and the two ends of nanocone, respectively, a continuum-based model is presented through which potential energy and interaction force are evaluated analytically. The van der Waals interactions between ion and nanocone are modeled by the 6–12 Lennard–Jones potential, while the electrostatic interactions between ion and two functional groups are modeled by the Coulomb potential. With respect to the proposed formulations, potential energy and interaction force distribution are presented by varying sign and magnitude of functional groups charge and geometrical parameters (size of small and wide ends of nanocone and its vertex angle). Using the fourth-order Runge–Kutta numerical integration scheme, the equation of motion is also solved to arrive at the time histories of separation distance and velocity of ion. An extensive study is performed to investigate the effects of sign and magnitude of functional groups charge, geometrical parameters, and initial conditions (initial separation distance and initial velocity) on the oscillatory behavior of ion-electrically charged open carbon nanocone oscillator. Numerical results demonstrate that the oscillation frequency of chloride ion inside an uncharged nanocone is respectively lower and higher than those generated inside a nanocone whose small end is decorated by positively and negatively charged functional groups. It is further shown that oscillation frequency is highly affected by the sign of electric charges distributed at the small end of nanocone. © IMechE 2018.
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R. Publication Date: 2019
Composites Part B: Engineering (13598368)168pp. 274-281
The present work is aimed at presenting a multi-stage hierarchical micromechanical model to investigate creep response of polymer nanocomposites containing randomly dispersed carbon nanotubes (CNTs). Two frequently real situations-encountered fundamental aspects affecting the polymer nanocomposite mechanical behavior including the CNT/polymer interphase region and CNT agglomeration are taken into account. It is assumed that the CNT to be a transversely isotropic material and the polymer matrix obeys a viscoelastic constitutive law. The multi-stage procedure homogenizes the nanocomposite by exploiting a unit cell-based micromechanical model coupled with Eshelby method. Generally, an excellent agreement is found between the results of the current model and available experiment. The outcomes clearly prove that for a more realistic prediction in the case of creep performance of CNT-polymer nanocomposites, considering the (i) random dispersion and (ii) transversely isotropic behavior of CNTs as well as (iii) viscoelastic interphase region is essential. Moreover, when CNTs are not well-dispersed into the polymer nanocomposites, the three significant factors together with the CNTs agglomerated state must be precisely incorporated in the analysis to achieve a more accurate estimation of the creep response. It is shown that the CNT agglomeration dramatically influences and degrades the creep resistance of the CNT-polymer nanocomposites. Also, the effects of CNT volume fraction and interphase characteristics on the nanocomposites creep behavior are extensively examined. © 2018 Elsevier Ltd
Pouyanmehr, R.,
Hosseini, K.,
Ansari, R.,
Alavi s.h., Publication Date: 2019
International Journal Of Applied And Computational Mathematics (23495103)5(6)
The purpose of the present work is to confirm the existence of different wave structures for the (2 + 1)-dimensional generalized Bogoyavlensky–Konopelchenko (2D-gBK) equation describing nonlinear waves in applied sciences. In this respect, based on the Hirota’s bilinear form and various test schemes, a variety of exact solutions, including breather-wave, rational, double soliton, mixed-type, cross-kink, and interaction solutions to the 2D-gBK equation are formally extracted. The dynamical structures of a series of selected solutions are investigated by portraying several 3-dimensional and density plots. © 2019, Springer Nature India Private Limited.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)233(9)pp. 1843-1853
The objective of this work is to investigate the coefficient of thermal expansion of carbon nanotube reinforced aluminum matrix nanocomposites in which aluminum carbide (Al4C3) interphase formed due to chemical interaction between the carbon nanotube and aluminum matrix is included. To this end, the micromechanical finite element method along with a representative volume element, which incorporates, carbon nanotube, interphase, and aluminum matrix is employed. The emphasis is mainly placed on the effect of Al4C3 interphase on the coefficient of thermal expansion of aluminum nanocomposites with random microstructures. The effects of interphase thickness, carbon nanotube diameter, and volume fraction on the thermomechanical response of aluminum nanocomposite are discussed. The results reveal that the effect of Al4C3 interphase on the coefficient of thermal expansion of the aluminum nanocomposites becomes more significant with (i) increasing the coefficient of thermal expansion volume fraction, (ii) decreasing the coefficient of thermal expansion diameter, and (iii) increasing the interphase thickness. It is clearly observed that the coefficient of thermal expansion varies nonlinearly with the carbon nanotube diameter; however, it decreases linearly as the carbon nanotube volume fraction increases. Furthermore, the axial and transverse coefficient of thermal expansions of aligned continuous and discontinuous carbon nanotube-reinforced aluminum nanocomposites with Al4C3 interphase are predicted. Also, the presented finite element method results are compared with the available experiment in the literature, rule of mixture, and concentric cylinder model results. © IMechE 2018.
Publication Date: 2019
Polymer Composites (02728397)40(6)pp. 2523-2533
In this study, the idea of using fiber metal laminate (FML) for cryogenic applications has been proposed. Considering the cryogenic durability of 5,000 series of aluminum alloys, a novel FML based on the aluminum alloy 5083-H111 was successfully developed. The changes in the mechanical properties of the mentioned FMLs, as well as traditional plain weave E-glass/epoxy (GE) composites after exposure to cryogenic aging in LN2 at a temperature of −196°C for 336 h was evaluated. In addition, an effort was made on improvement of the cryogenic durability of both laminate types by adding montmorillonite nanoclay particles into the polymeric matrix. The principal findings were the maximum flexural load, flexural stiffness, and impact strength of GE composites were negatively affected by cryogenic aging and decreased by 26.82, 5.13, and 14.06%, respectively, while these values for the aged FMLs were only 18.65, 4.54, and 9.56%, respectively. It was also found that the nanoclay could effectively improve the mechanical properties of both laminate types in pristine and aged conditions. This study can provide a preliminary guideline for the initial design of the cryogenic tanks based on FMLs. POLYM. COMPOS., 40:2523–2533, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics Engineers
Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(23)pp. 1935-1950
A unit cell-based micromechanical model is presented to investigate the effect of PZT-7A piezoelectric interphase on the effective magneto-electro-elastic properties of CoFe2O4 piezomagnetic matrix composites reinforced with piezoelectric fibers. The carbon fiber is coated with the PZT-7A piezoelectric material. The model is used to determine effective stresses, electric and magnetic field properties of the smart composite. By applying loads over the RVE of unit cell model in electric and magnetic fields, the in-plane strains, corresponding piezoelectric constants and corresponding piezomagnetic constants are obtained. The influences of interphase thickness on effective magneto-electro-elastic properties are investigated at different piezoelectric fiber volume fractions. © 2018, © 2018 Taylor & Francis Group, LLC.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)233(8)pp. 1542-1554
One of the issues with the widespread use of polymer matrix composites in marine applications is their high susceptibility to environmental degradation, particularly hygrothermal conditions. Therefore, the present research intends to contribute to the better protection of the marine polymer matrix composites through the introduction of a newly developed fiber metal laminate for marine applications. This type of fiber metal laminate consists of a marine aluminum alloy of 5083 alternating with glass fiber reinforced epoxy composite layers. In order to evaluate the characterization of the environmental durability of this novel material, the specimens made of fiber metal laminates as well as commercial woven glass–epoxy composites were exposed to hygrothermal aging and hygrothermal cycling in boiling salt water. Then, to study the structural degradation caused by exposure to salt water, the mechanical properties of fiber metal laminate and woven glass–epoxy specimens under three-point bending and impact loading were evaluated. Results show that exposure to the saline environment generally decreased the flexural strength of woven glass–epoxy and fiber metal laminate specimens, whereas a smaller deterioration in flexural stiffness of both laminate types was found. Moreover, it was observed that the hygrothermal conditioning in salt water did not affect significantly the impact properties of both the fiber metal laminate and woven glass–epoxy specimens as compared to the flexural properties. © IMechE 2018.
Mahmoodi m.j., M.J.,
Hassanzadeh-aghdam, M.K.,
Ansari, R. Publication Date: 2019
Journal of Intelligent Material Systems and Structures (15308138)30(1)pp. 32-44
In this study, a unit cell–based micromechanical approach is proposed to analyze the coefficient of thermal expansion of shape memory polymer nanocomposites containing SiO 2 nanoparticles. The interphase region created due to the interaction between the SiO 2 nanoparticles and shape memory polymer is modeled as the third phase in the nanocomposite representative volume element. The influences of the temperature, volume fraction, and diameter of the SiO 2 nanoparticles on the thermal expansion behavior of shape memory polymer nanocomposite are explored. It is observed that the coefficient of thermal expansion of shape memory polymer nanocomposite decreases with the increase in the volume fraction up to 12%. Also, the results reveal that with the increase in temperature, the shape memory polymer nanocomposite coefficient of thermal expansion linearly increases. The role of interphase region on the thermal expansion response of the shape memory polymer nanocomposite is found to be very important. In the presence of interphase, the reduction in nanoparticle diameter leads to lower coefficient of thermal expansion for shape memory polymer nanocomposite, while the variation of nanoparticles diameter does not affect the coefficient of thermal expansion in the absence of interphase. Based on the simulation results, the shape memory polymer nanocomposite coefficient of thermal expansion decreases as the interphase thickness increases. In addition, the contribution of interphase coefficient of thermal expansion to the shape memory polymer nanocomposite coefficient of thermal expansion is more significant than that of interphase elastic modulus. © The Author(s) 2018.
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R.,
Mehdipour, H. Publication Date: 2019
Mechanics of Materials (01676636)131pp. 121-135
Feasibility of using carbon nanotubes (CNTs) for improving the thermo-mechanical properties of titanium (Ti) matrix composites (TMCs) is studied by means of a multi-stage micromechanical approach. The hybrid Ti matrix nanocomposite (HTMNC) system consists of Ti-6Al-4 V alloy reinforced by unidirectional SiC fibers and randomly dispersed CNTs. An efficient micromechanics procedure is proposed to investigate the CNT aggregation encountered frequently in real engineering situations. The effects of the SiC fiber volume fraction, off-axis angle, aspect ratio and arrangement type as well as the CNT volume fraction, waviness, aspect ratio and non-uniform dispersion are examined on the HTMNC effective properties. Owing to their high Young's modulus and low coefficient of thermal expansion (CTE), the CNT use into the conventional TMCs is revealed to be effective at improving the resulting HTMNC thermo-mechanical properties. Also, the HTMNC elastic moduli and CTEs tend to further improvement by the use of straight CNTs. However, it is demonstrated that the CNT aggregation has a deterioration effect on the effective properties. Generally, the model predictions agree well with the experimental measurements. The results could be actually useful to guide design of general metal matrix composites containing CNTs with superior thermo-mechanical properties. © 2019
Publication Date: 2019
International Journal Of Nanoscience And Nanotechnology (24235911)15(1)pp. 11-19
This paper explores the mechanical properties and fracture analysis of C2N-h2D single-layer sheets using classical molecular dynamics (MD) simulations. Simulations are carried out based on the Tersoff potential energy function within Nose-Hoover thermostat algorithm at the constant room temperature in a canonical ensemble. The influences of boron (B) doping on the mechanical properties, i.e. Young's and bulk moduli and ultimate strength and strain of C2N-h2D single-layer sheets are studied and the effects of size and doping percentage on the aforementioned properties are explored. The results demonstrate lower strength and stiffness of C2N-h2D single-layer sheets compared to graphene. It is also demonstrated that unlike the strength of C2N-h2D single-layer sheet, the stiffness of C2N-h2D single-layer sheet is larger than that of silicene nanosheet. In addition, it is observed that doping of B atoms on C2N-h2D single-layer sheets intensely reduces the mechanical properties, whereas this reduction increases by rising the percentage of B-doping. Furthermore, the fracture process of C2N-h2D and B-doped C2N-h2D single-layer sheets is illustrated. © 2019 International Journal of Nanoscience and Nanotechnology.
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Darvizeh a., A. Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)233(4)pp. 676-686
The elastoplastic behavior of aluminum (Al) nanocomposites reinforced with aligned carbon nanotubes (CNTs) is characterized using a unit cell micromechanical model. The interphase zone caused by the chemical reaction between CNT and Al matrix is included in the analysis. To attain the elastoplastic stress–strain curve of the nanocomposites, the successive approximation method together with the von Mises yield criterion is employed. The effects of several important factors including the volume fraction and diameter of CNT, material properties, and size of interphase on the elastoplastic stress–strain curve of the nanocomposites during uniaxial tension are studied. The results indicate that the interphase characteristics significantly affect the elastoplastic behavior of the CNT-reinforced Al nanocomposites. It is also found that the yield stress of the nanocomposites rises with increasing CNT volume fraction or decreasing CNT diameter. Besides, the elastoplastic stress–strain curve of the CNT-reinforced Al nanocomposites is presented for multiaxial tension. The initial yield envelopes of the nanocomposites under longitudinal–transverse biaxial tension are provided too. Comparison between the elastic results of the present model with those of other available micromechanical analyses shows a very good agreement. © IMechE 2017.
Publication Date: 2019
Aerospace Science and Technology (12709638)91pp. 479-493
In this research, the elastoplastic postbuckling response of moderately thick rectangular plates subjected to in-plane loadings is analyzed by a novel numerical approach. The influence of transverse shear deformation is taken into account via the first-order shear deformation theory (FSDT). Also, the elastoplastic behavior is captured based on two theories of plasticity including the incremental theory (IT)(with the Prandtl-Reuss constitutive relations)and the deformation theory (DT)(with the Hencky constitutive relation). Moreover, it is assumed that the material of plate obeys the Ramberg-Osgood (RO)elastoplastic stress-strain relation. First, the matrix formulations of strain rates and constitutive relations are derived. In the next step, according to Hamilton's principle, the weak form of governing equations is derived which is then directly discretized using the variational differential quadrature (VDQ)technique. The discretization process is performed by accurate matrix derivative and integral operators of VDQ. Plates with various boundary conditions under uniaxial and equibiaxial compressions are considered. It is first indicated that the present results are in excellent agreement with the analytical solutions existing in the open literature. Thereafter, the influences of geometrical properties, boundary conditions, elastic modulus-to-nominal yield stress ratio and value of power c in the RO relation on the elastoplastic postbuckling paths of plates are studied. Furthermore, several comparisons are made between the predictions of IT and DT. © 2019 Elsevier Masson SAS
Publication Date: 2019
Plastics, Rubber and Composites (17432898)48(7)pp. 317-326
Effect of fibre/matrix interphase parameters, including thickness and material properties on the equivalent thermal conductivities of unidirectional fibre-reinforced polymer composites. A unit cell-based micromechanical method is proposed to evaluate the thermal conductivities of unidirectional multi-phase composites. The longitudinal thermal conductivity of unidirectional fibre-reinforced polymer matrix composites is seen to be independent of interphase region. When the thermal conductivity of interphase is higher than that of matrix, the increase of interphase thickness leads to an improvement in transverse thermal conductivity of fibre-reinforced polymer composites. The influences of fibre volume fraction, orientation angle and shape of cross-section as well as temperature on the thermal conducting behaviour are widely examined. The model predictions are in good agreement with the experimental data reported in the literature. © 2019, © 2019 Institute of Materials, Minerals and Mining Published by Taylor & Francis on behalf of the Institute.
Hasanzadeh, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Mechanics of Materials (01676636)129pp. 63-79
This paper investigates the overall elastic and piezoelectric properties of unidirectional piezoelectric fiber-reinforced polymer composites containing randomly oriented carbon nanotubes (CNTs). To this end, a multi-procedure micromechanics approach based on the Mori-Tanaka model is proposed. In the first step, the elastic properties of a nanocomposite consisting of randomly distributed CNTs in the polymer matrix is modeled. The formation of the interphase region due to non-bonded van der Waals (vdW) interaction between the CNTs and the polymer is taken into account in the micromechanical simulation. In the second step, considering the nanocomposite as a matrix and piezoelectric fiber as reinforcement, the elastic and piezoelectric properties of CNT-piezoelectric fiber-reinforced hybrid composites are predicted. The effects of volume fractions of CNT and piezoelectric fiber, and CNT diameter, thickness and adhesion exponent of the interphase on the hybrid composite elastic and piezoelectric coefficients are examined. The results clearly highlight the benefits of CNTs into the conventional piezoelectric composites from a structural point of view. The overall electro-mechanical properties of the piezoelectric fiber-reinforced polymer composites can be significantly enhanced with adding CNTs. It is found that the interphase region can play a crucial role in the effective properties of the piezoelectric hybrid composites. © 2018 Elsevier Ltd
Publication Date: 2019
Iranian Polymer Journal (10261265)28(1)pp. 87-97
Balsa cored sandwich structures with fiber-reinforced polymer (FRP) skins are widely used to produce lightweight, high-stiffness and cost-effective structural components used in marine applications. However, balsa is a hydrophilic material, which is severely susceptible to moisture attacks. Unintended water penetration from the damaged FRP skins into the balsa cored sandwich structures can lead to the core decay and delamination of the core near the free edges. Thus, in this work, a concept for improving the damage tolerance of balsa cored sandwich structures by replacing the FRP skins with fiber metal laminates (FMLs) is proposed. To characterize the mechanical properties of these novel sandwich structures, a wide range of mechanical tests including three-point bending, edgewise compression with buckling as well as Charpy and high-velocity impact test were carried out on balsa cored sandwich specimens made of FMLs. A traditional sandwich structure made of woven E-glass fiber/epoxy skins was also prepared and tested for exploring the effect of skin material on the mechanical response of the studied sandwich structures. The experimental results showed that balsa cored sandwich structures composed of FML skins have an outstanding mechanical performance compared with those having the E-glass fiber/epoxy skins. © 2018, Iran Polymer and Petrochemical Institute.
Bazdid-vahdati m., M.,
Oskouie, M.F.,
Ansari, R.,
Rouhi h., H. Publication Date: 2019
Mathematics and Mechanics of Solids (17413028)24(6)pp. 1893-1907
In this paper, within the framework of two-dimensional (2D) elasticity, a novel finite element formulation is proposed based on the micropolar theory (MPT) and the micromorphic theory (MMT). First, general formulations are developed for the micromorphic and micropolar continua in the context of 2D elasticity. Then, they are presented in a matrix form which is useful from the computational viewpoint. In the next step, using the matricized MPT and MMT formulations, a linear finite element approach including the effects of micro-deformation and micro-rotation degrees of freedom (DOFs) of material particles is developed, and a quadratic size-dependent element is proposed accordingly. Two test problems are solved to reveal the efficiency of the developed formulation. The influence of the length scale parameter on the bending of micromorphic and micropolar plates is illustrated in the given examples. Furthermore, comparisons are made between the results obtained from classical elasticity theory and those calculated based upon MPT and MMT. © The Author(s) 2018.
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Composite Interfaces (09276440)26(12)pp. 1035-1055
A continuum modeling based on finite element method (FEM) is performed using three-phase representative volume element (RVE) to investigate the thermal conductivities of multiphase composites reinforced by carbon fibers. The selected RVE consists of carbon fiber, matrix and fiber/matrix interphase. A comprehensive study is carried out to examine the effects of interphase features such as thickness and material properties on the effective thermal conductivities of multiphase composites. Moreover, the effects of carbon fiber volume fraction, orientation, various types of arrangement, i.e., random, uniform and different functionally graded distributions, waviness as well as matrix material properties on the effective thermal conductivities of multiphase composites are examined. The FEM predictions are in good agreement with the results of other numerical simulations available in the literature. Also, the FEM results are compared with the composite cylinder assemblage approach results. © 2019, © 2019 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2019
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)41(1)
The finite element method is used here to study the elastic properties of concentric boron nitride and carbon multi-walled nanotubes. Beam and spring elements are, respectively, employed to model the covalent bonds between atoms and nonbonding van der Waals interactions between atoms located on different walls. The double-walled and triple-walled nanotubes with different arrangements of boron nitride and carbon nanotubes are considered. It is shown that the elastic modulus of the concentric multi-walled BN and C nanotubes increases by increasing the ratio of nanotube length to its diameter (aspect ratio). In addition, the effect of aspect ratio on the elastic modulus of the armchair nanotubes is larger than that on the elastic modulus of the armchair nanotubes. Comparing the elastic modulus of the double-walled and triple-walled nanotubes, it is observed that the effect of number of walls on the elastic modulus of the concentric boron nitride and carbon multi-walled nanotube is negligible. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.
Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(13)pp. 1169-1177
The behavior of L-shaped samples made of multi-scale carbon nanotube/carbon fiber reinforced polyethylene under the bending test is investigated by using the extended finite element method. The mechanical properties of the multi-scale composite are obtained by a stochastic finite element mode. Initially, molecular dynamics simulations are used to compute the mechanical properties of nanotubes at the nanoscale. Then, by using the finite element method, the properties of the carbon nanotube/polyethylene nanocomposite are obtained. Considering the mechanical properties of the matrix as the properties of nanotube reinforced polyethylene, the carbon fibers are included into the composites in the next scale. © 2018, © 2018 Taylor & Francis Group, LLC.
Publication Date: 2019
Science and Engineering of Composite Materials (21910359)26(1)pp. 70-76
A multiscale finite element method is adopted in this paper to study the vibrational characteristics of polymer matrix composite plates reinforced with the combination of carbon fibers (CFs) and carbon nanotubes (CNTs). The effects of nanoscale and microscale are coupled through a two-step procedure. In the first step, random dispersion of CNTs into the polymer matrix is modelled using a three-phase representative volume element (RVE). In the selected RVE, the influence of the interphase formed because of non-bonded interactions between the polymer matrix and CNTs is taken into account. In the second step, the distribution of CFs into the composite is modelled, and the elastic properties of CF-CNT-polymer matrix hybrid composite are calculated for various values of volume fractions of reinforcement phases. Then, the free and forced vibration behaviors of composite plates are analyzed. It is considered that the plates have rectangular, circular, and annular shapes and are under clamped/simply supported edge conditions. The effects of CNT/CF reinforcement on the elastic modulus and density of composite and on the free/forced vibration response of the considered structures are investigated. It is shown that the vibrational behavior of plates is significantly affected by the hybrid reinforcement with CNT and CF. © 2019 Walter de Gruyter GmbH, Berlin/Boston 2019.
Publication Date: 2019
Thin-Walled Structures (02638231)145
The aim of this article is to investigate the vibrational behavior of rectangular and V-shaped atomic force microscopy (AFM) microcantilevers with an extended piezoelectric layer using the finite element method (FEM). Firstly, the results of 3D FEM simulation are compared to the experimental and analytical ones to assess the accuracy of the method. Then, the free and forced vibrations of rectangular and V-shape piezoelectric microcantilevers in the absence and presence of nonlinear interactions between the microcantilever tip and the surface sample are studied. A nonlinear spring is used in the finite element modeling to simulate the nonlinear attraction-repulsion interactions between the tip and the sample. The amplitude of the AFM microcantilever is considered to be comparably small, hence the geometric nonlinearity of the microcantilever is insignificant. In the free vibration part, the resonance frequencies and mode shapes are obtained. In the forced vibration cases, an AC voltage with the resonance frequencies obtained in the free vibration analysis is applied to the piezoelectric layer to operate the microcantilever. The resonance amplitude of the tip of AFM microcantilever is derived accordingly. All simulations are performed for two cases; the first one is a fixed microcantilever at the end and free to move and rotate, and the second one is a microcantilever whose rotational degree of freedom and lateral displacement is tied up with applying a symmetric constraint. So, an important study parameter in this work is the effect of torsional modes on the vibrational behavior of AFM piezoelectric microcantilevers. © 2019 Elsevier Ltd
Haghgoo, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Darvizeh a., A. Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)233(8)pp. 2813-2829
In the present study, the effect of PZT-5A piezoelectric interphase on the effective thermo-magneto-electro-elastic properties of CoFe 2 O 4 piezomagnetic matrix composites reinforced with carbon fibers is investigated. In this type of three-phase smart composite, the unidirectional fiber is coated with the piezoelectric shell. To this end, the fully coupled thermo-magneto-electro-elastic constitutive relations are developed for a unit cell-based micromechanical model in conjunction with a proper representative volume element. The influences of piezoelectric interphase thickness on the effective properties of the unidirectional smart composite are extensively investigated at different carbon fiber volume fractions up to 70%. The results demonstrate that piezoelectric interphase can greatly affect the overall thermo-magneto-electro-elastic properties of the smart composites. For two-phase smart composites, the present predictions are found to be in close proximity with the Mori–Tanaka results, which validates the present model. © IMechE 2018.
Publication Date: 2019
Thin-Walled Structures (02638231)135pp. 12-20
In this article, a variational numerical method is utilized to investigate the nonlinear free vibrations of magneto-electro-elastic (MEE) plates under thermal environment. To this end, first, the basic equations are written based on the first-order shear deformation theory and von Kármán's geometric nonlinearity. Next, the constitutive equations are represented in matrix form. In the context of Hamilton's principle, the quadratic and matricized form of energy functional is derived which is then directly discretized on space domain by a method called Variational Differential Quadrature (VDQ). Periodic time differential operators are also constructed for discretizing on time domain. The final solution is obtained by the pseudo arc-length continuation algorithm. The effects of applied electric voltage, applied magnetic potential, temperature change and geometrical parameters on the response curves of MEE plates with different types of boundary conditions are studied. © 2018 Elsevier Ltd
Moradweysi p., ,
Ansari, R.,
Gholami, R.,
Bazdid-vahdati m., M.,
Rouhi h., H. Publication Date: 2019
ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik (00442267)99(6)
In this article, an analytical approach is proposed for the problem of an elastic half-space under symmetrically distributed normal force with arbitrary profile including uniform pressure, Boussinesq flat-ended punch, conical punch and Hertz's spherical punch. The formulation of the work is on the basis of Mindlin's first strain gradient theory with five material length scale parameters. Also, the surface effects are taken into account using the Gurtin-Murdoch surface elasticity theory. The developed mathematical formulation is general so that it can be simply reduced to different strain gradient-based theories such as the modified versions of strain gradient and modified couple stress theories (MSGT and MCST), the simplified strain gradient theory (A-SGT), as well as the classical theory (CT). In the solution procedure, an analytical method is applied using the Fourier and Hankel transforms. In the numerical results, the effects of material length scale parameters and kind of punch on the surface displacements and stresses of the half-space are analyzed. The surface influences are also comprehensively studied. Moreover, comparisons are made between the predictions of MSGT, MCST, A-SGT and CT. This work shows that the material length scale parameters of Mindlin's first SGT play important roles in the response of half-space. Also, the presented results provide a comparison between the intensity of effects of strain gradient parameters and surface parameters. © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Hosseini, K.,
Ansari, R.,
Samadani f., F.,
Zabihi, A.,
Shafaroody a., ,
Mirzazadeh m., Publication Date: 2019
Acta Physica Polonica A (05874246)136(1)pp. 203-207
The light pulses propagation in optical fibers modeled by the dispersive cubic-quintic Schrödinger equation including high-order time derivatives is investigated in detail. For this purpose, the expa-function scheme is utilized along with a symbolic computation system to gain the exact solutions of the model. As an outcome, a wide range of exact solutions including dark and periodic solitary wave solutions are effectively derived, verifying the excellent performance of the scheme. © 2019 Polish Academy of Sciences. All rights reserved.
Publication Date: 2019
Journal Of Molecular Modeling (16102940)25(4)
The average pull-out force and interaction energy of polyethylene (PE) cross-linked functionalized carbon nanotubes (cfCNTs) embedded in polymer matrices (PE-cfCNTs@polymers) was studied using molecular dynamics (MD) simulations. Accordingly, the pull-out process of PE-cfCNTs from inside polymer matrices, i.e., Aramid and PE, was performed under displacement control. The results obtained were compared with those of pure carbon nanotube (CNT) incorporated into polymer matrices (pure CNT@polymers). The influence on the pull-out force and interaction energy between the CNT and polymer of the structure of polymer matrices, the weight percentage and two types of distribution patterns of cross-linked PE chains, namely mapped and wrapped, was investigated. The results indicate that the structure of the polymers and distribution patterns of cross-linked PE chains strongly affect important parameters related to interfacial properties. The average pull-out force of mapped and wrapped PE-cfCNTs@polymers increases as the weight of attached PE chains on the CNT surface increases. The effect of wrapped structures on increasing the pull-out force is greater than that of the mapped configurations. Also, the PE-cfCNTs@polymers show higher average pull-out forces than those of their pure counterparts. As the CNT pulls out from the polymer matrix, an approximately linear reduction in the absolute value of interaction energy with the pull-out displacement is observed. However, this trend is changed to some extent by imposing instability through the wrapped PE-cfCNTs. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)233(19-20)pp. 7003-7018
One of the main problems of polymer matrix composites in critical applications is their high sensitivity to thermal conditions. Therefore, an experimental study was performed to evaluate the thermal durability of traditional plain weave E-glass/epoxy as well as fiber metal laminates as a possible alternative in this case. In this way, both the laminate types were exposed to thermal aging at 130 ℃ for five weeks, and the plausible degradation is investigated through weight loss analyzes and mechanical testing. The possibility of improving the mechanical behavior of the studied laminates by nanoclay was also studied. The results demonstrated that the weight loss and mechanical degradation were more pronounced in thermally aged plain weave E-glass/epoxy composites. The results also indicated that nanoclay could enhance the mechanical properties of both laminates. On the basis of the results, the shielding role of aluminum layers and thermal resistance of nanoclay can synergistically offer a novel class of nano-fiber metal laminates with high thermal tolerance in thermo-oxidative conditions. © IMechE 2019.
Publication Date: 2019
Journal of Molecular Graphics and Modelling (10933263)92pp. 341-356
Herein, the interfacial properties of new three-dimensional (3D) configurations of metallic carbon, namely T6 and T14, incorporated to different polymer matrices (T6 and T14@polymers) are studied using molecular dynamics (MD) simulations. The effects of two types of shape models for T6 and T14, i.e. beam- and plate-like models, various square cross-sectional areas for the reinforcements, pull-out velocity and polymer structure on the interaction energy and pull-out force of final system are investigated. The results reveal that the interfacial resistance of the system is improved by imposing a high pull-out velocity to the nanofillers. For each pull-out velocity, the effect of beam-like T6 and T14@polycarbonate (beam-like T6 and T14@PC) on increasing average pull-out force is more remarkable than that of similar models surrounded by polypropylene (PP). The beam- and plate-like structures@polymers possess the lowest and highest interfacial resistance, respectively. As the aspect ratio (length-to-width ratio) of nanofillers changes from the lowest value to the highest one, the average pull-out force decreases. The average pull-out force of plate-like T6@polymers is higher than their plate-like T14 counterparts. Besides, higher absolute values of interaction energy in plate-like T6 and T14@polymers in comparison with others imply that the load-carrying capacity from the surrounding matrix to the plate-like nanofillers is significantly increased. © 2019 Elsevier Inc.
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2019
Journal of Intelligent Material Systems and Structures (15308138)30(3)pp. 463-478
The effects of interphase characteristics on the elastic behavior of randomly dispersed carbon nanotube–reinforced shape memory polymer nanocomposites are investigated using a three-dimensional unit cell–based micromechanical method. The interphase region is formed due to non-bonded van der Waals interaction between a carbon nanotube and a shape memory polymer. The influences of temperature, diameter, volume fraction, and arrangement type of carbon nanotubes within the matrix as well as two interphase factors, including adhesion exponent and thickness on the carbon nanotube/shape memory polymer nanocomposite’s longitudinal and transverse elastic moduli, are explored extensively. Moreover, the results are presented for the shape memory polymer nanocomposites containing randomly oriented carbon nanotubes. The obtained results clearly demonstrate that the interphase region plays a crucial role in the modeling of the carbon nanotube/shape memory polymer nanocomposite’s elastic moduli. It is observed that the nanocomposite’s elastic moduli remarkably increase with increasing interphase thickness or decreasing adhesion exponent. It is found that when the interphase is considered in the micromechanical simulation, the shape memory polymer nanocomposite’s elastic moduli non-linearly increase as the carbon nanotube diameter decreases. The predictions of the present micromechanical model are compared with those of other analytical methods and available experiments. © The Author(s) 2018.
Aghdasi p., P.,
Ansari, R.,
Rouhi, S.,
Goli m., ,
Gilakjani, H.A. Publication Date: 2019
Physica B: Condensed Matter (09214526)574
The adsorption of the hydrogen and fluorine atoms on the arsenene nanosheet is simulated herein. The density functional theory is utilized for this purpose. The influence of the H and F adsorptions on the elastic and plastic properties of the arsenene is investigated. It is shown that Young's modulus of the arsenene nanosheet under the uniaxial tension significantly degrades by the adsorption. Similarly, the bulk modulus under the biaxial strain experiences large reduction by the adsorption. For investigating the influence of the adsorption on the plastic properties of the arsenene nanosheet, the loading is extended until the sign of the plastic behavior is appeared. It is shown that under the uniaxial tension, as the elastic and bulk moduli, the plastic strain is also decreased. However, interestingly, it is observed that H and F adsorption leads to increasing the plastic strain under the biaxial loading. © 2019 Elsevier B.V.
Publication Date: 2019
Journal Of The Brazilian Society Of Mechanical Sciences And Engineering (16785878)41(1)
The vibrational behavior of polymer matrix reinforced by single-walled carbon nanotubes is investigated here. To this end, the finite element method is used. The effects of nanotube geometrical parameters and volume fraction on the natural frequency of the nanocomposites are explored. It is shown that the influence of the nanotube chirality on the vibrational behavior of the nanocomposite is not significant. However, increasing the diameter has an inverse effect on the natural frequency of the nanocomposites. Investigating the effect of volume fraction, it is shown that the nanocomposites with larger volume fractions possess larger frequencies. However, the influence of the volume fraction on the vibrational behavior of the nanocomposites diminishes for long single-walled carbon nanotubes. © 2019, The Brazilian Society of Mechanical Sciences and Engineering.
Publication Date: 2019
International Journal of Non-Linear Mechanics (00207462)116pp. 39-54
A numerical solution technique named as variational differential quadrature (VDQ) is adopted herein for the compressible nonlinear elasticity problems. The governing equations are obtained based on the virtual work principle by considering displacement as the unknown field. The neo-Hookean model is also considered for the hyperelastic behavior of material. In the solution method, an efficient vector–matrix formulation is developed from which the discretized governing equations are achieved from the weak form of equations in a direct approach. Simplicity in implementation and accuracy are among the features of the proposed approach. Moreover, it does not suffer from the locking problem and unphysical instabilities. Fast convergence rate and computational efficiency are other advantages of this method. A number of numerical examples are given to reveal the good performance of VDQ in the large deformation analysis of compressible and nearly-incompressible bodies. © 2019 Elsevier Ltd
Publication Date: 2019
Mathematics and Mechanics of Solids (17413028)24(12)pp. 3920-3956
We aimed to study the static deformation of geometrically nonlinear shell-type structures on the basis of micromorphic theory. Employing the most comprehensive model in the micro-continuum field, shells in low-dimensions and made of inhomogeneous materials are precisely investigated. The seven-parameter two-dimensional (2D) kinematic model is used which satisfies three-dimensional (3D) constitutive relations and represents the macro-deformation components in mid-surface area of the shell. Also, in the framework of micromorphic continua with three deformable director vectors, nine micro-deformation degrees of freedom, including micro-scale rotations, shears and stretches, are taken into account. Utilizing the energy approach in the convected curvilinear coordinate system leads to the general derivation of the variational formulations in Lagrangian description. High-order stress–strain relations are obtained via introducing the size-dependent as well as size-independent elasticity tensors for the isotropic micromorphic solid. Finally, an equivalent matrix–vector form of representation is proposed to facilitate the solution procedure of the extracted tensor-based formulation. Determining the kinetic and kinematic fields in terms of 16 macro and micro-deformation components, provides the opportunity to directly implement the interpolation-based solution methodologies, such as the finite element isogeometric analysis presented in Part II of this study. Two parts of the article, that are organized to be independent, contribute to the literature respectively from theoretical and computational perspectives. © The Author(s) 2019.
Publication Date: 2019
Mathematics and Mechanics of Solids (17413028)24(12)pp. 3753-3778
In Part I of this study, a variational formulation was presented for the large elastic deformation problem of micromorphic shells. Using the novel matrix-vector format presented for the kinematic model, constitutive relations, and energy functions, an isogeometric analysis (IGA)-based solution strategy is developed, which appropriately estimates the macro- and micro-deformation field components. Due to the capability of constructing exact geometries and the powerful mesh refinement tools, IGA can be successfully applied to solve the equilibrium equations with dominant nonlinear terms. It is known that different types of locking phenomena take place in the conventional finite element analysis of thin shells based on low-order elements. Non-standard finite element models with mixed interpolation schemes and additional degrees of freedom (DOFs) or the ones used the high-order Lagrangian shell elements which require high computational costs, are the available solutions to tackle locking issues. The present 16-DOFs IGA is found to be efficient because of possessing a good rate of convergence and providing locking-free stable responses for micromorphic shells. Such a conclusion is found from several comparative studies with available data in the well-known macro-scale benchmark problems based on the classical elasticity as well as the corresponding numerical examples studied in nano-scale beam-, plate-, cylindrical shell- and spherical shell-type structures on the basis of the micromorphic continuum theory. © The Author(s) 2019.
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(13)pp. 1104-1114
The low velocity impact response of beams made of carbon nanotube (CNT)/short carbon fiber (SCF)-reinforced polymer is investigated based on a hierarchical finite element approach. First, the random distribution of CNTs into the polymer matrix is modeled using a three-phase representative volume element (RVE); and the elastic modulus and density of CNT-reinforced polymer are predicted. In the RVE, the interphase region formed due to the interaction between CNTs and the matrix is considered. Then, reinforcement with SCFs is considered, and the elastic properties of SCF-CNT-polymer hybrid composite are obtained. Finally, the low velocity impact response of composite beams is analyzed. © 2018, © 2018 Taylor & Francis Group, LLC.
Ahmadi m., M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Journal of Alloys and Compounds (09258388)779pp. 433-439
The formation of Al4C3 interphase in carbon nanotube (CNT)-reinforced aluminum (Al) nanocomposites is a critical issue which must be well-known to more realistic estimations of mechanical behavior of such materials. In this work, the effect of Al4C3 interphase on the elastic modulus of Al nanocomposites reinforced with randomly distributed CNTs is investigated using a numerical micromechanical model based on the finite element method (FEM). Moreover, the influences of the CNT volume fraction and diameter on the elastic modulus of Al nanocomposites are explored. The results reveal that Al4C3 interphase significantly affects the elastic modulus of Al nanocomposites especially as the CNT diameter decreases. It can be observed that with increasing interphase thickness, the elastic modulus of the nanocomposite increases. The applicability of the presented model in predicting the elastic modulus of CNT-reinforced Al nanocomposites is investigated by comparing the results of the FEM with those of experiment available in the literature. Furthermore, the results of the FEM with and without Al4C3 interphase for aligned continuous and discontinuous CNT-reinforced Al nanocomposites are presented. It is found that the effect of the interphase on the elastic modulus of nanocomposites reinforced with continuous CNT is more important than that of nanocomposites reinforced with discontinuous CNT. © 2018 Elsevier B.V.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J. Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(23)pp. 1920-1934
The effects of adding silica nanoparticles on the elastic properties of glass-epoxy hybrid composites are investigated using a micromechanical method. Influences of silica nanoparticle volume fraction and diameter, the interphase elastic modulus and thickness, the glass fiber volume fraction and aspect ratio as well as off-axis angle on the elastic properties of unidirectional glass fiber-reinforced epoxy hybrid composites containing silica nanoparticles are studied. The results reveal that the addition of silica nanoparticles can improve the elastic modulus in the transverse direction, while the axial elastic modulus is not affected by silica nanoparticles. © 2018, © 2018 Taylor & Francis Group, LLC.
Hasanzadeh, M.,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(20)pp. 1700-1710
An elastoplastic constitutive model is proposed to evaluate the overall behavior of randomly oriented wavy carbon nanotube (CNT)-reinforced polymer nanocomposites under uniaxial and biaxial loadings. For an accurate prediction of the nanocomposite elastoplastic behavior, considering randomly oriented wavy CNTs into the matrix is essential. Effects of volume fraction, diameter, aggregation, and nonstraight state of the CNTs, thickness and adhesion exponent of the CNT/polymer interphase on the nanocomposite elastic–plastic stress–strain curves are investigated. The nanocomposite strengthening is improved with (1) increasing CNT volume fraction, (2) applying straight CNTs, (3) decreasing the CNT diameter, and (4) increasing the interphase thickness. © 2018, © 2018 Taylor & Francis Group, LLC.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)43(1)pp. 27-39
The thermoelastic response of polyimide nanocomposites reinforced with randomly oriented carbon nanotubes (CNTs) is analyzed. For this purpose, a unit cell micromechanics model together with a proper representative volume element is employed. The interphase region created due to the non-bonded interaction between the CNT and surrounding polyimide matrix is taken into account in the modeling of nanocomposite. The effects of various parameters such as alignment and random orientation of CNTs into polyimide matrix, volume fraction and diameter of CNTs, size, adhesion exponent and material properties of the interphase region on the coefficient of thermal expansion (CTE) of polyimide nanocomposite are investigated. The results reveal that in the presence of interphase, the CTE nonlinearly increases with the reduction of CNT diameter, whereas without considering interphase, the change of diameter does not affect the thermoelastic properties of polyimide nanocomposite. Also, it is found that the CTEs of nanocomposite with interphase are higher than those of nanocomposite without interphase. Additionally, it is shown that the CTE of polyimide nanocomposite containing randomly oriented CNTs rises with increasing thickness, CTE and stiffness of interphase. The results of the presented model are in very good agreement with experimental data. © 2017, Shiraz University.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(24)pp. 2047-2061
A multi-stage hierarchical micromechanical approach is presented to predict the elastic properties of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon nanotubes (CNTs). The influences of CF volume fraction and orientation, type of CFs arrangement, CNT volume fraction and geometrical features, and CNT/polymer interphase region on the mechanical characteristics of CF/CNT-reinforced polymer hybrid composites are explored. An excellent agreement is found between the predictions of the presented micromechanical method and available experiment. It is shown that adding the CNTs into the fibrous polymer composites raises the transverse elastic modulus, while the longitudinal elastic properties are not influenced by the CNTs. © 2018, © 2018 Taylor & Francis Group, LLC.
Rasoolpoor m., ,
Ansari, R.,
Hassanzadeh-aghdam, M.K. Publication Date: 2019
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)233(12)pp. 2419-2432
An efficient multiscale analysis is proposed to investigate the dynamic behavior of metal matrix nanocomposite beams reinforced by SiC nanoparticles under low-velocity impact loads. First, an analytical micromechanics model is developed to obtain the effective elastic properties of ceramic nanoparticle-reinforced metal matrix nanocomposite, and then the finite element method is used to predict the dynamic response of beams made of this nanocomposite material. Two important microstructural features, including size effect and agglomeration of nanoscale particles, are incorporated into the micromechanical analysis. The present simulation results for the elastic modulus and low-velocity impact response show good agreement with previously published results. The effects of volume percent, diameter and dispersion type of ceramic nanoparticles, geometrical features and boundary conditions of nanostructure, velocity and size of projectile on the contact force, and center deflection time histories of metal matrix nanocomposite beams are extensively examined. Analysis shows that homogenously distributed SiC nanoparticles into the metal matrix nanocomposites can obviously increase the nanostructure/projectile contact force and decrease both the beam center deflection and impact duration which is due to the enhancement of elastic properties. However, the ceramic nanoparticle agglomeration has an effect on the decrease of contact force and the increase of both the center deflection and impact duration. Also, it is concluded that decreasing nanoparticle size can increase the contact force and decrease the beam center deflection. © IMechE 2019.
Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Civil Engineering (22286160)43pp. 533-547
In this paper, the static bending of nanoscale beams is studied in the nonlinear regime. For this purpose, a size-dependent Timoshenko beam model is developed by which nonlocal and strain gradient effects are simultaneously captured. The most comprehensive nonlocal strain gradient model without any simplification is used herein. The strain gradient influences are considered based upon the most general form of strain gradient theory which can accommodate simpler theories such as the modified strain gradient and couple stress theories. Moreover, to take the nonlocal effects into account, the original integral form of Eringen’s nonlocal elasticity is employed. The governing equations are derived using the minimum total potential energy principle. Also, the formulation of model is represented in matrix–vector form with the aim of using in numerical approaches, especially in finite element or isogeometric analyses. To solve the governing equations of the developed integral nonlocal strain gradient model, a non-classical isogeometric analysis is proposed. The simultaneous effects of nonlocal and small-scale parameters on the nonlinear bending behavior of simply supported, clamped and clamped-free nanobeams are studied in the numerical results. Furthermore, the results obtained based on the differential and integral nonlocal models are presented for the comparison goal. © 2018, Shiraz University.
Gholami y., Y.,
Ansari, R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2019
European Physical Journal Plus (21905444)134(4)
In this article, the nonlinear bending behavior of rectangular nanoplates made of functionally graded materials (FGMs) is studied in the context of a variational formulation. To capture size effects, the most general form of strain gradient theory is employed. The three-dimensional (3D) elasticity theory is used for modeling the nanoplate. The governing equations are also derived in the discretized weak form using the variational differential quadrature (VDQ) method. Finally, the solution of the nonlinear bending problem is obtained by the pseudo arc-length continuation algorithm. In the numerical results, the effects of thickness-to-length scale ratio, side length-to-thickness ratio and material gradient index on the nonlinear bending response of nanoplates subject to different types of boundary conditions are analyzed. Moreover, a comparison is provided between the predictions of various strain gradient-based theories. © 2019, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2019
European Physical Journal Plus (21905444)134(10)
The geometrically nonlinear bending and postbuckling of nanoscale beams are investigated herein according to the two-phase fractional nonlocal continuum model. It is considered that the beams have been made from functionally graded materials (FGMs), and the Bernoulli-Euler beam model is employed for their modeling. The variational form of the governing fractional equation is obtained first by means of an energy approach. Thereafter, a novel numerical solution method is proposed named as fractional variational differential quadrature method (FVDQM). In FVDQM, which is applied to the variational statement of the problem in a direct way, a combination of the differential quadrature method and matrix operators is utilized. The efficiency of the proposed fractional nonlocal model is evaluated by molecular dynamics (MD) simulations. Selected numerical results are given to explore the influences of fractional order, nonlocality, length-to-thickness ratio and FG index on the nonlinear bending and postbuckling responses of FG nanobeams with various types of boundary conditions. © 2019, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2019
Polymer Composites (02728397)40(S2)
This article deals with the large amplitude free and forced vibration analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) annular sector plates based on a numerical approach. The modified rule of mixture is used to estimate the material properties. The equations of motion are developed based on the first-order shear deformation theory (FSDT) and the von Kármán geometric nonlinearity. First, the discretized form of energy functional of structure is given with the aid of variational differential quadrature method. Then, a time periodic discretization is performed and the frequency response of the nanocomposite plate is determined using the pseudo-arc length continuation method. After verifying the correctness of the proposed approach, a comprehensive parametric study is presented to investigate the effects of important factors on the nonlinear vibration characteristics of the FG-CNTRC annular sector plates. The results imply that the volume fraction and distribution type of nanotubes have considerable effects on the fundamental frequency as well as nonlinear frequency response curves. POLYM. COMPOS., 40:E1364–E1377, 2019. © 2018 Society of Plastics Engineers. © 2018 Society of Plastics Engineers
Rouhi h., H.,
Ebrahimi f., ,
Ansari, R.,
Torabi, J. Publication Date: 2019
European Journal of Mechanics, A/Solids (09977538)73pp. 268-281
The size-dependent geometrically nonlinear free and forced vibration behaviors of nanoscale beams are studied in this article using a numerical approach. The size effects are captured using Mindlin's second strain gradient theory (SSGT) in which the second- and third-order derivatives of displacement components are taken into account in the strain energy density. The basic relations are first derived using the Timoshenko beam theory and SSGT. Then, the variational differential quadrature (VDQ) method is adopted to solve the obtained governing equations in the context of variational formulation. Comprehensive numerical results are given to investigate the influences thickness-to-lattice parameter ratio on the nonlinear free and forced vibrations of nanobeams under different types of end conditions. Also, comparisons are made between the predictions of SSGT and the first strain gradient theory as well as the classical elasticity theory. © 2018 Elsevier Masson SAS
Publication Date: 2019
International Journal of Mechanical Sciences (00207403)151pp. 33-45
In the present paper, an attempt is made to adopt the variational differential quadrature (VDQ) technique for the large-amplitude vibration analysis of shell-type structures based on the six-parameter shell theory. The functional of energy in quadratic form is derived based on Hamilton's principle which is then directly discretized by the VDQ method. Although the derived formulation is general, the focus of paper is on the cylindrical and spherical shells. The nonlinear vibration problem is solved by means of the time periodic discretization method. The results reveal that the present numerical method can solve the problem accurately. It is also easy to implement due to its compact and explicit matrix formulation. Comprehensive numerical results are presented to study the effects of geometrical properties and boundary conditions on the frequency-response curves of cylindrical and spherical shells. Moreover, comparison studies are presented between the results of the six-parameter shell theory and the first-order shear deformation shell theory. © 2018 Elsevier Ltd
Publication Date: 2019
International Journal of Structural Stability and Dynamics (02194554)19(2)
In this paper, the size-dependent nonlinear pull-in behavior of rectangular microplates made from functionally graded materials (FGMs) subjected to electrostatic actuation is numerically studied using a novel approach. The small scale effects are taken into account according to Mindlin's first-order strain gradient theory (SGT). The plate model is formulated based on the first-order shear deformation theory (FSDT) using the virtual work principle. The size-dependent relations are derived in general form, which can be reduced to those based on different elasticity theories, including the modified strain gradient, modified couple stress and classical theories (MSGT, MCST and CT). The solution of the problem is arrived at by employing an efficient matrix-based method called the variational differential quadrature (VDQ). First, the quadratic form of the energy functional including the size effects is obtained. Then, it is discretized by the VDQ method using a set of matrix differential and integral operators. Finally, the achieved discretized nonlinear equations are solved by the pseudo arc-length continuation method. In the numerical results, the effects of material length scale parameters, side length-to-thickness ratio and FGM's material gradient index on the nonlinear pull-in instability of microplates with different boundary conditions are investigated. A comparison is also made between the predictions by the MSGT, MCST and CT. © 2019 World Scientific Publishing Company.
Publication Date: 2019
Applied Mathematical Modelling (0307904X)65pp. 627-660
The present study examines the nonlinear stability and free vibration features of multilayer functionally graded graphene platelet-reinforced polymer composite (FG-GPLRPC) rectangular plates under compressive in-plane mechanical loads in pre/post buckling regimes. The GPL weight fractions layer-wisely vary across the lateral direction. Furthermore, GPLs are uniformly dispersed in the polymer matrix of each layer. The effective Young's modulus of GPL-reinforced nanocomposite is assessed via the modified Halpin–Tsai technique, while the effective mass density and Poisson's ratio are attained by the rule of mixture. Taking the von Kármán-type nonlinearity into account for the large deflection of the FG-GPLRPC plate, as well as utilizing the variational differential quadrature (VDQ) method and Lagrange equation, the system of discretized coupled nonlinear equations of motions is directly achieved based upon a parabolic shear deformation plate theory; taking into account the impacts of geometric nonlinearity, in-plane loading, rotary inertia and transverse shear deformation. Afterwards, first, by neglecting the inertia terms, the pseudo-arc length approach is used in order to plot the equilibrium postbuckling path of FG-GPLRPC plates. Then, supposing a time-dependent disturbance about the postbuckling equilibrium status, the frequency responses of pre/post-buckled FG-GPLRC plate are obtained in terms of the compressive in-plane load. The influences of various vital design parameters are discussed through various parametric studies. © 2018 Elsevier Inc.
Gholami y., Y.,
Shahabodini a., A.,
Ansari, R.,
Rouhi h., H. Publication Date: 2019
Acta Mechanica (16196937)230(12)pp. 4157-4174
Based on the higher-order Cauchy–Born (HCB) rule, an atomistic-continuum multiscale model is proposed to address the large-amplitude vibration problem of graphene sheets (GSs) embedded in an elastic medium under various kinds of boundary conditions. By HCB, a linkage is established between the deformation of the atomic structure and macroscopical deformation gradients without any parameter fitting. The elastic foundation is formulated according to the Winkler–Pasternak model which considers both normal pressure and transverse shear stress effects. The weak form of nonlinear governing equations is derived via a variational approach, namely based on the variational differential quadrature (VDQ) method and Hamilton’s principle. In order to solve the obtained equations, a numerical scheme is adopted in which the generalized differential quadrature (GDQ) method together with a numerical Galerkin technique is utilized for discretization in the space domain, and the time-periodic discretization method is used to discretize in the time domain. The effects of the arrangement of atoms, the Winkler and Pasternak coefficients of the elastic foundation, and boundary conditions on the frequency–response curves of GSs are illustrated. It is revealed that the nonlinear effects on the response of GSs with larger size in armchair direction are less important. © 2019, Springer-Verlag GmbH Austria, part of Springer Nature.
Publication Date: 2019
Composite Structures (02638223)222
In this work, the large-amplitude free and forced vibrations of functionally graded carbon nanotube reinforced composite (FG-CNTRC) conical shells are investigated based on the higher-order shear deformation theory. In order to obtain the governing equations, the metricized energy functional of the structure is presented based on the higher-order shear deformation theory (HSDT) and von-Karman geometric nonlinearity. Then, the variational differential quadrature (VDQ) method is adopted to present the discretized energy functional. The numerical time differential operators together with the arc-length continuation scheme are utilized to solve the governing equations and find the free and forced vibration responses. In order to evaluate the influences of reinforcement factors and geometrical parameters on the nonlinear vibration behavior, various numerical results are reported. The numerical results reveal that the increase of semi-vertex angle of the shell increases the nonlinear to linear frequency ratio. © 2019 Elsevier Ltd
Publication Date: 2019
European Journal of Mechanics, A/Solids (09977538)73pp. 144-160
In the present study, based on the higher-order shear deformation plate theory, the unified numerical formulation is developed in variational framework to investigate the thermal buckling of different shapes of functionally graded carbon nanotube reinforced composite (FG-CNTRC) plates. Since the thermal environment has considerable effects on the material properties of carbon nanotubes (CNTs), the temperature-dependent (TD) thermo-mechanical material properties are taken into account. In order to present the governing equations, the quadratic form of the energy functional of the plate structure is derived and its discretized counterparts are presented employing the variational differential quadrature (VDQ) approach. The discretized equations of motion are finally obtained based on Hamilton's principle. In order to convenient application of differential quadrature numerical operators in irregular physical domain, the mapping procedure is considered in accordance to the conventional finite element formulation. Some comparison and convergence studies are performed to show validity and efficiency of the proposed approach. A wide range of numerical results are also reported to analyze the thermal buckling behavior of different shaped FG-CNTRC plates. © 2018 Elsevier Masson SAS
Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(9)pp. 816-824
Finite element modeling approach is used here to investigate the behavior of concentric multi-walled boron-nitride and carbon nanotubes under the compressive loadings. Double-walled and triple-walled concentric boron-nitride and carbon nanotubes with different arrangements and geometries are considered. It is shown that multi-walled boron-nitride nanotubes lose their stabilities at larger compressive forces than other arrangements in which at least one carbon wall exists. Comparing the armchair and zig-zag multi-walled nanotubes, the latter one has larger buckling force than the former one. It is also shown that the nanotubes with smaller radii have larger critical compressive forces than those with larger radii. © 2018, © 2018 Taylor & Francis Group, LLC.
Publication Date: 2019
Superlattices and Microstructures (10963677)135
The density functional theory is used here to investigate the elastic and plastic properties of the pristine and adsorbed bismuthene. The H, F, Cl and Br atoms are considered as the adsorbing atoms. The elastic moduli of the pristine and adsorbed nanosheet under uniaxial loading and their bulk moduli under biaxial strain are computed. It is shown that, adsorbing the bismuthene nanosheet by the mentioned atoms leads to decreasing its elastic and bulk moduli. The influence of the adsorption on the elastic modulus of the bismuthene is more prominent than its effect of the bulk modulus. Furthermore, it is shown that the yield strain of the bismuthene nanosheet under the uniaxial loading decreases by the adsorption. For the yield strain under the biaxial loading, a unique behavior is not observed. © 2019 Elsevier Ltd
Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)43pp. 285-294
In this article, the vibrational behavior of beam-type microstructures made of carbon nanotube-reinforced composite is studied based on a finite element approach accounting for micro-/nanoscale effects. It is considered that the surface of microbeams is perfectly bonded with a piezoelectric actuator layer. First, the random distribution of CNTs into the polymer matrix is modeled using a three-phase representative volume element (RVE), and the properties of CNT-reinforced polymer are determined for various volume fractions of CNT. In the selected RVE, the interphase region formed due to the interaction between CNTs and the matrix is taken into account. In the next step, natural frequencies of composite piezoelectric microbeams subject to different end conditions are calculated. The influences of CNT volume fraction, interphase, boundary conditions and geometrical properties on the results are investigated. © 2018, Shiraz University.
Publication Date: 2019
Journal of Molecular Graphics and Modelling (10933263)89pp. 74-81
In this article, molecular dynamics (MD) simulations are utilized to investigate the buckling behavior of carbon nanotubes (CNTs) containing ice nanotubes in the vacuum and aqueous environment. The obtained results show that unlike the critical strain, the critical buckling load of CNT containing ice nanotube is higher than that of pure CNT in the vacuum. It is also indicated that the sensitivity of critical buckling load and the critical strain of CNT containing ice nanotube to the variation of length decreases when the nanostructure is subjected to the aqueous environment. Additionally, it is observed that the calculated critical buckling load and the critical strain of CNTs filled with ice nanotubes in the aqueous environment are respectively larger and smaller than those obtained in the vacuum. It is further observed that CNTs lose their symmetric buckling mode shape as they are filled with ice nanotubes in the vacuum. The results of these simulations can be used as a benchmark for further studies in designing novel potential applications such as proton electronic-based nanoelectromechanical systems (NEMS). © 2019 Elsevier Inc.
Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)43pp. 603-620
This paper presents a unified higher-order shear deformable plate model to numerically examine the nonlinear vibration behavior of thick and moderately thick polymer nanocomposite rectangular plates reinforced by graphene platelets (GPLs). Four distribution patterns of graphene nanoplatelet nanofillers across the plate thickness are considered. The effective material properties of graphene platelet-reinforced polymer (GPL-RP) nanocomposite plate are approximately calculated by employing the modified Halpin–Tsai model and rule of mixture. Using a generalized displacement field, a unified mathematical formulation is derived based on Hamilton’s principle in conjunction with von Kármán geometrical nonlinearity. By selecting appropriate shape functions, the proposed unified nonlinear plate model can be reduced to that on the basis of Mindlin, Reddy, parabolic, trigonometric and exponential shear deformation plate theories. The investigation of nonlinear vibration behavior is performed by employing a multistep numerical solution approach. In this regard, the discretization process is done through the generalized differential quadrature method. Then, the discretized governing equations are solved by employing the numerical-based Galerkin technique, periodic time differential operators and pseudo-arc length continuation algorithm. A detailed parametric study is carried out to examine the effect of GPL distribution pattern, weight fraction, geometry of GPL nanofillers and boundary constraints on the nonlinear vibration characteristics of the GPL-RP nanocomposite rectangular plates. © 2018, Shiraz University.
Publication Date: 2019
Scientia Iranica (23453605)26(6F)pp. 3857-3874
This paper studies the free vibration characteristics of post-buckled Functionally Graded (FG) carbon nanotube (CNT) reinforced annular plates. The analysis was performed by employing a Generalized Differential Quadrature (GDQ)-type numerical technique and pseudo-arc length scheme. The material properties of FG-carbon nanotube reinforced composite (CNTRC) plates were evaluated by an equivalent continuum approach based on the modified rule of mixture. The vibration problem was formulated based on the First-order Shear Deformation Theory (FSDT) for moderately thick laminated plates and von Karman nonlinearity. By employing Hamilton's principle and a variational approach, the nonlinear equations and associated Boundary Conditions (BCs) were derived, which were then discretized by the GDQ method. The postbuckling behavior was investigated by plotting the secondary equilibrium path as the deection-load curves. Thereafter, the free vibration behaviors of pre- A nd post-buckled FG-CNTRC annular plates were examined. Effects of different parameters including types of BCs, CNT volume fraction, an outer radius-to-thickness ratio, and an inner-to-outer radius ratio were investigated in detail. © 2019 Sharif University of Technology. All rights reserved.
Mahmoodi m.j., M.J.,
Hassanzadeh-aghdam, M.K.,
Ansari, R. Publication Date: 2019
International Journal of Mechanics and Materials in Design (15691713)15(3)pp. 539-554
A physics-based nested hierarchical approach is established to investigate thermal conducting behavior of micro-filler (in the form of particle, short and long fiber)/nanoparticle-reinforced polymer hybrid nanocomposites. An effort is made to develop a unit cell-based micromechanical model predicting the thermal conductivities of general composite systems, including microscale filler-reinforced composites, nanoparticle-reinforced nanocomposites and microscale filler/nanoparticle-reinforced hybrid nanocomposites. The role of the nanoparticle/polymer interfacial thermal resistance is also considered in the analysis. The developed model presents a reasonable behavior compared with available experiments and other modeling methods for the thermal properties of composites and nanocomposites. The results are provided for two types of hybrid nanocomposites, including carbon micro-filler/silica (SiO2) nanoparticle-reinforced epoxy and glass micro-filler/SiO2 nanoparticle-reinforced epoxy systems. It is found that transverse thermal conducting behavior of general fibrous composites is significantly affected by adding the nanoparticles. However, due to the dominated role of the carbon fiber in the longitudinal direction, the longitudinal thermal conductivity of carbon fiber-reinforced composites is not influenced by the nanoparticles. Also, the thermal conductivities of both randomly oriented short fiber-reinforced composite and particulate composite systems can be improved with the addition of the nanoparticles. The obtained results could be useful to guide the design of hybrid nanocomposites with optimal thermal conductivities. © 2018, Springer Nature B.V.
Blooriyan s., ,
Ansari, R.,
Darvizeh a., A.,
Gholami, R.,
Rouhi h., H. Publication Date: 2019
Applied Mathematics and Mechanics (English Edition) (02534827)40(7)pp. 1001-1016
An analytical approach is proposed to study the postbuckling of circular cylindrical shells subject to axial compression and lateral pressure made of functionally graded graphene platelet-reinforced polymer composite (FG-GPL-RPC). The governing equations are obtained in the context of the classical Donnell shell theory by the von Kármán nonlinear relations. Then, based on the Ritz energy method, an analytical solution approach is used to trace the nonlinear postbuckling path of the shell. The effects of several parameters such as the weight fraction of the graphene platelet (GPL), the geometrical properties, and distribution patterns of the GPL on the postbuckling characteristics of the FG-GPL-RPC shell are analyzed. © 2019, Shanghai University and Springer-Verlag GmbH Germany, part of Springer Nature.
Blooriyan s., ,
Ansari, R.,
Darvizeh a., A.,
Gholami, R.,
Rouhi h., H. Publication Date: 2019
Materials Research Express (20531591)6(9)
An analytical approach is developed to study the pre- A nd post-buckling responses of circular cylindrical nanoscale shells subjected to lateral and axial loads as well as thermal environment. The effect of surface free energy as one of the key nanoscale effects is considered in the context of Gurtin-Murdoch surface elasticity theory. The nanoshell is made of functionally graded materials (FGMs) whose properties are calculated using power-law functions. The basic formulation is derived according to the classical shell theory together with the von-Karman nonlinear relations. Moreover, the physical neutral plane position is taken into consideration. Using the Ritz energy method, an analytical approach is also proposed to solve the problem. Comprehensive numerical results are presented to investigate the behavior of nanoshell under lateral pressure and axial load in thermal environment, in pre- A nd post-buckling domains. The influences of various parameters including the surface stress, FGM gradient index, temperature and geometrical parameters on the non-linear critical axial stress/lateral pressure are illustrated. © 2019 IOP Publishing Ltd.
Publication Date: 2019
Composites Part B: Engineering (13598368)167pp. 728-735
A two-step analytical electrical conductivity method is adopted to calculate the effective electrical conductivity of the carbon fiber (CF)-carbon nanotube (CNT)-polymer hybrid composite. First, CNTs are dispersed into the non-conducting polymer matrix and the electrical conductivity of the CNT-polymer composite is obtained. Then, CFs are randomly distributed in the CNT-polymer composite and the effective electrical conductivity of CF-CNT-polymer hybrid composite is estimated. The effect of critical parameters, including the volume fraction, alignment, agglomerated state and aspect ratio of the CNTs and the potential barrier height of the polymer on the hybrid composite electrical conductivity is evaluated. Also, the influence of the content and aspect ratio of CFs on the electric conductive behavior of the polymer hybrid composites is investigated. The results show that the polymer hybrid composite with larger aspect ratio and off alignment of CNTs presents a higher electrical conductivity. © 2019 Elsevier Ltd
Saffar a., ,
Darvizeh a., A.,
Ansari, R.,
Kazemi a., ,
Alitavoli, M. Publication Date: 2019
Journal of Failure Analysis and Prevention (18641245)19(6)pp. 1801-1814
In recent years, fibrous composite materials have been used to repair pipelines in combination with commonly employed standards such as ASTM B31G and ASTM PCC2. Reinforcement and repair of pipelines without interruption are the advantages of these new methods. Pipe repair by composite patches with considering various types of surface damages and crack has been investigated in many previous works. In the present paper, a comprehensive model has been developed to predict the critical pressure for several defect types in static pressure loading condition using the ABAQUS finite element software. The effect of various defect patterns in API X65 Grade steel pipes is investigated by a ductile damage criterion. The obtained results are assessed using available experimental data. The first ply failure theory is employed to predict failure in composite patches. The effects of boundary conditions are considered using a semi-infinite element. The results generated from finite element simulations are compared with those from ASTM PCC2 standard. Moreover, the required minimum patch thickness for different live internal pressures is proposed. The extended finite element method is also applied to study the effect of patch layer thickness on crack propagation. The effect of initial crack angle on the critical internal pressure with and without patch is investigated too. The results indicate that the z symmetric boundary conditions are appropriate for pipelines. The estimation of the burst pressure using a ductile damage criterion is shown to be in good agreement with experimental data and ASME B31G. Furthermore, the estimated values for patch layer thickness obtained by the present approach agree well with ASME PCC2 standard. The obtained results also clearly indicate that using composite patches has no considerable influence on prevention of crack propagation. © 2019, ASM International.
Samadani f., F.,
Ansari, R.,
Hosseini, K.,
Zabihi, A. Publication Date: 2019
Communications in Theoretical Physics (02536102)71(3)pp. 349-356
The current paper presents a thorough study on the pull-in instability of nanoelectromechanical rectangular plates under intermolecular, hydrostatic, and thermal actuations. Based on the Kirchhoff theory along with Eringens nonlocal elasticity theory, a nonclassical model is developed. Using the Galerkin method (GM), the governing equation which is a nonlinear partial differential equation (NLPDE) of the fourth order is converted to a nonlinear ordinary differential equation (NLODE) in the time domain. Then, the reduced NLODE is solved analytically by means of the homotopy analysis method. At the end, the effects of model parameters as well as the nonlocal parameter on the deflection, nonlinear frequency, and dynamic pull-in voltage are explored. © 2019 Chinese Physical Society and IOP Publishing Ltd.
Publication Date: 2019
Iranian Journal of Health and Environment (20083718)12(3)pp. 383-396
Background and Objective: Due to the existence of industries such as stainless steel, the presence of nickel (II) ions in water and wastewater has been reported at high concentrations. Removal of nickel (II) ions from wastewater and the environment are of primary importance. In this study, iron (III) oxide nanoparticles were studied as an adsorbent for removal of Ni (II) ions from water in the batch equilibrium system. Materials and Methods: FT-IR, SEM and XRD techniques were used to characterize the structure of the sample. To determine the optimum adsorption, the effect of important parameters such as pH, contact time, adsorbent weight and initial concentration were investigated. Also, thermodynamic study (Gibbs standard energy variations, enthalpy and entropy), isothermal studies (absorption capacity) and kinetic studies (absorbent effect with time) were investigated. Results: The results showed that the magnetic adsorbent had the highest removal efficiency of nickel (II) at pH 7, contact time 60 min, adsorbent dosage of 200 mg, and maximum removable concentration of 400 mg/L. Conclusion: With thermodynamic studies, it was determined that the reaction was endothermic and the spontaneous process was controlled using the entropy factor (ΔG°=-2.7 KJ/mol, ΔS°=+165.17 J/mol.K). In order to better understand the mechanism of adsorption, kinetics studies were carried out using the pseudo-first-order and pseudo-second-order models. Then, Langmuir and Freundlich adsorption isotherms were investigated to determine the adsorption capacity, and it was found that the adsorption data were well fitted to Freundlich model and the maximum adsorption capacity was 43.5 mg/g, which indicated high adsorption capacity and its multi-layers.Then, Langmuir and Freundlich adsorption isotherms were investigated and it was found that the adsorption data were well fitted to Freundlich model and maximum adsorption capacity (qmax =43.5 mg/g) was obtained which indicates good adsorption capacity of adsorbent and its multi-layers. © 2019, Tehran University of Medical Sciences. All rights reserved.
Publication Date: 2019
Thin-Walled Structures (02638231)144
In this study, the postbuckling analysis of functionally graded graphene platelets reinforced composite (FG-GPLRC) cylindrical shells is presented. The continuous uniform and functionally graded distribution of GPLs is considered through the thickness direction of the shell. In order to present the effective mechanical properties of GPL-reinforced composites the modified Halpin-Tsai micromechanical model is taken into account. On the basis of first-order shear deformation shell theory and von-Karman geometrically nonlinear relations, the nonlinear governing equations are present in the context of the variational formulation. Employing the Fourier series and variational differential quadrature (VDQ) numerical approach, the semi-analytical solution methodology is further presented. The pseud arc-length continuation method in conjunction with a load disturbance approach was utilized to solve the nonlinear governing equations and trace the postbuckling path. Note that based on the proposed formulation, the mode changes and secondary buckling can be considered through the postbuckling path. The results indicate that in addition to geometrical parameters, distribution patterns and weight fractions of GPLs have significant effects on the buckling and postbuckling characteristics of FG-GPLRC cylindrical shells. © 2019 Elsevier Ltd
Gholami y., Y.,
Gholami, R.,
Ansari, R.,
Rouhi h., H. Publication Date: 2019
International Journal for Multiscale Computational Engineering (15431649)17(6)pp. 583-606
Using a numerical variational approach, the nonlinear bending and postbuckling problems of rectangular plates made of nanocrystalline materials (NCMs) are addressed in this paper. The most general form of strain gradient theory is utilized in order to consider small-scale influences. Employing a micromechanical model, the effective properties of NCMs are calculated. Moreover, the plates are modeled based on the first-order shear deformation theory (FSDT) and the von Kármán hypothesis. The variational differential quadrature (VDQ) technique is applied to obtain and discretize the weak-form governing differential equations. In order to obtain the nonlinear bending and postbuckling responses, the pseudo-arc-length continuation algorithm is employed to solve the resulting discretized nonlinear equations. The effects of thickness-to-length scale ratio, average inclusion radius, the volume fraction of the inclusion phase, length-to-thickness ratio, and density ratio on the nonlinear bending, and postbuckling responses of plates under various boundary conditions are investigated. © 2019 by Begell House, Inc.
Publication Date: 2019
Europhysics Letters (02955075)125(4)
Based on the classical molecular-dynamics (MD) simulations, the vibrational behavior of cross-linked functionalized carbon nanotubes (CNTs) with polyethylene (PE) chains is studied under the applied mechanical tensile and compressive strains. So, different distribution patterns, namely mapped and wrapped distribution patterns are chosen. According to the results, it is seen that natural frequency of cross-linked functionalized CNTs reduces in which this reduction increases by increasing the weight percentage of attached chain. Under tensile strain, it is observed that the frequency of functionalized CNTs increases. Moreover, it is observed that the frequency shifts rise by increasing the applied tensile strain. By contrast, the compressive strain results in higher reductions in natural frequency of functionalized CNTs which considerably rises by increasing the applied strain. Moreover, it is shown that as the weight percentage of cross-linked functionalized CNTs increases, the sensitivity of the frequency shift to the applied tensile and compressive strains decreases and increases, respectively. © 2019 EPLA.
Publication Date: 2019
Materials Research Express (20531591)6(4)
The endohedral functionalization of single-walled carbon nanotubes with molecular species, nanowires (NWs) and nanoparticles is of great importance for fabrication and development of nanoelecronic devices, drug delivery and energy storage applications. This research intends to explore the axial buckling behavior of the endohedrally functionalized single-walled carbon nanotubes (SWCNTs) by various metallicNWs(mNW@SWCNT), i.e. aluminum, copper, iron, sodium, nickel (AlNW, CuNW, FeNW, NaNW,NiNW), considering all possible pentagonal configurations. Employing the molecular dynamics (MD) simulations, the results demonstrate that the structurally stable radius of SWCNTs for successful endohedral functionalization of SWCNTs with pentagonal NWsare different. Considering buckling analysis of models, it is observed that NWs, solely, cannot tolerate any axial compressive load and their structure becomes dramatically unstable under mechanical force. By insertingNWsinside SWCNTs, their pentagonal structures during simulation are preserved due to Vdw interaction ofNWandSWCNTuntil buckling occurs. Moreover, the buckling simulation results indicate that by increasing the length, the critical force ofmNW@SWCNT decreases and approximately tends to that of pure SWCNTs which is more considerable for AlNWs. Also, in the particular length, the encapsulation ofNWsinside the SWCNTs causes a considerable increase in the critical buckling forces particularly in smaller lengths. According to the attained results, functionalization of SWCNTs with E and S configuration of AlNWs improves the structural stability of SWCNTs more pronounced than other pentagonal NWs. ©2019 IOP Publishing Ltd.
Publication Date: 2019
Journal of Physics and Chemistry of Solids (00223697)131pp. 79-85
Modifying the intrinsic properties of carbon nanotubes (CNTs) through functionalization is of great interest. Also, mechanical behavior is of great importance in designing and analyzing nanoelectromechanical systems (NEMS) and nanocomposites. In this research, the structural properties and buckling behavior of functionalized single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) with pyrene-linked polyamide in vacuum and aqueous environments are investigated utilizing the classical molecular dynamics (MD) simulations. The gyration radius, critical force and critical strain of functionalized SWCNTs and DWCNTs are obtained and the effects of the weight percentage of functional group, radius and simulation environments on these parameters are explored. According to the results, it is observed that the gyration radius increases as the weight percentage of functional groups increases. Moreover, it is observed that the presence of water molecule in the simulation environments results in more expansion of functional group around the CNTs. Moreover, it is observed that the critical buckling force of functionalized CNTs is higher than that of pure CNTs and increases as the weight percentage increases. It is further observed that the presence of water molecules increases the critical force of functionalized CNTs, whereas its variation with the weight percentage decreases. Finally, it is demonstrated that although the critical strain of functionalized CNTs decreases, the weight percentage of functional group and the presence of water molecules do not have a considerable effect on the critical strain of functionalized CNTs. Furthermore, one can use these findings in designing and fabricating efficient NEMS and nanocomposites. © 2019 Elsevier Ltd
Publication Date: 2019
Toxicology Reports (22147500)6pp. 590-597
In this study, Prunus Cerasus Rock (PCR) and Poly (Styrene – co- Maleic Anhydride) modified with Melamine-Oxalic acid (SMA-MO) were used to prepare a cheap adsorbent through chemical modification. The maximum removal was observed at pH = 6.0 and adsorbent dose 1.5 g/L for initial Nickel -ions concentration 30 mg/L. Study of temperature effect proved that the process is endothermic. Langmuir and Freundlich isotherm models were used for equilibrium adsorption data. Langmuir isotherm proved to be a better fit. Pseudo first order and pseudo second order kinetic models were applied to analyze the kinetic mechanism of adsorption. © 2019
Publication Date: 2019
Journal Of Molecular Modeling (16102940)25(11)
Tensile properties such as Young’s modulus and ultimate tensile force are important properties in understanding the characteristics of nanocomposites. Besides, the importance of functionalization methods in modification of the unique mechanical and elastic properties of carbon nanotubes (CNTs) is being widely recognized. In this paper, the tensile properties of CNTs functionalized with carbene under physisorption of polymer chains, i.e., aramid and polyketone chains, are investigated by using a series of molecular dynamics (MD) simulations. The results illustrated that Young’s modulus of carbene-functionalized CNTs (cfCNTs) decreases by rising the weight percentage of carbene. By contrast, Young’s modulus of cfCNTs under physisorption of polymer chains (cfCNTs/polymers) increases as the carbene weight rises. In a particular carbene weight, Young’s modulus of cfCNTs/polymers decreases by increasing the chains of non-covalent functional groups. Moreover, it is shown that similar to Young’s modulus, ultimate tensile force of cfCNTs reduces by increasing the weight percentage of carbene whereas the ultimate tensile force of cfCNTs/polymers has an increasing trend with raising the carbene weight. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.
Parsapour h., H.,
Ajori, S.,
Ansari, R.,
Haghighi s., S. Publication Date: 2019
Diamond and Related Materials (09259635)92pp. 117-129
Young's modulus and the fracture of gold nanowires (GNWs) encapsulated inside single-walled carbon nanotubes (SWCNTs) are studied using molecular dynamics (MD) simulations. To investigate the mechanical behavior, two important parameters, i.e. ultimate tensile force and strain, are calculated. The obtained results from aforementioned nanostructures are compared with those of pure GNWs and SWCNTs. The results illustrate that SWCNTs filled with GNWs (GNWs@SWCNTs) and pure GNWs possess lower Young's moduli than those of pure SWCNTs in a similar length. As the length increases, Young's modulus of pure GNWs and GNWs@SWCNTs is reduced. In a particular length, the highest and lowest ultimate forces belong to the multishell GNWs@SWCNTs and pure multishell GNWs, respectively. Moreover, it is found that pure SWCNTs have the highest ultimate strains. Also, by rising the length, the ultimate tensile strain increases. To study the effect of selected boundaries on the tensile characteristics, the tensile loads are applied to the boundaries of surrounding SWCNTs instead of whole configuration (B model). The obtained results demonstrated that in the similar length, Young's modulus and ultimate force for B model are higher than those of A model, i.e. the model that the whole system is under the tensile loads. By contrast, in the particular length, B model shows lower ultimate strain compared to that of A model. © 2018 Elsevier B.V.
Publication Date: 2019
European Physical Journal D (14346060)73(8)
Abstract: As an inorganic quasi-1D nanostructure with non-cytotoxic properties, boron-nitride nanotubes have been the center of interest to researchers due to their high potential biocompatible applications. Due to the importance of functionalization in designing novel devices, the mechanical properties and buckling behavior of functionalized single- and double-walled boron-nitride nanotubes with 2-methoxy-N,N-dimethylethanamine (MDE) are investigated using molecular dynamics (MD) simulations. The calculated results demonstrate that Young’s moduli of BNNTs reduce, while critical buckling force and critical strain of BNNTs increase as MDE are attached to BNNTs. Moreover, it is observed that by increasing the MDE weight percentage, critical buckling force and critical strain of functionalized BNNTs reduce, unlike Young’s modulus. It is also observed that variations of the aforementioned parameters corresponding to DWBNNTs are less sensitive to MDE weight percentage compared to SWBNNTs and they lie between its inner and outer constituent functionalized SWBNNTs. Moreover, snapshots of buckling mode shapes of functionalized BNNTs are presented. Graphical abstract: [Figure not available: see fulltext.]. © 2019, EDP Sciences / Società Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2019
Computers and Mathematics with Applications (08981221)77(5)pp. 1294-1311
The main objective of the present study is to analyze the thermal buckling of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) quadrilateral plates. Functionally graded patterns are introduced for the distribution of the carbon nanotubes (CNTs) through the thickness direction of the plate. The effective material properties of nanocomposite plate reinforced by CNTs are considered to be temperature-dependent (TD) and estimated using the micromechanical model. By the use of minimum total potential energy principle and based on the first-order shear deformation theory of plates, the stability equations are obtained. In order to use the generalized differential quadrature (GDQ) method and solve the stability equations, the irregular domain of quadrilateral plate is transformed into regular computational domain employing the mapping technique. The efficiency and accuracy of the proposed approach are first validated. Then, a comprehensive parametric study is presented to examine the effects of model parameters on the thermal buckling of FG-CNTRC quadrilateral plates. The results indicate that considering temperature dependency of the material properties plays an important role in the stability of the FG-CNTRC quadrilateral plates subjected to thermal loading. © 2018 Elsevier Ltd
Publication Date: 2019
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)43pp. 723-732
On the basis of a nonlocal shell model, the thermal buckling analysis of carbon nanocones (CNCs) is presented. Using Donnell’s strain–displacement relations and considering Eringen’s nonlocal elasticity theory, the stability equations of CNCs are derived. Employing the generalized differential quadrature method and trigonometric expansion in axial and circumferential directions of CNC, the stability equations are solved. The mechanical properties of CNCs such as Young’s modulus and Poisson’s ratio are dependent on the apex angle. To show the accuracy of the present study, some numerical results are compared with those reported in the literature. Furthermore, the effects of nonlocal parameter, length-to-radius ratio, boundary conditions and apex angle on the thermal buckling load of CNCs are examined. The results indicate that the thermal buckling load decreases by increasing the nonlocal parameter and apex angle. © 2018, Shiraz University.
Publication Date: 2019
Composites Part B: Engineering (13598368)162pp. 167-177
A new micromechanical formulation based on a unit cell model is developed to predict the effective thermal conductivities of carbon nanotube (CNT)-shape memory polymer (SMP) nanocomposites. Model predictions considering interfacial thermal resistance between the CNT and SMP, agglomerated state of CNTs into the SMP matrix and CNT non-straight shape are in reasonable agreement with the experiment reported in the literature. It is found that the CNT agglomeration must be removed to obtain a maximum level of thermal conductivities of SMP nanocomposites. The effects of volume fraction, diameter, cross-section shape, arrangement type and waviness factors of CNTs as well as interfacial thermal resistance on the axial and transverse thermal conductivities of aligned CNT-reinforced SMP nanocomposites are extensively investigated. The results show that the alignment of CNTs into the SMP nanocomposites along the thermal loading can be an efficient way to dissipate the heat. When the CNT waviness increases, a nonlinear decrease in the axial thermal conductivity is occurred, however, the nanocomposite thermal conductivity along the transverse direction quickly rises. It is observed that the interfacial thermal resistance, cross-section shape and arrangement type of CNTs do not affect the axial thermal conductivity of CNT-SMP nanocomposites. But, the interfacial thermal resistance can play a key role in the transverse nanocomposite thermal conductivity. The present fundamental study is very important for understanding the thermal conducting behavior of CNT-SMP nanocomposites which may have a wide range of applications in temperature sensing elements and biological micro-electro-mechanical systems. © 2018 Elsevier Ltd
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2019
Mechanics of Advanced Materials and Structures (15210596)26(22)pp. 1858-1869
Coefficient of thermal expansion (CTE) of shape memory polymer (SMP) nanocomposites reinforced with randomly dispersed wavy carbon nanotubes (CNTs) is investigated using a unit cell-based micromechanical approach. The influences of temperature, volume fraction and waviness characteristics of the CNT, thickness, and adhesion exponent of the CNT/SMP interphase zone on the SMP nanocomposite CTE are extensively studied. A great reduction is observed in the nanocomposite CTE with the addition of the CNT to the SMP. Good agreement is observed between the results of the presented model considering randomly dispersed wavy CNTs into the polymer and existing experimental data. © 2018, © 2018 Taylor & Francis Group, LLC.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J. Publication Date: 2019
Mechanics of Materials (01676636)129pp. 80-98
This work is aimed at a comprehensive characterization of thermoelastic properties of shape memory polymer (SMP) nanocomposites containing carbon nanotubes (CNTs) via a micromechanical model. Two critical aspects affecting the CNT/polymer nanocomposite overall behavior including, the non-straight shape of CNTs and an interphase region formed due to non-bonded van der Waals interactions between a CNT and the SMP are considered. The influences of volume fraction, diameter, aspect ratio, waviness of the CNTs, size and adhesion exponent of the interphase and temperature on the elastic moduli and coefficients of thermal expansion (CTEs) of the CNT/SMP nanocomposites are investigated. The results indicate that the SMP nanocomposite elastic moduli enhance with (i) increasing both the CNT volume fraction and interphase thickness and (ii) decreasing both the CNT diameter and interphase adhesion exponent. Also, the longitudinal elastic modulus of SMP nanocomposites can be significantly increased by using straight CNTs, whereas the transverse elastic modulus improves by employing wavy CNTs. It is observed that the SMP nanocomposite CTEs decrease with the increase in CNT volume fraction, whereas the CNT diameter effect on the thermal expansion response can be ignored. Generally, the results of the presented model are found to be in very good agreement with experiments. © 2018
Publication Date: 2019
International Journal of Mechanics and Materials in Design (15691713)15(3)pp. 471-488
In this research, the thermoelastic response of unidirectional carbon fiber (CF)-reinforced polymer hybrid composites containing carbon nanotubes (CNTs) are analyzed using a physics-based hierarchical micromechanical modeling approach. The developed model consists of a unit cell-based scheme along with the Eshelby method which can consider random orientation, random distribution, directional behavior, non-straight shape of CNTs and interphase region generated due to the non-bonded van der Waals interaction between a CNT and the polymer matrix. The predictions are compared with the experimental data available in the literature and a quite good agreement is pointed out for the fibrous polymer composite, CNT-polymer nanocomposite and fiber/CNT-polymer hybrid composite systems. The influences of several factors, including volume fraction, aspect ratio, off-axis angle and arrangement type of CFs as well as CNT volume fraction on the thermoelastic behavior of CF/CNT-polymer hybrid composites are examined in detail. The results indicate that the transverse CTE of a unidirectional CF-reinforced composite is significantly improved due to the addition of CNTs, while the hybrid composite CTE in the longitudinal direction is negligibly affected by the CNTs. Also, it is found that the role of CNT in the hybrid composite thermoelastic behavior becomes more prominent as the CF aspect ratio decreases. © 2018, Springer Nature B.V.
Publication Date: 2019
Materials Research Express (20531591)6(12)
The vibration analysis of functionally graded carbon nanotube-reinforced composite plates with the arbitrarily shaped cutout is presented using a novel numerical approach called variational differential quadrature finite element method (VDQFEM). The governing equations are expressed in matrix form based on Mindlin's plate theory. In the proposed numerical approach, the space domain of the plate is first transformed into a number of sub-domains known as finite elements. Then, the variational differential quadrature (VDQ) discretization method is used within each element to obtain the mass and stiffness matrices. In order to use the VDQ method, the irregular domain of the element is transformed into a regular one employing the mapping technique. Finally, the assemblage procedure is performed to present total mass and stiffness matrices. The introduced numerical approach can be effectively used for structural analysis of arbitrarily shaped plates. A wide range of comparative and convergence studies are outlined to show the performance of the method. It is observed that the numerical results are rapidly converged and the proposed solution strategy can be successfully applied to examine the vibration of FG-CNTRC plates with different cutouts. © 2019 IOP Publishing Ltd.
Shahabodini a., A.,
Gholami y., Y.,
Ansari, R.,
Rouhi h., H. Publication Date: 2019
European Physical Journal Plus (21905444)134(10)
In the present article, an atomistic-continuum multiscale model is developed to study the free-vibration response of single-layered graphene sheets (SLGSs) embedded in an elastic medium based upon the higher-order Cauchy-Born (HCB) rule. In order to take both transverse shear stress and normal pressure into account, the elastic foundation is considered to be of Winkler-Pasternak type. The governing equations are derived within a variational formulation using a newly proposed method called Variational Differential Quadrature (VDQ). Using the VDQ approach together with the Generalized Differential Quadrature (GDQ) technique, the variational form of the governing equation is discretized in a computationally efficient manner. Finally, a generalized eigenvalue problem is solved to calculate the frequencies of SLGSs. The convergence and correctness of the presented numerical solutions are examined firstly. Then, a number of numerical examples are given to study the effects of boundary conditions, elastic medium and arrangement of atoms on the vibrational response of SLGSs. The present model does not involve any additional phenomenological input, and it considers size effect and material nonlinearity due to atomic interactions. © 2019, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2019
Materials Research Express (20531591)6(4)
The present study deals with the vibration analysis of sandwich cylindrical shells with the functionally graded carbon nanotube reinforced composite (FG-CNTRC) face sheets resting on elastic medium under internal pressure. Two FG-CNTRC face sheets along with homogeneous core are considered as the sandwich cylindrical shell. The overall mechanical properties of CNT-reinforced composites are presented in accordance to the refined rule of mixture. Based on the higher-order shear deformation theory (HSDT) and in the context of the variational differential quadrature (VDQ) method, the discretized version of governing equations is provided. Validation of the proposed model is demonstrated. Several numerical results are also represented to study the impacts of various material and geometrical factors on the vibration analysis of sandwich cylindrical shells. The results reveal that in the case of constant total thickness, increasing the core-to-face sheet thickness ratio decreases the dimensionless frequencies. ©2019 IOP Publishing Ltd.
Publication Date: 2019
Composites Part B: Engineering (13598368)158pp. 169-178
The creep behavior of polyimide nanocomposites containing silica (SiO2) nanoparticles is investigated employing a unit cell-based micromechanical method. The interphase region created due to the interfacial interaction between polyimide matrix and nanoparticle is incorporated in the analysis. Both random and regular distributions of nanoparticles into the polymer nanocomposites can be included in the modeling. Comparison between the results of the proposed model shows a good agreement with existing experiment. The results reveal that for a more realistic prediction in the case of creep behavior of SiO2/polyimide nanocomposites, considering the viscoelastic interphase is essential. Additionally, at a high volume fraction, it is necessary to consider the viscoelastic interphase together with random distribution of nanoparticles into the matrix for providing accurate predictions. The micromechanical model is utilized to evaluate the creep behavior of SiO2 nanoparticle/polyimide nanocomposite under biaxial and triaxial loads. © 2018 Elsevier Ltd
Publication Date: 2018
Composite Structures (02638223)205pp. 69-85
The main objective of the present study is to develop a hexahedral C1 continuous element for the three-dimensional nonlinear free vibration analysis of rectangular nano-plates with circular cutout based on the strain gradient elasticity theory. In the proposed element, in addition to the values of displacement components, the corresponding first, mixed second and mixed third order derivatives are taken into account as nodal values. Since arbitrary-shaped hexahedral elements are considered, spatial derivatives are presented using isoparametric formulation. To derive the nonlinear governing equations, the matrix form of kinetic and strain energies are written based on the three-dimensional strain gradient elasticity theory which can be reduced to the modified strain gradient theory (MSGT) and the modified couple stress theory (MCST). The accuracy and convergence of the numerical results are first investigated. In the parametric study, the nonlinear free vibration response of nano-plate is studied for different length scale parameters, geometrical factors and boundary conditions. © 2018 Elsevier Ltd
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R. Publication Date: 2018
Journal of Alloys and Compounds (09258388)739pp. 164-177
A reliable and optimal design of metal matrix nanocomposites (MMNCs) reinforced by nanoscale particles critically requires establishing the accurate material-characterizing relations of such new systems. So, this paper presents an inclusive model to predict the elastic modulus, thermal expansion coefficient, yield strength and ultimate tensile strength of MMNCs containing nanoparticles. Size factor and the agglomerated state for the nanoparticles into the metal matrix, generation of dislocations by thermal mismatch and Orowan strengthening mechanism are considered in the analysis. The influence of volume fraction and diameter of nanoparticles, material properties of matrix and temperature difference on the MMNCs effective thermoelastic and strength properties are studied in detail. Generally, the predicted values match well with experimental data. The results prove that for accurate estimations of the elastic modulus and thermal expansion properties of the MMNCs reinforced with uniformly dispersed nanoparticles, the size factor must be considered. The more realistic characterizations of the yield strength and ultimate tensile strength of the MMNCs containing uniformly distributed nanoparticles could only be achieved with considering both thermal mismatch and Orowan strengthening mechanism. Additionally, when the nanoparticles are not well dispersed into the metal matrix, speculating the nanoparticles agglomerated state to acquire a more realistic prediction is critically essential. The MMNCs thermomechanical characteristics can be significantly improved by (i) increasing volume fraction, (iii) decreasing the nanoparticle diameter and (iii) uniform dispersion into the metal matrix. © 2017 Elsevier B.V.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J.,
Darvizeh a., A.,
Hajati-modaraei a., Publication Date: 2018
Cement and Concrete Composites (09589465)90pp. 108-118
The thermal conductivities of cementitious nanocomposites reinforced by wavy carbon nanotubes (CNTs) are determined by the effective medium (EM) micromechanics-based method. The nanocomposite is composed of sinusoidally wavy CNTs as reinforcement and cement paste as matrix. The interfacial region between the CNTs and cementitious material is considered in the analysis. The effects of volume fraction and waviness parameters of CNTs, interfacial thermal resistance, type of CNTs placement within the matrix including aligned or randomly oriented CNTs, cement paste properties on the thermal conductivity coefficients of the nanocomposite are studied. The estimated values of the model are in very good agreement with available experimental data. Two parameters of CNT waviness and interfacial region contributions should be included in the modeling to predict realistic results for both aligned and randomly oriented CNT-reinforced nanocomposites. The results reveal that thermal conductivities K22 (transverse in-plane thermal conductivity) and K33 (longitudinal in-plane thermal conductivity) of the nanocomposites are remarkably dependent on the CNT waviness. Also, it is found that the CNT waviness moderately affects the thermal conductivity of a cementitious nanocomposite containing randomly oriented CNTs. However, the non-straight shape of CNTs does not influence the value of thermal conductivity K11 (transverse out of plane thermal conductivity). The achieved results can be useful to guide the design of cementitious nanocomposites with optimal thermal conductivity properties. © 2018 Elsevier Ltd
Publication Date: 2018
Thin-Walled Structures (02638231)133pp. 169-179
A higher-order isoparametric superelement is developed to study the vibration of functionally graded shells of revolution. The effective material properties of functionally graded materials (FGMs) vary continuously along the thickness direction of the shell in accordance with the power law distribution. The governing equations are presented based on the three-dimensional elasticity theory using Hamilton's principle. Since the isoparametric formulation is considered, a unified formulation is presented for all types of shells of revolution. The properties of the FG shells are graded through the thickness direction, and consequently, the analysis of such structures is quite difficult using conventional three-dimensional finite elements. The proposed superelement facilitates the analysis of FG shell structures. Different types of circular shell structures including cylindrical, conical, spherical and circular toroid are considered in this study. To show the accuracy and efficiency of the proposed superelement, different comparative studies are presented. © 2018 Elsevier Ltd
Publication Date: 2018
Applied Surface Science (01694332)427pp. 704-714
The buckling behavior of cross-linked functionalized carbon nanotubes (CNTs) with polyethylene (PE) chains under physical adsorption of polymers (cfCNTs/polymer) is studied by classical molecular dynamics (MD) simulations, and the results are compared with those for the pure CNTs under the physical adsorption of polymers. Considering non-covalent functionalization, the effect of type of functional group, i.e. aramid and PE chains, on the interactions between polymers and cfCNTs is investigated. Based on the results, the gyration radius of cfCNTs/polymer increases by raising the weight percentage of non-covalent polymer chains. Also, the simulation results for most cases demonstrate that the gyration radius of cfCNTs/polymer is larger than that of pure CNTs/polymer for the similar weight percentage of non-covalent polymer chains. Moreover, the critical buckling force and the critical buckling strain of the cfCNTs/polymer are lower than those of pure CNT/polymer for the similar weight percentage of non-covalent polymer chains, although some exceptions can be observed. Besides, by raising the weight percentage of non-covalent polymer chains, the critical buckling force cfCNTs/polymer increases for a specific weight percentage of cross-linked PE chains. © 2017 Elsevier B.V.
Publication Date: 2018
European Physical Journal D (14346060)72(2)
Abstract: The thermal conductivity of endohedrally functionalized single-walled carbon nanotubes (SWCNTs) with gold nanowires (GNWs) is studied by using a series of molecular dynamics (MD) simulations. The effect of geometrical parameters, i.e. length and radius of pure SWCNTs/GNWs/SWCNTs filled with GNWs on the thermal conductivity are investigated. Also, the influence of various structures of GNWs such as pentagonal and multishell-GNWs on the thermal conductivity of the system is explored. The results indicate that as the length of the system rises, the thermal conductivity increases. It is also found that the thermal conductivity of GNWs is considerably lower than that of pure SWCNTs and GNWs@SWCNTs at a constant length of SWCNT or GNWs. For long pure SWCNTs, by increasing the radii of nanotubes, the thermal conductivity increases. Moreover, the thermal conductivity of the multishell-GNWs@SWCNTs is obtained higher than that of pentagonal configurations for the same lengths of SWCNTs. Through inserting the GNWs inside the SWCNTs, by maintaining the natural properties of NWs due to endohedral functionalization, the thermal conductivity is increased. This finding can be used as a benchmark for more efficient design of NEMS based on metallic NWs. Graphical abstract: [Figure not available: see fulltext.]. © 2018, EDP Sciences, SIF, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
Applied Mathematical Modelling (0307904X)53pp. 653-672
Nonlinear vibration analysis of circular cylindrical shells has received considerable attention from researchers for many decades. Analytical approaches developed to solve such problem, even not involved simplifying assumptions, are still far from sufficiency, and an efficient numerical scheme capable of solving the problem is worthy of development. The present article aims at devising a novel numerical solution strategy to describe the nonlinear free and forced vibrations of cylindrical shells. For this purpose, the energy functional of the structure is derived based on the first-order shear deformation theory and the von–Kármán geometric nonlinearity. The governing equations are discretized employing the generalized differential quadrature (GDQ) method and periodic differential operators along axial and circumferential directions, respectively. Then, based on Hamilton's principle and by the use of variational differential quadrature (VDQ) method, the discretized nonlinear governing equations are obtained. Finally, a time periodic discretization is performed and the frequency response of the cylindrical shell with different boundary conditions is determined by applying the pseudo-arc length continuation method. After revealing the efficiency and accuracy of the proposed numerical approach, comprehensive results are presented to study the influences of the model parameters such as thickness-to-radius, length-to-radius ratios and boundary conditions on the nonlinear vibration behavior of the cylindrical shells. The results indicate that variation of fundamental vibrational mode shape significantly affects frequency response curves of cylindrical shells. © 2017 Elsevier Inc.
Publication Date: 2018
International Journal of Computational Materials Science and Engineering (2047685X)7(3)
In this paper, the free vibration and buckling behaviors of nanoscale beams with different boundary conditions are analyzed using the integral formulation of Eringen's nonlocal elasticity theory. To this end, both strain- A nd stress-driven nonlocal integral models are employed. The nanobeams are modeled according to the Euler-Bernoulli beam theory. Moreover, a novel numerical approach is proposed for solving the obtained governing equations. By this numerical method, which uses matrix differential and integral operators, the integral governing equation is directly solved and the difficulties related to converting the integral governing equation into the differential one are bypassed. Comparisons are made between the predictions of strain and stress-driven models about the vibration and buckling responses of nanobeams subject to various end conditions. The results indicate that based on the stress-driven model, the frequency and critical buckling load increase with increasing the nonlocal parameter, whereas they decrease when the strain-driven integral model is used. © 2018 World Scientific Publishing Europe Ltd.
Publication Date: 2018
Journal of Alloys and Compounds (09258388)767pp. 632-641
In the present work, elastic modulus of a hybrid aluminum matrix nanocomposite (HAMNC) reinforced with silicon carbide (SiC) whiskers and SiC nanoparticles is analyzed. To this end, a new multi-scale analytical model is developed to calculate the effective elastic modulus of the HAMNC. The SiC nanoparticle aggregation into the HAMNC, frequently encountered in real engineering situations, is simulated. The elastic modulus of HAMNC estimated by the analytical micromechanical model is compared with that directly measured by the experimental method and a good agreement is found between the two sets of results. The effects of volume fraction, aspect ratio and dispersion type of SiC whiskers as well as volume fraction, size and aggregation degree of SiC nanoparticles on the HAMNC elastic modulus are extensively investigated. It is found that the elastic modulus of the SiC whisker-reinforced composite is significantly improved due to the addition of SiC nanoparticles. The results show that the nanoparticle aggregation has a damaging effect on the HAMNC elastic modulus. It is observed that the HAMNC elastic modulus can be enhanced by (i) increasing SiC content, (ii) aligning the SiC whiskers, (iii) increasing the SiC whisker aspect ratio (iv) decreasing the SiC nanoparticle size and (v) uniform dispersion of SiC nanoparticles into the hybrid nanocomposite. The reported results by means of the analytical model can be actually useful to guide design of general hybrid metal matrix nanocomposites with superior effective properties. © 2018 Elsevier B.V.
Publication Date: 2018
Mechanics of Advanced Materials and Structures (15210596)25(6)pp. 500-511
Employing the variational differential quadrature (VDQ) method, the effects of initial thermal loading on the vibrational behavior of embedded single-walled carbon nanotubes (SWCNTs) based on the nonlocal shell model are studied. According to the first-order shear deformation theory and considering Eringen's nonlocal elasticity theory, the energy functionality of the system is presented and discretized using the VDQ method. The effects of thermal loading and elastic foundation are simultaneously taken into account. The use of the numerical discretization technique in the context of variational formulation reduces the order of differentiation in the governing equations and consequently improves the convergence rate. The accuracy of the present model is first checked by comparison with molecular dynamics simulation results and those of other methods. The effects of involved parameters are then investigated on the fundamental frequencies of thermally preloaded embedded SWCNTs. The results imply that the thermal loading has a significant effect on the vibration analysis of embedded SWCNTs. © 2018 Taylor & Francis Group, LLC.
Arjangpay a., ,
Darvizeh a., A.,
Yarmohammad tooski m., ,
Ansari, R. Publication Date: 2018
Composite Structures (02638223)184pp. 327-336
The low velocity impact response of a novel foam-based composite structure inspired by microstructural features of dragonfly wings is investigated through the use of FE model and experiments. A nonlinear progressive damage model of the composite skins is incorporated into the FE code by VUMAT subroutine. Inter-laminar damage is reproduced using interface cohesive elements and the foam core is modeled as a crushable foam material. The numerical results are compared with experimental data acquired by impact testing on bio-inspired structures consisting of E-glass/epoxy skins filled by polyurethane foam, where a good agreement is achieved. To assess the contribution of the sandwich vein on the impact behavior of the structure, a comparison is made between different veiny structures and monolithic laminates with the same materials under low velocity impact. It is concluded that the sandwich vein can limit the damage propagation and makes the rest of the structure remain intact. © 2017 Elsevier Ltd
Gholami, R.,
Darvizeh a., A.,
Ansari, R.,
Pourashraf t., Publication Date: 2018
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)42(2)
Mindlin’s strain gradient theory (SGT) is the most popular size-dependent higher-order gradient elasticity theory capable of describing the mechanical behavior of structures at micro-/nanoscale, in which the strain gradient terms are included in the strain energy density. In this article, based on Mindlin’s SGT and classical Donnell’s shell theory, the sizedependent nonlinear postbuckling characteristics of circular cylindrical micro-/nanoscale shells under the action of axial compressive loads are studied. For some specific values of the gradient-based material parameters, the present general micro-/nano-shell formulation can be reduced to those based on simple forms of the strain gradient elasticity theory such as the modified strain gradient theory and the modified couple stress theory. The micro-/nano-shells are assumed to be made from functionally graded materials whose properties vary across the thickness direction based on a power-law distribution function. To consider the geometric nonlinearity, the von Kármán relations are used. After obtaining the potential energy of the system including strain gradient effects, an analytical variational approach is utilized to solve the postbuckling problem for small-scale shells with simply supported ends. Finally, selected numerical results are presented to investigate the influence of different parameters such as volume fraction index, length scale parameter and radius-to-thickness ratio on the nonlinear postbuckling behavior of micro-/nano-shells. © Shiraz University 2017.
Gholami y., Y.,
Ansari, R.,
Gholami, R.,
Rouhi h., H. Publication Date: 2018
Thin-Walled Structures (02638231)131pp. 487-499
In the context of Gurtin-Murdoch (GM) surface elasticity theory, a size-dependent third-order shear deformable plate model is developed herein in order to study the nonlinear forced vibration behavior of rectangular nanoplates with considering surface stress effect. Nanoplates are assumed to be made of functionally graded materials (FGMs) whose properties are graded in the thickness direction based on a power-law distribution. First, the constitutive relations of GM model are matricized. Then, Hamilton's principle is used to derive the governing equations. The variational differential quadrature, a numerical Galerkin, time periodic discretization, and pseudo arc-length methods are also employed for numerical solution of the geometrically nonlinear forced vibration problem. The frequency-response curves of rectangular nanoplates with different boundary conditions are investigated for different values of thickness, power-law index, surface constants and side length-to-thickness ratio. The results reveal that the surface stress has an important influence on the frequency-response curve of nanoplates at very small scales. © 2018 Elsevier Ltd
Moradweysi p., ,
Ansari, R.,
Hosseini, K.,
Sadeghi f., F. Publication Date: 2018
Applied Mathematical Modelling (0307904X)54pp. 594-604
In this paper, the pull-in instability of doubly clamped nano-switches subjected to electrostatic and intermolecular forces are investigated. To this end, using Eringen's nonlocal elsticity theory, the static governing equation of nonlocal Timoshenko beam model is derived. The obtained equation which is a high-order nonlinear ordinary differential equation owing to the electrostatic and intermolecular forces is solved through the use of modified Adomian decomposition method (MADM). This method presents an analytical approximate solution by which the small scale effect on the static pull-in instability of nanobeam is examined. The results obtained from the present method are found to be in reasonable agreement with ones generated by the differential quadrature method (DQM) and experiment. A parametric study is carried out to study the effect of nonlocal parameter on the mid-point deflection, external forces, bending moment and shear force of doubly clamped nanobeams. Moreover, the results of nonlocal Timoshenko beam model are compared with those of nonlocal Euler–Bernoulli and classical beam models. © 2017 Elsevier Inc.
Publication Date: 2018
Composite Structures (02638223)185pp. 728-747
A numerical approach is adopted for the multiscale analysis of vibrations of single-walled carbon nanotubes (SWCNTs). The SWCNT is modeled by a hyperelastic membrane whose kinematics is described using the higher-order Cauchy-Born rule. The constitutive model is formulated exclusively in terms of the interatomic potential, so, it inherits the atomistic information and involves no other phenomenological input. The variational differential quadrature (VDQ) method is employed in which the continuum model is discretized using DQ, and a weak form of equation of motion is obtained via a variational approach. VDQ is computationally advantageous since it has a fast rate of convergence and can reproduce the results of molecular dynamics simulations. Detailed investigations into frequencies and mode shapes of SWCNTs with different geometrical parameters, boundary conditions and chiralities are carried out. It is found that short nanotubes display a coupling between the axial/torsional and bending modes. Also, as the tube diameter or length increases, mode transitions are made at several critical points. If the edge supports are more flexible and tube length is longer, the critical diameters are larger. Eventually, the vibration characteristics of axially strained nanotubes are analyzed, and it is concluded that SWCNTs with smaller radii have higher strain sensitivity. © 2017 Elsevier Ltd
Publication Date: 2018
Aerospace Science and Technology (12709638)77pp. 306-319
In this paper, a comprehensive numerical study is presented on the large-amplitude free vibration of sandwich annular plates integrated with functionally graded carbon nanotube-reinforced composite (FG-CNTRC) face sheets resting on elastic foundation. The sandwich plate is made of a homogeneous core and two FG-CNTRC face sheets whose material properties are estimated through a micromechanical model. Since the fundamental vibrational mode shapes of annular plates are axisymmetric, the governing equations are derived assuming the axisymmetric formulation. For this purpose, the quadratic form of total potential energy of the structure is presented based on the higher-order shear deformation theory (HSDT) of plates along with von-Karman nonlinear kinematic relations. The numerical differential and integral operators are then employed to discretize the energy functional in space and time domains. Finally, using the response of linear analysis and applying the pseudo-arc length continuation method, the nonlinear frequencies are obtained. After validating the results of proposed approach, detailed numerical results are given to analyze the effects of geometrical and material parameters on the nonlinear vibration of FG-CNTRC sandwich annular plates. © 2018 Elsevier Masson SAS
Publication Date: 2018
Physica B: Condensed Matter (09214526)534pp. 90-97
Due to the capability of Eringen's nonlocal elasticity theory to capture the small length scale effect, it is widely used to study the mechanical behaviors of nanostructures. Previous studies have indicated that in some cases, the differential form of this theory cannot correctly predict the behavior of structure, and the integral form should be employed to avoid obtaining inconsistent results. The present study deals with the bending analysis of nanoplates resting on elastic foundation based on the integral formulation of Eringen's nonlocal theory. Since the formulation is presented in a general form, arbitrary kernel functions can be used. The first order shear deformation plate theory is considered to model the nanoplates, and the governing equations for both integral and differential forms are presented. Finally, the finite element method is applied to solve the problem. Selected results are given to investigate the effects of elastic foundation and to compare the predictions of integral nonlocal model with those of its differential nonlocal and local counterparts. It is found that by the use of proposed integral formulation of Eringen's nonlocal model, the paradox observed for the cantilever nanoplate is resolved. © 2018 Elsevier B.V.
Publication Date: 2018
Meccanica (15729648)53(4-5)pp. 1115-1130
In this article, the size-dependent bending behavior of nanobeams made of functionally graded materials is studied through a numerical variational approach. The nonlocal effects are captured in the context of fractional calculus. The nanobeams are modelled based on the Euler–Bernoulli beam theory whose governing fractional equation is derived utilizing the minimum total potential energy principle. In the solution procedure, which is directly applied to the variational form of governing equation, the truncated Legendre series in conjunction with the Legendre operational matrix of fractional derivatives are employed for numerical integration of fractional differential equation. The strong form of the governing equation is also derived and solved to examine the accuracy and efficiency of the proposed solution approach as well as for the comparison purpose. The influences of fractional order, nonlocality and material gradient index on the bending characteristics of nanobeams subject to different end conditions are investigated. © 2017, Springer Science+Business Media B.V., part of Springer Nature.
Publication Date: 2018
Acta Mechanica Sinica/Lixue Xuebao (16143116)34(5)pp. 871-882
Eringen’s nonlocal elasticity theory is extensively employed for the analysis of nanostructures because it is able to capture nanoscale effects. Previous studies have revealed that using the differential form of the strain-driven version of this theory leads to paradoxical results in some cases, such as bending analysis of cantilevers, and recourse must be made to the integral version. In this article, a novel numerical approach is developed for the bending analysis of Euler–Bernoulli nanobeams in the context of strain- and stress-driven integral nonlocal models. This numerical approach is proposed for the direct solution to bypass the difficulties related to converting the integral governing equation into a differential equation. First, the governing equation is derived based on both strain-driven and stress-driven nonlocal models by means of the minimum total potential energy. Also, in each case, the governing equation is obtained in both strong and weak forms. To solve numerically the derived equations, matrix differential and integral operators are constructed based upon the finite difference technique and trapezoidal integration rule. It is shown that the proposed numerical approach can be efficiently applied to the strain-driven nonlocal model with the aim of resolving the mentioned paradoxes. Also, it is able to solve the problem based on the strain-driven model without inconsistencies of the application of this model that are reported in the literature. © 2018, The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
Waves in Random and Complex Media (discontinued) (17455049)28(3)pp. 426-434
Finding the exact solutions of nonlinear fractional differential equations has gained considerable attention, during the past two decades. In this paper, the conformable time-fractional Klein–Gordon equations with quadratic and cubic nonlinearities are studied. Several exact soliton solutions, including the bright (non-topological) and singular soliton solutions are formally extracted by making use of the ansatz method. Results demonstrate that the method can efficiently handle the time-fractional Klein–Gordon equations with different nonlinearities. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2018
Chaos, Solitons and Fractals (09600779)109pp. 14-25
In this article, the nonlinear chaotic and periodic dynamic responses of doubly curved functionally graded shallow shells subjected to harmonic external excitation are numerically investigated. Material characteristics of the shell are defined according to a simple power law distribution through the thickness. Based on the first-order shear deformation shell theory and using the Donnell nonlinear kinematic relations the set of the governing equations are derived. The Galerkin method together with trigonometric mode shape functions is applied to solve the equations of motion. Also, the nonlinearly coupled time integration of the governing equation of plate is solved employing fourth-order Runge–Kutta method. The effects of amplitude and frequency of external force on the nonlinear dynamic response of shells are investigated. The bifurcation diagram and largest Lyapunov exponent are employed to detect the amplitude and frequency of external force critical parameter of periodic and chaotic response of shallow shells under periodic force. Having known the critical values, phase portrait, Poincare maps, time history and power spectrum are presented to observe the periodic and chaotic behavior of the system. © 2018 Elsevier Ltd
Mahmoodi m.j., M.J.,
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2018
Journal of Alloys and Compounds (09258388)769pp. 397-412
In the present work, a nested micromechanical model is presented to analyze the biaxial initial damage envelopes of unidirectional silicon carbide (SiC) fiber-reinforced titanium (Ti) matrix hybrid nanocomposites containing SiC nanoparticles. Firstly, an effort is made to obtain the elastic modulus, yield strength and coefficient of thermal expansion (CTE) of the nanoparticle-reinforced metal matrix nanocomposites by developing an analytical micromechanical model. Size factor and agglomerated state for the nanoparticles into the metal matrix, generation of dislocations by nanoparticle/matrix thermal mismatch and Orowan strengthening mechanism are considered at the nanoscale. Then, a unit cell-based micromechanical model is proposed to extract the biaxial initial damage envelopes of the SiC nanoparticle/SiC fiber-reinforced metal matrix hybrid nanocomposites. The Fiber/matrix interfacial debonding and matrix yielding are included as the dominant damage modes. Also, thermal residual stress (RS) arisen from the fiber/matrix thermal mismatch during the MMC manufacturing process are considered in the analysis. A reasonable agreement is observed between the results of the present model and available experiments for both of the nanocomposite and hybrid nanocomposite thermomechanical properties. It is shown that the SiC nanoparticles are indeed a very effective strengthening agent for the MMCs which can postpone the deterioration initiation due to the interfacial debonding under transverse tension. The presented model is applied to examine the effects of several parameters, including the nanoparticles volume fraction, diameter, size factor and dispersion type and also the thermal mismatch and fiber/matrix interfacial conditions on the biaxial initial damage behavior of the metal matrix hybrid nanocomposites. © 2018 Elsevier B.V.
Publication Date: 2018
Fibers and Polymers (12299197)19(9)pp. 1956-1969
This article investigated the effect of adding montmorillonite nanoclay on the hygrothermal durability of glass/epoxy (GE) composites and fiber metal laminates (FMLs). Experimental results indicated that the addition of nanoclay to both GE composites and FMLs increases water absorption, but reduces diffusivity as compared with the neat specimens. The flexural strength, flexural stiffness and impact properties of GE composites were negatively affected by hygrothermal aging and decreased by 24.76 %, 18.98 %, and 9.53 %, respectively, while these values for the aged FMLs were only 10.05 %, 4.40 %, and 4.14 %, respectively. It was also found that the addition of nanoclay can enhance the flexural and impact properties of both laminate types especially GE composites in both the pristine and post-aging conditions. The GE composites filled with 3 % nanoclay exhibited the enhancement of 10.73 %, 8.03 %, and 6.95 % in flexural strength, flexural stiffness and impact strength over neat GE composites, whereas these values were found to be only 1.35 %, 0.50 %, and 0.51 % in FMLs with 3 % nanoclay. In addition, the aged GE specimens with 3 wt.% nanoclay showed 13.45 %, 16.20 %, and 7.23 % loss in flexural strength, flexural stiffness and impact strength, respectively, while these values for aged FMLs contain 3 wt.% nanoclay were 8.63 % and 3.82 %, and 1.13 %, respectively. © 2018, The Korean Fiber Society and Springer Nature B.V.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J.,
Darvizeh a., A. Publication Date: 2018
Composites Science and Technology (02663538)162pp. 93-100
Effects of silica nanoparticle aggregation on the creep behavior of polymer nanocomposites are analyzed. For this purpose, a hierarchical micromechanical model based on the Mori-Tanaka (M-T) scheme is proposed. Formation of interphase region due to the interfacial interaction between the polymer matrix and nanoparticle is incorporated in the modeling. Comparison between the proposed model results considering the viscoelastic interphase shows a good agreement with existing experiment. At the high volume fraction, when the nanoparticles are not well-dispersed into the polymer nanocomposites, it is necessary to consider the viscoelastic interphase together with the nanoparticle aggregation for providing accurate predictions. The results reveal the nanoparticle aggregation affects and degrades the polymer nanocomposite creep resistance. A uniform dispersion of nanoparticles into the matrix leads to a maximum level of the nanocomposite creep resistance. The influences of the nanoparticle volume fraction, diameter and the interphase characteristics on the nanocomposite creep behavior are investigated. © 2018 Elsevier Ltd
Publication Date: 2018
Journal of Alloys and Compounds (09258388)752pp. 476-488
The residual stresses (RSs) can be generated by the thermal mismatch between the carbon nanotubes (CNTs) and aluminum (Al) matrix during the manufacturing process of this type of nanocomposite materials. It may play a significant role in the strengthening capability of the CNT/Al nanocomposites. In this work, a micromechanics-based method is developed to a comprehensive analyze the effect of thermal RSs on the overall elastoplastic behavior of the CNT/Al nanocomposites. Also, the micromechanical model includes an agglomerated state for the CNTs within the Al nanocomposites. Generally, a good agreement is observed between the results of the present model and available experiment. The results clearly emphasize that for a more realistic prediction in the case of the overall elastoplastic behavior of CNT/Al nanocomposites, the consideration of thermal RSs in the micromechanical analysis is essential. It is found that the thermal RSs can seriously reduce both the yield strength and ultimate tensile strength of the nanocomposites. Moreover, the proposed model is employed to investigate the influences of several important parameters such as volume fraction, aspect ratio and directional behavior of CNTs, degree of CNT agglomeration within the matrix on the elastic modulus, thermal expansion behavior and overall elastoplastic response of CNT-reinforced Al nanocomposites. The herein reported results could be actually useful to guide an accurate modeling and the design of a wide range of metal matrix nanocomposites reinforced by CNTs. © 2018 Elsevier B.V.
Rajabiehfard r., R.,
Darvizeh a., A.,
Alitavoli, M.,
Ansari, R.,
Maghdouri e., Publication Date: 2018
Thin-Walled Structures (02638231)125pp. 21-37
This paper investigates the internal inversion process of mild steel tubes under axial impact analytically, numerically and experimentally using a die. The analytical model which is based on the energy method, is able to predict the shortening length of the tube and the required force for tube inversion considering tube thickness variation. In order to validate the analytical model, some experimental tests are performed on the steel tubes in a gas gun and the required force for tube inversion is obtained using an impact loading measurement system. The tube inversion process is also simulated using the finite element software Abaqus and finally the obtained results are compared with each other. In the present paper, the effect of impact parameters included the projectile mass and velocity, is investigated on deformation mechanism and energy absorption of the tubes in the internal inversion process. The effect of tube thickness and die radius are also studied in the mentioned process. It is observed that in the situation of constant projectile mass, increasing the impact velocity doesn't have a tangible effect on the inversion force and just increases the tube displacement, but if the impact velocity remains constant, increasing the projectile mass causes increase in the inversion force as well as increased tube displacement. It is also concluded that increasing the tube wall thickness increases the inversion force which makes the tube not to be a good absorbent and decreases the tube displacement. Comparing the experimental, analytical and numerical results provides good agreements between them. © 2018 Elsevier Ltd
Ansari, R.,
Norouzzadeh, A.,
Shakouri a.h., ,
Bazdid-vahdati m., M.,
Rouhi h., H. Publication Date: 2018
Thin-Walled Structures (02638231)124pp. 489-500
The micropolar theory (MPT), through taking the rotational degrees of freedom of material particles into account, is a suitable elasticity theory for the mechanical analysis of microstructures. In this article, the vibration behavior of microscale beams and plates is studied based on MPT. To this end, first, a three-dimensional (3D) formulation is developed for the micropolar continua which can be readily used in the finite element analyses. Then, a non-classical 3D element is introduced to investigate the free vibration characteristics of micropolar beams and plates. The microstructure effect on the frequencies of microbeams and microplates under different kinds of boundary conditions is illustrated. Also, the results of MPT are compared with those of classical theory and it is indicated that there is a considerable difference between their predictions at small scales. © 2017 Elsevier Ltd
Publication Date: 2018
Journal of Solid Mechanics (discontinued) (20087683)10(4)pp. 929-939
The multi-scale finite element method is used to study the vibrational characteristics of polymer matrix reinforced by single-walled silicon carbide nanotubes. For this purpose, the nanoscale finite element method is employed to simulate the nanotubes at the nanoscale. While, the polymer is considered as a continuum at the larger scale. The polymer nanotube interphase is simulated by spring elements. The natural frequencies of nanocomposites with different nanotube volume percentages are computed. Besides, the influences of nanotube geometrical parameters on the vibrational characteristics of the nanocomposites are evaluated. It is shown that reinforcing polymer matrix by single-walled silicon carbide nanotubes leads to increasing the natural frequency compared to neat resin. Increasing the length of the nanotubes at the same diameter results in increasing the difference between the frequencies of nanocomposite and pure polymer. Besides, it is observed that clamped-free nanocomposites experience a larger increase in the presence of the nanotubes than clamped-clamped nanotube reinforced polymers. © 2018 IAU, Arak Branch.
Publication Date: 2018
JVC/Journal of Vibration and Control (10775463)24(6)pp. 1123-1144
Free vibration analysis of embedded functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical, cylindrical shells and annular plates is carried out using the variational differential quadrature (VDQ) method. Pasternak-type elastic foundation is taken into consideration. It is assumed that the functionally graded nanocomposite materials have the continuous material properties defined according to extended rule of mixture. Based on the first-order shear deformation theory, the energy functional of the structure is calculated. Applying the generalized differential quadrature method and periodic differential operators in axial and circumferential directions, respectively, the discretized form of the energy functional is derived. Based on Hamilton’s principle and using the VDQ method, the reduced forms of mass and stiffness matrices are obtained. The comparison and convergence studies of the present numerical method are first performed and then various numerical results are presented. It is found that the volume fractions and functionally grading of carbon nanotubes play important roles in the vibrational characteristics of FG-CNTRC cylindrical, conical shells and annular plates. © 2016, © The Author(s) 2016.
Publication Date: 2018
European Physical Journal Plus (21905444)133(2)
This article presents an attempt to study the nonlinear resonance of functionally graded carbon-nanotube-reinforced composite (FG-CNTRC) annular sector plates excited by a uniformly distributed harmonic transverse load. To this purpose, first, the extended rule of mixture including the efficiency parameters is employed to approximately obtain the effective material properties of FG-CNTRC annular sector plates. Then, the focus is on presenting the weak form of discretized mathematical formulation of governing equations based on the variational differential quadrature (VDQ) method and Hamilton’s principle. The geometric nonlinearity and shear deformation effects are considered based on the von Kármán assumptions and Reddy’s third-order shear deformation plate theory, respectively. The discretization process is performed via the generalized differential quadrature (GDQ) method together with numerical differential and integral operators. Then, an efficient multi-step numerical scheme is used to obtain the nonlinear dynamic behavior of the FG-CNTRC annular sector plates near their primary resonance as the frequency-response curve. The accuracy of the present results is first verified and then a parametric study is presented to show the impacts of CNT volume fraction, CNT distribution pattern, geometry of annular sector plate and sector angle on the nonlinear frequency-response curve of FG-CNTRC annular sector plates with different edge supports. © 2018, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
Materials Research Express (20531591)5(1)
Presented herein is the study of grain size, grain surface energy and small scale effects on the nonlinear pull-in instability and free vibration of electrostatic nanoscale actuators made of nanocrystalline silicon (Nc-Si). A Mori-Tanaka micromechanical model is utilized to calculate the effective material properties of Nc-Si considering material structure inhomogeneity, grain size and grain surface energy. The small-scale effect is also taken into account using Mindlin's strain gradient theory. Governing equations are derived in the discretized weak form using the variational differential quadrature method based on the third-order shear defamation beam theory in conjunction with the von Kármán hypothesis. The electrostatic actuation is modeled considering the fringing field effects based upon the parallel plate approximation. Moreover, the Casimir force effect is considered. The pseudo arc-length continuation technique is used to obtain the applied voltage-deflection curve of Nc-Si actuators. Then, a time-dependent small disturbance around the deflected configuration is assumed to solve the free vibration problem. By performing a numerical study, the influences of various factors such as length scale parameter, volume fraction of the inclusion phase, density ratio, average inclusion radius and Casimir force on the pull-in instability and free vibration of Nc-Si actuators are investigated. © 2018 IOP Publishing Ltd.
Publication Date: 2018
International Journal of Applied Mechanics (17588251)10(3)
This paper aims to investigate the imperfection sensitivity of the post-buckling behavior and the free vibration response under pre- and post-buckling of nanoplates with various edge supports in the thermal environment. Formulation is based on the higher-order shear deformation plate theory, von Kármán kinematic hypothesis including an initial geometrical imperfection and Gurtin-Murdoch surface stress elasticity theory. The discretized nonlinear coupled in-plane and out-of-plane equations of motion are simultaneously obtained using the variational differential quadrature (VDQ) method and Hamilton's principle. To this end, the displacement vector and nonlinear strain-displacement relations corresponding to the bulk and surface layers are matricized. Also, the variations of potential strain energies, kinetic energies and external work are obtained in matrix form. Then, the VDQ method is employed to discretize the obtained energy functional on space domain. By Hamilton's principle, the discretized quadratic form of nonlinear governing equations is derived. The resulting equations are solved employing the pseudo-arc-length technique for the post-buckling problem. Moreover, considering a time-dependent small disturbance around the buckled configuration, the vibrational characteristics of pre- and post-buckled nanoplates are determined. The influences of initial imperfection, thickness, surface residual stress and temperature rise are examined in the numerical results. © 2018 World Scientific Publishing Europe Ltd.
Publication Date: 2018
Computers and Mathematics with Applications (08981221)75(2)pp. 486-502
The buckling analysis of thick composite annular sector plates reinforced with functionally graded carbon-nanotubes (CNTs) is presented under in-plane and shear loadings based on the higher-order shear deformation theory. It is considered that the plate is resting on the Pasternak-type elastic foundation. The overall material properties of functionally graded carbon nanotube-reinforced composites (FG-CNTRCs) are estimated through the micromechanical model. The governing equations are derived on the basis of the higher-order shear deformation plate theory, and the quadratic form of the energy functional of the system is presented. An efficient numerical method is presented in the context of variational formulation to obtain the discretized version of stability equations. The validation of the present study is demonstrated through comparisons with the results available in the literature and then comprehensive numerical results are given to investigate the impacts of model parameters on the stability of CNT-reinforced composite annular sector plates. © 2017 Elsevier Ltd
Publication Date: 2018
International Journal of Modern Physics B (02179792)32(14)
In this paper, a multi-scale modeling approach is used to study the effect of adding graphene sheets to concrete matrix on the thermal conductivity of the concrete. By computing the thermal conductivity of the graphene along the armchair and zigzag directions using molecular dynamics (MO) simulations, it is shown that the graphene sheets have orthotropic thermal behavior. Therefore, at the upper scale, in which the finite element (FE) method is used to obtain the thermal conductivity of the concrete/graphene nanocomposites, the graphene sheets are considered as orthotropic continuous sheets. It is shown that the improvement of the concrete thermal conductivity by adding the graphene sheets is directly related to the graphene sheet volume percentage and cross-sectional dimensions. © 2018 World Scientific Publishing Company.
Asadollahi a., ,
Ansari, R.,
Sohrabnezhad, S.,
Ostovar f., Publication Date: 2018
Global Nest Journal (17907632)20(3)pp. 598-609
In this research, the Ag2CO3-PANI composite was synthesized with a simple precipitation method and then used as an effective adsorbent for adsorption of Methylene Blue cationic dyes from aqueous solution. Characterization of the adsorbent was carried out using UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The various parameters such as pH, contact time, sorbent dosage, initial dye concentration, and dye solution temperature were investigated. The optimum photo-catalytic activity of Ag2CO3-PANI at a weight content of 50% PANI for the degradation of MB was almost 86% that is much higher than the pure Ag2CO3 and PANI. The results showed an efficient removal at pH 10.0, within 60 min, and by using 1 g L-1 Ag2CO3-PANI composite at the temperature of 32˚C. The kinetic and equilibrium data fit into pseudo-second-order kinetic (R2> 0.84) and Freundlich isotherm (R2> 0.99) models, respectively. Adsorption capacity (q0) calculated from Langmuir isotherm was found to be 55 mg/g. Thermodynamic studies indicated that the adsorption process was endothermic (ΔH°˃0). The adsorption/desorption experiments were carried out attaining regenerations of up to 97% from MB, using distilled water and 0.1N HCl. The composite indicated high efficiency adsorptive properties and high reusability. © 2018 Global NEST Printed in Greece. All rights reserved.
Publication Date: 2018
Mechanics of Advanced Materials and Structures (15210596)25(3)pp. 253-265
This article concerns the investigation of the vibrational behavior of double-walled carbon nanotubes/double-layered graphene sheets junctions using the finite element method. The bonds and atoms are modeled by beam and mass elements, respectively. Moreover, the van der Waals interactions are simulated by spring elements. The effects of the length of the nanotube and the dimensions of the nanosheet on the natural frequencies of the junctions are examined. It is shown that when the boundary conditions are applied on the nanotube, the geometrical parameters of nanotubes have a significant effect on the vibrational behavior of the junctions. © 2018 Taylor & Francis Group, LLC.
Publication Date: 2018
Multidiscipline Modeling in Materials and Structures (15736105)14(5)pp. 810-827
Purpose: It has been revealed that application of the differential form of Eringen’s nonlocal elasticity theory to some cases (e.g. cantilevers) leads to paradoxical results, and recourse must be made to the integral version of Eringen’s nonlocal model. The purpose of this paper, within the framework of integral form of Eringen’s nonlocal theory, is to study the bending behavior of nanoscale plates with various boundary conditions using the isogeometric analysis (IGA). Design/methodology/approach: The shear deformation effect is taken into account according to the Mindlin plate theory, and the minimum total potential energy principle is utilized in order to derive the governing equations. The relations are obtained in the matrix-vector form which can be easily employed in IGA or finite element analysis. For the comparison purpose, the governing equations are also derived based on the differential nonlocal model and are then solved via IGA. Comparisons are made between the predictions of integral nonlocal model, differential nonlocal model and local (classical) model. Findings: The bending analysis of nanoplates under some kinds of edge supports indicates that using the differential model leads to paradoxical results (decreasing the maximum deflection with increasing the nonlocal parameter), whereas the results of integral model are consistent. Originality/value: A new nonlocal formulation is developed for the IGA of Mindlin nanoplates. The nonlocal effects are captured based on the integral model of nonlocal elasticity. The formulation is developed in matrix-vector form which can be readily used in finite element method. Comparisons are made between the results of differential and integral models for the bending problem. The proposed integral model is capable of resolving the paradox appeared in the results of differential model. © 2018, Emerald Publishing Limited.
Publication Date: 2018
Thin-Walled Structures (02638231)127pp. 354-372
Presented in this paper is a size-dependent analysis of the surface stress and nonlocal influences on the free vibration characteristics of rectangular and circular nanoplates. Nanoplates are assumed to be made of functionally graded materials (FGMs) with two distinct surface and bulk phases. The nonlocal and surface effects are captured by the Eringen and the Gurtin-Murdoch surface elasticity theories, respectively. The Mori-Tanaka distribution scheme is also used for obtaining material properties of nanoplate. In addition to the conventional procedure of deriving the formulation, a novel matrix-vector form of the governing differential equations of motion is presented. This form has the capability of being used directly in the finite element method or isogeometric analysis. To show the effects of surface parameters and small scale influences on the vibrational behavior of rectangular and circular FGM nanoplates with various boundary conditions, several case studies are presented. © 2017 Elsevier Ltd
Publication Date: 2018
Scientia Iranica (23453605)25(3F)pp. 1864-1878
By taking the nonlocal and strain gradient effects into account, the vibrational behavior of Timoshenko micro- and nano-beams is studied in this paper based on a novel size-dependent model. The nonlocal effects are captured using both differential and integral formulations of Eringen's nonlocal elasticity theory. Moreover, the strain gradient inuences are incorporated into the model according to the most general form of strain gradient theory, which can be reduced to simpler strain gradient-based theories such as modified strain gradient and modified couple stress theories. Hamilton's principle is employed to derive the variational form of governing equations. The isogeometric analysis (IGA) is then utilized for the solution approach. Comprehensive results for the effects of smallscale and nonlocal parameters on the natural frequencies of beams under various types of boundary conditions are given and discussed. It is revealed that using the differential nonlocal strain gradient model for computing the fundamental frequency of cantilevers leads to paradoxical results, and one must recourse to the integral nonlocal strain gradient model to obtain consistent results. © 2018 Sharif University of Technology. All rights reserved.
Publication Date: 2018
Materials Research Express (20531591)5(1)
In this paper, the density functional theory is used to study the mechanical properties of pristine and doped arsenene. Fe, Ti and V doped arsenenes with the doping percentages of 25% and 50% are considered for investigation. Applying uniaxial and biaxial strains on the pristine and doped arsenene nanosheets, their Young's and bulk moduli are evaluated. It is observed that the elastic modulus of doped arsenene is smaller than that of pristine one. The most and least reductions in the elastic modulus of the arsenene nanosheet are for doping with Ti and V atoms, respectively. Also, the inharmonic region of the pristine arsenene is larger than that of doped ones. Finally, by increasing the applied strain, the plastic properties of arsenene are investigated. © 2018 IOP Publishing Ltd.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2018
International Journal of Engineering Science (00207225)130pp. 215-229
A multiscale micromechanical modeling approach is developed to predict elastic properties of carbon fiber (CF)-reinforced polymer hybrid composites. In this type of hybrid composite, the unidirectional fibers are coated with randomly oriented carbon nanotubes (CNTs). Two fundamental aspects affecting the mechanical behavior of the hybrid composites are investigated herein; namely, CNT non-straight shape and the existence of an interphase region between a CNT and the polymer matrix. An excellent agreement is observed between the predictions of the new micromechanical method and available experimental data. The results reveal that for an accurate prediction of the elastic properties of the CNT-coated CF-reinforced hybrid composite, the consideration of waviness and transversely isotropic behavior of CNT, CNT/polymer interphase region and random arrangement of CFs is essential. It is found that the contribution of CNTs to the elastic response of the hybrid composite in longitudinal direction can be neglected. However, transverse elastic modulus of the CNT-coated CF-reinforced hybrid composite is significantly improved over that of the conventional CF-reinforced composite without CNT coating. Also, the maximum value of transverse elastic modulus can be obtained when the uniformly aligned straight CNTs are radially grown on the surface of the horizontal CFs. © 2018 Elsevier Ltd
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R. Publication Date: 2018
Probabilistic Engineering Mechanics (02668920)53pp. 39-51
This work deals with a comprehensive study on the general off-axis mechanical properties of polymer nanocomposites reinforced by carbon nanotubes (CNTs) using a three-dimensional micromechanical model. The representative volume element (RVE) of the model consists of three phases including CNT, polymer matrix and interphase formed due to the non-bonded interaction between a CNT and the polymer. The CNTs are assumed to be transverse isotropic. Both random under several statistical distribution and regular arrangements of the CNTs within the matrix are considered in the analysis. The results are shown to be consistent with the results of other theoretical methods and experiment. Effects of various parameters, including the CNT aspect ratio, orientation, distribution, cross sectional shape and volume fraction, the interphase characteristics and the matrix material properties are examined on the effective elastic properties of CNT–reinforced polymer nanocomposites. The results reveal that the mechanical properties of the nanocomposite are extremely dependent on the CNTs off-axis angle. The interphase effect is more significant for the elastic modulus of 70°off-axis coupon. It is found that CNT volume fraction has the maximum effect for the longitudinal elastic modulus. For 90°coupons, elastic modulus of the nanocomposite is significantly affected by the matrix properties. The results obviously indicate that the elastic modulus, especially in the longitudinal direction increases up to a threshold value and then saturates as the CNT aspect ratio increases. Also, it is found that the CNT arrangement does not affect the longitudinal elastic modulus of CNT–polymer nanocomposites, whereas the transverse elastic modulus is significantly affected by the CNT arrangement. © 2018 Elsevier Ltd
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J. Publication Date: 2018
Mechanics of Materials (01676636)119pp. 1-15
A new approach combining three models is developed to evaluate the thermomechanical behavior of carbon nanotube-fiber reinforced metal matrix nanocomposites (CNT-FRMMCs). At first, the shear lag and Schapery models are modified to determine the mechanical and thermal characteristics of CNT-reinforced metal matrix, respectively. Then, the transverse elastic moduli and transverse/transverse biaxial initial yield envelope of CNT-FRMMCs are predicted using the simplified unit cell (SUC) micromechanical model together with a proper representative volume element (RVE) with r × c sub-cells. The effect of the mismatch in coefficients of thermal expansion (CTEs) between the constituents of the hybrid composite is considered. The results obviously reveal that both thermoelastic properties and initial yield surface of FRMMCs can be significantly improved with adding CNTs. The influences of volume fraction, geometrical and material properties of CNTs, fiber volume fraction, fibers arrangement type, temperature change and residual stresses (RSs) on the CNT-FRMMCs mechanical properties are explored extensively. It is observed that (i) increasing both CNT volume fraction and length and (ii) decreasing the CNT diameter can lead to a more improvement in the thermomechanical behavior of CNT-FRMMCs. The results show that adding CNTs into the FRMMCs can reduce the effect of thermal RSs on the biaxial initial yield envelope. © 2018
Publication Date: 2018
Mechanics of Materials (01676636)121pp. 1-9
Elastic-plastic and thermal expansion responses of aluminum (Al) matrix nanocomposites reinforced with silicon carbide (SiC) nanoparticles are investigated through a micromechanics analytical unit cell method. The formation of the interphase region between SiC nanoparticles and Al matrix is taken into account in the modeling of nanocomposites. The influences of some important parameters such as the thickness and material properties of the interphase, volume fraction and diameter of SiC nanoparticles on the elastic modulus, coefficient of thermal expansion (CTE) and elastoplastic stress-strain curve of the Al nanocomposites are studied in detail. The results clearly reveal high contribution of the interphase region to the overall mechanical and thermal behaviors of Al nanocomposites. It is found that when nanoparticle diameter is lower than about 150 nm, the decrease of SiC nanoparticle diameter leads to (i) an increment in mechanical properties both in the elastic and plastic regions and (ii) a reduction in CTE of the metal matrix nanocomposites. Also, the effect of interphase on the elastic modulus and CTE of Al nanocomposites becomes more important with the reduction of SiC nanoparticle diameter. Finally, the micromechanical model is employed to predict the elastoplastic behavior of SiC nanoparticle-reinforced Al nanocomposites subjected to multi-axial loading conditions in the presence and absence of the interphase region. © 2018 Elsevier Ltd
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R. Publication Date: 2018
Mechanics of Materials (01676636)118pp. 31-43
General off-axis mechanical behavior of fuzzy fiber-reinforced composites (FFRCs) is investigated using a 3-dimensional unit cell micromechanics model. In the FFRCs studied herein, uniformly aligned carbon nanotubes (CNTs) are radially grown on the circumferential surfaces of carbon fibers. The effects of orientation and volume fraction of carbon fiber, volume fraction of CNT, stiffness and thickness of the interphase region created due to non-boned interaction between the CNT and polymer matrix on the elastic response of the FFRCs are studied. The results reveal that the mechanical properties of the FFRCs are strongly dependent on the off-axis angle of carbon fiber. With the increase of off-axis angle from 0° up to 90° the elastic modulus of FFRC sharply decreases up to 45° and then its value increases, whereas without considering CNTs on the surface of carbon fiber, the elastic modulus continuously decreases. It is shown that the growth of CNTs on the surface of carbon fiber can lead to the highest enhancement for the elastic modulus of 90° on-axis coupon. Poisson's ratio of the FFRC rises with the increase of off-axis angle from 0° up to about 35° and then its value decreases. Also, the increase of CNT volume fraction yields a significant increase for the elastic modulus of 90° on-axis coupon, while rising carbon fiber volume fraction can substantially enhance the elastic modulus of 0° coupon. According to the obtained results, increasing both stiffness and thickness of the interphase can improve the elastic modulus of FFRC over the range of 0–90° especially for 90° on-axis coupon. The results predicted by the present model are much closer to the experiment than those predicted by the numerical simulations available in the literature. © 2017 Elsevier Ltd
Publication Date: 2018
Applied Surface Science (01694332)455pp. 171-180
In this paper, the interactions of polymer chains with single-walled carbon nanotubes (SWCNTs) are studied. To this end, molecular dynamics (MD) simulations are used. The effects of functionalization factor type and weight percent, polymer type, nanotube diameter and randomness of functionalization are studied. Comparing the results for (7,7) and (12,12) single-walled carbon nanotubes, it is observed that increasing the nanotube diameter results in decreasing the difference between interaction energies of different polymers/functionalized single-walled carbon nanotubes systems. Besides, it is observed that mapped distribution of the CH 2 -NH 2 amines on the single-walled carbon nanotube surface has not significant effect on the polymer/functionalized nanotube interaction energies. It is seen that functionalization of nanotubes by NH 2 amine results in more strength polymer/nanotube interactions than CH 2 -NH 2 amine. © 2018
Publication Date: 2018
Diamond and Related Materials (09259635)86pp. 173-178
In this article, for functionalized single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) with cross-linked polyethylene (PE) chains, the thermal conductivity is computed through the molecular dynamics (MD) simulations. Moreover, the effects of different weight percentages of PE chains and distribution patterns on the thermal conductivity are investigated. To calculate the thermal conductivity, an approach for determining the cross-section area is proposed. According to the results, the thermal conductivity decreases by attaching the functional groups to the wall of nanotubes. Additionally, as the weight percentage of functional group increases, the thermal conductivity decreases. It is also observed that increasing the number of nanotube walls results in less sensitivity of thermal conductivity to increasing the weight percentage of functional groups. © 2018 Elsevier B.V.
Publication Date: 2018
European Journal of Mechanics, A/Solids (09977538)69pp. 45-54
In this paper, the mechanical oscillatory behavior of a chloride ion inside a series of electrically charged carbon nanotubes (CNTs) is investigated using molecular dynamics (MD) simulations. The Tersoff-Brenner and 6–12 Lennard-Jones (LJ) potential functions are respectively employed to describe the interatomic interactions between carbon atoms and van der Waals (vdW) interactions between ion and CNT, while the Coulomb potential function is used to model the electrostatic interactions between ion and electric charges. The outer shell which is assumed to be either uncharged or positively charged is composed of identical units located concentrically with an equal distance. Two different cases named cases 1 and 2 are considered to incorporate the electrostatic interactions into the model. In the first one, both left and right ends of all units are electrically charged, whereas in the second one, only the left end of the left-most unit and the right end of the right-most unit are electrically charged. Numerical results are presented to examine the effects of type of decoration of electric charges and their magnitudes, geometrical parameters (number of units, length and radius of units and the distance between two neighboring units) and initial conditions (initial separation distance and initial velocity) on the dynamic behavior of system. A comparison is also made between the results of cases 1 and 2 with those of uncharged units. For given initial conditions, it is demonstrated that the oscillation frequency of case 1 is lower than that of case 2 and higher than that of pure nanotubes. It is further found that the highest escape velocity corresponds to case 1 followed by case 2 and uncharged nanotubes. © 2017 Elsevier Masson SAS
Publication Date: 2018
Journal of Modern Optics (13623044)65(7)pp. 847-851
One specific class of non-linear evolution equations, known as the Tzitzéica-type equations, has received great attention from a group of researchers involved in non-linear science. In this article, new exact solutions of the Tzitzéica-type equations arising in non-linear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov and Tzitzéica–Dodd–Bullough equations, are obtained using the expa function method. The integration technique actually suggests a useful and reliable method to extract new exact solutions of a wide range of non-linear evolution equations. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
Hosseini, K.,
Zabihi, A.,
Samadani f., F.,
Ansari, R. Publication Date: 2018
Optical and Quantum Electronics (discontinued) (03068919)50(2)
Under investigation in the present work is to study the unstable nonlinear Schrödinger’s equation which points out the time evolution of disturbances in marginally stable or unstable media. The expa and hyperbolic function methods are adopted to carry out this target in a straightforward way. A wide variety of new explicit exact solutions are successfully derived, proving the excellent performance of the schemes. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
Publication Date: 2018
European Physical Journal Plus (21905444)133(7)
The geometrically nonlinear bending behavior of carbon nanotube/fiber/polymer multiscale laminated composite (CNT-FPMLC) rectangular plates with various edge conditions subjected to the uniform transverse mechanical loading is investigated. Based on the Reddy’s third-order shear deformation plate theory and employing the von Kármán hypotheses and fundamental lemma of calculus of variations, the governing equilibrium equations including the shear deformation effect and geometrical nonlinearity together with associated boundary conditions are developed. The fiber micromechanics and the Halpin-Tsai relations are employed to approximately calculate the material properties of multiscale composite. Also, the carbon nanotubes (CNTs) are assumed to be distributed uniformly and oriented arbitrarily through the epoxy resin matrix. For the large deflection analysis, first, the generalized differential quadrature (GDQ) method is used to discretize the differential governing equations and corresponding boundary conditions resulting in a set of nonlinear algebraic equations. Then, the pseudo-arclength continuation technique is utilized to numerically solve the resulting nonlinear parameterized equations and subsequently obtain the load-deflection curve of CNT-FPMLC rectangular plates with different edge supports. Several numerical results are provided to reveal the influences of the weight percentage of single-walled and multi-walled CNTs, CNT aspect ratio, volume fraction of fibers, length-to-thickness ratio of plate and boundary conditions on the nonlinear responses of the CNT-FPMLC plates. © 2018, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
International Journal of Non-Linear Mechanics (00207462)101pp. 174-186
Surface influences on the nonlinear vibrations of micro- and nano-shells are investigated by an efficient numerical approach. The seven-parameter geometrically nonlinear first-order shear deformation shell theory in Lagrangian description is formulated for the bulk part of structure. To consider surface stress effects, the Gurtin–Murdoch surface elasticity theory with considerations proposed by Ru (2016) and Shaat et al. (2013) is employed. In this regard, two thin inner and outer surface layers are considered, and the corresponding constitutive relations are incorporated into the shell formulations. The stress–strain and strain–displacement relations are represented in a novel matrix–vector form by which the governing equations of motion are derived based on Hamilton's principle. The isogeometric analysis (IGA) is then utilized due to having the capability to construct exact geometries of shells and the associated powerful features. The obtained ordinary differential equations from IGA are finally solved by the periodic grid approach which can be considered as a suitable solution strategy for the analysis of free and harmonically forced vibrations of different structures. The present work contributes to the literature with developing the isogeometric model of size-dependent geometrically nonlinear shells subjected to large-amplitude vibrations. © 2018 Elsevier Ltd
Publication Date: 2018
Engineering Structures (18737323)156pp. 197-209
The geometrically nonlinear harmonically excited vibration of third-order shear deformable functionally graded graphene platelet-reinforced composite (FG-GPLRC) rectangular plates with different edge conditions is examined. The considered plate with NL-layers is made from a mixture of an isotropic polymer matrix and graphene platelets (GPLs) in each layer. The weight fraction of GPLs changes in a layer-wise manner. The modified Halpin-Tsai model and rule of mixture are utilized to compute the effective material properties of FG-GPLRCs. To mathematically model the vibrations of FG-GPLRC plates, the displacement field, strain tensor and constitutive relations as well as the energy functional of system including strain and kinetic energies and external work are represented in matrix forms as a function of the displacement components. Then, by simultaneous use of Hamilton's principle and an efficient numerical scheme namely, the variational differential quadrature (VDQ) technique, the weak form of discretized nonlinear equations of motion is obtained. The present model includes the influences of geometric nonlinearity, rotary inertia and transverse shear deformation. Furthermore, a multistep numerical approach based on the Galerkin method, time periodic discretization method and pseudo arc-length continuation technique in conjunction with the modified Newton-Raphson method is employed to solve the problem of nonlinear harmonically excited vibration of FG-GPLRC rectangular plates. Results are plotted in the form of frequency-response and force-response curves to indicate the effect of various parameters such as GPL distribution pattern, weight fraction, geometry of GPL nanofillers and boundary constraints of FG-GPLRC plates. © 2017 Elsevier Ltd
Ansari, R.,
Hasrati, E.,
Shakouri a.h., ,
Bazdid-vahdati m., M.,
Rouhi h., H. Publication Date: 2018
International Journal of Non-Linear Mechanics (00207462)106pp. 130-143
The present work is concerned with the application of the variational differential quadrature (VDQ) method (Faghih Shojaei and Ansari, 2017), in the area of computational mechanics, to the nonlinear large deformation analysis of shell-type structures. To this end, based on the six-parameter shell model, the functional of energy in quadratic form is derived based on Hamilton's principle which is then directly discretized by the VDQ technique. The formulation of article is presented in a general form so that it can be readily used for different structures such as beams, annular plates, cylindrical shells and hemispherical shells under various loading conditions. In order to reveal the accuracy of developed solution strategy, it is tested in several popular benchmark problems for the geometric nonlinear analysis of shells. The results show that the present numerical method is capable of yielding highly accurate solution in the nonlinear large deformation analysis of shells. It is also easy to implement due to its compact and explicit matrix formulation. © 2018 Elsevier Ltd
Publication Date: 2018
Meccanica (15729648)53(13)pp. 3415-3435
This article is aimed to investigate the geometrically nonlinear wave propagation of nano-beams on the basis of the most comprehensive size-dependent elasticity theory. To this end, the integral model of nonlocal elasticity theory in the most general form without any simplification in conjunction with the modified strain gradient theory is implemented in the analysis. Also, the Timoshenko beam model is utilized in the presented nonlocal strain gradient elasticity theory. By Hamilton’s principle, the governing integro-partial differential equations of motion are derived. Employing numerical integration and an efficient method called as periodic grid technique, a semi-analytical approach is presented for the solution procedure. To detect the impacts of nonlocality and small scale effects on the nonlinear wave propagation characteristics of beams at nanoscale, adequate numerical examples and comparison studies are presented. © 2018, Springer Nature B.V.
Publication Date: 2018
Journal of Intelligent Material Systems and Structures (15308138)29(5)pp. 944-968
Based on the nonlocal elasticity theory, a unified nonlocal, nonlinear, higher-order shear deformable nanoplate model is developed to investigate the size-dependent, large-amplitude, nonlinear vibration of multiferroic composite rectangular nanoplates with different boundary conditions resting on an elastic foundation. By considering a unified displacement vector and using von Kármán’s strain tensor, the strain–displacement components are obtained. Using coupled nonlocal constitutive relations, the coupled ferroelastic, ferroelectric, ferromagnetic, and thermal properties of multiferroic composite materials and small-scale effect are taken into account. The electric and magnetic potential distributions in the nanoplate are calculated via Maxwell’s electromagnetic equations. Furthermore, Hamilton’s principle is utilized to obtain the mathematical formulation associated with the coupled governing equations of motions and boundary conditions. The developed model enables us to consider the effects of rotary inertia and transverse shear deformation without using any shear correction factor. Also, it can be degenerated to the models based on the Kirchhoff and existing shear deformation plate theories. To solve the large-amplitude vibration problem, an efficient multistep numerical solution approach is utilized. Effects of various important parameters such as the type of the plate theory, and parameters of nonlocality and coupled fields on the nonlinear frequency response are investigated. © 2017, © The Author(s) 2017.
Publication Date: 2018
Aerospace Science and Technology (12709638)78pp. 118-129
This work deals with the numerical investigation of the geometrically nonlinear resonant dynamics of carbon nanotube/fiber/polymer multiscale laminated composite (CNT-FPMLC) rectangular plates with different boundary conditions. It is assumed that a uniform distributed harmonic excitation load in the transverse direction is applied to the CNT-FPMLC plates. The material properties of multiscale composite are estimated by means of the fiber micromechanics and Halpin–Tsai relations. Furthermore, it is assumed that the carbon nanotubes (CNTs) are distributed uniformly and oriented arbitrarily through the epoxy resin matrix. Based upon the Mindlin plate theory and using the von Kármán hypotheses, the governing equations of motion for the in-plane and out-of-plane motions including the effects of geometric nonlinearity, rotary inertia and shear deformation are achieved by means of the Hamilton's principle. In the solution process, the nonlinear partial differential equations of motions and associated boundary conditions are discretized via the generalized differential quadrature (GDQ) and afterward converted into a Duffing-type nonlinear time-varying set of ordinary differential equations via a numerical Galerkin approach. Then, the time periodic discretization method and the pseudo-arc length continuation technique are employed to solve the obtained equations in order to achieve the frequency–response curves associated with nonlinear free and forced resonances for the CNT-FPMLC rectangular plates with various edge supports. Finally, the influences of important design parameters including the weight percentage of single-walled and multi-walled CNTs, volume fraction of fibers, CNT aspect ratio, plate geometry and boundary conditions on the nonlinear resonant dynamics and linear natural frequencies of CNT-FPMLC rectangular plate are investigated in the numerical results. © 2018 Elsevier Masson SAS
Asadollahi a., ,
Sohrabnezhad, S.,
Ansari, R.,
Zanjanchi, M.A. Publication Date: 2018
Materials Science in Semiconductor Processing (13698001)87pp. 119-125
Polyaniline (PANI), a conjugated polymer, was used as a support to produce heterojunctions with Ag2CO3. The synthesized Ag2CO3-PANI composite with simple precipitation method, was characterized by UV–visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The optimum photocatalytic activity of Ag2CO3-PANI at a weight content of 50% PANI for the degradation of methylene blue (MB) was almost 86% that is much higher than the pure Ag2CO3 and PANI. The high visible light activity was mainly attributed to synergistic effects including the strong visible light absorption, the strong adsorption of MB upon the surface of PANI, high charge transfer and separation efficiency. to investigate stability, four cycle experiments on composite indicated the high photostability. Finally, a probable photocatalytic mechanism of charge transfer was proposed for the enhanced photocatalytic performance. © 2018 Elsevier Ltd
Publication Date: 2018
Cellulose Chemistry and Technology (05769787)52(3-4)pp. 271-282
This paper describes the potential use of α-Fe2O3 nanoparticles (α-Fe2O3 NPs) and α-Fe2O3 sawdust nanocomposite (α-Fe2O3/SD NC) toward the removal of arsenic from aqueous systems. The α-Fe2O3NPs were synthesized by the co-precipitation method on sawdust. The samples were characterized using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). SEM micrographs showed the formation of α-Fe2O3NPs within 40-60 nm in size, which were homogeneously dispersed on the sawdust surface. The adsorption experiments were performed in a batch system. The optimum pH value for the maximum removal of As(III) was found at a value of about 7. The monolayer adsorption amounts calculated based on the Langmuir adsorption model were 83.33 and 58.80 mgg-1 for α-Fe2O3 and α-Fe2O3/SD, respectively. The kinetic data obeyed the pseudo-second-order kinetic model. The high adsorption capacity was attributed to the high surface area of α-Fe2O3NPs and good dispersion α-Fe2O3NPs on the sawdust substrate. The experimental results suggest that α-Fe2O3/SDNC is a promising and cost-effective adsorbent for the removal of As(III) ions from aqueous solutions. © 2018 Editura Academiei Romane. All rights reserved.
Publication Date: 2018
Structural Concrete (14644177)19(6)pp. 1702-1712
Using a multiscale approach, the critical compressive load of a cylindrical shell made by concrete/graphene nanocomposite is computed. At the first step, using a multiscale method, the elastic modulus of concrete/graphene nanocomposites with different graphene volume percentages and sizes are evaluated. Then, the finite element method is used to obtain the critical compressive load of a cylindrical shell made by the concrete/graphene nanocomposites. It is observed that the elastic modulus and buckling load of the concrete/graphene nanocomposites are reduced by increasing the temperature. It is also shown that when the graphene sheets are directed along the external force, the mechanical properties of the concrete are improved more than the case in which the graphene sheets are randomly directed in the concrete matrix. © 2018 fib. International Federation for Structural Concrete
Publication Date: 2018
Advances in Applied Mathematics and Mechanics (20751354)10(1)pp. 184-208
This article investigates the geometrically nonlinear free vibration of piezoelectric-piezomagnetic nanobeams subjected to magneto-electro-thermal loading taking into account size effect using the nonlocal elasticity theory. To this end, the sizedependent nonlinear governing equations of motion and corresponding boundary conditions are derived according to the nonlocal elasticity theory and the first-order shear deformation theory with von Kármán-type of kinematic nonlinearity. The effects of size-dependence, shear deformations, rotary inertia, piezoelectric-piezomagnetic coupling, thermal environment and geometrical nonlinearity are taken into account. The generalized differential quadrature (GDQ) method in conjunction with the numerical Galerkin method, periodic time differential operators and pseudo arclength continuation method is utilized to compute the nonlinear frequency response of piezoelectric-piezomagnetic nanobeams. The influences of various parameters such as non-dimensional nonlocal parameter, temperature change, initial applied electric voltage, initial applied magnetic potential, length-to-thickness ratio and different boundary conditions on the geometrically nonlinear free vibration characteristics of piezoelectric-piezomagnetic nanobeams are demonstrated by numerical examples. It is illustrated that the hardening spring effect increases with increasing the non-dimensional nonlocal parameter, positive initial applied voltage, negative initial applied magnetic potential, temperature rise and decreases with increasing the negative initial applied voltage, positive initial applied magnetic potential and length-tothickness ratio. © 2018 Cambridge University Press. All rights reserved.
Publication Date: 2018
European Physical Journal Plus (21905444)133(8)
In this paper, three size-dependent formulations are developed for the analysis of Timoshenko nanobeams with various end conditions based on the nonlocal and strain gradient theories. The nonlocal governing equations are presented based on the stress-driven model of Eringen’s theory. First, a strain gradient Timoshenko beam model is developed. The governing equations of the integral stress-driven model, and then those of differential stress-driven model together with associated constitutive boundary conditions are obtained in the next step. With the aim of addressing the static bending and free vibration problems, the nonlocal governing equations in integral form are directly solved by constructing matrix differential and integral operators. Furthermore, the governing equations in differential form together with constitutive boundary conditions are discretized and solved via the mentioned operators. It is shown that there is a good agreement between the results obtained from solving the integral and differential governing equations of stress-driven nonlocal models. Several comparative studies are also conducted for the bending and vibration analyses of nanobeams based on the strain gradient and stress-driven nonlocal models. The results reveal that in both models, increasing the nonlocal/length scale parameter has a stiffening effect on the response of the system. However, the stiffening effect corresponding to the strain gradient model is more pronounced than that corresponding to the stress-driven nonlocal model. © 2018, Società Italiana di Fisica and Springer-Verlag GmbH Germany, part of Springer Nature.
Ajori, S.,
Ansari, R.,
Hassani r., R.,
Haghighi s., S. Publication Date: 2018
Journal Of Molecular Modeling (16102940)24(9)
Based on molecular dynamics (MD) simulations, the buckling analysis of a perfect carbon nanotorus is presented herein. First of all, the minimum length of single-walled carbon nanotubes (SWCNTs) with different radii is determined at which perfect toroidal CNTs can be formed without any ripple at the inner side of the rings. According to the results, by increasing the radius of SWCNT (r), the radius of its corresponding perfect nanotorus (R) increases. Also, for SWCNTs with various lengths, it is found that the buckling force and strain of related carbon nanotoruses increase by increasing R/r. In addition, as the perfect toroidal CNTs are arranged vertically in a column form in accordance with two different schemes, the effects of increasing the radius (R) and the number of carbon nanotoruses (the height of the column made by nanotoruses) on the buckling force and strain are investigated. Based on the results, as a fixed number of carbon nanotoruses with the same radius are arranged vertically in the column form, the buckling force and strain increase by increasing R/r. By contrast, increasing the height of the column made by carbon nanotoruses with similar radius leads to the reduction of buckling force and strain. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
Applied Mathematics and Mechanics (English Edition) (02534827)39(9)pp. 1219-1238
The purpose of the present study is to examine the impact of initial geometric imperfection on the nonlinear dynamical characteristics of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) rectangular plates under a harmonic excitation transverse load. The considered plate is assumed to be made of matrix and single-walled carbon nanotubes (SWCNTs). The rule of mixture is employed to calculate the effective material properties of the plate. Within the framework of the parabolic shear deformation plate theory with taking the influence of transverse shear deformation and rotary inertia into account, Hamilton’s principle is utilized to derive the geometrically nonlinear mathematical formulation including the governing equations and corresponding boundary conditions of initially imperfect FG-CNTRC plates. Afterwards, with the aid of an efficient multistep numerical solution methodology, the frequency-amplitude and forcing-amplitude curves of initially imperfect FG-CNTRC rectangular plates with various edge conditions are provided, demonstrating the influence of initial imperfection, geometrical parameters, and edge conditions. It is displayed that an increase in the initial geometric imperfection intensifies the softening-type behavior of system, while no softening behavior can be found in the frequency-amplitude curve of a perfect plate. © 2018, Shanghai University and Springer-Verlag GmbH Germany, part of Springer Nature.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Mahmoodi m.j., M.J. Publication Date: 2018
Journal of Alloys and Compounds (09258388)744pp. 637-650
Thermoelastic responses of carbon nanotube (CNT)-reinforced aluminum (Al) metal matrix nanocomposites (MMNCs) are studied comprehensively using an analytical micromechanical model. The effects of various parameters, including CNT volume fraction, cross-section shape, aspect ratio, directional behavior, non-straight shape, dispersion type, arrangement type, agglomerated state and generating the aluminum carbide (Al4C3) interphase between the CNT and Al matrix on the Al MMNCs coefficient of thermal expansion (CTE) are investigated. To verify the presented model for both aligned CNT-reinforced Al MMNC and randomly oriented CNT-reinforced Al MMNC systems, the predictions are well compared with the available experimental data in the literature. It is found that both cross-section shape and arrangement type of aligned CNTs do not affect the Al MMNC thermal expansion response. With increasing the CNT volume fraction, the transverse CTE of the aligned CNT-reinforced Al MMNCs increases up to the peculiar value and then decreases. However, the longitudinal CTE and the CTE of Al MMNCs containing randomly oriented CNTs continuously decrease by increasing the volume fraction. It is observed that the Al MMNC CTE is very sensitive to the CNT directional behavior, non-straight shape and the aspect ratio. The results indicate the CNT agglomerated state can degrade the Al MMNCs CTE. © 2018 Elsevier B.V.
Publication Date: 2018
Structural Engineering and Mechanics (12254568)68(3)pp. 313-323
A numerical study is performed to investigate the impacts of thermal loading on the vibration and buckling of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical shells. Thermo-mechanical properties of constituents are considered to be temperature-dependent. Considering the shear deformation theory, the energy functional is derived, and applying the variational differential quadrature (VDQ) method, the mass and stiffness matrices are obtained. The shear correction factors are accurately calculated by matching the shear strain energy obtained from an exact three-dimensional distribution of the transverse shear stresses and shear strain energy related to the first-order shear deformation theory. Numerical results reveal that considering temperature-dependent material properties plays an important role in predicting the thermally induced vibration of FG-CNTRC conical shells, and neglecting this effect leads to considerable overestimation of the stiffness of the structure. Copyright © 2018 Techno-Press, Ltd.
Publication Date: 2018
Microsystem Technologies (09467076)24(6)pp. 2775-2782
The nonlocal vibrations of Euler–Bernoulli nanobeams are studied in this paper within the framework of fractional calculus. It is assumed that the material properties are functionally graded in the thickness direction and are estimated using the power-law function. Hamilton’s principle is applied to drive the fractional equation of motion which is then solved based on a new numerical approach named as variational finite difference method (VFDM). VFDM is formulated by the finite difference method (FDM) and matrix differential/integral operators. Since the method is directly applied to the variational form of governing equation, it is advantageous over existing approaches used for the fractional nonlocal models. The effects of nonlocality, fractional parameters and gradient of material on the fundamental frequencies of nanobeams subject to fully clamped, fully simply supported and clamped-simply supported boundary conditions are analyzed through illustrative examples. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Publication Date: 2018
Materials Research Express (20531591)5(11)
The vibration and stability of functionally graded carbon nanotube-reinforced (FG-CNTRC) composite annular sector plates resting on Winkler-Pasternak elastic foundation subjected to a periodic radial compressive load are investigated for various boundary conditions. To this end, a shear deformable plate model is established according to a parabolic theory which can interpret the shear deformation and rotary inertia effects without using any shear correction factor. The modified micromechanical technique is employed to compute the effective material properties of the FG-CNTRCs. The discretized form of higher-order governing equations is directly accessed by employing Hamilton's principle and the variational differential quadrature (VDQ) method. In addition, by considering the applied radial compressive force as a periodic function, the discretized equations are expressed as the Mathieu-Hill equations, and then the instability regions are determined via the Bolotin's scheme. In numerical results, the effects of the CNT distribution pattern and volume fraction, geometry parameters, sector angle, elastic foundation and static load factor on the stability of FG-CNTRC annular sector plates subject to arbitrary edge conditions are thoroughly discussed. © 2018 IOP Publishing Ltd.
Publication Date: 2018
Archives of Civil and Mechanical Engineering (16449665)18(2)pp. 611-621
A finite element model based upon the density functional theory is developed to investigate the vibrational characteristics of armchair phosphorene nanotubes. To this end, the P[sbnd]P bonds are simulated by beam elements whose elastic properties are obtained from the analogy of molecular and structural mechanics. The effects of nanotube length, diameter and boundary conditions on the frequencies of armchair phosphorene nanotubes are evaluated. It is shown that the effect of nanotube radius on its natural frequency is weakened by increasing the nanotube aspect ratio. Comparing the first ten frequencies of armchair phosphorene nanotubes with different diameters, it is observed that the effect of diameter on the vibrational behavior of phosphorene nanotubes is more pronounced at higher modes. © 2017 Politechnika Wrocławska
Publication Date: 2018
Physica E: Low-Dimensional Systems and Nanostructures (13869477)104pp. 327-332
The vibrational behaviors of gold nanowires (GNWs) and hybrid GNWs@single-walled carbon nanotubes (SWCNTs) are studied by employing molecular dynamics (MD) simulations. The effects of geometrical parameters, i.e. length and diameter and various structures of enclosed GNWs in SWCNTs, i.e. multi-shell and pentagonal GNWs, on the natural frequency are investigated. The results show that by increasing the length, the natural frequency of system decreases. It is seen that the effect of length on the vibrational characteristic of SWCNT is more pronounced than GNWs and hybrid GNWs@SWCNTs models. Moreover, the results show that in the similar length, the highest and lowest natural frequencies are related to the pure SWCNTs and pure GNWs, respectively. Furthermore, the natural frequencies of hybrid GNWs@SWCNTs models are between the values of their constituent pure structures. It is also indicated that the natural frequency of SWCNTs with higher aspect ratios is less sensitive to the encapsulation than those with smaller aspect ratios. © 2018 Elsevier B.V.
Publication Date: 2017
Applied Physics A: Materials Science and Processing (14320630)123(4)
In this paper, the vibrational characteristics of zigzag phosphorene nanotubes are investigated by using a three-dimensional finite element model. The beam elements are used to simulate the P–P bonds in the structure of the phosphorene nanotubes. The elastic properties of the beam elements are computed from the similarity of energy terms in the molecular and structural mechanics. Besides, mass elements are located at the place of the atoms. Considering the zigzag phosphorene nanotubes with different diameters, it is shown that the effect of the diameter on the first natural frequencies of the nanotubes can be neglected. However, this effect increases for higher modes. Besides, at the same diameter, the zigzag phosphorene nanotubes with larger aspect ratios (length/diameter) have smaller frequencies. © 2017, Springer-Verlag Berlin Heidelberg.
Publication Date: 2017
Physica E: Low-Dimensional Systems and Nanostructures (13869477)88pp. 272-278
In this paper, the density functional theory calculations are used to obtain the elastic properties of zigzag phosphorene nanotubes. Besides, based on the similarity between phosphorene nanotubes and a space-frame structure, a three-dimensional finite element model is proposed in which the atomic bonds are simulated by beam elements. The results of density functional theory are employed to compute the properties of the beam elements. Finally, using the proposed finite element model, the elastic modulus of the zigzag phosphorene nanotubes is computed. It is shown that phosphorene nanotubes with larger radii have larger Young's modulus. Comparing the results of finite element model with those of density functional theory, it is concluded that the proposed model can predict the elastic modulus of phosphorene nanotubes with a good accuracy. © 2017 Elsevier B.V.
Publication Date: 2017
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)41(2)pp. 141-147
In this study, a micromechanics-based analytical model is proposed to evaluate the effective thermo-elastic properties of polymer matrix nanocomposite materials. Accuracy, simplicity and efficiency are the main features of this micromechanical model. The constituents of representative volume element of nanocomposites are treated as three distinct phases, consisting of nanofiller, polymer matrix and interphase around the nanofiller. Young's modulus and coefficient of thermal expansion of the interphase are continuously graded from those of the nanofiller to those of the polymer matrix. The effects of nanoparticle volume fraction, nanoparticle size, interphase thickness, nanofiller aspect ratio and number of layers in the interphase on the thermo-elastic properties of nanocomposites are studied. The comparison of results of the presented model with experimental data and other available micromechanical analysis demonstrates the validity of the proposed micromechanical model in the case of response of nanocomposites with graded properties of interphase. © 2016 Shiraz University.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2017
Journal of Composite Materials (00219983)51(20)pp. 2899-2912
A comprehensive investigation is carried out into the elastic behavior of carbon nanotube-reinforced polymer nanocomposites using two combined analytical micromechanical methods. A unit cell-based micromechanical method is developed to model the random distribution of carbon nanotubes within the polymer matrix. Also, the Eshelby method is used for modeling the random orientation state of carbon nanotubes within the matrix. Two fundamental aspects affecting the mechanical behavior of carbon nanotube/polymer nanocomposites, including the carbon nanotube waviness and the interphase formed due to the non-boned interaction between the carbon nanotube and the surrounding polymer, are considered in the unit cell method. Comparisons between the results of present method and experimental data reveal that for more realistic predictions, five important factors including, random orientation and random distribution of carbon nanotubes, interphase, waviness and transversely isotropic behavior of carbon nanotube should be considered in the modeling of carbon nanotube-reinforced polymer nanocomposites. The effects of volume fraction, number of waves and waviness factor of carbon nanotube as well as the type of random distribution of CNTs within the matrix on the elastic modulus of the polymer nanocomposites are studied. © 2017, © The Author(s) 2017.
Ansari, R.,
Shakouri a.h., ,
Bazdid-vahdati m., M.,
Norouzzadeh, A.,
Rouhi h., H. Publication Date: 2017
Journal of Computational and Nonlinear Dynamics (15551423)12(1)
Based on the micropolar elasticity theory, a size-dependent rectangular element is proposed in this article to investigate the nonlinear mechanical behavior of plates. To this end, a novel three-dimensional formulation for the micropolar theory with the capability of being used easily in the finite element approach is developed first. Afterward, in order to study the micropolar plates, the obtained general formulation is reduced to that based on the Mindlin plate theory. Accordingly, a rectangular plate element is developed in which the displacements and microrotations are estimated by quadratic shape functions. To show the efficiency of the developed element, it is utilized to address the nonlinear bending problem of micropolar plates with different types of boundary conditions. It is revealed that the present finite element formulation can be efficiently employed for the nonlinear modeling of small-scale plates by considering the micropolar effects. © 2017 by ASME.
Publication Date: 2017
Composite Structures (02638223)166pp. 202-218
By considering the small-scale effect based on the nonlocal elasticity theory, the nonlinear postbuckling of thick and moderately thick rectangular piezoelectric-piezomagnetic nanoplates with various edge supports subjected to the magneto-electro-thermo-mechanical loading is investigated. For this objective, a unified nonlinear higher-order shear deformable plate model is proposed. By adopting the nonlocal theory to capture the small-scale effect and utilizing a generalized displacement field to consider the influence of transverse shear deformation, unified size-dependent nonlinear governing equations and related boundary conditions are derived based on the virtual work principle in conjunction with von Kármán geometric nonlinearity. By choosing appropriate shape functions, the developed plate model can be reduced to the size-dependent Kirchhoff, Mindlin, Reddy, parabolic, trigonometric, hyperbolic and exponential shear deformable plate models. The nonlinear governing equations and boundary conditions are discretized using the generalized differential quadrature method first. Then, the pseudo arc-length continuation technique is used to solve the discretized equations and obtain the secondary equilibrium path of nanoplate in the postbuckling regime. In addition to providing significant guidelines for accurate prediction of the stability conditions nanoplates, extracting various plate models on the basis of any existing shear deformable plate theory becomes readily attainable by utilizing the proposed unified plate model. © 2017 Elsevier Ltd
Azarboni, H.R.,
Darvizeh a., A.,
Darvizeh m., M.,
Ansari, R. Publication Date: 2017
Meccanica (15729648)52(1-2)pp. 317-332
This paper focuses on the cavitation effect on nonlinear elastoplastic deformation rectangular aluminum plate subjected to underwater explosion loading. Cavitation is a phenomenon that may be occurred for plates in the process of underwater explosion forming. The total pressure of the explosion becomes zero at the cavitation time, so that the governing equations of motion will be different before and after the cavitation. As a result, in terms of analysis and design, the cavitation time is significant in studying the behavior of a rectangular plate at underwater explosive loading. Based on Hamilton principle and variation method the nonlinear equations of motion of an underwater rectangular plate subjected to explosive loading are obtained. Exact linear dynamic response of plate is derived by employing the eigen function and nonlinear dynamic response of plate is derived by employing the finite difference method (FDM). The linear and nonlinear work hardening material modeling is considered to define the elastoplastic stress–strain relations. Return mapping algorithm is applied to calculate the stress and strain in any steps of loading. Then, the displacement, velocity and generated stress of plate during cavitation time are calculated. Using von Mises yield criterion, one can distinguishes the cavitation with in elastic or plastic regimes. By recognizing the time of cavitation in the range of elastic or plastic, the displacement and velocity field of plate are determined in duration of explosive loading. Results show that the cavitation time is on the order of 5–10 μs. Depending on amount of charge mass and stand-off, the cavitation time may occur in elastic or plastic regime. The results obtained of linear exact solution considering the linear work hardening material modeling are compared to results obtained of FDM considering the linear and nonlinear work hardening material modeling. © 2016, Springer Science+Business Media Dordrecht.
Samadani f., F.,
Moradweysi p., ,
Ansari, R.,
Hosseini, K.,
Darvizeh a., A. Publication Date: 2017
Zeitschrift fur Naturforschung - Section A Journal of Physical Sciences (09320784)72(12)pp. 1093-1104
In this investigation, the homotopy analysis method (HAM) is utilized for the pull-in and nonlinear vibration analysis of nanobeams based on the stress-driven model (SDM) of nonlocal elasticity theory. The physical properties of nanobeams are assumed not to vary through the thickness. The nonlinear equation of motion and the corresponding boundary condition are derived on the basis of the Euler-Bernoulli beam theory. For the solution purpose, the Galerkin method is employed for reducing the nonlinear partial differential equation to a nonlinear ordinary differential equation in the time domain, and then, the resulting equation is analytically solved using the HAM. In the results section, the influences of different parameters, including nonlocal parameter, electrostatic and intermolecular van der Waals forces and fringing field effect changes on the pull-in and nonlinear vibration response are investigated. © 2017 Walter de Gruyter GmbH, Berlin/Boston 2017.
Publication Date: 2017
Composites Part B: Engineering (13598368)109pp. 197-213
The main objective of this paper is to present the buckling and vibration analysis of thermally pre-stressed functionally graded carbon-nanotube-reinforced composite (FG-CNTRC) annular sector plates resting on the elastic foundation via the variational differential quadrature (VDQ) method. The material properties of nanocomposite plate are considered to continuously vary across the thickness and are estimated according to the modified rule of mixture. The governing equations are derived on the basis of first order shear deformation theory. Applying two-dimensional generalized differential quadrature (GDQ) method, the energy functional of the structure is discretized. Then, based on Hamilton's principle and the VDQ method, the reduced forms of mass and stiffness matrices are obtained. After verifying the accuracy of the present method, comprehensive numerical results are presented to examine the effects of important parameters on the stability and vibrational behavior of the nanotube-reinforced composite annular sector plates. The results indicate that functionally graded distributions of CNTs in the thickness direction and the increase of elastic foundation coefficients can improve the stability of the structure. © 2016 Elsevier Ltd
Publication Date: 2017
Brazilian Journal Of Physics (01039733)47(6)pp. 606-616
The buckling analysis of functionalized carbon nanotubes (CNTs) is of great importance for the better understanding of mechanical behavior of nanocomposites. The buckling behavior of carbene-functionalized CNTs (cfCNTs) under physical adsorption of polymer chains (cfCNTs/polymers) is studied in this paper by the classical molecular dynamics (MD) simulations. In this regard, to investigate the interactions between non-covalent polymer chains and cfCNTs, two different non-covalent functional groups, i.e. polycarbonate (PC) and polypropylene (PP), are selected. The findings are compared with those of pure CNTs under the physical adsorption of polymer chains (pCNTs/polymers). The obtained results show that at a given weight percentage of non-covalent functional groups, the gyration radius of cfCNTs/polymers is higher than that of pCNTs/polymers. Furthermore, an increase in the critical buckling force of cfCNTs/polymers is dependent on the type of non-covalent polymer chains. For cfCNTs/PC and cfCNTs/PP, the critical buckling force is respectively lower and higher than that of pCNTs/polymers for the similar weight percentage of non-covalent functional groups. In addition, it is found that the critical buckling strain of cfCNTs/polymers is smaller than that of pCNTs/polymers for the same weight percentage of non-covalent polymer chains. © 2017, Sociedade Brasileira de Física.
Publication Date: 2017
Mechanics of Advanced Materials and Structures (15210596)24(14)pp. 1180-1188
Dynamic stability of embedded multi-walled carbon nanotubes (MWCNTs) in an elastic medium and thermal environment and subjected to an axial compressive force is studied based on the nonlocal elasticity and Timoshenko beam theory. The developed nonlocal beam model has the capability to consider the small scale effects. The generalized differential quadrature method is employed to discretize the dynamic governing differential equations of MWCNTs with various end supports. A parametric study is conducted to investigate the influences of static load factor, temperature change, nonlocal parameter, slenderness ratio, and spring constant of elastic medium on the dynamic stability characteristics of MWCNTs. © 2017 Taylor & Francis Group, LLC.
Publication Date: 2017
Advanced Powder Technology (15685527)28(1)pp. 304-313
Two serious problems for semiconductor photocatalysts are their poor photocatalytic activity and low stability. In this work, Ag2CO3 nanoparticles incorporated in mordenite zeolite (MOR) by a facile precipitation method. Silver bromide (AgBr) with different weight percentage (20%, 40% and 50%) was coupled into Ag2CO3-MOR composite and producing a series of novel AgBr/Ag2CO3-MOR nanocomposites. The effects of AgBr on the Ag2CO3–MOR catalyst for the photocatalytic degradation of methyl blue (MB) under visible light irradiation have been investigated. The structure, composition and optical properties of nanocomposites were investigated by UV–Visible diffuse reflectance spectroscopy (UV–Vis DRS), X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM). The prepared AgBr/Ag2CO3-MOR photocatalyst with the optimal content of AgBr (50 wt%) indicated higher photocatalytic activity than that of the Ag2CO3-MOR and Ag2CO3 for degradation of methylene blue (MB) under visible light irradiation. For studying of stability of nanocomposites, Fe+3 ions, as a cheap and available cocatalyst, was inserted into mordenite matrix (Fe3+/MOR) by impregnation method. The hybrid material (AgBr/Ag2CO3) was synthesized in the Fe3+/MOR matrix by precipitation method. The cycle experiments on the AgBr/Ag2CO3-Fe/MOR nanocomposite indicated that cocatalyst, not only to improve photocatalytic activity, but also enhance photoinduced stability of photosensitive silver compounds in all cycles with respect to MOR. On the basis of the experimental results, a possible mechanism for the enhanced photocatalytic activity and photoinduced stability of silver compounds by Fe3+ cocatalyst was proposed. The mordenite support played an important role in decreases of recombination of photogenerated electrons-holes and increases of MB absorption. The Fe cocatalyst reduced photocorrosion of silver compounds. © 2016 The Society of Powder Technology Japan
Publication Date: 2017
Optical and Quantum Electronics (discontinued) (03068919)49(4)
Nonlinear fractional Boussinesq equations are considered as an important class of fractional differential equations in mathematical physics. In this article, a newly developed method called the exp (- ϕ(ε)) -expansion method is utilized to study the nonlinear Boussinesq equations with the conformable time-fractional derivative. Different forms of solutions, including the hyperbolic, trigonometric and rational function solutions are formally extracted. The method suggests a useful and efficient technique to look for the exact solutions of a wide range of nonlinear fractional differential equations. © 2017, Springer Science+Business Media New York.
Publication Date: 2017
Physica E: Low-Dimensional Systems and Nanostructures (13869477)88pp. 194-200
Stress-strain relation in Eringen's nonlocal elasticity theory was originally formulated within the framework of an integral model. Due to difficulty of working with that integral model, the differential model of nonlocal constitutive equation is widely used for nanostructures. However, paradoxical results may be obtained by the differential model for some boundary and loading conditions. Presented in this article is a finite element analysis of Timoshenko nano-beams based on the integral model of nonlocal continuum theory without employing any simplification in the model. The entire procedure of deriving equations of motion is carried out in the matrix form of representation, and hence, they can be easily used in the finite element analysis. For comparison purpose, the differential counterparts of equations are also derived. To study the outcome of analysis based on the integral and differential models, some case studies are presented in which the influences of boundary conditions, nonlocal length scale parameter and loading factor are analyzed. It is concluded that, in contrast to the differential model, there is no paradox in the numerical results of developed integral model of nonlocal continuum theory for different situations of problem characteristics. So, resolving the mentioned paradoxes by means of a purely numerical approach based on the original integral form of nonlocal elasticity theory is the major contribution of present study. © 2017 Elsevier B.V.
Publication Date: 2017
Modern Physics Letters B (02179849)31(6)
This paper aims to study the thermal conductivity coefficient of aluminum matrices reinforced by single-walled carbon nanotubes. To obtain the thermal conductivity coefficient of the nanocomposites, a small temperature difference is applied on two opposite edges of a representative volume element. The nanotubes are distributed in Al matrix by using three different patterns, including random pattern, regular pattern with nanotube direction along the temperature difference and regular pattern with nanotube direction perpendicular to the temperature change. It is shown that the best enhancement in the thermal conductivity of aluminum matrix occurs by the regular distribution of the nanotubes along the temperature change. Also, increasing the volume fraction of nanotubes in aluminum matrix leads to increasing the thermal conductivity coefficient of the nanocomposite. © 2017 World Scientific Publishing Company.
Publication Date: 2017
EPJ Applied Physics (12860042)78(2)
Using the finite element method, multi-walled carbon nanotubes-based mass sensors are studied. The effects of different parameters such as number of walls of nanotube, nanotube diameter and nanotube length on the mass sensibility are explored. It is shown that the maximum sensitivity of nanotubes under clamped-free boundary conditions occurs when the mass is located at the farthest location from the clamped edge. Comparing the results of nanotubes with different walls, it is observed that single-walled carbon nanotubes are the best mass sensors. Moreover, it is represented that for large masses connected to the nanotubes, the mass sensor can only identify that an external mass added to it and the mass value is not identifiable. © EDP Sciences, 2017.
Publication Date: 2017
EPJ Applied Physics (12860042)80(3)
This paper aims to investigate the elastic modulus of the polypropylene matrix reinforced by carbon nanotubes at different temperatures. To this end, the finite element approach is employed. The nanotubes with different volume fractions and aspect ratios (the ratio of length to diameter) are embedded in the polymer matrix. Besides, random and regular algorithms are utilized to disperse carbon nanotubes in the matrix. It is seen that as the pure polypropylene, the elastic modulus of carbon nanotube reinforced polypropylene decreases by increasing the temperature. It is also observed that when the carbon nanotubes are dispersed parallelly and the load is applied along the nanotube directions, the largest improvement in the elastic modulus of the nanotube/polypropylene nanocomposites is obtained. © EDP Sciences, 2017.
Publication Date: 2017
International Journal of Modern Physics B (02179792)31(4)
This paper concerns the vibrational behavior of concentric double-walled and triple-walled carbon and boron nitride nanotubes using the finite element method. Armchair and zigzag nanotubes with different lengths and diameters are considered. Moreover, different boundary conditions are applied on the nanotubes. It is observed that in double-walled nanotubes, when the inner and outer layers are respectively from boron nitride and carbon, the frequencies are larger than those in the reverse arrangement. Investigating the effect of diameter on the first 10 natural frequencies of double-walled and triple-walled nanotubes showed that nanotubes with larger diameters possess smaller frequencies. The effect of diameter is more significant for higher modes. Finally, comparisons are made between the vibrational behavior of concentric carbon and boron nitride double-walled and triple-walled nanotubes. Considering the effect of vacancy defect on the vibrational characteristics of the nanotubes revealed that when all of the walls of the nanotubes are defective, the largest diminish occurs for the fundamental natural frequencies. © 2017 World Scientific Publishing Company.
Publication Date: 2017
Structural Engineering and Mechanics (12254568)64(3)pp. 329-337
This study concerns the vibrational behavior of multi-walled nested silicon-carbide and carbon nanotubes using the finite element method. The beam elements are used to model the carbon-carbon and silicon-carbon bonds. Besides, spring elements are employed to simulate the van der Waals interactions between walls. The effects of nanotube arrangement, number of walls, geometrical parameters and boundary conditions on the frequencies of nested silicon-carbide and carbon nanotubes are investigated. It is shown that the double-walled nanotubes have larger frequencies than triple-walled nanotubes. Besides, replacing silicon carbide layers with carbon layers leads to increasing the frequencies of nested silicon-carbide and carbon nanotubes. Comparing the first ten mode shapes of nested nanotubes, it is observed that the mode shapes of armchair and zigzag nanotubes are almost the same. Copyright © 2017 Techno-Press, Ltd.
Publication Date: 2017
Composite Structures (02638223)180pp. 760-771
A large deflection geometrically nonlinear analysis of functionally graded (FG) multilayer graphene platelet-reinforced polymer composite (GPL-RPC) rectangular plates subjected to uniform and sinusoidal transverse mechanical loadings is performed in this article. Based on the sinusoidal shear deformation plate theory and von Kármán nonlinear strain-displacement relations, the nonlinear governing equilibrium equations and boundary conditions are developed by using the principle of virtual work. It is assumed that the weight fraction of GPL nanofillers layer-wisely changes across the thickness of plate. The effective Young's modulus of FG-GPL-RPCs is approximately calculated via the modified Halpin-Tsai model. Also, the effective Poisson's ratio and mass density are determined by employing the rule of mixture. The investigation is performed by using a numerical solution approach. To evaluate the nonlinear bending stiffness of FG multilayer GPL-RPC plate, the discretization of governing equations and boundary conditions is carried out using the generalized differential quadrature (GDQ) method, and the pseudo arc-length continuation technique is employed to solve the set of nonlinear algebraic discretized equations to obtain the load-deflection curve. Numerical problems are given to reveal the influences of GPL distribution pattern, weight fraction, geometry of GPL nanofillers, length-to-thickness and edge conditions on nonlinear bending responses of the GPL-RPC plates. © 2017 Elsevier Ltd
Publication Date: 2017
Applied Mathematical Modelling (0307904X)43pp. 337-350
In this paper, the linear and nonlinear vibrations of fractional viscoelastic Timoshenko nanobeams are studied based on the Gurtin–Murdoch surface stress theory. Firstly, the constitutive equations of fractional viscoelasticity theory are considered, and based on the Gurtin–Murdoch model, stress components on the surface of the nanobeam are incorporated into the axial stress tensor. Afterward, using Hamilton's principle, equations governing the two-dimensional vibrations of fractional viscoelastic nanobeams are derived. Finally, two solution procedures are utilized to describe the time responses of nanobeams. In the first method, which is fully numerical, the generalized differential quadrature and finite difference methods are used to discretize the linear part of the governing equations in spatial and time domains. In the second method, which is semi-analytical, the Galerkin approach is first used to discretize nonlinear partial differential governing equations in the spatial domain, and the obtained set of fractional-order ordinary differential equations are then solved by the predictor–corrector method. The accuracy of the results for the linear and nonlinear vibrations of fractional viscoelastic nanobeams with different boundary conditions is shown. Also, by comparing obtained results for different values of some parameters such as viscoelasticity coefficient, order of fractional derivative and parameters of surface stress model, their effects on the frequency and damping of vibrations of the fractional viscoelastic nanobeams are investigated. © 2016 Elsevier Inc.
Publication Date: 2017
European Physical Journal Plus (21905444)132(7)
This paper deals with the mechanical oscillatory behavior of a C60 fullerene inside open carbon nanocones (CNCs). The fullerene molecule is assumed to enter the nanocone through its small end or wide end. Following our previously published study, semi-analytical expressions for the evaluation of vdW interactions are presented which facilitate obtaining a formula for oscillation frequency. The equation of motion is numerically solved to attain the time histories of separation distance and velocity of the fullerene molecule. Based on the conservation of the mechanical energy law, a new semi-analytical formula is also derived to accurately evaluate the oscillation frequency of the system. With respect to the present formulation, a detailed parametric study is conducted to gain an insight into the effects of both geometrical parameters (small-end radius, wide-end radius and vertex angle of nanocone) and initial conditions (initial separation distance and initial velocity) on the oscillatory behavior of C60 fullerene-open CNC oscillators. For given geometrical parameters and initial conditions, it is shown that higher oscillation frequencies can be achieved when the fullerene molecule enters the open nanocone through its small end. © 2017, Società Italiana di Fisica and Springer-Verlag GmbH Germany.
Publication Date: 2017
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)231(13)pp. 2540-2553
Lipid nanotubes with well-designed cylindrical structures, tunable dimensions and biocompatible membrane surfaces have found potential applications such as templates to create diverse one-dimensional nanostructures and nanocarriers for drug or gene delivery. In this regard, knowing the encapsulation process is of crucial importance for such developments. The aim of this paper is to study the suction and acceptance phenomena of metallic nanoparticles, and in particular silver and gold, inside lipid nanotubes using the continuum approximation and the 6-12 Lennard-Jones potential function. The nanoparticle is modelled as a perfect sphere and the lipid nanotube is assumed to comprise six layers, namely two head groups, two intermediate layers and two tail groups. Analytical expressions are derived through undertaking surface and volume integrals to evaluate van der Waals potential energy and interaction force of a nanoparticle entering a semi-infinite lipid nanotube. These expressions are then employed to determine the suction and acceptance energies of system. To ascertain the accuracy of the proposed analytical expressions, the multiple integrals of van der Waals interactions are evaluated numerically based on the differential quadrature method. A comprehensive study is conducted to get an insight into the effects of different geometrical parameters including radius of nanoparticles, innermost radius of lipid nanotube, head group and tail group thicknesses on the nature of suction and acceptance energies and van der Waals interactions. Numerical results show that maximum suction energy increases by enlarging the nanoparticle size, while it decreases by increasing the head group thickness or the tail group thickness. It is further found that gold nanoparticle experiences higher maximum suction energies inside lipid nanotubes compared to silver nanoparticle. © IMechE 2016.
Publication Date: 2017
Meccanica (15729648)52(7)pp. 1625-1640
In this work, elastic, thermoelastic and viscoelastic properties of functionally graded carbon nanotube reinforced polymer nanocomposites are investigated using a 3-dimensional micromechanics-based approach. The main advantage of the proposed micromechanical model is its ability to give closed-form formulation for predicting the effective properties of nanocomposites. In the micromechanical modeling, the interphase formed due to non-boned van der Waals interaction between the continuous CNT and polymer matrix is considered through employing an individual representative volume element. The validity of the model is examined by comparing its results with other theoretical approaches and experimental data available in the literature. The effects of various types of CNTs arrangement in the matrix, i.e. uniform distribution and different functionally graded distributions on the elastic, thermoelastic and viscoelastic properties of polymer nanocomposites are investigated in detail. Furthermore, random arrangement of CNTs in the matrix is modelled. The influences of CNT/polymer matrix interphase and CNT volume fraction on the effective properties of nanocomposites are also studied. Finally, the viscoelastic response of nanocomposites under multiaxial loading is extracted and interpreted. © 2016, Springer Science+Business Media Dordrecht.
Hassanzadeh-aghdam, M.K.,
Ansari, R.,
Darvizeh a., A. Publication Date: 2017
Composites Part A: Applied Science and Manufacturing (1359835X)96pp. 110-121
The coefficients of thermal expansion (CTEs) of unidirectional glass fiber-reinforced polyimide composites containing silica nanoparticles are investigated. To this end, a three-dimensional unit cell-based micromechanical model together with an individual representative volume element (RVE) with c × r × h sub-cells is proposed. The interphase region between silica nanoparticle and polyimide matrix is considered as an equivalent solid continuum. Comparisons are made between the results of present model with those of available cylinder model and experiment. The results reveal that with adding silica nanoparticles to glass fiber-reinforced polyimide composites, the transverse CTE of composite decreases, while its longitudinal CTE increases. The effects of fiber volume fraction and aspect ratio, interphase thickness and material properties, silica nanoparticle volume fraction and diameter on the thermal expansion behavior of silica nanoparticle-glass fiber-reinforced polyimide composites are studied. The obtained results could be useful to guide the design of composites with optimal CTEs. © 2017 Elsevier Ltd
Ansari, R.,
Bazdid-vahdati m., M.,
Shakouri a.h., ,
Norouzzadeh, A.,
Rouhi h., H. Publication Date: 2017
Mathematics and Mechanics of Solids (17413028)22(6)pp. 1438-1461
Within the framework of micromorphic elasticity theory, a finite element approach capable of capturing the microstructure effect is developed to describe the bending behavior of microplates. To this end, the micromorphic theory is generally formulated first. The matrix representation of this formulation is then given from which a prism micromorphic element, including the effects of micro-deformation degrees of freedom of material particles, is proposed. The element is applied to the bending problem of micromorphic rectangular and circular plates subject to different boundary conditions. Selected numerical results are presented to show the microstructure influence on the bending of plates with various geometrical parameters. It is revealed that the element is capable of predicting the mechanical behavior of micromorphic continua in an efficient way. © SAGE Publications.
Publication Date: 2017
International Journal of Modern Physics B (02179792)31(32)
The vibrational properties of double-walled carbon nanocones are investigated herein. The double-walled carbon nanocones with different geometries including apex angles and lengths are considered. The simply supported-simply supported, clamped-free and clamped-clamped boundary conditions are applied on the nanocones. A linear elastic beam-based finite element method is employed to obtain the frequencies of the double-walled carbon nanocones. Elastic beam elements are used to model the carbon-carbon bond in the structure of the nanocones. Besides, the spring elements are employed to describe the nonbonding van der Waals interactions between different layers. Natural frequencies and mode shapes of the double-walled carbon nanocones are extracted by solving the eigenvalue problem. It is observed that increasing the disclination angle of nanocones increases their natural frequency. However, increasing the nanocone's height leads to decreasing the frequency. © 2017 World Scientific Publishing Company.
Publication Date: 2017
Optik (00304026)130pp. 737-742
The nonlinear time-fractional Klein–Gordon equations play an important role in describing some physical events in solid state physics, nonlinear optics, and quantum field theory. In this paper, the time-fractional Klein–Gordon equations with quadratic and cubic nonlinearities in the sense of the conformable fractional derivative are solved via the modified Kudryashov method. A few new explicit exact solutions of these equations are formally constructed. Results confirm the efficiency of the modified Kudryashov method in handling the conformable time-fractional Klein–Gordon equations with quadratic and cubic nonlinearities. © 2016 Elsevier GmbH
Publication Date: 2017
Physica E: Low-Dimensional Systems and Nanostructures (13869477)93pp. 17-25
Using a finite element-based multi-scale modeling approach, the bending, buckling and free vibration of hybrid polymer matrix composites reinforced by carbon fibers and carbon nanotubes (CF/CNT-RP) are analyzed herein. Thick composite plates with rectangular, circular, annular and elliptical shapes are considered. First, the equivalent material properties of CF/CNT-RP are calculated for different volume fractions of CF and CNT. To accomplish this aim, a two-step procedure is presented through which the coupled effects of nano- and micro-scale are taken into account. In the first step, modeling of dispersion of CNTs into the polymer matrix is done with considering interphase formed by their chemical interaction with the matrix, and the equivalent properties of resulting composite material are determined accordingly. CFs are then dispersed into CNT-RP which is considered a homogenous material in this step. Both distributions of CNTs and CFs are assumed to be random. After computing the equivalent properties of CF/CNT-RP for different volume fractions of its constituents, the bending, buckling and free vibration analyses of plates with different shapes are performed. It is shown that the reinforcement of the polymer matrix with both CF and CNT significantly affects the bending, buckling and free vibration characteristics of plates. © 2017 Elsevier B.V.
Publication Date: 2017
Composite Structures (02638223)165pp. 25-43
The nonlinear flexural response of single-layer graphene sheets (SLGSs) resting on elastic matrix is studied using an atomistic-based second gradient continuum model. The higher-order Cauchy-Born rule is used to link the interatomic potential to the strain energy induced in the continuum without any parameter fitting. The graphene is modeled by a hyperelastic membrane whose elastic potential energy is exclusively written in terms of the interatomic potential. This results in a constitutive model independent of any additional phenomenological input and thickness. Moreover, through this linkage, both the material and geometrical nonlinearities are exactly reflected in the constitutive model. To solve the continuum boundary value problem, the differential quadrature (DQ) approach is employed in the context of a variational formulation, and the discretized weak form of the equilibrium equation is obtained. The static response of SLGSs under a uniformly distributed load is evaluated. It is found that the present multiscale model can reproduce the results of other coupled atomistic-continuum and full atomistic approaches with a small number of discrete points. Also, the effect of the second-order deformation gradient is found to be significant on the bending deflection of SLGS specifically on the one with high flexural stiffness. © 2016 Elsevier Ltd
Publication Date: 2017
Waves in Random and Complex Media (discontinued) (17455049)27(4)pp. 628-636
In this paper, the nonlinear Boussinesq equations with the conformable time-fractional derivative are solved analytically using the well-established modified Kudryashov method. As a consequence, a number of new exact solutions for this type of equations are formally derived. It is believed that the method is one of the most effective techniques for extracting new exact solutions of nonlinear fractional differential equations. © 2017 Informa UK Limited, trading as Taylor & Francis Group.
Publication Date: 2017
Optik (00304026)132pp. 203-209
Our concern in the present paper is to generate a few new explicit and exact solutions for the time-fractional Cahn–Allen and Cahn–Hilliard equations in the context of the conformable fractional derivative. A new version of Kudryashov method with the help of the Maple package is utilized to carry out this purpose. It is believed that the modified Kudryashov method is practically well suited; such that it can be adopted to a wide range of fractional differential equations (FDEs). © 2016 Elsevier GmbH
Publication Date: 2017
Optical and Quantum Electronics (discontinued) (03068919)49(8)
The paper deals with the Tzitzéica type nonlinear evolution equations arising in nonlinear optics and their new exact solutions. First, through the use of the Painlevé transformation and Lie symmetry method, the Tzitzéica, Dodd–Bullough–Mikhailov, and Tzitzéica–Dodd–Bullough equations are converted to nonlinear ordinary differential equations (NODEs), and then, a modified version of the improved tan (Φ(ξ) / 2) -expansion method, proposed by the authors, is adopted to generate new exact solutions of the reduced equations. The method truly recommends a reliable and capable technique to produce new exact solutions of a variety of nonlinear partial differential equations (NPDEs). © 2017, Springer Science+Business Media, LLC.
Publication Date: 2017
Optik (00304026)148pp. 85-89
The Tzitzéica type equations arising in nonlinear optics, including the Tzitzéica, Dodd–Bullough–Mikhailov, and Tzitzéica–Dodd–Bullough equations are solved analytically, in the present paper. A solution technique in the area of computational mathematics called the novel exponential rational function method is formally proposed for this purpose. As a consequence, a series of new exact solutions for the Tzitzéica type equations are obtained, proving the super performance of novel exponential rational function method. © 2017
Publication Date: 2017
International Journal of Applied Mechanics (17588251)9(8)
Employing an efficient numerical strategy, the nonlinear forced vibration analysis of composite cylindrical shells reinforced with single-walled carbon nanotubes (CNTs) is carried out. It is assumed that the distribution of CNTs along the thickness direction of the shell is uniform or functionally graded and the temperature dependency of the material properties is accounted. The governing equations are presented based on the first-order shear deformation theory along with von-Karman nonlinear strain-displacement relations. The vectorized form of energy functional is derived and directly discretized using numerical differential and integral operators. By the use of variational differential quadrature (VDQ) method, discretized nonlinear governing equations are obtained. Then, the time periodic differential operators are applied to perform the discretization procedure in time domain. Finally, the pseudo-arc length continuation method is employed to solve the nonlinear governing equations and trace the frequency response curve of the nanocomposite cylindrical shell. A comparison study is first presented to verify the efficiency and validity of the proposed numerical method. Comprehensive numerical results are then given to investigate the effects of the involved factors on the nonlinear forced vibration characteristics of the structure. The results show that the changes of fundamental vibrational mode shape have considerable effects on the frequency response curves of composite cylindrical shells reinforced with CNTs. © 2017 World Scientific Publishing Europe Ltd.
Publication Date: 2017
Computer Methods in Applied Mechanics and Engineering (00457825)324pp. 327-347
Due to axisymmetric fundamental vibrational mode shape, the most studies on the large-amplitude free vibration of annular plates have been presented based on the axisymmetric formulation. However, the initial thermal loading can change the vibration behavior of annular plates. To analyze this effect, the nonlinear free vibration of carbon nanotube (CNT) reinforced composite annular plates is investigated under thermal loading based on the asymmetric formulation. The material properties of the CNT-reinforced composites are assumed to vary continuously along the thickness direction and estimated through a micromechanical model by which the temperature-dependency is taken into account. The governing equations are derived on the basis of first-order shear deformation theory, and an efficient numerical variational method is employed to solve the problem. In this regard, the quadratic form of the energy functional is directly discretized using numerical differential and integral operators, and the pseudo-arc length continuation method is then applied to find the frequency response of the structure. The numerical results of asymmetric and axisymmetric formulations are compared and it is observed that in the presence of initial thermal loading, the axisymmetric analysis leads to inaccurate results and complete asymmetric formulation should be considered. © 2017 Elsevier B.V.
Publication Date: 2017
International Journal of Non-Linear Mechanics (00207462)97pp. 115-125
In this work, a thorough investigation is presented into the nonlinear resonant dynamics of geometrically imperfect shear deformable nanobeams subjected to harmonic external excitation force in the transverse direction. To this end, the Gurtin–Murdoch surface elasticity theory together with Reddy's third-order shear deformation beam theory is utilized to take into account the size-dependent behavior of nanobeams and the effects of transverse shear deformation and rotary inertia, respectively. The kinematic nonlinearity is considered using the von Kármán kinematic hypothesis. The geometric imperfection as a slight curvature is assumed as the mode shape associated with the first vibration mode. The weak form of geometrically nonlinear governing equations of motion is derived using the variational differential quadrature (VDQ) technique and Lagrange equations. Then, a multistep numerical scheme is employed to solve the obtained governing equations in order to study the nonlinear frequency–response and force–response curves of nanobeams. Comprehensive studies into the effects of initial imperfection and boundary condition as well as geometric parameters on the nonlinear dynamic characteristics of imperfect shear deformable nanobeams are carried out through numerical results. Finally, the importance of incorporating the surface stress effects via the Gurtin–Murdoch elasticity theory, is emphasized by comparing the nonlinear dynamic responses of the nanobeams with different thicknesses. © 2017 Elsevier Ltd
Publication Date: 2017
Composite Structures (02638223)174pp. 45-58
This study aims at numerically analyzing the nonlinear resonant dynamics of geometrically imperfect higher-order shear deformable functionally graded carbon nanotube-reinforced composite (FG-CNTRC) beams with various end conditions subjected to a harmonic transverse load. Introducing a generalized displacement field including various beam theories, employing Hamilton's principle and taking into account geometrical nonlinearity and initial imperfection, three nonlinear coupled equations and associated boundary expressions are obtained for geometrically imperfect FG-CNTRC beams. These equations formulate the longitudinal, transverse and rotational motions of FG-CNTRC beams. An efficient multistep numerical solution approach based on the generalized differential quadrature (GDQ) method, a numerical Galerkin-based scheme and time periodic discretization is employed to convert the time-dependent nonlinear partial differential equations (PDEs) into a Duffing-type nonlinear set of ordinary differential equations (ODEs) which can be solved via the pseudo arc-length continuation technique. Nonlinear resonant dynamics characteristics are illustrated in the form of frequency-response and force-response curves; highlighting the influences of initial geometrical imperfection, geometrical parameters, excitation frequency and boundary conditions. © 2017 Elsevier Ltd
Publication Date: 2017
Acta Mechanica Solida Sinica (08949166)30(4)pp. 416-424
The nonlinear vibrations of viscoelastic Euler–Bernoulli nanobeams are studied using the fractional calculus and the Gurtin–Murdoch theory. Employing Hamilton's principle, the governing equation considering surface effects is derived. The fractional integro-partial differential governing equation is first converted into a fractional–ordinary differential equation in the time domain using the Galerkin scheme. Thereafter, the set of nonlinear fractional time-dependent equations expressed in a state-space form is solved using the predictor–corrector method. Finally, the effects of initial displacement, fractional derivative order, viscoelasticity coefficient, surface parameters and thickness-to-length ratio on the nonlinear time response of simply-supported and clamped-free silicon viscoelastic nanobeams are investigated. © 2017
Publication Date: 2017
Journal of Reinforced Plastics and Composites (07316844)36(14)pp. 991-1008
The elastic modulus of curved single-walled carbon nanotube/polymer nanocomposites is studied. The effects of shape, number, and amplitude of curves and nanotube/matrix interphase on the mechanical properties of nanocomposites are investigated. Solid and hollow cylinder models are employed to model the nanotubes. Single-walled carbon nanotubes are selected with one, two, and three curves. The elastic modulus of polymer matrix reinforced by curved single-walled carbon nanotubes is compared with those of straight nanotube/polymer nanocomposites. Comparing the results with the results of the molecular dynamics simulations, it is shown that the employed model can predict the mechanical properties of nanocomposites with the error lower than that of 2%. The nanotubes with higher number of curves lead to weaker reinforcement of the matrix. Besides, increasing the diameter of the nanotube leads to better reinforcement of the nanocomposites. It is observed that the rule of mixtures cannot predict the elastic modulus of curved single-walled carbon nanotube/polymer nanocomposites correctly. Therefore, the rule of mixtures is modified to accurately predict the elastic modulus of polymer matrix reinforced by curved single-walled carbon nanotubes. © The Author(s) 2017.
Publication Date: 2017
Scientia Iranica (23453605)24(3)pp. 1615-1625
Electromechanical nanothermometers are instruments that work on the basis of the van der Waals (vdW) potential energy and interaction force of their constituent carbon nanotubes (CNTs). The CNT-based nanothermometers have two different configurations: telescope and shuttle configurations. In this article, based on the Lennard-Jones potential function together with the continuum approximation, first, the vdW potential energy and interaction force for a telescope configuration with finite CNTs are derived, which have not been obtained in the previous research studies. Thereafter, by employing the interaction force, the equation of motion between constituent CNTs is solved. Subsequently, a new semi-analytical expression is obtained which enables one to precisely evaluate the oscillation frequency. By employing the given formulae, effects of different system parameters on the vdW interactions and oscillation frequency are shown. © 2017 Sharif University of Technology. All rights reserved.
Publication Date: 2017
Journal of Alloys and Compounds (09258388)702pp. 388-398
This paper aims to investigate the mechanical properties of zigzag phosphorene nanotubes under the compressive loading. To this end, a finite element model is used whose elemental properties are computed by simulating the P[sbnd]P bonds in the structure of the phosphorene nanotubes by beam elements. It is shown that the critical compressive force of zigzag phosphorene nanotubes is significantly smaller than that of the single-walled carbon nanotubes with the same size and boundary conditions. By investigating the effect of aspect ratio and radius on the compressive characteristics of the phosphorene nanotubes, it is represented that the critical compressive force has an inverse and direct relation with the former and latter geometrical parameter, respectively. © 2017 Elsevier B.V.
Publication Date: 2017
Modern Physics Letters B (02179849)31(22)
The finite element method is used here to investigate the vibrational behavior of single-walled boron nitride nanotube/polymer nanocomposites. The polymer matrix is modeled as a continuous media. Besides, nanotubes are modeled as a space-frame structure. It is shown that increasing the length of nanotubes at a constant volume fraction leads to decreasing of the nanocomposite frequency. By investigating the effect of volume percentage on the frequencies of the boron nitride nanotube-reinforced polymer nanocomposites, it is observed that for short nanotubes, the nanocomposites with larger nanotube volume fractions have larger frequencies. Also, through studying the first 10 frequencies of nanocomposites reinforced by armchair and zigzag nanotubes, it is shown that the effect of chirality on the vibrational behavior of nanocomposite is insignificant. © 2017 World Scientific Publishing Company.
Publication Date: 2017
European Journal of Mechanics, A/Solids (09977538)62pp. 67-79
In this paper, mechanics of carbon nanotori molecules oscillating along the exterior of carbon nanotubes (CNTs) is fully investigated. On the basis of the continuum approximation in conjunction with the 6–12 Lennard-Jones (LJ) potential function, new semi-analytical expressions are given in terms of double integrals to evaluate van der Waals (vdW) potential energy and interaction force between the two interacting molecules. Furthermore, suction energy and acceptance condition, which are the two main characteristics of nanotube-based systems for applications such as drug delivery and so forth, are determined. Using the actual distribution of vdW force, the equation of motion is solved numerically to obtain time-dependent variables of system. Moreover, considering flexible nanotori and CNT molecules, the molecular dynamics (MD) simulations are conducted to assure the validity of the time history of system obtained from the continuum method. A novel semi-analytical expression is also proposed for the precise evaluation of oscillation frequency into which the effects of both geometrical parameters and initial conditions are incorporated. With respect to the present formulation, a comprehensive study into the effect of system parameters on the oscillation frequency is carried out. Numerical results demonstrate that the operating frequency of nanotori-CNT oscillator is in the gigahertz (GHz) range. © 2016 Elsevier Masson SAS
Ansari, R.,
Pourashraf t., ,
Gholami, R.,
Sahmani, S. Publication Date: 2017
Meccanica (15729648)52(1-2)pp. 283-297
In the present investigation, an analytical solution is proposed to predict the postbuckling characteristics of nanobeams made of functionally graded materials which are subjected to thermal environment and surface stress effect. To this end, a non-classical beam model on the basis of Gurtin–Murdoch elasticity theory in the framework of Euler–Bernoulli beam theory and concept of physical neutral surface is utilized which has the capability to consider the effect of surface stress and von Karman-type of kinematic nonlinearity. The size-dependent nonlinear governing equations are solved analytically for different end supports. The postbuckling equilibrium paths corresponding to various boundary conditions are given in the presence of surface stress corresponding to various beam thicknesses, material gradient indexes, temperature changes and buckling mode numbers. It is found that by increasing the values of temperature change, the equilibrium path is shifted to right and the normalized applied axial load decreases indicating that the effect of surface stress diminishes. © 2016, Springer Science+Business Media Dordrecht.
Publication Date: 2017
Applied Physics A: Materials Science and Processing (14320630)123(5)
Differential form of Eringen’s nonlocal elasticity theory is widely employed to capture the small-scale effects on the behavior of nanostructures. However, paradoxical results are obtained via the differential nonlocal constitutive relations in some cases such as in the vibration and bending analysis of cantilevers, and recourse must be made to the integral (original) form of Eringen’s theory. Motivated by this consideration, a novel nonlocal formulation is developed herein based on the original formulation of Eringen’s theory to study the buckling behavior of nanobeams. The governing equations are derived according to the Timoshenko beam theory, and are represented in a suitable vector–matrix form which is applicable to the finite-element analysis. In addition, an isogeometric analysis (IGA) is conducted for the solution of buckling problem. Construction of exact geometry using non-uniform rational B-splines and easy implementation of geometry refinement tools are the main advantages of IGA. A comparison study is performed between the predictions of integral and differential nonlocal models for nanobeams under different kinds of end conditions. © 2017, Springer-Verlag Berlin Heidelberg.
Publication Date: 2017
Egyptian Journal of Petroleum (11100621)26(2)pp. 375-389
In this study chelating resins have been considered to be suitable materials for the recovery of Copper (II) ions in water treatments. Furthermore, these modified resins were reacted with 1,2-diaminoethane in the presence of ultrasonic irradiation for the preparation of a tridimensional chelating resin on the Nano scale for the recovery of Copper (II) ions from aqueous solutions. This method which is used for removing and determining Copper (II) ions using copolymers derived resins of poly (styrene-alternative-maleic anhydride) (SMA) and atomic absorption spectroscopy. The method is simple, sensitive, inexpensive and fast. The various parameters such as pH, contact time, concentrations of metal ions, mass of resin, and agitation speed were investigated on adsorption effect. The adsorption behavior of Copper (II) ions were investigated by the synthesis of chelating resins at various pHs. The prepared resins showed a good tendency for removing the selected metal ions from aqueous solution, even at an acidic pH. Also, the prepared resins were examined for the removal of Copper (II) ions from real samples such as industrial wastewater and were shown to be very efficient at adsorption in the cases of Copper (II) ions. The pseudo-first-order, pseudo-second-order, and intra-particle diffusion kinetics equations were used for modeling of adsorption data and it was shown that pseudo-second-order kinetic equation could best describe the adsorption kinetics. The intra-particle diffusion study revealed that external diffusion might be involved in this case. The resins were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and X-ray diffraction analysis. © 2016 Egyptian Petroleum Research Institute
Publication Date: 2017
Materials Research Express (20531591)4(6)
The aim of the present study is to propose a unified size-dependent higher-order shear deformable plate model for magneto-electro-thermo-elastic (METE) rectangular nanoplates by adopting the nonlocal elasticity theory to capture the size effect, and by utilizing a generalized shape function to consider the effects of transverse shear deformation and rotary inertia. By considering various shape functions, the proposed plate model can be reduced to the nonlocal plate model based upon the Kirchhoff, Mindlin and Reddy plate theories, as well as the parabolic, trigonometric, hyperbolic and exponential shear deformation plate theories. The governing equations of motion and corresponding boundary conditions of METE nanoplates subjected to external in-plane, transverse loads as well as magnetic, electric and thermal loadings, are obtained using Hamilton's principle. Then, as in some case studies, the static bending, buckling, and free vibration characteristics of simply-supported METE rectangular nanoplates are investigated based upon the Navier solution approach. Numerical results are provided in order to investigate the influences of various parameters including the nondimensional nonlocal parameter, type of transverse loading, temperature change, applied voltage, and external magnetic potential on the mechanical behaviors of METE nanoplates. Furthermore, comparisons are made between the results predicted by different nonlocal plate models by utilizing the developed unified nonlocal plate model and selecting the associated shape functions. It is illustrated that by using the presented unified nonlocal plate model, the development of a nonlocal plate model based upon any existing higher-order shear deformable plate theory is a simple task. © 2017 IOP Publishing Ltd.
Publication Date: 2017
International Journal of Structural Stability and Dynamics (02194554)17(1)
This paper presents a nonlocal nonlinear first-order shear deformable plate model for investigating the buckling and postbuckling of magneto-electro-thermo elastic (METE) nanoplates under magneto-electro-thermo-mechanical loadings. The nonlocal elasticity theory within the framework of the first-order shear deformation plate theory along with the von Kármán-type geometrical nonlinearity is used to derive the size-dependent nonlinear governing partial differential equations and associated boundary conditions, in which the effects of shear deformation, small scale parameter and thermo-electro-magneto-mechanical loadings are incorporated. The generalized differential quadrature (GDQ) method and pseudo arc-length continuation algorithm are used to determine the critical buckling loads and postbuckling equilibrium paths of the METE nanoplates with various boundary conditions. Finally, the influences of the nonlocal parameter, boundary conditions, temperature rise, external electric voltage and external magnetic potential on the critical buckling load and postbuckling response are studied. © 2017 World Scientific Publishing Company.
Publication Date: 2017
Nonlinear Dynamics (0924090X)87(1)pp. 695-711
In this paper, the vibrational behavior of micro- and nano-scale viscoelastic beams under different types of end conditions in the linear and nonlinear regimes is investigated based on the fractional calculus. To capture the effects of small scale, the modified strain gradient theory is utilized. Also, the beams are modeled based on the Timoshenko beam theory, von Kármán nonlinear relations and the fractional Kelvin–Voigt viscoelastic model. Derivation of governing equations is performed using Hamilton’s principle. For the linear solution, the generalized differential quadrature and finite difference methods are employed. Moreover, in the nonlinear solution procedure, the Galerkin method is first used to convert the fractional integro-partial differential governing equations into fractional ordinary differential equations which are then arranged in an effective state-space form. The predictor–corrector technique is finally used to solve the set of nonlinear fractional time-dependent equations. Selected numerical results are given on the linear and nonlinear time responses of the fractional viscoelastic small-scale beams to study the effects of fractional-order, viscoelasticity coefficient and length scale parameter. © 2016, Springer Science+Business Media Dordrecht.
Publication Date: 2017
Global Nest Journal (17907632)19(1)pp. 7-16
In this study, nanocomposite of ceria sawdust (CeO2/SD) synthesized by precipitation method was utilized for removal of As (III) ions from aqueous solutions. Study of the process was done in column system. Characterization of the nano sized adsorbent particles was carried out using XRD and SEM techniques. The effects of important parameters, such as the value of initial pH, the flow rate, the influent concentration of arsenic and bed depth were studied in the column system. The Thomas model was applied for treatment of the adsorption data at different flow rate, influent concentration and bed depth. The bed-depth/service time analysis (BDST) model was also applied at different bed depth to predict the breakthrough curves. The two models were found suitable for describing the bio sorption process of the dynamic behavior of the CeO2/SD adsorbent in column investigation. Based on Thomas model, the equilibrium adsorption reached 8.28 mg g-1 when a As(III) polluted solution with influent concentration of As 10 mg l-1 passed through the column with a flow rate of 2 ml min-1. All the results suggested the presented nanocomposite as an efficient and cost effective adsorbent for removal of As (III) ions from aqueous solutions. © 2017 Global NEST Printed in Greece. All rights reserved.
Publication Date: 2017
Applied Mathematical Modelling (0307904X)49pp. 705-738
A new solution method in the area of computational mechanics is developed in this article, which is called variational differential quadrature (VDQ). The main idea of this method is based on the accurate and direct discretization of the energy functional in the structural mechanics. In the VDQ method, through developing an efficient matrix formulation and using an accurate integral operator, the discretized governing equations are derived directly from the weak form of the equations with no need for the analytical derivation of the strong form. This technique provides an alternative way to discretize the energy functional, which avoids the local interpolation and the assembly process of the methods of this kind. We first implement the VDQ method for the nonlinear elasticity theory considering the Green-St. Venant strain tensor; then we simplify the formulation further for the first-order shear deformable beam and plate theories. The final formulation of these cases demonstrates the simplicity of the implementation for the VDQ method in the numerical analysis of the structures, which is a major goal for this article. Using these examples, one can easily learn and apply this technique to other structures. To assess the performance of the VDQ method, we compare it with the generalized differential quadrature (GDQ) method and finite element method (FEM) in the case of bending analysis of Mindlin plates. It is indicated that computational cost of VDQ is less than that of GDQ, and the convergence rate of VDQ is faster than that of FEM. © 2017 Elsevier Inc.
Publication Date: 2017
Aerospace Science and Technology (12709638)60pp. 152-161
A numerical meshless discretization technique is developed within the framework of variational formulation to present the linear free vibration analysis of functionally graded carbon nanotube-reinforced composite (FG-CNTRC) elliptical plates. The effective material properties of nanocomposite plate are continuously varied across the thickness direction and are evaluated based on the extended rule of mixture. The governing equations are derived on the basis of the first order shear deformation theory. To this end, the matrix form of Hamilton's principle is first presented. Then, based on the moving least-squares (MLS) approximation and background cells approach, the meshless differential and integral operators are constructed to perform the discretization process. After conducting the comparison and convergence study, various numerical results are reported to explore the effects of concerned parameters on the natural frequencies of composite elliptical plates reinforced with carbon nanotubes (CNTs). Results reveal that functionally grading of CNTs through the thickness direction can considerably improve the vibrational characteristics of FG-CNTRC elliptical plates. © 2016 Elsevier Masson SAS
Publication Date: 2017
Computational Materials Science (09270256)128pp. 81-86
Fabrication of novel metallic and stable three-dimensional (3D) forms of carbon, i.e. T6 and T14, has recently attracted a lot of interest due to their various potential applications. In the present work, the vibrational behaviors of T6 and T14 with interlocking hexagons are studied via molecular dynamics (MD) simulations. The natural frequencies and mode shapes of T6 and T14 are obtained for beam- and plate-like models. Moreover, the effects of different geometrical parameters such as length, width and cross-sectional area on the vibrational behaviors of these nanostructures are investigated. Also, the natural frequency of models is compared to that of single-walled carbon nanotubes (SWCNTs) with relatively similar dimensions. The results indicate that the natural frequency is strongly sensitive to the geometry, especially in the models with shorter lengths. Furthermore, it is observed that the natural frequency of 3D metallic carbon nanostructures is smaller than that of SWCNTs. © 2016 Elsevier B.V.
Publication Date: 2017
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)231(18)pp. 3455-3461
A three-dimensional finite element model has been used here to study the vibrational behavior of silicon carbide nanosheets and nanotubes. The bonds of hexagonal lattices of SiC nanosheets have been modeled by structural beam elements, and at the corners, mass elements are placed instead of Si and C atoms. Moreover, molecular dynamics simulations are performed to verify the finite element model. Comparing the results of finite element model and molecular dynamics simulations, it is concluded that the utilized approach can predict the results of molecular dynamics simulations with a reasonable accuracy. It is observed that the atomic structure does not significantly affect the vibrational behavior of nanosheets. Besides, increasing the size of nanosheet results in decreasing the effect of geometry variation. As the aspect ratio of nanotubes increases, the effects of boundary conditions and length diminish so that the frequency envelopes tend to converge. © IMechE 2016.
Polymer nanofibers are being increasingly used for a wide range of applications owing to their high specific surface area. Electrospinning process, as a novel and effective method for producing nanofibers from various materials, has been used to fabricate nanofibrous membrane. Carbon nanotubes (CNTs) have a number of outstanding mechanical, electrical, and thermal properties, which make them attractive as reinforcement in polymer matrix. Incorporation of chapter provides a comprehensive review of current researches and developments in the field of electrospun CNT-polymer composite nanofiber with emphasis on the processing, properties, and application of composite nanofiber as well as the theoretical approaches on predicting mechanical behavior of CNT-polymer composites. The current limitations, research challenges, and future trends in modeling and simulation of electrospun polymer composite nanofibers are also discussed. © 2014 by Apple Academic Press, Inc. All rights reserved.
Ansari, R.,
Faghihnasiri m., ,
Shahnazari a., A.,
Malakpour s., S.,
Sahmani, S. Publication Date: 2016
Journal of Alloys and Compounds (09258388)687pp. 790-796
Zirconia (ZrO2) as an important ceramic material has widespread potential applications in various fields of nanotechnology such as solid-state electrolytes, electro-optical materials, structural materials and etc. In the present investigation, density functional theory (DFT) calculations using quasi-harmonic approximation (QHA) are carried out to predict the influence of temperature change on the elastic properties of a monolayer ZrO2nanosheet. To this end, the exchange−correlation functional is approximated based on the generalized gradient approximation with the Perdew− Burke−Ernzerhof flavor. Firstly, it is indicated that the temperature change has a small influence on the elastic properties of a monolayer ZrO2nanosheet. Nevertheless, by increasing the value of temperature, it is revealed that in an overall view, the Young's modulus of structure decreases, but the bulk modulus of structure increases. Additionally, it is observed that for a specific temperature range, the value of Young's modulus of ZrO2nanosheet is more sensitive to the temperature change than its bulk modulus. Furthermore, it is revealed that the reduction in the Young's modulus and the increment in the bulk modulus due to temperature change is only about 1 Pa, so the increase in the motion of phonons because of higher temperatures does not lead to a considerable influence on the elastic properties of a monolayer ZrO2nanosheet. © 2016 Elsevier B.V.
Ansari, R.,
Shahnazari a., A.,
Malakpour s., S.,
Faghihnasiri m., ,
Sahmani, S. Publication Date: 2016
Superlattices and Microstructures (10963677)97pp. 506-518
Molybdenum disulfide (MoS2) may be synthesized in a large variety of forms such as particles, monolayer and multilayers nanosheets/nanotubes, ropes and ribbons. Due to such diversity, several applications can be found for MoS2. In this paper, on the basis of density functional theory (DFT) calculations using the generalized gradient approximation (GGA) with the Perdew− Burke−Ernzerhof (PBE) exchange correlation, the elastic properties including Young's and bulk moduli together with plastic properties of MoS2 nanosheet under external electric field with magnitudes within the range of 0 V/ang–1.5 V/ang are determined. It is demonstrated that up to the magnitude of 1 V/ang, the external electric field has a negligible influence on the bulk modulus of MoS2 nanosheet. However, by applying an external electric field equal to 1.3 V/ang, a significant increase in the value of bulk modulus occurs. Additionally, by applying an external electric field equal to 1.5 V/ang, the bulk modulus decreases suddenly, showing the considerable influence of high external electric field on the bulk modulus of MoS2 nanosheet. Also, it is observed that the first and second critical strains of the MoS2 nanosheet subjected to biaxial strain are smaller than those of the MoS2 nanosheet under uniaxial strain. Furthermore, it is revealed that for the both uniaxial and biaxial loading cases, by increasing the magnitude of external electric field, the stability of MoS2 nanosheet decreases. © 2016 Elsevier Ltd
Publication Date: 2016
Superlattices and Microstructures (10963677)97pp. 125-131
The buckling behavior of a novel three-dimensional metallic carbon nanostructure known as T6 is investigated herein employing the molecular dynamics (MD) simulations. The models are prepared on the basis of two beam- and plate-like structures to study the effects of size and geometry on the critical buckling force and critical strain. It is observed that the range of critical force for the beam-like and plate-like T6 with different geometrical parameters is approximately identical. Moreover, it is demonstrated that the critical buckling force decreases and increases by increasing the length and the width of T6, respectively. Moreover, it is shown that critical strain of beam-like T6 decreases by increasing the length, whereas, in the case of plate-like T6, the critical strain only fluctuates around 2% by increasing the width. It is further found that the buckling parameters of T6 are not comparable with those of single-walled carbon nanotubes (SWCNTs) and graphene with a relatively similar dimension. The critical buckling force and critical strain of T6 are considerably smaller than those of SWCNT and larger than those of graphene. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Nonlinear Dynamics (0924090X)84(4)pp. 2403-2422
In this work, the size-dependent geometrically nonlinear free vibration of functionally graded (FG) microplates is investigated. For this purpose, with the aid of Hamilton’s principle, a nonclassical rectangular microplate model is developed based on Mindlin’s strain gradient theory, Mindlin’s plate theory and the von Kármán geometric nonlinearity. For some specific values of the length scale material parameters, the simple form of size-dependent mathematical formulation based on the modified strain gradient theory (MSGT) and modified couple stress theory is obtained. The generalized differential quadrature method, numerical Galerkin scheme, periodic time differential operators and pseudo arc-length continuation method are utilized to determine the geometrically nonlinear free vibration characteristics of FG microplates with different boundary conditions. The parametric effects of thickness-to-material length scale ratio, material gradient index, length-to-thickness ratio, length-to-width ratio and boundary conditions on the nonlinear free vibration characteristics of FG microplates are studied through various numerical examples presented. It is found that a considerable difference exists between the results of various elasticity theories at small values of length scale parameter. A more precise prediction can be provided by using the size-dependent plate model based on the MSGT. © 2016, Springer Science+Business Media Dordrecht.
Ansari, R.,
Faghih shojaei, M.,
Ebrahimi f., ,
Rouhi h., H.,
Bazdid-vahdati m., M. Publication Date: 2016
Engineering with Computers (14355663)32(1)pp. 99-108
Based on Mindlin’s strain gradient elasticity and Euler–Bernoulli beam theory, a non-classical beam element capable of considering micro-structure effects is developed. To accomplish this aim, the higher-order tensors of energy pairs in the energy functional are vectorized and written in the quadratic representation, from which the stiffness and mass matrices of the element are obtained. In comparison with the classical Euler–Bernoulli beam element, the new element needs one additional nodal degree of freedom (DOF) which results in a total of three DOFs per node. The formulation of the paper is general so that it can be reduced to that based on the modified couple stress theory, the modified strain gradient theory, and the classical elasticity theory. To show the reliability of the proposed element, the bending and free vibration problems of microbeams under different kinds of end conditions are addressed. It is revealed that the present finite element results are in excellent agreement with the ones achieved through analytical solutions. © 2015, Springer-Verlag London.
Ansari, R.,
Pourashraf t., ,
Gholami, R.,
Rouhi h., H. Publication Date: 2016
Applied Mathematics and Mechanics (English Edition) (02534827)37(7)pp. 903-918
The size-dependent nonlinear buckling and postbuckling characteristics of circular cylindrical nanoshells subjected to the axial compressive load are investigated with an analytical approach. The surface energy effects are taken into account according to the surface elasticity theory of Gurtin and Murdoch. The developed geometrically nonlinear shell model is based on the classical Donnell shell theory and the von Kármán’s hypothesis. With the numerical results, the effect of the surface stress on the nonlinear buckling and postbuckling behaviors of nanoshells made of Si and Al is studied. Moreover, the influence of the surface residual tension and the radius-to-thickness ratio is illustrated. The results indicate that the surface stress has an important effect on prebuckling and postbuckling characteristics of nanoshells with small sizes. © 2016, Shanghai University and Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Pourashraf t., ,
Gholami, R.,
Shahabodini a., A. Publication Date: 2016
Composites Part B: Engineering (13598368)90pp. 267-277
This paper presents an analytical solution procedure for the nonlinear postbuckling analysis of piezoelectric functionally graded carbon nanotubes reinforced composite (FG-CNTRC) cylindrical shells subjected to combined electro-thermal loadings, axial compression and lateral loads. The carbon nanotubes are assumed to be aligned and straight with uniform and functionally graded distributions in the thickness direction. The kinematics and constitutive relations are written on the basis of the classic theory and the von Kármán nonlinear strain-displacement relations of large deformation. Applying the Ritz energy approach, analytical solutions are proposed for the nonlinear critical axial load, lateral pressure as well as the load-shortening ratio of the piezoelectric FG-CNTRC shell. Numerical results are presented to study the effects of dimensional parameters, CNT volume fraction, distribution type of the reinforcement and piezoelectric thickness on the nonlinear buckling behavior of the piezoelectric nanocomposite shell. It is revealed that the carrying capacity of the structure increases as the shell is integrated by the piezoelectric layers and reinforced by higher CNT volume fraction. Furthermore, FGX- and FGO- CNTRC piezoelectric shells are indicated to have higher and lower carrying capacities compared to UD-CNTRC piezoelectric shells, respectively. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Acta Mechanica (16196937)227(6)pp. 1767-1781
Surface stresses can significantly affect the mechanical behavior of structures when they are scaled down to deep submicron dimensions. The Gurtin–Murdoch surface elasticity theory has the capability to capture the size-dependent behavior of nanostructures due to the surface stress effect in a continuum manner. The present work is concerned with the application of Gurtin–Murdoch theory to the nonlinear free vibration analysis of circular cylindrical nanoshells with considering surface stress and shear deformation effects. The nonlinear governing equations of motion together with the corresponding boundary conditions are firstly derived using Hamilton’s principle, the first-order shear deformation shell theory and von Kármán’s assumption. An analytical approach is then presented to solve the nonlinear free vibration problem. Selected numerical results are given to illustrate the effects of surface energy on the nonlinear free vibration behavior of shear deformable nanoshells with different material and geometrical parameters. It is shown that there is a large difference between the results of Gurtin–Murdoch theory and those of its classical counterpart for very thin nanoshells. © 2016, Springer-Verlag Wien.
Ansari, R.,
Torabi, J.,
Faghih shojaei, M.,
Hasrati, E. Publication Date: 2016
Composite Structures (02638223)157pp. 398-411
Buckling analysis of axially-compressed functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical panels is presented employing the variational differential quadrature (VDQ) method. The material properties of nanocomposite conical panel are assumed to be graded along the thickness direction and are estimated through the micromechanical model. To present the energy functional of the structure, the first-order shear deformation theory is utilized. Applying the generalized differential quadrature (GDQ) method in axial and circumferential directions, the discretized form of energy functional is obtained. Then, based on Hamilton's principle and matrix relations, the reduced form of stiffness matrices is derived. A comparison between the obtained results and those given in the literature shows the accuracy of the present approach. Numerical results indicate that volume fractions and distribution patterns of CNTs have significant effects on the buckling load of FG-CNTRC conical panels. © 2016 Elsevier Ltd
Publication Date: 2016
Journal Of Molecular Modeling (16102940)22(12)
Functionalized carbon nanotubes (CNTs) can be used for improving the mechanical properties and load transfer in nanocomposites. In this research, the buckling behavior of perfect and defective cross-linked functionalized CNTs with polyethylene (PE) chains is studied employing molecular dynamics (MD) simulations. Two different configurations with the consideration of vacancy defects, namely mapped and wrapped, are selected. According to the results, critical buckling force of cross-linked functionalized CNTs with PE chains increases as compared to pure CNTs, especially in the case of double-walled carbon nanotubes (DWCNTs). By contrast, it is demonstrated that critical strain of cross-linked functionalized CNTs decreases as compared to that of pristine CNTs. Also, it is observed that increasing the weight percentage leads to the higher increase and the decrease in critical buckling force and strain of cross-linked functionalized CNTs, respectively. Moreover, the presence of defect considerably reduces both critical buckling force and strain of cross-linked functionalized CNTs. Finally, it is shown that the critical buckling strain is more sensitive to the presence of defects as compared to critical buckling force. © 2016, Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
Physica B: Condensed Matter (09214526)481pp. 80-85
Synthesizing polyphenylene polymer, a two-dimensional hydrocarbon known as porous graphene, has led to the initiation of a new age in nanoscience. In this investigation, molecular dynamics (MD) simulations are carried out to study the mechanical properties of porous graphene such as Young's modulus, Poisson's ratio, bulk modulus and ultimate strength and strain. The fracture initiation and propagation pattern of porous graphene are also considered in this study. The results show that Young's and bulk moduli of porous graphene are lower than those of graphene, graphene and graphyne. Unlikely, it is also observed that its Poisson's ratio is considerably more than that of graphene, graphene and graphyne. Furthermore, it is found out that Young's and bulk moduli as well as fracture strain and ultimate stress are extremely size-dependent and also the porous graphene can be considered as an isotropic material. © 2015 Elsevier B.V.
Publication Date: 2016
European Physical Journal Plus (21905444)131(2)pp. 1-22
Research concerning the fabrication of nano-oscillators with operating frequency in the gigahertz (GHz) range has become a focal point in recent years. In this paper, a new type of GHz oscillators is introduced based on a C60 fullerene inside a cyclic peptide nanotube (CPN). To study the dynamic behavior of such nano-oscillators, using the continuum approximation in conjunction with the 6-12 Lennard-Jones (LJ) potential function, analytical expressions are derived to determine the van der Waals (vdW) potential energy and interaction force between the two interacting molecules. Employing Newton's second law, the equation of motion is solved numerically to arrive at the telescopic oscillatory motion of a C60 fullerene inside CPNs. It is shown that the fullerene molecule exhibits different kinds of oscillation inside peptide nanotubes which are sensitive to the system parameters. Furthermore, for the precise evaluation of the oscillation frequency, a novel semi-analytical expression is proposed based on the conservation of the mechanical energy principle. Numerical results are presented to comprehensively study the effects of the number of peptide units and initial conditions (initial separation distance and velocity) on the oscillatory behavior of C60 -CPN oscillators. It is found out that for peptide nanotubes comprised of one unit, the maximum achievable frequency is obtained when the inner core oscillates with respect to its preferred positions located outside the tube, while for other numbers of peptide units, such frequency is obtained when the inner core oscillates with respect to the preferred positions situated in the space between the two first or the two last units. It is further found out that four peptide units are sufficient to obtain the optimal frequency. © 2016, Società Italiana di Fisica and Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
Physica B: Condensed Matter (09214526)482pp. 28-37
This article aims to present a comprehensive study on the oscillatory behavior of concentric carbon nanocones (CNCs) inside carbon nanotubes (CNTs) using a continuum approach. To this end, the optimum radius of nanotube for which the nanocone lies on the tube axis is determined based on the distribution of suction energy. Using the Runge-Kutta numerical integration scheme, the equation of motion is solved numerically to attain the time history of displacement and velocity of nanocone. It is observed that the oscillation of nanocone occurs with respect to its axial equilibrium distance which moves further away from the middle axis of nanotube as the number of pentagons increases. A novel semi-analytical expression as a function of geometrical parameters, initial conditions and cone vertex direction is also proposed for the precise evaluation of oscillation frequency. With respect to the proposed frequency expression, a detailed parametric study is conducted to get an insight into the effects of number of pentagons, cone vertex direction and initial conditions on the oscillatory behavior of CNC-CNT oscillators. It is found that nanocones with more pentagons generate greater maximum frequencies inside nanotubes. Furthermore, it is shown that higher maximum frequencies can be achieved if the nanocone enters the nanotube from base. © 2015 Elsevier B.V. All rights reserved.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Darabi m.a., M.A. Publication Date: 2016
Applied Mathematical Modelling (0307904X)40(23-24)pp. 9872-9891
Presented herein is a comprehensive study on the size-dependent coupled longitudinal-transverse-rotational free vibration behavior of post-buckled functionally graded (FG) micro- and nano-beams based on the most general Mindlin's strain gradient theory. The current model enables us to incorporate size effects via introducing material length scale parameters and is developed in the framework of the first-order shear deformable beam model and the von Karman geometric nonlinearity. The FG micro- and nano-beams, whose volume fraction is expressed by using a power law function, are assumed to be made of a mixture of metals and ceramics. By using Hamilton's principle, the nonlinear governing equations and associated boundary conditions are derived for FG micro- and nano-beams in the postbuckling domain. Afterwards, the governing equations and boundary conditions are discretized using the generalized differential quadrature (GDQ) method in conjunction with a direct approach without linearization, before solving numerically by Newton's method. The effects of length scale parameter, length-to-thickness ratio, material gradient index and boundary conditions on the postbuckling path and frequency of FG micro- and nano-beams are carefully investigated. Finally, numerical results obtained from both the modified strain gradient theory (MSGT) and modified couple stress theory (MCST) are compared. © 2016
Azarboni, H.R.,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2016
Applied Mathematical Modelling (0307904X)40(21-22)pp. 9527-9545
In this study, we use transport equations to investigate the dynamic buckling of an imperfect elastoplastic beam, including the effect of axial stress waves, when subjected to an impulsive load. Thus, the governing equations for the elastoplastic behavior of the material are extracted using mass, energy, and momentum transport equations. We assume that the passage of the shock wave through the control volume creates five phases with four boundary discontinuities, i.e., the initial elastic phase, initial plastic phase, fluid phase, secondary plastic phase, and secondary elastic phase. Transport equations are used in integral form as well as non-physical variables to eliminate the discontinuity conditions in the governing equations. These equations are also used for continuum modeling of the elastoplastic behavior of the beam under an impulsive load and a continuous model is presented. Finally, the time histories of stress, strain, and velocity wave propagation along the beam are presented, and the results are validated based on comparisons with known solutions. © 2016 Elsevier Inc.
Azarboni, H.R.,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2016
Thin-Walled Structures (02638231)107pp. 57-65
The present study was aimed to investigate the influence of forcing frequency on nonlinear dynamic pulse buckling of imperfect rectangular plates with six different boundary conditions. The Galerkin's approximate method on the basis of polynomial and trigonometric mode shape functions is used to reduce the governing nonlinear partial differential equations to ordinary nonlinear differential equations. Moreover a numerical study of these governing equations is accomplished by Runge Kutta integration methods. The convergence of the polynomial and trigonometric mod shape functions are investigated to compute the dynamic response of plate. The effects of frequency of impulse loading and boundary conditions on the deflection histories of plate are studied. The dynamic response of plate subjected to impulsive loading with different forcing frequency is compared to results obtained by exponential impulsive loading. The results show that, by increasing the forcing frequency of impulsive loading, the maximum displacement of plate increases and converge with lower values to response of plate subjected to exponential impulse. Moreover, different boundary conditions and various pulse functions have significant influence on the dynamic response of the plate. © 2016 Elsevier Ltd.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Rouhi h., H. Publication Date: 2016
Science and Engineering of Composite Materials (21910359)23(1)pp. 107-121
A numerical solution method was developed to investigate the postbuckling behavior and vibrations around the buckled configurations of symmetrically and unsymmetrically laminated composite Timoshenko beams subject to different boundary conditions. The Hamilton principle was employed to derive the governing equations and corresponding boundary conditions which are then discretized by introducing a set of matrix differential operators. The pseudo-arc-length continuation method was used to solve the postbuckling problem. To study the free vibration that takes place around the buckled configurations, the corresponding eigenvalue problem was solved by means of the postbuckling configuration modes obtained in the previous step. The static bifurcation diagrams for composite beams with different lay-up laminates are given, and it is shown that the lay-up configuration considerably affects the magnitude of critical buckling load and postbuckling behavior. The study of the vibrations of composite beams with different laminations around the buckled configurations indicates that the natural frequency in the prebuckling domain increases as the stiffness of a beam increases, while there is no specific relation between the lay-up lamination and natural frequency in the postbuckling domain which necessitates conducting an accurate analysis in this area. © 2016 by De Gruyter 2016.
Ansari, R.,
Norouzzadeh, A.,
Gholami, R.,
Faghih shojaei, M.,
Darabi m.a., M.A. Publication Date: 2016
Microfluidics and Nanofluidics (16134982)20(1)
This paper is aimed to examine the geometrically nonlinear vibration and stability of nanoscale pipe conveying fluid incorporating surface stress effect. To approach this, the von-Karman hypothesis and Timoshenko beam theory are used to model the nanoscale pipe as a nonlinear Timoshenko nanobeam. Then, Hamilton’s principle and the Gurtin–Murdoch continuum elasticity are used to derive the governing equations of motion and associated boundary conditions incorporating the surface stress effect. Afterward, by the generalized differential quadrature method and harmonic balance method, the obtained nonlinear differential equations are discretized and simplified, before solving numerically through the Newton–Raphson method. The effects of the surface stress parameters on the stability and imaginary and real parts of frequency of nanopipes are discussed. Results are performed for nanopipes with different end supports made of silicon (Si) and aluminum (Al). © Springer-Verlag Berlin Heidelberg 2016.
Publication Date: 2016
Zeitschrift fur Angewandte Mathematik und Physik (14209039)67(4)
The present work aims to investigate the mechanical oscillatory behavior of ions, and in particular Li +, Na +, Rb + and Cl - ions, inside a cyclo[(–d-Ala–l-Ala)4–] peptide nanotube using the continuum approximation along with the 6–12 Lennard–Jones (LJ) potential function. Assuming that each peptide unit is comprised of an inner and an outer tube, the van der Waals (vdW) potential energy and interaction force between an ion and a cyclic peptide nanotube (CPN) are determined analytically. With respect to the present formulations, a detailed parametric study is conducted on the vdW potential energy and interaction force distributions by varying the number of peptide units. Employing the conservation of mechanical energy principle, a novel expression for precise evaluation of oscillation frequency is introduced. To verify the accuracy of the proposed frequency expression, the results obtained from energy equation are compared with the ones predicted through solving the equation of motion numerically. The effects of number of peptide units and initial conditions including initial separation distance and velocity on the oscillatory behavior of various ions inside CPNs are explored. Among the considered ions, Cl - ion is found to generate the highest frequency. According to the potential energy profile, one oscillatory zone for one peptide unit and different oscillatory zones for more than one peptide unit are observed. Numerical results indicate that optimal frequency decreases with increasing the number of peptide units and almost remains unchanged when the number of peptide units exceeds four. © 2016, Springer International Publishing.
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J.,
Ansari, R. Publication Date: 2016
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)230(19)pp. 3361-3371
A three-dimensional micromechanics-based analytical model is developed to investigate the influence of interphase on the thermo-mechanical properties of three-phase composites. The representative volume element (RVE) of composites is extended to c × r × h cells in three dimensions and the RVE consists of three phases including filler, matrix and interphase. The arrangement state of filler within the matrix materials is assumed to be random with uniform distribution. Fillers are surrounded by the interphase in the whole composite. The effects of interphase such as its thickness and stiffness on the thermo-mechanical properties of composite with various aspect ratios of filler are studied. The results illustrate that while the effects of interphase is significant for composites with randomly distributed spherical particles, it turns to be less effective as the aspect ratio of filler of composite increases. Moreover, the results demonstrate that the effect of interphase on the thermo-mechanical properties of fibrous composites in the transverse direction is more significant than that of fiber composites in the longitudinal direction. © 2016 Institution of Mechanical Engineers.
Publication Date: 2016
International Journal of Mechanical Sciences (00207403)115pp. 45-55
Creep-recovery behavior of polymer nanocomposites reinforced by carbon nanotubes (CNTs) is investigated using a 3-dimensional unit cell-based micromechanical model. The representative volume element (RVE) of the model consists of three phases including aligned CNTs, polymer matrix and CNT/polymer interphase formed due to non-bonded van der Waals interaction. The CNTs and polymer are assumed to be as transversely isotropic elastic and isotropic nonlinear viscoelastic materials, respectively. The effects of volume fraction and diameter of the CNTs, loading level and interphase including the materials behavior and size on the creep-recovery strain of the nanocomposite are examined. The predicted elastic and creep-recovery responses for pure polymer and CNT-reinforced polymer nanocomposite are found to be in good agreement with available experiment. Also, the isochronous stress-strain curves during the creep cycle for the nanocomposite under transverse and axial loadings are presented. The results clearly demonstrate that the overall transverse creep strain is dependent on the polymer nonlinear viscoelastic behavior and interphase material, as the applied loading increases. The results also reveal that the overall behavior of the nanocomposite is similar to the elastic response in the axial direction. Moreover, the isochronous stress-strain curves are extracted for biaxial and triaxial loading. © 2016 Elsevier Ltd.
Publication Date: 2016
Composites Part B: Engineering (13598368)90pp. 512-522
Viscoelastic response of carbon nanotubes (CNTs) reinforced polyimide nanocomposites subjected to the action of uniaxial and biaxial loads is studied using a micromechanical model based on the unit-cell method. The developed micromechanical model is simple and efficient, and provides closed-form expressions for the effective viscoelastic response of nanocomposites. The representative volume element (RVE) of nanocomposites consists of three phases including continuous CNTs, polyimide matrix and interphase. The state of dispersion of CNTs into the polymer matrix is considered to be random. The obtained elastic and viscoelastic responses are found to be in good agreement with those predicted through other methods and experimental data. The model is then used to study the effects of interphase materials (elastic and viscoelastic) on the creep behavior of nanocomposites. Also, the effects of stress level, CNT radius and interphase on the viscoelastic response of nanocomposites under uniaxial and equi-biaxial including transverse/transverse and longitudinal/transverse loading conditions are examined. © 2015 Elsevier Ltd. All rights reserved.
Ansari, R.,
Bazdid-vahdati m., M.,
Shakouri a.h., ,
Norouzzadeh, A.,
Rouhi h., H. Publication Date: 2016
Meccanica (15729648)51(8)pp. 1797-1809
Based on the micromorphic theory (MMT), a size-dependent plate element is developed for the finite element analysis of materials with considering the microstructure effect. To this end, the strain energy and constitutive relations of MMT are generally written first. The relations are represented in the matrix form so as to obtain the finite element matrices. Then, based on the first-order shear deformation theory, the matricized formulation is reduced for the case of a plate model, and the micromorphic plate element is formulated accordingly. In order to show the efficiency of the developed element, it is utilized to address the bending problem of micromorphic plates subject to various kinds of boundary conditions. In the numerical results, the effects of small scale and other parameters on the bending behavior of micromorphic plates are studied. It is revealed that the present finite element formulation can be efficiently used in the analysis of small-scale structures owing to considering micro-deformation and micro-rotation degrees of freedom of material particles. © 2015, Springer Science+Business Media Dordrecht.
Publication Date: 2016
Superlattices and Microstructures (10963677)93pp. 18-26
In this paper, the oscillatory behavior of double-walled boron-nitride nanotubes is investigated based on the molecular dynamics (MD) simulations. The MD simulations are performed using the Lennard-Jones and Tersoff-like potential functions. The influences of friction between the walls of inner and outer tubes, flexibility, velocity and outer length-to-inner length ratio on the frequency of oscillations are studied. The results show that the flexibility increases the frequency during the simulation. Furthermore, it is observed that by increasing the initial velocity, the frequency decreases. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)230(1)pp. 190-205
Using molecular dynamics simulations, the interfacial characteristics of polypropylene chains with single-walled carbon nanotubes are studied. The effects of different parameters (including initial orientation of polypropylene chain relative to nanotube, temperature, nanotube chirality and radius, and chain length) on the polypropylene/nanotube interactions are examined. Besides, the behavior of multiple polypropylene chains around a single-walled carbon nanotube is studied. It is shown that the final structure of polymer chain adsorbed on the single-walled carbon nanotube surface is independent of initial angle between polypropylene chain and the nanotube axis. Moreover, it is observed that armchair nanotubes are better candidates to reinforce the polypropylene matrix nanocomposites than zigzag nanotubes with the same geometry. © IMechE 2015.
Ansari, R.,
Faghih shojaei, M.,
Shakouri a.h., ,
Rouhi h., H. Publication Date: 2016
Journal of Computational and Nonlinear Dynamics (15551423)11(5)
Based on Mindlin's strain gradient elasticity and first-order shear deformation plate theory, a size-dependent quadrilateral plate element is developed in this paper to study the nonlinear static bending of microplates. In comparison with the classical first-order shear deformable quadrilateral plate element, the proposed element needs 15 additional nodal degrees-of-freedom (DOF) including derivatives of lateral deflection and rotations with respect to coordinates, which means a total of 20DOFs per node. Also, the developed strain gradient-based finite-element formulation is general so that it can be reduced to that on the basis of modified couple stress theory (MCST) and modified strain gradient theory (MSGT). In the numerical results, the nonlinear bending response of microplates for different boundary conditions, length-scale factors, and geometrical parameters is studied. It is revealed that by the developed nonclassical finite-element approach, the nonlinear behavior of microplates with the consideration of strain gradient effects can be accurately studied. Copyright © 2016 by ASME.
Publication Date: 2016
International Journal of Mechanical Sciences (00207403)113pp. 1-9
In this article, the nonlinear free vibration behavior of circular cylindrical nanoshells is investigated within the framework of surface stress elasticity theory. To accomplish this goal, a nonlinear shell model is developed based upon the model proposed by Ru [Continuum Mech. Thermodyn., 2016, vol. 28, pp. 263-273] and the classical shell theory. The geometric nonlinearity is taken into account using von Kármán's hypothesis. Hamilton's principle is also utilized to derive the governing equations including surface effects. Thereafter, using the multiple scales method, an analytical solution is obtained for the nonlinear free vibrations of simply-supported nanoshells. In the numerical results, the influences of surface stress, initial surface tension, length-to-radius and radius-to-thickness ratios on the vibration characteristics of nanoshells are studied. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Composite Structures (02638223)154pp. 707-723
The aim of this paper is to numerically investigate the geometrically nonlinear primary resonance of third-order shear deformable functionally graded carbon nanotube reinforced composite (FG-CNTRC) rectangular plates with various edge supports subjected to a harmonic excitation transverse force. The nanocomposite plates are composed of a mixture of matrix and single-walled carbon nanotubes (SWCNTs), and the effective mechanical properties are obtained by means of the rule of mixture. Employing the von Kármán hypotheses and Reddy's third-order shear deformation plate theory, the nonlinear equations of motion for the in-plane and out-of-plane directions as well as the corresponding boundary conditions are derived using Hamilton's principle. In the numerical solution procedure, the generalized differential quadrature (GDQ) method is used for the discretization, and a numerical Galerkin scheme is then employed to convert the discretized nonlinear partial differential equations (PDEs) into a Duffing-type nonlinear time-varying set of ordinary differential equations (ODEs). Afterwards, a time periodic discretization and the pseudo-arc length continuation method are utilized to determine the frequency- and force-responses of FG-CNTRC plates. Moreover, the curves corresponding to the nonlinear free vibration are provided. The influences of important parameters on the frequency-response and force-response curves of the FG-CNTRC plates are studied in the numerical results. © 2016 Elsevier Ltd
Publication Date: 2016
Physica E: Low-Dimensional Systems and Nanostructures (13869477)84pp. 84-97
The size-dependent static buckling responses of circular, elliptical and skew nanoplates made of functionally graded materials (FGMs) are investigated in this article based on an isogeometric model. The Eringen nonlocal continuum theory is implemented to capture nonlocal effects. According to the Gurtin-Murdoch surface elasticity theory, surface energy influences are also taken into account by the consideration of two thin surface layers at the top and bottom of nanoplate. The material properties vary in the thickness direction and are evaluated using the Mori-Tanaka homogenization scheme. The governing equations of buckled nanoplate are achieved by the minimum total potential energy principle. To perform the isogeometric analysis as a solution methodology, a novel matrix-vector form of formulation is presented. Numerical examples are given to study the effects of surface stress as well as other important parameters on the critical buckling loads of functionally graded nanoplates. It is found that the buckling configuration of nanoplates at small scales is significantly affected by the surface free energy. © 2016 Elsevier B.V. All rights reserved.
Publication Date: 2016
Smart Materials and Structures (09641726)25(9)
Considering the small scale effect together with the influences of transverse shear deformation, rotary inertia and the magneto-electro-thermo-mechanical coupling, the linear free vibration of magneto-electro-thermo-elastic (METE) rectangular nanoplates with various edge supports in pre- and post-buckled states is investigated herein. It is assumed that the METE nanoplate is subjected to the external in-plane compressive loads in combination with magnetic, electric and thermal loads. The Mindlin plate theory, von Kármán hypothesis and the nonlocal theory are utilized to develop a size-dependent geometrically nonlinear plate model for describing the size-dependent linear and nonlinear mechanical characteristics of moderately thick METE rectangular nanoplates. The nonlinear governing equations and the corresponding boundary conditions are derived using Hamilton's principle which are then discretized via the generalized differential quadrature method. The pseudo-arc length continuation approach is used to obtain the equilibrium postbuckling path of METE nanoplates. By the obtained postbuckling response, and taking a time-dependent small disturbance around the buckled configuration, and inserting them into the nonlinear governing equations, an eigenvalue problem is achieved from which the frequencies of pre- and post-buckled METE nanoplates can be calculated. The effects of nonlocal parameter, electric, magnetic and thermal loadings, length-to-thickness ratio and different boundary conditions on the free vibration response of METE rectangular nanoplates in the pre- and post-buckled states are highlighted. © 2016 IOP Publishing Ltd.
Publication Date: 2016
Scientia Iranica (23453605)23(6)pp. 3099-3114
In this study, the size-dependent post-buckling behavior of Magneto-Electro-Thermo-Elastic (METE) nanobeams with different edge supports is investigated. Based on the nonlocal first-order shear deformation beam theory and considering the von Karman hypothesis, a size-dependent nonlinear METE nanobeam model is developed, in which the effects of small-scale parameter and thermo-electro-magnetic-mechanical loadings are incorporated. A numerical solution procedure based on the Generalized Differential Quadrature (GDQ) and pseudo arc-length continuation methods is utilized to describe the size-dependent post-buckling behavior of METE nanobeams under various boundary conditions. The effects of different parameters such as nonlocal parameter, external electric voltage, external magnetic potential, and temperature rise on the post-buckling path of METE nanobeams are explored. The results indicate that increasing the nondimensional nonlocal parameter, imposed positive voltage, negative magnetic potential, and temperature rise decreases the critical buckling load and post-buckling load-carrying capacity of METE nanobeams, while an increase in the negative voltage and positive magnetic potential leads to a considerable increase of critical buckling load as well as post-buckling strength of the METE nanobeams. © 2016 Sharif University of Technology. All rights reserved.
Ansari, R.,
Shahabodini a., A.,
Faghih shojaei, M. Publication Date: 2016
Physica E: Low-Dimensional Systems and Nanostructures (13869477)76pp. 70-81
In the present work, a three-dimensional (3D) elastic plate model capturing the small scale effects is developed for the free vibration of functionally graded (FG) nanoplates resting on elastic foundations. The theoretical model is formulated employing the nonlocal differential constitutive relations of Eringen in conjunction with the 3D equations of motion of elasticity.The material properties are assumed to vary continuously along the thickness of the nanoplate in accordance with the power law formulation. Through extending the generalized differential quadrature (GDQ) method to the three-dimensional case, the governing equations are simultaneously discretized in every three coordinate directions and are then recast to the standard form of an eigen value problem. Solving the acquired problem, the natural frequencies of the nanoplates with different boundary conditions are calculated. The convergence behavior of the numerical results is checked out and comparison studies are conducted to make sure of the accuracy and reliability of the present model. Finally, the dependence of the vibration behavior of the nanoplate on edge conditions, elastic coefficients of the foundation, scale coefficient, mode number, material and geometric parameters are discussed. © 2015 Elsevier B.V.
Publication Date: 2016
Acta Mechanica Sinica/Lixue Xuebao (16143116)32(5)pp. 841-853
Based on the nonlocal elasticity theory, the vibration behavior of circular double-layered graphene sheets (DLGSs) resting on the Winkler- and Pasternak-type elastic foundations in a thermal environment is investigated. The governing equation is derived on the basis of Eringen’s nonlocal elasticity and the classical plate theory (CLPT). The initial thermal loading is assumed to be due to a uniform temperature rise throughout the thickness direction. Using the generalized differential quadrature (GDQ) method and periodic differential operators in radial and circumferential directions, respectively, the governing equation is discretized. DLGSs with clamped and simply-supported boundary conditions are studied and the influence of van der Waals (vdW) interaction forces is taken into account. In the numerical results, the effects of various parameters such as elastic medium coefficients, radius-to-thickness ratio, thermal loading and nonlocal parameter are examined on both in-phase and anti-phase natural frequencies. The results show that the thermal load and elastic foundation respectively decreases and increases the fundamental frequencies of DLGSs. © 2016, The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
Composites Part B: Engineering (13598368)95pp. 196-208
An efficient numerical method within the framework of variational formulation is employed to study the buckling and vibration of axially-compressed functionally graded carbon nanotube-reinforced composite (FG-CNTRC) conical shells. The effective material properties of functionally graded composite conical shell are estimated based on the extended rule of mixture. To derive the governing equations, the matrix form of Hamilton's principle is first presented on the basis of the first order shear deformation theory. Then, employing the generalized differential quadrature (GDQ) method in axial direction and periodic differential operators in circumferential direction, the numerical differential and integral operators are introduced to perform the discretization process. The comparison study is carried out to verify the accuracy and efficiency of the proposed method. Numerical results indicate that the volume fraction and types of distribution of CNTs have considerable effects on the buckling and vibration characteristics of FG-CNTRC conical shells subjected to axial loadings. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Applied Physics A: Materials Science and Processing (14320630)122(12)
Employing the variational differential quadrature method, the free vibration of carbon nanocones (CNCs) embedded in an elastic foundation, is studied based on nonlocal elasticity theory. On the basis of the first-order shear deformation theory, the energy functional of the CNC is presented and then discretized by employing the generalized differential quadrature method in the axial direction and periodic differential operators in the circumferential direction. According to Hamilton’s principle and using matrix relations, the reduced forms of mass and stiffness matrices are readily obtained. The results of present study are compared to those obtained by molecular mechanics to verify the proposed approach. In addition, the effects of nonlocal parameter, boundary conditions, semi-apex angle and both Winkler and Pasternak coefficients of elastic foundation are examined on the vibrational behavior of CNCs. The results indicate that the increase in nonlocal parameter and elastic foundation coefficients decreases and increases the fundamental frequency of CNCs, respectively. © 2016, Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Darvizeh a., A. Publication Date: 2016
Mechanics of Materials (01676636)101pp. 14-26
A three-dimensional micromechanics-based analytical model is developed to investigate the elastic modulus and biaxial initial yield surface of aligned carbon nanotube (CNT)-reinforced aluminum (Al) nanocomposites. The Von-Mises yield criterion is used to obtain the yielding behavior of the nanocomposites under biaxial transverse-transverse and transverse-longitudinal loadings. The interphase region formed due to the interfacial reaction between the CNT and Al matrix is considered in the micromechanical modeling. The effects of geometry and material properties of the interphase and CNT volume fraction on the elastic modulus and biaxial initial yield surface of nanocomposites are studied. The elastic modulus obtained by the present model is in very good agreement with that reported from available molecular dynamics (MD) simulations and experiment. It is found that the effect of interphase is more important for the transverse elastic modulus of the nanocomposite as compared to the longitudinal elastic modulus. Also, the results reveal that the size of the biaxial initial yield surfaces of the nanocomposites, especially in transverse-longitudinal loading, is significantly affected by the interphase properties. © 2016 Elsevier Ltd
Publication Date: 2016
Journal Of Molecular Modeling (16102940)22(1)pp. 1-11
Molecular dynamics simulations are used to study the physical and mechanical properties of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites. The effects of nanotube atomic structure, diameter, and volume fraction on the polymer density distribution, polymer atom distribution, stress–strain curves of nanocomposites and Young’s, and shear moduli of single-walled carbon nanotubes/poly(ethylene oxide) nanocomposites are explored. It is shown that the density of polymer, surrounding the nanotube surface, has a peak near the nanotube surface. However, increasing distance leads to dropping it to the value near the density of pure polymer. It is seen that for armchair nanotubes, the average polymer atoms distances from the single-walled carbon nanotubes are larger than the polymer atom distance from zigzag nanotubes. It further is shown that zigzag nanotubes are better candidates to reinforce poly (ethylene oxide) than their armchair counterparts. © 2016, Springer-Verlag Berlin Heidelberg.
Publication Date: 2016
Brazilian Journal Of Physics (01039733)46(3)pp. 361-369
Molecular dynamics (MD) simulations is used to study the adsorption of polyethylene (PE) and poly(ethylene oxide) (PEO) on the functionalized single-walled carbon nanotubes (SWCNTs). The effects of functionalization factor weight percent on the interaction energies of polymer chains with nanotubes are studied. Besides, the influences of different functionalization factors on the SWCNT/polymer interactions are investigated. It is shown that for both types of polymer chains, the largest interaction energies associates with the random O functionalized nanotubes. Besides, increasing temperature results in increasing the nanotube/polymer interaction energy. Considering the final shapes of adsorbed polymer chains on the SWCNTs, it is observed that the adsorbed conformations of PE chains are more contracted than those of PEO chains. © 2016, Sociedade Brasileira de Física.
Publication Date: 2016
International Journal of Mechanical Sciences (00207403)119pp. 155-169
Buckling of anisotropic piezoelectric cylindrical shells subjected to axial compression and lateral pressure is investigated based on the new modified couple stress theory and using the shear deformation theory with the von Kármán geometrical nonlinearity. By applying the principle of minimum potential energy, the governing equations and boundary conditions are derived. Unlike the classical continuum model, the present model is size-dependent, and the size effects are captured using the new modified couple stress theory. The critical buckling load is obtained for simply supported, clamped-simply supported and clamped piezoelectric cylindrical shells. A detailed numerical study is carried out to discuss the effects of different parameters, such as material length scale parameter, thickness ratio, length ratio, load interaction parameter and the external electric voltage on the critical buckling load. The critical buckling load is found to be significantly size-dependent, especially for large values of thickness and small values of length ratio. Besides, the influence of load interaction parameter is found to be negligible for large values of length and small values of thickness ratio. © 2016 Elsevier Ltd
Publication Date: 2016
International Journal of Modern Physics B (02179792)30(5)
The vibrational behavior of double-walled carbon nanotubes is studied by the use of the molecular structural and cylindrical shell models. The spring elements are employed to model the van der Waals interaction. The effects of different parameters such as geometry, chirality, atomic structure and end constraint on the vibration of nanotubes are investigated. Besides, the results of two aforementioned approaches are compared. It is indicated that by increasing the nanotube side length and radius, the computationally efficient cylindrical shell model gives rational results. © 2016 World Scientific Publishing Company.
Publication Date: 2016
Journal Of Molecular Modeling (16102940)22(3)pp. 1-8
The adsorption of biomolecules on the walls of carbon nanotubes (CNTs) in an aqueous environment is of great importance in the field of nanobiotechnology. In this study, molecular dynamics (MD) simulations were performed to understand the mechanical vibrational behavior of single- and double-walled carbon nanotubes (SWCNTs and DWCNTs) under the physical adsorption of four important biomolecules (L-alanine, guanine, thymine, and uracil) in vacuum and an aqueous environment. It was observed that the natural frequencies of these CNTs in vacuum reduce under the physical adsorption of biomolecules. In the aqueous environment, the natural frequency of each pure CNT decreased as compared to its natural frequency in vacuum. It was also found that the frequency shift for functionalized CNTs as compared to pure CNTs in the aqueous environment was dependent on the radius and the number of walls of the CNT, and could be positive or negative. © 2016, Springer-Verlag Berlin Heidelberg.
Ebrahimi f., ,
Ansari, R.,
Faghih shojaei, M.,
Rouhi h., H. Publication Date: 2016
Meccanica (15729648)51(10)pp. 2493-2507
The postbuckling problem of Euler–Bernoulli (EB) microbeams under different boundary conditions is addressed in this paper using a non-classical finite element (FE) approach with a novel beam element. The proposed element is capable of considering the strain gradient effects and hence is appropriate to use at microscale. First, based on Mindlin’s strain gradient theory (SGT), a size-dependent EB beam model including strain gradient effects is developed. Then, by a FE approach, the non-classical beam element is constructed which needs two additional degrees of freedom per node as compared to the classical EB beam element. The new element is based upon Mindlin’s SGT, and can be easily reduced to that based on various higher-order elasticity theories such as the modified versions of strain gradient and couple stress theories. Selected numerical results are presented to show the reliability of the developed FE formulation, and also to study the small scale influences on the bifurcation diagrams of microbeams. © 2016, Springer Science+Business Media Dordrecht.
Publication Date: 2016
Physica E: Low-Dimensional Systems and Nanostructures (13869477)80pp. 69-81
In this research, a continuum-based model is presented to explore potential energy, force distribution and oscillatory motion of ions, and in particular chloride ion, inside carbon nanotubes (CNTs) decorated by functional groups at two ends. To perform this, van der Waals (vdW) interactions between ion and nanotube are modeled by the 6-12 Lennard-Jones (LJ) potential, whereas the electrostatic interactions between ion and functional groups are modeled by the Coulomb potential and the total interactions are analytically derived by summing the vdW and electrostatic interactions. Making the assumption that carbon atoms and charge of functional groups are all uniformly distributed over the nanotube surface and the two ends of nanotube, respectively, a continuum approach is utilized to evaluate the related interactions. Based on the actual force distribution, the equation of motion is also solved numerically to arrive at the time history of displacement and velocity of inner core. With respect to the proposed formulations, comprehensive studies on the variations of potential energy and force distribution are carried out by varying functional group charge and nanotube length. Moreover, the effects of these parameters together with initial conditions on the oscillatory behavior of system are studied and discussed in detail. It is found out that chloride ion escapes more easily from negatively charged CNTs which is followed by uncharged and positively charged ones. It is further shown that the presence of functional groups leads to enhancing the operating frequency of such oscillatory systems especially when the electric charges of ion and functional groups have different signs. © 2016 Elsevier B.V. All rights reserved.
Publication Date: 2016
EPJ Applied Physics (12860042)74(1)
The considerable demand for novel materials with specific properties has motivated the researchers to synthesize supramolecular nanostructures through different methods. Porous graphene is the first two-dimensional hydrocarbon synthesized quite recently. This investigation is aimed at studying the mechanical properties of atom-decorated (functionalized) porous graphene by employing density functional theory (DFT) calculation within both local density approximations (LDA) and generalized gradient approximations (GGA). The atoms are selected from period 3 of periodic table as well as Li and O atom from period 2. The results reveal that metallic atoms and noble gases are adsorbed physically on porous graphene and nonmetallic ones form chemical bonds with carbon atom in porous graphene structure. Also, it is shown that, in general, atom decoration reduces the values of mechanical properties such as Young's, bulk and shear moduli as well as Poisson's ratio, and this reduction is more considerable in the case of nonmetallic atoms (chemical adsorption), especially oxygen atoms, as compared to metallic atoms and noble gases (physical adsorption). © EDP Sciences, 2016.
Publication Date: 2016
Composite Structures (02638223)152pp. 45-61
In this paper, the size-dependent formulation of shear deformable functionally graded piezoelectric (FGP) cylindrical nanoshells is developed based on a new modified couple stress theory. After the general formulation, the buckling of FGP cylindrical nanoshells under pressure is investigated by using the first order shear deformable shell model. The material properties are assumed to be varied along thickness direction according to the power law distribution. The equilibrium equations and boundary conditions are obtained by using the minimum potential energy principle. A buckling analysis of simply-supported FGP cylindrical nanoshells under uniform lateral external pressure is carried out and the effects of different parameters on the critical pressure are examined. The effects of geometrical, electrical and material properties, such as material length scale parameter, length, thickness, external electric voltage and material property gradient index, on the critical pressure are illustrated. It is indicated that the critical pressure is significantly size-dependent. © 2016 Elsevier Ltd.
Ansari, R.,
Hasrati, E.,
Faghih shojaei, M.,
Gholami, R.,
Mohammadi v., V.,
Shahabodini a., A. Publication Date: 2016
Latin American Journal of Solids and Structures (16797825)13(4)pp. 632-664
In this paper, a size-dependent microscale plate model is developed to describe the bending, buckling and free vibration behaviors of microplates made of functionally graded materials (FGMs). The size effects are captured based on the modified strain gradient theory (MSGT), and the formulation of the paper is on the basis of Mindlin plate theory. The presented model accommodates the models based upon the classical theory (CT) and the modified couple stress theory (MCST) if all or two scale parameters are set to zero, respectively. By using Hamilton’s principle, the governing equations and related boundary conditions are derived. The bending, buckling and free vibration problems are considered and are solved through the generalized differential quadrature (GDQ) method. A detailed parametric and comparative study is conducted to evaluate the effects of length scale parameter, material gradient index and aspect ratio predicted by the CT, MCST and MSGT on the deflection, critical buckling load and first natural frequency of the microplate. The numerical results indicate that the model developed herein is significantly sizedependent when the thickness of the microplate is on the order of the material scale parameters. © 2016, Brazilian Association of Computational Mechanics. All rights reserved.
Publication Date: 2016
Applied Mathematical Modelling (0307904X)40(4)pp. 3128-3140
Based upon the Gurtin-Murdoch elasticity theory capturing the surface stress effect, a size-dependent continuum model is developed to investigate the free vibrations of nanoscale cylindrical shells. The equations of motion including the surface stress effect are derived based on the first-order shear deformation theory (FSDT) and using Hamilton's principle. A Galerkin-based closed-form solution technique together with modal beam functions is also utilized to solve the problem. Comprehensive results for the size-dependent vibration behavior of nanoshells under various boundary conditions are given. The results from the present analysis, where possible, are shown to be in very good agreement with the existing data from the literature. A comparison is also made between the predictions of surface stress model and those of its classical counterpart, and it is revealed that the surface stress has a significant influence on the resonant frequency of very thin nanoshells. Moreover, the effects of surface properties including surface elastic moduli, surface residual tension and surface mass density on the vibration characteristics of nanoshells are studied. © 2015.
Publication Date: 2016
Journal of Mechanics (18118216)32(5)pp. 539-554
In this paper, a non-classical plate model capturing the size effect is developed to study the forced vibration of functionally graded (FG) microplates subjected to a harmonic excitation transverse force. To this, the modified couple stress theory (MCST) is incorporated into the first-order shear deformation plate theory (FSDPT) to account for the size effect through one length scale parameter, only. Strong form of nonlinear governing equations and associated boundary conditions are obtained using Hamilton's principle. The solution process is implemented on two domains. The generalized differential quadrature (GDQ) method is first employed to discretize the governing equations on the space domain. A Galerkin-based scheme is then applied to extract a reduced set of the nonlinear equations of Duffing-type. On the second domain, through a time differentiation matrix operator, the set of ordinary differential equations are transformed into the discrete form on time domain. Eventually, a system of the parameterized nonlinear equations is acquired and solved via the pseudo-arc length continuation method. The frequency response curve of the microplate is sketched and the effects of various material and geometrical parameters on it are evaluated. © Copyright 2016 The Society of Theoretical and Applied Mechanics.
Publication Date: 2016
Physica E: Low-Dimensional Systems and Nanostructures (13869477)75pp. 266-271
In recent decades, mathematical modeling and engineering applications of fractional-order calculus have been extensively utilized to provide efficient simulation tools in the field of solid mechanics. In this paper, a nonlinear fractional nonlocal Euler-Bernoulli beam model is established using the concept of fractional derivative and nonlocal elasticity theory to investigate the size-dependent geometrically nonlinear free vibration of fractional viscoelastic nanobeams. The non-classical fractional integro-differential Euler-Bernoulli beam model contains the nonlocal parameter, viscoelasticity coefficient and order of the fractional derivative to interpret the size effect, viscoelastic material and fractional behavior in the nanoscale fractional viscoelastic structures, respectively. In the solution procedure, the Galerkin method is employed to reduce the fractional integro-partial differential governing equation to a fractional ordinary differential equation in the time domain. Afterwards, the predictor-corrector method is used to solve the nonlinear fractional time-dependent equation. Finally, the influences of nonlocal parameter, order of fractional derivative and viscoelasticity coefficient on the nonlinear time response of fractional viscoelastic nanobeams are discussed in detail. Moreover, comparisons are made between the time responses of linear and nonlinear models. © 2015 Elsevier B.V. All rights reserved.
Publication Date: 2016
Composites Part B: Engineering (13598368)95pp. 301-316
The present study deals with the nonlinear postbuckling and free vibration of third-order shear deformable rectangular nanoplate with various edge supports in the pre- and post-buckling regimes incorporating the surface effects. The Gurtin-Murdoch surface stress elasticity theory in conjunction with the third-order shear deformation plate theory is used for the size-dependent mathematical modeling of the nanoplates. The von Kármán-type kinematic nonlinearity is used to consider the nonlinear behavior of the nanoplate subjected to the in-plane loadings. The normal stress is assumed to be changed cubically through the thickness direction of nanoplate to satisfy the equilibrium conditions between on the surfaces and bulk layers. The size-dependent coupled in-plane and out-of-plane governing differential equations of motion and corresponding boundary conditions are derived by means of an energy method based on Hamilton's principle. The generalized differential quadrature (GDQ) method and pseudo-arc length continuation are employed to obtain the postbuckling load-deflection curves of nanoplates with various edge supports. A time-dependent small disturbance around the buckled configuration is considered to analyze the free vibration of postbuckled nanoplates. The effects of thickness and surface parameters on the postbuckling path and free vibration characteristics of nanoplates in the pre- and post-buckling regimes are studied. Also, a comparison is made between the results based upon the surface stress elasticity and classical continuum theories so as to show the significance of surface effects. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Composite Structures (02638223)136pp. 669-683
By developing a nonlinear microstructure-dependent third-order shear deformable beam model based on the most general form of Mindlin's strain gradient elasticity theory (SGT) and the von Kármán hypothesis, the size-dependent nonlinear mechanical behavior of a microbeam made of functionally graded materials (FGMs) are described. The matrix representations of classical and non-classical kinematic and constitutive relations are obtained first. Then, the variation of energy functional is obtained in a matrix form. Afterwards, the variational differential quadrature (VDQ) rule is utilized to directly derive the discretized form of nonlinear governing equations of motion on the space domain. The periodic time differential operators and the pseudo arc-length continuation method are also used to solve the nonlinear problems of microbeams including the nonlinear free and forced vibration as well as nonlinear bending and postbuckling. The effects of length-scale parameter and boundary conditions on the microstructure-dependent nonlinear mechanical characteristics of FGM microbeams are investigated. The present model accommodates the simple forms of microstructure-dependent formulations based on the modified strain gradient theory (MSGT) and modified couple stress theory (MCST) for some specific values of the material length scale parameters. The results predicted by MSGT, MCST and classical theory are compared. © 2015 Elsevier Ltd.
Publication Date: 2016
International Journal of Applied Mechanics (17588251)8(4)
This paper deals with the size-dependent geometrically nonlinear free vibration of magneto-electro-thermo elastic (METE) nanoplates using the nonlocal elasticity theory. The mathematical formulation is developed based on the first-order shear deformation plate theory, von Karman-type of kinematic nonlinearity and nonlocal elasticity theory. The influences of geometric nonlinearity, rotary inertia, transverse shear deformation, magneto-electro-thermal loading and nonlocal parameter are considered. First, the generalized differential quadrature (GDQ) method is utilized to reduce the nonlinear partial differential equations to a system of time-dependent nonlinear ordinary differential equations. Afterwards, the numerical Galerkin method, periodic time differential operators and pseudo-arc length continuation algorithm are employed to compute the nonlinear frequency versus the amplitude for the METE nanoplates. The presented methodology enables one to describe the large-amplitude vibration characteristics of METE nanoplates with various sets of boundary conditions. A detailed parametric study is carried out to analyze the important parameters such as the nondimensional nonlocal parameter, external electric potential, external magnetic potential, temperature change, length-to-thickness ratio, aspect ratio and various edge conditions on the nonlinear free vibration characteristics of METE nanoplates. The results demonstrate that considering the size effect on the vibration response of METE nanoplate results in decreasing the natural frequency, a remarkable increasing effect on the hardening behavior and subsequently increasing the nonlinear-to-linear frequency ratio. © 2016 World Scientific Publishing Europe Ltd.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R. Publication Date: 2016
International Journal for Multiscale Computational Engineering (15431649)14(1)pp. 65-80
This paper addresses the problem of size-dependent axisymmetric postbuckling behavior of annular shear deformable nanoplates by taking into consideration surface effects. A size-dependent continuum plate model is developed based on the Gurtin–Murdoch elasticity theory, the first-order shear deformation theory, and the von Kármán geometrically nonlinear relations. It is assumed that the annular nanoplate is subjected to compressive axisymmetric radial loads. By using the Gurtin–Murdoch theory, the influences of surface stress and residual surface stress are incorporated into the formulation. Afterward, according to the virtual work principle, the size-dependent geometrically nonlinear governing equations and associated boundary conditions of first-order shear deformable nanoplates are obtained. The obtained set of nonlinear equations is discretized and solved via the generalized differential quadrature method and pseudo-arc-length continuation method. Then, the postbuckling behavior of nanoplates made of silicon and aluminum with different boundary conditions is carefully studied. The results obtained from classical and non-classical theories are compared for the first three postbuckling modes. In addition, the effects of the surface elastic modulus, residual surface stress, thickness, and radius ratio on the postbuckling response of annular nanoplates are examined. © 2016 by Begell House, Inc.
Publication Date: 2016
Thin-Walled Structures (02638231)105pp. 172-184
The free vibration and instability characteristics of nanoshells made of functionally graded materials (FGMs) with internal fluid flow in thermal environment are studied in this paper based upon the first-order shear deformation shell theory. In order to capture the size effects, Mindlin's strain gradient theory (SGT) is utilized. The mechanical and thermal properties of FG nanoshell are determined by the power-law relation of volume fractions. The Knudsen number is considered to analyze the slip boundary conditions between the flow and wall of nanoshell, and the average velocity correction parameter is used to obtain the modified flow velocity of nano-flow. The governing partial differential equations of motion and associated boundary conditions are derived by Hamilton's principle. An analytical solution method is also employed to solve the governing equations under the simply-supported end conditions. Then, some numerical examples are presented to investigate the effects of fluid velocity, longitudinal and circumferential mode numbers, length scale parameters, material properties, temperature difference and compressive axial loads on the natural frequencies, critical flow velocities and instability of system. © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016
Applied Surface Science (01694332)366pp. 233-244
The non-cytotoxic properties of Boron-nitride nanotubes (BNNTs) and the ability of stable interaction with biomolecules make them so promising for biological applications. In this research, molecular dynamics (MD) simulations are performed to investigate the structural properties and stability characteristics of single- and double-walled BNNTs under physical adsorption of Flavin mononucleotide (FMN) in vacuum and aqueous environments. According to the simulation results, gyration radius increases by rising the weight percentage of FMN. Also, the results demonstrate that critical buckling force of functionalized BNNTs increases in vacuum. Moreover, it is observed that by increasing the weight percentage of FMN, critical force of functionalized BNNTs rises. By contrast, critical strain reduces by functionalization of BNNTs in vacuum. Considering the aqueous environment, it is observed that gyration radius and critical buckling force of functionalized BNNTs increase more considerably than those of functionalized BNNTs in vacuum, whereas the critical strains approximately remain unchanged. © 2016 Elsevier B.V. All rights reserved.
Publication Date: 2016
Acta Astronautica (00945765)118pp. 72-89
Surface stress and surface inertia effects may play a significant role in the mechanical characteristics of nanostructures with a high surface to volume ratio. The objective of this study is to present a comprehensive study on the surface stress and surface inertia effects on the large amplitude periodic forced vibration of first-order shear deformable rectangular nanoplates. To this end, the Gurtin-Murdoch theory, first-order shear deformation theory (FSDT) and Hamilton's principle are employed to develop a non-classical continuum plate model capable of taking the surface stress and surface inertia effects and also the rotary and in-plane inertias into account. To solve numerically the geometrically nonlinear forced vibration of nanoplates with different boundary conditions, the generalized differential quadrature (GDQ) method, numerical Galerkin scheme, periodic time differential operators and pseudo arc-length continuation method are employed. The effects of parameters such as thickness, surface residual stress, surface elasticity, surface mass density, length-to-thickness ratio, width-to-thickness ratio and boundary conditions on the nonlinear forced vibration of rectangular nanoplates are fully investigated. The results demonstrate that surface effects on the nonlinear frequency response of aluminum (Al) nanoplate are more prominent in comparison with the silicon (Si) nanoplate. © 2015 IAA. Published by Elsevier Ltd. All rights reserved.
Publication Date: 2016
International Journal of Innovation Management (13639196)(3)
In the recent, the aspect of foresight is considered globally important. Specially, it has gained a meaningful position in strategic planning. This study examines the quantitative relationships between strategic foresight, ambidexterity and competitiveness of firms. Based on the literature review, it appears that strategic foresight has positive impact on organisational ambidexterity which in turn contributes to competitive advantage. We have utilised structural equations modeling (SEM) to empirically test the mentioned relationships in Iran's nanotechnology firms. Results show that the degree of strategic foresight has a direct effect on organisational ambidexterity which in turn affects competitive advantage. © 2016 Imperial College Press.
Rajabiehfard r., R.,
Darvizeh a., A.,
Darvizeh m., M.,
Ansari, R.,
Alitavoli, M.,
Sadeghi h., Publication Date: 2016
Thin-Walled Structures (02638231)107pp. 315-326
In this paper, the dynamic buckling of axisymmetric circular cylindrical shells subjected to axial impact is investigated theoretically and experimentally. The von Mises yield criterion is used for the elastic–plastic cylindrical shell made of linear strain hardening material in order to derive the constitutive relations between stress and strain increments. Nonlinear dynamic circular cylindrical shell equations are solved with using finite difference method for two types of loading which are stationary cylindrical shells impacted axially and traveling cylindrical shells impacted against a rigid wall. Experimental tests for two types of loading are performed by gas gun. Theoretical and experimental results for cylindrical shells under axial impact for different loading conditions are reported and it is found that there is a good agreement between them. © 2016
Ansari, R.,
Oskouie, M.F.,
Gholami, R.,
Sadeghi f., F. Publication Date: 2016
Composites Part B: Engineering (13598368)89pp. 316-327
In this study, free vibration behavior of piezoelectric Timoshenko nanobeams in the vicinity of postbuckling domain is investigated based on the nonlocal elasticity theory. It is assumed that the piezoelectric nanobeam is subjected to an axial compression force, an applied voltage and a uniform temperature change. Using Hamilton principle, the governing differential equations of motion incorporating von Kármán geometric nonlinearity and the corresponding boundary conditions are derived and then discretized on the basis of generalized differential quadrature (GDQ) scheme. After solving the parameterized equations using Newton-Raphson technique, a dynamic analysis based on a numerical solution strategy is performed to predict the natural frequencies of piezoelectric nanobeams associated with both prebuckling and postbuckling domains. Numerical results are presented to study the effects of nonlocal parameter, temperature rise and external electric voltage on the size-dependent vibration behavior of piezoelectric nanobeams with clamped-clamped (C-C), clamped-simply supported (C-SS) and simply supported-simply supported (SS-SS) end conditions. It is demonstrated that these parameters may shift the postbuckling domain to higher or lower applied axial loads. © 2016 Elsevier Ltd. All rights reserved.
Ansari, R.,
Hassanzadeh-aghdam, M.K.,
Mahmoodi m.j., M.J. Publication Date: 2016
Acta Mechanica (16196937)227(12)pp. 3475-3495
The effects of carbon nanotube (CNT) waviness on the elastic characterizations of polymer nanocomposites are investigated using a three-dimensional unit cell-based micromechanical model. The most important advantages of this model are its accuracy, simplicity, and efficiency. Both random and regular CNT arrangements can be included in the modeling. The wavy CNTs are modeled as sinusoidal solid CNT fibers while at any location along the length of CNT, the CNT is considered as transversely isotropic material. The polymer and interphase formed due to non-bonded interaction between a CNT and the polymer are assumed to be homogeneous and isotropic as well. Results show that the effect of CNT waviness is not important for the effective coefficients C11, C12, and C13 of the nanocomposites. CNT waviness plays a critical role in determining the effective coefficients C22, C23, C33, and C44 of the nanocomposites. Also, it is found that the CNT waviness slightly affects the effective values of C55 and C66. The effects of volume fraction of CNT and interphase on the mechanical properties of the nanocomposite are examined. Comparison of the present model results shows very good agreement with other available micromechanical analysis and experiment. As comparing with the finite element method, the present model requires much less computational time for obtaining the effective properties of the nanocomposites. Consequently, the results emphasize that all four important parameters, i.e., CNT behavior and waviness, CNT random arrangement, and interphase contributions, should be precisely included in the modeling to predict a more realistic outcome. © 2016, Springer-Verlag Wien.
Gholami, R.,
Darvizeh a., A.,
Ansari, R.,
Sadeghi f., F. Publication Date: 2016
European Journal of Mechanics, A/Solids (09977538)58pp. 76-88
In this research, a size-dependent first-order shear deformable model is developed based on the Mindlin's strain gradient elasticity theory to analyze the free vibration and axial buckling of circular cylindrical micro-/nano-shells. The size-dependent governing equations and corresponding boundary conditions are established through Hamilton's principle. For some specific values of the gradient-based material parameters, the most general form of shell formulation can be reduced to those based on simple forms of the strain gradient elasticity theory such as the modified strain gradient theory (MSGT), modified couple stress theory (MCST) and strain gradient theory (SGT). To illustrate the characteristics of a micro-/nano-shell obtained by the size-dependent shell formulation, the axial buckling and free vibration problems of a simply-supported (SS) microshell are analyzed by employing a Navier-type solution. Selected numerical results are presented to get an insight into the effects of dimensionless material length scale parameters, length-to-radius ratio and circumferential mode number on the non-dimensionless natural frequencies and buckling loads. For comparison purpose, the non-dimensional natural frequencies and buckling loads predicted by MSGT, MCST, SGT and classical theory (CT) are also presented. It is shown that the effect of small scale is more prominent for lower values of dimensionless length scale parameter. © 2016 Elsevier Masson SAS. All rights reserved.
Ansari, R.,
Shahabodini a., A.,
Faghih shojaei, M. Publication Date: 2016
Composite Structures (02638223)139pp. 167-187
Superlative properties of nanocomposites have motivated considerable research efforts in recent years. Nanocomposite plates of quadrilateral shapes are important structural components used in a variety of engineering structures. This article aims to develop a variational formulation to describe the vibrational behavior of functionally graded (FG) nanocomposite straight-sided quadrilateral plates reinforced by carbon nanotubes (CNTs) in thermal environments. Various profiles of single-walled carbon nanotubes (SWCNTs) distribution along the thickness are taken into consideration. The mathematical formulation is developed in the variational form based on the first order shear defamation plate theory (FSDPT) with consideration of thermal effects. Discretization process of the energy functional is done on a computational domain using a mapping-differential quadrature (DQ) methodology. Discrete form of the governing equations is directly derived from a weak formulation which does not involve any transformation and discretization of the high order derivatives appeared in the equations of the strong form. Numerical results are given and compared with the ones reported in the literature to evaluate the convergence behavior and accuracy of the proposed solution. Subsequently, the influences of temperature on natural frequencies of the nanocomposite quadrilateral plates with different geometric parameters, CNT distributions in thickness direction and boundary conditions are investigated. © 2015 Elsevier Ltd.
Publication Date: 2016
European Journal of Mechanics, A/Solids (09977538)60pp. 166-182
In this paper, the free vibration characteristics of embedded functionally graded carbon nanotube-reinforced composite (FG-CNTRC) spherical shells are studied based on a numerical approach. The elastic foundation is considered to be Pasternak-type. Moreover, the extended rule of mixture is used so as to obtain the material properties of FG-CNTRC. The shell is also modeled according to the first-order shear deformation shell theory. The energy functional of the structure is obtained first. Using differential operators, the discretized form of the energy functional is derived. By means of the variational differential quadrature (VDQ) method, the reduced forms of mass and stiffness matrices are then obtained. Selected numerical results are given to investigate the effects of different parameters such as elastic foundation coefficients, boundary conditions, CNT volume fraction, thickness-to-radius ratio and type of distribution of CNT on the vibrations of FG-CNTRC spherical shells. © 2016 Elsevier Masson SAS
Publication Date: 2016
EPJ Applied Physics (12860042)76(2)
Current study concerns the vibrational behavior of single-walled carbon nanotube/graphene junctions using the finite element method. The effects of different parameters including nanotube and graphene geometry/boundary conditions on the vibrations of nanotube/graphene junction are investigated. Two types of junctions are considered. In the first type, the nanotube is connected to one side of graphene, while in the second type, both sides of the graphene are connected to nanotubes. It is shown that increasing the height-to-length ratio of graphene results in decreasing the fundamental natural frequency of the junctions. When the boundary conditions are imposed on the graphene, increasing the radius of carbon nanotube leads to decreasing the frequency. Moreover, the frequencies of the second type models are larger than those of the first type. © 2016 EDP Sciences.
Publication Date: 2016
Materials Research Express (20531591)3(12)
This paper aims to investigate the vibrational properties of single-layered boron nitride nanosheet/ single-walled boron nitride nanotube junctions. To this end, the finite element (FE) (approach is employed.Considering the similarity of molecular mechanics and structural mechanics, the mechanical properties of the utilized FE approach can be derived. The junctions with nanotubes at one side and both sides of the nanosheet are considered. It is shown that the frequencies of both sides located nanotubes are always larger than those of one side located nanotube. Moreover, the influences of geometrical parameters of nanosheet and nanotube on the frequencies of boron nitride nanosheet/ nanotube junctions are studied. It is observed that the vibrational behavior of the considered junctions has an inverse relation to the nanotube and nanosheet dimensions. ©2016 IOP Publishing Ltd.
Ansari, R.,
Gholami, R.,
Norouzzadeh, A.,
Darabi m.a., M.A. Publication Date: 2016
Arabian Journal for Science and Engineering (21914281)41(11)pp. 4359-4369
The aim of this paper was to investigate the wave propagation of nanotubes conveying fluid by considering the surface stress effect. To this end, the nanotube is modeled as a Timoshenko nanobeam. According to the Gurtin–Murdoch continuum elasticity, the surface stress effect is incorporated into the governing equations of motion obtained from the Hamilton principle. The governing differential equations are solved by generalized differential quadrature method. Then, the effects of the thickness, material and surface stress modulus, residual surface stress, surface density and flow velocity on spectrum curves of nanotubes predicted by both classical and non-classical theories are studied. The first three fundamental modes including flexural, axial, and shear waves of nanotubes are considered. © 2016, King Fahd University of Petroleum & Minerals.
Ansari, R.,
Faghihnasiri m., ,
Malakpour s., S.,
Sahmani, S. Publication Date: 2015
Superlattices and Microstructures (10963677)82pp. 90-102
Abstract The aim of present study is to investigate the effect of external electric field on the elastic and structural properties of a (3,3) armchair boron nitride nanotube (BNNT). To accomplish this purpose, the density functional theory (DFT) within the generalized gradient approximation (GGA) framework is employed. The calculations are performed employing Plane-Wave basis set and pseudopotentials. The structural and elastic properties of armchair BNNT are predicted in the presence of electric field parallel and perpendicular to tube axis. The homogeneous electric fields are applied to BNNT on the basis of the estimated optimized wave function. The obtained results indicate that in contrast to the perpendicular field, the external electric field along tube axis causes considerable changes in the value of bond length and atomic positions. Moreover, it is found that by applying electric field along tube axis direction, Young's modulus of BNNT decreases about 13% compared to that in the absence of external electric field, which means a significant reduction in the axial stiffness of BNNT. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Superlattices and Microstructures (10963677)79pp. 15-20
In this article, a first principles investigation is conducted into the mechanical properties of hexagonal zinc oxide monolayer nanosheets (h-ZnO). The calculations are based on the density functional theory (DFT) within the generalized gradient approximation (GGA) and using the Perdew-Burke-Ernzerhof (PBE) exchange correlation. The elastic properties of h-ZnO including Young's modulus, Poisson's ratio, bulk and shear modulus are computed in the harmonic region. The calculated value of Poisson's ratio is in good agreement with the one reported in the literature and higher than that of graphene. It is also found that Young's, bulk and shear moduli of h-ZnO are smaller than those of graphene. The present results can be useful in the study of ZnO-based nanostructures. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Applied Physics A: Materials Science and Processing (14320630)120(4)pp. 1399-1406
Synthesis of hybrid nanotubes to overcome the drawbacks of individual pure nanotubes in order to apply them in novel nanodevices has attracted great interest of researchers. To this end, pure single- and double-walled boron nitride nanotubes together with carbon and boron nitride double-walled hybrid nanotubes are simulated through molecular dynamics simulations in order to study their vibrational behavior. The natural frequency of nanotubes is computed, and the effects of geometrical parameters and boundary conditions on the natural frequency are investigated. According to the generated results, the natural frequency of boron nitride nanotubes is higher than that of their carbon counterpart and nanotubes with clamped boundary conditions possess the highest natural frequency compared to other types of boundary conditions. Also, the natural frequency of double-walled hybrid nanotubes is found to be between those of pure double-walled boron nitride and carbon nanotubes with small lengths. It is found that the natural frequency of double-walled hybrid nanotubes is less sensitive to length increase compared to pure double-walled carbon and boron nitride ones, leading to higher frequencies at greater lengths. Finally, to study the variation in natural frequency with the length, a rational curve is fitted to each data set and the corresponding constants are computed. © 2015, Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Faghih shojaei, M.,
Ebrahimi f., ,
Rouhi h., H. Publication Date: 2015
Archive of Applied Mechanics (14320681)85(7)pp. 937-953
Based on Mindlin’s strain gradient elasticity theory capturing microscale effects, a new extended Timoshenko beam element is proposed to study the postbuckling behavior of microbeams. So as to develop the size-dependent finite element formulation, the higher-order tensors of energy pairs in the energy functional are vectorized and represented in the quadratic form. In comparison with the standard Timoshenko beam element, the present one needs two further nodal degrees of freedom including derivatives of lateral translation and rotation. The Hermite polynomials are also implemented as shape functions. The developed model is general so that its formulation can be used for modified couple stress, modified strain gradient and classical elasticity theories. In the numerical results, the influences of the small-scale factor, geometrical parameters and boundary conditions on the bifurcation diagrams of microbeams are examined. © 2015, Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Darabi m.a., M.A. Publication Date: 2015
International Journal of Applied Mechanics (17588251)7(5)
In this paper, a geometrically nonlinear first-order shear deformable nanoplate model is developed to investigate the size-dependent geometrically nonlinear free vibrations of rectangular nanoplates considering surface stress effects. For this purpose, according to the Gurtin-Murdoch elasticity theory and Hamilton's principle, the governing equations of motion and associated boundary conditions of nanoplates are derived first. Afterwards, the set of obtained nonlinear equations is discretized using the generalized differential quadrature (GDQ) method and then solved by a numerical Galerkin scheme and pseudo arc-length continuation method. Finally, the effects of important model parameters including surface elastic modulus, residual surface stress, surface density, thickness and boundary conditions on the vibration characteristics of rectangular nanoplates are thoroughly investigated. It is found that with the increase of the thickness, nanoplates can experience different vibrational behavior depending on the type of boundary conditions. © 2015 Imperial College Press.
Publication Date: 2015
Current Applied Physics (15671739)15(9)pp. 1062-1069
This article presents analytical explicit frequency expressions for investigating the vibrations of single-layer graphene sheets (SLGSs). The interatomic potential is incorporated into a nonlocal continuum plate model through establishing a linkage between the strain energy density induced in the continuum and nonlocal plate constitutive relations. The model which is independent of scattered value of Young's modulus is then applied and explicit frequency formulas for the SLGSs with different edge conditions are derived using static deflection function of the nanoplate under uniformly distributed load. The reliability of the present formulation is verified by the results obtained by the molecular dynamics (MD) simulations and other research workers. The formulas are of a simple short form enabling quick and accurate evaluation of the frequency of the SLGSs and also simple calibration of scale coefficient by the use of MD simulations results. © 2015 Elsevier B.V. All rights reserved.
Ansari, R.,
Faghih shojaei, M.,
Rouhi h., H.,
Hosseinzadeh m., Publication Date: 2015
Applied Mathematical Modelling (0307904X)39(10-11)pp. 2849-2860
This paper proposes an efficient numerical method in the context of variational formulation and on the basis of Rayleigh-Ritz technique to address the free vibration problem of laminated composite conical shells. To this end, the energy functional of Hamilton's principle is written in a quadratic form using matrix relations first. Displacements are then approximated via a linear combination of base functions, by which the number of final unknowns reduces. After that, the strain tensor is discretized by means of matrix differential quadrature (DQ) operators. In the next step, using Taylor series and DQ rules, a matrix integral operator is constructed which is embedded into the stiffness matrix so as to discretize the quadratic representation of energy functional. Finally, the reduced form of mass and stiffness matrices are readily obtained from the aforementioned discretized functional. To obtain the natural frequencies of conical shell, hybrid harmonic-beam base functions are employed as modal displacement functions. The accuracy of the present numerical method is examined by comparing its results with those from the published literature. It is revealed that the method is capable of accurately solving the problem with a little computational effort and ease of implementation. © 2014 Elsevier Inc.
Ansari, R.,
Malakpour s., S.,
Faghihnasiri m., ,
Sahmani, S. Publication Date: 2015
Superlattices and Microstructures (10963677)82pp. 188-200
Abstract Molybdenum disulfide (MoS2) is a unique semiconductor with a honeycomb structure like graphite, which has the ability to form various nanostructures with distinct characteristics. In the present study, the elastic, structural and electronic properties of armchair and zigzag MoS2 nanotubes with different diameters are investigated using the density functional theory (DFT). The DFT calculations are performed within the framework of generalized gradient approximation and using the Perdew-Burke-Ernzerhof (PBE) exchange model. It is demonstrated that for all of the considered MoS2 nanotubes anharmonicity exists, except for (6,6) MoS2 nanotube. Moreover, it is found that by increasing the tube diameter, Young's modulus of both armchair and zigzag MoS2 nanotubes increases. Also, it is observed that all of armchair MoS2 nanotubes are indirect band gap-type. On the other hand, all of zigzag MoS2 nanotubes have band gaps with the type of direct in F point. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
EPJ Applied Physics (12860042)70(1)
In this article, by using the molecular mechanics approach, the torsional buckling behavior of chiral multi-walled silicon carbide nanotubes (MWSiCNTs) is analytically investigated. The force constants of the molecular mechanics are theoretically obtained through establishing a linkage between the molecular mechanics and the quantum mechanics. First, surface Young's modulus, Poisson's ratio, flexural rigidity and atomic structure of silicon carbide (SiC) sheets are calculated according to the density functional theory (DFT) within the framework of the generalized gradient approximation and using the exchange correlation of Perdew-Burke-Ernzerhof. A closed-form expression is proposed by which through knowing the chirality of an MWSiCNT, the critical buckling shear strain can be quickly and accurately evaluated. The critical buckling shear strain is obtained for various types of chirality and different number of walls. It is concluded that with the increase of number of walls, the value of critical buckling shear strain decreases and nanotubes tend to be more unstable. Also, among all the chiral nanotubes, the one with chiral angle of (n, n/2) has the minimum value of critical buckling shear strain. © EDP Sciences, 2015.
Publication Date: 2015
Thin-Walled Structures (02638231)93pp. 169-176
In the present investigation, an exact solution is proposed for the nonlinear forced vibration analysis of nanobeams made of functionally graded materials (FGMs) subjected to thermal environment including the effect of surface stress. The material properties of functionally graded (FG) nanobeams vary through the thickness direction on the basis of a simple power law. The geometrically nonlinear beam model, taking into account the surface stress effect, is developed by implementing the Gurtin-Murdoch elasticity theory together with the classical Euler-Bernoulli beam theory and using a variational approach. Hamilton's principle is utilized to obtain the nonlinear governing partial differential equation and corresponding boundary conditions. After that, the Galerkin technique is employed in order to convert the nonlinear partial differential equation into a set of nonlinear ordinary differential equations. This new set is then solved analytically based on the method of multiple scales which results in the frequency-response curves of FG nanobeams in the presence of surface stress effect. It is revealed that by increasing the beam thickness, the surface stress effect diminishes and the maximum amplitude of the stable response is shifted to the higher excitation frequencies. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Applied Mathematical Modelling (0307904X)39(10-11)pp. 3050-3062
The modified couple stress theory, as a theory capable of capturing size effects, is implemented to study the vibration characteristic of a postbuckled microbeam. To this end, a modified couple stress Euler-Bernoulli beam model containing geometric nonlinearity is considered. Within the framework of a variational formulation and based on Hamilton's principle, the governing equation and corresponding boundary conditions are derived. By eliminating time-dependent terms, the governing equation of vibration is reduced to that of buckling problem for the microbeam subjected to an axial load. The critical buckling loads and their corresponding mode shapes are predicted through an exact solution for various boundary conditions. Afterwards, the vibration analysis of a simply-supported microbeam is investigated around the obtained postbuckling configuration. It is found that the stiffness of microbeam predicted by the modified couple stress model is higher than that predicted by the classical model. Additionally, it is demonstrated that the natural frequencies by considering all of the vibration modes except the first mode are independent of the buckling load. The influences of the dimensionless length-scale parameter, Poisson's ratio, various boundary conditions and the number of buckled modes on the critical buckling loads and natural frequency are fully investigated. © 2014 Elsevier Inc.
Gholami, R.,
Ansari, R.,
Darvizeh a., A.,
Sahmani, S. Publication Date: 2015
International Journal of Structural Stability and Dynamics (02194554)15(4)
A nonclassical first-order shear deformation shell model is developed to analyze the axial buckling and dynamic stability of microshells made of functionally graded materials (FGMs). For this purpose, the modified couple stress elasticity theory is implemented into the first-order shear deformation shell theory. Unlike the classical shell theory, the newly developed shell model contains an internal material length scale parameter to capture efficiently the size effect. By using the Hamilton's principle, the higher-order governing equations and boundary conditions are derived. Afterward, the Navier solution is utilized to predict the critical axial buckling loads of simply-supported functionally graded (FG) microshells. Moreover, the governing equations are written in the form of Mathieu-Hill equations and then Bolotin's method is employed to determine the instability regions. A parametric study is conducted to investigate the influences of static load factor, axial wave number, dimensionless length scale parameter, material property gradient index, length-to-radius and length-to-thickness aspect ratios on the axial buckling and dynamic stability responses of FGM microshells. It is revealed that size effect plays an important role in the value of critical axial buckling load and instability region of FGM microshells especially corresponding to those with lower aspect ratios. © 2015 World Scientific Publishing Company.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Sahmani, S. Publication Date: 2015
European Journal of Mechanics, A/Solids (09977538)49pp. 251-267
A Mindlin microplate model based on the modified strain gradient elasticity theory is developed to predict axisymmetric bending, buckling, and free vibration characteristics of circular/annular microplates made of functionally graded materials (FGMs). The material properties of functionally graded (FG) microplates are assumed to vary in the thickness direction. In the present non-classical plate model, the size effects are captured through using three higher-order material constants. By using Hamilton's principle, the higher-order equations of motion and related boundary conditions are derived. Afterward, the generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations along with various types of edge supports. Selected numerical results are given to indicate the influences of dimensionless length scale parameter, material index and radius-to-thickness ratio on the deflection, critical buckling load and natural frequency of FG circular/annular microplates. © 2014 Elsevier Masson SAS. All rights reserved.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Rouhi h., H. Publication Date: 2015
ZAMM Zeitschrift fur Angewandte Mathematik und Mechanik (00442267)95(9)pp. 939-951
In this research, the axial buckling and postbuckling configurations of single-walled carbon nanotubes (SWCNTs) under different types of end conditions are investigated based on an efficient numerical approach. The effects of transverse shear deformation and rotary inertia are taken into account using the Timoshenko beam theory. The nonlinear governing equations and associated boundary conditions are derived by the virtual displacements principle and then discretized via the generalized differential quadrature method. The small scale effect is incorporated into the model through Eringen's nonlocal elasticity. To obtain the critical buckling loads, the set of linear discretized equations are solved as an eigenvalue problem. Also, to address the postbuckling problem, the pseudo arc-length continuation method is applied to the set of nonlinear parameterized equations. The effects of nonlocal parameter, boundary conditions, aspect ratio and buckling mode on the critical buckling load and postbuckling behavior are studied. Moreover, a comparison is made between the results of Timoshenko beam model and those of its Euler-Bernoulli counterpart for various magnitudes of nonlocal parameter. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Publication Date: 2015
Applied Physics A: Materials Science and Processing (14320630)118(3)pp. 845-854
This paper is concerned with the axial buckling behavior of multi-walled silicon carbide nanotubes (MWSiCNTs) based upon a molecular mechanics model. To this end, the mechanical properties of silicon carbide sheets are obtained according to the density functional theory within the framework of the generalized gradient approximation. Through establishing a linkage between the quantum mechanics and the molecular mechanics, the force constants of the total potential energy are obtained theoretically. A closed-form expression is proposed from which by knowing the chirality of the MWSiCNT, its critical buckling strain can be calculated as quickly and accurately as possible. The effects of chirality and number of walls on the critical buckling strain of MWSiCNTs are carefully investigated. It is concluded that with increasing the number of walls of nanotubes, their stability decreases. The effects of diameter and number of walls on the critical buckling strain of MWSiCNTs under axial load get more pronounced at lower diameters. Besides, it is found that the minimum critical buckling strain is related to nanotubes with (Formula presented.) chiral vectors. © 2014, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Computational Materials Science (09270256)101pp. 260-266
A three-dimensional finite element (FE) formulation based on a spring-mass model is presented to investigate the mechanical properties of single-walled carbon nanocones (SWCNCs). The rotational spring elements together with longitudinal ones are employed for modeling the covalent bond between the carbon atoms, and the carbon atoms are modeled by mass elements. Analytical expressions for Young's and shear moduli of SWCNCs with five feasible apex angles are obtained in terms of axial and torsion loads, respectively. The effects of geometrical parameters on the mechanical properties of SWCNCs are investigated. It is found that the apex angle of SWCNCs has a significant influence on their Young's and shear moduli. Moreover, in contrast to the results of similar works in the literature, the present results reveal that the length and small radius of nanocones do not play a major role in their mechanical properties. It is shown that with increasing small radius, Young's modulus slightly increases. To assess the accuracy of the developed FE formulation, molecular dynamics simulations are also conducted. © 2015 Elsevier B.V. All rights reserved.
Ansari, R.,
Gholami, R.,
Sahmani, S.,
Norouzzadeh, A.,
Bazdid-vahdati m., M. Publication Date: 2015
Acta Mechanica Solida Sinica (08949166)28(6)pp. 659-667
In the present paper, the dynamic stability of multi-walled carbon nanotubes (MWCNTs) embedded in an elastic medium is investigated including thermal environment effects. To this end, a nonlocal Timoshenko beam model is developed which captures small scale effects. Dynamic governing equations of the carbon nanotubes are formulated based on the Timoshenko beam theory including the effects of axial compressive force. Then a parametric study is conducted to investigate the influences of static load factor, temperature change, nonlocal parameter, slenderness ratio and spring constant of the elastic medium on the dynamic stability characteristics of MWCNTs with simply-supported end supports. © 2015 The Chinese Society of Theoretical and Applied Mechanics.
Ansari, R.,
Faghihnasiri m., ,
Malakpour s., S.,
Sahmani, S. Publication Date: 2015
Superlattices and Microstructures (10963677)83pp. 498-506
In the current investigation, ab initio calculations are performed to explore the influence of electric field on the mechanical properties of bilayer boron nitride with AB stacking order (AB-2LBN). To accomplish this, density functional theory (DFT) within the framework of generalized gradient approximation (GGA) is implemented. It is demonstrated that the electric field has significant effects on Young's modulus and Poisson's ratio of AB-2LBN when its magnitude is small. With increasing the magnitude of electric field, these effects diminish so that the mechanical properties with and without considering the electric field become approximately identical. Also, it is shown that the equilibrium strain energy decreases linearly by increasing the magnitude of applied electric field. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Superlattices and Microstructures (10963677)77pp. 54-63
Carbon nanotube (CNT) modification processes are of great importance for good dispersion of CNTs and load transfer issues in nanocomposites. Among these processes, polymer covalent functionalization is found to be an effective way to alter the mechanical properties and behavior of pristine CNTs. Therefore, the mechanical properties and buckling behavior of diethyltoluenediamines (DETDA) functionalized CNTs are investigated employing molecular dynamics (MD) simulations. The results demonstrate that as the polymer weight percentage increases, Young's modulus and critical buckling load increase almost linearly for both regular and random polymer distributions, whereas critical strain decreases with different trends depending on the type of polymer distribution. Finally, the buckling mode shapes of the presented models are illustrated and it was revealed that there are some differences between the mode shapes of functionalized CNTs and those of pristine CNTs. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2015
Physica E: Low-Dimensional Systems and Nanostructures (13869477)70pp. 129-134
This work aims to comprehensively study the effect of oxygen chemisorption on the elastic properties of carbon nanotubes (CNTs). To this end, a molecular mechanics model is used along with the density functional theory (DFT) calculations. This investigation is conducted for oxygenated carbon nanotubes (O-CNTs) with various types of chirality including armchair, zigzag and chiral. On the basis of DFT, the force constants used in the total potential energy of system are calculated. Moreover, Young's modulus and Poisson's ratio of oxygenated graphene sheet (O-graphene) are determined based on the DFT. The results show that by adsorption of oxygen atoms, the stiffness of graphene reduces about 23%. The bending stiffness of O-graphene is obtained corresponding to adsorption on the inside and outside of the nanotubes. It is revealed that for an arbitrary value of diameter, Young's modulus of zigzag O-CNTs is smaller than that of chiral O-CNTs and the latter one is also smaller than that of armchair O-CNTs, while a reverse trend is found for the variation of Poisson's ratio with the chirality. © 2015 Elsevier B.V.All rights reserved.
Alijani a., ,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2015
Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications (20413076)229(2)pp. 146-165
In this paper, the elasto-plastic pre- and post-buckling behavior of beams made of functionally graded materials subjected to mechanical loading is investigated. A continuum-based finite element formulation is developed to determine the major characteristics of buckling. The arc-length algorithm is employed to analyze the stability problem. A plane stress von Mises model with isotropic hardening is utilized for the elasto-plastic nonlinear analysis of the beam. Basic idea in geometric and material nonlinear analysis of functionally graded material beams is to use the plasticity capacity of metal phase as a ductile material during loading. The influences of number of axial modes, material index, geometrical parameters and boundary conditions on the critical buckling point, pre- and post-buckling paths, plastic bifurcation point and stress distribution are fully studied. A good agreement between generated results and existing data in the literature is observed. © 2013 IMechE.
Ansari, R.,
Hasrati, E.,
Faghih shojaei, M.,
Gholami, R.,
Shahabodini a., A. Publication Date: 2015
Physica E: Low-Dimensional Systems and Nanostructures (13869477)69pp. 294-305
In this paper, the nonlinear forced vibration behavior of composite plates reinforced by carbon nanotubes is investigated by a numerical approach. The reinforcement is considered to be functionally graded (FG) in the thickness direction according to a micromechanical model. The first-order shear deformation theory and von Kármán-type kinematic relations are employed. The governing equations and the corresponding boundary conditions are derived with the use of Hamilton's principle. The generalized differential quadrature (GDQ) method is utilized to achieve a discretized set of nonlinear governing equations. A Galerkin-based scheme is then applied to obtain a time-varying set of ordinary differential equations of Duffing-type. Subsequently, a time periodic discretization is done and the frequency response of plates is determined via the pseudo-arc length continuation method. Selected numerical results are given for the effects of different parameters on the nonlinear forced vibration characteristics of uniformly distributed carbon nanotube- and FG carbon nanotube-reinforced composite plates. It is found that with the increase of CNT volume fraction, the flexural stiffness of plate increases; and hence its natural frequency gets larger. Moreover, it is observed that the distribution type of CNTs significantly affects the vibrational behavior of plate. The results also show that when the mid-plane of plate is CNT-rich, the natural frequency takes its minimum value and the hardening-type response of plate is intensified. © 2015 Elsevier B.V. All rights reserved.
Ansari, R.,
Oskouie, M.F.,
Sadeghi f., F.,
Bazdid-vahdati m., M. Publication Date: 2015
Physica E: Low-Dimensional Systems and Nanostructures (13869477)74pp. 318-327
Abstract In this article, the free vibration of a fractional viscoelastic Timoshenko nanobeam is studied through inserting fractional calculus as a viscoelastic material compatibility equations in nonlocal beam theory. The material properties of a single-walled carbon nanotube (SWCNT) are used and two solution procedures are proposed to solve the obtained equations in the time domain. The former is a semi-analytical approach in which the Galerkin scheme is employed to discretize the governing equations in the spatial domain and the obtained set of ordinary differential equations is solved using a direct numerical integration scheme. On the contrary, the latter is entirely numerical in which the governing equations of system on the spatial and time domains are first discretized using general differential quadrature (GDQ) technique and finite difference (FD) scheme, respectively and then the set of algebraic equations is solved to arrive at the time response of system under different boundary conditions. Considering the second solution procedure as the main approach, its validity and accuracy are verified by the semi-analytical approach which is more difficult to enter various boundary conditions. Numerical results are also presented to get an insight into the effects of fractional derivative order, nonlocal parameter, viscoelasticity coefficient and nanobeam length on the time response of fractional viscoelastic Timoshenko nanobeams under different boundary conditions. © 2015 Elsevier B.V.
Ansari, R.,
Malakpour s., S.,
Faghihnasiri m., ,
Ajori, S. Publication Date: 2015
Nano (17937094)10(3)
In some cases such as assembling nanodevices and nanobiosensing, the effect of electric filed on the mechanical properties of nanomaterials is important and should be taken into account. The aim of this work is to investigate the effect of electric field on the mechanical properties of hexagonal boron-nitride (h-BN) using density functional theory (DFT) calculations. The results show the high sensitivity of mechanical properties to the magnitude and direction of electric field. It is observed that imposing the electric field on the armchair direction, unlike the zigzag direction, increases the magnitude of elastic properties of h-BN especially in the case of Poisson's ratio. It is further observed that the electric field perpendicular to h-BN has a negligible effect on its mechanical properties. © 2015 World Scientific Publishing Company.
Publication Date: 2015
Journal Of Molecular Modeling (16102940)21(12)pp. 1-11
Molecular dynamics (MD) simulations were used to study the adsorption of different polymer chains on functionalized double-walled carbon nanotubes (DWCNTs). The nanotubes were functionalized with two different amines: NH2 (a small amine) and CH2-NH2 (a large amine). Considering three different polymer chains, all with the same number of atoms, the effect of polymer type on the polymer–nanotube interaction was studied. In general, it was found that covalent functionalization considerably improved the polymer–DWCNT interaction. By comparing the results obtained with different polymer chains, it was observed that, unlike polyethylene and polyketone, poly(styrene sulfonate) only weakly interacts with the functionalized DWCNTs. Accordingly, the smallest radius of gyration was obtained with adsorbed poly(styrene sulfonate). It was also observed that the DWCNTs functionalized with the large amine presented more stable interactions with polyketone and poly(styrene sulfonate) than with polyethylene, whereas the DWCNTs functionalized with the small amine showed better interfacial noncovalent bonding with polyethylene. © 2015, Springer-Verlag Berlin Heidelberg.
Hasanzadeh m., ,
Mottaghitalab v., ,
Ansari, R.,
Radavi moghadam b., ,
Haghi a.k., Publication Date: 2015
Cellulose Chemistry and Technology (05769787)49(3-4)pp. 237-257
Polymer nanofibers are being increasingly used for a wide range of applications owing to their high specific surface area. The electrospinning process, as a novel and effective method for producing nanofibers from various materials, has been utilized to fabricate nanofibrous membranes. Carbon nanotubes (CNTs) have a number of outstanding mechanical, electrical, and thermal properties, which make them attractive as reinforcement in a polymer matrix. The incorporation of CNT into polymer nanofibers can improve the properties of electrospun nanofibrous composites. This paper provides a comprehensive review of current research and development in the field of electrospun CNT-polymer composite nanofiber with emphasis on the processing, properties, and application of composite nanofiber, as well as the' theoretical approaches to predicting the mechanical behavior of CNT-polymer composites. The current limitations, research challenges, and future trends in modeling and simulation of electrospun polymer composite nanofibers are also discussed.
Publication Date: 2015
Journal Of Molecular Modeling (16102940)21(3)pp. 1-7
In this paper, the mechanical properties of fully oxygenated silicon carbide nanotubes (O2-SiCNTs) are explored using a molecular mechanics model joined with the density functional theory (DFT). The closed-form analytical expressions suggested in this study can easily be adapted for nanotubes with different chiralities. The force constants of molecular mechanics model proposed herein are derived through DFT within a generalized gradient approximation. Moreover, the mechanical properties of fully oxygenated silicon carbide (O2-SiC) sheet are evaluated for the case that the oxygen atoms are adsorbed on one side of the SiC sheet. According to the results obtained for the bending stiffness of O2-SiC sheet, one can conclude that the O2-SiC sheet has isotropic characteristics. © 2015, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Solid State Communications (00381098)201pp. 1-4
Graphane is a two-dimensional structure consisting of a flat monolayer graphene sheet fully covered with hydrogen atoms attached to its carbon atoms in an alternating pattern. The unique properties of graphane make it suitable for different applications. In this paper, the mechanical properties of the most stable conformer of graphane, the so-called chair-like, are extensively investigated using density functional theory (DFT) scheme within the framework of the generalized gradient approximation (GGA) and the well-known Perdew-Burke-Ernzerhof (PBE) exchange correlation. It is shown that the hydrogenation has significant influences on the mechanical properties of graphene sheet. In particular, it is found that the elastic, bulk and shear moduli and Poisson's ratio of the chair-graphane are significantly smaller than those of graphene. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2015
European Journal of Mechanics, A/Solids (09977538)49pp. 283-292
Based on the continuum approximation and Lennard-Jones (LJ) potential, mechanics of nested spherical fullerenes, known as carbon onions, inside multi-walled carbon nanotubes (MWCNTs) is investigated in this study. To this end, direct method is first utilized to determine van der Waals (vdW) interaction force and potential energy between a carbon onion molecule and a semi-infinite MWCNT. According to this method, the interactions between each pair of shells from carbon onion and CNT are summed up over all of the pairs. Thereafter, the suction and acceptance energies for carbon onions entering semi-infinite MWCNTs are evaluated. On the basis of Newton's second law, an analytical expression is then presented to predict the oscillation frequency of a carbon onion molecule inside a MWCNT of finite length. The effect of geometrical parameters on the nature of suction and acceptance energies, vdW interactions and oscillatory characteristics of carbon onion-MWCNT oscillators is thoroughly examined. For a given carbon onion structure, it is found that there exists an optimal value for the number of nanotube shells beyond which the maximum oscillation frequency does not increase considerably. Furthermore, the maximum oscillation frequency decreases as the carbon onion gets larger. © 2014 Elsevier Masson SAS. All rights reserved.
Publication Date: 2015
Journal of Physics and Chemistry of Solids (00223697)85pp. 264-272
Abstract The fabrication of nanoscale oscillators working in the gigahertz (GHz) range and beyond has now become the focal center of interest to many researchers. Motivated by this issue, this paper proposes a new type of nano-oscillators with enhanced operating frequency in which both the inner core and outer shell are electrically charged. To this end, molecular dynamics (MD) simulations are performed to investigate the mechanical oscillatory behavior of ions, and in particular chloride ion, tunneling through electrically charged carbon nanotubes (CNTs). It is assumed that the electric charges with similar sign and magnitude are evenly distributed on two ends of nanotube. The interatomic interactions between carbon atoms and van der Waals (vdW) interactions between ion and nanotube are respectively modeled by Tersoff-Brenner and Lennard-Jones (LJ) potential functions, whereas the electrostatic interactions between ion and electric charges are modeled by Coulomb potential function. A comprehensive study is conducted to get an insight into the effects of different parameters such as sign and magnitude of electric charges, nanotube radius, nanotube length and initial conditions (initial separation distance and velocity) on the oscillatory behavior of chloride ion-charged CNT oscillators. It is shown that, the chloride ion frequency inside negatively charged CNTs is lower than that inside positively charged ones with the same magnitude of electric charge, while it is higher than that inside uncharged CNTs. It is further observed that, higher frequencies are generated at higher magnitudes of electric charges distributed on the nanotube. © 2015 Elsevier Ltd.
Ansari, R.,
Hasrati, E.,
Gholami, R.,
Sadeghi f., F. Publication Date: 2015
Composites Part B: Engineering (13598368)83pp. 226-241
This paper deals with the forced vibration behavior of nonlocal third-order shear deformable beam model of magneto-electro-thermo elastic (METE) nanobeams based on the nonlocal elasticity theory in conjunction with the von Kármán geometric nonlinearity. The METE nanobeam is assumed to be subjected to the external electric potential, magnetic potential and constant temperature rise. Based on the Hamilton principle, the nonlinear governing equations and corresponding boundary conditions are established and discretized using the generalized differential quadrature (GDQ) method. Thereafter, using a Galerkin-based numerical technique, the set of nonlinear governing equations is reduced into a time-varying set of ordinary differential equations of Duffing type. The pseudo-arc length continuum scheme is then adopted to solve the vectorized form of nonlinear parameterized equations. Finally, a comprehensive study is conducted to get an insight into the effects of different parameters such as nonlocal parameter, slenderness ratio, initial electric potential, initial external magnetic potential, temperature rise and type of boundary conditions on the natural frequency and forced vibration characteristics of METE nanobeams. © 2015 Elsevier Ltd. All rights reserved.
Azarboni, H.R.,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2015
Thin-Walled Structures (02638231)94pp. 577-584
In this paper, the nonlinear dynamic pulse buckling of imperfect rectangular plate subjected to sinusoidal, exponential, damping and rectangular pulse functions with six different boundary conditions is investigated. In order to solve the large deformation equations of plate, Galerkin method together with trigonometric mode shape functions is applied. Also, the nonlinear coupled time integration of the governing equation of plate is a solved employing fourth-order Runge-Kutta method. The effects of boundary conditions, pulse functions, initial imperfection, force pulse amplitude and geometrical parameters of the shock spectrum of a plate and deflection histories of plate for impulsive, dynamic and quasi-periodic force loads are studied. In this study, the effects of boundary conditions, pulse functions, initial imperfection, force pulse amplitude and geometric parameter in nonlinear dynamic response are investigated. According to the results for impulsive loading, the displacement response reaches its peak after shock duration and in the dynamic and quasi-static pulse loading, the maximum response of plate occurs during and before shock duration. Moreover, with increasing the loading amplitude, length of the plate and initial imperfection, the maximum displacement of plate increases. Different boundary conditions and various pulse functions have significant influence on the dynamic response of the plate. By increasing the restriction in supports, the resistance ability against deformation and stability of plate increases. © 2015 Elsevier Ltd. All rights reserved.
Alijani a., ,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2015
Thin-Walled Structures (02638231)95pp. 170-182
Abstract In this article, the nonlinear buckling behavior of imperfect cylinders made of isotropic, composite and functionally graded materials is studied. A continuum-based semi-analytical finite element formulation is introduced to study the nonlinear behavior of cylinders under thermal loads. A method is proposed to implement the initial geometric imperfection of the cylinder by transformation of structure due to deformation gradients. The influences of geometrical parameters, different materials and imperfection factors are investigated on pre- and post-buckling paths. A comparison is made between the classical von Kármán-based and continuum-based approaches to ensure the validation of the results and to study the applicability of the von-Kármán approximation. © 2015 Elsevier Ltd.
Publication Date: 2015
Physica E: Low-Dimensional Systems and Nanostructures (13869477)69pp. 1-12
Presented herein is a comprehensive study on the mechanics of concentric and eccentric C60 fullerenes inside open carbon nanocones (CNCs) on the basis of the continuum approximation along with the 6-12 Lennard-Jones (LJ) potential function. For concentric configuration, new analytical expressions are derived to evaluate van der Waals (vdW) potential energy and interaction force between the two interacting molecules. Also, semi-analytical expressions in terms of double integrals are extracted to determine the potential energy of an offset C60 fullerene inside open CNCs. The proposed expressions are demonstrated to be dependent on whether the fullerene enters the open nanocone through the small end or the wide end. The effects of geometrical parameters such as small end radius, wide end radius and vertex angle of open nanocone on the distributions of vdW potential energy and interaction force are fully investigated. It is found that the fullerene molecule undergoes an asymmetrical motion inside CNCs. Moreover, for concentric and eccentric configurations, preferred position of system, for which potential energy reaches its minimum value, is obtained for different sizes of nanocone. ©2015 Elsevier B.V. All rights reserved.
Publication Date: 2015
Applied Physics A: Materials Science and Processing (14320630)121(1)pp. 223-232
The properties and behavior of carbon nanotubes (CNTs) in aqueous environment due to their considerable potential applications in nanobiotechnology and designing nanobiosensors have attracted the attention of researchers. In this study, molecular dynamics simulations are carried out to investigate the vibrational characteristics of single- and double-walled CNTs containing ice nanotubes (a new phase of ice) in vacuum and aqueous environments. The results demonstrate that formation of ice nanotubes inside the CNTs reduces the natural frequency of pure CNTs. Moreover, it is demonstrated that increasing the number of walls considerably reduces the sensitivity of frequency to the presence of ice nanotube inside CNT. Additionally, it is shown that increasing the length decreases the effect of ice nanotube on reducing the frequency. The calculation of natural frequency of CNTs in aqueous media demonstrates that the interaction of CNTs with water molecules considerably reduces the natural frequency up to 50 %. Finally, it is demonstrated that in the case of CNTs with one free end in aqueous environment, the CNT does not vibrate in its first mode, and its frequency is between the frequencies of first and second modes of vibration. © 2015, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Brazilian Journal Of Physics (01039733)45(1)pp. 10-18
By using molecular dynamics simulations, the interaction between a single-walled carbon nanotube and three different polymers has been studied in this work. The effects of various parameters such as the nanotube geometry and temperature on the interaction energy and radius of gyration of polymers have been explored. By studying the snapshots of polymers along the single-walled carbon nanotube, it has been shown that 50 ps can be considered as a suitable time after which the shape of polymer chains around the nanotube remains almost unchanged. It is revealed that the effect of temperature on the interaction energy and radius of gyration of polymers in the range of 250 to 500 K is not significant Also, it is shown that the interaction energy depends on the nanotube diameter. © 2014, Sociedade Brasileira de Física.
Publication Date: 2015
European Physical Journal D (14346060)69(12)
This study is concerned with the oscillatory behavior of metallic nanoparticles, and in particular silver and gold nanoparticles, inside lipid nanotubes (LNTs) using the continuum approximation along with the 6-12 Lennard-Jones (LJ) potential function. The nanoparticle is modeled as a dense sphere and the LNT is assumed to be comprised of six layers including two head groups, two intermediate layers and two tail groups. To evaluate van der Waals (vdW) interactions, analytical expressions are first derived through undertaking surface and volume integrals which are then validated by a fully numerical scheme based on the differential quadrature (DQ) technique. Using the actual force distribution between the two interacting molecules, the equation of motion is directly solved utilizing the Runge-Kutta numerical integration scheme to arrive at the time history of displacement and velocity of the inner core. Also, a semi-analytical expression incorporating both geometrical parameters and initial conditions is introduced for the precise evaluation of oscillation frequency. A comprehensive study is conducted to gain an insight into the influences of nanoparticle radius, LNT length, head and tail group thicknesses and initial conditions on the oscillatory behavior of the metallic nanoparticles inside LNTs. It is found that the escape velocity and oscillation frequency of silver nanoparticles are higher than those of gold ones. It is further shown that the oscillation frequency is less affected by the tail group thickness when compared to the head group thickness. Graphical abstract: [Figure not available: see fulltext.] © 2015 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
Sahmani, S.,
Bahrami m., ,
Aghdam, M.M.,
Ansari, R. Publication Date: 2015
Applied Mathematical Modelling (0307904X)39(13)pp. 3678-3689
The effects of surface energy are generally ignored in traditional continuum elasticity. However, due to the high surface to volume ratio in nanostructures, this is not the case for them. In this work, the nonlinear postbuckling characteristics of circular nanoplates are predicted in the presence of surface energy effects including surface elasticity and residual surface tension. For this objective, Gurtin-Murdoch elasticity theory is implemented into the classical higher-order shear deformation plate theory. In order to satisfy the balance conditions on the surfaces of nanoplate, it is assumed the normal stress of the bulk is distributed cubically through the thickness of nanoplate. Virtual work's principle in conjunction with von Karman geometric nonlinearity is utilized to derive non-classical nonlinear governing differential equations of motion and related boundary conditions. Afterwards, an efficient numerical methodology based generalized differential quadrature (GDQ) method is carried out using the shifted Chebyshev-Gauss-Lobatto grid points to discretize the governing partial differential equations. Then, the Galerkin's method is employed to reduce the set of nonlinear equations into a time-varying set of ordinary differential equations of Duffing type. At the end, the pseudo arc-length continuation technique is utilized in order to obtain the solution of the parameterized equation. © 2014 Elsevier Inc..
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R.,
Alijani a., Publication Date: 2015
Scientia Iranica (23453605)22(3)pp. 779-791
In this paper, the pre- and post-buckling behavior of beams made of Functionally Graded Materials (FGMs), a mixture of ceramic and metal, under separate mechanical and thermal loading, is studied. To this end, the finite element formulation is established, based on the Euler-Bernoulli beam theory. The effects of geometrical nonlinearity and imperfection are taken into account. The arc-length algorithm is employed to obtain the secondary path beyond the bifurcation point. The influences of material index, imperfection, geometrical parameters and different boundary conditions of simply-supported, clamped-simply and clamped-clamped, on the post-buckling characteristics of FGM beams, are thoroughly investigated. The results generated are compared with the existing data in the literature and good agreements are achieved. The investigation undertaken here proves the necessity of performing post-buckling analysis on FGM beams, especially with simply-supported end conditions. © 2015 Sharif University of Technology. All rights reserved.
Publication Date: 2015
Applied Physics A: Materials Science and Processing (14320630)119(3)pp. 1039-1045
In this paper, mechanical properties and buckling behavior of single-walled silicon carbide nanocones (SWSiCNCs) are studied using a finite element method. The elastic moduli of SWSiCNCs with different dimensions including different apex angles and lengths are presented. For large apex angles, it is shown that the effect of nanocone length on the elastic modulus can be neglected. Besides, the critical compressive forces of SWSiCNCs are computed. The influences of dimensions and boundary conditions on the buckling behavior of SWSiCNs are studied in detail. The results show that increasing the nanocone apex angle leads to decreasing the critical compressive force. © 2015, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
Superlattices and Microstructures (10963677)80pp. 196-205
Molecular mechanics theory has been widely used to investigate the mechanical properties of nanostructures analytically. However, there is a limited number of research in which molecular mechanics model is utilized to predict the elastic properties of boron nitride nanotubes (BNNTs). In the current study, the mechanical properties of chiral single-walled BNNTs are predicted analytically based on an accurate molecular mechanics model. For this purpose, based upon the density functional theory (DFT) within the framework of the generalized gradient approximation (GGA), the exchange correlation of Perdew-Burke-Ernzerhof is adopted to evaluate force constants used in the molecular mechanics model. Afterwards, based on the principle of molecular mechanics, explicit expressions are given to calculate surface Young's modulus and Poisson's ratio of the single-walled BNNTs for different values of tube diameter and types of chirality. Moreover, the values of surface Young's modulus, Poisson's ratio and bending stiffness of boron nitride sheets are obtained via the DFT as byproducts. The results predicted by the present model are in reasonable agreement with those reported by other models in the literature. © 2015 Elsevier Ltd. All rights reserved.
Ansari, R.,
Mirnezhad m., M.,
Rouhi h., H.,
Bazdid-vahdati m., M. Publication Date: 2015
Engineering Computations (02644401)32(6)pp. 1837-1866
Purpose - Based on the molecular mechanics approach, the purpose of this paper is to analytically investigate the torsional buckling behavior of single-walled silicon carbide nanotubes (SiCNTs) with different values of diameter and chiral angles. Design/methodology/approach - To this end, the mechanical properties and atomic structure of a silicon carbide (SiC) sheet are evaluated based on the density functional theory (DFT) within the framework of the generalized gradient approximation. After that force constants of the total potential energy are theoretically obtained through establishing a linkage between the viewpoints of the quantum mechanics and molecular mechanics. Explicit expressions are presented to obtain the critical buckling shear strain corresponding to different types of chirality. The present model is capable to calculate the torsional buckling behavior of SiCNTs related to various chiral angles. The critical buckling shear strain is obtained for various types of chirality and compared with each other. Findings - It is concluded that for all diameters, zigzag nanotubes are more stable than armchair ones. Besides it is found that the minimum critical buckling shear strain is for nanotubes with (n, n/2) chiral vector. Originality/value - Investigating the torsional buckling behavior of single-walled SiCNTs with different values of diameter and chiral angle. Obtaining the mechanical properties and atomic structure of the SiC sheet based on the DFT calculations. Establishing a linkage between the molecular mechanics and quantum mechanics and obtaining the force constants of the molecular mechanics. Presenting the closed-form expression to calculate the critical buckling shear strain of single-walled SiCNTs corresponding to various types of chirality. © Emerald Group Publishing Limited.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Darabi m.a., M.A. Publication Date: 2015
Composite Structures (02638223)127pp. 87-98
In this paper, the nonlinear bending and postbuckling characteristics of Mindlin rectangular microplates made of functionally graded (FG) materials are studied based on the modified couple stress theory (MCST). This theory facilitates considering size dependency through introducing material length scale parameters. The FG microplates, whose volume fraction is expressed by a power law function, are considered to be made of a mixture of metals and ceramics. By considering the physical neutral plane position, the stretching-bending coupling is eliminated in both nonlinear governing equations and boundary conditions of FG microplates. With the aid of MCST and the principle of virtual work, the governing equations and corresponding boundary conditions are derived. Then, the obtained governing equations and boundary conditions are discretized through the generalized differential quadrature (GDQ) method. Finally, the resulting nonlinear parameterized equations are solved by the pseudo-arclength continuation technique. The effects of material gradient index, length scale parameter, length-to-thickness ratio, and boundary conditions on the nonlinear bending and postbuckling responses of FG microplates are investigated. © 2015 Elsevier Ltd.
Publication Date: 2015
Composite Structures (02638223)126pp. 216-226
In this article, a nonlocal geometrically nonlinear beam model is developed for magneto-electro-thermo-elastic (METE) nanobeams subjected to external electric voltage, external magnetic potential and uniform temperature rise. The effects of transverse shear deformation, rotary inertia and geometric nonlinearity are taken into account through using the Timoshenko beam theory together with von Kármán's hypothesis. Also, the size-dependent nonlinear forced vibration behavior of METE nanobeams under different model parameters is studied based on an efficient numerical solution procedure. The governing equations and boundary conditions are obtained on the basis of Hamilton's principle which are then discretized via the generalized differential quadrature (GDQ) method. A numerical Galerkin procedure is employed to derive the Duffing-type equations. The resulting equations are discretized on time domain using a set of time differential matrix operators that are defined based on the derivatives of a periodic base function. The pseudo arc-length continuation algorithm is finally applied to obtain the response curves of METE nanobeams with different types of end conditions. In the numerical results, the influences of temperature change, nonlocal parameter, external electric voltage and external magnetic potential on the nonlinear forced vibration behavior of METE nanobeams are explored. It is shown that the hardening-type response of nanobeams intensifies as the nonlocal parameter increases. In addition, the effects of external magnetic potential and electric voltage on the response curves are significant especially for simply-supported nanobeams. © 2015 Elsevier Ltd.
Ansari, R.,
Pourashraf t., ,
Gholami, R.,
Sahmani, S.,
Ashrafi m.a., Publication Date: 2015
International Journal of Optomechatronics (15599620)9(2)pp. 111-130
In the present study, the resonant frequency and flexural sensitivity of atomic force microscope (AFM) microcantilevers are predicted incorporating size effects. To this end, the modified strain gradient elasticity theory is applied to the classical Euler-Bernoulli beam theory to develop a non-classical beam model which has the capability to capture size-dependent behavior of microcantilevers. On the basis of Hamilton's principle, the size-dependent analytical expressions corresponding to the frequency response and sensitivity of AFM cantilevers are derived. It is observed that by increasing the contact stiffness, the resonant frequencies of AFM cantilevers firstly increase and then tend to remain constant at an especial value. Moreover, the resonant frequencies of AFM cantilevers obtained via the developed non-classical model is higher than those of the classical beam theory, especially for the values of beam thickness close to the internal material length scale parameter. © 2015, Copyright © Taylor & Francis Group, LLC.
Ansari, R.,
Gholami, R.,
Norouzzadeh, A.,
Sahmani, S. Publication Date: 2015
Microfluidics and Nanofluidics (16134982)19(3)pp. 509-522
In this article, the vibration and dynamic instability of cylindrical microshells made of functionally graded materials (FGMs) and containing flowing fluid are studied. In order to take the size effects into account, the modified couple stress elasticity theory is used in conjunction with the classical first-order shear deformation shell theory. The material properties of FGM microshells are considered to be graded in the thickness direction on the basis of the power-law function. By using Hamilton’s principle, the non-classical governing differential equations of motion and related boundary conditions are derived. Subsequently, a Navier-type exact solution method is carried out to obtain the imaginary and real parts of natural frequencies of different modes for various values of fluid velocity, length scale parameter, material property gradient index, compressive axial load, and length-to-radius ratio. It is found that for microshells with lower length-to-radius ratios, the system diverges at lower values of fluid velocity. Also, it is demonstrated that by increasing the value of material property gradient index of FGM microshell, the natural frequency of the first mode and the critical flow velocity of the system increase. © 2015, Springer-Verlag Berlin Heidelberg.
Publication Date: 2015
European Journal of Mechanics, A/Solids (09977538)53pp. 19-33
Higher-order gradient continuum mechanics theories are of critical importance as they can afford to describe the size-dependent mechanical behavior of micro-scale structures. In this article, based on the most general form of strain gradient elasticity theory, a new extended Timoshenko beam element capable of accommodating size effects is introduced. To this end, the higher-order tensors of energy pairs in the energy functional are vectorized and represented in the quadratic form first. This gives way to realize the stiffness and mass matrices of the newly proposed element. Compared to the standard Timoshenko beam element, the new element requires two additional nodal degrees of freedom (d.o.f.) consisting of derivatives of lateral translation and rotation, which means a total of 4 d.o.f. per node. Therefore, the Hermite functions are employed to construct the shape functions of this new element. The proposed element is indicated to exhibit stiffer character, making it desirable when dealing with the problems at the microscale. Also, the standard Timoshenko beam element is recovered when the small scale factor tends to zero. Using this new element, the free vibration and bending of Timoshenko microbeams are investigated. The results are compared with those available in the literature and excellent agreement is achieved. © 2015 Elsevier Masson SAS. All rights reserved.
Ansari, R.,
Rouhi, S.,
Mirnezhad m., M.,
Aryayi, M. Publication Date: 2015
Archives of Civil and Mechanical Engineering (16449665)15(1)pp. 162-170
Boron nitride nanotubes, like carbon nanotubes, possess extraordinary mechanical properties. Herein, a three-dimensional finite element model is proposed in which the nanotubes are modeled using the principles of structural mechanics. To obtain the properties of this model, a linkage between the molecular mechanics and the density functional theory is constructed. The model is utilized to study the buckling behavior of single-walled boron nitride nanotubes with different geometries and boundary conditions. It is shown that at the same radius, longer nanotubes are less stable. However, for sufficiently long nanotubes the effect of side length decreases. © 2014 Politechnika Wrocławska.
Publication Date: 2015
Applied Surface Science (01694332)332pp. 640-647
The importance of covalent and non-covalent functionalization approaches for modification the properties of carbon nanotubes is being more widely recognized. To this end, elastic properties and buckling behavior of oxygenated CNT with atomic oxygen and hydroxyl under physical adsorption of PE (Polyethylene) and PEO (Poly (ethylene oxide)) are determined through employing the molecular dynamics (MD) simulations. The results demonstrate that non-covalent bonding of polymer on the surface of oxygenated CNT causes reductions in the variations of critical buckling load and critical strain compared to oxygenated CNTs. Critical buckling load and critical strain of oxygenated CNT/polymer are higher than those of oxygenated CNT. Also, it is demonstrated that critical buckling load and critical strain values in the case of oxygenated CNT/polymer are independent of polymer type unlike the value of Young's modulus. It is shown that variations of Young's modulus decrease as PE adsorbed on the surface of oxygenated CNT. Moreover, the presence of oxygen atom on PEO chain leads to bigger variations of Young's modulus with weight percentage of chemisorbed component, i.e. atomic oxygen and hydroxyl. It is also demonstrated that Young's modulus reduces more considerably in the presence of PEO chain compared to PE one. © 2015 Elsevier B.V. All rights reserved.
Publication Date: 2015
Superlattices and Microstructures (10963677)82pp. 113-123
Through doping boron nitride nanotubes, their band gaps could be controlled which results in extending the range of their applications particularly in nanosensors. In this article, the structural and elastic properties of Be and Mg doped boron nitride nanotubes with various chiralities are studied based on ab initio density functional calculations. In order to perform the density functional theory (DFT) calculations, the exchange correlation of Perdew-Burke-Ernzerhof within the generalized gradient approximation (GGA) framework is employed. It is observed that doping Be and Mg atoms increases the equilibrium strain energy of boron nitride nanotubes. Furthermore, it is found that among all of the considered nanotubes, an increase in the value of Young's modulus of (4, 4) armchair boron nitride nanotube through doping Be atom instead of boron atom is so considerable. © 2015 Elsevier Ltd. All rights reserved.
Publication Date: 2015
International Journal of Non-Linear Mechanics (00207462)77pp. 193-207
The size-dependent non-linear pull-in instability and free vibration of electrostatically actuated microswitches with the consideration of Casimir force effect are studied using a numerical solution approach. To this end, a non-classical non-linear beam model is developed based on Mindlin's strain gradient elasticity and the Timoshenko beam theory. The geometric non-linearity is taken into account according to the von Kármán hypothesis. Also, the microswitches are assumed to be made of functionally graded materials (FGMs). To obtain the size-dependent governing equations and boundary conditions, the virtual work principle is applied. The presented equations can be simply reduced to those on the basis of modified versions of strain gradient and couple stress theories (MSGT and MCST) as well as the classical elasticity theory. For solving the problem, the generalized differential quadrature (GDQ) method and the pseudo arc-length continuation technique are employed. In the numerical results, the influences of different parameters such as length scale parameter, Casimir force, material gradient index and geometrical properties on the pull-in instability and free vibration of actuated microswitches are examined. © 2015 Elsevier Ltd.
Ansari, R.,
Gholami, R.,
Norouzzadeh, A.,
Darabi m.a., M.A. Publication Date: 2015
Acta Mechanica Sinica/Lixue Xuebao (16143116)31(5)pp. 708-719
Abstract: Presented in this paper is a precise investigation of the effect of surface stress on the vibration characteristics and instability of fluid-conveying nanoscale pipes. To this end, the nanoscale pipe is modeled as a Timoshenko nanobeam. The equations of motion of the nanoscale pipe are obtained based on Hamilton’s principle and the Gurtin–Murdoch continuum elasticity incorporating the surface stress effect. Afterwards, the generalized differential quadrature method is employed to discretize the governing equations and associated boundary conditions. To what extent important parameters such as the thickness, material and surface stress modulus, residual surface stress, surface density, and boundary conditions influence the natural frequency of nanoscale pipes and the critical velocity of fluid is discussed. Graphical Abstract: [Figure not available: see fulltext.] © 2015, The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Rouhi h., H. Publication Date: 2015
Journal of Thermal Stresses (01495739)38(6)pp. 651-664
A size-dependent finite element (FE) formulation including surface free energy effect is developed in this article to study the post-buckling behavior of nanofilms under the action of thermal loads. The Gurtin-Murdoch surface elasticity theory is utilized to consider the surface effects. Moreover, the principle of virtual work is used so as to derive the equilibrium equations. The proposed FE formulation is based on the first-order shear deformation theory (FSDT). The von Kármán nonlinear relations are also employed to take the geometric nonlinearity into account. After deriving the FE equations, the resulting set of parameterized non-linear equations is solved using the pseudo arc-length continuation algorithm, and bifurcation diagrams of nanofilms are obtained. Selected numerical results are presented for the influences of surface stress on the thermal post-buckling characteristics of nanofilms subject to different types of boundary conditions. Copyright © Taylor & Francis Group, LLC.
Ansari, R.,
Faghih shojaei, M.,
Shahabodini a., A.,
Bazdid-vahdati m., M. Publication Date: 2015
Composite Structures (02638223)131pp. 753-764
In this paper, the three dimensional (3D) nonlocal bending and vibration analyses of functionally graded (FG) nanoplates are presented using a novel numerical solution method which is called variational differential quadrature (VDQ) due to its numerical essence and the framework of implementation. Through this approach, a quadratic weak formulation of 3D nonlocal elasticity for the considered phenomena is presented. Two types of the distribution of functionally graded materials (FGMs) namely power law distribution and exponentially varied along the thickness of the plate are considered. The energy quadratic representation of the problems is first obtained based on the 3D theory of elasticity. A weak form of local governing equations is then derived from this representation by a variational approach. To incorporate the effects of small size into the local model, a size-dependent energy functional based on the nonlocal elasticity theory is developed. By introducing this functional into Hamilton's principle, the discretized equations of motion including size effects are derived. By the VDQ method, the need for derivation of strong statement of the problems through minimizing the energy functional in the differential quadrature formulation is bypassed. In several numerical examples, the obtained results are compared with the available solutions in the literature, and the validity and high accuracy as well as fast convergence rate of the VDQ are indicated. It is also found that the small scale has a decreasing effect on the stiffness of nanoplates. © 2015 Elsevier Ltd.
Publication Date: 2015
Acta Mechanica (16196937)226(9)pp. 2955-2972
This study is concerned with the torsional buckling behavior of chiral multi-walled carbon nanotubes (MWCNTs) based on a molecular mechanics model. An analytical solution is carried out to calculate the elastic critical buckling shear strain of MWCNTs with different types of chirality. To determine the force constants used in the molecular mechanics model, on the basis of quantum mechanics, density functional theory is employed. Through comparison of the results obtained from the present molecular mechanics model and ones from available molecular dynamics simulations, the validity of the present approach is assessed. The influence of chirality on the critical buckling shear strain of nanotubes is then investigated. It is indicated that nanotubes with (n, n/2) chirality buckle at lower values of critical buckling shear strain compared with zigzag and armchair nanotubes. © 2015, Springer-Verlag Wien.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Bazdid-vahdati m., M.,
Rouhi h., H. Publication Date: 2015
Computer Methods in Applied Mechanics and Engineering (00457825)295pp. 56-76
In this article, based on the most general form of strain gradient theory (MGSGT), a novel extended triangular Mindlin plate element is proposed. To accomplish this aim, first, the quadratic form of energy functional is obtained by vectorizing the higher-order tensors of energy pairs, from which the stiffness and mass matrices of the element are readily derived. In comparison with the standard Mindlin plate element, the new element needs three additional nodal degrees of freedom (DOF) including derivatives of lateral deflection and rotations, which means a total of nine DOFs per node. Also, as compared to the standard Mindlin plate element which requires only C0 shape functions, the present one requires C1 continuous smooth shape functions due to second derivatives of deflection and rotations. Hence, cubic polynomials are used to interpolate the displacement components. The new element can be reduced to that based on the modified strain gradient theory (MSGT) and the modified couple stress theory (MCST). Moreover, the standard Mindlin plate element is recovered when the gradient-based material parameters tend to zero. The Mindlin microplates with different boundary conditions are considered as the problem under study whose free vibration and bending are analyzed. The results are compared with the exact solutions and excellent agreement is achieved. © 2015 Elsevier B.V.
Rouhi, S.,
Alizadeh y., Y.,
Ansari, R.,
Aryayi, M. Publication Date: 2015
Modern Physics Letters B (02179849)29(26)
Molecular dynamics simulations are used to study the mechanical behavior of single-walled carbon nanotube reinforced composites. Polyethylene and polyketone are selected as the polymer matrices. The effects of nanotube atomic structure and diameter on the mechanical properties of polymer matrix nanocomposites are investigated. It is shown that although adding nanotube to the polymer matrix raises the longitudinal elastic modulus significantly, the transverse tensile and shear moduli do not experience important change. As the previous finite element models could not be used for polymer matrices with the atom types other than carbon, molecular dynamics simulations are used to propose a finite element model which can be used for any polymer matrices. It is shown that this model can predict Young's modulus with an acceptable accuracy. © 2015 World Scientific Publishing Company.
Ansari, R.,
Ashrafi m.a., ,
Pourashraf t., ,
Sahmani, S. Publication Date: 2015
Acta Astronautica (00945765)109pp. 42-51
The buckling and vibration responses of nanoplates made of functionally graded materials (FGMs) subjected to thermal loading are studied in prebuckling domain with considering the effect of surface stress. To accomplish this purpose, Gurtin-Murdoch elasticity theory is incorporated into the classical plate theory to develop a non-classical plate model including the surface effects. The material properties of FGM nanoplate are considered to be graded in the thickness direction on the basis of the power law function. Hamilton's principle is utilized to derive size-dependent governing differential equations of motion and associated boundary conditions. Selected numerical results are presented to indicate the importance of surface stress effect. It is revealed that in the presence of surface stress effect, the influence of material property gradient index on the critical thermal buckling load is more prominent for FGM nanoplates with lower length-to-thickness ratios. Also, by increasing the natural frequency of FGM nanoplate, the role of surface stress effect in the value of critical thermal buckling load is more prominent. © 2014 IAA. Published by Elsevier Ltd. All rights reserved.
Publication Date: 2015
Physica B: Condensed Matter (09214526)462pp. 8-14
Carbon nanotube functionalization for designing devices with atomic precision has been of great importance in recent years. This article studies the vibration behavior of single-walled carbon nanotubes (SWCNTs) and double-walled carbon nanotubes (DWCNTs) functionalized with amine and amide groups employing molecular dynamics (MD) simulations. The results demonstrate that the natural frequency of CNTs reduces considerably through attaching functional groups to them. Also, it is demonstrated that the natural frequency of DWCNTs is less sensitive to functional groups in comparison with their constituent inner and outer functionalized tubes. Further, it is indicated that the functionalization performed has its most pronounced effect on SWCNTs with small aspect ratios. © 2015 Elsevier B.V. All rights reserved.
Publication Date: 2015
Physica B: Condensed Matter (09214526)459pp. 58-61
Functionalization of carbon nanotubes (CNTs) can be viewed as an important process by which the dispersion and solubility of CNTs in the matrices of nanocomposites are improved. Covalent functionalization can affect the mechanical behavior of CNTs. In this paper, the vibrational behavior of diethyltoluenediamines (DETDA) functionalized CNTs is investigated utilizing molecular dynamics simulations in canonical ensemble at room temperature. The models of simulations are divided into two categories of functionalized CNTs with regular and random distributions of DETDA polymers. The results demonstrate that natural frequency of functionalized CNTs is lower than that of pristine ones. Also, it is observed that buckling phenomenon occurs during vibration for functionalized CNTs with regular distribution of polymers. It is further observed that polymer mass and van der Waals (vdW) forces are responsible for frequency changes in functionalized CNTs with random and regular distribution patterns of CNTs, respectively. © 2014 Elsevier B.V.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Darabi m.a., M.A. Publication Date: 2014
International Journal of Non-Linear Mechanics (00207462)67pp. 16-26
Presented herein is a comprehensive investigation on the size-dependent pull-in instability of geometrically non-linear rectangular nanoplates including surface stress effects undergoing hydrostatic and electrostatic actuations. To this end, based on the Gurtin-Murdoch theory, a non-classical continuum plate model capable of incorporating size-effects is developed; then, by means of the principle of virtual work, the governing equations of the actuated nanoplate are obtained. Subsequently, the generalized differential quadrature (GDQ) method is used to discretize the governing equations and associated boundary conditions, before solving numerically by the pseudo arc-length algorithm. Finally, the influences of important parameters including the geometrical non-linearity, thickness of the nanoplate, surface elastic modulus, residual surface stress and boundary conditions on the pull-in behavior of the actuated nanoplate are thoroughly studied. In addition, the effect of the material on the pull-in voltage and pressure is investigated by comparing the results obtained from nanoplates made of two different materials including aluminum (Al) and silicon (Si). © 2014 Elsevier Ltd.
Publication Date: 2014
Current Applied Physics (15671739)14(10)pp. 1360-1368
The purpose of this study is to describe the axial buckling behavior of chiral single-walled carbon nanotubes (SWCNTs) using a combined continuum-atomistic approach. To this end, the nonlocal Flugge shell theory is implemented into which the nonlocal elasticity of Eringen incorporated. Molecular mechanics is used in conjunction with density functional theory (DFT) to precisely extract the effective in-plane and bending stiffnesses and Poisson's ratio used in the developed nonlocal Flugge shell model. The Rayleigh-Ritz procedure is employed to analytically solve the problem in the context of calculus of variation. The results generated from the present hybrid model are compared with those from molecular dynamics simulations as a benchmark of good accuracy and excellent agreement is achieved. The influences of small scale factor, commonly used boundary conditions and chirality on the critical buckling load are fully explored. It is indicated that the importance of the small length scale is affected by the type of boundary conditions considered. © 2014 Elsevier B.V. All rights reserved.
Publication Date: 2014
Physica E: Low-Dimensional Systems and Nanostructures (13869477)58pp. 63-66
Based on the continuum approximation together with Lennard-Jones potential, a new semi-analytical method is developed to investigate the van der Waals interaction between two parallel carbon nanotori. Considering that atomistic approaches, such as classical molecular dynamics and density functional theory, are often computationally expensive, the present continuum method can be alternatively used for theoretical modeling of interaction force and energy between nanostructures. Following the present method, a semi-analytical expression is given in terms of double integrals which can be used to obtain the potential energy and interaction force. Investigating the effects of geometrical parameters on the potential energy and interaction force distributions reveals the oscillatory behavior of two parallel carbon nanotori and the plausibility of using them as the ideal traps for atoms and particles. © 2013 Elsevier B.V. All rights reserved.
Mahmoudinezhad e., E.,
Ansari, R.,
Basti a., A.,
Hemmatnezhad m., M. Publication Date: 2014
Computational Materials Science (09270256)85pp. 121-126
An accurate spring-mass model, in the context of a three-dimensional finite element formulation, is developed for investigating the vibrational characteristics of single-walled carbon nanotubes (SWCNTs). Atoms are replaced by lumped mass elements at their locations and appropriate spring-type elements are defined as interconnections between the atoms in order to simulate the interatomic interactions. The effect of out of plane angle variation energy is incorporated into the model. The obtained results for the fundamental frequency of single-walled carbon nanotubes of various kinds are graphically illustrated. The influences of some commonly-used boundary conditions and changes in the nanotube geometrical parameters on vibration frequencies are examined. The numerical results show good agreement with other published results in the literature. Also, some novel relations are deduced which can be more useful in predicting the fundamental frequency of SWCNTs with great number of atoms. © 2013 Elsevier B.V. All rights reserved.
Darvizeh a., A.,
Darvizeh m., M.,
Ansari, R.,
Meshkinzar, A. Publication Date: 2014
Journal of Mechanical Science and Technology (1738494X)28(10)pp. 4199-4212
In this paper, the energy absorption characteristics of grooved circular tubes are investigated under quasi-static loading condition. For experiments, thick-walled tubes with circumferential grooves are prepared. The grooves divide the thick-walled tube into several shorter thin-walled portions. Specimens are subjected to axial crushing load to observe the effect of distribution of circular grooves on the deformation mechanism and energy absorption capacity. Geometrical parameters of the specimens are designed utilizing the Taguchi method to cover a reasonably wide range of groove length-to-wall thickness ratios. An analytical approach based on the concept of energy dissipation through the plastic hinges is applied. Taking the effect of strain hardening into account, the obtained analytical results are in good agreement with the experimental ones. The agreement between analytical and experimental results may indicate the validity of the proposed analytical approach. Desirable mechanism of deformation observed justifies the pre-forming method for obtaining favorable energy absorption characteristics. © 2014, The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Alijani a., ,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2014
Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science (20412983)228(2)pp. 199-217
This article introduces a new semi-analytical nonlinear finite element formulation for thin cylinders according to a continuum-based approach. A comparison between the continuum-based approach and the classical approach for the buckling behavior of isotropic and orthotropic perfect cylinders validates the results. The classical approach is defined according to thin shell theories based on the von Karman approximation. A mathematical modeling for geometry imperfection of cylinders is derived according to a continuum-based approach whose results are compared with the results of the classical approach for imperfect cylinders. The influence of neglecting some nonlinear terms in the classical approach for perfect and imperfect cylinders on the buckling path is investigated. In the buckling analysis, two methods, i.e. the perturbation and load disturbance methods, which undertake to switch to the post-buckling path, are compared to each other. © IMechE 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.
Publication Date: 2014
JVC/Journal of Vibration and Control (10775463)20(5)pp. 773-785
Carbon nanotube oscillators which can generate frequencies in the gigahertz range have attracted much attention in recent years. A number of studies on double-walled carbon nanotube (DWCNT) oscillators can be found in the literature, while other mechanisms of these oscillators with a higher number of oscillating nanotubes have not been well studied. This paper aims to investigate the motion properties of triple-walled carbon nanotube (TWCNT) oscillators in which the inner and middle tubes have telescopic motions with respect to the outer tube. To this end, the continuum approximation together with the Lennard-Jones potential function is utilized. In comparison with DWCNT oscillators, the triple-walled ones have shown a variety of motion patterns. In this respect, different types of motion patterns are classified and demonstrated. Moreover, it is observed that these nano-oscillators are so sensitive to their initial conditions. For this reason, a phase division of initial separation distances that generate different motion patterns is also presented. © 2012 The Author(s).
Publication Date: 2014
Superlattices and Microstructures (10963677)68pp. 16-26
In the current investigation, the influences of in-plane electric field and temperature change on Young's modulus of boron nitride nanosheets (BNNs) are studied for both armchair and zigzag chiralities. To this end, the density functional theory (DFT) and quasi-harmonic approximation (QHA) are applied to calculate the total energy of the system. It is found that in the presence of temperature change, by applying the electric field along the zigzag and armchair directions, Young's modulus of BNNs decreases and increases, respectively. Moreover, it is revealed that the range of variation in Young's modulus of zigzag BNNs corresponding to different values of electric field is generally lower than that of armchair ones, but the slope of this variation with temperature for zigzag BNNs is more than Armchair ones. Also, it is observed that the rate of variation of Young's modulus with temperature at lower values is sharper than that at higher temperatures. This behavior can be useful in designing electro-thermo-mechanical nanosensors. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Chemical Physics Letters (00092614)616pp. 120-125
Atomic decoration of carbon nanotubes (CNTs) is an effective way to alter the key properties of pristine CNTs. Elastic properties and axial buckling behavior of atomic oxygen and hydroxyl chemisorbed single-walled CNTs are explored employing molecular dynamics (MD) simulations. Our results demonstrate that the structure of chemisorbed CNTs changes compared to pristine CNT which considerably depends on the distribution pattern of chemisorbed oxygen and -hydroxyl. The results also demonstrate that chemisorption of atomic oxygen and -hydroxyl reduces Young's modulus and critical strain while increases the critical force of CNTs. Buckling mode shape of chemisorbed CNTs depends on the distribution pattern. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Superlattices and Microstructures (10963677)65pp. 64-70
This paper aims to compute the elastic properties and large deformation of two-dimensional silicene, a low buckled honeycomb structure of silicon, under uniaxial and biaxial tension by implementing molecular dynamics simulations in canonical ensemble (NVT). The results demonstrate that Young's and bulk moduli and ultimate stress of silicene nanosheet are lower than those of graphene. Ultimate strain is found to be higher than that of graphene for armchair silicene, unlike the zigzag one. Moreover, Poisson's ratio of silicene is found to be greater than that of its carbon counterpart due to longer Si-Si bond length and its low buckled honeycomb structure. Further, it is observed that bulk modulus is strongly size-dependent and it decreases by increasing the length of nanosheet. Finally, the silicene behavior under large deformation and fracture pattern are investigated and the formation of topological defects and silicon chains are observed. It is further revealed that the silicene is noticeably weaker than graphene in zigzag direction. © 2013 Elsevier Ltd. All rights reserved.
Publication Date: 2014
JVC/Journal of Vibration and Control (10775463)20(5)pp. 670-678
In the present study, the free vibration characteristics of single-and double-walled carbon nanotubes (SWCNTs and DWCNTs) are investigated on the basis of a nonlocal elastic shell model. Eringen's nonlocal elasticity equations are applied to the classical Donnell shell theory to incorporate the size-effects into the vibration analysis of carbon nanotubes (CNTs). An exact solution is developed for the governing equations of the nonlocal elastic shell model with the inclusion of size effects. Molecular dynamics (MD) simulations are performed to obtain fundamental frequencies of SWCNTs and DWCNTs with different values of aspect ratio and types of chirality. To derive the appropriate values of a nonlocal parameter for vibrations of SWCNTs and DWCNTs, the results of the continuum model are matched with those of MD simulations. This study shows that the small scale effects in the nonlocal model make nanotubes more flexible. © 2012 The Author(s).
Publication Date: 2014
International Journal for Computational Methods in Engineering Science and Mechanics (15502295)15(5)pp. 401-412
The microscale vibration characteristics of microbeams made of functionally graded materials (FGMs) are investigated based on the strain gradient Reddy beam theory capable of capturing the size effect. The non-classical governing differential equations, together with the corresponding boundary conditions, are obtained using Hamilton's principle. Then, the free vibration problem of simply supported FGM microbeams is solved using the Navier solution. The natural frequencies of FGM microbeams are calculated corresponding to a wide range of dimensionless length scale parameters, material property gradient indices, and aspect ratios to illustrate the influences of size effect on the vibrational response of FGM microbeams. © 2014 Taylor & Francis Group, LLC.
The application of graphene as a nanosensor in measuring strain through its band structure around the Fermi level is investigated in this paper. The mechanical properties of graphene as well as its electronic structure are determined by using the density functional theory calculations within the framework of generalized gradient approximation. In the case of electronic properties, the simulations are applied for symmetrical and asymmetrical strain distributions in elastic range; also the tight-binding approach is implemented to verify the results. It is indicated that the energy band gap does not change with the symmetrical strain distribution but depend on the asymmetric strain distribution, increasing strain leads to band gap opening around the Fermi level. © 2014, IGI Global.
Zajkani, A.,
Darvizeh a., A.,
Darvizeh m., M.,
Ansari, R. Publication Date: 2014
Journal of Strain Analysis for Engineering Design (03093247)49(2)pp. 86-111
An incremental integrated modeling is presented to obtain high-rate dynamic viscoplastic behavior of annular sector plates. The large amplitude shock loads are imparted uniformly over the plate's surface. Using the first-order shear deformation theory including the nonlinear Von-Kármán system, incremental differential equations are derived for nonaxisymmetric motion of the plate. A combined strain hardening law, in conjunction with special physical-based viscoplastic models, is applied to consider the material nonlinearity. Evaluation of the viscoplastic constitutive equations is accomplished by a semi-implicit scheme of the return mapping technique. An efficient algorithm is applied by the cutting-plane iteration to enforce plasticity admissibility during evolution of yield surface. A pseudo-spectral collocation methodology is implemented based on the Chebyshev polynomials in order to calculate displacement fields stepwise. Velocity and inertia terms are discrete by the Houbolt marching method. The nonlinear terms are eliminated by the quadratic extrapolation. The aliasing phenomenon caused by collocation treatment of nonlinear terms is controlled by applying an exponential filtering. A number of sector plates with different thicknesses, angularities, sector angles and boundary conditions are examined. The maximum transverse deflections, the effective plastic strain, dynamic yield stress, plastic works and temperatures are obtained. The present modeling is validated by comparing results with other approaches available in literature. © IMechE 2013.
Publication Date: 2014
Superlattices and Microstructures (10963677)74pp. 85-99
The molecular mechanics is combined here with density functional theory to develop an accurate model for single-walled zinc sulfide nanotubes. It is shown that based on the resemblance between nanotubes and space frame structures, nanotubes can be modeled as a combination of beam and mass elements. Using the developed model, the vibrational behavior and stability characteristics of single-walled zinc sulfide nanotubes with different geometries and under different boundary conditions are investigated. It is observed that the side length of nanotubes affect its vibrational behavior. However, this effect will reduce for longer nanotubes. Besides, it is shown that the stability of nanotubes have a strong dependence on geometry parameters for short nanotubes. However, for sufficiently long nanotube this dependence would diminish. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Nano (17937094)9(4)
This paper investigates the mechanical properties of hydrogenated silicon carbide nanotubes (H-SiCNTs) using a molecular mechanics model in conjunction with the density functional theory (DFT). Analytical expressions presented in this study can be employed for nanotubes with different chiralities. Four different positions of adsorptions are considered in this paper and it is shown that the most stable state happens when hydrogen atoms are adsorbed on silicon and carbon atoms at the two opposite sides of hexagonal phase of silicon carbide. This paper will contribute to future research on similar studies of H-SiCNTs in the specific area as the force constants used in the molecular mechanics models regarding the hydrogen adsorption are proposed. Also, the mechanical properties and atomic structure of hydrogenated silicon carbide (H-SiC) sheet for different states of adsorption are determined using the DFT. The results for bending stiffness of H-SiC sheets indicate the isotropic behavior of these materials. © 2014 World Scientific Publishing Company.
Publication Date: 2014
Superlattices and Microstructures (10963677)72pp. 204-218
The physical and mechanical properties of single-walled carbon nanotubes reinforced poly (phenylacetylene) are investigated here. Polymer density distribution, polymer atom distribution, stress-strain curve of single-walled carbon nanotubes/poly (phenylacetylene) and tensile and shear moduli of resulted nanocomposites are studied. It is shown that the polymer atom distribution at the nanotube/polymer interface is not uniform. It is observed that nanotube diameter and volume fraction do not affect polymer atom distribution around the single-walled carbon nanotubes significantly. Studying the effect of embedding nanotube in poly (phenylacetylene) on the tensile modulus of nanocomposite, it is shown that longitudinal Young's modulus is improved drastically. However, transverse moduli are not significantly improved compared to pure polymer. © 2013 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601)378(38-39)pp. 2876-2880
In recent years, synthesizing inorganic nanostructures such as boron nitride nanotubes (BNNTs) has led to extensive studies on their exceptional properties. In this study, the torsional vibration behavior of boron-nitride nanotubes (BNNTs) is explored on the basis of molecular dynamics (MD) simulation. The results show that the torsional frequency is sensitive to geometrical parameters such as length and boundary conditions. The axial vibration is found to be induced by torsional vibration of nanotubes which can cause instability in the nanostructure. It is also observed that the torsional frequency of BNNTs is higher than that of their carbon counterpart. Moreover, the shear modulus is predicted by incorporating MD simulation numerical results into torsional vibration frequency obtained through continuum-based model of tubes. Finally, it is seen that the torsional frequency of double-walled boron-nitride nanotubes (DWBNNTs) is between the frequencies of their constituent inner and outer tubes. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Physica E: Low-Dimensional Systems and Nanostructures (13869477)63pp. 283-292
The meshless local Petrov-Galerkin (MLPG) method is implemented to analyze the free vibration and axial buckling characteristics of single-walled carbon nanotubes (SWCNTs) with different boundary conditions. To this end, a nonlocal shell model accounting for the small scale effect is used. In the theoretical formulations, a variational form of the Donnell shell equations is constructed over a local sub-domain which leads to derivation of the mass, stiffness and geometrical stiffness matrices. Comprehensive results for the resonant frequencies and critical axial buckling loads of SWCNTs are presented. The influences of boundary conditions, nonlocal parameter and geometrical parameters on the mechanical behavior of SWCNTs are fully investigated. The results obtained from the present numerical scheme are shown to be in good agreement with those from exact solution for simply-supported SWCNTs and those of molecular dynamics simulations. It is shown that the natural frequencies and critical axial buckling loads of SWCNTs are strongly dependent on the small scale effect and geometrical parameters. © 2014 Elsevier B.V.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Sadeghi f., F. Publication Date: 2014
Composite Structures (02638223)113(1)pp. 316-327
This research deals with the forced vibration behavior of nanocomposite beams reinforced by single-walled carbon nanotubes (SWCNTs) based on the Timoshenko beam theory along with von Kármán geometric nonlinearity. For the carbon-nanotube reinforced composite (CNTRC) beams, uniform distribution (UD) and three types of functionally graded (FG) distribution patterns of SWCNT reinforcements are considered. It is assumed that the material properties of FG-CNTRC beams are graded in the thickness direction and estimated through the rule of mixture. The nonlinear governing equations and corresponding boundary conditions are derived based on the Hamilton principle and discretized by means of the generalized differential quadrature (GDQ) method. After that, a Galerkin-based numerical technique is employed to reduce the set of nonlinear governing equations into a time-varying set of ordinary differential equations of Duffing type. Since the nanobeam responds periodically to harmonic excitations, a set of periodic differential matrix operators is introduced to discretize the Duffing equations on the time domain using the derivatives of a periodic base function. The vectorized form of final nonlinear parameterized equations is then solved through the use of pseudo-arc length continuum technique. Numerical results are presented to examine the effects of different parameters such as nanotube volume fraction, slenderness ratio, dimensionless damping parameter, dimensionless transverse force, CNT distributions and boundary conditions on the natural frequencies and frequency responses of FG-CNTRC beams. © 2014 Elsevier Ltd.
Faghih shojaei, M.,
Ansari, R.,
Mohammadi v., V.,
Rouhi h., H. Publication Date: 2014
Archive of Applied Mechanics (14320681)84(3)pp. 421-440
A numerical solution methodology is proposed herein to investigate the nonlinear forced vibrations of Euler-Bernoulli beams with different boundary conditions around the buckled configurations. By introducing a set of differential and integral matrix operators, the nonlinear integro-differential equation that governs the buckling of beams is discretized and then solved using the pseudo-arc-length method. The discretized governing equation of free vibration around the buckled configurations is also solved as an eigenvalue problem after imposing the boundary conditions and some complicated matrix manipulations. To study forced and nonlinear vibrations that take place around a buckled configuration, a Galerkin-based numerical method is applied to reduce the partial integro-differential equation into a time-varying ordinary differential equation of Duffing type. The Duffing equation is then discretized using time differential matrix operators, which are defined based on the derivatives of a periodic base function. Finally, for any given magnitude of axial load, the pseudo -arc-length method is used to obtain the nonlinear frequencies of buckled beams. The effects of axial load on the free vibration, nonlinear, and forced vibrations of beams in both prebuckling and postbuckling domains for the lowest three vibration modes are analyzed. This study shows that the nonlinear response of beams subjected to periodic excitation is complex in the postbuckling domain. For example, the type of boundary conditions significantly affects the nonlinear response of the postbuckled beams. © 2013 Springer-Verlag Berlin Heidelberg.
Publication Date: 2014
Composite Structures (02638223)110(1)pp. 219-230
In the present investigation, a numerical analysis is conducted to predict size-dependent nonlinear free vibration characteristics of third-order shear deformable microbeams made of functionally graded materials (FGMs). For this purpose, the modified strain gradient elasticity theory and von Karman geometric nonlinearity are implemented into the classical third-order shear deformation beam theory to develop a nonclassical higher-order beam model including three additional length scale parameters to capture size effect efficiently. It is assumed that the material properties of the FGM microbeams are evaluated by the Mori-Tanaka homogenization technique. On the basis of the Hamilton's principle, the size-dependent nonlinear governing differential equations of motion and associated boundary conditions are derived and then discretized along various end supports by employing generalized differential quadrature (GDQ) method. A direct iterative process corresponding to both positive and negative deflection cycles is adopted. Secondly, a parametric study is performed to demonstrate the influences of the values of dimensionless length scale parameter, material property gradient index and length to thickness aspect ratio on the linear and nonlinear natural frequencies of FGM microbeams. © 2013 Elsevier Ltd.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Rouhi h., H. Publication Date: 2014
Journal of Mechanics (18118216)30(2)pp. 161-172
Based on the Timoshenko beam model, the nonlinear vibration of microbeams made of functionally graded (FG) materials is investigated under different boundary conditions. To consider small scale effects, the model is developed based on the most general form of strain gradient elasticity. The nonlinear governing equations and boundary conditions are derived via Hamilton's principle and then discretized using the generalized differential quadrature technique. A pseudo-Galerkin approach is used to reduce the set of discretized governing equations into a time-varying set of ordinary differential equations of Duffing-type. The harmonic balance method in conjunction with the Newton-Raphson method is also applied so as to solve the problem in time domain. The effects of boundary conditions, length scale parameters, material gradient index and geometrical parameters are studied. It is found that the importance of the small length scale is affected by the type of boundary conditions and vibration mode. Also, it is revealed that the classical theory tends to underestimate the vibration amplitude and linear frequency of FG microbeams. © 2014 The Society of Theoretical and Applied Mechanics, R.O.C.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Rouhi h., H. Publication Date: 2014
European Journal of Mechanics, A/Solids (09977538)45pp. 143-152
In this article, the nonlinear free vibration behavior of Timoshenko nanobeams subject to different types of end conditions is investigated. The Gurtin-Murdoch continuum elasticity is incorporated into the Timoshenko beam theory in order to capture surface stress effects. The nonlinear governing equations and corresponding boundary conditions are derived using Hamilton's principle. A numerical approach is used to solve the problem in which the generalized differential quadrature method is applied to discretize the governing equations and boundary conditions. Then, a Galerkin-based method is numerically employed with the aim of reducing the set of partial differential governing equations into a set of time-dependent ordinary differential equations. Discretization on time domain is also done via periodic time differential operators that are defined on the basis of the derivatives of a periodic base function. The resulting nonlinear algebraic parameterized equations are finally solved by means of the pseudo arc-length continuation algorithm through treating the time period as a parameter. Numerical results are given to study the geometrical and surface properties on the nonlinear free vibration of nanobeams. © 2013 Elsevier Masson SAS. All rights reserved.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Darabi m.a., M.A. Publication Date: 2014
Composite Structures (02638223)114(1)pp. 124-134
This paper investigates the size-dependent vibrational behavior of functionally graded (FG) rectangular Mindlin microplates including geometrical nonlinearity. The FG Mindlin microplate is considered to be made of a mixture of metal and ceramic according to a power law distribution. To this end, based on the modified couple stress theory (MCST) and Hamilton's principle, the governing equations of motion and associated boundary conditions are derived. In the solution procedure, the set of nonlinear partial differential equations is discretized through the generalized differential quadrature (GDQ) method. Afterwards, the numerical Galerkin scheme is employed to convert the discretized partial differential equations of motion to the Duffing-type ordinary differential equations. The periodic time differential operators introduced based on the derivatives of a periodic base function are used to discretize differential equations on the time domain. Finally, the pseudo arc-length continuation method is utilized to numerically solve the set of nonlinear algebraic parameterized equations. The effects of the important parameters including material gradient index, length-to-thickness ratio, length scale parameter, and boundary conditions on the vibrational characteristics of rectangular Mindlin microplate are thoroughly discussed. © 2014 Elsevier Ltd.
Ansari, R.,
Shahabodini a., A.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R. Publication Date: 2014
Physica E: Low-Dimensional Systems and Nanostructures (13869477)57pp. 126-137
Due to the high surface to volume ratio of the nanoscale domain, the surface stress effect is a major concern in the analysis of mechanical response of the nanomaterials and nanostructures. This paper is concerned with the applicability of a continuum model including the surface properties for describing the bending and buckling configuration of the nanoscale plates. The Gurtin-Murdoch surface theory of elasticity is first incorporated into Mindlin's plate theory. Then, the principle of virtual work is applied to derive the size-dependent governing equations along with various boundary conditions. To solve the governing equations, the generalized differential quadrature (GDQ) method is employed. The critical uniaxial and biaxial buckling loads and the maximum deflection of the nanoplate due to a uniform transverse load are calculated in the presence and absence of the surface effects for various edge conditions. It is found that the significance of the surface effects on the response of the nanoplate relies on its size, type of edge support and selected surface constants. © 2013 Elsevier Ltd. All rights reserved.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Sahmani, S. Publication Date: 2014
Composites Part B: Engineering (13598368)60pp. 158-166
This paper aims to present nonlinear forced vibration characteristics of nanobeams including surface stress effect. By considering the local geometrical nonlinearity based on von Karman relation, a new formulation of the Timoshenko beam model is developed through the Gurtin-Murdoch elasticity theory in which the effect of surface stress is incorporated. By using a variational approach on the basis of Hamilton's principle, the size-dependent equations of motion and associated boundary conditions are obtained. The generalized differential quadrature (GDQ) method is employed to discretize the non-classical governing differential equations over the spatial domain by using the shifted Chebyshev-Gauss-Lobatto grid points. Subsequently, a Galerkin-based numerical approach is put to use in order to reduce the set of nonlinear equations into a time-varying set of ordinary differential equations of Duffing-type. In the next step, the time domain is discretized via spectral differentiation matrix operators which are defined based on the derivatives of a periodic base function. Finally, the pseudo arc-length method is employed to solve the resulting nonlinear parameterized algebraic equations. The frequency-response curves for forced vibration behavior of nanobeams including the effect of surface stress are predicted corresponding to various values of beam thickness, length to thickness ratio and surface elastic constants. It is revealed that by incorporating the surface stress effect, the maximum amplitude occurs at lower excitation frequencies and the wide of region of the response tends to decrease. © 2013 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Acta Mechanica (16196937)225(2)pp. 609-623
A unified analytical approach is applied for investigating the vibrational behavior of grid-stiffened composite cylindrical shells considering the flexural behavior of the ribs. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of the shell in order to obtain the equivalent stiffness parameters of the whole panel. The stiffeners are modeled as a beam and considered to support shear loads and bending moments in addition to the axial loads. Therefore, the corresponding stiffness terms are taken into consideration while obtaining the stiffness matrices due to the stiffeners. Theoretical formulations are based on first-order shear deformation shell theory, which includes the effects of transverse shear deformation and rotary inertia. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stokes' transformation. In order to validate the obtained results, a 3-D finite element model is also built using ABAQUS CAE software. Results obtained from two types of analyses are compared with each other, and good agreement has been achieved. Furthermore, the influence of variations in the shell thickness and changes of the boundary conditions on the shell frequencies is studied. The results obtained are novel and can be used as a benchmark for further studies. © 2013 Springer-Verlag Wien.
Publication Date: 2014
Applied Surface Science (01694332)292pp. 958-970
Molecular dynamics simulations are used to study the interactions between polyethylene and single-walled carbon nanotubes. The effect of initial angle of polyethylene chain and nanotube axis is investigated. To study the influence of nanotube geometry on the interfacial properties of polyethylene/nanotube system, a range of nanotubes with different radii are considered. Besides, the influences of temperature and polyethylene chain length on the final conformation of polyethylene chain adsorbed on the nanotube surface are studied. It is shown that the polymer chain structures adsorbed on the armchair and zigzag single-walled carbon nanotubes are almost similar. Finally, systems containing a nanotube placed at the center of multiple polyethylene chains are studied. Long parallel patterns are observed in the final morphologies of multiple chains placed beside the single-walled carbon nanotube. © 2013 Elsevier B.V.
Publication Date: 2014
Nano (17937094)9(3)
In this research, mechanics of concentric ellipsoidal fullerenes inside open carbon nanocones (CNCs) is investigated. To this end, using continuum approximation in conjunction with Lennard-Jones (LJ) potential function, quadruple-integral expressions associated with van der Waals (vdW) potential energy and interaction force are first derived. For determination of these expressions, it is assumed that the fullerene molecule enters the open CNC through the small end or wide end. Thereafter, an efficient approach based on the differential quadrature (DQ) method is proposed to numerically evaluate the obtained quadruple integrals. The proposed method takes advantage of computing multidimensional integrals efficiently with using appropriate number of grid points. By introducing DQ-based operational matrices of differentiation and integration, the quadruple-integral expressions are estimated over their domains. Moreover, new semianalytical expressions are introduced in terms of triple integrals to evaluate vdW interactions. The validity and accuracy of the introduced numerical method are proved by comparing the results obtained through this method with ones achieved via the semianalytical expressions. The ease of implementation and quick answer of the demonstrated numerical solution enable us to comprehensively examine the effects of different geometrical parameters such as small end radius wide end radius and vertex angle of nanocone on the distributions of vdW potential energy and interaction force. The results reveal that the ellipsoidal fullerene undergoes an asymmetrical motion along the axis of open CNC. © 2014 World Scientific Publishing Company.
The structure of carbon nanotubes is recognized to be suitable for medical applications such as encapsulating drugs or genes with the aim of targeted deliveries. In this regard, knowing about the suction force exerted on a nonoscale object which is supposed to be sucked into a carbon nanotube, and whether the object is accepted by the carbon nanotube are important issues to be studied. In this chapter, considering the nanoscale object as a carbon nanotube, a new semi-analytical method is developed to determine the van der Waals interaction between two concentric single-walled carbon nanotubes. © 2014, IGI Global.
Publication Date: 2014
Shock and Vibration (10709622)2014
The vibrational behavior of single-walled carbon nanocones is studied using molecular structuralmethod and molecular dynamics simulations. In molecular structural approach, point mass and beam elements are employed to model the carbon atoms and the connecting covalent bonds, respectively. Single-walled carbon nanocones with different apex angles are considered. Besides, the vibrational behavior of nanocones under various types of boundary conditions is studied. Predicted natural frequencies are compared with the existing results in the literature and also with the ones obtained by molecular dynamics simulations. It is found that decreasing apex angle and the length of carbon nanocone results in an increase in the natural frequency. Comparing the vibrational behavior of single-walled carbon nanocones under different boundary conditions shows that the effect of end condition on the natural frequency is more prominent for nanocones with smaller apex angles. Copyright © 2014 R. Ansari et al.
Publication Date: 2014
Fibers and Polymers (12299197)15(6)pp. 1123-1128
The adsorption of poly(phenylacetylene), polystyrene sulfonate and polyvinyl pyrrolidone on the surface of the armchair and zigzag single-walled carbon nanotubes is studied by using molecular dynamics simulations. The wrapping process of polymer chains around the nanotubes is pursued graphically. It is shown that at 20ps, the polymer chains are adsorbed on the nanotube surface. The interaction energy between nanotubes and polymer chains is computed. The effect of nanotube diameter and temperature on the interaction energy is investigated. It is shown that increasing the nanotube diameter results in increasing the energy. However, the effect of temperature on the interaction energy is negligible. The radius of gyration of polymer chains is also computed. It is shown that nanotube diameter has an insignificant role in the radius of gyration of polymer chains. © 2014 The Korean Fiber Society and Springer Science+Business Media Dordrecht.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Sahmani, S. Publication Date: 2014
International Journal of Engineering Science (00207225)75pp. 1-10
A modified continuum model is developed to predict the postbuckling deflection of nanobeams incorporating the effect of surface stress. To have this problem in view, the classical Timoshenko beam theory in conjunction with the Gurtin-Murdoch elasticity theory is utilized to propose non-classical beam model taking surface stress effect into account. The geometrical nonlinearity is considered in the analysis using the von Karman assumption. By employing the principle of virtual work, the size-dependent governing differential equations and related boundary conditions are derived. On the basis of the shifted Chebyshev-Gauss-Lobatto grid points, the generalized differential quadrature (GDQ) method is adopted as an accurate, simple and computational efficient numerical solution to discretize the non-classical governing differential equations along with various end supports. Selected numerical results are worked out to demonstrate the nonlinear equilibrium paths of the postbuckling behavior of nanobeams corresponding to different values of beam thickness, buckling mode number, surface elastic constants, and various types of boundary conditions. © 2013 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Advances in Acoustics and Vibration (16876261)
A unified analytical approach is applied to investigate the vibrational behavior of grid-stiffened cylindrical shells with different boundary conditions. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of shell in order to obtain the equivalent stiffness parameters of the whole panel. Theoretical formulation is established based on Sanders' thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. A 3D finite element model is also built using ABAQUS software which takes into consideration the exact geometric configuration of the stiffeners and the shell. The achievements from the two types of analyses are compared with each other and good agreement has been obtained. The Influences of variations in shell geometrical parameters, boundary condition, and changes in the cross stiffeners angle on the natural frequencies are studied. The results obtained are novel and can be used as a benchmark for further studies. The simplicity and the capability of the present method are also discussed. © 2014 G. H. Rahimi et al.
Gholami, R.,
Darvizeh a., A.,
Ansari, R.,
Hosseinzadeh m., Publication Date: 2014
Meccanica (15729648)49(7)pp. 1679-1695
In this paper, a size-dependent first-order shear deformable shell model is developed based upon the modified strain gradient theory (MSGT) for the axial buckling analysis of functionally graded (FG) circular cylindrical microshells. It is assumed that the material properties of FG materials, which obey a simple power-law distribution, vary through the thickness direction. The principle of virtual work is utilized to formulate the governing equations and corresponding boundary conditions. Numerical results are presented for the axial buckling of FG circular cylindrical microshells subject to simply-supported end conditions and the effects of material length scale parameter, material property gradient index, length-to-radius ratio and circumferential mode number on the size-dependent critical buckling load are extensively studied. For comparison purpose, the critical buckling loads predicted by modified couple stress theory (MCST) and classical theory (CT) are also presented. Results show that the size effect plays an important role for lower values of dimensionless length scale parameter. Moreover, it is observed that the critical buckling loads obtained based on MSGT are greater than those obtained based on MCST and CT. © 2014 The Author(s).
Ansari, R.,
Norouzzadeh, A.,
Gholami, R.,
Faghih shojaei, M.,
Hosseinzadeh m., Publication Date: 2014
Physica E: Low-Dimensional Systems and Nanostructures (13869477)61pp. 148-157
The size-dependent nonlinear free vibration and instability of fluid-conveying single-walled boron nitride nanotubes (SWBNNTs) embedded in thermal environment are studied in this paper. The fluid-conveying SWBNNT is modeled as a Timoshenko beam by which the effects of transverse shear deformation and rotary inertia is taken into consideration. The modified strain gradient theory is used to capture the size effect. To consider the nonlinear effect, the geometric nonlinearity, based on von Kármáns assumption is introduced to develop the nonlinear governing equations of motion. By employing Hamiltons principle, the governing equations and associated boundary conditions are derived. Thereafter, a numerical solution procedure based on the generalized differential quadrature (GDQ) is introduced, according to which the nonlinear governing equations and the corresponding boundary conditions are discretized via the operational matrix of differentiation. The discretized equations are then solved analytically through the harmonic balance approach. Effects of different parameters including material length scale parameter, spring and damping constants of surrounding viscoelastic medium, and flow velocity on the nonlinear free vibration and instability of SWBNNTs are examined. © 2014 Elsevier B.V.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Rouhi h., H. Publication Date: 2014
Journal of Thermal Stresses (01495739)37(2)pp. 174-201
This article reports on the thermal instability of functionally graded (FG) annular microplates with different boundary conditions. The modified strain gradient elasticity theory is employed to capture size effects. The non-linear governing equations and boundary conditions are derived based on the first-order shear deformation theory (FSDT) and virtual displacements principle. The generalized differential quadrature technique is implemented so as to discretize. To obtain the critical buckling temperature, the set of linear discretized governing equations is solved as an eigenvalue problem. Also, the non-linear problem of thermal postbuckling is solved by the pseudo arc-length continuation method. The effects of boundary conditions, length scale parameter, and the variation of material through the thickness and geometrical properties on both critical buckling temperature and thermal postbuckling behavior are studied. Copyright © Taylor & Francis Group, LLC.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Darabi m.a., M.A. Publication Date: 2014
Latin American Journal of Solids and Structures (16797825)11(13)pp. 2351-2378
In this paper, the free vibration behavior of post-buckled functionally graded (FG) Mindlin rectangular microplates are described based on the modified couple stress theory (MCST). This theory enables the consideration of the size-effect through introducing material length scale parameters. The FG microplates made of a mixture of metal and ceramic are considered whose volume fraction of components is expressed by a power law function. By means of Hamilton’s principle, the nonlinear governing equations and associated boundary conditions are derived for FG microplates in the postbuckling domain. The governing equations and boundary conditions are then discretized by using the generalized differential quadrature (GDQ) method before solving numerically by the pseudo-arclength continuation technique. In the solution procedure, the postbuckling problem of microplates is investigated first. Afterwards, the free vibration of microplates around the buckled configuration is discussed. The effects of dimensionless length scale parameter, material gradient index and aspect ratio on the on the postbuckling path and frequency of FG microplates subject to arbitrary edge supports are thoroughly discussed. © 2014, Brazilian Association of Computational Mechanics. All rights reserved.
Ansari, R.,
Rouhi, S.,
Aryayi, M.,
Mirnezhad m., M. Publication Date: 2014
Acta Mechanica Solida Sinica (08949166)27(4)pp. 429-440
This paper is aimed to propose a three-dimensional model which would be used for investigation on the mechanical behavior of single-layered zinc oxide nanosheets. To develop this model, molecular mechanics is coupled with the density functional theory. Simulating the hexagonal lattices of nanosheets as a hexagonal mechanical structure composed of structural beam elements, the buckling behavior of zinc oxide nanosheets is studied. Effects of different parameters on the stability of armchair and zigzag nanosheets are examined. It is shown that the buckling forces of zigzag nanosheets are slightly greater than those of armchair ones. However, with increasing size of nanosheets the effect of atomic structure on the stability of nanosheets diminishes. By studying the effect of end conditions on the buckling behavior of nanosheets, it is shown the stability of nanosheets is affected significantly by boundary conditions.
Publication Date: 2014
Superlattices and Microstructures (10963677)72pp. 230-237
Importance of synthesizing graphene-substrate hybrid structure to open a band gap in graphene and apply them in novel nanoelectronic devices is undeniable. Graphene/hexagonal boron-nitride (h-BN) hybrid bilayer is an important type of these structures. The synthesized h-BN/graphene is found to have interesting electrical properties which is very sensitive to the change of the interlayer distance. This has encourages researchers to tune the energy and band gap of such structures. A change in the interlayer distance can also alter the mechanical properties, considerably, due to the variation of interaction energies. The current study is aimed to characterize the mechanical properties variation with interlayer distance change for h-BN/graphene hybrid bilayer structure. To this end, density functional theory calculations are employed within the generalized gradient approximation (GGA) framework. The results demonstrate that there are different possible equilibrium interlayer distances between layers related to two types of layer configuration, i.e. AA and AB. It is found that increasing the interlayer distance causes reduction of Young's modulus. Also, Young's modulus of hybrid structure is approximately between those of graphene/graphene and h-BN/h-BN bilayer structures and also lower than pristine monolayer graphene and graphite. Unlike the pure bilayer structures, Poisson's ratio of hybrid bilayer structure is found to be higher than those of pristine monolayer graphene and h-BN nanosheets. © 2014 Elsevier Ltd. All rights reserved.
Publication Date: 2014
Acta Astronautica (00945765)105(2)pp. 417-427
This investigation deals with the free vibration characteristics of circular higher-order shear deformable nanoplates around the postbuckling configuration incorporating surface effects. Using the Gurtin-Murdoch elasticity theory, a size-dependent higher-order shear deformable plate model is developed which takes account all surface effects including surface elasticity, surface stress and surface density. Geometrical nonlinearity is considered based on the von Karman type nonlinear strain-displacement relationships. Also, in order to satisfy the balance conditions between bulk and surfaces of nanoplate, it is assumed that the normal stress is distributed cubically through the thickness of nanoplate. Hamilton's principle is utilized to derive non-classical governing differential equations of motion and related boundary conditions. Afterwards, an efficient numerical methodology based on a generalized differential quadrature (GDQ) method is employed to solve numerically the problem so as to discretize the governing partial differential equations along various edge supports using Chebyshev-Gauss-Lobatto grid points and pseudo arc-length continuation technique. A comparison between the results of present non-classical model and those of the classical plate theory is conducted. It is demonstrated that in contrast to the prebuckling domain, for a specified value of axial load in the postbuckling domain, increasing the plate thickness leads to higher frequencies. © 2014 IAA. Published by Elsevier Ltd. All rights reserved.
Sahmani, S.,
Bahrami m., ,
Aghdam, M.M.,
Ansari, R. Publication Date: 2014
Composite Structures (02638223)118(1)pp. 149-158
Given the high surface to volume ratio, the nonlinear forced vibration behavior of third-order shear deformable nanobeams in the presence of the both effects of surface stress and that of surface inertia is investigated. Gurtin-Murdoch elasticity theory is utilized within the framework of third-order shear deformation beam theory to develop a novel non-classical beam model to incorporate surface effects into the forced vibration analysis of nanobeams. A cubic variation through the thickness of nanobeam is considered for the normal stress component of the bulk in order to satisfy the surface equilibrium equations. Hamilton's principle is used to derive size-dependent nonlinear governing differential equations of motion. The equations are solved numerically using generalized differential quadrature method with an iterative algorithm on the basis of shifted Chebyshev-Gauss-Lobatto grid points. Subsequently, based on the Galerkin's technique, the set of nonlinear partial differential equations are reduced into a timevarying set of ordinary differential equations of Duffing type. At the end, the pseudo arc-length method is employed to solve the set of nonlinear equations of the time domain. It is observed that by increasing the beam thickness, surface effects on the nonlinear forced vibration behavior of nanobeam diminish which leads to increasing the deviation from the linear response. © 2014 Elsevier Ltd.
Publication Date: 2014
Composite Structures (02638223)116(1)pp. 552-561
The prime aim of the current study is to predict the free vibration behavior of third-order shear deformable nanobeams in the vicinity of postbuckling configuration and in the presence of surface effects which includes surface elasticity, residual surface stress and surface inertia. To accomplish this end, Gurtin-Murdoch elasticity theory within the framework of third-order shear deformation beam theory is employed. In order to satisfy the balance conditions between the bulk and surfaces of nanobeam, a cubic distribution is considered for the normal stress through the thickness. By using Hamilton's principle, the non-classical governing differential equations of motion including von Karman geometric nonlinearity are derived. After using generalized differential quadrature (GDQ) method to discretize the governing equations on the basis of Chebyshev-Gauss-Lobatto grid points, the pseudo-arc length continuation technique is utilized to solve the eigenvalue problem. The natural frequencies of nanobeam corresponding to the both prebuckling and postbuckling domains are obtained for various buckling mode shapes based on the numerical solution strategy. It is demonstrated that in the prebuckling domain of the first vibration mode shape, increasing of beam thickness leads to lower natural frequency for all types of boundary conditions, but this behavior becomes reverse in the postbuckling domain. © 2014 Elsevier Ltd.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Sahmani, S. Publication Date: 2014
Composite Structures (02638223)112(1)pp. 358-367
Postbuckling behavior of circular nanoplates and their free vibration characteristics in the vicinity of postbuckling domain are investigated with the consideration of surface stress effect. To this end, Mindlin's plate theory in conjunction with the Gurtin-Murdoch elasticity theory is utilized to derive nonlinear equations of motion incorporating geometric nonlinearity and surface stress effect. On the basis of generalized differential quadrature (GDQ) method, the non-classical governing differential equations are discretized along simply-supported and clamped boundary conditions and are then parameterized and solved using the pseudo arc-length continuation method. The postbuckling configurations of axisymmetric circular nanoplates are obtained as a function of applied axial compressive load based on the static analysis. Afterward, on the basis of dynamic analysis, the natural frequencies and associated mode-shapes of circular nanoplates corresponding to both prebuckling and postbuckling domains are predicted including surface stress effect. It is revealed that by decreasing the magnitude of thickness, the surface stress effect on the postbuckling configurations of nanoplates becomes more prominent. Moreover, the effect of surface stress may shift the postbuckling domain to higher or lower applied axial loads, depending on the magnitude and sign of surface elastic constants. These anticipations are the same corresponding to various edge supports. © 2014 Elsevier Ltd.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Sahmani, S. Publication Date: 2014
Acta Astronautica (00945765)102pp. 140-150
The prime aim of the current study is to investigate the pull-in instability characteristics of hydrostatically and electrostatically actuated circular nanoplates including surface stress effect. Gurtin-Murdoch elasticity theory is incorporated into the classical plate theory to develop a non-classical plate model considering surface stress effect. The governing size-dependent differential equations of a hydrostatically and electrostatically actuated circular nanoplate are discretized along with simply-supported and clamped boundary conditions using the generalized differential quadrature (GDQ) method. Selected numerical results are given to indicate the capability of the present size-dependent plate model for predicting the normalized pull-in voltage and pull-in hydrostatic pressure of nanoplates with inclusion surface stress effect. It is found that the pull-in phenomenon of actuated nanoplate is strongly size-dependent. The results indicate that surface stress effect plays a more significant role in the pull-in phenomenon of nanoplates of lower thicknesses. This investigation might be helpful to evaluate the mechanical characteristics of electrostatical actuators. © 2014 IAA.
Publication Date: 2014
Journal of Analytical Chemistry (16083199)69(9)pp. 875-882
Polyaniline (PANI) chemically coated on polyvinylchloride (PVC) membrane based on a neutral carrier 7,16-didecyl-1,4,10,13-tetraoxa-7,16- diazacyclooctadecane (Kryptofix 22 DD) as the active component has been developed for determination of pH values ranging from pH 0.1-1. Effect of experimental parameters such as membrane composition, nature and amount of plasticizer, lipophilic additives and thickness of PANI film on the potential response of the pH electrode was investigated. The electrode has an apparent Nernstian response slope of 54.5 ± 0.4 mV/pH (at 20°C). The equilibrium water content of the electrode was determined in pure water and NaCl solution (I = 0.1 mol/kg). The electrode had low electric resistance, good potential stability and reproducibility (±1.5 mV, n = 10). It had a rapid potential response to changes of pH (15 s). The excellent performance in terms of linearity, stability and fast response makes this device suitable for pH measurements in highly acidic media. © 2014 Pleiades Publishing, Ltd.
Publication Date: 2014
Current Applied Physics (15671739)14(8)pp. 1072-1077
Based on molecular dynamics simulations, the mechanical properties and buckling behavior of boron-nitride nanotubes under the action of torsional load are investigated. According to the results, the torsional properties of a boron-nitride nanotube are higher than those of its carbon counterpart. The effect of geometrical parameters on these parameters is also investigated. It is observed that by increasing the radius of nanotubes of the same length, unlike the critical shear strain, the critical torque considerably increases. The effect of chirality is also found to be negligible in the cases of critical shear strain and buckling mode, unlike the critical torque. © 2014 Elsevier B.V. All rights reserved.
Ansari, R.,
Ashrafi m.a., ,
Pourashraf t., ,
Hemmatnezhad m., M. Publication Date: 2014
Shock and Vibration (10709622)2014
On the basis of modified couple stress theory, the postbuckling behavior of the Euler-Bernoulli microscale FG beams is investigated by means of an exact solution method. The modified couple stress theory as a nonclassical continuum theory is capable of interpreting the size dependencies which become more significant at micro/nanoscales. The Von-Karman type nonlinear strain-displacement relationships are employed. The thermal effects are also incorporated into formulation. The governing equation of motion and the corresponding boundary conditions are derived using Hamilton's principle. The material properties are assumed to be graded in the thickness direction according to the power-law distribution. A closed-form solution is obtained for the postbuckling deformation which is beyond the critical buckling load. To study the vibrations taking place in the vicinity of a buckled equilibrium position, the linear vibration problem is exactly solved around the first three buckled configurations. The natural frequencies of the lowest vibration modes around each of the first three buckled configurations are obtained. The influences of power-law exponent, boundary condition, length scale parameter, and thermal environment changes on the static deflection and free vibration frequencies are studied. A comparison is also made between the present results and those obtained via the classical beam theories. Copyright © 2014 R. Ansari et al.
Faghih shojaei, M.,
Ansari, R.,
Mohammadi v., V.,
Rouhi h., H. Publication Date: 2014
Journal of Computational and Nonlinear Dynamics (15551423)9(2)
In this article, a numerical solution methodology is presented to study the postbuckling configurations and free vibrations of Timoshenko beams undergoing postbuckling. The effect of geometrical imperfection is taken into account, and the analysis is carried out for different types of boundary conditions. Based on Hamilton's principle, the governing equations and corresponding boundary conditions are derived. After introducing a set of differential matrix operators that is used to discretize the governing equations and boundary conditions, the pseudo-arc length continuation method is applied to solve the postbuckling problem. Then, the problem of free vibration around the buckled configurations is solved as an eigenvalue problem using the solution obtained from the nonlinear problem in the previous step. This study shows that, when the axial load in the postbuckling domain increases, the vibration mode shape of buckled beam corresponding to the fundamental frequency may change. Another finding that can be of great technical interest is that, for all types of boundary conditions and in both prebuckling and postbuckling domains, the natural frequency of imperfect beam is higher than that of ideal beam. Also, it is observed that, by increasing the axial load, the natural frequency of both ideal and imperfect beams decreases in the prebuckling domain, while it increases in the postbuckling domain. The reduction of natural frequency in the transition area from the prebuckling domain to the postbuckling domain is due to the severe instability of the structure under the axial load. © 2014 by ASME.
Publication Date: 2014
Shock and Vibration (10709622)2014
The vibration behavior of piezoelectric microbeams is studied on the basis of the modified couple stress theory. The governing equations of motion and boundary conditions for the Euler-Bernoulli and Timoshenko beam models are derived using Hamilton's principle. By the exact solution of the governing equations, an expression for natural frequencies of microbeams with simply supported boundary conditions is obtained. Numerical results for both beam models are presented and the effects of piezoelectricity and length scale parameter are illustrated. It is found that the influences of piezoelectricity and size effects are more prominent when the length of microbeams decreases. A comparison between two beam models also reveals that the Euler-Bernoulli beam model tends to overestimate the natural frequencies of microbeams as compared to its Timoshenko counterpart. © 2014 R. Ansari et al.
Publication Date: 2014
Mechanics Research Communications (00936413)56pp. 130-135
The purpose of this study is to analytically investigate the free vibration of carbon nanocones (CNCs) under different types of boundary conditions. The Donnell shell theory and nonlocal elasticity are used to derive the governing equations of motion. The analytical Galerkin method together with beam mode shapes as weighting functions is employed to solve the problem. Making use of the beam modal functions enables us to examine the role of boundary condition in the vibrational behavior of CNCs. The effects of boundary conditions, semivertex angle and nonlocal parameter on the response of CNCs are explored. © 2014 Elsevier Ltd. All rights reserved.
Ansari, R.,
Mahmoudinezhad e., E.,
Alipour a., A.,
Hosseinzadeh m., Publication Date: 2013
Journal of Computational and Theoretical Nanoscience (15461955)10(9)pp. 2209-2215
This paper aims at exploring the characteristics of a single methane molecule encapsulated in semiinfinite single-walled carbon nanotubes. On the basis of Lennard-Jones potential function along with the continuum approximation and applied mathematics, single integrals are presented to formulate the van der Waals interaction energy and suction energy between a single methane molecule and a carbon nanotube. The preferred position and orientation of methane with regard to the nanotube axis has been fully investigated for different nanotube radii. To this end, it is assumed that the whole molecule rotates in all directions inside the nanotube. It is found that for certain radii of nanotubes in which the suction energy imparted to methane is negative, the whole methane molecule is symmetric with respect to the tube axis when it is inside the carbon nanotube. But, when the suction energy has positive values, as the tube radius increases the methane molecule gets closer to the wall of nanotube and finally locates near its wall in the form of a downward tripod. Furthermore, the optimum nanotube radius which gives rise to maximum suction energy has been calculated. The results obtained in this study can be conducted as means of further investigations for methane storage in carbon nanotubes. © 2013 American Scientific Publishers. All rights reserved.
Publication Date: 2013
Communications in Nonlinear Science and Numerical Simulation (10075704)18(3)pp. 769-784
Amongst possible new nanomechanical devices created based on carbon nanostructures, high-frequency nanoscale oscillators, or the so-called gigahertz oscillators have attracted much attention. In this paper, the oscillatory behavior of spherical fullerenes inside carbon nanotubes is thoroughly investigated. To this end, the continuum approximation together with Lennard-Jones potential is used to evaluate the van der Waals potential energy and interaction force. The equation of motion is directly solved based on the actual force distribution between the two nanostructures, without any simplifying assumption. A semi-analytical expression is obtained for the oscillation frequency into which the effect of initial conditions is incorporated. Thereafter, this newly derived expression is utilized in order to present a comprehensive study on the effects of different system variables such as geometrical parameters and initial conditions on the oscillation frequency. Based upon these studies, some new features of such oscillations have been revealed. © 2012 Elsevier B.V.
Publication Date: 2013
Carbon (00086223)55pp. 44-52
The G-band mode frequency of single-walled carbon nanotubes (SWCNTs) is studied on the basis of a new equivalent spring model. To this end, the out of plane angle variation energy is incorporated into the model in order to obtain more precise results. Furthermore, a new analytical expression is introduced to evaluate the force constant corresponding to this kind of energy. For SWCNTs of different chiralities, the vibrational frequencies corresponding to axial and circumferential modes are determined. Also, the effects of diameter and chirality on the behavior of these frequencies are completely investigated. For a given diameter, it is found that the frequency of axial mode is always higher than that of the circumferential mode, regardless of the tube chirality. This finding may shed light on some contradictory reports in the literature. It is also found that the G-band mode frequency increases as the tube diameter gets larger, approaching the asymptotic value of 1592 cm-1 for large nanotubes. Additionally, the results indicate that the G-band mode frequency is slightly affected by the tube chirality. © 2012 Elsevier Ltd. All rights reserved.
Ansari, R.,
Hosseini, K.,
Darvizeh a., A.,
Daneshian b., Publication Date: 2013
Applied Mathematics and Computation (18735649)219(10)pp. 4977-4991
A non-classical model for the free vibrations of nanobeams accounting for surface stress effects is developed in this study. Based on Gurtin-Murdoch elasticity theory, the influence of surface stress is incorporated into the Euler-Bernoulli beam theory. A compact finite difference method (CFDM) of sixth order is employed for discretizing the non-classical governing differential equation to obtain the natural frequencies of nanobeams subject to different boundary conditions. To check the validity of the present numerical solution, based on an exact solution, an explicit formula for the fundamental frequency of simply-supported nanobeams is obtained. Good agreement between the results of exact and numerical solutions is achieved, confirming the validity and accuracy of the present numerical scheme. The comparison between the results generated by CFDM with those obtained by the conventional finite difference method (FDM) further reveals the advantages of the compact method over its classical counterpart. The influences of beam thickness, surface density, surface residual stress, surface elastic constants, and boundary conditions on the natural frequencies of nanobeams are also investigated. It is indicated that the effect of surface stress on the vibrational response of a nanobeam is dependent on its aspect ratio and thickness. © 2012 Elsevier Inc. All rights reserved.
Publication Date: 2013
Composite Structures (02638223)100pp. 323-331
In this article, a nonlocal Flügge shell model incorporating interatomic potentials is developed to study the buckling behavior of an axially loaded single-walled carbon nanotube (SWCNT). The theory incorporates the relations resulting from establishing a linkage between the strain energy induced in the continuum and the potential energy stored in the atomic bonds, using the so-called Cauchy-Born rule, into the constitutive relations of Eringen's nonlocal elasticity theory. An exact solution is implemented to solve the set of coupled field equations. In comparison to classical models, the present model provides a much better fit to molecular dynamics (MDs) simulations results and proposes the appropriate value of nonlocal parameter for SWCNTs with simply-supported end conditions. Furthermore, the model developed herein is independent of the nanotube wall thickness and Young's modulus whose values are scattered in the literature. © 2013 Elsevier Ltd.
Publication Date: 2013
Meccanica (15729648)48(6)pp. 1355-1367
In this paper, an analytical solution based on a molecular mechanics model is developed to evaluate the mechanical properties of armchair and zigzag single-walled carbon nanotubes (SWCNTs). Adopting the Perdew-Burke-Ernzerhof (PBE) exchange correlation, the density functional theory (DFT) calculations are performed within the generalized gradient approximation (GGA) to evaluate force constants used in the molecular mechanics model. After that, based on the principle of molecular mechanics, explicit expressions are proposed to obtain surface Young's modulus, Poisson's ratio and surface shear modulus of SWCNTs corresponding to both types of armchair and zigzag chiralities. Based on the DFT calculations, it is found that the flexural rigidity of graphene is independent of the type of chirality which indicates the isotropic characteristic of this material. Moreover, it is observed that for the all values of nanotube diameter, surface Young's modulus for the armchair nanotube is more than that of zigzag nanotube. It is shown that the trend predicted by the present model is in good agreement with other models which confirms the validity as well as the accuracy of the present molecular mechanics model. © 2012 Springer Science+Business Media Dordrecht.
Publication Date: 2013
International Journal for Computational Methods in Engineering Science and Mechanics (15502295)14(1)pp. 40-44
In this work, on the basis of a nonlocal elastic plate model, the free vibration of monolayer graphene sheets is studied. An explicit formula for estimating the fundamental frequencies of a monolayer graphene sheet from its static deflection under a uniformly distributed load is obtained. The main advantage of this formula is in its simplicity and accuracy, enabling quick calibration of the nonlocal parameter using molecular dynamics results. The influences of the nonlocality and boundary conditions on the free vibration of monolayer graphene sheets are also investigated. © 2013 Copyright Taylor and Francis Group, LLC.
Publication Date: 2013
Phosphorus, Sulfur and Silicon and the Related Elements (10426507)188(10)pp. 1394-1401
Methyl phosphonic dichloride (MPDC) and dimethyl methyl phosphonate (DMMP) are two important organophosphorus compounds used in the preparation of many toxic organophosphorus compounds such as nerve agents. This paper deals with the application of polyaniline coated on a glass slide surface as a sensor for the detection of some of the stimulant nerve agents such as MPDC and DMMP. The sensing behavior of polyaniline films toward MPDC and DMMP vapors via electrical conductivity changes of the polymer film using the standard four-point probe technique was investigated. The effects of the chemical concentration and the polymer thickness on the conductivity and conductivity stability of the polymer were also studied. The vapors of nerve agent stimulants affect the PANi film by the p-doping mechanism and lead to an increase in the conductivity of the polymer. The response times of the PANi film to MPDC and DMMP vapors are very fast, and the conductivity of the polymer increases with the increase in the concentration of the samples. © 2013 Copyright Taylor and Francis Group, LLC.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Sahmani, S. Publication Date: 2013
International Journal for Multiscale Computational Engineering (15431649)11(4)pp. 389-405
According to the theory of thermal elasticity mechanics, thermal buckling characteristics of microbeams made of functionally graded materials (FGMs) are presented. The material properties of FGM microbeams are considered to be graded in the thickness direction on the basis of the Mori-Tanaka homogenization scheme. Based on the strain gradient elasticity theory, a size-dependent elastic beam model within the framework of the Timoshenko beam theory is developed containing three internal material length scale parameters to interpret size effect. By using Hamilton's principle, the higher-order governing differential equations of motion and related boundary conditions are derived. Afterward, the generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations along various end supports and then the critical thermal buckling loads of FGM microbeams with three commonly used sets of boundary conditions are determined. The applicability of the present nonclassical beam model to predict thermal buckling behavior of FGM microbeams is established via various numerical results. It is found that the difference between thermal buckling of microbeams subjected to the uniform, linear, and nonlinear temperature distributions is more significant corresponding to the higher values of material property gradient index. © 2013 by Begell House, Inc.
Ansari, R.,
Malakpour s., S.,
Faghihnasiri m., ,
Ajori, S. Publication Date: 2013
Journal of Nanotechnology in Engineering and Medicine (19492944)4(3)
Recently, synthesized inorganic two-dimensional monolayer nanostructures are very promising to be applied in electronic devices. This article explores the mechanical properties of a monolayer molybdenum disulfide (MoS2) including Young's bulk and shear moduli and Poisson's ratio by applying density functional theory (DFT) calculation based on the generalized gradient approximation (GGA). The results demonstrate that the elastic properties of MoS2 nanosheets are less than those of graphene and hexagonal boron-nitride (h-BN) nanosheets. However, their Poisson's ratio is found to be higher than that of graphene and h-BN nanosheet. It is also observed that due to the special structure of MoS2, the thickness of nanosheet changes when the axial strain is applied. Copyright © 2013 by ASME.
Publication Date: 2013
Mechanics Research Communications (00936413)47pp. 18-23
The mechanics of a C60 fullerene oscillating in a carbon nanotube (CNT) is investigated using continuum approximation and molecular dynamics (MD) simulations. The Lennard-Jones and Tersoff-Brenner potential functions are employed in this study; the former in the continuum model and both in the MD simulations. The results from the continuum model agree well with those from discrete model when nanotubes are assumed rigid. The flexibility effect of nanotubes on the oscillatory behavior is also examined using the MD simulations. It is shown the oscillation frequency slightly decreases during the simulation for flexible tubes, while it remains constant for rigid ones. © 2012 Elsevier Ltd.
Publication Date: 2013
Journal of Nanomechanics and Micromechanics (21535434)3(1)pp. 9-15
In the past decade, gigahertz nano-oscillators have attracted much attention. Of particular interest are nested carbon nanotubes with telescopic movements. Recent work on this type of oscillator has led to new results and new insights into such oscillatory systems. That work has also led to the introduction of a special initial velocity at which the oscillatory frequency is unique and independent of the core length. This finding stimulates the idea of developing a nondimensional formulism for the oscillatory frequency of such systems, which is the prime objective of the work undertaken herein. The results generated are in nondimensional form and cover a wide range of system parameters. Utilizing the new formulas derived, different aspects of the oscillatory frequency are studied and discussed. The generality of the formulation presented in this paper provides a better perception of such systems and helps in designing the system parameters. © 2013 American Society of Civil Engineers.
Sahmani, S.,
Ansari, R.,
Gholami, R.,
Darvizeh a., A. Publication Date: 2013
Composites Part B: Engineering (13598368)51pp. 44-53
Size-dependent dynamic stability response of higher-order shear deformable cylindrical microshells made of functionally graded materials (FGMs) and subjected to simply supported end supports is investigated. Material properties of the microshells vary in the thickness direction according to the Mori-Tanaka scheme. The modified couple stress elasticity theory in conjunction with the classical higher-order shear deformation shell theory is utilized to develop non-classical shell model containing additional internal length scale parameter to interpret size effect. The differential equations of motion and boundary conditions are derived by using Hamilton's principle. The governing equations are then written in the form of Mathieu-Hill equations and then Bolotin's method is employed to determine the instability regions. Selected numerical results are given to indicate the influences of internal length scale parameter, material property gradient index, static load factor and axial wave number on the dynamic stability behavior of FGM microshells. It is found that the width of the instability region for an FGM microshell increases with the decrease of the value of dimensionless length scale parameter. Moreover, it is shown that the classical shell model has an overestimated prediction for the width of instability region corresponding to the FGM microshells especially with lower values of material property gradient index. © 2013 Elsevier Ltd.
Darvizeh a., A.,
Darvizeh m., M.,
Ansari, R.,
Meshkinzar, A. Publication Date: 2013
Thin-Walled Structures (02638231)71pp. 81-90
In this paper, analytical and experimental investigations are performed on the energy absorption characteristics of circumferentially grooved thick-walled circular tubes filled with low density and very low strength polyurethane foam typical of cushioning material. Thick-walled grooved tubes filled with low density foam are prepared for experiments. The results are also compared with the ones for the geometrically identical empty tubes. Employing the Taguchi method for designing the geometrical parameters of the specimens leads to a suitable range of groove length-to-wall thickness ratios to be covered. Based on the concept of energy dissipation through the circumferential plastic hinges during the successive folding of the specimens, an analytical approach is proposed. In addition, the amount of energy dissipated due to the interaction between tube metal and foam material is expressed by a conventional semi-empirical equation. A new constant, Cav, for low strength foam material is found by fitting the experimental data. The modified analytical model is in reasonable agreement with the experiments. This may indicate the validity of the proposed analytical model. The obtained results show that grooved thick-walled tubes filled with low strength foams can offer favorable energy absorption capacity and stability. Euler buckling is prevented due to the grooves and specific energy absorption is increased approximately twice that of the empty tubes. Structural effectiveness is increased nearly two times that of the empty tubes. © 2013 Elsevier Ltd.
Publication Date: 2013
Journal Of Theoretical And Applied Physics (22517227)7(1)
The present paper is concerned with the free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium and based on Eringen's nonlocal elasticity theory. The effects of the transverse shear deformation and rotary inertia are included according to the Timoshenko beam theory. The governing equations of motion which are coupled with each other via the van der Waals interlayer forces have been derived using Hamilton's principle. The thermal effect is also incorporated into the formulation. Using the statically exact beam element with displacement fields based on the first order shear deformation theory, the finite element method is employed to discretize the coupled governing equations which are then solved to find the natural frequencies. The effects of the small scale parameter, boundary conditions, thermal effect, changes in material constant of the surrounding elastic medium, and geometric parameters on the vibration characteristics are investigated. Furthermore, our analysis includes nonlocal double-walled carbon nanotubes with different boundary conditions between inner and outer tubes which seem to be scarcely considered in the literature, and the corresponding given results for this case can be considered as a benchmark for further studies. Comparison of the present numerical results with those from the open literature shows an excellent agreement. © 2013, Hemmatnezhad and Ansari; licensee Springer.
Publication Date: 2013
Mechanics and Industry (22577777)14(5)pp. 367-382
In this paper, an analytical solution is developed for free vibration analysis of conical fiber metal shells. In order to find constitutive relations, the assumptions of thins hells are used and the governing equations are based on Love's theory. The Galerkin method is employed to solve the governing equations in which beam functions are used to approximate the mode shapes. Using beam functions enables us to assess the effects of different boundary conditions on the frequency response of the shells. Numerical comparisons of the present and previously published results confirm the accuracy of the current approach. Additionally, the influences of geometrical parameters and embedding aluminum plies in different layers of the structure on natural frequency of the conical shells with various boundary conditions are investigated. It can be observed that the more the aluminum plies are used, the greater natural frequency of the structure will be reached. Except the clamped-free boundary conditions, the results also indicate that if the aluminum plies are embedded in the top and bottom layers of the laminate, natural frequency reaches its maximum value. © 2013 AFM, EDP Sciences.
Publication Date: 2013
Applied Mathematical Modelling (0307904X)37(18-19)pp. 8495-8504
The large-amplitude free vibration analysis of functionally graded beams is investigated by means of a finite element formulation. The Von-Karman type nonlinear strain-displacement relationships are employed where the ends of the beam are constrained to move axially. The effects of the transverse shear deformation and rotary inertia are included based upon the Timoshenko beam theory. The material properties are assumed to be graded in the thickness direction according to the power-law distribution. A statically exact beam element which devoid the shear locking effect with displacement fields based on the first order shear deformation theory is used to study the geometric nonlinear effects on the vibrational characteristics of functionally graded beams. The finite element method is employed to discretize the nonlinear governing equations, which are then solved by the direct numerical integration technique in order to obtain the nonlinear vibration frequencies of functionally graded beams with different boundary conditions. The influences of power-law exponent, vibration amplitude, beam geometrical parameters and end supports on the free vibration frequencies are studied. The present numerical results compare very well with the results available from the literature where possible. Some new results for the nonlinear natural frequencies are presented in both tabular and graphical forms which can be used for future references. © 2013 .
Publication Date: 2013
Materials Science and Engineering: A (09215093)561pp. 34-39
This paper explores the mechanical properties of perfect and defective γ-graphyne, a lattice of sp-sp2-hybridized carbon atoms, as a graphene allotrope using the classical molecular dynamics simulations. These simulations are carried out on the basis of the Tersoff-Brenner potential function with the Nose-Hoover thermostat algorithm in canonical ensemble. In this examination, the influences of vacancy defects on mechanical properties of γ-graphyne such as Young's modulus, ultimate stress and strain and Poisson's ratio are studied. The results demonstrated lower strength and stiffness of this new graphene allotrope than those of graphene. Also, it is observed that in comparison with the mapped vacancy defects, the random vacancy ones are more responsible for the change in the mechanical properties of γ-graphyne. Furthermore, the fracture pattern of defective γ-graphyne is considered. © 2012 Elsevier B.V.
Publication Date: 2013
Superlattices and Microstructures (10963677)53(1)pp. 223-231
The mechanical properties of multilayer boron nitride (BN) with various stacking orders are characterized by ab initio calculations. Based on the density functional theory (DFT), the values of elastic constants of AB bilayer, ABA and ABC trilayer and graphite-like BN in the harmonic elastic deformation range are revealed. DFT calculations are performed in the context of generalized gradient approximation (GGA) and by adopting the Perdew-Burke-Ernzerhof (PBE) exchange correlation. This investigation shows that Young's modulus and Poisson's ratio of multilayer BN are lower than those of monolayer BN. A comparative study on the mechanical properties of multilayer BN with different stacking orders is presented. It is indicated that the mechanical properties of multilayer BN are dependent on the number of layers and their stacking order. © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2013
Journal of Mechanical Science and Technology (1738494X)27(11)pp. 3363-3370
This study investigates the mechanical characteristics of single-walled carbon nanotubes (CNTs) inside open single-walled carbon nanocones (CNCs). New semi-analytical expressions are presented to evaluate van der Waals (vdW) interactions between CNTs and open CNCs. Continuum approximation, along with the the Lennard-Jones (LJ) potential function, is used in this study. The effects of geometrical parameters on alterations in vdW potential energy and the interaction force are extensively examined for the concentric CNT-open CNC configuration. The CNT is assumed to enter the nanocone either through the small end or the wide end of the cone. The preferred position of the CNT with respect to the nanocone axis is fully investigated for various geometrical parameters. The optimum nanotube radius minimizing the total potential energy of the concentric configuration is determined for different radii of the small end of the cone. The examined configuration generates asymmetric oscillation; thus, the system constitutes a nano-oscillator. © 2013 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
This review aims to describe the art of handling animplemented molecular dynamics(MD) simulation program, for the special case of carbon nanotubes. The procedure presented in this review can be used in order to investigate different computational experiments on carbon nanotubes via MD simulations. © 2011 Nova Science Publishers, Inc. All rights reserved.
Publication Date: 2013
Applied Mathematics and Mechanics (English Edition) (02534827)34(10)pp. 1187-1200
By the atomistic and continuum finite element models, the free vibration behavior of single-walled carbon nanotubes (SWCNTs) is studied. In the atomistic finite element model, the bonds and atoms are modeled by the beam and point mass elements, respectively. The molecular mechanics is linked to structural mechanics to determine the elastic properties of the mentioned beam elements. In the continuum finite element approach, by neglecting the discrete nature of the atomic structure of the nanotubes, they are modeled with shell elements. By both models, the natural frequencies of SWCNTs are computed, and the effects of the geometrical parameters, the atomic structure, and the boundary conditions are investigated. The accuracy of the utilized methods is verified in comparison with molecular dynamic simulations. The molecular structural model leads to more reliable results, especially for lower aspect ratios. The present analysis provides valuable information about application of continuum models in the investigation of the mechanical behaviors of nanotubes. © 2013 Shanghai University and Springer-Verlag Berlin Heidelberg.
Publication Date: 2013
JVC/Journal of Vibration and Control (10775463)19(1)pp. 75-85
The large-amplitude free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium is investigated by means of a finite element formulation. A double-beam model is utilized in which the governing equations of layers are coupled with each other via the van der Waals interlayer forces. The Von Karman type nonlinear strain-displacement relationships are employed where the ends of the nanotube are constrained to move axially. The effects of the transverse shear deformation and rotary inertia are included based upon the Timoshenko beam theory. A superconvergent beam element which devoid the shear locking effect with displacement fields based on the first order shear deformation theory is used to study the geometric nonlinear effects on the vibrational characteristics of these beam-modeled nanotubes. In this kind of beam element, the interpolating functions are obtained using the exact solution of the static analysis of the beam. The finite element method is employed to discretize the nonlinear governing equations, which are then solved by the direct numerical integration technique to obtain the nonlinear vibration frequencies of double-walled carbon nanotubes with different boundary conditions. The effects of material constant of the surrounding elastic medium and the geometric parameters on the vibrational behavior are investigated. For a double-walled carbon nanotube with different boundary conditions between inner and outer tubes, the nonlinear frequencies are obtained apparently for the first time. The present numerical results are validated by comparing the linear and nonlinear frequencies of double-walled carbon nanotubes with those available in the literature where possible. This comparison illustrates that the present scheme yields very accurate results in predicting the nonlinear frequencies. © The Author(s) 2011 Reprints and permissions: sagepub.co.uk/ journalsPermissions.nav.
Publication Date: 2013
Journal of Applied Mechanics (00218936)80(2)
In this paper, the vibrational behavior of double-walled carbon nanotubes (DWCNTs) is studied by a nonlocal elastic shell model. The nonlocal continuum model accounting for the small scale effects encompasses its classical continuum counterpart as a particular case. Based upon the constitutive equations of nonlocal elasticity, the displacement field equations coupled by van der Waals forces are derived. The set of governing equations of motion are then numerically solved by a novel method emerged from incorporating the radial point interpolation approximation within the framework of the generalized differential quadrature method. The present analysis provides the possibility of considering different combinations of layerwise boundary conditions. The influences of small scale factor, layerwise boundary conditions and geometrical parameters on the mechanical behavior of DWCNTs are fully investigated. Explicit expressions for the nonlocal frequencies of DWCNTs with all edges simply supported are also analytically obtained by a nonlocal elastic beam model. Some new intertube resonant frequencies and the corresponding noncoaxial vibrational modes are identified due to incorporating circumferential modes into the shell model. A shift in noncoaxial mode numbers, not predictable by the beam model, is also observed when the radius of DWCNTs is varied. The results generated also provide valuable information concerning the applicability of the beam model and new noncoaxial modes affecting the physical properties of nested nanotubes. Copyright © 2013 by ASME.
Publication Date: 2013
Composite Structures (02638223)95pp. 430-442
The prime aim of the present study is to predict the free vibration behavior of microplates made of functionally graded materials (FGMs). The material properties of FGM microplates are assumed to be varied across the thickness of the microplates according to the Mori-Tanaka homogenization technique. On the basis of strain gradient elasticity theory, a non-classical higher-order shear deformable plate model containing three material length scale parameters is developed which can effectively capture the size dependencies. By using Hamilton's principle, the size-dependent governing differential equations of motion and associated boundary conditions are derived. To evaluate the natural frequencies of FGM microplates, a Navier-type closed-form solution is carried out in which the generalized displacements are stated as multiplication of undetermined functions with known trigonometric functions so as to satisfy identically the simply-supported boundary conditions at all edges. Selected numerical results are presented to reveal the influences of dimensionless length scale parameter, material property gradient index and aspect ratio on the free vibration characteristics of FGM microplates. It is found that by approaching the thickness of microplates to the value of internal material length scale parameter, the natural frequency increases considerably. © 2012 Elsevier Ltd.
Publication Date: 2013
Acta Mechanica Sinica/Lixue Xuebao (16143116)29(4)pp. 622-632
Electromechanical carbon nanothermometers are devices that work based on the interactions and relative motions of double-walled carbon nanotubes (DWCNTs). In this paper, the mechanics of carbon nanotubes (CNTs) constituting two well-known configurations for nanothermometer, namely shuttle configuration and telescope configuration are fully investigated. Lennard-Jones (LJ) potential function along with the continuum approximation is employed to investigate van derWaals (vdW) interactions between the interacting entities. Accordingly, semi-analytical expressions in terms of single integrals are obtained for vdW interactions. Acceptance condition and suction energy are studied for the shuttle configuration. In addition, a universal potential energy is presented for the shuttle configuration consisting of two finite CNTs. Also, for the telescope configuration, extensive studies are performed on the distributions of potential energy and interaction force for various radii and lengths of CNTs. It is found that these geometrical parameters have a considerable effect on the potential energy. © 2013 The Chinese Society of Theoretical and Applied Mechanics; Institute of Mechanics, Chinese Academy of Sciences and Springer-Verlag Berlin Heidelberg.
Publication Date: 2013
Journal of Vibration and Acoustics (15288927)135(5)
This paper aims to present a thorough investigation into the mechanics of a C60 fullerene oscillating within the center of a carbon nanotube bundle. To model this nanoscale oscillator, a continuum approximation is used along with a classical Lennard-Jones potential function. Accordingly, new semianalytical expressions are given in terms of single integrals to evaluate van der Waals potential energy and interaction force between the two nanostructures. Neglecting the frictional effects and using the actual van der Waals force distribution, the equation of motion is directly solved. Furthermore, a new semianalytical formula is derived from the energy equation to determine the precise oscillation frequency. This new frequency formula has the advantage of incorporating the effects of initial conditions and geometrical parameters. This enables us to conduct a comprehensive study of the effects of significant system parameters on the oscillatory behavior. Based upon this study, the variation of oscillation frequency with geometrical parameters (length of tubes or number of tubes in bundle) and initial energy (potential energy plus kinetic energy) is shown. Copyright © 2013 by ASME.
Ansari, R.,
Mohammadi v., V.,
Faghih shojaei, M.,
Gholami, R.,
Sahmani, S. Publication Date: 2013
Composites Part B: Engineering (13598368)55pp. 240-246
In the present paper, an attempt is made to numerically investigate the postbuckling response of nanobeams with the consideration of the surface stress effect. To accomplish this, the Gurtin-Murdoch elasticity theory is exploited to incorporate surface stress effect into the classical Euler-Bernoulli beam theory. The size-dependent governing differential equations are derived and discretized along with various end supports by employing the principle of virtual work and the generalized differential quadrature (GDQ) method. Newton's method is applied to solve the discretized nonlinear equations with the aid of an auxiliary normalizing equation. After solving the governing equations linearly, to obtain each eigenpair in the nonlinear model, the linear response is used as the initial value in Newton's method. Selected numerical results are given to show the surface stress effect on the postbuckling characteristics of nanobeams. It is found that by increasing the thickness of nanobeams, the postbuckling equilibrium path obtained by the developed non-classical beam model tends to the one predicted by the classical beam theory and this anticipation is the same for all selected boundary conditions. © 2013 Elsevier Ltd. All rights reserved.
Publication Date: 2013
Applied Mathematical Modelling (0307904X)37(12-13)pp. 7338-7351
The biaxial buckling behavior of single-layered graphene sheets (SLGSs) is studied in the present work. To consider the size-effects in the analysis, Eringen's nonlocal elasticity equations are incorporated into the different types of plate theory namely as classical plate theory (CLPT), first-order shear deformation theory (FSDT), and higher-order shear deformation theory (HSDT). An exact solution is conducted to obtain the critical biaxial buckling loads of simply-supported square and rectangular SLGSs with various values of side-length and nonlocal parameter corresponding to each type of nonlocal plate model. Then, molecular dynamics (MD) simulations are performed for a series of armchair and zigzag SLGSs with different side-lengths, the results of which are matched with those obtained by the nonlocal plate models to extract the appropriate values of nonlocal parameter relevant to each type of nonlocal elastic plate model and chirality. It is found that the present nonlocal plate models with their proposed proper values of nonlocal parameter have an excellent capability to predict the biaxial buckling response of SLGSs. © 2013 Elsevier Inc.
Publication Date: 2013
Applied Physics A: Materials Science and Processing (14320630)113(1)pp. 145-153
In the present investigation, the axial buckling and post-buckling configurations of single-walled carbon nanotubes (SWCNTs) are studied including the thermal environment effect. For this purpose, Eringen's nonlocal elasticity continuum theory is implemented into the classical Euler-Bernoulli beam theory to represent the SWC-NTs as a nonlocal elastic beam model. A closed-form analytical solution is carried out to analyze the static response of SWCNTs in their post-buckling state in which the axial buckling load is assumed to be beyond the critical axial buckling load. Common sets of boundary conditions, named simply supported-simply supported (SS-SS), clamped-clamped (C-C), and clamped-simply supported (C-SS), are considered in the investigation. Selected numerical results are given to represent the variation of the carbon nanotube's mid-span deflection with the applied axial load corresponding to various nonlocal parameters, length-to-diameter aspect ratios, temperature changes, and end supports. Moreover, a comparison between the post-buckling behaviors of SWCNTs at low- and high-temperature environments is presented. It is found that the size effect leads to a decrease of the axial buckling load especially for SWC-NTs with C-C boundary conditions. Also, it is revealed that the value of the temperature change plays different roles in the post-buckling response of SWCNTs at low- and high-temperature environments. © Springer-Verlag Berlin Heidelberg 2012.
Publication Date: 2013
Composite Structures (02638223)95pp. 88-94
The present article is concerned with the applicability of an elastic plate theory incorporating the interatomic potentials for biaxial buckling and vibration analysis of single-layer graphene sheets (SLGSs) and accounting for the small scale effects. For this purpose, the relations based on the interatomic potential and Eringen's nonlocal equation are incorporated into the classical plate theory. The former relations are obtained through constructing a linkage between the strain energy induced in the continuum and the potential energy stored in the atomic bonds using the Cauchy-Born rule. The nonlocal governing equations of motion for buckling and vibration of the SLGSs with simply-supported boundary conditions are exactly solved and explicit formulae for the frequencies and critical buckling load are derived. The results generated from the present model are compared with those of molecular dynamic (MD) simulations and the other previously reported ones and a good agreement is achieved. The model developed herein is independent of Young's modulus which is of an ambiguous definition in the literature. It is found that the small scale effect on buckling and vibrational response of the SLGSs is profound and it becomes more prominent when the side length is low. © 2012 Elsevier Ltd.
Publication Date: 2013
Astronomy and Astrophysics (00046361)552
Aims. Stars twinkle because their light propagates through the atmosphere. The same phenomenon is expected on a longer time scale when the light of remote stars crosses an interstellar turbulent molecular cloud, but it has never been observed at optical wavelengths. The aim of the study described in this paper is to fully simulate the scintillation process, starting from the molecular cloud description as a fractal object, ending with the simulations of fluctuating stellar light curves. Methods. Fast Fourier transforms are first used to simulate fractal clouds. Then, the illumination pattern resulting from the crossing of background star light through these refractive clouds is calculated from a Fresnel integral that also uses fast Fourier transform techniques. Regularisation procedure and computing limitations are discussed, along with the effect of spatial and temporal coherency (source size and wavelength passband). Results. We quantify the expected modulation index of stellar light curves as a function of the turbulence strength-characterised by the diffraction radius Rdiff-and the projected source size, introduce the timing aspects, and establish connections between the light curve observables and the refractive cloud. We extend our discussion to clouds with different structure functions from Kolmogorov-type turbulence. Conclusions. Our study confirms that current telescopes of ∼4 m with fast-readout, wide-field detectors have the capability of discovering the first interstellar optical scintillation effects. We also show that this effect should be unambiguously distinguished from any other type of variability through the observation of desynchronised light curves, simultaneously measured by two distant telescopes. © 2013 ESO.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Sahmani, S. Publication Date: 2013
Composite Structures (02638223)100pp. 385-397
In the present investigation, the bending, buckling and free vibration responses of Timoshenko microbeams made of functionally graded materials (FGMs) are studied. To take size effect into account, the most general strain gradient elasticity theory is incorporated into the classical Timoshenko beam theory to develop a size-dependent beam model containing five additional material length scale parameters. The model accommodates the beam models based on the strain gradient theory (SGT), the modified strain gradient theory (MSGT), the modified couple stress theory (MCST) and the classical theory (CT) as special cases. By using Hamilton's principle, the governing equations and corresponding boundary conditions are derived. Afterward, the governing equations and associated boundary conditions are discretized by employing generalized differential quadrature (GDQ) method. Selected numerical results are given to demonstrate the size-dependent mechanical characteristics of FGM microbeams. Moreover, a comparison between the various beam models on the basis of MCST, MSGT and CT are presented. It is observed that the critical buckling loads and natural frequencies predicted by the beam models based on MSGT and CT are the maximum and minimum values, respectively. By increasing the value of length scale parameter, the deflection curve of FGM microbeam tends to the curve obtained by CT. © 2013.
Publication Date: 2013
Applied Mathematical Modelling (0307904X)37(23)pp. 9499-9515
Presented herein is the prediction of buckling behavior of size-dependent microbeams made of functionally graded materials (FGMs) including thermal environment effect. To this purpose, strain gradient elasticity theory is incorporated into the classical third-order shear deformation beam theory to develop a non-classical beam model which contains three additional internal material length scale parameters to consider the effects of size dependencies. The higher-order governing differential equations are derived on the basis of Hamilton's principle. Afterward, the size-dependent differential equations and related boundary conditions are discretized along with commonly used end supports by employing generalized differential quadrature (GDQ) method. A parametric study is carried out to demonstrate the influences of the dimensionless length scale parameter, material property gradient index, temperature change, length-to-thickness aspect ratio and end supports on the buckling characteristics of FGM microbeams. It is revealed that temperature change plays more important role in the buckling behavior of FGM microbeams with higher values of dimensionless length scale parameter. © 2013 Elsevier Inc.
Mohammadi v., V.,
Ansari, R.,
Faghih shojaei, M.,
Gholami, R.,
Sahmani, S. Publication Date: 2013
Nonlinear Dynamics (0924090X)73(3)pp. 1515-1526
In the present study, the dynamic pull-in instability and free vibration of circular microplates subjected to combined hydrostatic and electrostatic forces are investigated. To take size effects into account, the strain gradient elasticity theory is incorporated into the Kirchhoff plate theory to develop a nonclassical plate model including three internal material length scale parameters. By using Hamilton's principle, the higher-order governing equation and the corresponding boundary conditions are obtained. Afterward, a generalized differential quadrature (GDQ) method is employed to discritize the governing differential equations along with simply supported and clamped edge supports. To evaluate the pull-in voltage and vibration frequencies of actuated microplates, the hydrostatic-electrostatic actuation is assumed to be calculated by neglecting the fringing field effects and utilizing the parallel plate approximation. Also, a comparison between the pull-in voltages predicted by the strain gradient theory and the degenerated ones is presented. It is revealed that increasing the dimensionless internal length scale parameter or decreasing the applied hydrostatic pressures leads to higher values of the pull-in voltage. Moreover, it is found that the value of pull-in hydrostatic pressure decreases corresponding to higher dimensionless internal length scale parameters and applied voltages. © 2013 Springer Science+Business Media Dordrecht.
Ansari, R.,
Gholami, R.,
Mohammadi v., V.,
Faghih shojaei, M. Publication Date: 2013
Journal of Computational and Nonlinear Dynamics (15551423)8(2)
This article is concerned with the development of a distributed model based on the modified strain gradient elasticity theory (MSGT), which enables us to investigate the size-dependent pull-in instability of circular microplates subjected to the uniform hydrostatic and nonuniform electrostatic actuations. The model developed herein accommodates models based on the classical theory (CT) and modified couple stress theory (MCST), when all or two material length scale parameters are set equal to zero, respectively. On the basis of Hamilton's principle, the higher-order nonlinear governing equation and corresponding boundary conditions are obtained. In order to linearize the nonlinear equation, a step-by-step linearization scheme is implemented, and then the linear governing equation is discretized along with different boundary conditions using the generalized differential quadrature (GDQ) method. In the case of CT, it is indicated that the presented results are in good agreement with the existing data in the literature. Effects of the length scale parameters, hydrostatic and electrostatic pressures, and various boundary conditions on the pull-in voltage and pull-in hydrostatic pressure of circular microplates are thoroughly investigated. Moreover, the results generated from the MSGT are compared with those predicted by MCST and CT. It is shown that the difference between the results from the MSGT and those of MCST and CT is considerable when the thickness of the circular microplate is on the order of length scale parameter. © 2013 American Society of Mechanical Engineers.
Publication Date: 2013
Archive of Applied Mechanics (14320681)83(10)pp. 1439-1449
On the basis of the modified strain gradient elasticity theory, the free vibration characteristics of curved microbeams made of functionally graded materials (FGMs) whose material properties vary in the thickness direction are investigated. A size-dependent first-order shear deformation beam model is developed containing three internal material length scale parameters to incorporate small-scale effect. Through Hamilton's principle, the higher-order governing equations of motion and boundary conditions are derived. Natural frequencies of FGM curved microbeams corresponding to different mode numbers are evaluated for over a wide range of material property gradient index, dimensionless length scale parameter and aspect ratio. Moreover, the results obtained via the present non-classical first-order shear deformation beam model are compared with those of degenerated beam models based on the modified couple stress and the classical theories. It is found that the difference between the natural frequencies predicted by the various beam models is more significant for lower values of dimensionless length scale parameter and higher values of mode number. © 2013 Springer-Verlag Berlin Heidelberg.
Publication Date: 2013
Scientia Iranica (23453605)20(6)pp. 2314-2322
A hybrid continuum-atomistic approach is developed to describe the buckling behavior of axially loaded chiral boron nitride nanotubes (BNNTs) with different boundary conditions. The set of the stability equations is established based on the nonlocal elasticity of Eringen and Donnell shell theory. The molecular mechanics are implemented in conjunction with the Density Functional Theory (DFT) to obtain the effective in-plane and bending stiffnesses and Poisson's ratio of BNNTs. The problem is analytically solved by the use of a direct variational method. The influences of geometrical parameters, nonlocal parameters and boundary conditions on the critical buckling loads are thoroughly explored. © 2013 Sharif University of Technology. All rights reserved.
Ansari, R.,
Rouhi, S.,
Mirnezhad m., M.,
Aryayi, M. Publication Date: 2013
Physica E: Low-Dimensional Systems and Nanostructures (13869477)53pp. 22-28
The buckling behavior of single-layered silicon carbide nanosheets (SLSiCNSs) is investigated by employing an atomistic finite element model. Preserving the discrete nature of nanosheets, the beam elements are used to model the Si-C bounds. The effects of aspect ratio and boundary conditions on the stability of zigzag and armchair SLSiCNSs have been studied. Based on the results, it is observed that the buckling forces of small sheets are strongly size-dependent. However, the size-dependent behavior will diminish for larger sheets. Comparing the buckling force of armchair and zigzag nanosheets with same geometries and boundary conditions shows that the buckling force is independent of chirality. © 2013 Elsevier B.V. All rights reserved.
Ansari, R.,
Malakpour s., S.,
Faghihnasiri m., ,
Ajori, S. Publication Date: 2013
Superlattices and Microstructures (10963677)64pp. 220-226
Carbon nanotubes (CNTs) with their extraordinary properties have been recognized as one of the most promising nanomaterials ever discovered. This paper presents a density functional theory (DFT) study on the structural and elastic properties of CNTs with different chiralities containing Fe atoms (Fe-CNT). In the first step, the effects of Fe encapsulation on the radius and energy of CNTs are investigated. It is observed that, unlike armchair CNTs, the equilibrium radius of zigzag CNTs increases after Fe encapsulating. Different positions for the Fe atom inside CNTs are considered. The results reveal that depending on the size and chirality of CNTs, several possible stable sites for the Fe atom inside CNTs exist. In the next step, for the most stable Fe-CNT structure, Young's modulus is computed and it is seen that the encapsulation of Fe atoms reduces the stiffness of CNTs. © 2013 Elsevier Ltd. All rights reserved.
Ansari, R.,
Rouhi, S.,
Mirnezhad m., M.,
Sadeghiyeh f., Publication Date: 2013
Applied Physics A: Materials Science and Processing (14320630)112(3)pp. 767-774
The free vibration and axial buckling of achiral zinc oxide nanotubes (ZnONTs) are studied in this paper based on a three-dimensional finite-element model in which bonds are modeled using beam elements and mass elements are placed at the joints of beams instead of atoms. To determine the mechanical properties of the nanotubes, a linkage is established between molecular mechanics and density functional theory. The fundamental frequency and critical buckling load of ZnONTs with different geometries, chiralities and boundary conditions are calculated. It is shown that zigzag nanotubes are more stable than armchair ones. Investigating the effect of aspect ratio on the critical force shows that longer nanotubes are less stable. Also, it is indicated that increasing the length of the nanotubes will result in decreasing the frequency. Moreover, as the aspect ratio increases, the effect of end conditions diminishes. © 2013 Springer-Verlag Berlin Heidelberg.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Sahmani, S. Publication Date: 2013
Journal of Applied Mechanics (00218936)80(2)
The classical continuum theory cannot be directly used to describe the behavior of nanostructures because of their size-dependent attribute. Surface stress effect is one of the most important size dependencies of structures at this submicron size, which is due to the high surface to volume ratio of nanoscale domain. In the present study, the nonclassical governing differential equation together with corresponding boundary conditions are derived using Hamilton's principle, into which the surface energies are incorporated through the Gurtin-Murdoch elasticity theory. The model developed herein contains intrinsic length scales to take the size effect into account and is used to analyze the free vibration response of circular nanoplates including surface stress effect. The generalized differential quadrature (GDQ) method is employed to discretize the governing size-dependent differential equation along with simply supported and clamped boundary conditions. The classical and nonclassical frequencies of circular nanoplates with various edge supports and thicknesses are calculated and are compared to each other. It is found that the influence of surface stress can be different for various circumferential mode numbers, boundary conditions, plate thicknesses, and surface elastic constants. © 2013 American Society of Mechanical Engineers.
Publication Date: 2013
Journal of Thermal Stresses (01495739)36(2)pp. 152-159
In this article, based on the oscillations of atoms due to the thermal effects (i.e., thermal phonons), Young's modulus of a hexagonal boron nitride sheet at different environment temperatures is investigated. To this end, the density functional theory (DFT) and quasi-harmonic approximation (QHA) are applied to calculate the energies of electrons and phonons, respectively, and then to obtain the total energy of the system. Unlike graphene, Young's modulus of boron nitride sheets tends to considerably increase with the increase of temperature to a specific value about 800 K. For the temperatures greater than 800 K, variation of Young's modulus with temperature is not considerable so that it can be neglected at high temperatures. It is also discerned that when temperature is high, the effect of phonon energy on Young's modulus is negligible. © 2013 Copyright Taylor and Francis Group, LLC.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Darabi m.a., M.A. Publication Date: 2013
Journal of Thermal Stresses (01495739)36(5)pp. 446-465
This article is aimed at developing a nonclassical Mindlin rectangular functionally graded material (FGM) microplate based on the strain gradient theory (SGT) to study the thermal buckling behavior of microplates with different boundary conditions. This theory comprises material length scale parameters to interpret size effects. The developed model encompasses classical and modified couple stress Mindlin microplate models, if all the material length scale parameters or two of them are taken to be zero, respectively. The Mindlin rectangular FGM microplate is considered to be made of a mixture of metal and ceramic of which the volume fraction is described through a power low function. According to Hamilton's principle and the generalized differential quadrature (GDQ) method, the stability equations and associated boundary conditions are obtained and discretized, respectively. Current formulations provide a possibility to have all types of boundary conditions which herein, FGM microplates with three commonly used boundary conditions are considered. Three different types of thermal loads including uniform, linear and nonlinear temperature rises along the thickness of FGM microplates are considered. The dimensionless critical buckling temperature difference (DCBTD) predicted by SGT is compared with that of modified couple stress theory (CST) and classical theory (CT) which it is found that CST and CT underestimate the DCBTD. Also, effects of the boundary conditions, length scale parameter and material gradient index of FGM microplates on the DCBTD are judiciously investigated. © 2013 Taylor and Francis Group, LLC.
Ansari, R.,
Shahabodini a., A.,
Rouhi h., H.,
Alipour a., A. Publication Date: 2013
Journal of Thermal Stresses (01495739)36(1)pp. 56-70
Described in the current study is the thermal buckling behavior of multi-walled carbon nanotubes (WCNTs) via a nonlocal atomistic-based shell model. The model including the effects of small-scale length and the van der Waals (vdW) forces between adjacent nanotubes is established through the incorporation of the interatomic potential into the nonlocal Flügge shell theory. This model links the strain energy density induced in the continuum to Eringen's nonlocal constitutive relations. The set of coupled field equations are analytically solved for two types of temperature distribution. The present model is of a distinguishing feature which is its independence from the widely scattered values of Young's modulus and the effective wall thickness of carbon nanotubes. © 2013 Taylor & Francis Group, LLC.
Ansari, R.,
Faghih shojaei, M.,
Gholami, R.,
Mohammadi v., V.,
Darabi m.a., M.A. Publication Date: 2013
International Journal of Non-Linear Mechanics (00207462)50pp. 127-135
The thermal postbuckling characteristics of microbeams made of functionally graded materials (FGMs) undergoing thermal loads are investigated based on the modified strain gradient theory (MSGT). The volume fraction of the ceramic and metal phases of FGM microbeams is expressed by using a power low function. The non-classical beam model presented herein is capable of interpreting size effects through introducing material length scale parameters and encompasses the modified couple stress theory (MCST) and classical theory (CT). Based on the non-linear Timoshenko beam theory and the principle of virtual work, the stability equations and associated boundary conditions are derived and are then solved through the generalized differential quadrature (GDQ) method in conjunction with a direct approach without linearization. The influences of the material gradient index, length scale parameter, and boundary conditions on the thermal postbuckling behavior of FGM microbeams are comprehensively investigated. Also, this study compares the results obtained from the MSGT with those from CT. The effect of geometrical imperfection on the buckling deformation of microbeams in prebuckled and postbuckled states is discussed. © 2012 Elsevier Ltd.
Publication Date: 2013
Journal of Vibration and Acoustics (15288927)135(5)
In the current study, the torsional vibration of carbon nanotubes is examined using the strain gradient theory and molecular dynamic simulations. The model developed based on this gradient theory enables us to interpret size effect through introducing material length scale parameters. The model accommodates the modified couple stress and classical models when two or all material length scale parameters are set to zero, respectively. Using Hamilton's principle, the governing equation and higher-order boundary conditions of carbon nanotubes are obtained. The generalized differential quadrature method is utilized to discretize the governing differential equation of the present model along with two boundary conditions. Then, molecular dynamic simulations are performed for a series of carbon nanotubes with different aspect ratios and boundary conditions, the results of which are matched with those of the present strain gradient model to extract the appropriate value of the length scale parameter. It is found that the present model with properly calibrated value of length scale parameter has a good capability to predict the torsional vibration behavior of carbon nanotubes. Copyright © 2013 by ASME.
Publication Date: 2013
JVC/Journal of Vibration and Control (10775463)19(5)pp. 708-719
This article deals with the development and use of different gradient beam theories in order to predict the vibrational behavior of single-walled carbon nanotubes (SWCNTs). To address the problem of free vibration, the Euler-Bernoulli and Timoshenko beam theories in conjunction with the gradient elasticity theories including stress, strain and combined strain/inertia are implemented. The generalized differential quadrature method is employed to numerically solve the problem which can treat various boundary conditions. The results generated from the present gradient models are compared with those from molecular dynamics simulations as a benchmark of good accuracy and the proper values of small length scales used in the gradient models are proposed. This study shows prominent differences between various gradient models when the nanotube becomes very short (for aspect ratios of approximately lower than six). It is indicated that applying the strain gradient elasticity by incorporation of inertia gradients yields more reliable results especially for shorter length SWCNTs on account of two small-scale factors related to the inertia and strain gradients. Moreover, since with the reduction in the aspect ratio of nanotubes the effects of boundary conditions become dominant, a discussion is given to investigate the influence of end conditions on the vibrational characteristics of SWCNTs. © 2012 The Author(s).
Publication Date: 2013
Physica E: Low-Dimensional Systems and Nanostructures (13869477)47pp. 12-16
The free vibration characteristics of circular and square single-layered graphene sheets (SLGSs) are investigated by developing a finite element formulation based on an accurate spring mass model. According to the present atomistic structural model, nodes are defined at the atom locations and suitable three-dimensional spring-type elements are employed to connect these nodes which are representing interatomic interactions. Natural frequencies and their associated vibration modes are obtained for SLGSs of different geometries. Molecular dynamics simulations are also conducted to validate the results obtained from the finite element model developed herein and excellent agreement has been found. It is shown that in the case of rectangular SLGSs, the frequency will be independent of area when the width becomes very small. © 2012 Elsevier B.V. All rights reserved.
Publication Date: 2013
Iranian Journal Of Science And Technology, Transactions Of Mechanical Engineering (22286187)37(M2)pp. 91-105
This article describes an investigation into the free vibration of double-walled carbon nanotubes (DWCNTs) using a nonlocal elastic shell model. Eringen)s nonlocal elasticity is implemented to incorporate the scale effect into the Donnell shell model. Also, the van der Waals interaction between the inner and outer nanotubes is taken into account. A new numerical solution method from incorporating the radial point interpolation approximation within the framework of the generalized differential quadrature (GDQ) method is developed to solve the problem. DWCNTs with arbitrary layerwise boundary conditions are considered in this paper. It is shown that applying the local Donnell shell model leads to overestimated results and one must recourse to the nonlocal version to reduce the relative error. Also, this work reveals that in contrast to the beam model, the present nonlocal elastic shell model is capable of predicting some new non-coaxial inter-tube resonances in studying the vibrational response of DWCNTs. © Shiraz University.
Hosseini, K.,
Biazar j., ,
Ansari, R.,
Gholamin p., Publication Date: 2012
Mathematical Methods in the Applied Sciences (10991476)35(9)pp. 993-999
Different analytic methods have been proposed to solve differential equations, so far. In this paper, a novel analytic method that efficiently solves ODEs is presented. This method requires only the calculation of the first Adomian polynomial, namely A 0, and does not need to solve the functional equation in each iteration, as well as provides less computational work than other existing methods. Some important ordinary differential equations including the Lane-Emden equation of index m, the logistic nonlinear differential equation, and the Riccati equation are considered to illustrate the efficiency of the proposed algorithm. Copyright © 2012 John Wiley & Sons, Ltd.
Publication Date: 2012
Journal of Mechanics of Materials and Structures (15593959)7(2)pp. 195-211
Developed herein is a comprehensive geometrically nonlinear size-dependent microscale Timoshenko beam model based on strain gradient and von Kármán theories. The nonlinear governing equations and the corresponding boundary conditions are derived from employing Hamilton's principle. A simply supported microbeam is considered to delineate the nonlinear size-dependent free vibration behavior of the presented model. Utilizing the harmonic balance method, the solution for free vibration is presented analytically. The influence of the geometric parameters, Poisson's ratio, and material length-scale parameters on the linear frequency and nonlinear frequency ratio are thoroughly investigated. The results obtained from the present model are compared, in special cases, with those of the linear strain gradient theory, linear and nonlinear modified couple stress theory, and linear and nonlinear classical models; excellent agreement is found. It is concluded that the nonlinear natural frequency and nonlinear frequency ratio predicted by strain gradient theory are more precise than those from the other theories mentioned, especially for shorter beams. © 2012 by Mathematical Sciences Publishers.
Mahmoudinezhad e., E.,
Ansari, R.,
Basti a., A.,
Hemmatnezhad m., M. Publication Date: 2012
Computational Materials Science (09270256)62pp. 6-11
An accurate spring-mass model, in the context of a three-dimensional finite element formulation, is developed for estimating Young's and shear modulus of single-walled carbon nanotubes (SWCNTs). Lumped mass elements are placed at the atom locations and appropriate spring-type elements are defined as interconnections between the atoms in order to simulate the inter-atomic interactions. Based on the variation of the Brenner potential function, a simple way of computing the force constants used in the model developed is proposed. The obtained results for Young's and shear modulus of SWCNTs for various kinds are graphically illustrated. Further, the influences of changes in the nanotube radius on the mechanical behavior are examined. The numerical results show good agreement with other published results in the literature. © 2012 Elsevier B.V. All rights reserved.
Kazemi e., E.,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2012
Acta Mechanica (16196937)223(10)pp. 2225-2242
The paper is focused on the elastic buckling behavior of piezocomposite elliptical cylindrical shell finite element formulation. The formulation is based on the shear deformation theory, and the serendipity quadrilateral eight-node element is used to study the elastic behavior of elliptical cylindrical shells. The straindisplacement relations are accurately accounted for in the formulation. The contributions of work done by the applied load are also incorporated. A constant gain displacement control algorithm coupling the direct and inverse piezoelectric effect is applied to provide active control of composite non-circular shells in a selfmonitoring and self-controlling system. The governing equations obtained using the principle of minimum potential energy are solved through an eigenvalue approach. The influences of elliptical cross-sectional parameter and displacement feedback gain (G d) values on the critical buckling loads of elliptical cylindrical shells are examined. © 2012 Springer-Verlag.
Publication Date: 2012
Journal of Engineering Materials and Technology (00944289)134(1)
In the current work, the vibration characteristics of single-walled carbon nanotubes (SWCNTs) under different boundary conditions are investigated. A nonlocal elastic shell model is utilized, which accounts for the small scale effects and encompasses its classical continuum counterpart as a particular case. The variational form of the Flugge type equations is constructed to which the analytical Rayleigh-Ritz method is applied. Comprehensive results are attained for the resonant frequencies of vibrating SWCNTs. The significance of the small size effects on the resonant frequencies of SWCNTs is shown to be dependent on the geometric parameters of nanotubes. The effectiveness of the present analytical solution is assessed by the molecular dynamics simulations as a benchmark of good accuracy. It is found that, in contrast to the chirality, the boundary conditions have a significant effect on the appropriate values of nonlocal parameter. © 2012 American Society of Mechanical Engineers.
Publication Date: 2012
Physica E: Low-Dimensional Systems and Nanostructures (13869477)44(4)pp. 764-772
In this article, an atomistic model is developed to study the buckling and vibration characteristics of single-layered graphene sheets (SLGSs). By treating SLGSs as spaceframe structures, in which the discrete nature of graphene sheets is preserved, they are modeled using three-dimensional elastic beam elements for the bonds. The elastic moduli of the beam elements are determined via a linkage between molecular mechanics and structural mechanics. Based on this model, the critical compressive forces and fundamental natural frequencies of single-layered graphene sheets with different boundary conditions and geometries are obtained and then compared. It is indicated that the compressive buckling force decreases when the graphene sheet aspect ratio increases. At low aspect ratios, the increase of aspect ratios will result in a significant decrease in the critical buckling load. It is also indicated that increasing aspect ratio at a given side length results in the convergence of buckling envelops associated with armchair and zigzag graphene sheets. The influence of boundary conditions will be studied for different geometries. It will be shown that the influence of boundary conditions is not significant for sufficiently large SLGSs. © 2011 Elsevier B.V. All rights reserved.
Ansari, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Gholami, R.,
Darabi m.a., M.A. Publication Date: 2012
Journal of Mechanics of Materials and Structures (15593959)7(10)pp. 931-949
Presented herein is a comprehensive study on the buckling and postbuckling analysis of microbeams made of functionally graded materials (FGMs) based on the modified strain gradient theory. The present model is developed in the skeleton of the Timoshenko beam theory and the von Karman geometric nonlinearity, and enables one to consider size effects through introducing material length scale parameters. Also, the current model can be reduced to the modified couple stress and classical models if two or all material length scale parameters are set equal to zero, respectively. Utilizing a power law function, the volume fraction of the ceramic and metal phases of the functionally graded microbeam is expressed. The stability equations and corresponding boundary conditions are derived using Hamilton's principle and then solved through the generalized differential quadrature (GDQ) method in conjunction with a direct approach without linearization. The effects of the length scale parameter, slenderness ratio, material gradient index and boundary conditions on the buckling and postbuckling behavior of microbeams are carefully studied. Furthermore, the non-dimensional critical axial load of microbeams predicted by modified strain gradient and classical theories for the first three postbuckling modes is investigated and it is observed that the classical theory underestimates the non-dimensional critical axial load, especially at higher postbuckling modes. In addition, the influence of imperfections on the deflection of microbeams in prebuckled and postbuckled states is discussed.
Publication Date: 2012
Applied Mathematics and Mechanics (English Edition) (02534827)33(10)pp. 1287-1300
The behavior of a water molecule entering carbon nanotubes (CNTs) is studied. The Lennard-Jones potential function together with the continuum approximation is used to obtain the van der Waals interaction between a single-walled CNT (SWCNT) and a single water molecule. Three orientations are chosen for the water molecule as the center of mass is on the axis of nanotube. Extensive studies on the variations of force, energy, and velocity distributions are performed by varying the nanotube radius and the orientations of the water molecule. The force and energy distributions are validated by those obtained from molecular dynamics (MD) simulations. The acceptance radius of the nanotube for sucking the water molecule inside is derived, in which the limit of the radius is specified so that the nanotube is favorable to absorb the water molecule. The velocities of a single water molecule entering CNTs are calculated and the maximum entrance and the interior velocity for different orientations are assigned and compared. © Shanghai University and Springer-Verlag.
Publication Date: 2012
Journal of Pressure Vessel Technology (00949930)134(6)pp. 61202-10
The elastic analysis of two different kinds of radially heterogeneous pressure vessels is conducted in this paper. As a first kind of heterogeneous pressure vessels, a multilayered pipe with different material properties in different layers is considered. Another kind of heterogeneous pressure vessels is a thick hollow cylinder made of functionally graded material (FGM). On the basis of the finite difference method, the timedependent deformation, strain and stress distributions of both kinds of heterogeneous pipes are obtained under the different kinds of thermomechanical loadings. In this investigation, it is assumed that the pressure and temperature are symmetrical about the axis of the cylinder. Also, the material properties are considered to be independent of temperature. Results obtained from the present method are compared with the existing data. © 2012 by ASME.
Mirnezhad m., M.,
Modarresi m., ,
Ansari, R.,
Roknabadi, M.R. Publication Date: 2012
Journal of Thermal Stresses (01495739)35(10)pp. 913-920
The temperature dependence of the thermo-mechanical behavior of materials is of great importance in many engineering applications where the precise properties of materials over an extended temperature range are needed. The objective of this work is to present a density functional study to predict the temperature variation of Young's modulus of graphene. To this end, the energies of phonons as well as thermodynamic functions are calculated from phonon calculations via the quasi-harmonic approximation. It is observed that with the increase of strain the phonon energy decreases. Also, by increasing temperature up to a special value which is around 400K, Young's modulus decreases appreciably. For the temperatures higher than 400K, Young's modulus decreases with a lower rate and tends to be constant at high temperatures. The results obtained are in a good agreement with the experimental data previously reported in the literature. © 2012 Copyright Taylor and Francis Group, LLC.
Publication Date: 2012
Journal of Applied Physics (10897550)111(1)
Size- and chirality-dependent mechanical properties of single-walled zinc oxide nanotubes (ZnONTs) under four different states of hydrogen adsorption have been investigated in this paper. A molecular mechanics model is developed to derive analytical expressions for surface Young's modulus and Poisson's ratio of chiral hydrogenated ZnONTs (H-ZnONTs). On the basis of quantum mechanics, density functional theory (DFT) is utilized to obtain the force constants of molecular mechanics theory. Also, the values of surface Young's modulus, bending stiffness, Poisson's ratio, and atomic structure of a hydrogenated zinc oxide (H-ZnO) sheet associated with the four positions of adsorption are determined via the DFT calculations. The related results indicate that the bending stiffness of a H-ZnO sheet is chirality-independent. The present analysis provides the possibility of considering nanotubes with different types of chirality. It is indicated that, for all positions of hydrogen adsorption, the values of surface Young's modulus for armchair H-ZnONTs are higher than those of zigzag H-ZnONTs and the results of chiral H-ZnONTs are between the results of armchair and zigzag nanotubes. Also, the maximum stability happens when the hydrogen atoms are adsorbed on zinc and oxygen atoms at the two opposite sides of a ZnO sheet. © 2012 American Institute of Physics.
Publication Date: 2012
Journal of Mathematical Analysis and Applications (10960813)387(2)pp. 807-814
In recent years, many approaches have been utilized for finding the exact solutions of nonlinear systems of partial differential equations. In this paper, the first integral method introduced by Feng is adopted for solving some important nonlinear systems of partial differential equations, including, KdV, Kaup-Boussinesq and Wu-Zhang systems, analytically. By means of this method, some exact solutions for these systems of equations are formally obtained. The results obtained confirm that the proposed method is an efficient technique for analytic treatment of a wide variety of nonlinear systems of partial differential equations. © 2011 Elsevier Inc.
Publication Date: 2012
Solid State Communications (00381098)152(2)pp. 56-59
Explicit expressions are given to study the biaxial buckling of monolayer graphene sheets. Based upon the continuum mechanics, a plate model is adopted in which the small length scale effect is incorporated into the governing equation through the nonlocal elasticity theory of Eringen. By employing the Galerkin method, analytical expressions are derived which allow quick and accurate calculation of the critical buckling loads of monolayer graphene sheets with various boundary conditions from the static deflection under a uniformly distributed load. The effectiveness of the present study is assessed by molecular dynamics simulations as a benchmark of good accuracy. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2012
International Journal of Nanoscience (17935350)11(2)
In this study, a novel semi-analytical approach is presented to evaluate the preferred position of an offset inner single-walled carbon nanotube (SWCNT) with reference to the cross-section of outer one. Moreover, on the basis of the continuum method utilized together with Lennard-Jones potential function, suction energy and acceptance condition for a SWCNT entering the outer one are investigated. Using netting analysis, the optimum configuration is determined to minimize the potential energy. To obtain the nature of interaction force, a universal potential curve is presented for an offset inner tube entering various semi-infinite outer ones. Lastly, based on the direct method, the mechanics of multi-walled carbon nanotubes (MWCNT) is investigated. © 2012 World Scientific Publishing Company.
Publication Date: 2012
International Journal for Computational Methods in Engineering Science and Mechanics (15502295)13(3)pp. 202-209
Presented in this paper are the vibration characteristics of single-walled carbon nanotubes (SWCNTs) with different boundary conditions. A nonlocal shell model accounting for the size effect is adopted. The set of governing equations of motion are numerically solved using a semi-analytical finite element method. The effectiveness of the present nonlocal shell model is assessed by molecular dynamics simulations as a benchmark of good accuracy. The significance of the small size effects on the resonant frequencies is indicated to be dependent on the sizes, boundary conditions of nanotubes, and the tube wall thickness varying within 0.066 nm to 0.34 nm. Copyright © Taylor & Francis Group, LLC.
Publication Date: 2012
Superlattices and Microstructures (10963677)51(2)pp. 274-289
In this paper, the effects of two main types of structural defects, i.e. Stone-Wales and single vacancy, on the mechanical properties of single-layered graphene sheets (SLGSs) are investigated. To this end, molecular dynamics simulations based on the Tersoff-Brenner potential function and Nose-Hoover thermostat technique are implemented. The results obtained have revealed that the presence of defects significantly reduces the failure strain and the intrinsic strength of SLGSs, while it has a slight effect on Young's modulus. Furthermore, the examination of loading in both armchair and zigzag directions demonstrated that SLGSs are slightly stronger in the armchair direction and defects have lower effect in this direction. Considering the fracture mechanism, the failure process of defective and perfect graphene sheets is also presented. © 2011 Elsevier Ltd. All rights reserved.
Mirnezhad m., M.,
Ansari, R.,
Seifi m., ,
Rouhi h., H.,
Faghihnasiri m., Publication Date: 2012
Solid State Communications (00381098)152(10)pp. 842-845
This paper investigates the mechanical properties of graphene subjected to adsorption of molecular hydrogen through an ab initio approach. First, using density functional theory (DFT) with both generalized gradient and local density approximation functionals, the most stable configuration for physisorption of molecular hydrogen on the graphene is determined. All possible adsorption sites are considered, and it is revealed that the most stable state happens above the center of a hexagon with the equilibrium distance of 2.7 when the axis of the hydrogen molecule is parallel to the graphene surface. Thereafter, DFT calculations are performed to obtain the in-plane stiffness and Poisson's ratio of graphene under the above-mentioned adsorption position. It is found that the effect of hydrogen physisorption on the mechanical properties of graphene is not very significant. © 2012 Elsevier Ltd. All rights reserved.
Mirnezhad m., M.,
Ansari, R.,
Rouhi h., H.,
Seifi m., ,
Faghihnasiri m., Publication Date: 2012
Solid State Communications (00381098)152(20)pp. 1885-1889
In the present work, the mechanical properties of graphyne, a class of graphene allotropes with carbon triple bonds, subjected to the hydrogen chemisorption are studied using a first-principles density functional approach. Two configurations for the maximum of hydrogen adsorption are considered: (I) adsorption of hydrogen atoms on carbon atoms at the two opposite sides of graphyne sheet and (II) adsorption of hydrogen atoms on carbon atoms at the same side of graphyne sheet. Formation energy for hydrogenated graphyne (H-graphyne) corresponding to these states of adsorption is calculated and it is indicated that state (I) is more stable than state (II). Density functional calculations within the generalized gradient approximation (GGA) in the harmonic elastic deformation range are performed to obtain the elastic constants of graphyne and H-graphyne in state (I). This study shows that H-graphyne has an in-plane stiffness of 125 N/m and a Poisson's ratio of 0.23. It is observed that the in-plane stiffness of H-graphyne is lower than that of graphyne. This clearly reveals the destructive effect of hydrogen adsorption on the mechanical properties of graphyne. The results of this paper are helpful for the design of future nanodevices in which H-graphyne acts as their basic element. © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2012
Journal of Nanotechnology in Engineering and Medicine (19492944)3(1)
On the basis of the continuum approximation along with Lennard-Jones potential function, new semi-analytical expressions are presented to evaluate the van der Waals interactions between an ellipsoidal fullerene and a semi-infinite single-walled carbon nanotube. Using direct method, these expressions are also extended to model ellipsoidal carbon onions inside multiwalled carbon nanotubes. In addition, acceptance and suction energies which are two noticeable issues for medical applications such as drug delivery are determined. Neglecting the frictional effects and by imposing some simplifying assumptions on the van der Waals interaction force, a simple formula is given to evaluate the oscillation frequency of ellipsoidal carbon onions inside multiwalled carbon nanotubes. Also, the effects of the number of tube shells and ellipsoidal carbon onion shells on the oscillatory behavior are examined. It is shown that there exists an optimal value for the number of tube shells beyond which the oscillation frequency remains unchanged. © 2012 by ASME.
Publication Date: 2012
Nonlinear Dynamics (0924090X)67(1)pp. 373-383
The large-amplitude free vibration analysis of double-walled carbon nanotubes embedded in an elastic medium is investigated by means of a finite element formulation. A double-beam model is utilized in which the governing equations of layers are coupled with each other via the van der Waals interlayer forces. Von-Karman type nonlinear strain-displacement relationships are employed where the ends of the nanotube are constrained to move axially. The amplitude-frequency response curves for large-amplitude free vibrations of single-walled and double-walled carbon nanotubes with arbitrary boundary conditions are graphically illustrated. The effects of material constant of the surrounding elastic medium and the geometric parameters on the vibration characteristics are investigated. For a double-walled carbon nanotube with different boundary conditions between inner and outer tubes, the nonlinear frequencies are obtained apparently for the first time. Comparison of the results with those from the open literature is made for the amplitude-frequency curves where possible. This comparison illustrates that the present scheme yields very accurate results in predicting the nonlinear frequencies. © 2011 Springer Science+Business Media B.V.
Publication Date: 2012
Acta Mechanica (16196937)223(12)pp. 2523-2536
This paper investigates the large-amplitude free vibration of a double-walled carbon nanotube (DWCNT) surrounded by an elastic medium in the presence of temperature change. Based on continuum mechanics, a nonlocal elastic beam model is employed in which nanotubes are coupled together via the van der Waals (vdW) interlayer interactions. The Pasternak foundation model and a nonlinear vdW model are utilized to describe the surrounding elastic medium effect and the vdW interlayer interactions, respectively. DWCNTs with different boundary conditions are analyzed utilizing the Timoshenko beam theory that considers the shear deformation and rotary inertia effects. The governing equations are derived from Hamilton's principle; the Galerkin method is utilized to discretize the governing equations. The influences of the nonlocal parameter, spring constant, carbon nanotube aspect ratio, and temperature change on the nonlinear free vibration characteristics of a double-walled carbon nanotube with different boundary conditions are thoroughly investigated. It is deduced that the nonlocal parameter, spring constant, and the aspect ratio play significant roles for the value of the nonlinear frequency. Also, the temperature change and the type of boundary conditions have an effect on the nonlinear frequency. © Springer-Verlag 2012.
Publication Date: 2012
Nano (17937094)7(3)
In this paper, a nonlocal Flugge shell model is utilized to investigate the axial buckling behavior of double-walled carbon nanotubes (DWCNTs) under various boundary conditions. According to the nonlocal elasticity theory, the displacement field equations coupled by the van der Waals interaction are derived. The set of governing equations of motion is then solved by the RayleighRitz method. The present analysis can treat boundary conditions in a layer-wise manner. The effects of nonlocal parameter, layer-wise boundary conditions and geometrical parameters on the mechanical behavior of DWCNTs are examined. Furthermore, molecular dynamics simulations are performed to assess the validity of the results and also to predict the appropriate values of nonlocal parameter. It is found that the type of boundary conditions affects the proper value of nonlocal parameter. © 2012 World Scientific Publishing Company.
Publication Date: 2012
Nonlinear Dynamics (0924090X)67(3)pp. 2241-2254
A nonlocal elastic beam model is developed to investigate the small scale effects on the large-amplitude vibration analysis of embedded multiwalled carbon nanotubes (MWCNTs) at an elevated temperature. The nested slender nanotubes are coupled with each other through the van der Waals (vdW) interlayer interaction. The curvature-dependent vdW force employed incorporates not only pairwise nearest-neighbor but also nonneighbor interactions between nested nanotubes. The incremental harmonic balance method is adopted to analytically solve the nonlinear equations that are governed by the vibrations of nested nanotubes. The influences of small scale parameter, geometrical parameters, temperature rise, and the elastic medium are fully examined. © 2011 Springer Science+Business Media B.V.
Publication Date: 2012
Journal of Thermal Stresses (01495739)35(4)pp. 326-341
Presented herein is the thermal buckling analysis of multi-walled carbon nanotubes on the basis of nonlocal Flugge shell model capturing small scale effects. Based upon the continuum mechanics, a multiple-shell model is adopted in which the nested tubes are coupled with each other through the van der Waals interlayer interaction. The utilized van der Waals model incorporating the interlayer interactions between any two layers, whether adjacent or non-adjacent is curvature dependent. To analytically solve the problem, the Rayleigh-Ritz method was implemented to the variational form equivalent to the Flugge type equations. The present analysis provides the possibility of considering different combinations of layerwise boundary conditions. It is shown that the shell-like thermal buckling is significantly sensitive to the nonlocal parameter variation, whereas the column-like thermal buckling remains unaffected when the nonlocal parameter is varied. Copyright © Taylor & Francis Group, LLC.
Ansari, R.,
Rouhi, S.,
Aryayi, M.,
Mirnezhad m., M. Publication Date: 2012
Scientia Iranica (23453605)19(6)pp. 1984-1990
Silicon carbide nanotubes possess outstanding properties which enable them to have many applications. The buckling behaviour of silicon carbide nanotubes have been studied here. To do this, a 3D finite element method, known as space frame model has been proposed. Molecular mechanics are linked to density functional theory to derive the properties of this finite element method. It has been shown that the critical buckling force will diminish with increasing aspect ratio. Also, it is represented that increasing the aspect ratio will result in reducing the effect of boundary conditions. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.
Publication Date: 2012
Scientia Iranica (23453605)19(3)pp. 919-925
Based on the nonlocal Bernoulli-Euler and Timoshenko beam theories, the dynamic stability of embedded single-walled carbon nanotubes (SWCNTs) under axial compression is studied in a thermal environment. The developed nonlocal models have the capability to interpret small scale effects. A Winkler-type elastic foundation is employed to represent the interaction of the SWCNT and the surrounding elastic medium. The free vibration and axial buckling of SWCNTs are discussed as subset problems. A parametric study is conducted to investigate the influences of the static load factor, temperature change, nonlocal elastic parameter, slenderness ratio and spring constant of the elastic medium on the dynamic stability characteristics of the SWCNTs, with simply-supported boundary conditions. It is found that the difference between instability regions predicted by local and nonlocal beam theories is significant for nanotubes with lower aspect ratios. Moreover, it is observed that in contrast to high temperature environments, at low temperatures, increasing the temperature change moves the origins of the instability regions to higher excitation frequencies and leads to further stability of the system at lower excitation frequencies. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.
Publication Date: 2012
Journal of Nanotechnology in Engineering and Medicine (19492944)3(1)
There are many new nanomechanical devices created based on carbon nanostructures among which gigahertz oscillators have generated considerable interest to many researchers. In the present paper, the oscillatory behavior of ellipsoidal fullerenes inside single-walled carbon nanotubes is studied comprehensively. Utilizing the continuum approximation along with Lennard-Jones potential, new semi-analytical expressions are presented to evaluate the potential energy and van der Waals interaction force of such systems. Neglecting the frictional effects, the equation of motion is directly solved on the basis of the actual force distribution between the interacting molecules. In addition, a semi-analytical expression is given to determine the oscillation frequency into which the influence of initial conditions is incorporated. Based on the newly derived expression, a thorough study on the various aspects of operating frequencies under different system variables such as geometrical parameters and initial conditions is conducted. Based on the present study, some new aspects of such nano-oscillators have been disclosed. © 2012 American Society of Mechanical Engineers.
Ansari, R.,
Alisafaei f., F.,
Alipour a., A.,
Mahmoudinezhad e., E. Publication Date: 2012
Journal of Physics and Chemistry of Solids (00223697)73(6)pp. 751-756
Based on the continuum Lennard-Jones model, the van der Waals interaction of two concentric and eccentric carbon nanocones with different or identical sizes are investigated in this paper. Also, on the basis of classical mathematical modeling techniques, a new semi-analytical solution is given to evaluate the van der Waals potential energy and interaction force distributions of two concentric carbon nanocones. Finally, a universal potential energy is presented for the carbon nanocones. © 2012 Elsevier Ltd. All rights reserved.
Publication Date: 2012
Journal of Applied Physics (10897550)112(12)
This article presents a comprehensive study on the mechanics of carbon nanotubes (CNTs) oscillating in CNT bundles. Using the continuum approximation along with Lennard-Jones (LJ) potential function, new semi-analytical expressions in terms of double integrals are presented to evaluate van der Waals (vdW) potential energy and interaction force upon which the equation of motion is directly solved. The obtained potential expression enables one to arrive at a new semi-analytical formula for the exact evaluation of oscillation frequency. Also, an algebraic frequency formula is extracted on the basis of the simplifying assumption of constant vdW force. Based on the present expressions, a thorough study on various aspects of operating frequencies under different system parameters is given, which permits fresh insight into the problem. The strong dependence of oscillation frequency on system parameters, such as the extrusion distance and initial velocity of the core as initial conditions for the motion is indicated. Interestingly, a specific initial velocity is found at which the oscillation frequency is independent of the core length. In addition, a relation between this specific initial velocity and the escape velocity is disclosed. © 2012 American Institute of Physics.
Ansari, R.,
Kazemi e., E.,
Mahmoudinezhad e., E.,
Sadeghi f., F. Publication Date: 2012
Journal of Nanotechnology in Engineering and Medicine (19492944)3(1)pp. 1-7
Cisplatin is one of the most widely prescribed chemotherapy drugs to treat different types of cancers. However, this anticancer drug has a number of side effects such as kidney and nerve damages, anaphylactic reactions, hearing loss, nausea, and vomiting that strongly restrict its function. In the present study, single-walled carbon nanotubes (SWCNTs) are used as protective drug carriers which can decrease these severe side effects to some extent. Using the hybrid discrete-continuum model in conjunction with Lennard-Jones potential, new semi-analytical expressions in terms of single integrals are given to evaluate van der Waals (vdW) potential energy and interaction force between an offset cisplatin and a SWCNT. In addition, molecular dynamics (MD) simulations are conducted to validate the results of such a hybrid approach. The preferred location and orientation of cisplatin while entering SWCNTs are determined. It is shown that the equilibrium condition of the drug may be affected by the radius of nanotube, the orientation of cisplatin, and the distance between the central molecule of the drug (Pt) and the left end of nanotube. Furthermore, the influence of equilibrium condition on the distributions of vdW interactions is investigated. © 2012 by ASME.
Publication Date: 2012
Communications in Nonlinear Science and Numerical Simulation (10075704)17(4)pp. 1965-1979
The free vibration response of single-walled carbon nanotubes (SWCNTs) is investigated in this work using various nonlocal beam theories. To this end, the nonlocal elasticity equations of Eringen are incorporated into the various classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Reddy beam theory (RBT) to consider the size-effects on the vibration analysis of SWCNTs. The generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations of each nonlocal beam theory corresponding to four commonly used boundary conditions. Then molecular dynamics (MD) simulation is implemented to obtain fundamental frequencies of nanotubes with different chiralities and values of aspect ratio to compare them with the results obtained by the nonlocal beam models. Through the fitting of the two series of numerical results, appropriate values of nonlocal parameter are derived relevant to each type of chirality, nonlocal beam model, and boundary conditions. It is found that in contrast to the chirality, the type of nonlocal beam model and boundary conditions make difference between the calibrated values of nonlocal parameter corresponding to each one. © 2011 Elsevier B.V.
Ansari, R.,
Shahabodini a., A.,
Alipour a., A.,
Rouhi h., H. Publication Date: 2012
Proceedings of the Institution of Mechanical Engineers, Part N: Journal of Nanoengineering and Nanosystems (17403499)226(2)pp. 51-60
In this article, the biaxial buckling of a single layer graphene sheet is investigated. The model is established through the incorporation of an interatomic potential into non-local elastic plate theory to take into account the size effects and to circumvent the use of the Young's modulus of a single layer graphene sheet since there is no accurate value of this property available in the literature. The model links the strain energy density induced in the continuum to Eringen's non-local constitutive relations. By using the Galerkin method, explicit formulas for the critical buckling stresses of a single layer graphene sheet with arbitrary edge supports are derived from its static deflection due to a uniformly distributed load. The influences of the small size of the system and boundary conditions on the critical buckling load of the single layer graphene sheet are studied. It is found that the critical buckling load at large side lengths is almost independent of the type of boundary condition and compressive loading and is nearly immune to size effects. The analytical expressions provide a simple and quick way to evaluate accurate values of the critical buckling load. Indeed, the lack of complexity in the formulas allows a simple prediction of the value of the scale parameter that closely matches the one obtained using the complex molecular dynamics simulation technique. © 2012 IMechE.
Publication Date: 2012
Journal of Computational and Nonlinear Dynamics (15551423)7(3)pp. 1-9
In the current study, the nonlinear free vibration behavior of microbeams made of functionally graded materials (FGMs) is investigated based on the strain gradient elasticity theory and von Karman geometric nonlinearity. The nonclassical beam model is developed in the context of the Timoshenko beam theory which contains material length scale parameters to take the size effect into account. The model can reduce to the beam models based on the modified couple stress theory (MCST) and the classical beam theory (CBT) if two or all material length scale parameters are taken to be zero, respectively. The power low function is considered to describe the volume fraction of the ceramic and metal phases of the FGM microbeams. On the basis of Hamilton’s principle, the higher-order governing differential equations are obtained which are discretized along with different boundary conditions using the generalized differential quadrature method. The dimensionless linear and nonlinear frequencies of microbeams with various values of material property gradient index are calculated and compared with those obtained based on the MCST and an excellent agreement is found. Moreover, comparisons between the various beam models on the basis of linear and nonlinear types of strain gradient theory (SGT) and MCST are presented and it is observed that the difference between the frequencies obtained by the SGT and MCST is more significant for lower values of dimensionless length scale parameter. © 2012 by ASME.
Ansari, R.,
Gholami, R.,
Faghih shojaei, M.,
Mohammadi v., V.,
Darabi m.a., M.A. Publication Date: 2012
Journal of Engineering Materials and Technology (00944289)134(4)
This paper is aimed to investigate the size-dependent pull-in behavior of hydrostatically and electrostatically actuated rectangular nanoplates including surface stress effects based on a modified continuum model. To this end, based on the Gurtin-Murdoch theory and Hamilton's principle, the governing equation and corresponding boundary conditions of an actuated nanoplate are derived; the step-by-step linearization scheme and the differential quadrature (GDQ) method are used to discretize the governing equation and associated boundary conditions. The effects of the thickness of the nanoplate, surface elastic modulus and residual surface stress on the pull-in instability of the nanoplate are investigated. Plates made of two different materials including aluminum (Al) and silicon (Si) are selected to explain the variation of the pull-in voltage and pressure with respect to plate thickness. © 2012 American Society of Mechanical Engineers.
Publication Date: 2012
Composites Part B: Engineering (13598368)43(8)pp. 2985-2989
The present work aims at investigating the vibrational characteristics of single-walled carbon nanotubes (SWCNTs) based on the gradient elasticity theories. The small-size effect, which plays an essential role in the dynamical behavior of nanotubes, is captured by applying different gradient elasticity theories including stress, strain and combined strain/inertia ones. The theoretical formulations are established based upon both the Euler-Bernoulli and the Timoshenko beam theories. To validate the accuracy of the present analysis, molecular dynamics (MDs) simulations are also conducted for an armchair SWCNTs with different aspect ratios. Comparisons are made between the aforementioned different gradient theories as well as different beam assumptions in predicting the free vibration response. It is shown that implementation of the strain gradient elasticity by incorporating inertia gradients yields more reliable results especially for shorter length SWCNTs on account of two small scale factors corresponding to the inertia and strain gradients. Also, the difference between two beam models is more prominent for low aspect ratios and the Timoshenko beam model demonstrates a closer agreement with MD results. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2012
Current Applied Physics (15671739)12(3)pp. 707-711
In the present work, the vibration characteristics of single- and double-walled carbon nanotubes under various layerwise boundary conditions at different lengths are investigated. This is accomplished by the use of molecular dynamics simulations based on the Tersoff-Brenner and Lennard-Jones potential energy functions. The effects of initial tensile and compressive strains on the resonant frequency of carbon nanotubes are also taken into consideration. From the results generated, it is observed that the natural frequency of carbon nanotubes is strongly dependent on their boundary conditions especially when tubes are shorter in length. The natural frequency and its dependence on tube end conditions reduce by increasing the tube length. The natural frequency of DWCNTs lies between those of the constituent inner and outer SWCNTs and is nearer to those of the outer one. It is further observed that the natural frequency is highly sensitive to tensile and compressive strains. The frequency shift occurring in the presence of small initial strains is positive for tensile strains and negative for compressive strains. The results obtained provide valuable information for calibrating the small scaling parameter of the nonlocal models for the vibration problem of carbon nanotubes. © 2011 Elsevier B.V. All rights reserved.
Ansari, R.,
Gholami, R.,
Hosseini, K.,
Sahmani, S. Publication Date: 2011
Mathematical and Computer Modelling (08957177)54(11-12)pp. 2577-2586
In the present paper, the free vibration characteristics of nanobeams embedded in an elastic medium are investigated. Inclusion of size effects is considered in the analysis by incorporating Eringen's nonlocal elasticity continuum into the classical Euler-Bernoulli beam theory. To include the surrounding elastic medium, the Pasternak elastic foundation model is utilized, including shear deformation of the elastic medium. A high-order compact finite difference method (CFDM) is employed for sixth-order discretization of the nonlocal beam model to obtain the fundamental frequencies of nanobeams corresponding to three commonly used boundary conditions, namely simply supported-simply supported, clamped-clamped, and clamped-free. Numerical results are presented to indicate the accuracy of the method based on the sixth-order discretization for predicting the vibrational response of embedded nanobeams subject to various boundary conditions. © 2011 Elsevier Ltd.
Darvizeh m., M.,
Darvizeh a., A.,
Shaterzadeh a.r., ,
Ansari, R. Publication Date: 2011
Journal of Thermal Stresses (01495739)34(1)pp. 75-93
In this paper, the thermal buckling of piezoelectric composite shells of revolution under uniform and linear thermal distributions and selected boundary conditions is investigated by using the semi-analytical finite element. The effects of different parameters such as the type of temperature distributions through the thickness, fiber angles, arrangements of piezoelectric patches and amount of displacement feedback control gain are examined. The results obtained from the present analysis are validated, where possible, with those available in the literature. Copyright © Taylor &Francis Group, LLC.
Publication Date: 2011
Computational Materials Science (09270256)50(10)pp. 3050-3055
Axial buckling characteristics of single-walled carbon nanotubes (SWCNTs) including thermal environment effect are studied in this paper. Eringen's nonlocal elasticity equations are incorporated into the classical Donnell shell theory to establish a nonlocal elastic shell model which takes small-scale effects into account. The Rayleigh-Ritz technique is implemented in conjunction with the set of beam functions as modal displacement functions to consider the four commonly used boundary conditions namely as simply supported-simply supported, clamped-clamped, clamped-simply supported, and clamped-free in the buckling analysis. Selected numerical results are presented to demonstrate the influences of small scale effect, aspect ratio, thermal environment effects and boundary conditions in detail. It is found that the value of aspect ratio has different effects on the critical axial buckling loads of SWCNTs in low and high temperature environments. Also, it is observed that the difference between the thermal axial buckling responses of SWCNTs relevant to various boundary conditions is more prominent for higher values of nonlocal elasticity constant. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011
International Journal of Engineering Science (00207225)49(11)pp. 1244-1255
A new frontier of research in the area of computational nanomechanics is to study the behavior of structures at very small length scales. As the dimensions of a structure approach the nanoscale, the classical continuum theories may fail to accurately predict the mechanical behavior of nanostructures. Among these nanostructures, nanobeams are attracting more and more attention due to their great potential engineering applications. One of the most important factors that influence the behavior of such submicron-sized structures is surface stress effect because of their high surface to volume ratio. In this paper, a non-classical solution is proposed to analyze bending and buckling responses of nanobeams including surface stress effects. Explicit formulas are proposed relevant to each type of beam theory to evaluate the surface stress effects on the displacement profile and critical buckling load of the nanobeams. Numerical results are presented to demonstrate the difference between the behaviors of the nanobeam predicted by the classical and non-classical solutions which depends on the magnitudes of the surface elastic constants. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2011
International Journal of Mechanical Sciences (00207403)53(9)pp. 786-792
In the present study, the free vibration response of double-walled carbon nanotubes (DWCNTs) is investigated. Eringens nonlocal elasticity equations are incorporated into the classical Donnell shell theory accounting for small scale effects. The RayleighRitz technique is applied to consider different sets of boundary conditions. The displacements are represented as functions of polynomial series to implement the RayleighRitz method to the governing differential equations of nonlocal shell model and obtain the natural frequencies of DWCNTs relevant to different values of nonlocal parameter and aspect ratio. To extract the proper values of nonlocal parameter, molecular dynamics (MD) simulations are employed for various armchair and zigzag DWCNTs, the results of which are matched with those of nonlocal continuum model through a nonlinear least square fitting procedure. It is found that the present nonlocal elastic shell model with its appropriate values of nonlocal parameter has the capability to predict the free vibration behavior of DWCNTs, which is comparable with the results of MD simulations. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2011
Journal of Nanotechnology in Engineering and Medicine (19492944)2(3)
Using the Lennard-Jones potential, continuum modeling of the van der Waals potential energy and interaction force distributions are investigated for the eccentric and concentric single-walled carbon nanocones inside the single-walled carbon nanotubes. Furthermore, a new semi-analytical solution is presented to evaluate the van der Waals interaction of the nanocone located on the axis of the nanotube. Eccentric and concentric configurations of these nanostructures are also investigated to obtain the preferred position of the nanocone inside the nanotubes. Finally, the optimum radius of a carbon nanotube for which the preferred location of carbon nanocones is along the tube axis is found. © 2011 American Society of Mechanical Engineers.
Ansari, R.,
Motevalli, B.,
Montazeri a., ,
Ajori, S. Publication Date: 2011
Solid State Communications (00381098)151(17)pp. 1141-1146
Carbon nanostructures such as carbon nanotubes (CNTs) and graphene sheets have attracted great attention due to their exceptionally high strength and elastic strain. These extraordinary mechanical properties, however, can be affected by the presence of defects in their structures. When a material contains multiple defects, it is expected that the stress concentration of them superposes if the separation distances of the defects are low, which causes a more reduction of the strength. On the other hand, it is believed that if the defects are far enough such that their affected areas are distinct, their behavior is similar to a material with single defect. In this article, molecular dynamics (MD) is used to explore the influence of separation distance of double vacancy defects on the mechanical properties of single-layered graphene sheets (SLGSs). To this end, critical stress and strain of SLGSs containing double vacancy with different distances are determined and the results are compared with those of perfect SLGSs and graphene sheets with single vacancy defect. The results reveal that the ultimate strength of the SLGS with double vacancy tends to the one with a single vacancy when the separation distance becomes further. In this regard, the threshold distance beyond which double defects behave like a single one is examined. Finally, Young's modulus of perfect, single and double vacancy defected graphene sheets with different separation distances is determined. It is concluded that this property is slightly affected by the separation distance. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2011
Composite Structures (02638223)94(1)pp. 221-228
Investigated herein is the free vibration characteristics of microbeams made of functionally graded materials (FGMs) based on the strain gradient Timoshenko beam theory. The material properties of the functionally graded beams are assumed to be graded in the thickness direction according to the Mori-Tanaka scheme. Using Hamilton's principle, the equations of motion together with corresponding boundary conditions are obtained for the free vibration analysis of FGM microbeams including size effect. A detailed parametric study is performed to indicate the influences of beam thickness, dimensionless length scale parameter, and slenderness ratio on the natural frequencies of FGM microbeams. Moreover, a comparison between the various beam models on the basis of the classical theory (CT), modified couple stress theory (MCST), and strain gradient theory (SGT) is presented for different values of material property gradient index. It is observed that the value of gradient index play an important role in the vibrational response of the microbeams of lower slenderness ratios. It is further observed that by increasing the length-to-thickness ratio of the microbeam, the value of dimensionless natural frequency tends to decrease for all amounts of the gradient index. © 2011 Elsevier Ltd.
Publication Date: 2011
Computational Materials Science (09270256)50(4)pp. 1406-1413
Based on the continuum approximation together with Lennard-Jones potential, a new semi-analytical method is developed to determine the van der Waals interaction between two single-walled carbon nanotubes. Neglecting the frictional effects, acceptance condition and suction energy for an inner tube entering semi-infinite outer ones are obtained and nature of interaction force is investigated. The maximum suction energy configurations are found by netting analysis. Using this procedure, the optimum configurations are obtained to minimize the potential energy. Also, a universal potential curve is presented for an inner tube entering various semi-infinite outer ones. Finally, on the basis of the direct method, suction energy and acceptance condition are obtained for multi-walled carbon nanotubes. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2011
Computational Materials Science (09270256)50(11)pp. 3091-3100
The present article deals with the vibrational analysis of multi-layered graphene sheets with different boundary conditions amongst sheets. An elastic multiple-plate model is utilized in which the nested plates are coupled with each other through the van der Waals interlayer force. The interaction of van der Waals forces between adjacent and non-adjacent layers and the reaction from the surrounding media are included in the Reissner-Mindlin-type field equations on which the theoretical formulation is based. The set of coupled equations of motion for the multi-layered graphene sheets is then solved by the generalized differential quadrature method. The numerical analysis presented herein provides the possibility of considering various combinations of layerwise boundary conditions in a multi-layered graphene sheet. Based on exact solution, explicit formulas for the frequencies of a double-layered graphene sheet with all edges simply supported are also obtained. The results of the present numerical solution are shown to be in excellent agreement with those of exact solution for simply supported graphene sheets. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011
Mathematical and Computer Modelling (08957177)53(5-6)pp. 927-938
The present work deals with the problem of the nonlinear vibrations of multi-walled carbon nanotubes embedded in an elastic medium. A multiple-beam model is utilized in which the governing equations of each layer are coupled with those of its adjacent ones via the van der Waals interlayer force. The variational iteration method (VIM) is adopted to obtain the amplitude-frequency curves for large-amplitude vibrations of single-, double- and triple-walled carbon nanotubes. The influences of changes in material constants of the surrounding elastic medium and the geometric parameters on the vibration characteristics of multi-walled carbon nanotubes are investigated. The results from the VIM solution are compared and shown to be in excellent agreement with the available solutions from the open literature. The capability of the present analytical technique is clarified in terms of numerical accuracy as well as computational efficiency. © 2010 Elsevier Ltd.
Publication Date: 2011
Journal of Mechanical Science and Technology (1738494X)25(9)pp. 2365-2375
Buckling analysis of nanobeams is investigated using nonlocal continuum beam models of the different classical beam theories namely as Euler-Bernoulli beam theory (EBT), Timoshenko beam theory (TBT), and Levinson beam theory (LBT). To this end, Eringen's equations of nonlocal elasticity are incorporated into the classical beam theories for buckling of nanobeams with rectangular cross-section. In contrast to the classical theories, the nonlocal elastic beam models developed here have the capability to predict critical buckling loads that allowing for the inclusion of size effects. The values of critical buckling loads corresponding to four commonly used boundary conditions are obtained using state-space method. The results are presented for different geometric parameters, boundary conditions, and values of nonlocal parameter to show the effects of each of them in detail. Then the results are fitted with those of molecular dynamics simulations through a nonlinear least square fitting procedure to find the appropriate values of nonlocal parameter for the buckling analysis of nanobeams relevant to each type of nonlocal beam model and boundary conditions. analysis. © 2011 The Korean Society of Mechanical Engineers and Springer-Verlag Berlin Heidelberg.
Publication Date: 2011
Physica E: Low-Dimensional Systems and Nanostructures (13869477)43(6)pp. 1171-1178
A nonlocal Timoshenko beam model is developed to study the nonlinear vibrations of embedded multiwalled carbon nanotubes (MWCNTs) in thermal environments. The Timoshenko beam model, unlike its BernoulliEuler beam counterpart, takes the effects of transverse shear deformation and rotary inertia into consideration. These effects become more significant for short-length nanotubes that are normally encountered in applications such as nanoprobes. The nested nanotubes are coupled via the van der Waals (vdW) force that considers interactions between adjacent and non-adjacent nested nanotubes. The set of coupled nonlinear equations are then analytically solved using the harmonic balance approach. The effects of small-scale parameter, nanotube geometries, temperature change and the elastic medium are investigated. © 2011 Elsevier B.V. All rights reserved.
Publication Date: 2011
Journal of Vibration and Acoustics (15288927)133(5)
Nested carbon nanotubes exhibit telescopic oscillatory motion with frequencies in the gigahertz range. In this paper, our previously proposed semi-analytical expression for the interaction force between two concentric carbon nanotubes is used to solve the equation of motion. That expression also enables a new semi-analytical expression for the precise evaluation of oscillation frequency to be introduced. Alternatively, an algebraic frequency formula derived based on the simplifying assumption of constant van der Waals force is also given. Based on the given formulas, a thorough study on different aspects of operating frequencies under various system parameters is conducted, which permits fresh insight into the problem. Some notable improvements over the previously drawn conclusions are made. The strong dependence of oscillatory frequency on system parameters including the extrusion distance and initial velocity of the core as initial conditions for the motion is shown. Interestingly, our results indicate that there is a special initial velocity at which oscillatory frequency is unique for any arbitrary length of the core. A particular relationship between the escape velocity (the minimum initial velocity beyond which the core will leave the outer nanotube) and this specific initial velocity is also revealed. © 2011 American Society of Mechanical Engineers.
Publication Date: 2011
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601)375(9)pp. 1255-1263
Eringen's nonlocality is incorporated into the shell theory to include the small-scale effects on the axial buckling of single-walled carbon nanotubes (SWCNTs) with arbitrary boundary conditions. To this end, the Rayleigh-Ritz solution technique is implemented in conjunction with the set of beam functions as modal displacement functions. Then, molecular dynamics simulations are employed to obtain the critical buckling loads of armchair and zigzag SWCNTs, the results of which are matched with those of nonlocal shell model to extract the appropriate values of nonlocal parameter. It is found that in contrast to the chirality, boundary conditions have a considerable influence on the proper values of nonlocal parameter. © 2011 Elsevier B.V.
Publication Date: 2011
International Journal of Engineering Science (00207225)49(11)pp. 1204-1215
Surface stress is one of the most considerable reasons which cause extraordinary mechanical responses of nanomaterials and nanostructures due to the high surface to volume ratio of the systems at this submicron size. In the present study, the free vibration characteristics of nanoplates including surface stress effects are investigated based on the continuum modeling approach. To this end, Gurtin-Murdoch continuum elasticity approach is incorporated into the different types of plate theory namely as classical plate theory (CLPT) and first-order shear deformation theory (FSDT) to develop non-classical continuum plate models for free vibration analysis of the nanoplates including surface stress effects. Closed-form analytical solution accounting for the influence of surface stress on the vibrational behavior of nanoplates is derived. Selected numerical results are given to quantitatively assess the surface stress effects on the natural frequencies of the nanoplates. It is found that the difference between the results predicted by the classical and non-classical solutions relies on the sign and magnitude of the surface elastic constants. © 2011 Elsevier Ltd. All rights reserved.
Publication Date: 2011
Current Applied Physics (15671739)11(3)pp. 692-697
A single-beam model is presented for investigating the nonlinear vibrations of single-walled carbon nanotubes (SWNTs) embedded in an elastic medium. The thermal effect is also incorporated into the formulation. The variational iteration method is used to solve the corresponding nonlinear differential equation. The amplitude-frequency curves for large-amplitude vibrations are graphically illustrated. The influences of thermal effect, some commonly used boundary conditions, changes in material constant of the surrounding elastic medium and variations of geometrical parameters on the vibration characteristics of nanotubes are studied. The results obtained are compared, where possible, with those from the open literature. This comparison clarifies the accuracy as well as the capability of the present method. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2011
Journal of Thermal Stresses (01495739)34(12)pp. 1271-1281
In this paper, the thermal buckling behavior of single-walled carbon nanotubes (SWCNTs) embedded in an elastic medium is studied. To this end, the SWCNTs are modeled based on the nonlocal Timoshenko beam theory into which the effect of the elastic medium is incorporated The generalized differential quadrature (GDQ) method is employed to discretize the governing differential equations and to consider different commonly used boundary conditions (BCs). For simply supported BCs, the results obtained from the present analysis are compared with the ones from the exact solution and an excellent agreement has been achieved. The effects of the aspect ratio, nonlocal parameter and the Winkler parameter on the dimensionless critical buckling temperature are carefully investigated. Copyright © Taylor & Francis Group, LLC.
Publication Date: 2011
Journal of Thermal Stresses (01495739)34(8)pp. 817-834
In this article, a semi-analytical finite element approach based on the nonlocal elastic shell model is proposed to study the thermal buckling of multiwalled carbon nanotubes (MWCNTs). By taking nonlocality into consideration, the small scale effect is incorporated into the model presented herein. Based upon the Eringen nonlocal elasticity, the displacement field equations coupled by the van der Waals interaction force are derived. Comprehensive results for the thermal buckling of multiwalled carbon nanotubes are given. The influences of the small scale parameter and boundary conditions on the thermal instability of MWCNTs are examined. It is indicated that the possibility of the radial buckling mode of deformation due to radially elevated temperature is significantly higher than that of axial buckling mode of deformation due to uniformly reduced temperature when carbon nanotubes experience thermal loads. Copyright © Taylor & Francis Group, LLC.
Publication Date: 2011
Physica E: Low-Dimensional Systems and Nanostructures (13869477)44(2)pp. 373-378
In the current study, a nonlocal elastic shell model is developed to investigate the axially compressed buckling response of multi-walled carbon nanotubes (MWCNTs) considering thermal environment effect. To this end, Eringens nonlocal elasticity equations are incorporated into the classical Donnell shell theory to represent the MWCNTs as elastic multi-walled shell models coupled with the van der Waals interaction forces between the adjacent layers. Exact solution is presented to obtain the critical axial buckling loads of the nanotubes in thermal environment corresponding to different values of nonlocal elasticity parameter, axial and circumferential wavenumbers, temperature change and aspect ratio of the nanotube. It is found that the effect of small-scale is more prominent for MWCNTs having smaller diameters and a fewer number of walls. It is further found that the low and high temperature environments have contrary influences on the axial buckling of MWCNTs. © 2011 Elsevier B.V. All rights reserved.
Shaterzadeh a.r., ,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R. Publication Date: 2011
Journal of Thermal Stresses (01495739)34(10)pp. 1035-1053
In this article, the thermal post-buckling of shells of revolution under the action of uniform thermal load is investigated. To discretize the problem, the semi-analytical finite element method has been employed. The nonlinear equations are then solved by means of the Newton-Raphson algorithm in conjunction with the Arc length method. The effect of initial imperfection is also considered. The results obtained from the present analysis are compared to the published results in the literature to show the accuracy and robustness of the present method in predicting the nonlinear thermal buckling of shells of revolution. © 2011 Taylor & Francis Group, LLC.
Publication Date: 2011
Composite Structures (02638223)93(9)pp. 2419-2429
A nonlocal elastic plate model accounting for the small scale effects is developed to investigate the vibrational behavior of multi-layered graphene sheets under various boundary conditions. Based upon the constitutive equations of nonlocal elasticity, derived are the Reissner-Mindlin-type field equations which include the interaction of van der Waals forces between adjacent and non-adjacent layers and the reaction from the surrounding media. The set of coupled governing equations of motion for the multi-layered graphene sheets are then numerically solved by the generalized differential quadrature method. The present analysis provides the possibility of considering different combinations of layerwise boundary conditions in a multi-layered graphene sheet. Based on exact solution, explicit expressions for the nonlocal frequencies of a double-layered graphene sheet with all edges simply supported are also obtained. The results from the present numerical solution, where possible, are indicated to be in excellent agreement with the existing data from the literature. © 2011 Elsevier Ltd.
Publication Date: 2011
Scientia Iranica (23453605)18(6)pp. 1313-1320
In this paper, the vibrational behavior of functionally graded cylindrical shells with intermediate ring supports is studied. Theoretical formulation is established based on Sanders' thin shell theory. The governing equations of motion are derived, using an energy functional and by applying the Ritz method. Using an appropriate set of displacement functions, the energy equations lead to an eigenvalue problem whose roots are the natural frequencies of vibration. Material properties are assumed to be graded in the thickness direction, according to the power-law volume fraction function. A functionally graded cylindrical shell, made up of a mixture of ceramic and metal, is considered. The influence of some commonly used boundary conditions and the effect of changes in shell geometrical parameters and variations in ring support position on vibration characteristics are studied. The results obtained for a number of particular cases show good agreement with those available in the open literature. © 2012 Sharif University of Technology. Production and hosting by Elsevier B.V. All rights reserved.
Publication Date: 2010
Numerical Methods for Partial Differential Equations (10982426)26(2)pp. 490-500
This work deals with applying the homotopy perturbation method to the problem of the nonlinear vibrations of multiwalled carbon nanotubes embedded in an elastic medium. A multiple-beam model is utilized in which the governing equations of each layer are coupled with those of its adjacent ones via the van der Waals interlayer forces. The amplitude-frequency curves for large-amplitude vibrations of single-walled, double-walled, and triple-walled carbon nanotubes are obtained. The influence of changes in material constants of the surrounding elastic medium on the vibration characteristics of multiwalled carbon nanotubes is discussed. The comparison of the generated results with those from the open literature illustrates that the solutions obtained are of very high accuracy and clarifies the capability and the simplicity of this method. © 2009 Wiley Periodicals, Inc.
Publication Date: 2010
Physica E: Low-Dimensional Systems and Nanostructures (13869477)43(1)pp. 58-69
An atomistic finite element model is developed to study the buckling behavior of single-walled carbon nanotubes with different boundary conditions. By treating nanotubes as space-frame structures, in which the discrete nature of nanotubes is preserved, they are modeled using three-dimensional elastic beam elements for the bonds and point mass elements for the atoms. The elastic moduli of the beam elements are determined via a linkage between molecular mechanics and structural mechanics. Based on this model, the critical compressive forces of single-walled carbon nanotubes with different boundary conditions, geometries as well as chiralities are obtained and then compared. It is indicated that at low aspect ratios, the critical buckling load of nanotubes decreases considerably with increasing aspect ratios, whereas at higher aspect ratios, buckling load slightly decreases as the aspect ratio increases. It is also indicated that increasing aspect ratio at a given radius results in the convergence of buckling envelops associated with armchair and zigzag nanotubes. © 2010 Elsevier B.V.
Due to the importance of buckling analysis of composite structures in different branches of industry a comparative study of buckling behavior of composite plates is presented in here. Mathematical modeling developed in the present work for generally laminated plates are based on GDQR and R-R method. To show the ability and robustness of the mathematical modeling in handling buckling analysis, results obtained from GDQR and R-R are compared with each other and some available results based on experimental and analytical works. The efficiency and reliability of the GDQR in comparison with R-R method on the buckling behavior is also discussed. © 2010 by Nova Science Publishers, Inc. All rights reserved.
Haftchenari h., ,
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R.,
Sharma c.b., Publication Date: 2010
Composite Structures (02638223)78pp. 333-347
Free vibration analysis of composite cylindrical shells with different boundary conditions is presented in this paper using differential quadrature method (DQM). Equations of motion are derived based on first order shear deformation theory taking the effects of shear deformation and rotary inertia terms into account. By applying the differential quadrature formulation and the required modified relationships for implementing the different boundary conditions, equations of motion of a circular cylindrical shell are transformed into a set of algebraic equations. By solving this algebraic system natural frequencies of circular cylindrical shells made of fibrous composite materials with different fibre angles are evaluated. The results thus obtained are then compared with some available results and a good agreement is observed. In all the cases studied here efficiency, ease and usefulness of the DQM are well illustrated. © 2010 by Nova Science Publishers, Inc. All rights reserved.
Publication Date: 2010
Composite Structures (02638223)92(5)pp. 1100-1109
Based on the three-dimensional anisotropic elasticity, the stress analysis of multi-layered filament-wound composite pipes subjected to cyclic internal pressure and temperature loading is conducted in this article. The time-dependent stress, strain and deformation distributions are numerically obtained by the use of the finite difference technique. The pressure and temperature are considered to be symmetrical about the axis of the cylinder and independent of the axial coordinate. Each layer of the pipes is made of a homogeneous, anisotropic and linearly elastic material and it is assumed that the material properties do not change with increasing the temperature. The shear extension coupling is also considered because of lay-up angles. Numerical results obtained from the present model are compared with other published results and good agreement has been achieved. © 2009 Elsevier Ltd. All rights reserved.
Publication Date: 2010
Physica E: Low-Dimensional Systems and Nanostructures (13869477)42(8)pp. 2058-2064
Based upon a nonlocal shell model accounting for the small-scale effects, the vibration characteristics of single-walled carbon nanotubes (SWCNTs) with different boundary conditions subjected to initial strain are studied in this paper. The set of governing equations of motion is numerically solved by a method that emerged from incorporating the radial point interpolation approximation within the framework of the generalized differential quadrature method. The effectiveness of the present nonlocal shell model is assessed by the molecular dynamics simulations as a benchmark of good accuracy. Accordingly, nonlocal parameters for clamped and cantilever SWCNTs with thicknesses of 0.066 and 0.34 nm are proposed due to the uncertainty that exists in defining nanotube wall thickness. The simulation results show that the resonant frequencies of SWCNTs are very sensitive to the initial strain, although small. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2010
Computational Materials Science (09270256)49(4)pp. 831-838
In this article, a nonlocal plate model which accounts for the small scale effects is developed to study the vibrational characteristics of multi-layered graphene sheets with different boundary conditions embedded in an elastic medium. On the basis of the constitutive equations of nonlocal elasticity, the Mindlin-type equations of motion coupled together through the van der Waals interaction are derived. The finite element method is implemented to discretize the set of coupled field equations. The influences of the small scale parameter, length of a square plate and the elastic medium on the mechanical behavior of multi-layered graphene sheets are investigated. The results obtained from the present numerical solution have been compared with the existing data from the literature and good agreement has been found. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2010
Physics Letters, Section A: General, Atomic and Solid State Physics (03759601)375(1)pp. 53-62
Vibration analysis of single-layered graphene sheets (SLGSs) is investigated using nonlocal continuum plate model. To this end, Eringens's nonlocal elasticity equations are incorporated into the classical Mindlin plate theory for vibrations of rectangular nanoplates. In contrast to the classical model, the nonlocal model developed in this study has the capability to evaluate the natural frequencies of the graphene sheets with considering the size-effects on the vibrational characteristics of them. Solutions for frequencies of the free vibration of simply-supported and clamped SLGSs are computed using generalized differential quadrature (GDQ) method. Then, molecular dynamics (MD) simulations for the free vibration of various SLGSs with different values of side length and chirality are employed, the results of which are matched with the nonlocal model ones to derive the appropriate values of the nonlocal parameter relevant to each boundary condition. It is found that the value of the nonlocal parameter is independent of the magnitude of the geometrical variables of the system. © 2010 Elsevier B.V. All rights reserved.
Publication Date: 2010
Applied Composite Materials (0929189X)17(2)pp. 225-241
In this paper, a unified analytical approach is applied to investigate the vibrational behavior of composite cylindrical shells. Theoretical formulation is established based on Sanders' thin shell theory. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. The Influence of some commonly used boundary conditions and the effect of variations in shell geometrical parameters on the shell frequencies are studied. The results obtained for a number of particular cases show good agreement with those available in the open literature. The simplicity and the capability of the present method are also discussed. © 2009 Springer Science+Business Media B.V.
Calculation of overall response of thin orthotropic cylindrical shells is presented. Due to the obvious importance of the effects of transverse shear deformation and rotary inertia, these terms are included in the analysis. The exact method is modified to predict the dynamic behavior of an orthotropic circular cylindrical shell. The modal forms are assumed to have the axial dependence in the form of a simple Fourier series. By using the present modified exact analysis various aspects such as influence of boundary conditions, changes in shell geometrical parameters, changes in the directions of orthotropy, etc., on the frequencies, mode shapes and modal forces are studied. Analytical results are shown to be in good agreement with some available experimental and theoretical results. © 2010 by Nova Science Publishers, Inc. All rights reserved.
An analytical investigation of the buckling problem of composite shells with radius variation is presented. Different types of loading such as compressive and external can be applied. Flügge's shell equations, modified for anisotropic laminated materials are used.The modal forms are assumed to have axial dependency in the form of simple Fourier series. To implement the present method to find the buckling load of composite tubes with different boundary conditions the derivatives of Fourier series are legitimized using Stocke's transformation. The mathematical model presented includes the radius variations at the cross section of tubes in the form of function including imperfection factor. The analytical procedure developed in this work for finding the buckling loads yields an exact equation which is simpler than the exact method adopted by other research workers . The results are presented in the form of buckling diagrams and figures showing the mode shapes. © 2010 by Nova Science Publishers, Inc. All rights reserved.
This paper deals with thermal buckling analysis of functionally graded moderately thick plates. Material properties are assumed to be graded in the thickness direction according to volume fraction power law distribution. The formulations are based on first order shear deformation plate theory. Mathematical modeling developed in the present work for FGMs plates are based on GDQR. To show the ability and robustness of the mathematical modeling in handling thermal buckling analysis, results obtained from GDQR are compared with some available analytical results in the literature. The effects of dimensions of plates, the functionally graded index, the temperature distribution and boundary conditions are discussed in details. © 2010 by Nova Science Publishers, Inc. All rights reserved.
Darvizeh m., M.,
Darvizeh a., A.,
Shaterzadeh a.r., ,
Ansari, R. Publication Date: 2010
Journal of Thermal Stresses (01495739)33(5)pp. 441-458
In this paper, the thermal buckling of composite shells with selected boundary conditions under uniform and linearly distributed thermal load is investigated. The theoretical modeling procedure is based on semi-analytical finite element method. The effects of important structural parameters such as amount of cut-out at apex, fiber angles as well as temperature distributions are taken into consideration. The obtained results from the present analysis are compared with some available published results to show the accuracy and robustness of the present method. Copyright © Taylor & Francis Group, LLC.
Publication Date: 2009
International Journal of ChemTech Research (discontinued) (09744290)1(4)pp. 1398-1402
Organic conducting polymers are usually used as electrode deposited film, powder or free standing films. The electrochemical properties (e.g. electroactivity) of conducting polymers are usually studied as very thin deposited films (thickness<1micron). In this research, a special cell design was employed for simultaneous characterization of electroactivity and resistometry of the conducting electroactive polymers prepared as free standing film or membrane. PPy membranes doped with some benzene sulfonates were synthesized electrochemically, then the electrical conductivity and electroactivity of the films was measured after synthesized.
Publication Date: 2009
Communications in Nonlinear Science and Numerical Simulation (10075704)14(12)pp. 4246-4263
In this paper, using the continuum approximation together with Lennard-Jones potential, a new semi-analytical expression is given to evaluate the van der Waals interaction between two single-walled carbon nanotubes. Based on this expression, two new formulations are also proposed to model multi-walled carbon nanotubes. In the first one, the interactions between each pair of shells from the inner and outer tubes are summed up over all of the pairs, whereas in the second formulation, a set of correction factors are applied to convert the results of double-walled carbon nanotubes to the correlated multi-walled ones. With respect to the present formulations, extensive studies on the variations of force distributions are performed by varying nanotube geometries so that the important features of the geometrical parameters are explored. Moreover, an acceptance condition for a nanotube at rest which is to be sucked into a semi-infinite nanotube is obtained. The influence of different geometrical parameters on the acceptance condition and suction energy, two main characteristics of nanotube-based systems for applications such as drug delivery and so on, is fully demonstrated. Lastly, an interesting relation for the maximum value of suction energy in terms of geometrical parameters is also extracted in this study. © 2009 Elsevier B.V. All rights reserved.
Publication Date: 2008
Composite Structures (02638223)85(4)pp. 284-292
In this study, a general analytical approach is presented to investigate vibrational behavior of functionally graded shells. Theoretical formulations, based on first order shear deformation shell theory, take into consideration transverse shear deformation and rotary inertia effects. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stoke's transformation. Material properties are assumed to be temperature-dependent and graded in the thickness direction according to different volume fraction functions. These functions are assumed to have power-law, sigmoid and exponential distributions. A FGM cylindrical shell made up of a mixture of ceramic and metal is considered. The Influence of some commonly used boundary conditions, the effect of variations of volume fractions and shell geometrical parameters on the vibration characteristics are studied. The results obtained for a number of particular cases show good agreement with those available in the literature. © 2007 Elsevier Ltd. All rights reserved.
Darvizeh m., M.,
Haftchenari h., ,
Darvizeh a., A.,
Ansari, R.,
Sharma c.b., Publication Date: 2006
Composite Structures (02638223)74(4)pp. 495-502
A calculation of overall dynamic response of thin orthotropic cylindrical shells is presented. Due to the obvious importance of the effects of transverse shear deformation and rotary inertia, these terms are included in the analysis. The exact method is modified to predict the dynamic behavior of an orthotropic circular cylindrical shell. The modal forms are assumed to have the axial dependence in the form of a simple Fourier series. By using the present modified exact analysis various aspects such as influence of boundary conditions, changes in shell geometrical parameters, changes in the directions of orthotropy, etc., on the frequencies, mode shapes and modal forces are studied. Analytical results are shown to be in good agreement with some available experimental and theoretical results. © 2005 Elsevier Ltd. All rights reserved.
Darvizeh m., M.,
Haftchenari h., ,
Darvizeh a., A.,
Ansari, R.,
Alijani a., Publication Date: 2005
WSEAS Transactions on Information Science and Applications (17900832)2(8)pp. 1195-1201
In this study a composite cylindrical shell is loaded under a steady-state axisymmetric voltage and analyzed using a semi-analytical finite element method. An attempt has been made to define a critical buckling voltage for a single layer cylindrical composite shell under a clamped-clamped boundary condition at different fiber orientation and length to radius ratios. The voltage to cause instability is derived from fundamental equations of the piezoelectric constitutive relations. Critical buckling voltage applied to a cylindrical composite shell can be determined by employing a piezoelectric actuator.
Darvizeh m., M.,
Darvizeh a., A.,
Ansari, R.,
Sharma c.b., Publication Date: 2004
Composite Structures (02638223)63(1)pp. 69-74
Due to the importance of buckling analysis of composite structures in various industrial applications a comparative study of buckling behavior of composite plates is presented here. Mathematical modelling developed in the present work for generally laminated plates is based on generalized differential quadrature rule (GDQR) and R-R method. To show the ability and robustness of the mathematical modeling in handling buckling analysis, results obtained using GDQR and R-R are compared with each other and also with some available results based on experimental and analytical works. The efficiency and reliability of the GDQR in comparison with R-R method on the buckling behavior is also discussed. © 2003 Elsevier Ltd. All rights reserved.
