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International Journal of Damage Mechanics (10567895) (1)
Damage measurement of materials is a crucial challenge for researchers and engineers in manufacturing industries. In this study, based on the image processing technique, a developed approach for determining the Lemaitre’s ductile damage parameter by the direct measurement method is proposed. For this purpose, first, the micrographs pictures are provided by a scanning electron microscope to attain the damage evolution behavior of St37 steel. Then, prediction results of the suggested method and the Lemaitre’s direct approach as well as the microhardness technique and also a lately published numerical method in damage propagation, crack initiation, and ductile fracture of a few tensile samples are compared with the corresponding experimental tests. The comparison reveals the higher efficiency and accuracy of the current approach. Therefore, it is concluded that the new presented method is a reliable approach to achieve the Lemaitre’s ductile damage parameter and predict the damage evolution behavior of ductile materials. © The Author(s) 2024.
Archive of Applied Mechanics (09391533) (1)
Damage growth phenomenon in sheet metal forming processes is one of the most important issues in the manufacturing industries. Predicting the onset and location of crack can help engineers to postpone the failure as well as to produce safe parts. In this research, first, six different calibration methods are employed for the Bao-Wierzbicki damage criterion. Then, to evaluate the accuracy of the calibration approaches, a few conventional sheet metal forming processes with the positive stress triaxiality are numerically simulated. Finally, the numerical predicted results are compared with the empirical tests. The comparisons reveal that the hyperbolic quadratic hyperbolic 3 (HQH3) method is the best calibration approach, due to its accuracy and the fewer number of required experimental tests for the calibration. © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2024.
Journal of Constructional Steel Research (0143974X)
To improve the accuracy of the original Lemaitre's ductile damage model under various loading conditions, this study proposes an enhanced version of the model for sheet metal forming processes under plane stress assumptions by incorporating a functional material-dependent damage parameter. For this aim, the theoretical framework, constitutive equations, and a robust numerical explicit algorithm for the new model are first derived. Subsequently, a comprehensive calibration process is widely performed using a varying number of calibration points to optimize the functional ductile damage parameter. In the following, a user-defined subroutine is developed to numerically simulate the damage behavior of several SS304 stainless steel specimens subjected to different loading conditions, including the Erichsen's forming test. The accuracy of the novel criterion is thoroughly investigated and fully validated by the corresponding empirical observations. Finally, the numerically predicted fracture locus and forming limit diagram of the material are compared with the relevant practical data. The comparison strongly highlights the improved predictive capability and reliability of the enhanced model. © 2025
Engineering Failure Analysis (13506307)
Accurate prediction of ductile damage is a critical challenge for the safe design of sheet metal structures. The Lemaitre's ductile damage model has been widely used for prediction of ductile damage, however its accuracy fully depends on loading conditions and calibration range. This paper eliminates this limitation by proposing a 2D Lode improved model (LIM) of the original Lemaitre (OL) for sheet metals. The modification incorporates the Lode parameter, a crucial, often-neglected factor influencing damage evolution. First, the LIM's theoretical framework and constitutive equations for the plane stress conditions in sheet metals including the Lode parameter is completely presented. Then, numerical approaches such as counting search and Taguchi methods are employed and validated for identification of the model parameters. Finally, to evaluate the LIM's performance, a user-defined VUMAT subroutine is developed for numerically simulation of numerous specimens under diverse loading conditions as well as to assess the model's effectiveness and reliability. The numerical simulation results are compared with experimental data and the comparison demonstrates a significant improvement in accuracy of the LIM rather than the OL ductile damage model. © 2024 Elsevier Ltd
International Journal of Precision Engineering and Manufacturing (22347593) (1)
In the machining processes, chip removal can be performed by the applied forces. Therefore, predicting the required forces and energy is an essential challenge to reach the efficient processes. In this research, employing various ductile damage models of the continuum damage mechanics (CDM), a few machining processes such as 3D plane machining, 3D drilling, and turning are numerically simulated. Using the numerical simulations of finite element method (FEM), variations of the applied forces on the workpiece and the maximum force as well as the mechanism of chip formation during the machining processes are estimated. Besides, to assess the ductile damage models, the numerical simulation results are compared with the experimental results. The comparison reveals that the Ayada, Ayada negative, and Johnson–Cook damage criteria can accurately predict the required forces and respectively are the reliable models for numerical simulations of chip removal in the machining processes. © 2023, The Author(s), under exclusive licence to Korean Society for Precision Engineering.
Engineering Fracture Mechanics (00137944)
Large-scale fiber bridging makes a significant impact on fatigue delamination growth (FDG) in fiber-reinforced polymer composites. As bilinear cyclic cohesive zone modeling (CCZM) is not a promising modeling tool in this case, another solution is needed. The present study aims to evaluate a new easily-calibrating trilinear CCZM framework for modeling the FDG in glass/epoxy double cantilever beam (DCB) laminates with large-scale fiber bridging. First, mode I delamination growth, characterized by a significant R-curve effect, is experimentally determined under both quasi-static and high cycle fatigue regimes. Next, trilinear forms of the Turon et al. and the Kawashita-Hallett damage models are developed to predict such fatigue delamination behavior. Results show that the accuracy and efficiency of the proposed trilinear CCZM framework are enhanced by increasing the bridging length of the composite structure. Additionally, the Kawashita-Hallett trilinear model yields the most consistent and precise predictions with the least computational time. © 2024 Elsevier Ltd
The present study is an original try toward establishing a simple, inclusive, and verified fatigue design methodology tied with finite element analysis (FEA) to boost the design quality before running expensive and arduous preclinical tests. First, a reliable framework is established for material selection (Ti-6Al-4V) and life estimation (an “infinite-life” viewpoint) considering the role of microstructure, processing, stress concentration, physiological environment, and manufacturing. Second, an efficiently simplified FEA framework is introduced for analysis of both “preclinical” and “clinical” situations. Third, the extended finite element method with phantom nodes coupled with virtual crack closure technique (XFEMPN-VCCT) in Abaqus is used to investigate the three-dimensional crack propagation and life estimation in the stem (a damage tolerance viewpoint). Results are then verified and validated using several analytical solutions, numerical results, and clinical data. Infinite-life results reveal that the simple methodology proposed in this paper is an efficient tool for evaluating and improving a stem design with the least loss of time and money. Damage tolerance studies show that three-dimensional XFEMPN-VCCT suffers from mesh sensitivity, dependency on the damage extrapolation parameter, and error in calculating the strain energy release rate. Additionally, it is demonstrated that the remaining useful life of a stem with a propagating long fatigue crack might be significantly shorter than the values predicted in the literature. © 2023, Springer Nature B.V.
Mechanics Based Design of Structures and Machines (15397734) (5)
Damage is a progressive physical process that results in fracture. Recently, study of damage and failure in materials, particularly ductile metals has been of great importance for mechanical and structural engineers. So far, numerous criteria have been presented to predict damage behavior in ductile metals, each criterion is known by its advantages, disadvantages, and accuracy. One of the most famous models has been proposed by Lemaitre which is an accurate model and requires only one parameter to attain damage behavior of materials. In this article, employing the Lemaitre's ductile damage criterion, a new explicit, simple, and quick method is suggested to numerically determine the Lemaitre's damage parameter and damage behavior of ductile metals. This approach is much easier and cheaper than former conventional experimental methods because only needs a simple standard tensile test. Accuracy of the current numerical approach is validated through the experimental tests such as the standard, single and double notched tensile tests, and also the Nakazima fracture test. The numerical simulation results show suitable accuracy together with negligible percentage of error and perfect correlation in comparison with the experimental results. © 2021 Taylor & Francis Group, LLC.
Iranian Journal of Science and Technology - Transactions of Mechanical Engineering (22286187) (4)
In this study, quasi-static fracture of cracked specimens made of functionally graded material is numerically investigated. As the main contribution and objective of the current work, material property variations in the longitudinal direction are continuously implemented for both of integration points and nodes; therefore, stress field is precisely attained for singular points like crack tip. Furthermore, functionally graded Fe–Cu plates are constructed via a new powder metallurgy method and experimentally tested by three-point bending. Various damage criteria such as maximum principal stress, maximum principal strain, maximum nominal stress, maximum nominal strain, quadratic nominal stress and quadratic nominal strain are employed to predict the crack initiation. Besides, minimum strain energy density (MSED) and maximum tangential stress (MTS) criteria are utilized to reveal the crack growth. To evaluate the mentioned criteria, the numerical results are compared with the experimental tests. The comparison shows that the stress-based criteria are more accurate than the strain-based ones and the MSED criterion has better accuracy rather than the MTS. © 2023, The Author(s), under exclusive licence to Shiraz University.
Mechanics Based Design of Structures and Machines (15397734) (9)
Prediction of damage evolution in ductile metals is among the most important challenges ahead of researchers. Most of damage models are divided into micromechanical and continuum damage mechanics models. In this paper, a fully coupled elastic-plastic-damage subroutine of Lemaitre’s ductile damage model is implemented. Employing the model, damage initiation, propagation, and fracture of steel samples under shear loadings are predicted and compared with the GTN and extended GTN (EGTN) models. The comparison reveals that although the EGTN model shows more realistic results rather than the GTN, but the Lemaitre’s model has a more accurate prediction for shear dominant damage evolution. © 2021 Taylor & Francis Group, LLC.
Engineering Failure Analysis (13506307)
Achieving a reliable prediction of damage evolution behavior in ductile metals is among the most important challenges of researchers. In this paper, first, based on continuum damage mechanics (CDM) and Lemaitre's ductile damage model, a VUMAT subroutine is developed and implemented into the Abaqus/Explicit code. A lately proposed numerical method is applied to determine material dependent damage parameter for ductile metals like AL-5052 H32 aluminum and X30Cr13 steel alloys. Then, the model is employed to assess damage evolution behavior in different ductile sheet metals and shapes. Finally, the numerical simulation results of damage initiation, growth, and crack onset are attained and validated by experimental and contributed results of literature. It is concluded that the recently presented numerical method in combination with the CDM-based Lemaitre's ductile damage model can successfully estimate the Lemaitre's ductile damage parameter and accurately predict damage evolution behavior of ductile metals under different loading and boundary conditions. © 2022 Elsevier Ltd
Fatigue and Fracture of Engineering Materials and Structures (8756758X) (8)
The present study aims to evaluate and improve the remeshing-free fatigue crack growth (FCG) simulation and life estimation through two developing FEM-VCCT and XFEMPN-VCCT algorithms in Abaqus. First, new energy-based forms of the Paris, Walker, and Elber FCG models are implemented by a user subroutine, a novel systematic meshing strategy is proposed, and some challenging features of these algorithms are investigated. Despite the success of this methodology in enhancing efficiency, decreasing the run-time, and preventing potential errors, it is observed that the XFEMPN-VCCT algorithm has some fundamental errors such as a serious overestimation in FCG life prediction. Thus, a novel “adaptive VCCT” is introduced and implemented by a Python script in Abaqus in the form of a new XFEMPN-AVCCT algorithm. It is finally concluded that the adaptive VCCT can significantly enhance the accuracy of FCG simulation and life estimation. © 2022 John Wiley & Sons Ltd.
Engineering Fracture Mechanics (00137944)
In this study, virtual crack closure technique (VCCT) and extended finite element method (XFEM) are coupled to each other as XFEM-VCCT approach to simulate mode I fatigue delamination growth in composites, employing the direct cyclic method in Abaqus. Both two-dimensional plane strain and three-dimensional finite element models under force and displacement control are considered. Numerical simulation results are compared with the existed experimental test data for double cantilever beam (DCB) specimens and validated. Finally, challenges ahead of VCCT and XFEM-VCCT are discussed in detail and the appropriate method for modeling fatigue delamination growth in laminated composites under high cycle loading is suggested. It is found that simulation of the DCB fatigue delamination via the displacement control loading leads to more accurate results in comparison to the force control. VCCT was found as a suitable method for simulation of fatigue delamination growth in 2D and 3D-shell models. While XFEM-VCCT shows high accuracy and low computational time in 3D-solid finite element models. The key conclusion is that the XFEM-VCCT coupled approach is independent of time increment, whereas the time increment is more effective on the results of VCCT analysis, and it affects the run-time significantly. © 2021 Elsevier Ltd
In this paper, radiant tubes distortion of cracking furnaces plants has been modeled in operation conditions by the finite element method (FEM). The coils are made of 25Cr 35NiNb, and Baily-Norton formulation has been used for modeling the creep behavior. Tubes operational pressure and temperature have been achieved by since coils to complete the cracking process have a limitation in reducing skin temperature. If to economic reasons and to reach the appropriate timeframe for production and fulfillment of sales obligations, operation time before decoking increases from 60 days to 62 days, high operation temperature in the final two days passes from temperature calculated by normal numerical integration techniques and field observations, respectively. Analysis results have compared increasing values of coil tubes length in real conditions. Due to the coils operational process, the parameters affecting their distortion have been investigated. The phenomenon of ballooning and excessive distortion has also been studied by changing tubes internal pressure. © 2021 Institution of Structural Engineers
International Journal of Automotive and Mechanical Engineering (22298649) (1)
Crash boxes are usually used in the transportation and automobile industries. Important parameters such as material, boundary conditions, geometry, impact energy consists of striker mass and velocity, and plastic deformation history can influence on the maximum energy absorption and impact load of these structures. In this research first, crash behaviour of extruded aluminium circular tubes under axial impact loading with rigid and elastic boundary conditions are studied. Then, effect of the elastic support on the tube energy absorption is numerically and experimentally investigated. In the following, the numerical results are compared with the practical observations and validated. Finally, it is revealed that employing the elastic support leads to changing deformation mode and significantly reduces the maximum impact load. © Universiti Malaysia Pahang, Malaysia.
Archive of Applied Mechanics (09391533) (9)
In brittle or quasi-brittle materials, mechanical fracture phenomenon occurs suddenly and without any warning. Therefore, prediction of brittle materials failure is an essential challenge confronting design engineers. In this research, using the conventional finite element method (CFEM) and extended finite element method (XFEM) based on linear elastic fracture mechanics, rupture behavior of U-notch specimens under mixed mode loadings are numerically and practically studied. As the main contribution and objective of the current study, two different fracture criteria established on CFEM and six various criteria founded on XFEM are employed to numerically predict load carrying capacity and crack initiation angle of the U-notch samples. Also, the load carrying capacity and crack initiation angle are experimentally obtained from tensile tests of the U-notch instances under planar mixed mode loading to verify the simulation results. The empirical results are compared with the corresponding estimated values achieved by CFEM and XFEM methods which permit to assess the accuracy of the mentioned criteria in predicting the load carrying capacity and crack initiation angle of U-notch coupons subjected to mixed mode loadings, as the novelty of the investigation. The comparison shows that although both the CFEM and XFEM can properly predict the load carrying capacity and crack initiation angle, applying the XFEM in addition to reduce the computational costs and mesh sensitivity is more precise. Besides, a comparison between the XFEM results denotes that stress-based models are significantly more accurate than strain-based types in predicting the load carrying capacity and crack initiation angle of the U-notch instances under mixed mode loading. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
International Journal of Engineering, Transactions A: Basics (17281431) (10)
Ductile fracture process usually occurs due to the accumulation, growth, and combination of defects or cracks of material and is called ductile damage. Failure in materials can be predicted, using damage mechanics and damage criteria. On the other hand, most of the materials depended on the manufacturing process, are formed in warm or hot conditions so that; the temperature affects on the probable damage initiation. In this study first, a number of conventional hot forming processes of aluminum alloys such as forming process by tail gas, hydroforming, and blank forming with punch are simulated by finite element method and employing different damage criteria, and damage initiation in them is predicted. Then, the obtained numerical results are compared with the experimental results achieved from empirical experiments and validated. Finally, the damage criteria are classified based on the accuracy of the predicted results and the most appropriate criteria for predicting the damage in hot forming processes are introduced. It is concluded that Brozzo and Ayada damage criteria are the most proper criteria for predicting the damage initiation in the hot forming processes.
International Journal of Crashworthiness (13588265) (2)
Thin-walled structures like crash tubes may be used as energy absorption members in automobile chassis. There have been a lot of investigations into the behaviour of these parts on the frontal crash. The main task of previous researches has been to predict the energy absorption and maximum impact force in shell structure. The energy absorption and maximum impact force depend on many parameters such as boundary conditions, the history of plastic deformation during metalworking, geometry, material, and impact energy (mass and velocity of striker). In this paper, the crash behaviour of a circular tube made of the extruded aluminium alloy EN AW-7108 T6 is studied. In this study, by creating elastic and plastic boundary conditions instead of rigid boundary conditions on the bottom of a crash box, the stress-strain sensitivity effect on box behaviour during a crash is considered. In addition, the effect of elastic and plastic boundary conditions on the energy absorption of circular tubes under impact force is numerically investigated. The ductile failure criterion is employed to accurately obtain crashworthiness simulation results. Results reveal that the use of elastic boundary can change deformation mode and decrease the maximum impact force. © 2014 Taylor & Francis.
International Journal of Advanced Manufacturing Technology (02683768) (9-12)
Forming limit diagram (FLD) is a useful criterion for damage prediction, but not suitable for complex operations. Hooputra’s ductile damage (HDD) is a proper failure criterion which relies on three relatively difficult experimental tests for each material. In this paper, first, using the FLD criterion, the required difficult experimental tests of HDD criterion are simulated and the HDD parameters for St14 steel are numerically estimated. Then, to evaluate the obtained HDD parameters, damage behavior of the material in a number of benchmark tests is numerically predicted, employing the HDD criterion. Finally, the simulated results are compared with the practical observations and the identified HDD parameters are validated. Comparison of the results reveals the HDD parameters can be numerically and properly extracted, utilizing the FLD and avoiding the difficult experimental tests. © 2014, Springer-Verlag London.
Steel Research International (16113683)
Damage of materials is the progressive physical process by which they break. The mechanics of damage is the study, through mechanical variables, of the mechanisms involved in this deterioration when the materials are subjected to loading. Common methods to measure damage parameter in ductile materials are variations of the elasticity modulus and the micro-hardness. In this paper, first, the possibility of variation of the elasticity modulus to determine the damage parameter for thin sheets is studied. To achieve this goal, Lemaitre's damage parameter for St 14 steel sheet is identified by using the variations of the elasticity modulus. Then, the calculated parameter from experimental results is applied in a fully coupled elastic-plastic-damage subroutine which has been developed into an Explicit code, to predict the damage behaviour of St14 thin sheet. The numerical results are compared with the empirical observations, to validate the identified damage parameter. Comparison of the numerical and experimental results shows proper and satisfactory adaptation. Hence, it is concluded that the measuring method of variations of elasticity modulus is reliable as a method to measure damage parameter as well as micro-hardness method for thin sheet metals. © 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
Applied Mechanics and Materials (16627482)
Prediction of sheet metal forming limits or analysis of forming failures is a very sensitive problem for design engineers of sheet forming industries. In this paper, first, damage behaviour of St14 steel (DIN 1623) is studied in order to be used in complex forming conditions with the goal of reducing the number of costly trials. Mechanical properties and Lemaitre's ductile damage parameters of the material are determined by using standard tensile and Vickers micro-hardness tests. A fully coupled elastic-plastic-damage model is developed and implemented into an explicit code. Using this model, damage propagation and crack initiation, and ductile fracture behaviour of hemispherical punch bulging process are predicted. The model can quickly predict both deformation and damage behaviour of the part because of using plane stress algorithm, which is valid for thin sheet metals. Experiments are also carried out to validate the results. Comparison of the numerical and experimental results shows good adaptation. Hence, it is concluded that finite element analysis in conjunction with continuum damage mechanics can be used as a reliable tool to predict ductile damage and forming limit in sheet metal forming processes. © (2012) Trans Tech Publications, Switzerland.
Acta Mechanica Solida Sinica (18602134) (6)
Prediction of forming limit in sheet metal forming is among the most important challenges confronting researchers. In this paper, a fully coupled elastic-plastic-damage model has been developed and implemented into an explicit code. Due to the adoption of the plane stress and finite strain theories, model can predict deformation and damage of parts quickly and accurately. Also, damage initiation, propagation, and fracture in some operations are predicted and validated with experiments. It is concluded that finite strain combined with continuum damage mechanics can be used as a quick tool to predict ductile damage, fracture, and forming limits in sheet metal forming processes. © 2012 The Chinese Society of Theoretical and Applied Mechanics.
Key Engineering Materials (10139826)
Various thin-walled pails with fairly complex shapes are produced from sheet metals such as automotive panels and other structural parts. In these processes, damage and fracture may be observed on the work piece, and formability plays a fundamental role. Therefore, determination of forming limits and prediction of rupture modes in these operations is very important for process design engineers. In this paper, first, based on plane stress elasto-plasticity and finite strain theories a fully coupled elastic-plastic-damage model is used to predict damage evolution in one sheet metal forming process with nonlinear and complex strain paths. As the plane stress algorithm is valid for thin sheet metals and finite strain theory is recommended for large deformations or rotations, the model is able to quickly predict both deformation and damage behaviour of the parts with nonlinear and complex strain paths. The numerical simulations are compared with experimental tests. Comparison of the numerical and experimental results shows that the proposed damage model is accurate for various forming conditions. Hence, it is concluded that finite element method combined with continuum damage mechanics, can be used as a reliable and rapid tool to predict damage evolution in sheet metal forming processes with nonlinear and complex strain paths. © (2011) Trans Tech Publications.
Determination of forming limit in sheet metal forming processes is very important and can reduce the number of costly trials. Therefore numerous numerical and experimental analyses have been reported. In this paper, 3D model of hydro-forming process of T-shape tube was simulated by finite element method. An integral ductile damage model, coupled with von Mises plastic criterion, has been applied to predict where and when onset of ductile rupture occurs in the process. Model is based on damage evolution and accounts nonlinear strain paths. Results have been compared with experimental tests and empirical observations. Because of bending effects and nonlinear strain paths assumptions, the ductile damage model showed good agreement with experimental tests and empirical observations. The results were satisfactory and acceptable. Hence ductile damage model can be used as a reliable criterion in prediction of ductile fracture in sheet metal forming processes.
