salima bouvier - Academia.edu (original) (raw)
Papers by salima bouvier
Computational Materials Science, 2005
The present paper aims at reviewing some recent progress in developing advanced constitutive mode... more The present paper aims at reviewing some recent progress in developing advanced constitutive models which are devoted to the description of the anisotropic work-hardening behaviour under strain-path changes at large strains of metallic materials. After reviewing some microscopic and macroscopic experimental evidence, a physically-based phenomenological model using four internal state tensor variables is presented. This model can be simplified into several classical phenomenological models in order to take into account either the isotropic or the kinematic hardening or both. The implementation of the proposed models in the in-house finite element code DD3IMP is briefly recalled. Numerical simulations of the stamping of a curved rail are carried out in order to evaluate the accuracy and the efficiency of the proposed models in modelling the springback.
International Journal of Plasticity, 2006
On the basis of the microstructural evolution after two-stage non proportional loading at finite ... more On the basis of the microstructural evolution after two-stage non proportional loading at finite strains, a so-called microstructural model was developed by that accurately describes the macroscopic anisotropic behaviour such as the Bauschinger effect, the work-hardening stagnation and the work-softening of polycrystalline metals. Many intragranular deformation mechanisms, corresponding to the formation and the evolution of persistent dislocation structures, have been taken into account in choosing the scalar and tensorial internal variables of the elastoplastic model and postulating their evolution equations. In the work discussed here, after a detailed description of Teodosiu-Hu model, several rheological tests and their numerical simulations on different polycrystalline materials are performed in order to evaluate the accuracy and the efficiency of the proposed model. To this aim, a sensitivity study of the material parameters is first carried out in order to show their different effects on the macroscopic behaviour. Therefore, a strategy for their identification is discussed. Regarding to the respective mechanical response of several materials, two simplifications of the proposed model are presented in order to take into account their specific behaviour. Finally, identification of the proposed models is performed and compared to more classical anisotropic work-hardening phenomenological models.
Journal of Materials Processing Technology, 2006
The characterization of the plastic behaviour of rolled metal sheets at large strains is a critic... more The characterization of the plastic behaviour of rolled metal sheets at large strains is a critical ingredient of any finite element analyse software aimed at predicting stress and strain distributions and the eventual occurrence of defects in sheet metal forming. On the other hand, due to the reduced thickness of such rolled sheets, the experimental techniques available for their characterization
Journal of Materials Processing Technology, 2006
... Finally, the application of these techniques to various rolled metal sheets, illustrates the ... more ... Finally, the application of these techniques to various rolled metal sheets, illustrates the ability of simple shear experiments to ... is much more accurate than the technique using deformation gauges that may slightly change the material hardness. 3. Characterization of the plastic.
International Journal for Numerical Methods in Engineering, 2009
Modelling of plastic anisotropy requires the definition of stress potentials (coinciding with the... more Modelling of plastic anisotropy requires the definition of stress potentials (coinciding with the yield criteria in case of the associated flow rules) or, alternatively, plastic strain-rate potentials. The latter approach has several advantages whenever material parameters are determined by means of texture measurements and crystal plasticity simulations. This paper deals with a phenomenological description of anisotropy in elastoplastic rate-insensitive models by using strain-rate potentials. A fully implicit time integration algorithm is developed in this framework and implemented in a static-implicit finite element code. Algorithmic details are discussed, including the derivation of the consistent (algorithmic) tangent modulus and the numerical treatment of the yield condition. Typical sheet forming applications are simulated with the proposed implementation, using the recent non-quadratic strain-rate potential Srp2004-18p. Numerical simulations are carried out for materials that exhibit strong plastic anisotropy. The numerical results confirm that the presented algorithm exhibits the same generality, robustness, accuracy, and time efficiency as state-of-the-art yield criterion-based algorithms. Copyright © 2009 John Wiley & Sons, Ltd.
International Journal of Plasticity, 2009
In the work presented in this paper, several strain rate potentials are examined in order to anal... more In the work presented in this paper, several strain rate potentials are examined in order to analyze their ability to model the initial stress and strain anisotropy of several orthotropic sheet materials. Classical quadratic and more advanced non-quadratic strain rate potentials are investigated in the case of FCC and BCC polycrystals. Different identifications procedures are proposed, which are taking into account the crystallographic texture and/or a set of mechanical test data in the determination of the material parameters.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005
The aim of the present work is the analysis of the evolution of the microstructure and texture of... more The aim of the present work is the analysis of the evolution of the microstructure and texture of a dualphase steel in connection with the macroscopic behavior. Two-stage sequences are carried out in order to investigate the effect of strain-path changes, both at the macroscopic and the microscopic scales. The goal is the achievement of a more comprehensive explanation of the anisotropic behavior under complex strain-path changes for this type of steel (i.e., dual-phase steels). Transmission electron microscopy (TEM) microstructures as well as X-ray diffraction textures are examined after several sequences of simple shear/simple shear loadings. The evolutions of texture are analyzed through comparison with predictions made with the viscoplastic Taylor-Bishop-Hill (TBH) model; its influence on macroscopic values of stress is also quantified. As for the microstructural evolutions, in all investigated cases, it is clear that the dislocation structures which are formed in various grains are strongly dependent on the orientation of the grain, as in the case of previously investigated steel.[1] However, some differences are observed, compared to a simpler single-phase material, which are explained by the differences observed in the initial state and which are then related to the macroscopic behavior.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005
The aim of the present work is to analyse the evolution of the microstructure of a dual-phase ste... more The aim of the present work is to analyse the evolution of the microstructure of a dual-phase steel in term of dislocation organization under two-stage strain-path changes sequences in connection with the crystallographic grain orientation in order to achieve a more comprehensive explanation of the anisotropic behaviour under complex strain-path changes for these steels at room temperature. The mechanical tests are performed using sequences of simple shear tests and/or uniaxial tensile tests with three different strain-path changes, namely monotonic, Bauschinger and orthogonal loading. After monotonic deformation, well-defined dislocation walls are developed whose orientation depends on the grain orientation. After a Bauschinger strain-path change, a partial dissolution of the preformed dislocation sheets is observed whereas after an orthogonal strain-path change they remain in most grains. However, their number and their orientations become more and more compatible with the last deformation mode, with strain increase.
ABSTRACT With a view to environmental, economic and safety concerns, car manufacturers need to de... more ABSTRACT With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase predictive capability, reduce parameter identification cost and allow for robust and time-effective finite element simulations. For this purpose, a 3D physically based model at large strain with dislocation density evolution approach was presented in IDDRG2009 by the authors [1]. This model allows the description of work-hardening's behavior for different loading paths (i.e. uni-axial tensile, simple shear and Bauschinger tests) taking into account several data from microstructure (i.e. grain size, texture, etc...). The originality of this model consists in the introduction of microstructure data in a classical phenomenological model in order to achieve work-hardening's predictive character for different metals from the same grade. Indeed, thanks to a microstructure parameter set for an Interstitial Free steel, it is possible to describe work-hardening behavior for different loading paths of other IF steels by only changing the mean grain size and the chemical composition. During sheet metal forming processes local material points may experience multi-axial and multi-path loadings. Before simulating actual industrial parts, automotive manufacturers use validation tools-e.g. the Cross-Die stamping test. Such typical stamping tests enable the evaluation of a complex distribution of strains. The work described is an implementation [2] of a 3D dislocation based model in ABAQUS/Explicit and its validation on a Finite Element (FE) Cross-Die model. In order to assess the performance and relevance of the 3D dislocation based model in the simulation of industrial forming applications, the results of thinning profiles predicted along several directions and the strain distribution were obtained and compared with experimental results for IF steels with grain sizes varying in the 8-22 mum value range.
International Journal of Plasticity, 2007
In this paper, anisotropic strain rate potentials based on linear transformations of the plastic ... more In this paper, anisotropic strain rate potentials based on linear transformations of the plastic strain rate tensor were reviewed in general terms. This type of constitutive models is suitable for application in forming simulations, particularly for finite element analysis and design codes based on rigid plasticity. Convex formulations were proposed to describe the anisotropic behavior of materials for a full 3-D plastic strain rate state (5 independent components for incompressible plasticity). The 4th order tensors containing the plastic anisotropy coefficients for orthotropic symmetry were specified. The method recommended for the determination of the coefficients using experimental mechanical data for sheet materials was discussed. The formulations were shown to be suitable for the constitutive modeling of FCC and BCC cubic materials. Moreover, these proposed strain rate potentials, called Srp2004-18p and Srp2006-18p, led to a description of plastic anisotropy, which was similar to that provided by a generalized stress potential proposed
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009
For numerical simulation of sheet metal forming, more and more advanced phenomenological function... more For numerical simulation of sheet metal forming, more and more advanced phenomenological functions are used to model the anisotropic yielding. The latter can be described by an adjustment of the coefficients of the yield function or the strain-rate potential to the polycrystalline yield surface determined using crystal plasticity and X-ray measurements. Several strain-rate potentials were examined by the present authors
Computational Materials Science, 2005
The present paper aims at reviewing some recent progress in developing advanced constitutive mode... more The present paper aims at reviewing some recent progress in developing advanced constitutive models which are devoted to the description of the anisotropic work-hardening behaviour under strain-path changes at large strains of metallic materials. After reviewing some microscopic and macroscopic experimental evidence, a physically-based phenomenological model using four internal state tensor variables is presented. This model can be simplified into several classical phenomenological models in order to take into account either the isotropic or the kinematic hardening or both. The implementation of the proposed models in the in-house finite element code DD3IMP is briefly recalled. Numerical simulations of the stamping of a curved rail are carried out in order to evaluate the accuracy and the efficiency of the proposed models in modelling the springback.
International Journal of Plasticity, 2006
On the basis of the microstructural evolution after two-stage non proportional loading at finite ... more On the basis of the microstructural evolution after two-stage non proportional loading at finite strains, a so-called microstructural model was developed by that accurately describes the macroscopic anisotropic behaviour such as the Bauschinger effect, the work-hardening stagnation and the work-softening of polycrystalline metals. Many intragranular deformation mechanisms, corresponding to the formation and the evolution of persistent dislocation structures, have been taken into account in choosing the scalar and tensorial internal variables of the elastoplastic model and postulating their evolution equations. In the work discussed here, after a detailed description of Teodosiu-Hu model, several rheological tests and their numerical simulations on different polycrystalline materials are performed in order to evaluate the accuracy and the efficiency of the proposed model. To this aim, a sensitivity study of the material parameters is first carried out in order to show their different effects on the macroscopic behaviour. Therefore, a strategy for their identification is discussed. Regarding to the respective mechanical response of several materials, two simplifications of the proposed model are presented in order to take into account their specific behaviour. Finally, identification of the proposed models is performed and compared to more classical anisotropic work-hardening phenomenological models.
Journal of Materials Processing Technology, 2006
The characterization of the plastic behaviour of rolled metal sheets at large strains is a critic... more The characterization of the plastic behaviour of rolled metal sheets at large strains is a critical ingredient of any finite element analyse software aimed at predicting stress and strain distributions and the eventual occurrence of defects in sheet metal forming. On the other hand, due to the reduced thickness of such rolled sheets, the experimental techniques available for their characterization
Journal of Materials Processing Technology, 2006
... Finally, the application of these techniques to various rolled metal sheets, illustrates the ... more ... Finally, the application of these techniques to various rolled metal sheets, illustrates the ability of simple shear experiments to ... is much more accurate than the technique using deformation gauges that may slightly change the material hardness. 3. Characterization of the plastic.
International Journal for Numerical Methods in Engineering, 2009
Modelling of plastic anisotropy requires the definition of stress potentials (coinciding with the... more Modelling of plastic anisotropy requires the definition of stress potentials (coinciding with the yield criteria in case of the associated flow rules) or, alternatively, plastic strain-rate potentials. The latter approach has several advantages whenever material parameters are determined by means of texture measurements and crystal plasticity simulations. This paper deals with a phenomenological description of anisotropy in elastoplastic rate-insensitive models by using strain-rate potentials. A fully implicit time integration algorithm is developed in this framework and implemented in a static-implicit finite element code. Algorithmic details are discussed, including the derivation of the consistent (algorithmic) tangent modulus and the numerical treatment of the yield condition. Typical sheet forming applications are simulated with the proposed implementation, using the recent non-quadratic strain-rate potential Srp2004-18p. Numerical simulations are carried out for materials that exhibit strong plastic anisotropy. The numerical results confirm that the presented algorithm exhibits the same generality, robustness, accuracy, and time efficiency as state-of-the-art yield criterion-based algorithms. Copyright © 2009 John Wiley & Sons, Ltd.
International Journal of Plasticity, 2009
In the work presented in this paper, several strain rate potentials are examined in order to anal... more In the work presented in this paper, several strain rate potentials are examined in order to analyze their ability to model the initial stress and strain anisotropy of several orthotropic sheet materials. Classical quadratic and more advanced non-quadratic strain rate potentials are investigated in the case of FCC and BCC polycrystals. Different identifications procedures are proposed, which are taking into account the crystallographic texture and/or a set of mechanical test data in the determination of the material parameters.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 2005
The aim of the present work is the analysis of the evolution of the microstructure and texture of... more The aim of the present work is the analysis of the evolution of the microstructure and texture of a dualphase steel in connection with the macroscopic behavior. Two-stage sequences are carried out in order to investigate the effect of strain-path changes, both at the macroscopic and the microscopic scales. The goal is the achievement of a more comprehensive explanation of the anisotropic behavior under complex strain-path changes for this type of steel (i.e., dual-phase steels). Transmission electron microscopy (TEM) microstructures as well as X-ray diffraction textures are examined after several sequences of simple shear/simple shear loadings. The evolutions of texture are analyzed through comparison with predictions made with the viscoplastic Taylor-Bishop-Hill (TBH) model; its influence on macroscopic values of stress is also quantified. As for the microstructural evolutions, in all investigated cases, it is clear that the dislocation structures which are formed in various grains are strongly dependent on the orientation of the grain, as in the case of previously investigated steel.[1] However, some differences are observed, compared to a simpler single-phase material, which are explained by the differences observed in the initial state and which are then related to the macroscopic behavior.
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2005
The aim of the present work is to analyse the evolution of the microstructure of a dual-phase ste... more The aim of the present work is to analyse the evolution of the microstructure of a dual-phase steel in term of dislocation organization under two-stage strain-path changes sequences in connection with the crystallographic grain orientation in order to achieve a more comprehensive explanation of the anisotropic behaviour under complex strain-path changes for these steels at room temperature. The mechanical tests are performed using sequences of simple shear tests and/or uniaxial tensile tests with three different strain-path changes, namely monotonic, Bauschinger and orthogonal loading. After monotonic deformation, well-defined dislocation walls are developed whose orientation depends on the grain orientation. After a Bauschinger strain-path change, a partial dissolution of the preformed dislocation sheets is observed whereas after an orthogonal strain-path change they remain in most grains. However, their number and their orientations become more and more compatible with the last deformation mode, with strain increase.
ABSTRACT With a view to environmental, economic and safety concerns, car manufacturers need to de... more ABSTRACT With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase predictive capability, reduce parameter identification cost and allow for robust and time-effective finite element simulations. For this purpose, a 3D physically based model at large strain with dislocation density evolution approach was presented in IDDRG2009 by the authors [1]. This model allows the description of work-hardening's behavior for different loading paths (i.e. uni-axial tensile, simple shear and Bauschinger tests) taking into account several data from microstructure (i.e. grain size, texture, etc...). The originality of this model consists in the introduction of microstructure data in a classical phenomenological model in order to achieve work-hardening's predictive character for different metals from the same grade. Indeed, thanks to a microstructure parameter set for an Interstitial Free steel, it is possible to describe work-hardening behavior for different loading paths of other IF steels by only changing the mean grain size and the chemical composition. During sheet metal forming processes local material points may experience multi-axial and multi-path loadings. Before simulating actual industrial parts, automotive manufacturers use validation tools-e.g. the Cross-Die stamping test. Such typical stamping tests enable the evaluation of a complex distribution of strains. The work described is an implementation [2] of a 3D dislocation based model in ABAQUS/Explicit and its validation on a Finite Element (FE) Cross-Die model. In order to assess the performance and relevance of the 3D dislocation based model in the simulation of industrial forming applications, the results of thinning profiles predicted along several directions and the strain distribution were obtained and compared with experimental results for IF steels with grain sizes varying in the 8-22 mum value range.
International Journal of Plasticity, 2007
In this paper, anisotropic strain rate potentials based on linear transformations of the plastic ... more In this paper, anisotropic strain rate potentials based on linear transformations of the plastic strain rate tensor were reviewed in general terms. This type of constitutive models is suitable for application in forming simulations, particularly for finite element analysis and design codes based on rigid plasticity. Convex formulations were proposed to describe the anisotropic behavior of materials for a full 3-D plastic strain rate state (5 independent components for incompressible plasticity). The 4th order tensors containing the plastic anisotropy coefficients for orthotropic symmetry were specified. The method recommended for the determination of the coefficients using experimental mechanical data for sheet materials was discussed. The formulations were shown to be suitable for the constitutive modeling of FCC and BCC cubic materials. Moreover, these proposed strain rate potentials, called Srp2004-18p and Srp2006-18p, led to a description of plastic anisotropy, which was similar to that provided by a generalized stress potential proposed
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2009
For numerical simulation of sheet metal forming, more and more advanced phenomenological function... more For numerical simulation of sheet metal forming, more and more advanced phenomenological functions are used to model the anisotropic yielding. The latter can be described by an adjustment of the coefficients of the yield function or the strain-rate potential to the polycrystalline yield surface determined using crystal plasticity and X-ray measurements. Several strain-rate potentials were examined by the present authors