https://sam.ensam.eu:443 The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material. Mon, 13 Jul 2026 06:37:21 GMT 2026-07-13T06:37:21Z http://hdl.handle.net/10985/10376 Détermination des diagrammes de perte d’ellipticité par une approche micromécanique FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; BERVEILLER, Marcel; LEMOINE, Xavier La striction et la rupture au cours de l’opération d’emboutissage figurent parmi les principaux phénomènes limitant les déformations maximales admises par les métaux. Ces phénomènes sont liés à la microstructure des matériaux ainsi qu’aux conditions de sollicitation. Afin de caractériser l’aptitude au formage d’un matériau, et ce pour différents modes de déformations, Keeler (1965) et Goodwin (1968) ont introduit la notion de Courbe Limite de Formage (CLF). L'inconvénient de cette représentation est sa forte dépendance au chemin de déformation, ce qui suppose qu’elle doit être déterminée pour chaque type de trajet de déformation. L’idée d’Arrieux (1982) fut de rechercher une représentation indépendante du trajet de chargement, ce qui donna naissance aux courbes limites de formage en contraintes. Les diagrammes de perte d'ellipticité (PDE) représentés dans l’espace des déformations principales dans celui des contraintes principales à partir d’une approche micromécanique sont présentés dans ce poster. Ces diagrammes sont qualitativement similaires aux CLF mais beaucoup plus restrictifs. L’influence de certains paramètres sur le tracé de ces courbes est étudiée. Sun, 01 Jan 2006 00:00:00 GMT http://hdl.handle.net/10985/10376 2006-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak BERVEILLER, Marcel LEMOINE, Xavier La striction et la rupture au cours de l’opération d’emboutissage figurent parmi les principaux phénomènes limitant les déformations maximales admises par les métaux. Ces phénomènes sont liés à la microstructure des matériaux ainsi qu’aux conditions de sollicitation. Afin de caractériser l’aptitude au formage d’un matériau, et ce pour différents modes de déformations, Keeler (1965) et Goodwin (1968) ont introduit la notion de Courbe Limite de Formage (CLF). L'inconvénient de cette représentation est sa forte dépendance au chemin de déformation, ce qui suppose qu’elle doit être déterminée pour chaque type de trajet de déformation. L’idée d’Arrieux (1982) fut de rechercher une représentation indépendante du trajet de chargement, ce qui donna naissance aux courbes limites de formage en contraintes. Les diagrammes de perte d'ellipticité (PDE) représentés dans l’espace des déformations principales dans celui des contraintes principales à partir d’une approche micromécanique sont présentés dans ce poster. Ces diagrammes sont qualitativement similaires aux CLF mais beaucoup plus restrictifs. L’influence de certains paramètres sur le tracé de ces courbes est étudiée. http://hdl.handle.net/10985/10060 Effect of microstructural and morphological parameters on the formability of BCC metal sheets FRANZ, Gérald; ABED-MERAIM, Farid; BERVEILLER, Marcel The determination of forming limit strains in sheet metal forming industry is a useful way for quantifying metals in terms of formability. However, such forming limit diagrams (FLDs) remain very difficult to obtain experimentally. Therefore, the numerical prediction of forming limit strains represents a convenient alternative to replace this time consuming and expensive experimental process. Moreover, a combined theoretical-numerical model allows investigating the impact of essential microstructural aspects (e.g., initial and induced textures, dislocation density evolution, softening mechanisms, ...) and deformation mechanisms on the ductility of polycrystalline aggregates. In this paper, the impact of microstructural and morphological parameters, particularly the mean grain size, on the formability limit of BCC materials is investigated. To this end, an elastic-plastic self-consistent (EPSC) polycrystalline model, coupled with a bifurcation-based localization criterion, is adopted to numerically simulate FLDs. The FLDs thus determined using the Bifurcation-EPSC model for an IF-Ti single-phase steel are compared to the FLDs given by ArcelorMittal, demonstrating the predictive capability of the proposed approach in investigations of sheet metal formability. The role of the averaging scheme is also shown to be significant by comparing the critical limit strains predicted with the self-consistent scale-transition scheme to those obtained with the more classical full-constraint Taylor model. Finally, numerical simulations for different values of mean grain size are provided in order to analyze the impact of mean grain size on the formability of BCC metal sheets. In this study, an elastic-plastic self-consistent (EPSC) polycrystalline model is coupled with a bifurcation-based localization criterion to investigate relationships between microstructural and morphological properties and formability of single-phase BCC steels. The interest in such a combined theoretical-numerical prediction tool is to classify materials in terms of ductility and to optimize material properties or to design new grades of steel with enhanced in-use mechanical properties. Wed, 01 Jan 2014 00:00:00 GMT http://hdl.handle.net/10985/10060 2014-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BERVEILLER, Marcel The determination of forming limit strains in sheet metal forming industry is a useful way for quantifying metals in terms of formability. However, such forming limit diagrams (FLDs) remain very difficult to obtain experimentally. Therefore, the numerical prediction of forming limit strains represents a convenient alternative to replace this time consuming and expensive experimental process. Moreover, a combined theoretical-numerical model allows investigating the impact of essential microstructural aspects (e.g., initial and induced textures, dislocation density evolution, softening mechanisms, ...) and deformation mechanisms on the ductility of polycrystalline aggregates. In this paper, the impact of microstructural and morphological parameters, particularly the mean grain size, on the formability limit of BCC materials is investigated. To this end, an elastic-plastic self-consistent (EPSC) polycrystalline model, coupled with a bifurcation-based localization criterion, is adopted to numerically simulate FLDs. The FLDs thus determined using the Bifurcation-EPSC model for an IF-Ti single-phase steel are compared to the FLDs given by ArcelorMittal, demonstrating the predictive capability of the proposed approach in investigations of sheet metal formability. The role of the averaging scheme is also shown to be significant by comparing the critical limit strains predicted with the self-consistent scale-transition scheme to those obtained with the more classical full-constraint Taylor model. Finally, numerical simulations for different values of mean grain size are provided in order to analyze the impact of mean grain size on the formability of BCC metal sheets. In this study, an elastic-plastic self-consistent (EPSC) polycrystalline model is coupled with a bifurcation-based localization criterion to investigate relationships between microstructural and morphological properties and formability of single-phase BCC steels. The interest in such a combined theoretical-numerical prediction tool is to classify materials in terms of ductility and to optimize material properties or to design new grades of steel with enhanced in-use mechanical properties. http://hdl.handle.net/10985/10445 Strain localization analysis using a multiscale model FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; LEMOINE, Xavier; BERVEILLER, Marcel The development of a relevant constitutive model adapted to sheet metal forming simulations requires an accurate description of the most important sources of anisotropy, i.e. the slip processes, the intragranular substructure changes and the texture development. During plastic deformation of thin metallic sheets, strain-path changes often occur in the material resulting in macroscopic effects. These softening/hardening effects must be correctly predicted because they can significantly influence the strain distribution and may lead to flow localization, shear bands and even material failure. The main origin of these effects is related to the intragranular microstructure evolution. This implies that an accurate description of the dislocation patterning during monotonic or complex strain-paths is needed to lead to a reliable constitutive model. First, the behaviour at the mesoscopic scale (which is the one of the grain or the single crystal) is modelled by a micromechanical law written within large strain framework. Hardening is taking into account by a matrix whose internal variables are the mean dislocation densities on each slip system. This crystal plasticity based model is implemented into a large strain self-consistent scheme, leading to the multiscale model which achieves, for each grain, the calculation of plastic slip activity, with help of regularized formulation drawn from viscoplasticity. An improvement of this model is suggested with the introduction of intragranular microstructure description. The substructure of a grain is described taking into account the experimental observations as stress-strain curves and TEM micrographs. Following Peeters’ approach, three local dislocations densities, introduced as internal variables in the multiscale model, allow representing the spatially heterogeneous distributions of dislocations inside the grain. Rate equations, based on the consideration of associated creation, storage and annihilation, are used to describe the dislocation cells evolution. The coupling of the substructure to the critical shear stresses is performed thanks to the concepts of isotropic hardening, latent hardening and polarity. Moreover, a ductility loss criterion, first introduced by Rice, based on the ellipticity loss of the elastic-plastic tangent modulus, is used in these two models to plot Ellipticity Loss Diagrams (ELD). Qualitative comparisons are made with experimental Forming Limit Diagrams (FLD) for ferritic steel involving simple and complex loading paths. In particular, it is shown that numerical ELD have a shape close to experimental FLD and reproduce qualitatively the effects due to complex loading paths. The impact of intragranular microstructure on strain localization is studied thanks to comparisons between ELD plotted with the two models. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10445 2007-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak LEMOINE, Xavier BERVEILLER, Marcel The development of a relevant constitutive model adapted to sheet metal forming simulations requires an accurate description of the most important sources of anisotropy, i.e. the slip processes, the intragranular substructure changes and the texture development. During plastic deformation of thin metallic sheets, strain-path changes often occur in the material resulting in macroscopic effects. These softening/hardening effects must be correctly predicted because they can significantly influence the strain distribution and may lead to flow localization, shear bands and even material failure. The main origin of these effects is related to the intragranular microstructure evolution. This implies that an accurate description of the dislocation patterning during monotonic or complex strain-paths is needed to lead to a reliable constitutive model. First, the behaviour at the mesoscopic scale (which is the one of the grain or the single crystal) is modelled by a micromechanical law written within large strain framework. Hardening is taking into account by a matrix whose internal variables are the mean dislocation densities on each slip system. This crystal plasticity based model is implemented into a large strain self-consistent scheme, leading to the multiscale model which achieves, for each grain, the calculation of plastic slip activity, with help of regularized formulation drawn from viscoplasticity. An improvement of this model is suggested with the introduction of intragranular microstructure description. The substructure of a grain is described taking into account the experimental observations as stress-strain curves and TEM micrographs. Following Peeters’ approach, three local dislocations densities, introduced as internal variables in the multiscale model, allow representing the spatially heterogeneous distributions of dislocations inside the grain. Rate equations, based on the consideration of associated creation, storage and annihilation, are used to describe the dislocation cells evolution. The coupling of the substructure to the critical shear stresses is performed thanks to the concepts of isotropic hardening, latent hardening and polarity. Moreover, a ductility loss criterion, first introduced by Rice, based on the ellipticity loss of the elastic-plastic tangent modulus, is used in these two models to plot Ellipticity Loss Diagrams (ELD). Qualitative comparisons are made with experimental Forming Limit Diagrams (FLD) for ferritic steel involving simple and complex loading paths. In particular, it is shown that numerical ELD have a shape close to experimental FLD and reproduce qualitatively the effects due to complex loading paths. The impact of intragranular microstructure on strain localization is studied thanks to comparisons between ELD plotted with the two models. http://hdl.handle.net/10985/10061 Effect of microstructural and physical mechanisms on mechanical properties of single-phase steels FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak The current work aims to investigate the impact of microstructural and physical mechanisms on the macroscopic behavior and ductility of single-phase steels. For this purpose, an advanced multiscale model, accounting for intragranular microstructure development and evolution, is coupled with a formability limit criterion based on bifur- cation theory. The overall response for polycrystalline aggregates is obtained from a large-strain elastic-plastic single crystal constitutive law, using a self-consistent scale-transition scheme. This approach takes into account essential microstructural aspects such as initial and induced textures, dislocation densities, softening mecha- nisms so that the behav uring complex loading paths is properly described. Focus will be placed here on the relationship between intragranular microstructure of B.C.C. steels and their ductility. The model allows interesting qualitative study in terms of formability limits for various dislocation networks, during monotonic loading tests applied to single-phase steels, with the aim of helping in the design of new materials. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/10061 2013-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak The current work aims to investigate the impact of microstructural and physical mechanisms on the macroscopic behavior and ductility of single-phase steels. For this purpose, an advanced multiscale model, accounting for intragranular microstructure development and evolution, is coupled with a formability limit criterion based on bifur- cation theory. The overall response for polycrystalline aggregates is obtained from a large-strain elastic-plastic single crystal constitutive law, using a self-consistent scale-transition scheme. This approach takes into account essential microstructural aspects such as initial and induced textures, dislocation densities, softening mecha- nisms so that the behav uring complex loading paths is properly described. Focus will be placed here on the relationship between intragranular microstructure of B.C.C. steels and their ductility. The model allows interesting qualitative study in terms of formability limits for various dislocation networks, during monotonic loading tests applied to single-phase steels, with the aim of helping in the design of new materials. http://hdl.handle.net/10985/10008 Impact of intragranular substructure parameters on the forming limit diagrams of single-phase B.C.C. steels FRANZ, Gérald; ABED-MERAIM, Farid; BERVEILLER, Marcel An advanced elastic-plastic self-consistent polycrystalline model, accounting for intragranular microstructure development and evolution, is coupled with a bifurcation-based localization criterion and applied to the numerical investigation of the impact of microstructural patterns on ductility of single-phase steels. The proposed multiscale model, taking into account essential microstructural aspects, such as initial and induced textures, dislocation densities, and softening mechanisms, allows us to emphasize the relationship between intragranular microstructure of B.C.C. steels and their ductility. A qualitative study in terms of forming limit diagrams for various dislocation networks, during monotonic loading tests, is conducted in order to analyze the impact of intragranular substructure parameters on the formability of single-phase B.C.C. steels. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/10008 2013-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BERVEILLER, Marcel An advanced elastic-plastic self-consistent polycrystalline model, accounting for intragranular microstructure development and evolution, is coupled with a bifurcation-based localization criterion and applied to the numerical investigation of the impact of microstructural patterns on ductility of single-phase steels. The proposed multiscale model, taking into account essential microstructural aspects, such as initial and induced textures, dislocation densities, and softening mechanisms, allows us to emphasize the relationship between intragranular microstructure of B.C.C. steels and their ductility. A qualitative study in terms of forming limit diagrams for various dislocation networks, during monotonic loading tests, is conducted in order to analyze the impact of intragranular substructure parameters on the formability of single-phase B.C.C. steels. http://hdl.handle.net/10985/10435 Strain localization analysis using a large strain self-consistent approach FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; LEMOINE, Xavier; BERVEILLER, Marcel The development of a relevant constitutive model adapted to sheet metal forming simulations requires an accurate description of the most important sources of anisotropy, i.e. the slip processes, the intragranular substructure changes and the texture development. During plastic deformation of thin metallic sheets, strain-path changes often occur in the material resulting in macroscopic effects. These softening/hardening effects must be correctly predicted because they can significantly influence the strain distribution and may lead to flow localization, shear bands and even material failure. The main origin of these effects is related to the intragranular microstructure evolution. This implies that an accurate description of the dislocation patterning during monotonic or complex strain-paths is needed to lead to a reliable constitutive model. A crystal plasticity model coupled with an intragranular microstructure description, inspired by Peeters' works, is used to determine the single crystal behaviour and to describe the dislocation cells evolution. The scale transition between the local behaviour and the polycrystalline one is realized thanks to a large strain self-consistent approach. Moreover, the introduction of a ductility loss criterion, first introduced by Rice, based on the ellipticity loss of the elastic-plastic tangent modulus, is used to plot Ellipticity Loss Diagrams (ELD). Qualitative comparisons are made with experimental Forming Limit Diagrams (FLD) for ferritic steel for simple and complex loading paths. In particular, it is shown that numerical ELD have a shape close to experimental FLD and reproduce qualitatively the effects due to complex loading paths. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10435 2007-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak LEMOINE, Xavier BERVEILLER, Marcel The development of a relevant constitutive model adapted to sheet metal forming simulations requires an accurate description of the most important sources of anisotropy, i.e. the slip processes, the intragranular substructure changes and the texture development. During plastic deformation of thin metallic sheets, strain-path changes often occur in the material resulting in macroscopic effects. These softening/hardening effects must be correctly predicted because they can significantly influence the strain distribution and may lead to flow localization, shear bands and even material failure. The main origin of these effects is related to the intragranular microstructure evolution. This implies that an accurate description of the dislocation patterning during monotonic or complex strain-paths is needed to lead to a reliable constitutive model. A crystal plasticity model coupled with an intragranular microstructure description, inspired by Peeters' works, is used to determine the single crystal behaviour and to describe the dislocation cells evolution. The scale transition between the local behaviour and the polycrystalline one is realized thanks to a large strain self-consistent approach. Moreover, the introduction of a ductility loss criterion, first introduced by Rice, based on the ellipticity loss of the elastic-plastic tangent modulus, is used to plot Ellipticity Loss Diagrams (ELD). Qualitative comparisons are made with experimental Forming Limit Diagrams (FLD) for ferritic steel for simple and complex loading paths. In particular, it is shown that numerical ELD have a shape close to experimental FLD and reproduce qualitatively the effects due to complex loading paths. http://hdl.handle.net/10985/26446 Approche micromécanique de l’influence des trajets de déformations sur la limite de formabilité des aciers FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; BERVEILLER, Marcel An elastic-plastic single-crystal behaviour based on a micromechanical description is formulated in large strains. Self-consistent model leads to macroscopic behaviour. This one is coupled with Rice criterion to predict the apparition of instabilities. FLD are plotted for monotonic or complex loadings. The results agree with experimental observations. Mon, 01 Aug 2005 00:00:00 GMT http://hdl.handle.net/10985/26446 2005-08-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak BERVEILLER, Marcel An elastic-plastic single-crystal behaviour based on a micromechanical description is formulated in large strains. Self-consistent model leads to macroscopic behaviour. This one is coupled with Rice criterion to predict the apparition of instabilities. FLD are plotted for monotonic or complex loadings. The results agree with experimental observations. http://hdl.handle.net/10985/10476 A multiscale model based on intragranular microstructure - Prediction of dislocation patterns at the microscopic scale FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; LEMOINE, Xavier; BERVEILLER, Marcel A large strain elastic-plastic single crystal constitutive law, based on dislocation annihilation and storage, is implemented in a new self-consistent scheme, leading to a multiscale model which achieves, for each grain, the calculation of plastic slip activity, with help of regularized formulation drawn from visco-plasticity, and dislocation microstructure evolution. This paper focuses on the relationship between the deformation history of a BCC grain and induced microstructure during monotonic and two-stage strain paths. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10476 2007-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak LEMOINE, Xavier BERVEILLER, Marcel A large strain elastic-plastic single crystal constitutive law, based on dislocation annihilation and storage, is implemented in a new self-consistent scheme, leading to a multiscale model which achieves, for each grain, the calculation of plastic slip activity, with help of regularized formulation drawn from visco-plasticity, and dislocation microstructure evolution. This paper focuses on the relationship between the deformation history of a BCC grain and induced microstructure during monotonic and two-stage strain paths. http://hdl.handle.net/10985/8875 Strain localization analysis for single crystals and polycrystals: Towards microstructure-ductility linkage FRANZ, Gérald; ABED-MERAIM, Farid; BERVEILLER, Marcel In this paper, we performed a strain localization analysis for single crystals and polycrystals, with the specific aim of establishing a link between the microstructure-related parameters and ductility. To this end, advanced large-strain elastic plastic single crystal constitutive modeling is adopted, accounting for the key physical mechanisms that are relevant at the microscale, such as dislocation storage and annihilation. The self-consistent scale-transition scheme is then used to derive the overall constitutive response of polycrystalline aggregates, including the essential microstructural aspects (e.g., initial and induced textures, dislocation density evolution, and softening mechanisms). The resulting constitutive equations for single crystals and polycrystals are coupled with two strain localization criteria: bifurcation theory, which is also related to the loss of ellipticity in the associated boundary value problem, and the strong ellipticity condition, which is presented in full detail along with mathematical links allowing for hierarchical classification in terms of conservativeness. The application of the proposed coupling to single crystals and polycrystals allows the effect of physical microstructural parameters on material ductility to be investigated. Consistent results are found for both single crystals and polycrystals. In addition, forming limit diagrams (FLDs) are constructed for IF-Ti single-phase steels with comparison to the reference results, demonstrating the predictive capability of the proposed approach in investigations of sheet metal formability. The results of the self-consistent scheme are systematically compared to those of the more classical full-constraint Taylor model, both in terms of the impact of microstructural parameters on ductility and in terms of the predicted formability limits and the level of the associated limit strains. Finally, we investigated the impact of strain-path changes on formability through the analysis of the effect of prestrain on the FLDs. Tue, 01 Jan 2013 00:00:00 GMT http://hdl.handle.net/10985/8875 2013-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BERVEILLER, Marcel In this paper, we performed a strain localization analysis for single crystals and polycrystals, with the specific aim of establishing a link between the microstructure-related parameters and ductility. To this end, advanced large-strain elastic plastic single crystal constitutive modeling is adopted, accounting for the key physical mechanisms that are relevant at the microscale, such as dislocation storage and annihilation. The self-consistent scale-transition scheme is then used to derive the overall constitutive response of polycrystalline aggregates, including the essential microstructural aspects (e.g., initial and induced textures, dislocation density evolution, and softening mechanisms). The resulting constitutive equations for single crystals and polycrystals are coupled with two strain localization criteria: bifurcation theory, which is also related to the loss of ellipticity in the associated boundary value problem, and the strong ellipticity condition, which is presented in full detail along with mathematical links allowing for hierarchical classification in terms of conservativeness. The application of the proposed coupling to single crystals and polycrystals allows the effect of physical microstructural parameters on material ductility to be investigated. Consistent results are found for both single crystals and polycrystals. In addition, forming limit diagrams (FLDs) are constructed for IF-Ti single-phase steels with comparison to the reference results, demonstrating the predictive capability of the proposed approach in investigations of sheet metal formability. The results of the self-consistent scheme are systematically compared to those of the more classical full-constraint Taylor model, both in terms of the impact of microstructural parameters on ductility and in terms of the predicted formability limits and the level of the associated limit strains. Finally, we investigated the impact of strain-path changes on formability through the analysis of the effect of prestrain on the FLDs. http://hdl.handle.net/10985/10382 Influence de la microstructure intragranulaire sur l'évolution des surfaces de charge d'un acier ferritique lors de trajets de déformation monotones et complexes FRANZ, Gérald; ABED-MERAIM, Farid; BEN ZINEB, Tarak; LEMOINE, Xavier; BERVEILLER, Marcel Deux modèles micromécaniques de comportement élastoplastique, développés en adoptant une formulation en transformations finies et couplés à une technique de transition d’échelle autocohérente, sont utilisés pour étudier l'évolution des surfaces de charge d'un acier ferritique polycristallin lors de changements de trajets de déformation. L'importance de l'impact de la microstructure intragranulaire sur l'anisotropie du comportement lors de trajets complexes est montrée par l'intégration de la modélisation de la microstructure intragranulaire dans l'un de ces modèles.; Two micromechanical elastic-plastic behaviour models, developed within the framework of finite transformations and coupled with self consistent scale transition approach, are used to study the evolution of yield surfaces of polycrystalline ferritic steels during strain path changes. The importance of the impact of intragranular microstructure on behaviour anisotropy under complex loadings is shown thanks to the introduction of intragranular microstructure modelling in one of these models. Mon, 01 Jan 2007 00:00:00 GMT http://hdl.handle.net/10985/10382 2007-01-01T00:00:00Z FRANZ, Gérald ABED-MERAIM, Farid BEN ZINEB, Tarak LEMOINE, Xavier BERVEILLER, Marcel Deux modèles micromécaniques de comportement élastoplastique, développés en adoptant une formulation en transformations finies et couplés à une technique de transition d’échelle autocohérente, sont utilisés pour étudier l'évolution des surfaces de charge d'un acier ferritique polycristallin lors de changements de trajets de déformation. L'importance de l'impact de la microstructure intragranulaire sur l'anisotropie du comportement lors de trajets complexes est montrée par l'intégration de la modélisation de la microstructure intragranulaire dans l'un de ces modèles. Two micromechanical elastic-plastic behaviour models, developed within the framework of finite transformations and coupled with self consistent scale transition approach, are used to study the evolution of yield surfaces of polycrystalline ferritic steels during strain path changes. The importance of the impact of intragranular microstructure on behaviour anisotropy under complex loadings is shown thanks to the introduction of intragranular microstructure modelling in one of these models.