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International audience; The bending process of an industrial connector is considered and investigated via numerical simulation using a crystal plasticity finite element model (CPFEM). The process consists of sequentially bending a 0.1 mm thick copper-based alloy (CuBe2) with progressive tools into a miniature cylindrical connector of around 1 mm in diameter. The paper focuses on the prediction of springback through the influence of several key-parameters of the numerical simulations. The finite element characteristics, single crystal plasticity model features and the number of grains in the sheet thickness are investigated in order to highlight relevant and influential parameters in CPFEM based microforming process simulations. The influence of the elastic properties is analyzed and a modification of the Peirce-Asaro-Needleman single crystal hardening law is taken into account in order to improve the description of reverse strain path changes. Finally, the numerical results are discussed and compared to the springback measured during the industrial process of the cylindrical connector. It is demonstrated, through the very good agreement with the experimental results, that such approach can be useful to simulate industrial processes.

International audience; Large strain hardening is the main material description ingredient for cold bulk forming process simulations. Hardening identification of large strains is a trade-off between cost, standardization and the ability to represent the experiment, but there are no standard procedures to date. In this proposed approach, large strains (larger than 1) are reached using an industrial wire drawing process, and measured data for identification are obtained from standard tensile tests. Fast semi-analytical post-processing was possible despite the significant process-inherited strain heterogeneity. The parameters of state-of-the-art hardening models were identified, and the robustness was demonstrated to reach far beyond the strain level attained in the experiments. As a consequence, accurate and robust large strain hardening modelling was achieved from standard (tensile test) acquisition by using industrial wire drawing pre-strains.

International audience; Abrupt strain path changes without elastic unloading have been used in the literature to investigate the yield surface of sheet metals, both experimentally and theoretically. Such pioneering studies emphasized an apparent non-normality of the plastic strain rate tensor with respect to the trace of the yield surface in stress space, following such a strain-path change. They inspired numerous subsequent developments of plasticity models including non-associated flow rules. In this paper, this type of abrupt strain-path changes is investigated using state-of-the-art plasticity models. The aim is to emphasize the respective contributions of elasticity, isotropic-kinematic hardening, and rate sensitivity, to the apparent violation of the normality condition. The results show that these classical ingredients of plasticity models significantly contribute to the apparent vertex and loss of normality. These effects are quantified for typical sheet metals subject to biaxial-to-shear orthogonal strain path change.

Forging in semi-solid state significantly extends the possibilities of classical hot forging. In order to fully exploit its potential, the process requires a specific and demanding environment, penalizing its industrial deployment. In this context, an alternative route is proposed. In the proposed process, semi-solid zones at the heart of the material coexist with surrounding solid zones within the part. The outcome is an optimized process where the benefits of thixoforging are reached at a significant extent within the classical process framework of hot forging. The paper investigates this proposal up to a full-scale proof-of concept in an industrial setting. Thixofranc project (Région Lorraine and Région Champagne Ardennes, TACA project (IRT M2P) and ISEETECH (forging equipment)

This paper shows that non-linearity of mechanical behaviour of metal in the elastic regime has an influence on the forming process. Discrete Dislocation Dynamics simulations show that pure elastic behaviour is altered when reversible dislocation displacements occur even in the very beginning of the elastic stage. The influence of such a non-linearity has an impact on the results of numerical simulations of industrial forming of very thin metal sheets of copper.

International audience; The aim of this work is to develop a dislocation density based model for IF and DP steels that incorporates details of the microstructure evolution at the grain-size scale. The model takes into account (i) the contribution of the chemical composition for the prediction of the initial yield stress, (ii) the description of initial texture anisotropy by incorporating grain-size dependent anisotropy coefficients in Hill’48 yield criterion, (iii) the contribution of three dislocation density “families” that are associated with forward, reverse and latent structures. It reproduces the macroscopic transient behaviors observed when strain-path changes occur. The model is implemented in FE code in order to assess its predictive capabilities in case of industrial applications.

The prediction of forming limit diagrams (FLDs) is of significant interest to the sheet metal forming industry. Although a large variety of plastic instability criteria have been developed during the previous decades, there is still a lack of comparison of their respective theoretical bases. The aim of this paper is to present the theoretical formulations of a representative selection of diffuse necking and strain localization criteria based on the maximum force principle, the Marciniak-Kuczyński method and the bifurcation approach. The theoretical foundations and underlying assumptions for each criterion are specified prior to their application to several materials to determine the associated FLDs. The capability of the criteria to predict the formability of thin metal sheets is discussed and a classification of some of the criteria is attempted according to their order of occurrence in terms of the localization prediction. CNRS et Région Lorraine

International audience; Many criteria have been developed during last decades to predict diffuse or localized necking and shear banding. The lack of confrontation of these models with each other on relevant applications makes their choice difficult for the designer. It is proposed to reformulate these plastic instability criteria in an unified framework, to compare their theoretical bases to establish links between them and then to highlighten their limitations. In the case of diffuse necking, a comparison is made between the criteria based on bifurcation analysis and on those based on maximum force principle for elastic-plastic materials. In the case of localized modes, it is shown that the predictions of the Marciniak - Kuczynski approach, based on a multizone model, tend to those of the loss of ellipticity criterion when the initial defect size tends to zero (no initial defect introduced). In the case of elasto-viscoplastic behavior, an approach based on a linear stability analysis is mentioned.

Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grain-size dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial back-stress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few “simply measurable” microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.; International audience; Sheet metal forming processes involve multi-axial strain paths. For the numerical simulation of such processes, an appropriate constitutive model that properly describes material behavior at large strain is required. For accurate and time-effective simulations, it is crucial to use plasticity models based on physics, as material macroscopic behavior is closely related to the evolution of the associated microstructures. Accordingly, a large strain work-hardening phenomenological model that incorporates the intragranular microstructure evolution through a dislocation density approach is proposed. The model is defined by a yield criterion and hardening laws that are all grain-size dependent. The classical Hill criterion in which grain-size dependency was introduced is proposed. Hardening laws are given by a combination of kinematic and isotropic contributions that respectively take into account the evolution with strain of cell blocks formed by geometrically necessary boundaries (GNBs) and individual dislocation cells delineated by incidental dislocation boundaries within cell blocks (IDBs). On the one hand, IDBs evolution contribution is described by a modified Rauch et al. isotropic model, which is able to describe work-hardening stagnation and work-softening. On the other hand, GNBs evolution contribution is described by a grain-size dependent tensorial back-stress expression proposed by Aouafi et al. [2007] to describe the plastic anisotropy and Bauschinger effect. Moreover, the proposed model aims to accurately predict steel behavior through an innovative approach by only changing few “simply measurable” microstructure data (e.g. chemical composition, grain size…). The predictive capabilities of the model are assessed for interstitial free (IF) and dual phase (DP) steels with grain sizes varying respectively in the 8-40 µm and 1-10 µm value range. Different loading paths are analyzed, namely the uniaxial tensile test, reversal simple shear and orthogonal tests.

A physically based elasto-visco-plastic constitutive model is presented and compared to experimental results for three different mild steels. The experiments consist of tensile tests ranging from quasi-static conditions up to strain rates of 103 s-1 as well as quasi-static simple and reverse shear tests at different amounts of pre-strain. Additional two-step sequential mechanical tests (Bauschinger and orthogonal effects) have been performed to further evaluate the ability of the model to describe strain-path changes at moderate/large strains. The model requires significantly fewer material parameters compared to other visco-plasticity models from the literature, while being able to describe some of the main features of the strain-rate sensitivity of mild steels. Accordingly, the parameter identification is simple and intuitive, requiring a relatively small set of experiments. The strain-rate sensitivity modeling is not restricted to a particular hardening law and thus provides a general framework in which advanced hardening equations can be adopted.; International audience; A physically based elasto-visco-plastic constitutive model is presented and compared to experimental results for three different mild steels. The experiments consist of tensile tests ranging from quasi-static conditions up to strain rates of 103 s-1 as well as quasi-static simple and reverse shear tests at different amounts of pre-strain. Additional two-step sequential mechanical tests (Bauschinger and orthogonal effects) have been performed to further evaluate the ability of the model to describe strain-path changes at moderate/large strains. The model requires significantly fewer material parameters compared to other visco-plasticity models from the literature, while being able to describe some of the main features of the strain-rate sensitivity of mild steels. Accordingly, the parameter identification is simple and intuitive, requiring a relatively small set of experiments. The strain-rate sensitivity modeling is not restricted to a particular hardening law and thus provides a general framework in which advanced hardening equations can be adopted.

International audience; A physically based elasto-visco-plastic constitutive model is presented and compared to experimental results for a DD14 mild steel. The model requires significantly fewer material parameters compared to other visco-plasticity models from the literature while exhibiting very good accuracy. Accordingly, the parameter identification is simple and intuitive, requiring a relatively small set of experiments. The strain-rate sensitivity modeling is not restricted to a particular hardening law and thus provides a general framework in which advanced hardening equations can be adopted and compared. The model has been implemented in the commercial finite element code Abaqus/Explicit. First predictions compared to experiments are analyzed and underline the effect of hardening law and strain-rate sensitivity on 3D finite element simulations. The model has been also applied as the basis for a homogenization approach at the phase scale; preliminary investigations showed the benefits of coupling such an approach with scale-transition technique where microstructure-relevant data can explicitly enter the model and may be used for material design simulations.

This paper investigates a recently developed elasto-plastic constitutive model. For this purpose, the model was implemented in a commercial finite element code and was used to simulate the cross-die deep drawing test. Deep drawing experiments and numerical simulations were conducted for five interstitial-free steels and seven dual-phase steels, each of them having a different thickness and strength. The main interest of the adopted model is a very efficient parameter identification procedure, due to the physical background of the model and the physical significance of some of its parameters and state variables. Indeed, the dislocation density, grain size, and martensite volume fraction explicitly enter the model’s formulation, although the overall approach is macroscopic. For the dual-phase steels, only the chemical composition and the average grain sizes were measured for the martensite and ferrite grains, as well as the martensite volume fraction. The mild steels required three additional tensile tests along three directions, in order to describe the plastic anisotropy. Information concerning the transient mechanical behavior after strain-path changes (reverse and orthogonal) was not collected for each material, but for only one material of each family of steels (IF, DP), based on previous works available in the literature. This minimalistic experimental base was used to feed the numerical simulations for the twelve materials that were confronted to deep drawing experiments in terms of thickness distributions. The results suggested that the accuracy of the numerical simulations is very satisfactory in spite of the scarce experimental input data. Additional investigations indicated that the modeling of the transient behavior due to strain-path changes may have a significant impact on the simulation results, and that the adopted approach provides a simple and efficient alternative in this regard.; International audience; This paper investigates a recently developed elasto-plastic constitutive model. For this purpose, the model was implemented in a commercial finite element code and was used to simulate the cross-die deep drawing test. Deep drawing experiments and numerical simulations were conducted for five interstitial-free steels and seven dual-phase steels, each of them having a different thickness and strength. The main interest of the adopted model is a very efficient parameter identification procedure, due to the physical background of the model and the physical significance of some of its parameters and state variables. Indeed, the dislocation density, grain size, and martensite volume fraction explicitly enter the model’s formulation, although the overall approach is macroscopic. For the dual-phase steels, only the chemical composition and the average grain sizes were measured for the martensite and ferrite grains, as well as the martensite volume fraction. The mild steels required three additional tensile tests along three directions, in order to describe the plastic anisotropy. Information concerning the transient mechanical behavior after strain-path changes (reverse and orthogonal) was not collected for each material, but for only one material of each family of steels (IF, DP), based on previous works available in the literature. This minimalistic experimental base was used to feed the numerical simulations for the twelve materials that were confronted to deep drawing experiments in terms of thickness distributions. The results suggested that the accuracy of the numerical simulations is very satisfactory in spite of the scarce experimental input data. Additional investigations indicated that the modeling of the transient behavior due to strain-path changes may have a significant impact on the simulation results, and that the adopted approach provides a simple and efficient alternative in this regard.

ASME 2012 11th Biennial Conference on Engineering Systems Design and AnalysisVolume 1: Advanced Computational Mechanics; Advanced Simulation-Based Engineering Sciences; Virtual and Augmented Reality; Applied Solid Mechanics and Material Processing; Dynamical Systems and ControlNantes, France, July 2–4, 2012Conference Sponsors: InternationalISBN: 978-0-7918-4484-7; International audience; The present contribution consists of implementing an advanced GTN damage model as a “User Material subroutine” in the Abaqus FE code. This damage model is based on specific nucleation and growth laws. This model is applied to the prediction of the damage evolution and the stress state in notched specimens made of dual phase steel. By comparing numerical predictions with experimental results based on high-resolution X-ray absorption tomography, the numerical approach was improved and validated.

In this paper, we investigate the springback behavior of several advanced high-strength sheet steels (TRIP, Dual-Phase, ferrite-bainite) with thicknesses up to 4 mm. Samples were tested by means of the bending-under-tension (BUT) test. The BUT has been extensively applied, in the literature, to relatively thin (1 mm and thinner) sheet metals for automotive applications; the applicability of several guidelines from the literature was investigated in this work in the context of thick advanced high strength steel (AHSS) sheets and using a sample width of 12 mm. The monotonic decrease of springback as back force increased was confirmed for this category of sheet steels, and a general trend for the non-linear influence of the tool radius was observed. With the selected sample width, the effect of the secondary curvature was negligible. Conclusions and simple guidelines are drawn from the analysis with industrial sheet forming applications in mind.; International audience; In this paper, we investigate the springback behavior of several advanced high-strength sheet steels (TRIP, Dual-Phase, ferrite-bainite) with thicknesses up to 4 mm. Samples were tested by means of the bending-under-tension (BUT) test. The BUT has been extensively applied, in the literature, to relatively thin (1 mm and thinner) sheet metals for automotive applications; the applicability of several guidelines from the literature was investigated in this work in the context of thick advanced high strength steel (AHSS) sheets and using a sample width of 12 mm. The monotonic decrease of springback as back force increased was confirmed for this category of sheet steels, and a general trend for the non-linear influence of the tool radius was observed. With the selected sample width, the effect of the secondary curvature was negligible. Conclusions and simple guidelines are drawn from the analysis with industrial sheet forming applications in mind.

Strain localization, which occurs in metallic materials in the form of shear bands during forming processes, is one of the major causes of defective parts produced in the industry. Various instability criteria have been developed in the literature to predict the occurrence of these plastic instabilities. In this work, we propose to couple a GTN-type model [1,2], known for its widespread use to describe damage evolution in metallic materials, to the Rice’s [3] localization criterion. The implementation of the constitutive modeling is achieved via a user material (UMAT) subroutine in the commercial finite element code ABAQUS. Large deformations are taken into account within a three dimensional co-rotational framework. The effectiveness of the proposed coupling for the prediction of the formability of stretched metal sheets is shown and Forming Limit Diagrams (FLDs) are plotted for different materials. References [1] Gurson, A.L., Continuum theory of ductile rupture by void nucleation and growth: Part I- yield criteria and flow rules for porous ductile media. Journal of Engineering Materials and Technology, 99(1):2–15 (1977). [2] Needleman A., V. Tvergaard, An analysis of ductile rupture in notched bars, Journal of the Mechanics and Physics of Solids, 32, 461-490 (1984). [3] Rice, J. R., The localization of plastic deformation. Theoretical and applied mechanics. Koiter ed., 207-227 (1976).

In this contribution, the formulation of the SHB8PS continuum shell finite element is extended to anisotropic elastic-plastic behavior models with combined isotropic-kinematic hardening at large deformations. The resulting element is then implemented into the commercial implicit finite element code Abaqus/Standard via the UEL subroutine. The SHB8PS element is an eight-node, three-dimensional brick with displacements as the only degrees of freedom and a preferential direction called the thickness. A reduced integration scheme is adopted using an arbitrary number of integration points along the thickness direction and only one integration point in the other directions. The hourglass modes due to this reduced integration are controlled using a physical stabilization technique together with an assumed strain method for the elimination of locking. Therefore, the element can be used to model thin structures while providing an accurate description of the various through-thickness phenomena. Its performance is assessed through several applications involving different types of non-linearities: geometric, material and that induced by contact. Particular attention is given to springback prediction for a NUMISHEET benchmark problem.; International audience; In this contribution, the formulation of the SHB8PS continuum shell finite element is extended to anisotropic elastic-plastic behavior models with combined isotropic-kinematic hardening at large deformations. The resulting element is then implemented into the commercial implicit finite element code Abaqus/Standard via the UEL subroutine. The SHB8PS element is an eight-node, three-dimensional brick with displacements as the only degrees of freedom and a preferential direction called the thickness. A reduced integration scheme is adopted using an arbitrary number of integration points along the thickness direction and only one integration point in the other directions. The hourglass modes due to this reduced integration are controlled using a physical stabilization technique together with an assumed strain method for the elimination of locking. Therefore, the element can be used to model thin structures while providing an accurate description of the various through-thickness phenomena. Its performance is assessed through several applications involving different types of non-linearities: geometric, material and that induced by contact. Particular attention is given to springback prediction for a NUMISHEET benchmark problem.

Within the framework of sheet metal forming, the importance of hardening models for springback predictions has been often emphasized. While some specific applications require very accurate models, in many common situations simpler (isotropic hardening) models may be sufficient. In these conditions, investigation of the impact of hardening models requires well defined test configurations and accurate measurements to generate the reference data. Specific draw-bend tests have been especially conceived for this purpose. In this work, such a draw-bending experimental device has been designed, for use on a biaxial tension machine. Three different steel sheets have been tested (one mild steel sheet and two HSS sheets) with thicknesses between 0.8 and 2 mm. Up to three different back-force levels were used for the tests. Wall curvatures and springback angles were measured. Finite element simulations of the tests were performed. A parameter sensitivity analysis has been carried out in order to determine the numerical parameters ensuring accurate springback results. The tests were simulated using an isotropic hardening model and a combined isotropic-kinematic hardening model. The impact of the hardening model is explored for the various test configurations and conclusions are drawn concerning their relative importance.; International audience; Within the framework of sheet metal forming, the importance of hardening models for springback predictions has been often emphasized. While some specific applications require very accurate models, in many common situations simpler (isotropic hardening) models may be sufficient. In these conditions, investigation of the impact of hardening models requires well defined test configurations and accurate measurements to generate the reference data. Specific draw-bend tests have been especially conceived for this purpose. In this work, such a draw-bending experimental device has been designed, for use on a biaxial tension machine. Three different steel sheets have been tested (one mild steel sheet and two HSS sheets) with thicknesses between 0.8 and 2 mm. Up to three different back-force levels were used for the tests. Wall curvatures and springback angles were measured. Finite element simulations of the tests were performed. A parameter sensitivity analysis has been carried out in order to determine the numerical parameters ensuring accurate springback results. The tests were simulated using an isotropic hardening model and a combined isotropic-kinematic hardening model. The impact of the hardening model is explored for the various test configurations and conclusions are drawn concerning their relative importance.

The originality of the approach used here is to present stability conditions of metallic materials modeled by general phenomenological laws and to apply them to the study of the formability of thin metallic sheets. The constitutive equations are based on an elastic-viscoplastic model coupled with a classical isotropic damage model. Various classical isotropic and kinematic hardening models are considered here to reproduce the hardening behavior and the induced anisotropy, while the initial anisotropy of metallic rolled sheets is introduced by Hill’48 anisotropic yield function. Softening is taken into account by coupling the constitutive model with a scalar damage variable. This phenomenological variable is defined within the framework of continuum damage mechanics and represents the degradation of the elastic properties during the forming operations. The stability of the constitutive damageable elastic-viscoplastic system is then sought by means of linear perturbation approach. Application of this method to a mild steel and a dual phase steel leads to the determination of their formability limit diagrams. On the one hand, FLDs obtained with Rice’s criterion and with this stability criterion illustrate the theoretical relation between these criteria and on the other hand, a parametric study shows the influence of governing parameters of hardening, damage and strain rate sensitivity.; International audience; The originality of the approach used here is to present stability conditions of metallic materials modeled by general phenomenological laws and to apply them to the study of the formability of thin metallic sheets. The constitutive equations are based on an elastic-viscoplastic model coupled with a classical isotropic damage model. Various classical isotropic and kinematic hardening models are considered here to reproduce the hardening behavior and the induced anisotropy, while the initial anisotropy of metallic rolled sheets is introduced by Hill’48 anisotropic yield function. Softening is taken into account by coupling the constitutive model with a scalar damage variable. This phenomenological variable is defined within the framework of continuum damage mechanics and represents the degradation of the elastic properties during the forming operations. The stability of the constitutive damageable elastic-viscoplastic system is then sought by means of linear perturbation approach. Application of this method to a mild steel and a dual phase steel leads to the determination of their formability limit diagrams. On the one hand, FLDs obtained with Rice’s criterion and with this stability criterion illustrate the theoretical relation between these criteria and on the other hand, a parametric study shows the influence of governing parameters of hardening, damage and strain rate sensitivity.

Because prevention of forming defects has become one of the major industrial challenges, various experimental and theoretical approaches have been developed to predict sheet metal formability. The main theoretical models can be summarized as: the maximum force principle, according to which necking is associated with the maximum load in a uniaxial tensile test; Marciniak-Kuczyński (M-K) two-zone analysis, based on an initial thickness defect in the sheet; bifurcation theory, predicting diffuse necking with general bifurcation criterion or localized modes corresponding to loss of ellipticity; and more recently, linear stability analysis by means of linearization of perturbed equilibrium equations. Considering this variety of models, a careful comparison of numerical Forming Limit Diagrams (FLDs) along with in-depth understanding of their theoretical foundations is required to help select relevant localization criteria. In this paper, the theoretical bases of M-K and Rice's criteria are first reviewed, which are then applied to steels modeled by elasto-plastic constitutive equations coupled with damage. It is shown that the FLDs obtained with the M-K model tend to those yielded by Rice's criterion in the limit of vanishing initial imperfections. ANR Formef & Région Lorraine

International audience; The aim of this paper is to give an overview of the theoretical basis of the most significant and commonly used localization criteria reformulated into a unified framework, and to apply these criteria to different materials in order to determine their formability domains. After giving a general material description based on a phenomenological approach, theoretical foundations of localization criteria are presented together with their advantages and drawbacks. These criteria rely on diverse theories: maximum load principle, bifurcation analysis, Marciniak-Kuczynski analysis, and stability analysis by a linear perturbation method. They are then applied to a brass and a Dual Phase steel and the predicted Forming Limit Diagrams (FLD) are discussed.

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.

Lors des opérations de mise en forme de structures minces, des phénomènes d’instabilité peuvent se produire. En emboutissage, ces instabilités peuvent se manifester sous différentes formes comme par exemple la striction ou encore la localisation des déformations plastiques sous forme de bandes de cisaillement. Toutes ces instabilités conduisent soit à des défauts lors des opérations de mise en forme, ce qui se traduit par la mise au rebut de pièces, soit à l’adoption de méthodes de dimensionnement trop conservatives. La maîtrise de critères de prédiction des instabilités est donc un enjeu majeur dans le domaine concurrentiel des industries de la mise en forme. Depuis la seconde moitié du 20ème siècle, de nombreux travaux expérimentaux, théoriques ou numériques ont été menés afin de comprendre et prévoir ces phénomènes d’instabilité. Les travaux expérimentaux ont permis de déterminer le domaine de formabilité pour différentes classes de matériaux avec des Courbes Limites de Formage (CLF) (Keeler (1965), Goodwin (1968)). Différents travaux théoriques et numériques ont cherché à déterminer le domaine de formabilité tout en s’affranchissant des contraintes expérimentales. Parmi ces travaux, les principaux sont basés sur le principe de force maximum (Swift (1952), Hill (1952), Hora et al. (1996)), d’analyse de bifurcation (Hill (1958), Stören et Rice (1975), Rice (1976), Valanis (1989), Bigoni et Hueckel (1991)), d’analyse par la méthode de perturbation (Dudzinski et Molinari (1991), Benallal (1997), Keryvin (1999)) ou sur l’existence d’un défaut initial (Marciniak et Kuczyński (1967), Hutchinson et Neale (1978), Kuroda et Tvergaard (2000)). Cet article porte sur l’étude des critères de Marciniak-Kuczyński ou M-K et de Hill. Un algorithme général du critère M-K, basé sur une méthode de résolution explicite, le modèle de Hill et un modèle de comportement phénoménologique sont présentés puis appliqués au tracé de courbes limites de formage.; National audience; Lors des opérations de mise en forme de structures minces, des phénomènes d’instabilité peuvent se produire. En emboutissage, ces instabilités peuvent se manifester sous différentes formes comme par exemple la striction ou encore la localisation des déformations plastiques sous forme de bandes de cisaillement. Toutes ces instabilités conduisent soit à des défauts lors des opérations de mise en forme, ce qui se traduit par la mise au rebut de pièces, soit à l’adoption de méthodes de dimensionnement trop conservatives. La maîtrise de critères de prédiction des instabilités est donc un enjeu majeur dans le domaine concurrentiel des industries de la mise en forme. Depuis la seconde moitié du 20ème siècle, de nombreux travaux expérimentaux, théoriques ou numériques ont été menés afin de comprendre et prévoir ces phénomènes d’instabilité. Les travaux expérimentaux ont permis de déterminer le domaine de formabilité pour différentes classes de matériaux avec des Courbes Limites de Formage (CLF) (Keeler (1965), Goodwin (1968)). Différents travaux théoriques et numériques ont cherché à déterminer le domaine de formabilité tout en s’affranchissant des contraintes expérimentales. Parmi ces travaux, les principaux sont basés sur le principe de force maximum (Swift (1952), Hill (1952), Hora et al. (1996)), d’analyse de bifurcation (Hill (1958), Stören et Rice (1975), Rice (1976), Valanis (1989), Bigoni et Hueckel (1991)), d’analyse par la méthode de perturbation (Dudzinski et Molinari (1991), Benallal (1997), Keryvin (1999)) ou sur l’existence d’un défaut initial (Marciniak et Kuczyński (1967), Hutchinson et Neale (1978), Kuroda et Tvergaard (2000)). Cet article porte sur l’étude des critères de Marciniak-Kuczyński ou M-K et de Hill. Un algorithme général du critère M-K, basé sur une méthode de résolution explicite, le modèle de Hill et un modèle de comportement phénoménologique sont présentés puis appliqués au tracé de courbes limites de formage.

La mise en forme de tôles métalliques implique bien souvent de grandes déformations accompagnées de trajets de chargement complexes. Pour améliorer la prédiction via la simulation numérique de la forme finale des pièces, des modèles de comportement plus physiques doivent être considérés. On se propose ici d’étudier la localisation des déformations durant la mise en forme de tôles d’acier à haute résistance. Plus précisément, on aborde la prédiction des courbes limites de formage (CLF) de ces tôles en trajets directs et séquentiels. Généralement, une bonne prédiction de la localisation des déformations nécessite la prise en compte de l’endommagement dans le modèle de comportement. Ainsi, un modèle de comportement élasto-plastique couplé à un modèle d’endommagement a été considéré. Le couplage est réalisé dans le cadre de l’approche de la mécanique de l’endommagement continu (Lemaitre et Chaboche, 1986). L’écrouissage du matériau est pris en compte en introduisant le modèle microstructural de Teodosiu et Hu (1998). Ce modèle permet de tenir compte des phénomènes de changement de trajets de déformation induits lors de la mise en forme des tôles. Dans le but de définir des points limites associés à la localisation de la déformation et qui représenteront les points de la CLF, un critère de localisation est également introduit (critère de Rice, 1976). Le modèle de comportement résultant, combiné au critère de localisation, a été implanté dans le code de calcul par éléments finis Abaqus/Standard en utilisant la routine UMAT pour le comportement et la routine UVARM pour le critère.Comme application, des simulations de tests rhéologiques avec des chargements directs et séquentiels ont été réalisées afin de montrer simultanément les phénomènes de transition liés au changement de trajets de déformation et ceux relatifs à l’endommagement. Enfin, des CLF à localisation ont été tracées pour différents trajets de déformation.; National audience; La mise en forme de tôles métalliques implique bien souvent de grandes déformations accompagnées de trajets de chargement complexes. Pour améliorer la prédiction via la simulation numérique de la forme finale des pièces, des modèles de comportement plus physiques doivent être considérés. On se propose ici d’étudier la localisation des déformations durant la mise en forme de tôles d’acier à haute résistance. Plus précisément, on aborde la prédiction des courbes limites de formage (CLF) de ces tôles en trajets directs et séquentiels. Généralement, une bonne prédiction de la localisation des déformations nécessite la prise en compte de l’endommagement dans le modèle de comportement. Ainsi, un modèle de comportement élasto-plastique couplé à un modèle d’endommagement a été considéré. Le couplage est réalisé dans le cadre de l’approche de la mécanique de l’endommagement continu (Lemaitre et Chaboche, 1986). L’écrouissage du matériau est pris en compte en introduisant le modèle microstructural de Teodosiu et Hu (1998). Ce modèle permet de tenir compte des phénomènes de changement de trajets de déformation induits lors de la mise en forme des tôles. Dans le but de définir des points limites associés à la localisation de la déformation et qui représenteront les points de la CLF, un critère de localisation est également introduit (critère de Rice, 1976). Le modèle de comportement résultant, combiné au critère de localisation, a été implanté dans le code de calcul par éléments finis Abaqus/Standard en utilisant la routine UMAT pour le comportement et la routine UVARM pour le critère.Comme application, des simulations de tests rhéologiques avec des chargements directs et séquentiels ont été réalisées afin de montrer simultanément les phénomènes de transition liés au changement de trajets de déformation et ceux relatifs à l’endommagement. Enfin, des CLF à localisation ont été tracées pour différents trajets de déformation.

Automotive industries are more and more subject to restrictive environmental constraints. Weight reduction of structures seems to be an interesting way to satisfy these requirements. This can be achieved either by using new materials, such as high strength steels or by adopting appropriate dimensioning methods to predict the occurrence of strain localization. Forming Limit Diagram (FLD) is a concept widely used to characterize the formability of thin metal sheets. Analytical determination of FLDs is usually based on the use of localization criteria. Some of the existing material instability criteria are for example based on empirical observations, on the maximum load principle [1-3], on the existence of an initial defect in the sheet [4], on a perturbation method [5] or on bifurcation analysis [6]. Although numerous criteria have been developed, they all have advantages but also drawbacks and limitations. Their confrontation on a wide range of materials is still insufficiently developed to compare their respective capability of accurately predicting FLDs for new materials. Adaptations of some criteria to advanced constitutive laws are also made necessary by the use of new high strength materials. The aim of this paper is to give a general formulation of some localization criteria allowing the comparison of the predicted FLDs for a wide range of materials. An implementation of these criteria coupled with different phenomenological constitutive laws is presented and compared for different materials including an aluminium alloy, a brass and a dual phase steel.; International audience; Automotive industries are more and more subject to restrictive environmental constraints. Weight reduction of structures seems to be an interesting way to satisfy these requirements. This can be achieved either by using new materials, such as high strength steels or by adopting appropriate dimensioning methods to predict the occurrence of strain localization. Forming Limit Diagram (FLD) is a concept widely used to characterize the formability of thin metal sheets. Analytical determination of FLDs is usually based on the use of localization criteria. Some of the existing material instability criteria are for example based on empirical observations, on the maximum load principle [1-3], on the existence of an initial defect in the sheet [4], on a perturbation method [5] or on bifurcation analysis [6]. Although numerous criteria have been developed, they all have advantages but also drawbacks and limitations. Their confrontation on a wide range of materials is still insufficiently developed to compare their respective capability of accurately predicting FLDs for new materials. Adaptations of some criteria to advanced constitutive laws are also made necessary by the use of new high strength materials. The aim of this paper is to give a general formulation of some localization criteria allowing the comparison of the predicted FLDs for a wide range of materials. An implementation of these criteria coupled with different phenomenological constitutive laws is presented and compared for different materials including an aluminium alloy, a brass and a dual phase steel.

Dans cet article, une modélisation des différentes phases (ferrite, perlite etc.…) d’un acier multiphasé est proposée moyennant une loi phénoménologique à base physique. La description unifiée du comportement viscoplastique peut être décrite à partir de lois de type sinus hyperbolique. Dans cette optique, une loi en sinus hyperbolique est utilisée afin de décrire de façon physiquement acceptable l’ensemble des comportements asymptotiques du comportement viscoplastique. L’écrouissage de chacune des phases est de type combiné (isotrope et cinématique) incluant l’effet de vitesse de déformation propre au comportement visqueux. A partir d’un modèle de comportement monotone unidimensionnel d’inspiration métallurgique, nous développons une formulation tridimensionnelle incrémentale, en déterminant l’expression du potentiel dont découlent les lois de comportement correspondantes. La capacité du modèle ainsi obtenu à décrire le comportement élasto-viscoplastique d’une phase est testée au travers de simulations de tests rhéologiques décrivant différents chemins de déformation à différentes vitesses de déformation. Une discussion basée sur la comparaison de ces simulations avec des résultats expérimentaux sur un acier 100% ferritique est présentée.; International audience; Dans cet article, une modélisation des différentes phases (ferrite, perlite etc.…) d’un acier multiphasé est proposée moyennant une loi phénoménologique à base physique. La description unifiée du comportement viscoplastique peut être décrite à partir de lois de type sinus hyperbolique. Dans cette optique, une loi en sinus hyperbolique est utilisée afin de décrire de façon physiquement acceptable l’ensemble des comportements asymptotiques du comportement viscoplastique. L’écrouissage de chacune des phases est de type combiné (isotrope et cinématique) incluant l’effet de vitesse de déformation propre au comportement visqueux. A partir d’un modèle de comportement monotone unidimensionnel d’inspiration métallurgique, nous développons une formulation tridimensionnelle incrémentale, en déterminant l’expression du potentiel dont découlent les lois de comportement correspondantes. La capacité du modèle ainsi obtenu à décrire le comportement élasto-viscoplastique d’une phase est testée au travers de simulations de tests rhéologiques décrivant différents chemins de déformation à différentes vitesses de déformation. Une discussion basée sur la comparaison de ces simulations avec des résultats expérimentaux sur un acier 100% ferritique est présentée.

In this work, an advanced anisotropic elastic-plasticity model is combined with a damage model and a strain localization criterion in the aim to describe accurately the mechanical behavior of sheet metals. Large strain, fully three-dimensional, implicit time integration algorithms are developed for this model and implemented in the finite element code Abaqus. The resulting code is used to predict the strain localization limits as well as the springback after forming of sheet steels. The impact of strain-path dependent hardening models on the limit strains and on the amount of springback is addressed.; International audience; In this work, an advanced anisotropic elastic-plasticity model is combined with a damage model and a strain localization criterion in the aim to describe accurately the mechanical behavior of sheet metals. Large strain, fully three-dimensional, implicit time integration algorithms are developed for this model and implemented in the finite element code Abaqus. The resulting code is used to predict the strain localization limits as well as the springback after forming of sheet steels. The impact of strain-path dependent hardening models on the limit strains and on the amount of springback is addressed.

In continuum mechanics, plastic anisotropy is described using anisotropic stress potentials or, alternatively, strain‐rate potentials. In this work, a stress update algorithm is developed for this later case. The implicit, backward Euler method is adopted. A specific numerical treatment is required to deal with the plasticity criterion, which is not defined explicitly. Also, a sub‐stepping procedure is adopted in order to deal with the strong nonlinearity of the yield surfaces when applied to FCC materials. The resulting algorithm is implemented in the static implicit version of the Abaqus FE code. Several recent plastic potentials have been implemented in this framework and their parameters identified for a number of BCC and FCC materials. Numerical simulations of a cup drawing process are performed in order to address the robustness of the implementation and the ability of these potentials to predict e.g. earing for materials with different anisotropy.

Ce travail consiste à étudier par simulation le phénomène du retour élastique dans le procédé d’emboutissage des tôles métalliques. Un modèle phénoménologique d’élasto-plasticité, incluant deux modèles d’écrouissage combiné, a été implanté dans le code d’éléments finis ABAQUS/Standard, via la routine UMAT, suivant un schéma d’intégration implicite. Des simulations de tests rhéologiques, à trajet direct et séquentiels, ont été réalisées pour montrer la capacité de chaque modèle à reproduire les phénomènes de changement de trajet de déformation. Également, un essai d’emboutissage spécialement conçu pour mettre en évidence le retour élastique a été étudié. L’influence du modèle d’écrouissage sur le niveau du retour élastique a été mise en évidence pour différents paramètres du procédé, notamment l’effort de serrage du serre-flan.; Ce travail consiste à étudier par simulation le phénomène du retour élastique dans le procédé d’emboutissage des tôles métalliques. Un modèle phénoménologique d’élasto-plasticité, incluant deux modèles d’écrouissage combiné, a été implanté dans le code d’éléments finis ABAQUS/Standard, via la routine UMAT, suivant un schéma d’intégration implicite. Des simulations de tests rhéologiques, à trajet direct et séquentiels, ont été réalisées pour montrer la capacité de chaque modèle à reproduire les phénomènes de changement de trajet de déformation. Également, un essai d’emboutissage spécialement conçu pour mettre en évidence le retour élastique a été étudié. L’influence du modèle d’écrouissage sur le niveau du retour élastique a été mise en évidence pour différents paramètres du procédé, notamment l’effort de serrage du serre-flan.

International audience; Sheet metal forming processes often involve complex loading sequences. To improve the prediction of some undesirable phenomena, such as springback, physical behavior models should be considered. This paper investigates springback behavior predicted by advanced elastoplastic hardening models which combine isotropic and kinematic hardening and take strain-path changes into account. A dislocation-based microstructural hardening model formulated from physical observations and the more classical cyclic model of Chaboche have been considered in this work. Numerical implementation was carried out in the ABAQUS software using a return mapping algorithm with a combined backward Euler and semi-analytical integration scheme of the constitutive equations. The capability of each model to reproduce transient hardening phenomena at abrupt strain-path changes has been shown via simulations of sequential theological tests. A springback analysis of strip drawing tests was performed in order to emphasize the impact of several influential parameters, namely: process, numerical and behavior parameters. The effect of the two hardening models with respect to the process parameters has been specifically highlighted.

International audience; The impact of material models on the numerical simulation of springback is investigated. The study is focused on the strain-path sensitivity of two hardening models. While both models predict the Bauschinger effect, their response in the transient zone after a strain-path change is fairly different. Their respective predictions are compared in terms of sequential test response and of strip-drawing springback. For this purpose, an accurate and general time integration algorithm has been developed and implemented in the Abaqus code. The impact of several numerical parameters is also studied in order to assess the overall accuracy of the finite element prediction. For some test geometries, both material and numerical parameters are shown to clearly influence the springback behavior at a large extent. Moreover, a general trend cannot always be extracted, thus justifying the need for the finite element simulation of the stamping process.

The constitutive equation of the isothermal steady-state behaviour of semi-solid materials is described with a micro-macro modelling. It is based on the application of the micromechanics concept of “coated inclusion” to semi-solid behaviour and the introduction of an evolving bimodal distribution of the liquid and solid phases. The micro-macro modelling is implemented in the FE code Forge2. The influence of the normal and abnormal namely softening stress–strain rate relationship on thixoforging is analyzed using compression and extrusion tests simulations.

In sheet metal forming process, the material usually undergoes large deformations, complex loading histories and its mechanical behavior can be modeled by constitutive equations. Despite the great efforts paid to develop advanced hardening models considering the Bauschinger effect, the reliability and applicability of the developed hardening models still needs to be investigated, both experimentally and theoretically. In the first part, based on the developed hardening models, some classical and advanced models are selected are implemented by using Euler explicit implementation method. After that, the developed numerical instruments in current work are applied to investigate the prediction of the yield surface evolution, which show that some apparent violation of the normality condition can be simulated using models based on associated plasticity. The second part mainly focuses on characterizing and discriminating for selecting material models. Firstly some characterizations tests including complex loading path are performed to identify material parameters and bending-under-tension discriminant test is built to investing springback behavior that can sort out the best model.; Dans le processus de formage de tôle, le matériau subit généralement de grandes déformations, des historiques de chargement complexes et son comportement mécanique peut être modélisé par des équations constitutives. Malgré les efforts considérables déployés pour développer des modèles d’écrouissage avancés tenant compte de l'effet de Bauschinger, la fiabilité et l'applicabilité des modèles d’écrouissage développés doivent encore être étudiés, à la fois expérimentalement et théoriquement. Plusieurs types de modèles d’écrouissage sont implantés numériquement dans cette thèse. Ils sont utilisés pour étudier la prévision de l'évolution de la surface de plasticité, ce qui montre qu'une certaine violation apparente de la condition de normalité peut être simulés modèles basés sur la plasticité associée. La deuxième partie porte principalement sur la caractérisation et la discrimination pour la sélection de modèles de matériaux. Premièrement, certains tests de caractérisation, y compris les trajets de chargement complexes, sont effectués pour identifier les paramètres des matériaux, puis le test discriminant de pliage sous tension est conçu pour l’investissement d’un comportement de retour élastique capable de déterminer le meilleur modèle.

In sheet metal forming process, the material usually undergoes large deformations, complex loading histories and its mechanical behavior can be modeled by constitutive equations. Despite the great efforts paid to develop advanced hardening models considering the Bauschinger effect, the reliability and applicability of the developed hardening models still needs to be investigated, both experimentally and theoretically. In the first part, based on the developed hardening models, some classical and advanced models are selected are implemented by using Euler explicit implementation method. After that, the developed numerical instruments in current work are applied to investigate the prediction of the yield surface evolution, which show that some apparent violation of the normality condition can be simulated using models based on associated plasticity. The second part mainly focuses on characterizing and discriminating for selecting material models. Firstly some characterizations tests including complex loading path are performed to identify material parameters and bending-under-tension discriminant test is built to investing springback behavior that can sort out the best model.; Dans le processus de formage de tôle, le matériau subit généralement de grandes déformations, des historiques de chargement complexes et son comportement mécanique peut être modélisé par des équations constitutives. Malgré les efforts considérables déployés pour développer des modèles d’écrouissage avancés tenant compte de l'effet de Bauschinger, la fiabilité et l'applicabilité des modèles d’écrouissage développés doivent encore être étudiés, à la fois expérimentalement et théoriquement. Plusieurs types de modèles d’écrouissage sont implantés numériquement dans cette thèse. Ils sont utilisés pour étudier la prévision de l'évolution de la surface de plasticité, ce qui montre qu'une certaine violation apparente de la condition de normalité peut être simulés modèles basés sur la plasticité associée. La deuxième partie porte principalement sur la caractérisation et la discrimination pour la sélection de modèles de matériaux. Premièrement, certains tests de caractérisation, y compris les trajets de chargement complexes, sont effectués pour identifier les paramètres des matériaux, puis le test discriminant de pliage sous tension est conçu pour l’investissement d’un comportement de retour élastique capable de déterminer le meilleur modèle.

Due to the unique Transformation Induced Plasticity (TRIP) effect, 304 austenitic stainless steel (ASS) is widely used in many engineering areas. During working and manufacturing process or in service, it may undergo deformation over a wide range of strain rates and temperatures. The current work presents a systematic deformation behavior study of 304 ASS by both experiments and numerical simulations. With an original cooling device coupled to the split Hopkinson pressure bar system, the compression behavior at strain rates between 0.001 s-1 and 3000 s-1 and temperatures between -163°C and 172°C was investigated. An extension of the Rusinek-Klepaczko (RK) model considering strain-induced martensitic transformation (SIMT) phenomenon was also used to simulate the thermo-viscoplastic behavior of this steel. To study the deformation behavior at extremely high strain rates exceeding 3000 s-1, a new single shear zone (SSS) specimen has been proposed and validated. Then, the effects of strain rate between 3000 s-1 and 39000 s-1 was analyzed. Finally, with a specially designed cooling device, the ballistic impact behavior under initial projectile velocities between 80 and 180 m.s-1 and temperatures between -163°C and 200°C was studied. By comparison between experiments and numerical simulations for perforation, the previously obtained constitutive relations were validated.; L’acier inox austénitique 304 est utilisé pour de nombreuses applications industrielles, notamment à cause de l’effet TRIP qui lui confère des propriétés particulières. Au cours de son élaboration ou lorsqu’il est utilisé en service, il peut être soumis à différentes vitesses de déformation et températures. Le travail présenté ici vise à étudier le comportement de cet acier sous différents trajets de chargement. Tout d’abord, un système de refroidissement a été ajouté aux barres de Hopkinson pour étudier le comportement de cet acier en compression avec des vitesses de déformation comprises entre 0.001 s-1 et 3000 s-1 et des températures entre -163°C et 172°C. Le modèle de Rusinek-Klepaczko, qui prend en compte le phénomène de transformation martensitique, a été utilisé en parallèle pour simuler son comportement thermo-viscoplastique. Pour les vitesses de déformation au-delà de 3000 s-1, un nouveau design d’éprouvette de cisaillement a ensuite été proposé et validé et l’effet de la vitesse de déformation entre 3000 s-1 et 39000 s-1 a été étudié. Enfin, un autre système de refroidissement a été développé pour les essais d’impact et de perforation à différentes vitesses (entre 80 et 180 m.s-1) et températures (entre -163°C et 200°C) et les lois de comportement ont été validées en comparant expériences et simulations numériques.

The main objective of this thesis is to identify the parameters of a hot metal rheology model by using experimental data from an industrial press. In the first chapter, the principle of parameter identification is exposed. Uniaxial compression testing done on specialized devices serves as a case study. The notions of cost function, experimental design and rheological model are examined. A sensitivity analysis is also performed. The next chapter present the experimental tools used on the industrial press. Finally, the friction and thermal exchange that will happen during the tests are evaluated. The third chapter is about the inverse analysis on industrial press. Finite elements modelling of the compression is made and compared with the experiments. The identification results are then compared with the FORGE® software database and the material parameters found in chapter 1. A complex part is then simulated with these different parameters and compared with a real forging of this part. The fourth chapter uses the same methods as in chapter 3 to perform an identification on the rheological parameters of an Inconel 625. A microstructural model for the Inconel is then identified with industrial testing as reference.; L’objectif principale de cette thèse est de procéder à une identification paramétrique d’un modèle rhéologique de matériau métallique à chaud en utilisant des données expérimentales issues d’une presse industrielle. Dans le premier chapitre, le principe de l’identification paramétrique est exposé. Des essais de compressions uniaxiale faites sur machine d’essais spécialisés y servent alors comme cas d’étude. Les notions de choix de la fonction-coût, du plan d’expérience et du modèle y sont alors abordées ainsi qu’une analyse de sensibilité. Le chapitre suivant présente l’outillage utilisé pour faire les expériences sur presse. Enfin, une évaluation des échanges thermiques et des frottements que subis la pièce lors de l’essai est faite. Le troisième chapitre se concentre sur l’identification paramétrique proprement dite. Ainsi, des simulations par élément fini de la compression sont faites et comparées aux essais expérimentaux. Les résultats de l’identification sont discutés et comparés à ce que proposait initialement la base de données du logiciel FORGE® ainsi que les paramètres identifiés pour le même matériau au chapitre 1. Une simulation d’une pièce complexe avec ces différents jeux de paramètres est ensuite comparée avec le forgeage réel de cette pièce. Le quatrième chapitre reprend les acquis du troisième en faisant une identification paramétrique pour la rhéologie d’Inconel 625. Une tentative d’identification d’un modèle de microstructure pour l’Inconel à partir d’essais industriel termine ce manuscrit.

The main objective of this thesis is to identify the parameters of a hot metal rheology model by using experimental data from an industrial press. In the first chapter, the principle of parameter identification is exposed. Uniaxial compression testing done on specialized devices serves as a case study. The notions of cost function, experimental design and rheological model are examined. A sensitivity analysis is also performed. The next chapter present the experimental tools used on the industrial press. Finally, the friction and thermal exchange that will happen during the tests are evaluated. The third chapter is about the inverse analysis on industrial press. Finite elements modelling of the compression is made and compared with the experiments. The identification results are then compared with the FORGE® software database and the material parameters found in chapter 1. A complex part is then simulated with these different parameters and compared with a real forging of this part. The fourth chapter uses the same methods as in chapter 3 to perform an identification on the rheological parameters of an Inconel 625. A microstructural model for the Inconel is then identified with industrial testing as reference.; L’objectif principale de cette thèse est de procéder à une identification paramétrique d’un modèle rhéologique de matériau métallique à chaud en utilisant des données expérimentales issues d’une presse industrielle. Dans le premier chapitre, le principe de l’identification paramétrique est exposé. Des essais de compressions uniaxiale faites sur machine d’essais spécialisés y servent alors comme cas d’étude. Les notions de choix de la fonction-coût, du plan d’expérience et du modèle y sont alors abordées ainsi qu’une analyse de sensibilité. Le chapitre suivant présente l’outillage utilisé pour faire les expériences sur presse. Enfin, une évaluation des échanges thermiques et des frottements que subis la pièce lors de l’essai est faite. Le troisième chapitre se concentre sur l’identification paramétrique proprement dite. Ainsi, des simulations par élément fini de la compression sont faites et comparées aux essais expérimentaux. Les résultats de l’identification sont discutés et comparés à ce que proposait initialement la base de données du logiciel FORGE® ainsi que les paramètres identifiés pour le même matériau au chapitre 1. Une simulation d’une pièce complexe avec ces différents jeux de paramètres est ensuite comparée avec le forgeage réel de cette pièce. Le quatrième chapitre reprend les acquis du troisième en faisant une identification paramétrique pour la rhéologie d’Inconel 625. Une tentative d’identification d’un modèle de microstructure pour l’Inconel à partir d’essais industriel termine ce manuscrit.

The on-going trend on device miniaturization has increased the demand forminiature parts and boosted micro forming processes. However, the mechanical behavior of ultra-thin sheet metals is subjected to certain peculiarities which are driven from the reduced number of grains in the sheets. The present work aimed to provide a numerical tool for the prediction of the mechanical behavior of ultra-thin sheet metals. The mechanical behavior of two copper alloys, CuBe2 and CuFe2P, was experimentally characterized through several strain paths. Various characteristics have been revealed, such as the anisotropic response, Bauschinger effect and the decrease of the Young modulus.In order to build a modeling frame capable of describing thin metal sheets which exhibit a highly heterogeneous behavior and those whose response is more homogeneous, two modeling approaches were considered. On one hand, a phenomenological model based on the experimental results is chosen. On the other hand, a crystal plasticity based model, which takes into account the physical deformation mechanisms, is adopted. Both models were implementedin ABAQUS and SiDoLo softwares, under the finite strain formalism. Parametric identification strategies are devised and the influence of calibration on models performance is assessed.Ultimately, the modeling approaches were applied to the simulation of industrial processes and academic tests. A numerical study on relevant parameters for the prediction of springback has been performed. The accurate modeling of elasticity proved highly influential.; La course à la miniaturisation entraine une forte hausse de la demande encomposants aux dimensions submillimétriques et donne un essor considérable aux procédés de micro-formage. Cependant le comportement mécanique des tôles ultrafines, employées dans ces procédés présente des singularités liées à la réduction du nombre de grains. Cette thèse a eu pour objet de mettre en place un outil d’aide à la prédiction du comportement mécanique des tôles ultrafines.Expérimentalement, le comportement de deux alliages de cuivre, le CuBe2 et le CuFe2P, a été caractérisé sous divers types de chargement. Diverses caractéristiques ont été mises en évidence, notamment l’anisotropie de la réponse mécanique, l’effet Bauschinger ou encore ladégradation du module de Young.Afin d’obtenir un cadre de modélisation apte à la description de tôles présentant un comportement plus ou moins homogène, deux approches ont été retenues. La première consiste en une modélisation phénoménologique inspirée des observations macroscopiques. La seconde est une description, en plasticité cristalline, à l’échelle du grain du comportement mécanique, basée sur les mécanismes physiques de déformation. Les modèles retenus ont été intégrés dansles logiciels ABAQUS et SiDoLo dans le formalisme des grandes transformations. Des stratégies d’identification paramétrique des différents modèles sont développées et une analyse comparative de l’impact de l’identification sur les prévisions des modèles est proposée.Enfin les approches développées sont mises en oeuvre sur des procédés industriels et des tests académiques. Une étude sur des facteurs influençant la prédiction du retour élastique estréalisée. Elle a montré qu’une attention particulière doit être portée à la modélisation de l’élasticité.

This numerical investigation of an advanced Gurson–Tvergaard–Needleman (GTN) model is an extension of the original work of Ben Bettaieb et al. (2011). The model has been implemented as a user-defined material model subroutine (VUMAT) in the Abaqus/explicit FE code. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically based void nucleation and growth laws are considered, including an effect of the kinematic hardening. These new contributions are based and validated on experimental results provided by high-resolution X-ray absorption tomography measurements. Also, the numerical implementation of the kinematic hardening in this damage extension has obliged to readapt the classical triaxiality definition. Besides, a secondary fracture initiation criterion based on the ultimate average inter-cavities distance has been integrated to localize and quantify with good accuracy the strain distribution just before the material fails apart. The current damage model is applied in industrial conditions to predict the damage evolution, the stress state and the fracture initiation in various tensile thin flat sheet geometries and the cross-die drawing tests.; L'actuel investigation numérique du Gurson-Tvergaard-Needleman (GTN) modèle avancé est une extension du travail de Ben Bettaieb et al. (2011). Le modèle a été implémenté à l'aide d'une sous routine (VUMAT) contenu dans le code commerciale d'éléments finis Abaqus/explicit. Le modèle d'endommagement améliore l'original en intégrant les trois mécanismes d'endommagement, la nucléation, la croissance, et la coalescence des cavités. Le modèle d'endommagement intègre les lois de nucléation et de croissance basés sur les phénomènes purement physiques. Ces nouvelles contributions incluant l'influence de l'écrouissage cinématique, ont été validées par les résultats de mesures expérimentales de tomographie à rayon X à haute résolution. Aussi, l'implémentation numérique de l'écrouissage cinématique dans le modèle modifié a contraint de proposer et de réarranger la définition de la triaxialité que l'on trouve habituellement dans la littérature. A coté de cela, un second critère d'initiation à la rupture basé sur l'ultime distance inter-cavités a été inclue afin de localiser et de quantifier avec plus de précision la distribution des déformations peu avant que le matériau ne casse complètement. L'actuel modèle d'endommagement a été appliqué dans des conditions industrielles pour prédire l'évolution de l'endommagement, l'état de contraintes, et l'initiation à la rupture pour différentes géométries de tôles et sur des essais d'emboutissage de tôles minces.

This numerical investigation of an advanced Gurson-Tvergaard-Needleman (GTN) model is an extension of the original work of Ben Bettaieb et al. (2011). The model has been implemented as a user-defined material model subroutine (VUMAT) in the Abaqus/explicit FE code. The current damage model extends the previous version by integrating the three damage mechanisms: nucleation, growth and coalescence of voids. Physically based void nucleation and growth laws are considered, including an effect of the kinematic hardening. These new contributions are based and validated on experimental results provided by highresolution X-ray absorption tomography measurements. Also, the numerical implementation of the kinematic hardening in this damage extension has obliged to readapt the classical triaxiality definition. Besides, a secondary fracture initiation criterion based on the ultimate average intercavities distance has been integrated to localize and quantify with good accuracy the strain distribution just before the material fails apart. The current damage model is applied in industrial conditions to predict the damage evolution, the stress state and the fracture initiation in various tensile thin flat sheet geometries and the cross-die drawing tests.; L'actuelle investigation numérique du Gurson-Tvergaard-Needleman (GTN) modèle avancé est une extension du travail de Ben Bettaieb et al. (2011). Le modèle a été implémenté à l'aide d'une sous routine (VUMAT) contenu dans le code commerciale d'éléments finis Abaqus/explicit. Le modèle d'endommagement améliore l'original en intégrant les trois mécanismes d'endommagement, la nucléation, la croissance, et la coalescence des cavités. Le modèle d'endommagement intègre les lois de nucléation et de croissance basés sur les phénomènes purement physiques. Ces nouvelles contributions incluant l'influence de l'écrouissage cinématique, ont été validées par les résultats de mesures expérimentales de tomographie à rayon X à haute résolution. Aussi, l'implémentation numérique de l'écrouissage cinématique dans le modèle modifié a contraint de proposer et de réarranger la définition de la triaxialité que l'on trouve habituellement dans la littérature. A coté de cela, un second critère d'initiation à la rupture basé sur l'ultime distance inter-cavités a été inclue afin de localiser et de quantifier avec plus de précision la distribution des déformations peu avant que le matériau ne casse complètement. L'actuel modèle d'endommagement a été appliqué dans des conditions industrielles pour prédire l'évolution de l'endommagement, l'état de contraintes, et l'initiation à la rupture pour différentes géométries de tôles et sur des essais d'emboutissage de tôles minces.