Salima Bouvier

Analysis of Texture Evolution and hardening Behavior during Deep drawing with an improved mixed type FEM Element

In the present study, deep drawing simulations were investigated using a recently developed mixed type finite element (FE): the BWD3D. The main formulation of the element is described, with particular focus on the shear locking treatment. Two hardening models used in the presented simulations are described: the isotropic Swift’s model and the physically based microstructural Teodosiu and Hu model. Finally, deep drawing results, in terms of earing profile, are compared to experiment. Special attention is paid to the effects of texture evolution and hardening models; the method used to implement Teodosiu and Hu hardening model is also discussed.

Numerical investigation and experimental validation of a plasticity model for sheet steel forming

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 (DP) 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 models formulation, although the overall approach is macroscopic. For the DP 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.

Reflection on the measurement and use of the topography of the indentation imprint.

The goal of this paper is to study the main uses of the residual imprint of the indentation test. It also discusses the different technologies and methods employed in this context. The difficulties encountered when trying to exploit the full potentials of the imprint are thoroughly examined. A survey of the literature on the quantification of the pile-up clearly shows that there is a lack of consensus on the measurement of the residual imprint as well as on treatment methods. Therefore, in order to widen the application fields of the indentation residual imprint, relevant and standardized indicators should be established.

Application of a dislocation based model for Interstitial Free (IF) steels to typical stamping simulations

With a view to environmental, economic and safety concerns, car manufacturers need to design lighter and safer vehicles in ever shorter development times. In recent years, High Strength Steels (HSS) like Interstitial Free (IF) steels which have higher ratios of yield strength to elastic modulus, are increasingly used for sheet metal parts in automotive industry to meet the demands. Moreover, the application of sheet metal forming simulations has proven to be beneficial to reduce tool costs in the design stage and to optimize current processes. The Finite Element Method (FEM) is quite successful to simulate metal forming processes but accuracy largely depends on the quality of the material properties provided as input to the material model. Common phenomenological models roughly consist in the fitting of functions on experimental results and do not provide any predictive character for different metals from the same grade. Therefore, the use of accurate plasticity models based on physics would increase pred...

Deep drawing simulations with different polycrystalline models

The goal of this research is to study the anisotropic material behavior during forming processes, represented by both complex yield loci and kinematic‐isotropic hardening models. A first part of this paper describes the main concepts of the ‘Stress‐strain interpolation’ model that has been implemented in the non‐linear finite element code Lagamine. This model consists of a local description of the yield locus based on the texture of the material through the full constraints Taylor’s model. The texture evolution due to plastic deformations is computed throughout the FEM simulations. This ‘local yield locus’ approach was initially linked to the classical isotropic Swift hardening law. Recently, a more complex hardening model was implemented: the physically‐based microstructural model of Teodosiu. It takes into account intergranular heterogeneity due to the evolution of dislocation structures, that affects isotropic and kinematic hardening. The influence of the hardening model is compared to the influence of...

Microlithography Technique Advantages, Limits and Its Coupling with EBSD Measurements

This paper focuses on the microlithography technique. Its main steps are described as well as its key difficulties in order to clarify the technique potential. The microgrid dimension limits and the experimental procedure enabling digital image correlation are also presented to widen their application. The microgrid characteristics needed for Electron BackScattering Diffraction measurements are also discussed. The settings provided here enable the coupling of full-field strain measurement information with Electron BackScattering Diffraction analysis not only before deformation but also during the tensile test.

Finite Element Simulation of Sheet Metal Forming Using Anisotropic Strain‐Rate Potentials

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.

Strategy of Material Parameters Identification for Non Linear Mechanical Behavior: Sensitivity of FE Computation

The purpose of the present work is to analyze several aspects related to the connection between the constitutive models, their identification and the FEM predictions. Several issues are addressed: the experimental data base that should be used in the identification procedure, the choice of the mechanical tests involved (monotonous and/or non‐proportional loading, homogeneous or heterogeneous tests…), the identification strategies (direct or inverse FE optimization, simultaneous or sequential material parameters identification…). Besides its obvious interest, such study aim to find a good balance between the number and the type of relevant involved mechanical tests in material behavior characterization. This is an important issue for industrial applications.

Impact of the Parameter Identification of Plastic Potentials on the Finite Element Simulation of Sheet Metal Forming

In this work, an implicit, backward Euler time integration scheme is developed for an anisotropic, elastic‐plastic model based on strain‐rate potentials. The constitutive algorithm includes a sub‐stepping procedure to deal with the strong nonlinearity of the plastic potentials when applied to FCC materials. The algorithm is implemented in the static implicit version of the Abaqus finite element code. Several recent plastic potentials have been implemented in this framework. The most accurate potentials require the identification of about twenty material parameters. Both mechanical tests and micromechanical simulations have been used for their identification, for a number of BCC and FCC materials. The impact of the identification procedure on the prediction of ears in cup drawing is investigated.