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Elastoviscoplasticité des aciers polycristallins: modélisation micromécanique et physique. Applications au comportement dynamique et à l'effet Bake-Hardening

Abstract : The knowledge of the mechanical behavior of heterogeneous materials and their strain rate and temperature dependence is essential to control metal forming processes and the strength of steels under dynamic conditions. Drawing steels are polycrystalline materials which may contain several phases with different mechanical features, that means that both intergranular and intragranular mechanisms determine the behavior at the macroscopic scale. The micromechanical approach, for which the global response is obtained by applying the homogenization techniques to the single components responses, allows to take into account both microstructure and mechanical interactions between components. The local deformation mechanisms at high strain rates are physically based and are captured through single crystal behavior. This one is based on thermal activation theory in the case of cubic centered metals like mild steels. The strain hardening laws are written in terms of dislocation densities and take into account dynamic recovery effects. Two scale transition tools, called internal variables models and expressing rigorously the elastic-viscoplastic nature of mechanical interactions between grains, are used for a load with a fixed macroscopic strain rate. These are the Paquin et al.'s model and a new model which is based on a new approach to solve the selfconsistent scheme, using projection operator properties and translated fields inspired by the Kröner's idea. Both models are applied to different classes of materials and are compared to Kröner-Weng and hereditary type models. Numerical results resulting from the Paquin et al.'s model (the new model would be also suitable) are compared to experimental results obtained for different kinds of steels especially for monotonous deformation paths in tension (high strain rate hydraulic tensile device) and in shear (hydro-pneumatic bar and Hopkinson bar) for a large range of strain rates. The choice of physical nature parameters is made explicit and the strong thermo-mechanical coupling at high strain rates, leading to thermal softening processes, is taken into account trough the modeling. Another aspect concerns the modeling of the behavior of Bake-Hardenable steels (BH). This one is based on the account of micro mechanisms responsible for hardening after baking (aging). The BH level is due to both a hardening Cottrell effect and a hardening by formation of clusters and/or precipitates which form new obstacles to the motion of dislocations. Results from the micro-macro model are compared quantitatively to the experimental results in uniaxial tension from Soler, realized for different aging times and temperatures. The influence of the pre-deformation path is studied by simulating an equibiaxial deformation, followed by aging and a reload in uniaxial tension.
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https://pastel.archives-ouvertes.fr/pastel-00000882
Contributor : Ecole Arts Et Métiers Paristech <>
Submitted on : Wednesday, October 27, 2004 - 8:00:00 AM
Last modification on : Thursday, December 6, 2018 - 3:08:03 PM
Long-term archiving on: : Thursday, September 30, 2010 - 6:02:57 PM

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  • HAL Id : pastel-00000882, version 1

Citation

Stéphane Berbenni. Elastoviscoplasticité des aciers polycristallins: modélisation micromécanique et physique. Applications au comportement dynamique et à l'effet Bake-Hardening. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2002. Français. ⟨NNT : 2002ENAM0001⟩. ⟨pastel-00000882⟩

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