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Prédiction de la limite de formabilité des aciers multiphasés par une approche micromécanique

Abstract : The aim of this PhD thesis is to elaborate a predictive tool for the loss of ductility of polycrystalline multiphase steels during monotonous and sequential loading paths. Another major interest of this tool is to help design new materials thanks to knowledge of the impact of various physical and microstructural parameters on the ductility limit. At first, the elastic-plastic behavior at the local scale, i.e. at the grain level, is modeled using a micromechanical law formulated within the large strain framework. A rate-independent regularization technique, without introducing ratesensivity, is used to determine slip activity. The intragranular heterogeneities are introduced into the model following the original work of Peeters. The internal variables of the model are represented by three types of dislocation densities whose evolution is based on the mechanisms of creation, storage and annihilation. A comparison of the internal variable evolution with micrographs of grains of ferritic steel for monotonous and complex loadings allowed the validation of this modeling and demonstrates the macroscopic effects related to the intragranular microstructure. Secondly, the macroscopic behavior of the polycrystalline material is deduced from the singlecrystal behavior thanks to the self-consistent scheme in the sense of Hill. It is shown that this modeling allows the correct prediction of the behavior of multiphase steels. In a last part, a criterion based on the ellipticity loss of the elastic-plastic tangent modulus, the Rice criterion, is integrated once the macroscopic behavior is known. This criterion is used to plot forming limit diagrams, which have proven to be correct for various multiphase steels. Several attempts were undertaken as well in order to address possible differences with experiments.
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Submitted on : Friday, December 5, 2008 - 8:00:00 AM
Last modification on : Wednesday, March 24, 2021 - 10:34:02 AM
Long-term archiving on: : Friday, September 10, 2010 - 1:05:42 PM


  • HAL Id : pastel-00004332, version 1


Gérald Franz. Prédiction de la limite de formabilité des aciers multiphasés par une approche micromécanique. Sciences de l'ingénieur [physics]. Arts et Métiers ParisTech, 2008. Français. ⟨NNT : 2008ENAM0022⟩. ⟨pastel-00004332⟩



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