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Effets de longueur interne sur les propriétés effectives des polycristaux métalliques : applications aux aciers

Abstract : The objective of this work is to study the effects of internal lengths, as the grain size on the mechanical behavior of IF steels with micromechanical models. After a literature review about different length scale effects observed in plasticity (grain size effects...) and existing scale transition methods, this work is divided into three steps. First of all, a self-consistent scheme written for heterogeneous elastic-viscoplastic materials is used to study the grain size dispersion effects on the mechanical behavior of polycrystalline aggregates, ignoring the heterogeneities of crystallographic orientations. These effects are as important as those due to the average grain size and crystallographic texture. In a second time, the same transition scale scheme is used to study the combined effects of grain size dispersion and crystallographic orientation. It appears that the effect of the grain size dispersion is larger than the effect of crystallographic texture on the tensile behavior. The third step is to develop new approaches with non-uniform plastic deformation inside the grain, in order to capture the effects of grain size through new interaction laws. Thus, two different models are proposed : a ?discrete? one, considering dislocation distributions constrained by grain boundaries, and, an ?averaged? one, accounting for plastic strain gradient in the region close to grain boundaries. These new approaches allow to reproduce the grain size effects observed on the mechanical behavior of metallic materials, in particular for IF steels
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Submitted on : Thursday, March 29, 2018 - 1:53:59 PM
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Nicolas Nicaise. Effets de longueur interne sur les propriétés effectives des polycristaux métalliques : applications aux aciers. Autre. Université Paul Verlaine - Metz, 2009. Français. ⟨NNT : 2009METZ045S⟩. ⟨tel-01752668⟩



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