Lois de plasticité non locales et propagation des bandes de déformation associées à l'effet Portevin-Le Chatelier

Abstract : The Portevin-Le Chatelier effect consists in the propagation of bands of localized plastic deformation. Local models using the concept of negative strain rate sensitivity are unable to describe quantitatively the propagation phenomenon ; thus non-local models are considered, in a sample loaded at constant stress-rate. The second order strain gradient model, already used in the literature, reflects interactions due to internal stresses. It does not reproduce the experimental tendencies : the propagation velocity in a Al-5%Mg does not monotonically decrease with increasing stress-rates. Furthermore, the unstable and unattanable range of negative strain rate sensitivity is employed by the model. A second assuming that the bands propagation mechanism stems from the dislocations cross-slip is proposed. The model leads to a non-local equation of the reaction-diffusion type. A non linear "exact" analysis allows to build a cycle in the phase space and to determine the band velocity the predictions of the model are agreement with the decreasing experimental trend satisfying velocity levels are obtained for plausible values of the diffusion coefficient. The cycle is linearly unstable but the bands velocity is kept in the instability : the model does not rule out the occurence of irregular orbits close to the periodic cycle ; such the behaviour is suggested by some experiments
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Véronique Jeanclaude. Lois de plasticité non locales et propagation des bandes de déformation associées à l'effet Portevin-Le Chatelier. Autre. Université Paul Verlaine - Metz, 1993. Français. ⟨NNT : 1993METZ004S⟩. ⟨tel-01748954⟩

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