Caractérisation, modélisation et simulation numérique des instabilités plastiques dans les alliages Al-Mg

Abstract : Plastic instabilities refer to a wide family of material nonlinearities met in several solid materials. They correspond to a heterogeneous strain response under homogeneous loading conditions, and manifest as an erratic workhardening accompanied by strain localization bands that kinetics are sensitive to temperature and loading rate, among other material properties. This phenomenon hinders the industrial use of aluminium-magnesium alloys. It involves harmful mechanical and aesthetic consequences that can hardly be predicted at the design step. Constitutive models can recreate localization bands but they fail to accurately predict their kinematics. Moreover, they are subjected to several issues such as mesh sensitivity, a high computational cost or a complex parameters identification. The purpose of this work is to build a framework in which bands kinematics can be reliably predicted. First, the studied alloy is characterized by means of tensile tests in which the kinetics of individual bands are tracked using digital image correlation. Quantities of interest are then identified at the non-local scale of bands: their morphology, spatiotemporal distribution, the strain they carry and the energy they exchange. Based on these experimental results, a constitutive model is derived at the scale of localization bands. It embeds all the aforementioned macroscopic consequences of plastic instabilities. A numerical strategy is then proposed to tackle unidimensional simulations, with the purpose of justifying the feasibility of the approach. This work constitutes a first contribution to the simulation of localization bands through a direct modeling of their kinetics. The considered outlooks focus on three main aspects. First, the experimental characterization of instabilities beneath the bands scale. Also, the twodimensional deployment and the improvement of the model to fit concrete and industrial applications. Lastly, the use of the proposed framework for a greater variety of non-local behaviors.
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Baptiste Reyne. Caractérisation, modélisation et simulation numérique des instabilités plastiques dans les alliages Al-Mg. Mécanique des solides [physics.class-ph]. École centrale de Nantes, 2019. Français. ⟨NNT : 2019ECDN0033⟩. ⟨tel-02437346⟩

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