Etude du comportement thermo-mécanique et de l’endommagement d’un matériau énergétique granulaire par méthodes de Fourier

Abstract : This work aims to study the thermal and mechanical behavior of an energetic polycrystal. This material displays a quasi-brittle behavior and its thermal dilation coefficient decreases when it undergoes cooling-heating cycles.The study relies on the use of a Johnson-Mehl tessellation model which has non-convex grains, and a full-field numerical method based on the Fourier transform. The accuracy of such methods concerning cracked media are determined by comparison with Finite Elements computations. The numerical tool is then used to investigate different microstructural assumptions, from the simplest to the most sophisticated.The first computation is that of an undammaged polycrystal, which overestimates the overall mechanical properties. The attempt to account for porosity and the presence of binder gives interesting results, but the latter are not enough to reproduce the experimental behavior.Finally, different types of microcracks are investigated and two major conclusions are drawn. First, in its initial state, the material contains intergranular cracks, that are uncorrelated to the local microstructure. Such cracks can lower the elastic moduli and leave the thermal properties unaffected. To obtain a decrease in terms of thermal dilation coefficient, one must consider families of cracks which are correlated to the local crystal orientation, especially along the weak plane of the crystal.
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Jean-Baptiste Gasnier. Etude du comportement thermo-mécanique et de l’endommagement d’un matériau énergétique granulaire par méthodes de Fourier. Matériaux. PSL Research University, 2017. Français. ⟨NNT : 2017PSLEM051⟩. ⟨tel-01843398⟩

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