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Modélisation micromécanique de matériaux hétérogènes contenant des microfissures avec la Méthode des Eléments Discrets (MED)

Abstract : This PhD is part of the Marie Skłodowska-Curie action ATHOR project (Advanced THermomechanical multiscale mOdelling of Refractory linings), supported by the European Commission. Refractories are heterogenous ceramics, resistant at high temperatures for which, in many cases, pre-existent microcracks within the microstructure play a key role in sustaining thermal shocks. The Discrete Element Method (DEM) is considered as a major numerical tool that can help, in future, to design high-performance microstructures. Thus, the present PhD is focused on numerical simulations of refractory ceramics by considering their microstructures, heterogeneities including cracks, and their influence on fracture mechanics. This work has been managed within a partnership with the company “ITASCA consultants”. Within the Particle Flow Code (PFC), as main numerical framework, the Flat Joint Model (FJM) is chosen since this contact model can mimic the microstructure of interlocked grains, like the microstructure of refractories. To develop numerical models that can help to investigate the role played by the microstructure in the macroscopic thermomechanical behaviour, it is essential to have an accurate micro to macro multiscale approach of each key physical properties for thermal shocks, starting with elastic properties. In this way, as DEM is not, at this stage, as robust as FEM, a periodic homogenisation approach is proposed for such continuum media. This approach has been validated by comparing the obtained results to model materials, analytical and FEM models. At mesoscale, a DEM model using a statistical approach to mimic the mechanical influence of pre-existing microcracks is investigated. This technique has also been validated by experimental mechanical data. Subsequently, to check the proposed DEM model applicability, Wedge Splitting Test (WST) simulations are managed to investigate the fracturing process and qualitatively compared to DIC experimental outputs. In the end, a discrete/continuous hybrid model is proposed to optimise the WST simulations in order to save computational time. These key results open very interesting new ways to use DEM in predicting the thermomechanical behaviour of heterogeneous materials containing numerous microcracks that could propagate simultaneously.
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Farid Asadi. Modélisation micromécanique de matériaux hétérogènes contenant des microfissures avec la Méthode des Eléments Discrets (MED). Matériaux. Université de Limoges, 2021. Français. ⟨NNT : 2021LIMO0046⟩. ⟨tel-03420983⟩

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