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Simulation multi-échelles du comportement mécanique des carbures et des interfaces carbure-métal à partir des premiers principes

Abstract : Ferritic and austenitic steels as well a nickel-based alloys contains generally carbides. These carbides under mechanical load may display either interfacial or intra-precipitate fracture. The objective of this thesis is to simulate the fractures of various interfaces and carbides from the first principles. The evaluated fracture parameters may be input for cohesive zone models used in finite elements computations. Decohesion curves are obtained using the UBER model (Universal Bonding Energy Relation) based on the use of characteristic parameters of the interfaces or carbides such as the thickness, of the volume involved in the fracture process, its Young's modulus or its Griffith energy. To validate this model, tensile test simulations are performed by DFT (Density Functional Theory). Different carbides (Fe3C, Cr23C6 and TiC) have been studied during this thesis, varying the metallic atoms, the crystallographic structure and the magnetic order of the matrix. We conclude that depending on the nature of the carbide, the fracture is located either at the interface (Cr23C6) or inside the carbide (Fe3C). These crack initiation predictions are in agreement with many experimental observations. Finally, crystalline finite element calculations are performed. In the case of Cr23C6 carbides, the finite element calculations using the computed critical stress predict an interface crack initiation. In the case of titanium carbides, both interface and intra-precipitate carbide crack initiation are predicted.
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Elric Barbé. Simulation multi-échelles du comportement mécanique des carbures et des interfaces carbure-métal à partir des premiers principes. Matériaux. Sorbonne Université, 2018. Français. ⟨NNT : 2018SORUS209⟩. ⟨tel-02494442⟩

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