Approche multi-échelle du vieillissement et du comportement cyclique dans le tantale

Abstract : Designing complex structures requires an exhaustive knowledge of the materials used at both macroscopical and microscopical scales. In the case of tantalum, only few studies have been focused on the cyclic behaviour and on static strain aging's (aging in the sense of atoms diffusion to dislocations) influence on macroscopical behaviour and on the local strain fields. In order to extend the comprehension of microstructural mechanisms driving deformation, this study deals with experiments following the local strain fields evolution and with an appropriate modelling, taking into account microstructure explicitly.In a first step, a macroscopical study of aging and cyclic behaviour is presented. Several experimental techniques have been used in order to highlight a strain localisation band propagation associated to the anomalous yield point phenomenon. In parallel, a phenomenological EKMC (from Estrin, Kubin and McCormick) macroscopic model has been adopted, capturing the macroscopic behaviour (especially the anomalous yield point associated to static strain aging) ; and then used for several numerical investigations about the strain localisation occurence.Then, the study has been continued at the microscale in both numerical and experimental matters. Thus, several micrometrical matrixes of nickel dots have been led on the sample's surface. The have then been used for the experimental strain maps computation during an interrupted tensile test. The explicit computation of the microstructure through a specific generation of polycrystalline aggregates using free surface conditions has permitted to study the influence of aging on the local strain fields heterogeneity and to compare them with the experimental ones.Finally, a multi-scale study of the cyclic behaviour has been carried out. An interrupted fatigue test with microscopic observations and strain maps computations has been carried out, permitting the identification and quantification of the local strain heterogeneity up to the crack initiation. A computation of an equivalent loading has been done on a polycrystalline aggregate in order to set up a fatigue criterion based on physical quantities in agreement with experimental datas.
Keywords : Aging Tantalum Fatigue
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Damien Colas. Approche multi-échelle du vieillissement et du comportement cyclique dans le tantale. Autre. Ecole Nationale Supérieure des Mines de Paris, 2013. Français. ⟨NNT : 2013ENMP0047⟩. ⟨pastel-00957882⟩

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