Contribution à l'étude expérimentale et numérique à l'échelle de la microstructure de l'écaillage d'un alliage de titane

Abstract : Spalling is defined as a complete or partial separation of material resulting from the tension induced by the interaction of two waves. The final fracture results from a progressive process of voids nucleation which under the action of certain factors increase to coalesce. Ta6V is the most known and used titanium alloy. Its microstructure conditions in very first place the mechanical properties of material, and is an essential element in the analysis of damage. The titanium studied presents a dual a-b phase microstructure called WidmanstÉatten structure, composed of colonies of a phase lamellae separated by b phase. Series of impact tests have been performed on the gas launcher developed in LPMM. Ta6V uses the same mechanisms of spalling as steels, namely a phase of nucleation, growth and coalescence of voids. Due to the structure characteristic, voids nucleation occurs at privileged places. According to post-mortem microscopic observations of spall specimens, a fracture model has been developed. The goal is to determine the macroscopic stress of spalling in function of loading time and damage level via a meso-macro approach. In order to take into account the effect of particular microstructure of Ta6V and, at the same time, to reduce the intervening number of coefficients in this model, a complete numerical approach of impact tests is developed, via the finite element calculations, on a representative mesh of WidmanstÉatten structure to simulate micro-voids nucleation. Then, a crystalline constitutive law is implemented to calculate the local stress of micro-voids nucleation.
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Xavier Boidin. Contribution à l'étude expérimentale et numérique à l'échelle de la microstructure de l'écaillage d'un alliage de titane. Autre. Université Paul Verlaine - Metz, 2005. Français. ⟨NNT : 2005METZ019S⟩. ⟨tel-01752400⟩

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