Étude de la nocivité d'un défaut de fonderie sur la durée de vie en fatigue à haute température d'une aube monocristalline, cas du joint de grains

Abstract : The high pressure turbine blade of aeroengine are submitted to severe thermomechanical loading in service. The turbine blade are curently manufactured by directionnal solidification with oriented single crystal on the direction <001>, along the principal direction of the blade.The solidification process can induce different defects in the structure.This study is focused on a particular defect: the formation of two crystals in a blade. Defective turbine blades are composed of two grains with different orientation.The aim of this present thesis is to study the influence of the grain boundary on AM1 superalloy blade fatigue life. First, experimental investigations have been performed to understand at different temperatures, the influence of grain boundaries on fatigue fracture due to bending loadings. Notches have been introduced on turbine blades in order to accentuate solicitations on grain boundary. These experiments have evidenced the major role of grain boundary and grains orientations on turbine blade fatigue life.Then another experimental investigation has been carried out under low cycle fatigue on bicrystal specimens with tension/compression loading; the tensile principal stress is along the normal direction of the grain boundary mean plane. These tests allowed quantification of the fatigue life decrease due to the presence of grain boundary compared to the fatigue life of single crystal specimens.A failure criterion have been introduced in the damage constitutive behavior of single crystal AM1 developped by the Onera. This lifetime prediction model have been implemented in FE simulations. It allows the evaluation of the sensivity of grain boundary on turbine blade.
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Mélanie Leroy. Étude de la nocivité d'un défaut de fonderie sur la durée de vie en fatigue à haute température d'une aube monocristalline, cas du joint de grains. Autre. Ecole Nationale Supérieure des Mines de Paris, 2013. Français. ⟨NNT : 2013ENMP0065⟩. ⟨pastel-00963732⟩

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