Amorçage et micro-propagation de fissure en fatigue à haute température à partir de défauts dans un superalliage monocristallin

Abstract : High pressure turbine blades in aerojet engines are component that undergo severe thermo-mechanical loading condition. These blades are now made of single crystal nickel base superalloy because of its very high mechanical properties at high temperature. The directional solidification process generates casting defects as pores located in inter-dendritic spaces. With cycling loading, micro-crack can initiate and propagate to conduct to the ruin of the structure. The aim of this study is the initiation and micro-propagation of crack on defect. An experimental study has been carried on tubular notched specimen. These experimental results have shown that the visco-plasticity and the activation of oxidation conduct to short crack behaviour. A finite element analysis on tubular notch specimen mesh has shown the importance of plasticity generated by the defect on the short crack propagation. Then, a micro-propagation model has been developed to estimate the crack growth rate near the notch root. This model is based on a local approach using the stress field generated by the defect. The model takes into account the local plasticity due to the notch and also the embrittlement at the crack tip by the oxidation. This model is promising for the improvement of life prediction of crack initiation on cast pores.
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Submitted on : Monday, July 18, 2011 - 11:43:57 AM
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Marion Geuffrard. Amorçage et micro-propagation de fissure en fatigue à haute température à partir de défauts dans un superalliage monocristallin. Matériaux. École Nationale Supérieure des Mines de Paris, 2010. Français. ⟨NNT : 2010ENMP0067⟩. ⟨pastel-00609109⟩

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