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Fatigue sous très faibles amplitudes de contrainte : Analyse des mécanismes précurseurs de l’amorçage de fissures dans le cuivre polycristallin

Abstract : Abstract : This work aims to better understanding mechanisms leading to crack initiation in ductile single phase metals such as pure copper, loaded stress amplitudes lower than the conventional fatigue threshold and after about 109 cycles, the so-called Very High Cycle Fatigue regime. Tests were conducted using an ultrasonic technique at loafing frequency of 20 kHz. The mechanisms leading to crack initiation express (1) via slip bands at the specimen surface and (2) via self-heating due to intrinsic dissipation. Thermal maps were used to estimate the mean dissipation and its change with number of cycles and stress amplitudes. At the same time, the surface relief changes were characterized using optical, scanning electronic and atomic force microscopes. The stress amplitude required to observe the slip bands was found to decrease as a function of number of cycles. EBSD investigations combined with finites elements simulations accounting for elastic anisotropy of copper revealed the key role of (1) twin boundaries and (2) cross slip in slip band initiation.Keywords : Very High Cycle Fatigue, Slip bands, Cyclic microplasticity, Dissipation, Elastic anisotropy, Multicrystals simulation, Infrared thermography.
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Ngoc-Lam Phung. Fatigue sous très faibles amplitudes de contrainte : Analyse des mécanismes précurseurs de l’amorçage de fissures dans le cuivre polycristallin. Autre. Ecole nationale supérieure d'arts et métiers - ENSAM, 2012. Français. ⟨NNT : 2012ENAM0013⟩. ⟨pastel-00835203⟩

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