Caractérisation et modélisation micromécanique de la propagation de fissures fragiles par effet de l'hydrogène dans les alliages AA 7xxx

Abstract : We study the hydrogen embrittlement of the 7108 aluminum alloy. A specific experimental technique was developed : A hydrogen pre-charging, through few tens of microns of deposit of nickel, which prevents the dissolution of the aluminum substrate is used. It allows a comparison of the resistance to embrittlement of different model microstructures. We study the effect of heat treatment and intergranular precipitation on the susceptibility to hydrogen embrittlement for several macroscopic strain rates. Different failure modes and transitions between them are observed. Through numerical simulations, at the mesoscopic scale, the effect of the size of pre-weakened intergranular precipitates on the grain boundary toughness is estimated using a cohesive zone model. We further analyze the competition between the hydrogen diffusion toward the crack tip and crack velocity. For this purpose, a mechanical - diffusion coupling based on the hydrogen diffusion assisted by hydrostatic stress is elaborated. A critical crack velocity, beyond which hydrogen can no longer follow the crack, is highlighted. The influence of the grain boundary microstructure on this critical crack velocity is evaluated and its value is compared with an estimate of velocities obtained for different experimental macroscopic strain rates. We analyze the effect of hydrogen trapping by intergranular precipitates and hydrogen desorption by imposing a flux at the precipitates - matrix interfaces.
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Other. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2011. French. <NNT : 2011EMSE0611>


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Neji Ben Ali. Caractérisation et modélisation micromécanique de la propagation de fissures fragiles par effet de l'hydrogène dans les alliages AA 7xxx. Other. Ecole Nationale Supérieure des Mines de Saint-Etienne, 2011. French. <NNT : 2011EMSE0611>. <tel-00648428>

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