Study of fatigue damage in 7010 aluminum alloy

Microscopic mechanisms controlling the fatigue damage in 7010 aluminum alloy are analysed. Cracks are initiated by the fracture of second-phase particles. Particles located in grains with a twisted cubic texture have been observed as preferential damage sites. Cracks grow either along intergranular or transgranular paths both in recrystallized and unrecrystallized regions. The final rupture mechanism depends on the stress level: at low and intermediate fatigue stress amplitudes the failure occurs by the unstable propagation of single cracks; at very large stresses multiple crack coalescence is observed. A model for the fatigue damage accumulation is presented. First a crack deviation model based on linear elasticity is described. It enables one to predict if crack deviation is to occur when encountering a grain or subgrain boundary. Finally, a fatigue life time model is developed in order to predict the cycle number to rupture and the qualitative influence of microstructural parameters. Good agreement is observed between experimental and predicted results at intermediate fatigue stress amplitudes.