Fatigue crack propagation in aluminum plates with composite patch including plasticity effect

In this paper, we analyzed experimentally and numerically the behavior of fatigue crack in aluminum plates repaired with bonded composite patch. We studied the behavior of repaired crack in AA 2024 T3 and AA 7075 T6 under two levels of applied fatigue stresses: maximal stresses of 70 and 120？MPa at a load ratio of 0.1. In the experimental part, the fatigue life of unrepaired and repaired notched specimens were determined. In the numerical part, the J integral around repaired and unrepaired crack tips was calculated. The numerical and the experimental results were used to plot the crack velocity (da/dN) as a function of the J integral. The analysis was completed with scanning electron microscopic observations on fracture surfaces of repaired and unrepaired specimens. It was found that patch improves the fatigue life but this improvement is considerably reduced with the increase in the applied fatigue load. The Al 2024 T3 presents better resistance to fatigue crack propagation in both repaired and unrepaired cases