The influence of microstructure on the crack nucleation and growth under fretting-fatigue loading was investigated on different Al-Cu-Li alloys used for aerospace applications. The experimental study was divided into 3 distinct parts: - behaviour in fatigue with stress concentration, - crack resistance in fretting, - fretting-fatigue tests. Although all the investigated alloys exhibit a similar life time under the fatigue conditions tested, they present different (macroscopic and microscopic) crack path morphologies. ESBD analyses show that only UA-alloys were sensitive to grain orientation. The main factor influencing the crack path remains the precipitation state, because of the direct interaction with dislocation motion. Concerning the fretting tests, this study shows that cracking is not only controlled by contact conditions as assumed in the literature. For identical testing condition, UA alloys present a better behaviour in crack resistance than T8 alloys. This tendency is also true under fretting-fatigue condition. The fracture surfaces were analysed and allow to decompose fretting-fatigue mechanism in 3 steps: crack initiation induced by fretting, crack propagation under the influence of both fretting and fatigue loadings, then propagation only controlled by fatigue until final breaking.
