FATIGUE THERESHOLD IN A 2618A ALUMINIUM ALLOY

Abstract— This work is concerned with the determination of the fatigue threshold ΔK_th for an aluminium alloy. No dependency of ΔK_th with grain size was observed. Crack closure concepts were applied in order to explain the effect of mean stress and environment. The opening load P_op was determined by the compliance method. Results show no significant variation of P_op with environment (air or vacuum) but partially explain the influence of mean stress on crack growth rates. Fractographic analysis (SEM) of fracture surfaces and evolution of compliance diagrams suggest that a change of mechanism in crack propagation occurs when stage I changes to stage II growth.