Experimental study and modelling of short fatigue crack growth in aluminium alloy Al7010-T7451 under random loading

This paper presents work on short crack initiation and growth behaviour under random loading conditions. Newman's crack closure model was extended to include the influence of grain boundary on crack opening level by introducing the concept of constrained crack tip plasticity by grain boundary blocking. A dislocation-based crack growth model (the Navarro–Rios model) was used in conjunction with a crack closure model for lifetime prediction under random loading conditions. Crack growth tests were performed using hourglass shaped specimens of Al7010-T7451 under constant amplitude loading as well as a variety of random loading cases representing the load spectra encountered in various flight missions. A good agreement (within 14% difference) was achieved between the model results and the experimental data. Crack initiation and growth behaviour for constant-amplitude and random loading conditions was also examined by use of plastic replicas and SEM observations.