Margin effect on crack propagation of cold-worked hole under fatigue loading

A fatigue test program was carried out with the aim to study the effect of the cold working process on the fatigue crack propagation life. Plate specimens of 7475-T7351 aluminium alloy containing a pre-cracked fastener hole with different edge margins have been subjected to cyclic loading of constant amplitude. During a test, the fatigue crack length was monitored using a video-camera system; the results permitted to establish the evolution of the crack along the bore and across the short ligament of the specimen. Three-dimensional finite element simulation of the cold working process has been conducted for establishing the residual stress field around the fastener hole. The residual stress distribution resulting from the process was then combined with the applied stress for calculating the crack propagation life, taking into account the edge margin effect.