Predicting fatigue crack growth emanating from cold-expanded holes

Split sleeve Cold eXpansion (CX) is a common technique to improve fatigue behaviour of open holes as well as fastener holes at fatigue critical joints in aeronautical structures. For several decades it is applied in high loaded aeronautical components to extend their fatigue lives, taking into account the beneficial effect of the compressive residual stress induced by the CX technology on fatigue initiation. In order to predict the crack growth in the presence of residual stress (e.g. for fatigue life prediction in structural component containing initial flaw) it is very important to calculate accurately the Stress Intensity Factor (SIF) related to crack growing in 3D residual stress field. For this reason, a dedicated test campaign has been launched with the aim to collect crack growth data associated to a crack front emanating from a quarter circle artificial notch placed at the edge of the hole following the development from corner crack to complete through thickness crack.