• stress intensity factor
• residual stress fields
• fatigue crack propagation
• cold-expansion
• cold working
• XFEM

Split sleeve Cold eXpansion (CX) is a common technique to improve the fatigue behaviour of open holes as well as fastener holes in fatigue critical joints of aeronautical metallic structures. Many test evidences in the past have demonstrated the capability of cold expansion to provide fatigue life enhancement, such as longer inspection intervals or a general increased operational lifetime of the airframe. Thus for several decades it has been 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. However the healthy effects of the CX process are still not commonly considered in the design phase of an aircraft. In fact, in order to predict the crack growth in the presence of residual stresses, it is essential to calculate accurately the Stress Intensity Factor (SIF) related to a crack growing in 3D residual stress fields. The development of a predicting capability in this case remains still challenging, especially if the crack is located in regions with high stress gradients. For this purpose, a dedicated numerical strategy has been elaborated at UNIPI to solve the issues connected to the SIF evaluation and to model crack propagation in complex residual stress fields. The discontinuity has been modelled using both innovative methods (e.g. XFEM) and traditional approaches. A massive use of in-house Python codes has simplified and speed up the phases of model generation and data extraction. Finally the obtained results have been compared and validated through a focused experimental activity.