Numerical prediction of fatigue crack propagation in Cold-Expanded Holes

Split sleeve Cold eXpansion (CX) is a common technique to enhance 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 improvements, longer inspection intervals and a general increase of the operational lifetime of an airframe. Thus, for several decades, CX has been used to extend the fatigue life of highly loaded aeronautical components. However, the benefits introduced by the CX process are not usually considered in the design phase of an aircraft, also because the prediction of the crack propagation in 3D residual stress fields is still challenging. The paper presents a dedicated numerical strategy, developed to solve the issues connected with the SIF evaluation and to model crack growth in a complex residual stress field. The numerical procedure is based on an integrated approach, which manages pre- and post-processing data of Finite Element Analyses, with ABAQUS software, by means of “ad hoc” Python and Matlab codes.