Cold Work Simulation of Hole Expansion Process and Its Effect on Crack Closure

Using cold working fastener holes is a simple life enhancement procedure that strengthens metallic components by retarding crack growth around a hole. In the present paper, the residual stress field that is induced by the hole expansion process is obtained based on different material models, namely elastic perfect plastic, isotropic hardening and kinematic hardening using the three-dimensional finite element method. Moreover, crack closure analysis was performed following introduction of residual stress. The effect of modeling parameters such as the percent of cold work, remote tensile stress and crack length was also considered. Crack closure analysis indicates that the material model would affects normalized crack opening loads, especially at low level of remote tensile stress where small scale yielding is dominant. Cold work simulation results indicate that the residual stress variation through the thickness is considerable. At low stress level, the effect of material behavior model is considerable and at high stress levels the crack opening load is dropped. Moreover, increasing the cold work interference percent results in a higher and deeper compressive residual stress.