Study of an On-Line Crack Compliance Technique for Residual Stress Measurement Using 2D Finite Element Simulations of Fatigue Crack Growth

There are several methods available to measure residual stress fields present within a structural component. Recently a new so called on-line crack compliance technique has been proposed, which is based on linear elastic fracture mechanics. This experimental method uses incremental crack mouth opening displacements measured during fatigue crack growth testing to generate information on the existing residual stresses along the crack line. The present study employs two dimensional (2D) plane stress finite element simulations of fatigue crack growth from a cold worked hole to investigate the performance of this technique. Using the simulation results, the stress intensity factors due to the residual stress field normalized by the maximum applied stress intensity factor KIrs/KImax were obtained from the on-line crack compliance method. For validation, the J-integral approach was used to calculate KIrs/KImax values from fatigue crack growth simulations in an elastic material. The two methods generated nearly identical results. Fatigue crack growth was also simulated in an elastic-plastic material. Even though the stress intensity factor is not the appropriate crack tip characterizing technique for elastic-plastic material conditions, it is still investigated here to approximate the actual testing conditions, where plastic deformation near the crack tip is unavoidable. The KIrs/KImax solutions are presented for different cold work levels and applied loadings. Results indicate that the agreement between the elastic and elastic-plastic crack growth solutions is dependent on the maximum applied loading level, as might be expected.