Fatigue crack propagation in threshold regime under residual stresses

The effect of residual stress on the fatigue crack propagation was analysed for a loading regime close to threshold stress intensity factor range. Fatigue crack propagation experiments were performed on single-edge-notched bending specimens machined from a welded plate. The residual stresses induced a variation in the crack propagation rate along the crack front. By varying the stress ratio and the stress intensity factor range, different shapes of crack front can be realized. From the shape of the crack front and the variation of the crack front, the resulting residual stresses and local stress intensity can be determined by means of finite element modelling. By using some simplifications, it is possible to estimate the limit values of the stress intensity factor induced by the residual stresses at selected regions.