Effects of Compressive Residual Stress on Bending Fatigue Crack Propagation Behaviour

Testing for bending fatigue crack propagation under mixed-mode condition was carried out using fatigue and annealed slant pre-cracks with different slant angles, beta, defined as the angle between loading and crack directions in a rectangular plate. As a result, bending fatigue crack from the fatigue pre-crack with beta=45deg. propagated under mixed-mode condition with mode I and II stress intensity factors KI and KII, while bending fatigue cracks from the fatigue pre-crack of beta=60deg. and from the annealed pre-cracks with both slant angles of beta=60deg. and beta=45deg. propagated under mode I crack behavior. Furthermore, the estimated fracture angles calculated by maximum tangential criterion using the stress intensity factors, K I and K II, are in good agreement with the measurement ones except the fatigue pre-crack of beta=45deg. at the initial premium propagation. That is to say fatigue crack propagation behavior was effected by compressive residual stress around pre-crack while the slant angle p is smaller (such as beta=45deg. in this study). But the effect was disappeared if beta became bigger (such as beta=60deg.).