Studying on the Propagation Behavior of Bent Crack Bending from Slant Pre-Crack with Compressive Residual Stress

Abstract

For a slant pre-crack under mixed-mode conditions, a method is proposed in which mode Ⅰ and mode Ⅱ stress intensity factors(KI)mes and (KII)mes can be directly evaluated from the discontinuous displacement along it. The effect on fatigue pre-crack deformation behavior was discussed by comparing fatigue and annealed cracks. In general, using the biggest tangential stress criterion the direction propagating from the pre-cracks can be predicted by (KI)mes and (KII)mes calculated above. So testing for bending fatigue crack propagation under mixed-mode conditions was carried out using fatigue and annealed slant pre-cracks with slant angle β=450 defined as the angle between loading and pre-crack direction in a rectangular plate. As a result, for annealed pre-crack, the estimated fracture angle θest corresponded to the measured one θmes; On the other hand, for fatigue pre-crack,θmes is bigger than θest because of the compressive residual stress around the pre-crack.