Effect of bending stress parallel to the crack plane on J and the limit load of plates with surface cracks

The effect of bending stress parallel to the crack plane on J-integral of plates containing semi-elliptical surface cracks is investigated in this paper. Elastic and elastic-plastic finite element (FE) analyses are used to obtain J values for the surface-cracked plates under membrane stress or through-thickness bending stress normal to the crack plane or under biaxial membrane stresses plus through-thickness bending normal to the crack plane with/ without bending stress parallel to the crack plane. The FE results show that, as predicted by linear elastic fracture mechanics, the applied bending stress parallel to the crack plane does not affect the crack tip elastic J. However, it does affect the elastic-plastic J. A limit load (or reference stress) solution for a plate containing a rectangular surface crack under combined biaxial membrane stresses and biaxial bending stresses is developed, which shows good correlation to the elastic-plastic FE J via the reference stress J scheme, for both cases with/without the bending stress parallel to the crack plane. Based on the results of the investigation, a newly-developed local limit load model is updated to include the effects of bending stress parallel to the crack plane for use in structural integrity assessments.