Effects of biaxial loading on crack driving force and constraints for shallow semi-elliptical surface flaws

Three-dimensional, elastic-plastic finite element analyses have been carried out to investigate the effects of biaxial loading on J-integrals and Q-values for shallow semi-elliptical surface flaws in wide plates. Direct tension and pure bending loading of up to about 10 times the yield strain were applied to models with linear elastic-power hardening and tripartite material behaviours. Crack depths were limited to 15 percent of the plate thickness. Differences were observed between the effects of biaxiality on J-strain behaviour for cracks in semi-infinite plates and those in finite width plates. The cracked semi-infinite geometry was considered more representative of structural applications. In this case, biaxial loading gave a large increase in J-integrals compared to uniaxial loading, but had negligible effect on constraint, as measured using the Q-value.