Development and application of the strain energy density criterion to three-dimensional I-II mixed-mode fracture

In this paper a modified Strain Energy Density (SED) criterion is proposed to predict the initiation angle of the crack growth under three-dimensional mixed mode loading condition. Compared with several corresponding experiments, large amount of finite element analyses are implemented to give simple prescription of the modified SED. Influences of several factors such as material properties, in-plane constraint (T stress) and out-plane constraint (finite thickness) are considered. Three main conclusions are obtained: (1) The position of the characteristic distance is important in the modified SED criterion. The characteristic distance is insensitive to Poisson's ratio, hardening exponent, plate-thickness, T-stress and mode mixity on the mid-plane of a three-dimensional crack, however the initiation angle is sensitive to those parameters. (2) The modified SED criterion can be used to predict the crack initiation angle for different material properties and different mode mixity, including both the dimple failure type and the shear failure type. (3) The initiation angle determined from this criterion varies from the mid-plane to the surface plane for a three-dimensional crack. This kind of variation is larger for thicker plate and mode I predominated cases, which matches our experimental results.