The effect of the crack tip core region on the crack initiation angles under mixed mode loading

The problem of determining the crack initiation angles under mixed mode loading is still under discussion. The subject is of great interest to researchers in the field of fracture mechanics, especially in predicting crack propagation paths. Using LEFM approach, several criteria have been proposed in this respect, all of which assume a core region at the crack tip. The reason for defining the core region is that the exact stress and strain fields at the crack tip vicinity cannot be determined using LEFM. Some criteria assume a core region of constant radius while others use a variable radius. Although many studies have been directed towards understanding the nature of the core region, however, no or little efforts have been made to correlate the size and shape of the core region to the crack initiation angles. Furthermore, the effect of the core region on crack initiation angles under different loading conditions has not been thoroughly investigated. In this study, the characteristics of the core region and their influence on mixed mode crack initiation angles will be closely examined under different loading conditions. The results clearly show that there is a well-defined correlation between the shape of the core region and the crack initiation angles as predicted by most available criteria.