Geometry and size effects on fracture trajectory in a limestone rock under mixed mode loading

The mixed mode I/II fracture initiation angle and the crack growth trajectory of a soft rock (Guiting limestone) were investigated experimentally and theoretically for two different shaped test specimens with various sizes. It was observed that for similar mode mixities in the two specimens, the fracture paths grew in two different trajectories. It is shown that the observed crack path and the fracture initiation angle can be predicted theoretically by using a generalized form of the maximum tangential stress criterion. The main difference in the fracture initiation angles was found to be related to the magnitude and sign of the T-stress.