Font Size: 

The mixed mode I/II crack growth behavior of Guiting limestone was investigated using centre cracked circular disc (CCCD) and the edge cracked semi circular bend (SCB) specimens. It was observed that for similar mode mixities in the two different shaped specimens, the fracture paths grew in two different trajectories. The deviation of crack path from the initial crack line was more pronounced for the SCB specimen and also for mode II dominant loading conditions in both samples. It is shown that the observed crack path and the fracture initiation angle can be predicted theoretically by using the fracture parameters (KI, KII and T-stress) of the rock samples via a generalized form of the maximum tangential stress criterion. The main difference in the fracture trajectory was found to be related to the magnitude and sign of T-stress in the CCCD and SCB samples. Accordingly, the SCB specimen which has a considerable positive T-stress in mixed mode loading would have a larger fracture initiation angle in comparison with the CCCD specimen which has a very high negative T-stress for all mode mixities.