Brittle fracture in key-hole notches under mixed mode loading: Experimental study and theoretical predictions

Brittle fracture was studied experimentally and theoretically for key-hole notches under mixed mode loading. Brazilian disk specimen containing a dumbbell-shaped slit and made of polymethyl-methacrylate was proposed to measure the notch fracture toughness and the fracture initiation angle at room temperature. The experimental results were predicted by the maximum tangential stress and the mean stress criteria. Two groups of critical distances were utilized in the criteria. The first one was equal to that for sharp cracks and the second one was directly obtained from the fracture tests. It was found that both the criteria could predict the experimental results successfully.