A 3-D failure initiation criterion from a sharp V-notch edge in elastic brittle structures

A three-dimensional failure initiation criterion in brittle materials containing a sharp V-notch is presented and validated by experiments. It is based on simultaneous fulfilment of the stress requirement and a finite fracture mechanics energy release rate (ERR) requirement. Since the ERR cannot determine failure initiation direction for dominant mode III loading, the failure initiation orientation is determined solely by stress considerations and the force at fracture is determined by both ERR and stress requirements. Experiments on PMMA, Graphite and Macor V-notched specimens loaded by three modes demonstrated that predicted fracture load was mostly within 6.5% (RMS) of experimental values.