Angular distribution of energy release rates and fracture of piezoelectric solids

Applicability of energy release rate criteria to piezoelectric materials is examined in this paper. The angular distribution of strain and total energy release rates at a crack tip in a plane piezoelectric medium is first formulated by using a branched crack model. By relaxing the commonly held assumption of self-similar crack propagation and incorporating in the fracture toughness anisotropy, the criteria of modified strain energy release rate and modified total energy release rate are applied to discuss the propagation path of an impermeable crack. Numerical results indicate that the predictions based on the criterion of modified total energy release rate do not show qualitative agreement with experimental observations, whereas the predictions based on the criterion of modified strain energy release rate appear more promising. Based on the criterion of modified strain energy release rate, a crack tends to branch off from a straight path under a positive electric loading, regardless of crack orientation. An applied electric field can either promote or retard crack propagation depending on the direction of electric field, crack orientation and crack extension direction. The predictions made by the energy-based criteria are compared with those corresponding to a recently reported stress-based criterion.