Fracture of Conductive Cracks in Poled and Depoled PZT-4 Ceramics

Abstract

The present work reports experimental results on the fracture behavior of conductive cracks or deep conductive notches in poled and depoled PZT-4 ceramics. The fracture tests were conducted with compact tension specimens under purely mechanical loading, purely electrical loading and combined mechanical and electrical loading. Finite element calculations were carried out to obtain the energy release rate, the stress intensity factor and the intensity factor of electric field strength of the specimens. The results show that the critical energy release rate under purely either electrical or mechanical load is a constant, independent of the ligament length of the specimens. However, for both the poled and depoled ceramics, the electrical fracture toughness in terms of the critical energy release rate is much higher than the mechanical fracture toughness. The highly electrical fracture toughness arises from the greater energy dissipation around the conductive sharp notch tip under purely electrical loading, which is impossible under mechanical loading in the brittle ceramics. Furthermore, the critical energy release rate under combined electrical and mechanical loading depends on the weight of the electrical load in comparison with the mechanical load. We normalize the critical stress intensity factor by the critical stress intensity factor under purely mechanical loading and normalize the critical intensity factor of electric field strength by the critical intensity factor of electric field strength under purely electrical loading. Then, a quadratic function describes the relationship between the normalized critical stress intensity factor and the normalized critical intensity factor of electric field strength. This quadratic function may serve as a failure criterion for conductive cracks in piezoelectric ceramics.