In the present work, we experimentally and theoretically studied the failure behavior of electrically conductive cracks (deep notches) in thermally depoled PZT-4 ceramics, which were macroscopically dielectric, under mechanical and/or electrical loading. When the critical stress intensity factor was normalized by the critical stress intensity factor under purely mechanical loading and the critical electric intensity factor was normalized by the critical electric intensity factor under purely electric loading, the experimental results revealed that the failure behavior of the conductive cracks in the ceramics was described by a quadratic function of the normalized electric intensity factor versus the normalized stress intensity factor. Accordingly, we proposed herein a charge-free zone model to predict the failure behavior, by treating dielectric ceramics as mechanically brittle and electrically ductile materials. The charge-free zone model resulted in a failure criterion, which agreed perfectly with the experimental results.
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