Fracture criterion for a conducting crack in poled PZT-PIC 151 investigated by stable crack growth

The fracture behavior of conducting cracks in PZT (PIC 151) was investigated under combined mechanical and electrical loads in four-point bending. Controlled crack growth in a single-edge V-notch beam (SEVNB) specimen was achieved in a very stiff displacement controlled device. During the experiments a constant electric field was applied. The mechanical fracture resistance exhibited a strong dependence on the applied electric field. When applying a field anti-parallel to the poling direction the mechanical crack resistance was always decreased; at 500 V mm−1, it fell to zero. For electric fields applied in the poling direction, a change from facilitating to retarding crack propagation was observed during crack extension. This result is interpreted as a mechanical shielding effect which is built up during crack propagation. The experimental results are in surprisingly good agreement with the hypothesis of a fracture criterion based on the total crack tip energy release rate.