Indented crack growth during poling of a high displacement PZT material

The present paper presents the effect of poling field on the indented crack lengths and electromechanical properties of a PZT material of high technological interest, because of the relatively large strains it can generate (more than 1%). The tests were performed on bars that could be electrically characterized using electrical resonance. The bars were indented, so that they contained controlled surface cracks. The indentation cracks grew significantly more than twice their initial length during the application of a typical poling field 1.5 kV mm−1. This is a very surprising result compared to the behaviour observed for previously tested PZT materials and it highlights a potentially major problem for the application of the materials with the composition studied. Also of concern is the fact that most of the crack growth occurred at relatively low poling fields (less than 2 kV mm−1). No effect of domain reorientation at the crack tip could be observed and no anisotropy in crack growth appeared during the poling. The behaviour of the piezoelectric coefficient d31 and the evolution of cracks during poling at different electric fields were not clearly related.