Moire interferometer applied to a piezoceramic containing a simulated void

In this paper we describe the results of an ongoing experimental program to measure the strain distribution around a simulated void in a piezoceramic material subjected to large electric fields. The simulated void is a two-dimensional circular cylinder fabricated into the sample. Strain information is acquired with a Moire inteferometric system which permits both quantitative evaluation of surface strains and qualitative information regarding domain reorientation. Results indicate that large stresses/strains arise around the perimeter of the hole prior to domain reorientation. Domain switching initiates at the locations where the largest stress/strain occurs around the perimeter of the simulated void and do so to reduce the localized concentrations. During this evolutionary process the material contains a multi-domain structure with regions polarized in 180° apart. Domain switching appears to be predominately 180° without any 90° domain reorientation occurring at the mesoscopic level. Results suggest that large stress/strain concentrations around voids could be a source for electric fatigue degradation.