Variation of material properties of piezoelectric ceramics due to mechanical loading and evaluation of internal damage

In the present paper, lead zirconate titanate (PZT) piezoelectric ceramics were subjected to compressive mechanical loading, and static and fatigue fracture tests were performed. Each test was interrupted systematically after applying prescribed loading, and resonance and anti-resonance frequencies and an electrostatic capacity were measured by means of an impedance analyzer. Then an electromechanical coupling coefficient, a dielectric constant, an elastic coefficient and a piezoelectric constant as material properties of piezoelectric ceramics were evaluated from them. The variation of the material properties due to static and cyclic compressive loading was investigated experimentally. Further, since internal damage of materials affects their material properities, the damage was evaluated reversely from the variation of the elastic coefficient in the present paper. Then the development of internal damage due to mechanical loading was clarified on the basis of the continuum damage mechanics. From SEM micrograph of the fracture surface, it was found that the damage was microscopic cracks in the direction of compressive loading.