Damage Evaluation of Piezoelectric Ceramics from the Variation of the Elastic Coefficient under Static Compressive Stress

In the present article, columnar specimens of lead zirconate titanate (PZT) were subjected to static compressive stress, and the characteristics of fracture under compression were clarified. The fracture tests were interrupted at certain intervals, and resonance and anti-resonance frequencies and electrostatic capacity were measured by means of an impedance analyzer with the compressive stress unloaded. The interruption and measurement were repeated with the maximum stress increased up to the fracture. The material properties of the specimens such as the electromechanical coupling coefficient, the dielectric constant, the elastic coefficient, and the piezoelectric constant were evaluated based on the resonant properties, and the variation of the material properties in the process of the fracture were clarified experimentally. An elastic coefficient was also evaluated from stress— strain relations during the compression fracture tests, and the difference in the elastic coefficient depending on the method of evaluation was discussed. Furthermore, internal damage developed in the specimens during the compression fracture tests was evaluated based on the variation of the elastic coefficients indirectly as a scalar damage variable on the basis of the continuum damage mechanics. Features of the damage development and the dependence of the quantitative value of the damage variables on the evaluation method of the elastic coefficient were discussed. SEM micrographs of the fracture surface were observed and the causes of the damage were investigated.