A damage evolution equation for piezoelectric ceramics under compression-compression fatigue tests were formulated on the basis of previous experimental results within the framework of the continuum damage mechanics. In the previous experiments, columnar specimens of piezoelectric ceramics were subjected to compression-compression fatigue loading. The fatigue tests were suspended at specified intervals, and the resonance and anti-resonance frequencies and the electrostatic capacity of specimens were measured by an impedance analyzer. The loading and measurement were repeated up to the fatigue fracture. Material properties of piezoelectric ceramic specimens were calculated from the resonance and anti-resonance frequencies and the electrostatic capacity, and the variation of material properties during fatigue tests was elucidated. Development of internal damage within piezoelectric ceramics was evaluated as a damage variable by the variation of elastic coefficient on the basis of the continuum damage mechanics. An evolution equation of the damage variable was formulated by using fatigue life which was formulated as functions of the static fracture strength, the fatigue limit and the mean stress. Prediction of damage development was compared with experimental results and the validity of the formulation was verified.

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