Abstract

Mechanical fatigue of ferroelectric ceramics due to bipolar cyclic electric loading is examined. Beam specimens out of three different PZT materials were cut and precracks were initiated by Vickers indentation. The specimens were loaded by alternating electric fields varied from 0.9 to 1.0 and 1.5 times the coercive field E-c. In short intervals the crack propagation was measured. Before and after fatigue experiments electric polarisation and strain were measured as a function of the electric field. The crack growth rate decreases with increasing cycle number, and a saturation point is reached after approximately 10(5) cycles. A correlation between growth rates and ferroelectric strain was detected. Measured strain loops suggest that switching of ferroelectric domains undergoes a strong fatigue effect. Therefore after 10(6) cycles the elastic strain is not as strong a driving force for fur ther crack extension, rn addition fatigue-crack growth is strongly dependent on the material and the electric field strength.