Cyclic fatigue due to electric loading in ferroelectric ceramics

Mechanical fatigue of ferroelectric ceramics due to bipolar cyclic electric loading is examined. Beam specimens out of three different PZT materials w ere 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 t imes the coercive field E-c. In short intervals the crack propagation was m easured. Before and after fatigue experiments electric polarisation and str ain were measured as a function of the electric field. The crack growth rat e decreases with increasing cycle number, and a saturation point is reached after approximately 10(5) cycles. A correlation between growth rates and f erroelectric strain was detected. Measured strain loops suggest that switch ing of ferroelectric domains undergoes a strong fatigue effect. Therefore a fter 10(6) cycles the elastic strain is not as strong a driving force for f ur ther crack extension, rn addition fatigue-crack growth is strongly depen dent on the material and the electric field strength. (C) 1999 Elsevier Sci ence Limited. All rights reserved.