Abstract
Fatigue crack propagation tests of PZT ceramics were conducted by using 4 point bending of single edge-notched specimens under cyclic and static loading conditions. Domain switching (DS) in the vicinity of fatigue cracks in PZT ceramics was evaluated from the intensity ratio of 002 to 200 diffractions measured by X-ray microdiffraction. The change of the crack propagation rate with crack extension can be divided into three regions. In region I, the crack propagation rate decreases with increasing crack length, and then turn to increase in region III. In region II, the propagation rate is nearly constant. The crack propagation rate was higher in the order of cyclic fatigue with frequency of 30Hz, cyclic fatigue with 0.3Hz and static fatigue. DS near the crack tip was divided into two kinds : one is the residual DS left without load and the other was reversible during loading-unloading cycle. The amount of residual DS increased with crack extension. The decrease of crack propagation rate in region I was caused by the development of DS and interlocking between crack faces. In region III, the increase of the applied stress intensity factor became dominant, then accelerated crack propagation. Region II was the transitional region. The fatigue fracture surface made by static fatigue had the largest amount of residual DS and the largest fraction of intergranular fracture.
