Abstract
Piezo-electric ceramics, PZT, are used as actuators in mechanical structures, therefore the log-term reliability of actuators is required. Crystalline structure of PZT is changed by the ratio of chemical compositions. PZTs have rhombohedral structure at high ratio of Zr, tetragonal structure at a high ratio of Ti, and morphotropic phase boundary (MPB) at same ratio of Zr and Ti. In this study, 4-point bending tests of PZTs with three types crystal structure were conducted. Bending strength and fatigue crack propagation behaviors were investigated. Bending strength for tetragonal PZT was highest, that for MPB PZT was lowest Fatigue crack propagation rate could be divided into three regions: Region I was the region where crack propagation rate decreased, Region II was the minimum constant rate region, and Region III was the acceleration region. In Region El of high crack propagation rate, crack propagation rates for three crystalline structures follow the Paris's law. But, the crack propagation rate less than 10^<-7> m/cycle in early Region III was lower than the rate predicted by the Paris's law. Fracture surfaces after fatigue test were dominated by intergranular fracture.
