2018 Volume 18 Issue 3 Pages 199-205
Partially stabilized zirconia is a useful material toughened by a stress-induced transformation, and often applied in the medical field. However in our previous study an appreciable degradation of lifetime by cyclic loading was observed. And such a cyclic effect was supposed to be due to the occurrences of micro-cracks in transformation zone near the crack tip. In this study two methods adding pre-loading stress before adding cyclic loading stress were suggested to restrain the occurrences of micro-cracks. One is the method adding a pre-loading stress close to the transformation-induced stress before indenting a pre-crack to the surface of specimen, and the other is that adding a pre-loading stress more than the cyclic loading stress after the indentation. The test results indicated that the latter method could make the lifetime appreciably increase in cycling fatigue with a low applied stress. It was supposed that the transformation zone formed in front of crack tip by pre-loading stress restrains the occurrence of micro-cracks and the process zone wake extended behind crack tip with crack growth causes the increases of crack resistance due to the closure stress over the crack surface.
