Rolling contact fatigue tests of ceramics by various methods: Comparison of suitability to the evaluation of silicon nitrides

Results of rolling contact fatigue (RCF) tests by balls-on-rod (BOR) and two-roller methods have been compared to those by the balls-on-flat (BOF) method by using three different silicon nitride grades. Two were bearing grade (BG) and one was a general purpose (GP) grade. For a GP material, there was not much difference between the results of BOR and those of BOF, and the observations of a spalled region by BOR suggested similar spalling behavior to BOF. Meanwhile, for BG materials, most tests were terminated without spalling, but grooves, whose likely cause is inferred to be insufficient lubrication, were formed. As for the lifetime in BOR, however, the results for BG materials were much longer than those of the GP, demonstrating that the BOR result is qualitatively consistent with that of BOF, where instead most specimens failed in RCF by spalling or peeling. In the two-roller method, tests of a limited number of specimens were operated at high slip ratios of 10 % during longer cycles under low co