Intra-Ball and Inter-Ball Variability of Ring Crack Initiation Load of Silicon Nitride Bearing Balls

Abstract

When the ring crack initiation load P_R of ceramic bearing balls is measured at one position per ball, P_R shows considerable scatter as shown in a previous paper. In order to clarify which of the inter-ball variability and the inter-ball variability is responsible for this scatter, a new type of test was carried out in the present study on HIP-Si₃N₄ bearing balls in which P_R was measured at 8 positions per ball. Initiation of a ring crack was detected using acoustic emission (AE). From analysis of variance, it was shown that the scatter of P_R observed when measuring P_R at one position per ball was mainly due to the intra-ball variability or the spatial variation of P_R within one ball.