Tensile stress fatigue life model of silicon nitride ceramic balls

The RCF (rolling contact fatigue) life of ceramic balls is a reliable technique to assess whether or not they are suitable to be used in rolling bearings. The relation expression between failure probability and RCF life was deduced with Weibull fracture statistic method for the silicon nitride ceramic ball in ball–cylinder geometric model. The tensile stress life model about silicon nitride ceramic balls was set up between RCF life and contact stress on the basis of the correlative numerical solution between the rating life and the maximum contact stress. It is conceived basing on maximum principal tensile stress. The failure cause, fatigue phenomenon and mechanics of balls are analyzed. The analysis shows that considering the maximum tensile stress as fatigue failure critical stress is reasonable. It is indicated that the tensile stress life model is feasible through RCF test with different stress level. It is verified by the tensile stress life model that silicon nitride ceramic balls failed by the maximum principal tensile stress, not by the maximum shear stress. In comparison with the L–P shear stress life model, the tensile stress life model is reasonable for RCF life prediction of silicon nitride ceramic balls.