The influence of test lubricants on the rolling contact fatigue failure mechanisms of silicon nitride ceramic

Surface defects such as ring cracks are located on silicon nitride ceramic rolling elements. The random nature of ring crack position creates difficulties in predicting rolling contact fatigue (RCF) life. The influence of the lubricant on the RCF mechanism is difficult to determine due to the scattered nature of RCF life. In this study, a novel experimental technology was utilised to perform rolling contact fatigue tests. The test ceramic ball specimen with surface ring cracks is precisely located in the contact path. The rolling contact fatigue tests are performed on silicon nitride/steel elements using three different types of lubricating oils. Observation of damage progression is carried out to understand the mechanism of ceramic rolling contact fatigue failure. Experimental observations show that the secondary surface cracks are formed before fatigue spalling. Those surface cracks are crucial to the formation of ceramic fatigue failure. A boundary element model has been developed to investigate why the secondary surface cracks form and how crack face friction affects the formation of the secondary surface cracks. The surface traction effect is also investigated experimentally and numerically. Results from the experimental tests are in good agreement with the numerical analysis.