Precessional Slip and Microinclusion Effect on Fatigue Life of Bearing Rolling Element: An Integrated Life Estimation Model through Experimental and Analytical Investigation

This study presents an integrated mathematical model to predict the fatigue life of a bearing rolling element under the influence of both the microinclusion effect and the precessional slip. The relationship between microinclusion effect and precessional slip was modeled and validated for bearing balls undergoing Hertzian contact fatigue when working in a bearing. For the rolling element, a statistical approach was necessary due to the presence of slip and precession. To statistically determine how often the inclusion was loaded, ball spin frequency was estimated. Studying the ball motions in terms of spin, precession, and transverse slip at the ball-race contact provided an estimate of the frequency at which the inclusion contacted the race during one complete shaft cycle. The life model was completed to account for race and conformity defects, slip, precession, and the presence of microinclusions. The life predictions were compared with the experimental number of cycles to failure of bearing balls. Material characterization was run to calibrate the model. To validate the model, many bearing balls were subjected to fatigue testing by means of a test rig. After failure analysis, optical and scanning electron microscopy (SEM) inspection of the fractured surface, x-ray spectroscopy, and destructive testing analysis were performed to obtain the dimensions, position, and mechanical properties of the microinclusions.