Fatigue Failure and Ball Bearing Friction

Abstract

According to the standard method for calculation of life ratings for rolling contact bearings, failure is considered to occur at the initiation of the first spall in a rolling component surface. While this is acceptable for most bearing applications, in many applications bearing operation may effectively continue for a period of time during which spoiling progresses. As spoiling progresses, bearing friction and vibratory loading increase, eventually resulting in bearing seizure and mechanism failure. To estimate the amount of operating time available for corrective action; i.e., mechanism shutdown and bearing replacement, between initial spoiling and potential mechanism failure, an investigation into the friction occurring in a spalled-unspalled concentrated point contact was conducted using a ball/v-ring test rig to generate and progress spalls and a ball-disk rig to test traction. It was thereby determined for a spalled ball-raceway) contact, that a lubricant film of thickness sufficient to adequately “separate” the contacting surfaces can occur: With continuous ample supply of fluid lubricant, measured traction coefficients were only slightly greater than would be expected for unfailed contacts. Using the experimental results, an empirically based mathematical model was developed to estimate ball-raceway traction as a function of degree of spalling. These data will subsequently be used in ongoing studies to estimate rate of spall progression in bearing applications.