Angular contact ball bearing experimental spall propagation observations

Abstract

Modern applications require bearings to survive in severe environments or when subjected to extreme loads and speeds. Some application designs require that a damaged bearing survives a specified duration. In particular, a clearer understanding of spall propagation in bearings may help design engineers prevent rapid damage propagation events and thereby minimize catastrophic failures. This paper summarizes the mechanics governing spall propagation in bearings. Two angular contact ball bearings, one with a seeded fault and the other damage-free, were studied experimentally. A broadband design of experiment approach was used to monitor bearing damage evolution, including demonstration of the effects of impact loading a rolling element on a spall front. The presented vibration, strain, deflection, and oil debris monitor (ODM) data span a matrix of loads and speeds. Results discuss the ball impact on the spall front and include supporting evidence of the following observations. The impact acceleration vector followed the contact angle. The outside diameter of the bearing raceway experienced 450 g rms (root-mean-square) acceleration even in the presence of a small surface defect. The vibration signal was substantially attenuated by the surrounding structure. The spall propagation strain energy was in the 15–30 kHz range and well above the fifth fundamental ball pass frequency. The strain energy associated with propagation decreased with thrust load while the ball pass strain increased.