Dynamic interactions in spalled bearings: A coupled friction-IAS model for fault-induced torsional vibrations

Instantaneous angular speed (IAS)-based condition monitoring has emerged as a significant research topic since it offers advantages of short transfer paths, no periodic calibration, etc. However, the contribution of complex friction to IAS perturbations has not yet been effectively elaborated. The torsional vibration analysis of the IAS perturbation of bearings is usually simplified as the coupling of normal and tangential force in previous works. To address this issue, this study proposes a comprehensive dynamic model of a ball bearing with a localized spall on its outer race. Firstly, a method for calculating the time-varying friction moment considering the elastic hysteresis of raceway material, the differential sliding friction between ball and raceway, and the viscous resistance caused by lubrication is proposed. Secondly, the interactions of friction moments and the localized spall are introduced, which further elaborates on the influence of friction factors on IAS signal perturbation. Finally, simulation and experimental results validate the proposed model, and the effects of localized spalls on IAS signals on the IAS signals and the friction moments are analyzed. The detectability of the IAS signal is also discussed under different shaft speeds and external loads.