Study of Time-Varying Oil Film Damping and Contact Stiffness of Ball Bearings

In current scenarios, where the thrust is kept on the incipient fault detection and its size estimation, the dependency on the vibration signals and processing techniques is growing day by day. The correct understanding of the mechanism behind the sources of this signal is therefore called upon. Like other sources of damping, the effect of squeezed oil film damping on the vibration response of rolling element bearings cannot be overlooked. The variation in the squeezed film damping and contact stiffness, as a result of orbital motion of cage, and the resulting load distribution pattern play important role in determining the time-varying system behavior. The values of contact stiffness and damping are governed by multiple factors which necessitate their quantitative investigations to gain deep insight. In this work, the variation in squeezed film damping and contact stiffness in bearing owing to its orbital motion and that due to localized defect on outer race have been studied. The influence of operating parameters and defect geometry factors on dynamic contact characteristics have also been numerically investigated. A considerably large variation in the values of the contact parameters was witnessed with rotation, especially in the presence of defect. The variations were found as high as 89% in squeezed film damping and 38% in contact stiffness for the selected test bearing rotating at 1000 RPM under 100 N radial load. The consideration of such huge variations will help in correct simulation of the time localized responses of both healthy and defective bearings.