Analytical Modeling and Mechanism Analysis of Time-Varying Excitation for Surface Defects in Rolling Element Bearings

Surface defects, including dents, spalls, and cracks, for rolling element bearings are the most common faults in rotating machinery. The accurate model for the time-varying excitation is the basis for the vibration mechanism analysis and fault feature extraction. However, in conventional investigations, this issue is not well and fully addressed from the perspective of theoretical analysis and physical derivation. In this study, an improved analytical model for time-varying displacement excitations (TVDEs) caused by surface defects is theoretically formulated. First and foremost, the physical mechanism for the effect of defect sizes on the physical process of rolling element-defect interaction is revealed. According to the physical interaction mechanism between the rolling element and different types of defects, the relationship between time-varying displacement pulse and defect sizes is further analytically derived. With the obtained time-varying displacement pulse, the dynamic model for the deep groove bearings considering the internal excitation caused by the surface defect is established. The nonlinear vibration responses and fault features induced by surface defects are analyzed using the proposed TVDE model. The results suggest that the presence of surface defects may result in the occurrence of the dual-impulse phenomenon, which can serve as indexes for surface-defect fault diagnosis.