Cage Fracture of Planet Bearings Under Revolution-Rotation Coupled Conditions: Failure Mechanism and Vibration Features

Abstract

Planet bearings constitute critical components of planetary gear systems (PGS), comprising a cage and rollers. Rotating rollers preclude direct sliding between the planet gear and carrier, while the cage maintains roller spacing and ensures stable motions. Cage fracture is a typical failure under revolution–rotation coupled conditions, but the failure mechanism and vibration features are still unclear. To address this issue, this study first establishes a PGS dynamic model and a flexible cage model, revealing that reciprocating roller–cage impact constitutes the primary driver. Moreover, the evolution process of cage fracture is elucidated, encompassing high-cycle fatigue crack initiation, low-cycle fatigue propagation, and ultimate brittle fracture. Experimental results indicate that cage fracture induces significant elevations in RMS and standard deviation of time-domain signals, accompanied by pronounced sideband modulation and noise floor elevation near the meshing frequency and its harmonics. This investigation provides guidance for the life prediction and detection of cage fracture.