Failure analysis of the joint bearing of the main rotor of the Robinson R44 helicopter: A case study

The joint bearing of the main helicopter rotor is a vital dynamic component that affects the manoeuvrability, stability, and safety of the helicopter. Field research has shown that wear failure of the joint bearing of the main rotor of the Robinson R44 helicopter is relatively common. In this study, various analysis methods were used to investigate the failure behaviour of the joint bearing of the Robinson R44 helicopter. Subsequently, the failure reasons and wear mechanisms of the joint bearing were analysed using stereo microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron probe microanalysis, and X-ray photoelectron spectroscopy. The results showed that the reason for the wear failure of the joint bearing was severe damage to the fabric liner, with fracturing and tearing of the fibres. Continuous generation, spalling, extrusion, and regeneration of the polytetrafluoroethylene (PTFE) transfer film occurred between the inner ring and fabric liner, dominating the friction behaviour at the interface. Moreover, the wear damage at different circumferential positions of the fabric liner showed significant differences due to the working load conditions. The wear mechanisms of the joint bearing included fatigue wear, adhesive wear, and some abrasive wear and oxidation wear.