Real-time evaluation of wear condition in aviation self-lubricating bearings based on acoustic emission

Wear of the self-lubricating liner in aviation spherical plain bearings leads to increased clearance between the inner and outer rings, causing precision degradation of the control mechanism, thereby seriously threatening flight safety. Acoustic emission (AE)-based condition monitoring possesses many advantages such as high sensitivity, early-warning capability, and strong anti-interference performance, which can effectively address the limitation of traditional inspection methods in their inability to real-time characterize bearing operational states. First, a wear test setup with multiaxial loading capability for self-lubricating bearings and a split-type bearing base integrated with embedded AE sensors were designed, ensuring the fidelity of AE signal acquisition. Then, the evolutionary laws of AE signals from self-lubricating bearings in both time and frequency domains were studied, revealing the dual dominant frequency characteristics of AE signals and their dynamic energy evolution mechanism. A method for constructing bearing wear index based on acoustic emission time-frequency features and the multi-criteria feature selection strategy was proposed, enabling real-time assessment of the wear condition of self-lubricating bearings via wear index curves. It was found that the dynamic equilibrium of the PTFE transfer film in the bearing liner influences the energy distribution of AE frequency components. The critical transition interval for the test bearings between the running-in phase and stable wear phase was identified as 9 747 to 10 773 revolutions; and it was determined that the test bearings ultimately remained in the stable wear phase. Finally, the accuracy of the proposed wear index-based condition prediction method was validated using torque data. Furthermore, the micro-wear characteristics of the bearings were characterized through scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The migration behavior of the PTFE transfer film and the interfacial chemical composition under the final wear state demonstrated the consistency of the wear phase determination.