Acoustic emission monitoring of wear in aerospace self-lubricating bearing liner materials

Self-lubricating composite bearing liners are used in a range of aerospace systems including fixed wing and rotary wing applications such as a helicopter pitch links. In aerospace applications these bearings are subject to periodic replacement, irrelevant of wear condition, with manual inspections made at set intervals. There is a drive in many areas of aerospace to move from a scheduled replacement plan to an as required approach to increase asset availability and reduce maintenance costs whilst maintaining safety. This has led to a clear research and commercial drive to develop smart bearings that can identify the onset of critical damage and alert an operator of the need for replacement, effectively a Structural Health Monitoring (SHM) system. This paper presents a novel investigation of composite bearing liners in conjunction with Acoustic Emission (AE). The developed test programme and subsequent analysis clearly demonstrate that it is possible to monitor the complex wear process of the liner material using AE within a laboratory environment. Furthermore, a new approach to analysing AE signals is presented that could be integrated into a SHM system for asset management.