Damage detection of a PTFE liner matrix composite through the use of acoustic emission

Self-lubricating bearings are widely used within the aerospace industry and are commonly found in the pitch control assembly of rotorcraft and, as such, are critical parts due to their importance within the system. The dry lubricant present within these bearings acts as a consumable material which occupies the troughs of the inner race therefore forming a smooth sliding surface between inner and outer race via the deposition of third body particles. For this research the liner material is in the form of a woven composite, consisting of Polytetrafluoroethylene (PTFE) as the dry-lubricant and glass fibres as the reinforcing material, cured in a resin matrix. A cylinder-on-flat oscillating wear test bench developed within Cardiff University allowed for the gathering of physical data including temperature and Acoustic Emission (AE) signals during an accelerated wear test of the liner material. A radial load of 2.5 kN and oscillation frequency of 5Hz were applied to replicate typical operating conditions within a pitch control system. Frequency analysis techniques were carried out on the AE data, successfully identifying the transition from healthy contact into the failure region