In situ evaluation of wear surface by ultrasound

Real time monitoring of a worn surface during the sliding frictional process is of great importance for assessing the severity of the contact. The feasibility of an ultrasonic technique using a pulse-echo method of normal incident compressional waves was evaluated for its sensitivity to worn surface condition and subsurface damage due to sliding friction while the sliding is in progress. Worn surfaces exhibiting different levels of severity (mild, transitional and severe wear) were generated by varying the contact oscillation frequencies under a given load and amplitude using a reciprocating friction tester and these surfaces were in situ monitored by the ultrasonic system. The ultrasonic technique was shown to be highly effective in assessing the level of severity of the worn surface in real time during the wear process. The analysis of the ultrasonic waves, reflected from the worn surface region, revealed a close relationship between the surface and subsurface damage and the maximum echo-amplitude of the compressional waves. Both as-received and fast Fourier transformed echo-amplitudes clearly exhibited their dependence in magnitude on the grade of the wear of the surface subjected to friction. The wear depth can also be easily measured by calculating the change of the specimen thickness based on the wave speed measured for the specimen medium. (C) 2001 Elsevier Science B.V. All rights reserved.