Ultrasound enabled simultaneous measurement of coating wear depth and lubricant film thickness in a sliding bearing

•It is found that the amplitude of the incident signal remains unchanged while the phase changes with the wear depth.•A method for simultaneous measurement of both oil film thickness and coating wear is proposed.•A three-stage procedure is established for monitoring oil film thickness and coating wear simultaneously. Sliding bearings, serving as critical supporting components in rotating machinery, often work by riding on an ultra-thin oil film. The rupture of this oil film can cause wear of the soft coating on the bearing and even lead to catastrophic failures. This paper introduces a novel ultrasonic reflection-based approach to simultaneously measure both lubricant film thickness and coating wear depth. Through an analysis of the ultrasonic wave propagation in a worn bearing, it is observed that the echo waveform remains independent of wear depth but correlates with changes in the time of flight back to the transducer. Given this, the captured time or phase shift between the reflected and incident waves, together with the reduction in the wave amplitude, enables a simultaneous calculation of both oil film thickness and coating wear depth. The efficacy of the proposed method is validated through acoustic simulations and experiments with varied coating roughness.