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Stress Gradient Weighted by Surface Acoustic Wave Displacement: A Tool for Understanding Break-In Procedure in Friction Wear Test

The characteristics of the Rayleigh surface wave are investigated indirectly using the backward radiation of the incident ultrasonic wave in the scuffing specimens of AISI 1045 steel with various lubricated sliding surface conditions, and are then compared to the residual stress distribution measured by X-ray diffraction. Quantitative model analysis showed that the peak frequency of the spectrum of the backward radiated ultrasound mainly varies with the gradient of residual stress, which is sensitively related to the microfatigue density, and that the break-in procedure suppresses the variation of the gradient. The result in this study demonstrates the high potential of backward radiated ultrasound as a tool for nondestructive evaluation of subsurface gradients.