Pressure-Dependent Stiffnesses and Nonlinear Ultrasonic Response of Contacting Surfaces

Abstract

An experimental study of the pressure dependence of the interfacial stiffnesses of contacting solid-solid surfaces and their nonlinear ultrasonic responses is presented. To this purpose, the contact-pressure dependence of the reflection coefficients of longitudinal and transverse waves were measured at normal incidence to three types of contacting interfaces of aluminum blocks with different surface conditions, namely, polished surfaces, roughened surfaces and fractured surfaces. The results show remarkable influence of the surface condition on the pressure-dependent variation of the normal and tangential stiffnesses as well as their ratio. Based on the obtained stiffness-pressure relations, the second harmonic generation behavior for normal-incidence longitudinal wave is examined theoretically according to the foregoing theoretical results by a nonlinear interface model, and it is shown that smoother surfaces exhibit harmonic generation more significantly than rougher ones. Relevant experimental results are demonstrated for polished surfaces and discussed in comparison to the theoretical predictions.