Phase shift of the reflection coefficient of ultrasonic waves in the study of the contact interface

Abstract

Previous ultrasonic investigations of the loaded contact between rough surfaces produced the hypothesis that it is possible to estimate the contact stiffness and real contact area on the basis of measurements of the complex coefficient of reflection or transmission of longitudinal ultrasonic waves at the contact interface and a proposed acoustic model of contact. It has been shown previously that the contact stiffness and the real contact area resulting from measurements of the modulus of the coefficient of transmission are in a fairly good agreement with the contact stiffness and the real contact area predicted by the Bush-Gibson-Thomas model of contact of rough surfaces. In the present paper, further ultrasonic investigations of contact between rough surfaces are reported, based on measurement of the phase shift of the coefficient of reflection. The measurements were carried out for longitudinal ultrasonic waves of frequency 10 MHz reflected from the contact interface between ground steel samples and quartz samples, pressed together using hydrostatic pressure up to a contact pressure of 700 MPa. The results are compared with the outcomes of the theoretical model. The acoustic parameters involved in the theoretical model, i.e. the stiffness, assumed to be identical with the contact stiffness, and the coefficient of viscous friction, being a function of the real contact area, were evaluated on the basis of the Bush-Gibson-Thomas theoretical model of contact of rough surfaces.