Stiffness evaluation of contacting surfaces by bulk and interface waves.

This paper describes ultrasonic measurements of normal and tangential stiffnesses of the contacting interface between polished aluminum blocks subjected to nominal contact pressures up to about 3.8 MPa. These stiffnesses were evaluated by ultrasonic spectroscopy methods for the bulk (longitudinal and transverse) wave reflection coefficients and the anti-symmetric mode interface wave velocity. The measurements revealed the interfacial stiffnesses as functions of the frequency as well as the applied contact pressure. The ratio of the tangential and normal stiffnesses is discussed in the light of foregoing theoretical and experimental findings. Furthermore, possible explanations for the frequency dependence of the measured stiffnesses are reviewed, invoking the spatial inhomogeneity of the interfacial stiffness as well as its lossy nature.