In order to estimate the frictional contact conditions between a tool and a workpiece, we have proposed the newly developed method wherein the relative intensity of a reflected ultrasonic wave at the interface provides the measure of the contact ratio. As a fundamental experiment, we carried out the test of upsetting an aluminum cylinder. Turned surfaces of different roughness were tested under dry conditions, and partly tested under the condition of lubrication with mineral oil. In the experiment, the measured relative intensity was plotted against the contact ratio estimated from the surface profiles. It has been clarified that this method can accurately detect the transition of the contact ratio during the process of deformation, the distribution of the contact ratio over the interface, and the trapping behavior of lubricants affected by the viscosity. It has also been found that the method may be very useful for estimating the contact thermal resistance.
