THE USE OF ULTRASOUND TO INVESTIGATE ROUGH SURFACE CONTACT PHENOMENA

摘要

Reflection coefficient measurements have been made for three systems; aluminum-aluminum, rubber-perspex and graphite-graphite. In each case the measured frequency dependence of reflection coefficient was in good agreement with that predicted by the spring model and so it can be concluded that these experiments were performed in the low frequency regime. These reflection coefficient measurements were then converted to stiffness via the spring model. A numerical contact model was used to predict the interfacial stiffness. For all the systems considered differences were found between the experimental and the predicted interfacial stiffnesses. The cause of these differences is thought to be different in each case. In the aluminum system the difference was due to the effect of plasticity. In the rubber-perspex system problems arose due to the difficulty associated with obtaining an accurate dynamic modulus measurement. In the graphite system the difference was caused by the granular nature of the AGR graphite. These three system illustrate some of the problems associated with predicting interfacial stiffness using simple contact models. The way forward is to improve the contact models to account for some of these effects and, in the meantime, only use these models on isotropic, linear elastic systems or for rough estimates of stiffness.