Evaluation of Cylinrical Hertzian Contact using Guided Waves

This paper presents an ultrasonic method to evaluate the contact state of two solid boundaries using guided wave propagating between the joining surfaces. The main idea is that the guided wave travels with different wave velocity depending on the contact pressure of interface. Mathematical formulation for acoustic wave propagation at contacting solids was made to obtain the dispersive relation between acoustic wave and contact pressure. Three different kinds of steel block with cylindrical tip were machined and pressed together at various compression loads to form contact surfaces of different contacting condition. Guided wave reflected at the edge of the steel block was measured to determine wave speed using the time-of-flight, which increases sensitively with the load. Experimental results proved that contact states such as contact force and interfacial stiffness between two solid surfaces can be monitored by the acoustic wave speed of guided wave in the interface.