Numerical analysis on acoustic nonlinear phenomena between rough contact interfaces

Contact acoustic nonlinearity (CAN) between rough interfaces in solids are mainly caused by nonlinear stress-strain relationship between contact interfaces. According to classical Hertz theory, unidirectional normal contact stress between two rough interfaces was built as functions of interface parameters on roughness. Nonlinear spring stiffness was further deduced from such functions. Then two rectangular computational fields, contacted via a rough interface were selected to simulate wave propagation across the rough interfaces when imposed by static pressures and excited by a narrow ultrasonic pulse series source. The second harmonics in the diffracted wave is a main focus of the computation. Numerical results show that the intensity of CAN is obviously affected by ultrasonic amplitude, static pressure and roughness of the interface. The computation results gave a clear image on wave propagation across rough interfaces, which is probably very useful for applying CAN as a nondestructive testing method.