Nonlinear ultrasonic characterization of Lamb wave in a plate with contacting interfaces

Linear and nonlinear propagation characteristics of the lowest-order anti-symmetric-mode (A₀-mode) Lamb wave are investigated experimentally for a thin aluminum plate compressed between two aluminum blocks under different pressures. The wave-packet propagation behavior as well as the harmonic generation behavior are examined based on the short-time Fourier transform of the observed waveforms. The results show that the applied pressure influences the dispersive nature of Lamb wave, and brings about the occurrence of higher harmonics, especially odd-order harmonics, in a certain intermediate range of contact pressure. Such features can be utilized for nondestructive diagnosis of the interface contact conditions.