Quantitative Nonlinear Ultrasonic Spectroscopy for Imperfect Interfaces and Imperfect Bonding by Guided Waves

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High-amplitude Lamb waves were excited on plates with contact or adhesive interfaces, and the propagated waveforms were analyzed by the time-frequency analysis to extract the nonlinear spectral components such as higher harmonics. As a result, the harmonic components were found to change their amplitude depending on the contact or adhesive conditions. Therefore, nonlinear Lamb wave characteristics are promising as a tool for evaluating the contact or adhesive conditions of plates. From a theoretical point of view, the flexural wave propagation was examined based on the Mindlin plate theory with nonlinear interface model. Furthermore, the conditions for cumulative growth of Lamb wave harmonics were derived based on the dispersion relation of Lamb waves.