Nonlinear Ultrasonic Spectroscopy for Closed Defects and Microscopic Damage by Amplitude-Modulated Waves

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Nonlinear ultrasonic characteristics of contacting interfaces and micro-damage for amplitude-modulated waves have been investigated. First, for the burst wave containing two frequency components, the transmitted wave through a contacting interface between metal blocks has been shown to contain the difference frequency component. Second, for amplitude-modulated waves propagating in a unidirectional carbon/carbon composite, the transmitted wave has been shown to change significantly accompanying low-frequency component generation. This phenomenon has been discussed based on the perturbation analysis of ultrasonic wave propagation in a nonlinear elastic medium. It is expected that these nonlinear low-frequency components can characterize defects and damage when the higher-harmonic measurements are difficult to perform.