Quantitative Evaluation and Micromechanical/Elastodynamic Analysis of Nonlinear Ultrasonic Properties of Contacting and Weak Interfaces

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This research has been carried out to make a quantitative evaluation of nonlinear ultrasonic characteristics of contacting/weak-bonding interfaces as well as to give a sound theoretical explanation to them by micromechanical and elastodynamic analyses, thereby to contribute to the establishment of nonlinear ultrasonic characterization or monitoring method for these interfaces. First, the perturbation analysis of harmonic generation due to nonlinear ultrasonic effect has been reformulated in a more rigorous way based on a nonlinear interface model, and the relation between the nonlinear pressure-gap relation and the second harmonic amplitude has been clarified. Second, based on the vibration velocity measurement using a laser-Doppler vibrometer, a method has been established which converts the voltage output of a piezoelectric transducer to the displacement amplitude, as well as corrects for the frequency dependence of the transducer's sensitivity. This has enabled a quantitative experi … More mental evaluation of harmonic generation characteristics at contacting interface, and a quantitative comparison between the experimental data and the theoretical prediction. Third, the frequency dependence of the interfacial stiffnesses obtained from the bulk and interface wave measurements has been discussed in the light of spatial inhomogeneity of local stiffness as well as the viscous loss at the interface. Finally, a preliminary study has been carried out for nonlinear Lamb wave propagation characteristics along a plate under partial contact conditions, by measuring the higher harmonics in the velocity waveforms of the Lamb wave in a plate under different contact pressures. As a result, the generation of the third harmonics has been found to be a remarkable feature in this experiment. These findings are considered to be meaningful in the view of establishing a new characterization method for imperfect interfaces based on nonlinear ultrasonic characteristics of not only bulk waves but also guided waves such as Rayleigh or Lamb waves. Less