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

本研究旨在定量评价接触/弱键界面的非线性超声特性，并通过微观力学和弹性动力学分析对其进行合理的理论解释，从而有助于建立接触/弱键界面的非线性超声表征或监测方法。首先，基于非线性界面模型，对非线性超声效应产生谐波的摄动分析进行了更严格的重新表述，明确了非线性压隙关系与二次谐波幅值之间的关系；其次，在激光多普勒测振仪测量振动速度的基础上，建立了一种将压电换能器输出电压转换为位移幅值的方法，并对换能器灵敏度的频率依赖性进行了校正。对接触界面谐波产生特性进行了更深入的心理评价，并将实验数据与理论预测进行了定量比较。第三，从局部刚度的空间非均匀性和界面处的粘性损失出发，讨论了由体波和界面波测量得到的界面刚度的频率依赖性。最后，通过测量不同接触压力下板内Lamb波速度波形的高次谐波，对部分接触条件下非线性Lamb波沿板传播特性进行了初步研究。结果发现，在这个实验中，第三次谐波的产生是一个显著的特征。这些发现对于建立基于体波和瑞利波、兰姆波等导波非线性超声特性的非完美界面表征新方法具有重要意义。少

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