Development of ultrasonic nondestructive evaluation for large and complex structural members

本研究的目的是发展一种用于大型复杂结构的定量超声方法。主要研究内容包括：1.复杂结构构件波浪分析数值程序的开发；2.超声换能器和入射波场的特性评价；3.实验数据的应用。在第一个主题中，发展了将射线理论与边界元方法或有限差分法相结合的有效波分析方法。射线理论是一种在高频范围内的近似方法，如果散射体具有简单的几何形状，则需要很少的计算工作量。另一方面，边界单元法和有限差分法等数值方法也可用于分析任意复杂结构的波场。本文采用边界元和有限差分法的数值方法研究了…的复杂散射问题。缺陷引起的NG现象较多，而简单外边界上的反射和透射现象多用射线理论进行分析。在超声换能器和入射波的评价的第二个主题中，建立了从观测波形估计浸没换能器表面振动模式的反问题。该问题是一个典型的反问题，其求解的目标是最小化理论与测量之间的差异。采用Tikhonov正则化方法得到稳定解。在第三个主题中，将第一个主题中发展的数值方法应用于各种实验构型，包括台阶、缝隙、焊接缺陷、圆柱杆和厚板中的缺陷。将实验结果与数值计算结果进行了比较，两者吻合较好。在此基础上，利用SAAF和线性化逆方法对缺陷形状进行了可视化处理。结果表明，考虑了多条射线路径的影响，提高了缺陷形状成像的分辨率。较少

The aim of the present study is to develop a quantitative ultrasonic method for large complex structures. The following research topics have been investigated ; 1. Development of numerical codes for wave analysis of complex structure members, 2. Characteristic evaluation of ultrasonic transducers and incident wave fields, and 3. Application to experimental data. In the first topic, effective wave analysis methods, which combine a ray theory with a boundary element method or a finite difference method, have been developed. The ray theory is an approximation method in the high frequency range, which requires little computational effort if the scatterer has a simple geometric shape. On the other hand, numerical methods like boundary element method and finite difference method can be applied to analyze wave fields it arbitrary complex structures. In this study, the numerical methods of the boundary element method or the finite difference method were used to investigate the complex scatteri … More ng phenomena by flaws, whereas reflection and transmission on simple outer boundaries were analyzed by the ray theory. In the second topic of the evaluation of ultrasonic transducers and incident waves, the inverse problem was formulated to estimate the vibration modes on the surface of an immersion transducer from observed waveforms. The problem is a typical inverse problem, in which the solution is sought to minimize the difference between theory and measurement. The Tikhonov regularization method was adopted to obtain a stable solution. In the third topic, the numerical methods developed in the first topic were applied to various experimental configurations including step, slit, welding flaw, defects in cylindrical bar and thick plate. Comparison between experiment and numerical results showed a good agreement. The flaw shapes were, furthermore, visualized by means of SAAF and linearized inverse method. It was shown that the resolution of the imaging of flaw shapes has been improved by taking account of multiple ray paths. Less