Development of ultrasonic nondestructive evaluation for large and complex structural members

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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