Development of grobal ultrasonic nondestructive testing methods using surface waves and Lamb waves

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The main results obtained in this project are summarized as follows :1. Development of computational software for wave analysis and numerical simulations : Boundary element programs are developed for propagation and scattering of elastic waves in a plate and a waveguide. Far field expressions of Green's functions are used to improve the accuracy of the near field solutions around defects and to botain the scattered properties for various incident wave modes and defect configurations.2. Inverse scattering analysis an d visualization of defects : Linearized inversion analyzes based on the Born approximation and Kirchhoff approximation are developed for the reconstruction of defect shapes from detected ultrasonic data. In the numerical simulation, the inverse analyzes are applied to 2-D and 3-D defects in a solid and are investigated for the applicability for scattered data with the limited aperture problem. The inverse methods are also applied to experimental data obtained from immersed ultrasonic testings. The shapes of defects are reconstructed with good resolutions except for the case that adjacent defects are too closely located each other.3. Nondestructive measurement for a surface breaking crack in concrete : An inverse method to evaluate the depth and angle of a surface breaking crack is proposed using the characteristics of diffracted waves at the crack edge. The applicability of our method is verified in the numerical simulation using BEM and on-the-site experiments.