Ultrasonic nondestructive inspection demands more precise knowledge of sound propagation in materials. An approximate Gauss-Hermite (GM) model was developed a few years ago for the ultrasonic fields radiated into isotropic and anisotropic materials. In this dissertation, the validity of the GM model in a multilayered medium is evaluated. First, a method of finding the elastic constants of anisotropics is given. Comparisons between GM predictions and finite element predictions show good agreement around the central ray direction, but due to Fresnel approximation, the accuracy of GM model degrades away from the forward propagation direction. The GM model was used for sizing delaminations in a multilayered composite structure. This method, utilizing the reflected signal from the delamination, showed considerable improvement over the traditional sizing method. The model, with local ray tracing, was also used to predict the ultrasonic field beyond an irregularly shaped interface (step discontinuity), with good agreement with experiment.
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