| Ultrasonic guided waves are those waves propagating along waveguides---plates, pipes, interfaces between two half spaces, or the surface of an infinite half space. This dissertation investigates guided waves in pipe by theory, experiment, and numerical analysis.; To fully understand guided wave phenomenon in pipe, generalized three-dimensional guided waves are investigated. The infinite number of guided wave modes propagating in a pipe axial direction can be decomposed into axisymmetric and non-axisymmetric modes according to the symmetry with respect to the pipe circumference. Non-axisymmetric modes have the most general particle displacement distribution in three-dimensions, i.e., radial, axial and circumferential directions in pipe. Non-axisymmetric guided waves can be further decomposed into flexural longitudinal and flexural torsional modes depending on their wave characteristics, including dispersion curves and wave structures. Excitation and propagation characteristics of flexural torsional modes are first modeled by the author with the normal mode expansion technique.; Based on the phased array technique and a deconvolution algorithm, guided wave focusing experiments have been carried out in pipe with both flexural longitudinal and flexural torsional modes. Focusing experiments successfully increase the signal to noise ratio and enhance the power penetration ability of a guided wave. Focusing, not only improves defect detection possibilities, but also leads to quantitative defect characterization. Inspection systems and their modifications are also discussed.; To enhance the understanding of guided wave propagation in pipe, semi-analytical finite element simulations are carried out based on the lab 2D computer codes modified by the author. Compared to the general finite element method, the semi-analytical finite element method (SAFEM) combines a theoretical solution in one or two dimensions with a finite element solution in other dimensions. It is computationally highly efficient. Three-dimensional guided wave propagations and guided wave interactions with various kinds of defects are simulated by SAFEM. All these simulations not only verify experimental results but also help the understanding of wave and defect interactions and hence inspection processes.; Future directions of guided wave studies in pipe, including propagation through elbows, viscoelastic layers, mixed mode conversions and volumetric defect quantitative characterization are also discussed. (Abstract shortened by UMI.)... |
