New multitransducer techniques for crack characterization

This chapter describes the use of Travel Time Mode-Conversion (TTMC) techniques to relate crack characterization to relative time-of-flight information of the reflected, diffracted and mode-converted elastic waves. The wave propagation system is analyzed for a two dimensional problem in isotropic media, and the fundamental expressions which represent the TTMC technique are derived. The method is independent of both the distance between the transducers and the angle of incidence. Numerical modeling techniques based on finite difference schemes are presented. Structural integrity can be analyzed using the described scanning method. The TTMC technique can be extended to three dimensional surface-breaking cracks and sub-surface cracks or voids by rotating the system through 360 degrees to obtain a more complete description of the flaw