A geometrical diffraction theory has been worked out to analyze the fields generated by diffraction of high-frequency waves by cracks. The theory accounts for curvature of incident wavefronts, curvature of crack edges, and finite dimensions of the crack by providing first-order corrections to the results for a semi-infinite crack. The diffracted fields include direct diffractions from the crack edges as well as well as diffractions of signals which travel via the crack faces. On the faces of the crack the main contributions to the diffracted fields come from rays of surface waves. The directions of these surface-wave rays, and the amplitudes, wavelengths, and phases of the associated surface-wave motions have been related to the • corresponding quantities of the incident body-wave rays. Reflection and diffraction of surface-wave rays by the edge of a crack have also been analyzed. As an example, diffraction by a penny-shaped crack of a plane longitudinal wave under normal incidence has been considered in some detail. Explicit expressions are given for the diffracted fields. In these expressions a correction was introduced to extend the validity of the results to the normal axis through the center of the crack, which is a caustic axis. A simple expression for the scattering cross section is presented.
ASJC Scopus subject areas
- Arts and Humanities (miscellaneous)
- Acoustics and Ultrasonics