Wave front analysis in the scattering of a plane compressional pulse by a cylindrical elastic inclusion

• Main Author: Griffin, Jerry Howard
• Format: Others
• Published: 1974
• Online Access: https://thesis.library.caltech.edu/4063/1/Griffin_jh_1974.pdf; Griffin, Jerry Howard (1974) Wave front analysis in the scattering of a plane compressional pulse by a cylindrical elastic inclusion. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/AKFT-PB89. https://resolver.caltech.edu/CaltechETD:etd-10132005-083854 <https://resolver.caltech.edu/CaltechETD:etd-10132005-083854>

The plane-strain problem of a stress pulse striking an elastic circular cylindrical inclusion embedded in an infinite elastic medium is treated. The method used determines dominant stress singularities that arise at wave fronts from the focusing of waves refracted into the interior. It is found that a necessary and sufficient condition for the existence of a propagating stress singularity is that the incident pulse has a step discontinuity at its front. The asymptotic wave front behavior of the first few P and SV waves to focus are determined explicitly and it is shown that the contribution from other waves are less important. In the exterior, it is found that in most composite materials the reflected waves have a singularity at their wave front which depends on the angle of reflection. Also the wave front behavior of the first few singular transmitted waves is given explicitly. The analysis is based on the use of a Watson-type lemma, developed here, and Friedlander's method (see his book Sound Pulses, Cambridge, 1958). The lemma relates the asymptotic behavior of the solution at the wave front to the asymptotic behavior of its Fourier transform on time for large values of the transform parameter. Friedlander's method is used to represent the solution in terms of angularly propagating wave forms. This method employs integral transforms on both time and [theta], the circumferential coordinate. The [theta] inversion integral is asymptotically evaluated for large values of the time transform parameter by use of appropriate asymptotics for Bessel and Hankel functions and the method of stationary phase. The Watson-type lemma is then used to determine the behavior of the solution at singular wave fronts. The Watson-type lemma is generally applicable to problems which involve singular loadings or focusing in which wave front behavior is important. It yields the behavior of singular wave fronts whether or not the singular wave is the first to arrive. This application extends Friedlander's method to an interior region and physically interprets the resulting representation in terms of ray theory.