B. Hosten M. Deschamps A. Gerard
Lab. de Mecan. Phys., Univ. Bordeaux I, F-33405 Talence, France
University Bordeaux I and Catholic Univ. of America, Washington, DC 20064
The Lamb waves propagating in an elastic plate in vacuo generate compressional (L) and shear type (T) plate vibrations that are coupled due to the boundary conditions. Without such coupling, their phase-velocity dispersion curves would form two intersecting families, which at high frequency tend towards the elastic-wave speeds C[sub L] and C[sub T], respectively. It is shown that the coupling causes a repulsion of the dispersion curves, similar to that encountered in atomic physics for the energy levels of atoms combining into molecules, which prevents their intersection and at the same time exchanges the nature (L<->T) of the underlying vibrations. However, in the repulsion regions a succession of dispersion curves combines to asymptotically approach the uncoupled L or T dispersion curves, respectively. For the case of a plate bounded by fluid on one side, and vacuum on the other, the dispersion curves of the fluid-borne (Stoneley--Scholte type) wave, which is known from the studies of Grabovska and Talmant to be present in this case, and of the usual A[sub 0] Lamb wave exhibit a similar repulsion phenomenon.