Special characteristics of Lamb wave velocity dispersion.

摘要

Two computational methods have been developed for generating sets of velocity dispersion curves for Lamb and Rayleigh waves. The sets of dispersion curves describe Lamb and Rayleigh wave phase velocities as functions of fd, where, f is the frequency of the incident waves and d is the plate thickness. Points comprising these dispersion curves represent vibrational modes of the plate and correspond to poles and zeroes of the ultrasonic reflection coefficient, R(k;The software developed was used to analyze reflection coefficients for various geometries. It was applied to the following previously considered cases: plane waves incident on a half-space, a symmetrically loaded plate, and an asymmetrically loaded plate. The reflection coefficient for an asymmetrically loaded plate was primarily used in this work because, under the appropriate conditions it is applicable for all three cases.;The computational results are consistent with those generated from past techniques and experimental measurements. The new approaches are effective in cases where previous method have failed and they require notably less computational time. In addition, the effectiveness of the present techniques when applied to certain regions of the velocity dispersion curves has led to new insights on mode-mixing, modes with negative group velocity, and the significance of complex angles of incidence.