Wayne P. Rogers
Dept. of Mech. Eng., Univ. of Colorado, Boulder, CO 80309-0427
This paper presents a novel method to experimentally determine the elastic constants of a transversely isotropic plate using measurements of phase velocity of Rayleigh--Lamb waves. The forward problem, i.e., to calculate the phase velocity versus frequency curves given known elastic constants, has been solved by numerical solution to the appropriate dispersion equations. The problem attacked here is the inverse problem, i.e., to determine the elastic constants given experimental measurements of phase velocity as a function of frequency. These elastic constants may be found by simultaneous solution of five distinct dispersion equations corresponding to particular measurements of phase velocity and frequency. This approach yields accurate solutions provided that appropriate Lamb waves modes, frequencies, and plate directions are chosen. The experimental method employs a pair of variable-angle-beam-contact transducers used in a pitch--catch mode with a harmonic wave phase comparison technique to measure phase velocity over the frequency range of 30 kHz--1 MHz. Results are presented for several isotropic plates and for a unidirectional-continuous-glass-fiber-reinforced epoxy plate. The elastic constants calculated using this inverse procedure are then used in the forward problem in order to compare experimental results to theoretical predictions of the dispersion curves for the first few modes. [Work supported by NASA---Langley.]