Michael J. Anderson
Dept. of Mech. Eng., Univ. of Idaho, Moscow, ID 83843-1030
Christopher M. Fortunko
NIST, Boulder, CO 80303
Edwin M. Odom
Univ. of Idaho, Moscow, ID
A nonintrusive technique has been developed for measurement of the elastic moduli of reinforced polymer composite plates. Two ultrasonic transducers placed in a transmission configuration use air as the coupling medium to excite A0 Lamb waves in the plate sample. The phase speed of the plate waves at a given frequency is inferred from the angle of incidence for maximum transmission. Use of a low-impedance couplant gives several advantages beyond the nonintrusive nature of the technique. First, the influence of the gas medium is entirely decoupled from the determination of stiffness moduli. Second, a low-impedance couplant gives a high-quality factor, which enhances the potential precision of the technique. Gas coupled measurements of stiffness moduli on unidirectionally reinforced graphite/epoxy and glass/epoxy plates of thickness in the range (approximately equal to)1--6 mm are presented. Plate waves were excited over the frequency range 100--200 kHz. Stiffness moduli E[sub 11], E[sub 22], G[sub 12], and Poisson's ratio (nu)[sub 23] (fibers in the ``l'' direction) were obtained from the phase-speed/frequency data using least squares. Properties determined with the gas coupled technique are compared with static measurements, and with model predictions based upon the properties of the constituents and fiber-volume ratio.