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Guided wave propagation in fluid-coupled plates of fiber-reinforced composites has been investigated by studying ultrasonic reflection in these structures. From measurements of ultrasonic reflection on unidirectional graphite-epoxy plates over a range of incident angles, experimental dispersion curves using a total-transmission criterion for leaky plate waves have been constructed. Theoretical calculations with no adjustable parameters demonstrate excellent agreement with the experimental data. Unusual behavior observed in the fundamental total-transmission curve led to a reexamination of the mode identification criteria. Both the total-transmission curves and the normal modes of the fluid-coupled plate differ significantly from the result expected on the basis of the widely used Cremer coincidence condition to identify propagating plate waves. It is found that these differences are particularly pronounced in cases where the ratio of fluid to solid densities is high, as for composite materials. The existence of such behavior is also demonstrated numerically in a fluid-coupled aluminum plate by arbitrarily increasing the density of the fluid.
Nayfeh et al. (Sun,) studied this question.