Group velocity of Lamb waves in anisotropic plates: Comparison between theory and experiments

The motivation of this work is to study the group velocity of Lamb waves in anisotropic plates in order to understand the characteristics of the propagation of wave packets in arbitrary directions. The group velocity equations have been derived, taking into account the spatial dispersion (variation of the velocity with the direction of propagation) as well as the frequency dispersion. For bulk waves, it is already well known that anisotropy implies a difference between group velocity and phase velocity. It is shown here that this phenomenon occurs for Lamb waves as well, affecting both the velocity and the direction of propagation. An experimental demonstration is also given, using a plate composed of a unidirectional Glass Epoxy composite. The obtained experimental curves are in good agreement with the theoretical calculations.