The group velocity variation of Lamb wave in unidirectional laminated composite plate

The elastic waves in the plate are dispersive waves due to the characteristics of Lamb waves. However, S0 symmetric mode is less dispersive in the frequency region below the first cut-off frequency. The phase velocity dispersion curve from anti-symmetric and symmetric Lamb wave dispersion equation is calculated for unidirectional laminated composite plate. Slowness surface is sketched using phase velocity below the first cut-off frequency. The magnitude of group velocity and angle from this slowness surface are calculated and corrected in phase velocity curve. Corrected group velocities obtained from the phase velocity along the wave vector direction are compared with the measured group velocities by the varying propagation direction in composite plate. The measured group velocities are in good agreement with the corrected group velocity curve except near the fiber direction zone which is called the cusp region.