Ultrasonic Lamb waves offer an attractive method of damage detection in composite aerospace structures. However, in order to utilise these waves fully a basic understanding of their propagation in composites is required. The propagation of Lamb waves in composites is complicated by the anisotropic lay-up which can lead to the speed of the Lamb mode being dependent on the laminate lay-up and the direction of wave propagation. This study concentrated on the fundamental symmetric mode, S_0, and the fundamental anti-symmetric mode, A_0.A one-dimensional finite-element model has been developed to solve for Lamb wave solutions in anisotropic layered structures. The calculated dispersion curves for various composite lay-ups are presented together with plots of the through-thickness particle and stress component amplitudes. For the S_0 mode, the changes in the stress distributions and particle displacements as the frequency increases are described. Experimental measurements of the S_0 group velocity for various laminate lay-ups are compared to the predicted values from the model. The work concludes with a discussion of the implications of these results when Lamb waves are utilised for impact damage detection.
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