The interaction of Lamb waves with delaminations in composite laminates

The S₀ Lamb mode can propagate over distances of the order of 1 m in composite laminates and so has the potential to be used in long-range nondestructive inspection. This paper discusses the interaction of the S_Q Lamb mode with delaminations. The dispersion curves and the corresponding stress and displacement mode shapes of the lower order Lamb modes are obtained analytically and the interaction of the S₀ mode with delaminations at different interfaces in a composite laminate is then studied both by finite element analysis and by experiment. It is shown that the amplitude of the reflection of the S₀ mode from a delamination is strongly dependent on the position of the delamination through the thickness of the laminate and that the delamination locations corresponding to the maximum and minimum reflectivity correspond to the locations of maximum and minimum shear stress across the interface in the S₀ mode.