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 S0 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.

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This paper investigates Rayleigh wave interaction with simulated, surface breaking cracks using a finite element method, in which the scattered wave modes giving rise to the in-plane and out-of-plane displacements are presented. By looking at the contribution from all of the transmitted, reflected, and mode-converted signals at the crack, the magnitude of signal enhancement in the near field and the mechanism by which this occurs can be fully explained. Furthermore, oscillations in the Rayleigh wave reflection and transmission coefficients with crack depth in the far field can be explained by means of multiple reflected and transmitted wave modes at the crack, whose relative amplitudes are dependent on the crack depth. Results agree with previously published experimental measurements.

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