Evanescent Lamb Wave in Laminated Composites Elastic Plates

Evanescent waves are widely used in non-destructive evaluation to determine the shape and size of defects,as a result, it have become the focus of research. It is crucial to study the modal and dispersion relations of evanescent waves described by complex roots. However, it is relatively difficult to solve the roots of evanescent modes, especially for structures such as anisotropy and composites. In this paper, using the Legendre orthogonal polynomial method (LOPM), the guided wave characteristics of multilayer anisotropic elastic plates are studied by transforming the solution process into solving the eigenvalue problem of a matrix. Detailed formulas and Lamb wave dispersion diagrams are presented. The validity of LOPM is verified by comparing with the published data. Furthermore, the dispersion curves of the three-dimensional complex solutions are further drawn, and the relationship between the modes of complex and pure imaginary solutions is deeply discussed. Meanwhile, the influence of different thickness ratios on the dispersion characteristics of evanescent guided waves is also studied. Some instructive conclusions are obtained, which can guide the non-destructive testing of composite structures using evanescent waves.