The low-frequency scattering of the A0 Lamb wave from delaminations in quasi-isotropic composite laminates: theoretical and finite element studies

This paper presents a scattering analysis of the fundamental anti-symmetric (A0) Lamb wave at delaminations in quasi-isotropic (QI) composite laminates. The scattering characteristics are investigated using theoretical solutions and experimental verified three-dimensional (3D) finite element (FE) simulations. Analytical models based on the Mindlin plate theory and Born approximation are used to predict the A0 Lamb wave scattering at delaminations and the results are then compared with FE predictions. The delaminations are modelled as an inhomogeneity in an equivalent isotropic model of the QI composite laminates and as a volume split in the layered composite laminates for theoretical solutions and FE simulations, respectively. The results show that there is a good correlation between the theoretical solutions and FE results in the forward scattering amplitudes but there exists a larger discrepancy in the backward scattering amplitudes. In addition the FE predictions show that the fibre direction of the outer laminae has a pronounced influence on the forward and backward scattering amplitudes, which is not predicted by the theoretical solutions. This paper studies the feasibility of the common theoretical approach of modelling the delaminations as inhomogeneities which indicates the possibility of extending the Lamb wave diffraction tomography from isotropic plates to QI composite laminates.C. T. Ng, M. Veidt, L. R. F. Rose and C. H. Wan