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An analysis of the scattering characteristics of the fundamental anti-symmetric (A0) Lamb wave at a delamination in a quasi-isotropic composite laminate is presented. Analytical solutions for this problem do not exist due to the anisotropic nature and multilayer characteristics of composite laminates. This study uses a three-dimensional finite element (FE) method and experimental measurements to provide physical insight into the scattering phenomena. Good agreement is found between simulations and experimental measurements. The results show that the A0 Lamb wave scattering at a delamination in composite laminates is much more complicated than the scattering at a defect in isotropic plates. Scatter amplitudes and scatter directivity distributions depend on the delamination size to wavelength ratio and the through-thickness location of the delamination damage. The study also investigates the feasibility of the common experimental practice of simulating delamination damage by bonding masses to the surface of composite laminates for guided wave damage detection and characterization methodologies verifications. The results suggest that care is required to use bonded masses to simulate delamination damage for verifying and optimizing damage characterization techniques. In summary, the results of the investigation help to further advance the use of the A0 Lamb wave for damage detection and characterization.

ABSTRACT.A model for guided wave scattering from non-symmetric blind holes in isotropic plates using Poisson and Mindlin plate wave theories for in-plane and flexural wave modes, respectively, is presented. It makes use of the wave function expansion technique and coupling conditions at the defect boundary in order to evaluate the scattered far fields of the three fundamental guided wave modes. The results were compared to other analytical models as well as experimental measurements for mode conversion from S0 to A0. Measurements agreed well with predictions confirming the validity of the model, highlighting at the same time the strong frequency dependence of the scattering and mode conversion behaviour.

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On the authors' and employers' webpages: There are no format restrictions; files prepared and/or formatted by ASA, AIP, or its vendors (e.g., the PDF, PostScript, or HTML article files published in the online journals and proceedings) may be used for this purpose. If a fee is charged for any use of the posted article, ASA permission must be obtained.  An appropriate copyright notice must be included along with the full citation for the published paper and a Web link to ASA's official online version of the abstract. Lamb wave at through holes in composite laminates. Three-dimensional (3D) finite element (FE) simulations and experimental measurements are used to study the physical phenomenon.Unidirectional, bidirectional and quasi-isotropic composite laminates are considered in the study. The influence of different hole diameter to wavelength aspect ratios and different stacking sequences on wave scattering characteristics are investigated. The results show that amplitudes and directivity distribution of the scattered Lamb wave depend on these parameters. In the case of quasi-isotropic composite laminates, the scattering directivity patterns are dominated by the fiber orientation of the outer layers and are quite different for composite laminates with the same number of laminae but different stacking sequence. The study provides improved physical insight into the scattering phenomena at through holes in composite laminates, which is essential to develop, validate and optimize guided wave damage detection and characterization techniques.

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