The measurement of guided wave phase velocity is vital for the successful implementation of the guided wave technique for defect detection and material characterization. In this paper, an algorithm for quantitative phase velocity measurement based on f-k (frequency-wavenumber) transformation with a Gaussian fit peak-tracing is proposed. The versatility of the algorithm is demonstrated using numerically simulated data for a wide range of case studies, including non-dispersive, dispersive, dispersive with viscoelasticity, overlapping modes, and highly attenuative materials. It is further validated utilizing two experimental datasets. The maximum error in measuring phase velocity using experimental and numerical data is less than 0.8% when compared to the analytical value obtained using DISPERSE. The phase velocity values obtained with the proposed f-k transformation with a Gaussian fit peak-tracing algorithm are also compared with the conventional methods and found to be superior. Further, the proposed algorithm is suitable for evaluating the phase velocity of the coexistence of forward and reflected wave modes. Hence, the proposed algorithm is appropriate for measuring phase velocity where separation of modes or reflected signal is difficult to achieve, such as for a smaller specimen or even longer specimens with higher-order faster mode.

This article reports on the characterization of delamination damages in composite laminates using wave visualization method. A combination of plate-guided ultrasound and air-coupled ultrasonics is used to locate and visualize delaminations. The study focuses on the physics of Lamb wave propagation and interaction with delaminations at various through-thickness locations and positions. Three-dimensional finite element simulations are used to study, in detail, the changes in wave features such as mode velocity, wavelength and wave refraction in the delamination region. These wave features provide information on the location, position and orientation of the delamination. These studies are validated by experimental measurements. The influence of position of source and delamination on wave refraction in the delamination region is examined. This method also correlates the results obtained from experiments and finite element simulations to theoretical dispersion curves in order to distinctly determine the delamination location.

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