Delamination is one of the most dangerous failure modes in composite materials and must be detected promptly to ensure safety and reliaility. Laser ultrasonic technology (LUT) is a novel non-destructive testing (NDT) method that uses high-energy laser beams to generate ultrasonic waves through a non-contact manner for detection, which has advantages of non-contact detection, high resolution, high sensitivity to small defects, and the ability to simultaneously excite broadband ultrasonic waves of different modes. This research focus on the delamination detection in composite materials using laser-generated Lamb waves. Wavenumber domain analysis has been proven effective for damage detecion, which primarily involves constructing mode isolation filters to isolate wavenumber components sensitive to damage, followed by constructing window function filter bank to calculate local wavenumbers in the spatial domain for accurate damage imaging. Considering the multi-layered anisotropic characteristics of composite material, this research first investigates the combined effects of layer thickness, layup configuration, and fiber orientation on the wavefield's propagation directionality. Mode isolation filters are designed to match the wavefield's directivity pattern for accurate extraction of target wavenumber components. Furthermore, considering both the frequency-dependent sensitivity of Lamb waves to delamination and low signal-to-noise ratio conditions, the broadband scale-adaptive 2D wavelet filter bank is developed to quantitatively determine the optimal wavenumber filter width for each frequency component in the wavenumber-filtered wavefield, enabling high-precision imaging of delamination defects. Several experiments demonstrate that the proposed method can accurately locate the delamination depths in different CFRP specimens, achieving higher accuracy in visualizing delamination defects compared to conventional frequency-wavenumber filtering methods and local wavenumber estimation.

Laser ultrasonic,Lamb waves,Delamination,Composite material,Local wavenumber