SH-wave based defect imaging method for CFRP plates with variable thickness

Classical guided wave imaging methods find applicability in uniform-thickness plates or quasi-isotropic plates. To be compared with, the method presented in this paper advances damage imaging accuracy for both uniform-thickness and variable-thickness anisotropic plates by incorporating new compensation terms grounded in the theoretical excitation directivity of the quasi-SH0 mode in anisotropic material. Specifically, the nondispersive nature of the wave speed and skew angle of the quasi-SH0 mode in the low- fd states (frequency-thickness-product lower than the cut-off value of SH1 mode) is established through dispersion curves and wave structure calculations. Additionally, employing the elastic dynamics reciprocity theorem reveals that the directivity of this mode is also nondispersive in the low- fd states. Therefore, the quasi-SH0 mode is theoretically insensitive to thickness variation. Experiment validated these theoretical calculations. On this basis, this paper proposed an integrated imaging method that utilises transmitted and reflected wave information by incorporating matching pursuit algorithm, cross-correlation analysis, probabilistic reconstruction and delay-and-sum method that incorporates new compensation terms based on the quasi-SH0 mode theory. Experimental validation of uniform-thickness carbon fibre-reinforced polymer (CFRP) plates and variable-thickness CFRP plates shows the insensitivity of this method to structural thickness variation, enabling effective imaging of damage in such anisotropic structures.