Frequency-dependent scattering of wideband laser-generated Rayleigh waves for vertical surface crack characterization

Wideband laser-generated Rayleigh waves have been extensively exploited for surface crack characterization, most of which, nonetheless, are of a nature of either numerical simulation or experimental observation. Earlier, an elastodynamic reciprocity theorem-based theoretical model was proposed by the authors Xu L et al 2022 Ultrasonics 118 106578, Xu L et al 2021 J. Sound Vib. 509 116226, aimed at scrutinizing the interaction of narrowband Rayleigh-Lamb waves with a surface or subsurface crack. In this study, the model is extended to a wideband scenario to analytically explore the interaction of a wideband laser-generated Rayleigh wave with a surface crack, as well as the resultant crack-scattered Rayleigh wavefield. First, under the narrowband scenario, a dimensionless parameter is formulated based on the closed-form solution to the magnitude of the narrowband scattered Rayleigh wavefield, revealing that the scattering effect of a surface crack on the Rayleigh wave is frequency-dependent and there exists a characteristic frequency, at which the crack-scattered Rayleigh wavefield manifests the strongest intensity. Similarly, under the wideband scenario, such dependence can be calibrated by a spectral damage indicator (SDI), which facilitates the evaluation of the severity of the surface crack using the wideband laser-generated Rayleigh wave. Proof-of-concept simulation is performed to verify the model. Quantitative agreement between the analytical and numerical results validates the accuracy of the proposed model and SDI. Experiment is also conducted to demonstrate the effectiveness of the frequency-dependent scattering of wideband laser-generated Rayleigh waves for vertical surface crack characterization.