Defects Detection and Localization in Underwater Plates Using Laser Laterally Generated Pure Non-Dispersive S 0 Mode

When working in humid environments, corrosion defects are easily produced in metallic plates. For defect detection in underwater plates, symmetric modes of Lamb waves are widely used because of their characteristics including long propagating distance and high sensitivity to defects. In this study, we extend our previous work by applying the laser laterally generated S₀ mode to detection and localization of defects represented by artificial notches in an aluminum plate immersed in water. Pure non-dispersive S₀ mode is generated in an underwater plate by lateral laser source irradiation and its <i>fd</i> (frequency&#183;thickness) range is selected by theoretical calculation. Using this lateral excitation, the S₀ mode is enhanced; meanwhile, the A₀ mode is effectively suppressed. The mode-converted A₀ mode from the incident S₀ mode is used to detect and localize the defect. The results reveal a significantly improved capability to detect defects in an underwater plate using the laser laterally generated S₀ mode, while that using A₀ is limited due to its high attenuation. Furthermore, owing to the long propagating distance and the non-dispersion characteristics of the S₀ generated by the lateral laser source, multiple defects can also be detected and localized according to the mode conversion at the defects.

Abstract licence: CC BY

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