Defect Detection Using the Lamb Mode S0 by Pulsed Laser Laterally Illuminating on a Side of the Plate

In recent years, Lamb waves have been widely used to inspect plate-like structures, where antisymmetric modes are usually applied due to their high out-of-plane displacement and long propagating distance under normal circumstances. However, their dispersive behavior and leakage character in liquid-loaded plates make them unable to distinguish defects in some cases. In this paper, the pure S-0 mode with a high amplitude and small dispersion is generated, which is implemented by a pulsed laser laterally illuminating on a side of the plate symmetrically. Experiments are carried out in a 0.2 mm aluminum plate. The experimental result shows strong agreement with simulation, which indicates that this method can restrain the A(0) mode and improve the S-0 mode efficiently. Moreover, experimental measurements for defect detection in the plates fully immersed in water are carried out preliminarily. These results indicate that this optical method for generating the pure S-0 mode could be useful for defect detection in air and underwater conditions.