Experimental Generation and Analysis of Lamb Waves in Aluminium and Glass/Epoxy Composite Plates

As an efficient mean of non-destructive evaluation of sheet type structures, Lamb waves or guided waves outperform other techniques. It is the most commonly used waves for plates and pipes. In view of this, laser-based ultrasonics is a fast-growing technique. However, the complexity arises due to simultaneous generation of modes. Hence, the utility of laser-generated signals restricted. The objective of this research is to devise a technique to selectively generate low frequency components of Lamb waves in thin plates of aluminium and glass/epoxy composite plates. A specially tailored arrangement of an arrayed-line slit is inserted in the path of laser beam. The recorded signals for plates of different thickness are analysed using Fourier and wavelet analysis. Finally, time of arrival of different frequency components is obtained from the analysis and corresponding group velocities are extracted. Experimental results closely corroborate the theoretical framework of guided waves in structures.