Dispersion and its implications on flaw detection using guided waves

Guided waves, including Lamb waves, are getting more and more attention as they provide a new approach to scan and evaluate the material integrity, especially for products of large size. The major differences between guided waves and primary bulk waves are the nature of particle vibrations, boundary requirements for propagation, dispersive nature, different wave structures for different modes etc. Accordingly, the capability to sense the flaws also varies with different modes. Knowing the structure of the propagating media, it is essential to identify an appropriate mode of guided wave to suit the required flaw detection. One of the characteristic properties of guided waves is their dispersive nature. The graphical representation of these waves on the phase and frequency planes constitutes dispersion curves. For selecting an appropriate mode of guided wave to implement a flaw detection technique, knowledge of the dispersion characteristics is essential. In this paper the experimental work, data gathered and inferences derived on the dispersive characteristic of Lamb waves/guided waves and its impact on flaw detection is reported. Also the impact of dispersion characteristics on pulse energy, frequency spectrum of a pulse and pulse duration are experimentally analysed and reported.