Lamb wave generation in composite plates with a thin linear array of piezoelectric elements

Abstract

Since Lamb waves are very efficient in the nondestructive testing of composite plates, new transducers are developed nowadays. They may be movable, stuck onto the surface, or integrated into the plates (‘‘smart structures’’). In order to detect defaults with few transducers, a multi-element linear array transducer has been developed to generate single-mode Lamb waves able to propagate over long distances. Movable prototypes were designed in order to evaluate their ability to generate the appropriate waves. Then, composite plates have been equipped with the same kind of transducers consisting of several thin PZT plates. High response levels have been obtained using a unidirectional composite with propagation along the fiber direction. Results for cross-ply laminates were inferior but still acceptable. The main result obtained during this experimental work was the understanding of the generation process for this kind of transducer. Unlike comb transducers, each element generates a separate wave and suitable time delays or spacing between the elements can improve the global response in accordance with linear rules. Furthermore, the delays are easily determined from the responses of each element. This behavior is very interesting as default detection is possible using the properties of the generation process.