Behaviour of an embedded piezoceramic transducer for Lamb wave generation in mechanical loading

The concept of a built-in structural health monitoring system has attracted great interest as such systems may allow reduced maintenance cost and increased safety. One attractive technique to realise such a system in composites is to use embedded transducers to generate Lamb waves. The damage in the structure is detected by determining the change in the character of the Lamb waves as an effect of damage. In this paper, the performance of embedded piezoceramic transducers used as Lamb-wave generators was investigated. The composite specimens with a piezoceramic transducer embedded in the midplane were subjected to tensile and compressive static loading as well as fatigue loading. A surface-attached acoustic emission sensor further detected the Lamb waves. Measurements of the impedance were also performed during static loading to evaluate the electrical conduction of the piezoceramic transducer. During static loading, the embedded piezoceramic transducers functioned near to the final failure of the composite without significant changes in the generated Lamb waves, although the microscopic examination indicated damage. Debonding between the surfaces of the piezoceramic element and the interconnectors as well as failure in the piezoceramic element had occurred. In fatigue, for a stress ratio of - 1, the piezoceramic transducers also showed a large working range. The amplitude and frequency of the Lamb waves, generated by the piezoceramic transducers, were not significantly changed after a large number of cycles, around 50000-100000 cycles at strain levels of +/- 0.20%. The changes in terms of amplitude and frequency of the Lamb waves, occurring after a large number of cycles, were associated with increasing matrix cracks in the specimen.