Active Health Monitoring of Composites by Embedded PZT Transducers: A Comprehensive Study of Embedment Effects, Novel Processing Techniques and a Lamb Wave Mode Filtering Tool

The work encompasses a study of interaction between embedded PZT transducers and composite structures as well as technique improvement to simplify Lamb waves analysis. The design of embedded PZT transducers was improved by reducing the stress concentrations in composites. The experiments, performed in static loading, indicated that the embedded PZT transducer did not significantly reduce the strength of the composite. Further investigations were conducted to evaluate the performance of the improved PZT transducer used as a Lamb wave generator embedded in composites subjected to mechanical loading. The tests were performed in static and fatigue loading. The study showed a large working range of the embedded PZT transducers. A post processing technique based on wavelets was developed for damage assessment. This method focused on the wavelet coefficients from the Lamb wave response decomposition, improving the damage detection capabilities. The other technique was devoted to filtering the Lamb waves by the use of multi-element transducers. This technique allowed the reduction of the effect of a Lamb wave mode towards another