Structural Health Monitoring of Glass/Epoxy Composite Plates Using PZT and PMN-PT Transducers

The structural health monitoring of composite structures presents many challenges, ranging from sensors’ reliability and sensitivity to signal processing and a robust assessment of life to failure. In this research project, sensors constructed with both PZT-4 ceramic and single-crystal PMN-PT, i.e., $Pb(Mg1/3Nb2/3)O3−PbTiO3$⁠, were investigated for structural health monitoring of composite plates. Fiberglass/epoxy specimens were manufactured with a delamination starter located in the middle of the plate, and were subjected to axial tensile fatigue at a high stress ratio. A surface-mounted PMN-PT pair and a surface-mounted PZT-4 pair were positioned on each side of the delamination starter and excited in turns at set intervals during fatigue loading. This project had two goals: (1) assess the performance of the two piezoelectric materials and (2) develop a signal processing technique based on wavelet transforms capable of detecting damage features that are independent of the transducers (being damaged concurrently to the host composite specimens) and thus can estimate life to failure of the composite specimens. Results indicate that the PMN-PT transducers may be more resilient to fatigue damage of the host structure and possibly generate less dispersive Lamb waves. However, these aspects are compounded with higher costs and manufacturing difficulties. Moreover, the proposed signal processing method shows promise in estimating impending failure in composites: It could, in principle, capture and quantify the complex wave propagation problem of dispersion, scattering, and mode conversion across a delamination front, and it will be further investigated.