Structural health monitoring of polymer-matrix composite using embedded piezoelectric ceramic transducers during several four-points bending tests

This article investigates the interest of a promising methodology, dealing with the use of an in-situ piezoelectric (PZT) disk to perform real-time Structural Health Monitoring (SHM) of glass fiber-reinforced polymer (GFRP) composites submitted to various four-points bending loadings: monotonic, load-unload and incremental load until failure. The real-time in-situ SHM is conducted acquiring the electrical signature (capacitance) variation of the embedded PZT transducer. To establish the link between the PZT capacitance response and the occurring physical phenomena, especially damage, a multi-instrumentation composed of external Non-Destructive Testing techniques (Acoustic Emission (AE) and Digital Image Correlation (DIC)) was implemented on the tested specimens, so that it was possible to make multi-physical couplings between the various obtained measurements and the PZT capacitance curves. It was shown that the PZT capacitance is very sensitive to damage initiation and progression inside the polymer-matrix composite material until its failure, mainly due to the specimens Neutral Fiber (NF) vertical offset which changes the piezoelectric coupling between the host composite and the transducer. Consequently, the SHM potential of such a PZT disk is highlighted, opening the way for its use in real technical structures submitted to bending loadings, such as aircraft wings. (paper)