Development and modeling of a self-sensing composite laminate interleaved with piezoelectric nanofibers and CFRP electrodes.
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The components made of FRP with a laminate structure are subject to delamination when external forces are applied perpendicularly to the laminate plane. Cracks caused by impact often develop within the laminate without any visible damage on the surface, until reaching a critical size that leads to the sudden failure of the component. Several Structural Health Monitoring (SHM) systems have been developed to monitor the structural integrity of the component in real-time. These kinds of systems require the use of sensors. In many cases, it is useful to place commercial sensors inside the composite between the laminate plies, in order to prevent exposure to environmental conditions, electronic interferences and impacts, that may affect the proper functioning of the sensors. Sensors based on the Fibre Bragg Grating (FBG) can be integrated, alternatively, piezoelectric ceramic-based wafers, such as those in lead zirconate titanate (PZT), can be integrated within the laminate. The main problems with embedding extrinsic sensors within the laminate are their size and the different nature of the materials from which the sensors are made. In this study, the epoxy matrix of a composite laminate, based on Glass Fiber Reinforced Plastic (GFRP), was made piezoelectrically active due to the integration of a PVDF-TrFE nanofiber mat. A first pair of Carbon Fiber Reinforced Plastic (CFRP) layers were used as electrodes to collect the piezoelectric signal. A second pair as electrode to shield the sensor from Electromagnetic interference (EMI). Through a Design of Experiment (DoE), the effect of PVDF-TrFE/GFRP volume ratio and amount of GFRP between signal electrodes and shielding electrodes were analysed, in terms of electromechanical responses. A lumped electric model was developed to explore the sensor performances using the electrical, mechanical and geometrical properties of the single components.