Development of a self-sensing composite laminate based on PZT nanofibers for impact localization
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One of the most critical aspects of composite materials in aerospace applications is their vulnerability to impact loads. Recently, several Structural Health Monitoring (SHM) systems have been developed to monitor in real-time the event of an impact and therefore the structural integrity of the component [1]. The most advanced systems allow impact localization by triangulation techniques, exploiting the propagation of elastic waves in the laminate. However, these systems require sensors integrated within the composite, such as Bragg gratings or ceramic piezoelectric transducers, which due to their fragility and millimetric dimension detrimental affect the intrinsic resistance of the hosting material [2]. In this work, it is proposed a non-invasive method for the piezoelectric functionalization of composite laminates by interleaving between Glass Fibre Reinforced Prepreg (GFRP) layers lead zirconate titanate (PZT) nanofibers and brass sheets to collect the piezoelectric signal. The impact strength was evaluated by Low Velocity Impact (LVI) test and micrographic analysis of the cross-section. The experimental results show that laminates intercalated with PZT nanofibers have a sensitivity lower than the ones integrated with commercial sensors, but have higher impact resistance, comparable to the reference one. A GFRP 300x200 mm plate with PZT nanofiber-based sensors interspersed at the 4 corners was fabricated. It was then impacted at various points according to a 4 x 5 grid pattern with a pitch of 40 mm. The piezoelectric signals generated by the sensors were acquired simultaneously and the Time of Arrival (ToA) of the elastic wave generated by the impact was calculated using the Akaike criterion (AIC). Therefore, knowing the difference between the time of arrival and the sensor's position, the point of impact was located using simple trigonometric formulas. The average error in locating the point of impact committed by the laminate intercalated with PZT nanofibers resulted in 35 mm, compared to 31 mm for the commercial sensors, without detrimental negatively affecting the intrinsic resistance of the hosting material.