Percorrer por autor "Limpo, Joana Valente"
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- Mechanical and Piezoresistive Sensing of GFRP Modified with MWCNTs under Monotonic and Cyclic Loading for Structural Health MonitoringPublication . Limpo, Joana Valente; Pereira, João Pedro Nunes; Silva, Abílio Manuel Pereira da; Parente, João Miguel NunesFiber-reinforced composites, specifically polymer fiber-reinforced composites, have gained increased popularity among scientists and engineers. This results from their optimized properties, including mechanical strength, reduced weight, low density, chemical inertness, freedom in design, and good response to fatigue, among many others. This is reflected in many sectors, including the aeronautical and aerospace fields, where these composites have been replacing the more traditional materials, like metal. However, despite all the advantages of composites, due to their nature, some behavioral aspects, especially damage-wise, are not fully understood, hindering their use for certain functions. One of those functions is the structural health monitoring of components, which goal is to have components and structures be able of in situ monitor of their own condition, without the disadvantages of embedded sensors. With this in mind, this study analyzed the impact of the addition of varying carbon nanotube concentrations, 0.3 wt% and 0.4 wt% MWCNTs, to find an optimized concentration for better piezoresistive properties. Beyond that, the 0.3 wt% and 0.4 wt% MWCNT-reinforced laminates were subjected to multiple flexural tests, from monotonic to cyclic, and with increased deformation, to mimic possible in service conditions and preview their possible behavior under each situation. SEM imaging was done post testing, to link the mechanical and electrical data obtained with the damage suffered by the specimens. Overall, the results pointed to better mechanical properties for the samples with 0.3 wt% nanotubes, which can be a sign of poor interface properties for the higher nanoparticle concentration. On the other hand, the electrical data concluded the samples with 0.4 wt% MWCNT were the most sensitive and presented more stable results. In summary, by adding carbon nanotubes to the glass-fiber-reinforced laminates, it was possible to create a material with self-sensing capabilities, and real-time monitoring of the structure was achieved. The mechanical data reinforced the importance of manufacturing and dispersion processes, especially with increasing nanoparticle concentrations and the electrical resistance results concluded there is a relation between a material’s damage and electrical signal.