Ballistic characterization of nanostructured composite materials for aerospace applications

The manuscript is arranged in three main parts. In the first chapter the nanocomposite manufacturing is described. As far as the CNTfilled polymeric composites are concerned, a carbon nanotube functionalization process by thermal and chemical treatments has been performed, and Scanning Electron Microscopy (SEM) analysis, as well as Raman and FT-IR spectroscopies were used to verify the surface modifications of the CNTs by the added radical groups. Then, the manufacturing of the CNT-reinforced epoxy composite has been carried out, and Differential Scanning Calorimetry (DSC) was used to analyze the polymerization process for the nano-reinforced thermosetting polymer systems. SEM investigations were also performed to assess the nanocomposites quality in terms of nanoparticle dispersion and material homogeneity. Regarding the STF-reinforced materials, STFs have been synthesized in a single step reaction through high power ultrasound technique, and characterized in terms of their rheological properties. The shear thickening fluid is prepared by ultrasound irradiation of silica nanoparticles dispersed in liquid polyethylene glycol polymer. Then, STF-reinforced fabrics have been realized by soaking layers of several types of Kevlar in STF/ethanol solution; the morphology of the as-realized fabrics, in particular for what concerns the STF/fibers interaction, has been deeply investigated by SEM analysis. In the second chapter the realization and the characterization of the in-house built Coil Gun device for ballistic applications is presented. The realization of such experimental apparatus, and mostly the optimization with a view to space debris testing plane, is quite complex since the fundamental machine parameters have high non-linearity behavior. With the aim to perform an as accurate as possible ballistic characterization, both theoretical issues and experimental preliminary results of the prototypal device are widely presented and discussed. In the third chapter the results of the ballistic characterization of the realized nanocomposite materials are reported. The response of the manufactured materials to several levels of impact energy is widely investigated. Charpy impact and weight drop tests were performed to obtain a preliminary ballistic characterization of the CNTVI reinforced epoxy composites in the low energy impact range. In order to assess the influence of the nanoparticles content as well as the effectiveness of the nano-filler itself and after chemical treatments, samples with different percentages of functionalized CNTs embedded in two different epoxy resins were tested and compared with samples reinforced by pristine CNTs and micrometric graphite powder. Finally, the response of CNT-reinforced epoxy materials and STF-reinforced Kevlar fabrics was experimentally investigated by Coil Gun ballistic tests at different impact energy: the effects of the nanoparticles on the penetration failure and the impact absorbing mechanism is analyzed and discussed.