Manufacturing and Characterization of Continuous Nanofiber-Reinforced Composites

Fiber-reinforced composite laminates are some of the most advanced structural materials available. However, delamination remains a critical challenge due to its prevalence in structures and ability to cause catastrophic failure. Recently, high-temperature composites are at the forefront of polymer-matrix composites research, but they are prone to microcracking followed by delamination. Nanoreinforcement of interfaces by continuous nanofibers has been proposed earlier at UNL and produced increased interlaminar fracture resistance in conventional advanced composites. However, no studies have yet been conducted on emerging high-temperature composites. Also, there is insufficient information on the translatability of observed modes I and II interlaminar fracture toughness improvements to the structural performance level. The main objectives of this dissertation were to explore feasibility of nanofiber-based delamination suppression in high-temperature laminates and to study translation of delamination suppression via nanofiber-interleaving to the performance of composite structural volumes. Unidirectional carbon/epoxy and carbon/cyanate ester composites were reinforced with continuous nanofiber interleaves electrospun from polyacrylonitrile or polyimide, and their fracture mechanics performance was characterized and compared. Significant improvements in modes I and II fracture resistance were demonstrated with the high-temperature material for the first time. The improvements in material properties were also translated to the structural performance of laminates with and without holes and L-shaped composites. Nanofiber-reinforced specimens continued to perform better than pristine specimens, and the high-temperature material showed greater improvements. To mimic the controlled anisotropy and high fiber volume fraction of traditional advanced laminates, laminated nanocomposites reinforced with aligned, continuous nanofibers were fabricated and characterized. Results prove the feasibility of manufacturing nanolaminates with distinct oriented plies, high nanofiber volume fractions, and improved properties. Lastly, feasibility of nanofiber structure tailoring with graphene nanoribbons and MXenes was explored. It was shown that incorporation of MXene nanoparticles can lead to significant improvements in the graphitic structure of the templated carbon nanofibers. Overall, this dissertation provides novel results on continuous nanofiber-reinforcement of high-temperature composites and advanced composite structures. The knowledge gained will contribute to the extension of electrospun nanofibers from the laboratory to industrial applications. Advisor: Yuris Dzeni