Novel design and manufacturing of advanced multifunctional structural nanocomposites containing self-healing fibers and graphene sheets with structural health monitoring capabilities
In the first part of this thesis, a direct, one-step tri-axial electrospinning process was used to fabricate multi-walled fibers with a novel architecture. Different healing agents were encapsulated inside the fibers with two separate protective walls. Presence of an extra layer in the fiber structure facilitated the encapsulation of healing agents and extended the efficiency of the healing functionality. We first took a systematical optimization approach to produce tri-axial hollow electrospun fibers with tunable fiber diameters and surface morphology. Next, the effect of tri-axial hollow fibers as a primary reinforcement and co-reinforcement in the presence of glass fibers was scrutinized from a material selection point of view. Furthermore, multi-walled fibers were utilized to encapsulate different healing agents inside the fibers and successful and recurring self-healing ability were achieved while preserving the mechanical properties of the composites. In the second part of this study, three different architectural designs were developed for manufacturing advanced multi-scale reinforced epoxy based composites in which graphene sheets and carbon fibers were utilized as nano- and micro-scale reinforcements, respectively. Graphene/carbon fiber/epoxy composites in various graphene sheet arrangements showed enhancements in in-plane and out of plane mechanical performances. In the hybrid composites, remarkable improvements were observed in the work of fracture by ~55% and the flexural strength by ~51% as well as a notable enhancement on other mechanical properties. In addition, integration of conductive reinforcement in the epoxy matrix enabled us to develop composite structures with high electrical and thermal conductivity, self-heating and de-icing functionalities
