For the next-generation of high speed and heavy lift rotorcraft, vibratory loads in forward flight are expected to be severe leading to fatigue conditions and increased operational and maintenance cost. In this project we explore a potential solution to this need in the form of a new class of hierarchically organized graphene/carbon-fiber and graphene/glass-fiber composites that show potential to significantly enhance fatigue properties. We disperse nano-additives, including nanoparticles and graphene, in epoxy and the resulting nanocomposite is used as matrix for the more classical woven carbon and glass fiber composites. We also aim to disperse nano-additives in the interface between matrix and fibers such to improve the fatigue properties of these interfaces. This solution is based on our observation of significant fatigue resistance increase in epoxy-based nanocomposites compared with pure epoxy. We use a combination of modeling and experiments to achieve this goal. The experimental program includes the production of the epoxy-based nanocomposite, mechanical testing and structural characterization. The characterization of the woven fiber composite, as well as that of the fiber-matrix interfaces are also performed. Modeling is performed to determine the optimal concentration and distribution of nano-fillers that would lead to enhanced fatigue resistance. Modeling also indicates how the nano-scale deformation mechanisms influence the microscale deformation and failure modes, which in turns provides clues for material improvement.
