In this work, unidirectional multi-scale composites were manufactured and mechanically tested. Carbon nanotubes (CNTs) were grown onto the surfaces of AGY S2-Glass fibers, Grafil 34-700 carbon fibers and Hexcel IM7 carbon fibers using an in-line continuous chemical vapor deposition-based growth process. The processing parameters peculiar to the growth system were growth chamber temperature, catalyst concentration and line speed. These were varied to observe the effect on the CNT growth and parent filament degradation. These processed filaments were wound into unidirectional panels and infused with EPON™ 828 Epoxy. Unidirectional tension and compression tests were conducted in the reinforcement direction and the in-plane and interlaminar shear responses were also characterized.

The effects of processing on micro-morphology were observed via electron microscopy of the CNT-enhanced filaments. The concentration and type of growth directly affected the composite physical properties, specifically fiber volume and bulk density. Increases in growth chamber temperature, chamber residence time and catalyst concentrations each led to a greater volume of CNTs grown on the filament surfaces. Greater volume of CNTs prevents close packing of the filaments, thus decreasing fiber volume and density.

The fiber volume directly affects composite mechanical properties in the reinforcement direction. A uniform coating of short CNTs creates a multi-length scale composite that exhibits increases in strength, stiffness and functional extension in the fiber direction. For in-plane and interlaminar shear, a larger volume of CNTs was shown to increase ultimate shear strength and post-failure toughness. These Fiber-CNT-Epoxy composites can be tailored for specific applications based on mechanical property requirements.