Processing and characterization of infusion-processed hybrid composites with in situ grown aligned carbon nanotubes

Hybrid composite materials enhanced with aligned CNTs directly grown on fibers of woven cloths are fabricated by a vacuum-assisted resin infusion process for the first time. A vacuum-assisted resin infusion process can significantly build upon and expand the hybrid composite work already developed using hand-layup to a more scalable and relevant processing technology. Chemical vapor deposition (CVD) is used for growing aligned CNTs on the alumina fiber surfaces of woven fabrics, creating a nanostructured "fuzzy fiber (FF)" hierarchical architecture. The aligned CNTs grown in situ on alumina-fiber woven fabrics serve as interlaminar and intralaminar reinforcement. FF woven fabrics and baseline (wihout CNTs) alumina woven fabrics are formed on a mold plate, and an aerospace-grade resin-transfer molding (RTM) resin is infused into the laminates by vacuum-assisted resin infusion. Optical and scanning electron microscopy (SEM) are used to characterize these composites. In these microphotographs, no difference in terms of void fraction (less than 1%) and overall distribution of CNTs and resin-fiber ratios are observed between the baseline and FF composites. CNTs are noted to remain on the surface of alumina fibers during the infusion process and are not observed in the excess resin pulled through the laminates. The effect of the CNT distribution within the FF composite is further assessed using electrical impedance spectroscopy testing in the in-plane and transverse directions. Employment of resin infusion process for FF woven fabrics should greatly simplify the development of new composite materials with significantly-enhanced mechanical and electrical as well as thermal properties.