Interlaminar Reinforcement of Composites via Tailored CNT Nanomorphologies

The Phase I effort of this STTR aimed to reinforce ply-drop laminates. When laminates taper from a thicker to thinner cross section, the termination of plies locally create resin pockets that can reduce the life of a part due to the lower strength of the resin compared to the fibers, local stress concentrations, and the propensity for voids in these resin rich areas. Thus, Metis Design Corporation (MDC) and MIT have collaborated to demonstrate the use of Carbon Nanotubes (CNT) to solve this problem. During the Phase I STTR effort, MDC demonstrate the use of patterned and buckled CNT layers: NAnoengineered InterLaminar Scaffolding (NAILS). Strategically placed vertically-aligned carbon nanotubes (VA-CNT) in the ply-drop region not only provided strengthening fibers, but prevented adjacent plies from being peeled apart, and helped draw resin into voids through capillary pressure. Flat IM7/8552 specimens exhibited 5-7.5% increase in static SBS strength, while tapered specimen strength increased by 15% with NAILS reinforcement. This translated to a 3x increase in fatigue life of flat specimens subject to dynamic SBS, and a 5x increase in fatigue life for tapered specimens. The goal of the Phase II effort is to mature the NAILS technique such that it can be adopted commercially, with a focus on demonstrating a Navy component, specifically a flex-beam.