NC State researchers develop self-healing fiber-reinforced polymer composite

Researchers at North Carolina State University have developed a fiber-reinforced polymer (FRP) composite that is capable of repairing its own structural damage more than a thousand times. FRP composites are made of layered glass, carbon, or other fibers within a polymer matrix, and are widely used in wind turbines, aircraft, and aerospace vehicles due to their strength-to-weight ratio. However, a persistent failure mode in these materials is interlaminar delamination, in which cracks separate fiber layers from the surrounding matrix. The NC State study looked at tackling this by incorporating a thermoplastic healing substance – 3D printed as an interlayer – onto the fiber reinforcement. The result: a doubled or quadrupled resistance to delamination compared with standard composites. The real innovation happened when electrified carbon-based layers within the composite generated heat upon damage being inflicted. This caused portions of the thermoplastic interlayer to melt and seep into fractures, and led to a re-bonding of the delaminated interfaces. Automated testing subjected the material to 5cm delaminations followed by self-healing cycles across 1,000 repetitions over 40 days. The research team described performance results as having an order of magnitude beyond their previous record. “Because our composite starts off significantly tougher than conventional composites, this self-healing material resists cracking better than the laminated composites currently out there for at least 500 cycles. And while its interlaminar toughness does decline after repeated healing, it does so very slowly,” stated Jack Turicek, a PhD candidate and co-author of the study, which was published in the Proceedings of the National Academy of Sciences. Projections based on healing frequency suggested the material could last 125 years if repaired quarterly, or 500 years with only annual rejuvenation cycles. Jason Patrick, corresponding author and Associate Professor of Civil, Construction, and Environmental Engineering at NC State, stated the technology would “significantly drive down costs and labor associated with replacing damaged composite components, and reduce the amount of energy consumed and waste produced by many industrial sectors – because they’ll have fewer broken parts to manually inspect, repair or throw away.” Patrick, through his company Structeryx Inc., was already licensing the technology at the time of publication.