Imagine trying to design machines that will last forever, regardless of use or destination. Instead of those machines requiring a steady stream of spare parts (essentially impossible for space probes or exoplanetary landers to haul or acquire), they’ll be able to heal their super-durable “flesh” more than a thousand times. Sound too good to be true?
Not to researchers at North Carolina State University, because they’ve created a fiber-reinforced polymer (FRP) composite that could make such machines a reality. In their Proceedings of the National Academy of Sciences paper “Self-healing for the Long Haul: In situ Automation Delivers Century-scale Fracture Recovery in Structural Composites,” PhD candidates Jack Turicek and Zach Phillips, along with Dr. Kalyana Nakshatrala (Professor of Civil and Environmental Engineering at the University of Houston) reveal how their material’s self-healing technique works.
When cracks form inside composites that separate fiber layers from the matrix, the UNC material repairs that interlaminar delamination using an electrically melted material that seeps into the cracks and bonds the separated layers.
That’s excellent news for every person and every industry depending on cars, aerospace vehicles, wind turbines, and a range of structures using fiber-reinforced polymer (FRP) composites, which are made of layers of glass, carbon, or other fibers in a polymer matrix. While all FRPs are extremely strong despite their relatively light weight, UNC’s self-healing FRP composites are even stronger than typical FRP composites, and compared with the standard FRP composite lifespan of decades (a problem since the 1930s), are practically immortal.
Now, while “practically immortal” doesn’t mean these new FRP composites will actually last an eternity, they could last centuries, thus vastly outliving generations of people who designed and used the machines built from these composites. Such longevity also delivers enormous ecological benefits from reduced harvesting, processing, and production of materials, and also major cost savings.
According to Jason Patrick, corresponding author and associate professor of civil, construction, and environmental engineering at NCU, the innovation will “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.” With his patent, Patrick and his company Structeryx Inc. are already licensing the technology.
So, what allows the Structeryx FRP composites to exceed standard composite performance? One aspect is a thermoplastic healing substance 3D-printed as a polymer interlayer onto the fiber reinforcement. That interlayer doubles or even quadruples resistance to delamination.
The second innovation is the insertion of carbon-based layers that heat up when electrified. That heating causes some of the thermoplastic to melt and seep into large and tiny fissures, thus re-gluing delaminated interfaces. Imagine Iron Man’s armor with a layer of self-melting metal that “bleeds” into and repairs cracks, or the Cylon bio-metal that strengthened damaged areas of the Battlestar Galactica.
Jason Patrick, NC State University
How long will the Structeryx FRP composite last in the real world? So far, testing suggests a very, very long time. If the material requires healing once per season, it could last 125 years. But if it needs only annual rejuvenation, it could last half a millennium. Automated testing that inflicted 5-cm delaminations, followed by self-healing, for a thousand cycles over 40 days, proved an order-of-magnitude performance beyond the team’s previous record.
“Because our composite starts off significantly tougher than conventional composites,” says Turicek, “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.”
That performance means massive benefits for wind turbines, airplanes, and certainly spaceships, space stations, and interplanetary probes far from any possible repair shop.
Source: North Carolina State University