By Malcolm Azania - Traditional carbon fiber (pictured) is strong and lightweight, but can be difficult to repair once damaged
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.
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