Tech Briefs Magazine - January 2023 - 9

Q & A
A Self-Healing Structural Composite
Jason Patrick, Assistant Professor of civil,
construction, and environmental engineering
at North Carolina State University, and
his team have developed a new composite
material for applications like airplane wings
and wind turbine blades in which hidden
defects and damage can self-heal.
Tech Briefs: Could you please describe your system and
how it works?
Patrick: A typical fiber-reinforced composite has two primary
phases, the reinforcement - the fibrous phase. The other being
an encompassing matrix. For this system, we're reinforcing
an epoxy matrix with glass and carbon fiber.
Our self-healing system relies on the addition of two other
materials. A thermoplastic, which we 3D print directly onto the
primary reinforcement - glass or carbon. And we also include
resistive heaters, which are layered structural reinforcement.
The interior layer contains an electrically conductive network
of conductive carbon whiskers. Both exterior
layers, sandwiched around the network
of carbon whiskers, are glass fiber reinforcement.
The glass electrically insulates
the heater, so you don't experience shorting,
particularly in carbon-fiber reinforced
composites, which are conductive just like
the network of carbon whiskers. Electrical
power input to the heater interlayer(s)
melts the thermoplastic agent, which flows
into cracks and heals the damage.
Tech Briefs: So, how would one decide
when to initiate a repair?
Patrick: That's a great question. At this
stage, with what we have developed, we envision
healing as a maintenance cycle that
the structural system would go through. For
instance, with an aircraft, after a specified
number of flight hours, you would apply
the heating and automatically repair any
internal damage. Or you can think about
a leveraging a system that has heaters embedded
for deicing. Thus, every time you
activate the deicing system it also repairs
the structure. But the nice part is that you
don't have to locate the damage. Wherever
there's a crack, the molten healing agent is
going to flow into the crack and repair it.
Another thing that we are exploring
right now is self-sensing that will not only
detect damage in order to trigger the healTech
Briefs, January 2023
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9
ing to occur, but also monitor the repair process it as it evolves,
so that we can quantify the extent of mechanical recovery
during service.
Tech Briefs: I have a feeling this will have important
effects in the world.
Patrick: Yes, I think it's a new structural mindset. We won't
need bulky overdesigns or manual inspection to try and locate
subsurface damage.
Tech Briefs: What are your thoughts about the future?
Patrick: I think that the most likely early applications will be
safety-critical or difficult-to-access structures. For example, rotating
components such as helicopter blades, or wind turbine
blades, both of which have been known to delaminate, and can
present a life-threatening situation.
To read the full interview, visit www.techbriefs.com.
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Tech Briefs Magazine - January 2023

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