Airplanes of the future could be self-healing

Bryn Nelson Columnist

Airplane, heal thyself.

A new technology inspired by the self-healing powers of plants and animals may allow damaged planes to fix themselves on the fly and point out even minuscule holes to mechanics upon landing. If the technique pans out, then aircraft, wind turbines and perhaps even spaceships of the future may boast embedded circulatory systems with an epoxy resin that can bleed into holes or cracks and then fluoresce under ultraviolet light to mark the damage like a bruise during follow-up inspections.

The system could be a particular boon for lightweight, plastic-based composites known as fiber-reinforced polymers. Such polymers have recently grown in popularity with aircraft, spacecraft, automotive and wind-turbine manufacturers, who use the materials like protective layers of skin.

“Their Achilles heel is that they are quite susceptible to damage that is often undetectable to the eye,” said Ian Bond, an aerospace engineer at Bristol University in the United Kingdom. “Users of composites spend a lot of time trying to detect this damage and worrying about what happens when it grows.”

With funding from the Engineering and Physical Sciences Research Council, Bond and his collaborators have set out to compensate for the flaw with hollow glass fibers inspired by biological systems. “Most natural materials have an ability to heal and look after themselves when they’re damaged,” he said. With a similarly arranged network of vessels at vulnerable spots like the underbelly, doors, hatchways, wheel wells and wing bottoms, he reasoned, so might an aircraft.

Like clotting blood
At its base, the hierarchical system his team designed boasts a two-part epoxy system. The epoxy and a hardener fill adjacent hollow glass fibers that, when broken due to a debris strike or other damage, release their contents and mix to form a plug, somewhat akin to clotting blood. Matched pairs of those filled glass fibers are arranged within the plane’s structural skin, a larger network of carbon fibers embedded in stacked layers of plastic.

Adding a fluorescent dye to the epoxy could mark patched-up damage in need of more permanent repairs, though it would work only on fairly translucent surfaces. “The analogy is very much a bruise,” Bond said. “You hurt yourself and you know you’ve been hurt.”

For black carbon fiber composites not amenable to a color change, magnetic nanoparticles could be added to the epoxy and a handheld magnet-based scanner used to detect changes in their relative distribution due to a newly formed epoxy plug.

Highlighting both the difficulty and desire to effectively detect aircraft damage, other scientists have turned to an infrared camera that points out defects below the surface, ultrasonic waves that monitor the growth of defects that could become cracks, and optical fiber sensors that measure strains and temperatures within the composite structure in real time.

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