Airplanes get old, and over time their skins can develop tiny holes and cracks. Mechanics are good at spotting these problems during regular maintenance checks, but a technique developed in Britain that mimics natural healing could allow airplanes to repair themselves.
Researchers at the Engineering and Sciences Research Council are developing composite materials that "bleed" resin when stressed or damaged, effectively creating a "scab" that fixes the damage. It’s an innovation that could drastically improve air safety, foster the development of lighter aircraft and bring biomimicry to aviation.
"This project represents just the first step", says Dr. Ian Bond, the aerospace professor leading the research. "We’re also developing systems where the healing agent isn’t contained in individual glass fibres but actually moves around as part of a fully integrated vascular network, just like the circulatory systems found in animals and plants. Such a system could have its healing agent refilled or replaced and could repeatedly heal a structure throughout its lifetime. Furthermore, it offers potential for developing other biological-type functions in man-made structures, such as controlling temperature or distributing energy sources."
Think about the body’s healing process and the technology behind self-healing plastics is easy to grasp.
When we cut ourselves, sticky cells called platelets clump together near the wound to create a plug that stops the bleeding and begins the healing. The principle behind the self-healing plastic Bond has developed at University of Bristol technique is remarkably similar.
The composite material is made from hollow fibers filled with epoxy resin. When a hole or crack appears, the resin leaks out and seals the break and returns it to 80 to 90 percent of its original strength. The epoxy is colored, making it easy for mechanics to spot the repairs and make a permanent fix. Slight damage incurred during flight (and we’re talking a tiny tear or crack, not a gaping hole), would be fixed in the time that it takes a small cut to stop bleeding.
“This approach can deal with small-scale damage that’s not obvious to the naked eye but which might lead to serious failures in structural integrity if it escapes attention,” Bond says. “It’s intended to complement rather than replace conventional inspection and maintenance routines, which can readily pick up larger-scale damage, caused by a bird strike, for example.”
Self-healing would improve the overall reliability and safety of fiber-reinforced polymers, making them a more acceptable alternative to aluminum. That would bring lighter – and more fuel efficient, therefore less polluting – airplanes, automobiles and spacecraft. The researchers believe the technology could be commercially adopted in about four years.
Photo of F-117A Nighthawk fighter by Flickr user James Gordon.
Second photo, of fractured fiber-reinforced polymer under ultraviolet lighting to show how the resin "bleeds" into damaged areas, by Engineering and Sciences Research Council.