Aircraft using fiber-reinforced polymer (FRP) composites may be able to use a "self-healing" technique to repair cracks and small holes - even in flight.
Engineers at Bristol University, with funding from the Engineering and Physical Sciences Research Council (EPSRC) developed the technique. Here's how it works:
If a tiny hole/crack appears in the aircraft (e.g. due to wear and tear, fatigue, a stone striking the plane etc), epoxy resin would 'bleed' from embedded vessels near the hole/crack and quickly seal it up, restoring structural integrity.
The ingenious technique works by filling hollow glass fibers contained in FRP composites with special epoxy resin and hardener. If there is a break, the resin flows out, sealing the damaged area, and then hardens. The picture shown above illustrates how the epoxy resin bleeds into the damaged area.
"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," says Dr Ian Bond, who has led the project. "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."
Update 28-Apr-2012: In his 1951 novel Asteroid of Fear, Raymond Z. Gallun wrote about self-sealing plastic that was used in space to protect against damage by micrometeorites.
It even had an inter-skin layer of gum that could seal the punctures that grain-of-sand-sized meteors might make.
End update.
As far as it's use in aircraft is concerned, this kind of material may remind readers of the self-healing Borg cubes; the process can be seen at about 2'40" into the following video:
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