Aerospace engineers at Bristol University, with funding from the Engineering and Physical Sciences Research Council (EPSRC) have developed a new technique that mimics healing processes found in nature which could enable damaged aircraft to mend themselves automatically, even during a flight.
It has potential to be applied wherever fiber-reinforced polymer (FRP) composites are used. These are composite material comprising a polymer matrix reinforced with fibers. The fibers are usually fiberglass, carbon, or aramid, while the polymer is usually an epoxy, vinyl ester or polyester thermosetting plastic. These lightweight, high-performance materials are proving increasingly popular not only in aircraft but also in car, wind turbine and even spacecraft manufacture. The new self-repair system could therefore have an impact in all these fields.
The technique works like this.
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. By mixing dye into the resin, any ’self-mends’ could be made to show as coloured patches that could easily be pinpointed during subsequent ground inspections, and a full repair carried out if necessary.
One of the innovative aspect of this technique involves filling the hollow glass fibres contained in FRP composites with resin and hardener. If the fibres break, the resin and hardener ooze out, enabling the composite to recover up to 80-90% of its original strength — comfortably allowing a plane to function at its normal operational load.
According to Dr Ian Bond, who has led the project:
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. 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.
This ‘Bleeding Composites: Damage Detection and Repair Using a Biomimetic Approach’ research project concluded at the end of April 2008 and took 3-years. The total funding it received from EPSRC was around £171,000.
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