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Self-repairing aircraft could revolutionise aviation safety

Flying colours: fractured fibre-reinforced polymer under UV illumination

A
new technique that mimics healing processes found in nature could
enable damaged aircraft to mend themselves automatically, even during a
flight.

As well as the obvious safety benefits, this
breakthrough could make it possible to design lighter aeroplanes in
future (see below). This would lead to fuel savings, cutting costs for
airlines and passengers and reducing carbon emissions too.

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.

This simple but
ingenious technique, similar to the bruising and bleeding/healing
processes we see after we cut ourselves, has been developed by
aerospace engineers at Bristol University, with funding from the
Engineering and Physical Sciences Research Council (EPSRC). It has
potential to be applied wherever fibre-reinforced polymer (FRP)
composites are used. 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’s innovative aspect 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.

No hollow achievement: hollow glass fibres embedded in carbon fibre reinforced plastic could be the key to safer flying.

“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.”

By
further improving the already excellent safety characteristics of FRP
composites, the self-healing system could encourage even more rapid
uptake of these materials in the aerospace sector. A key benefit would
be that aircraft designs including more FRP composites would be
significantly lighter than the primarily aluminium-based models
currently in service. Even a small reduction in weight equates to
substantial fuel savings over an aircraft’s lifetime.

“This
project represents just the first step”, says Ian Bond. “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.”

The new
self-repair technique developed by the current EPSRC-funded project
could be available for commercial use within around four years.