USAGE OF COMPOSITE MATERIALS

The most widely used composite material in tactical aircraft
is a carbon fibre/epoxy mix.Carbon epoxy has eclipsed boron
based composites because it is much cheaper to produce,easier
to machine and drill, and can be formed into complex shapes
to produce structural members such as spars and ribs. Other
fibers typified by Kevlar also are being used in aircraft production.
Kevlar is less dense than carbon fibres but has inferior mechanical
properties. It is used in pressure vessels, for ballistic protection
and as lightweight fibreglass non-structural parts. Composites
have displaced conventional materials such as aluminum because
they have several advantages. They have lower density and
greater strength and stiffness than aluminum, therefore a smaller
lighter structure can carry the same load. Studies conducted by
Boeing indicate that a 38 per cent composite structural weight
can result in a 40 per cent reduction in empty weight, 39 per
cent reduction in wing area and a 33 per cent fuel saving for
the same mission profile when compared to an aircraft of
conventional metal structure. Another big advantage is that
composites are relatively insensitive to flaws. Fatigue testing
of composite structures demonstrated their high resistance to
cracking and that fractures generally do not propagate.
Composite materials are very stable and so are not subject
to corrosion as aremetallic structures. However, in the design
process, careful attention must be paid to composite-metal
interaction because through galvanic action some metals will
corrode when in contact with carbon fibre/resin laminate.