Composite
materials for construction, engineering, and other similar applications
are formed by combining two or more materials in such a way that the
constituents are still distinguishable and not fully blended. One
example is concrete, which uses cement as a binding material in
combination with aggregate, like gravel, as
a reinforcement. In many cases, concrete uses rebar as a second
reinforcement, making it a three-phase composite, because of the three
elements involved.
This type of material takes advantage of the different strengths and abilities of its different elements.
In the case of mud and straw bricks, for example, mud is an excellent
binding material, but it cannot stand up to compression and force well.
Straw, on the other hand, is well able to withstand compression without
crumbling or breaking, and so it serves to reinforce the binding action
of the mud. Humans have been creating composite materials to build
stronger and lighter objects for thousands of years.
The
majority of composite materials use two constituents: a binder or
matrix and a reinforcement. The reinforcement is stronger and stiffer,
forming a sort of backbone, while the matrix keeps the reinforcement in a
set place. The binder also protects the reinforcement, which may be
brittle or breakable, as in the case of the long glass fibers used in
conjunction with plastics to make fiberglass. Generally, composites have
excellent compressibility combined with good tensile strength, making
them versatile in a wide range of situations.
Engineers
building anything, from a patio to an airplane, look at the unique
stresses that their construction will undergo. Extreme changes in
temperature, external forces, and water or chemical erosion are all
accounted for in an assessment of needs. When building an aircraft, for
example, engineers need lightweight, strong material that can insulate
and protect passengers while surfacing the aircraft. An aircraft made of
pure metal could fail catastrophically if a small crack appeared in the
skin of the airplane. On the other hand, one integrating
reinforced materials such as fiberglass, graphite, and other hybrids
will be stronger and less likely to break up at stress points in
situations involving turbulence.
Many
composites are made in layers or plies, with a woven fiber
reinforcement sandwiched between layers of plastic or another similar
binder. These materials have the advantage of being very moldable, as in
the hull of a fiberglass boat. Composites have revolutionized a number
of industries, especially the aviation industry, in which the
development of higher quality materials allows companies to build bigger and better aircraft.