Composite materials for construction, engineering, and other similar applications are formed by combining two or more materials in such a way that the constituents of the composite materials are still distinguishable, and not fully blended. One example of a composite material is concrete, which uses cement as a binding material in combination with 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.
Composite materials take advantage of the different strengths and abilities of different materials. 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, composite materials 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, aircraft integrating reinforced composite materials such as fiberglass, graphite, and other hybrids will be stronger and less likely to break up at stress points in situations involving turbulence.