A composite material with respect to materials science and engineering can be defined as a materials system composed of a mixture or combination of two or more micro- or macroconstituents that differ in form and chemical composition and are essentially insoluble in
each other.
Some fiber-reinforced-plastic composite materials are made with synthetic fibers of glass, carbon, and aramid. Of these three fibers, glass fibers are the lowest in cost and have intermediate strength and highest density when compared to the others. Carbon fibers have high strength, high modulus, and low density but are expensive and so are used only for applications requiring their especially high strength-to-weight ratio. Aramid fibers have high strength and low density but are not as stiff as carbon fibers. Aramid fibers are also relatively expensive and so are used for applications where a high strength-to-weight ratio is required along with better flexibility than carbon fibers. The most commonly used matrices for glass fibers for fiber-reinforced-plastic composites are the polyesters, whereas the most commonly used matrices for carbon-fiber-reinforced plastics are the epoxies. Carbon-fiber-reinforced-epoxy composite materials are used extensively for aircraft and aerospace applications. Glass-fiber-reinforced-polyester composite materials have a much wider usage and find application in the building, transportation, marine, and aircraft industries, for example.
Concrete is a ceramic composite material consisting of aggregate particles (i.e., sand
and gravel) in a hardened cement paste matrix usually made with portland cement.
Concrete as a construction material has advantages that include usable compressive
strength, economy, castability on the job, durability, fire resistance, and aesthetic appearance.
The low tensile strength of concrete can be increased significantly by reinforcement
with steel rods. A further improvement in the tensile strength of concrete is attainable
by introducing residual compressive stresses in the concrete at positions of high tensile
loading by prestressing with steel reinforcements.
Wood is a natural composite material consisting essentially of cellulose fibers bonded
together by a matrix of polymeric material made up mainly of lignin. The macrostructure
of wood consists of sapwood, which is made up primarily of living cells and which
carries the nutrients, and heartwood, which is composed of dead cells. The two main types
of woods are softwoods and hardwoods. Softwoods have exposed seeds and narrow
(needlelike) leaves, whereas hardwoods have covered seeds and broad leaves. The
microstructure of wood consists of arrays of cells mainly in the longitudinal direction of
the tree stem. Softwoods have long, thin-walled tubular cells called tracheids, whereas hardwoods have a dense cell structure that contains large vessels for the conduction of fluids.
Wood as a construction material has advantages that include usable strength, economy, ease
of workability, and durability if properly protected.
Bone is the natural composite material in the human body. It is made up of a mixture
of organic (collagen) and inorganic (hydroxyapatite) materials. The macrostructure of
bone consists of two distinct types of bony tissues: cortical and cancellous. Bone behaves
in an anisotropic manner consistent with composite materials. It is also important to note
that bone is stronger in compression.
