What Are Composite Materials?
A composite material is one in which two or more separate materials have been combined to make a single construct having more desirable properties. What many people don't realize is that composites are probably the most common structural materials in the world, and have always been an essential part of their lives. Concrete, paper, corrugated cardboard, plywood, fiberglass, bamboo, cornstalks, trees, bricks... all are composite materials. Far from being a new invention, composite materials are the main structural elements of nature. Take a close look at the grain and structure of a piece of wood, and you will see how its strength comes from a structure of fibers bound together side by side.
Man's first use of such composite materials was probably the adobe brick. Mud or clay can be shaped and dried into a hard block, but that kind of block has little load bearing strength and can be easily crushed by the weight of other blocks on top of it. At some point in time, it was found that mixing dried grass or straw into the mud produced a brick with superior properties, a brick that could bear much greater loads without being crushed than a brick of plain dried mud could bear.
Plywood is another example. In plywood, thin sheets, or 'plies' of wood are laminated together. In each ply, the wood fibers runs in one particular direction, and each ply is aligned in a different direction than the adjacent plies. This gives the resulting stack of wood plies an optimum strength in all directions, making plywood a very versatile and useful structural material. A third example of a composite material is reinforced concrete, used in the construction of bridges and buildings. Steel rods are encased in a matrix of concrete, producing reinforced concrete, which has much better strength and load-bearing properties than concrete that has not been reinforced.
