A composite material is made by combining two or more materials – often ones that have very different properties. The two materials work together to give the composite unique properties.
However, within the composite you can easily tell the different materials apart as they do not dissolve or blend into each other.
People have been making composites for many thousands of years. One early example is mud bricks. Mud can be dried out into a brick shape to give a building material. It is strong if you try to squash it (it has good compressive strength) but it breaks quite easily if you try to bend it (it has poor tensile strength). Straw seems very strong if you try to stretch it, but you can crumple it up easily. By mixing mud and straw together it is possible to make bricks that are resistant to both squeezing and tearing .
Another ancient composite is concrete. Concrete is a mix of aggregate (small stones or gravel), cement and sand. It has good compressive strength (it resists squashing). In more recent times it has been found that adding metal rods or wires to the concrete can increase its tensile (bending)
strength. Concrete containing such rods or wires is called reinforced concrete.
How it’s done
Most composites are made of just two materials. One is the matrix or binder. It surrounds and binds together fibres or fragments of the other material, which is called the reinforcement.
Now Days examples
The first modern composite material was fibreglass. It is still widely used today for building boats, sports equipment such as bicycles, building panels and many car bodies. The matrix is a plastic and the reinforcement is glass that has been made into fine threads and often woven into a sort of cloth.
On its own the glass is very strong but brittle and it will break if bent sharply.
Some advanced composites are now made using carbon fibres instead of glass. These materials are lighter and stronger than fibreglass. They are used in aircraft structures and expensive sports equipment such as bicycles ,tennis bats and even formula 1 cars.
Carbon nanotubes have also been used successfully to make new composites. These are even lighter and stronger than composites made with ordinary carbon fibres. They do, however, offer possibilities for making lighter cars and aircraft .
More than 20 % of the modern largest passenger airliners are made of composite materials with carbon fibres.
Why use composites?
The biggest advantage composite materials is that they give light , strong design flexibility products , It can be moulded into complex shapes. By choosing an appropriate combination of matrix and reinforcement material, a new material can be made that exactly meets the requirements of a particular application.