Composite materials
A composite materialMaterial made from two or more different materials with contrasting properties. consists of two or more materialsThings that are used, sometimes to make other things. with different propertiesThe characteristics of something. In chemistry, chemical properties include the reactions a substance can take part in. Physical properties include colour and boiling point.. They are combined to produce a material with improved properties. This means that they have a broad range of uses.
Most composite materials have two components:
- the reinforcementFibres or other material that make up the bulk of a composite material.
- the matrixThe substance that binds the reinforcement together in a composite material., which binds the reinforcement together
The table shows some examples of composite materials.
| Composite material | Reinforcement | Matrix |
| Reinforced concrete | Steel | Concrete |
| Fibreglass | Glass fibres | Polymer resin |
| Carbon fibre reinforced polymer | Carbon fibres | Polymer resin |
| Chipboard | Wood chips | Resin glue |
| Composite material | Reinforced concrete |
|---|---|
| Reinforcement | Steel |
| Matrix | Concrete |
| Composite material | Fibreglass |
|---|---|
| Reinforcement | Glass fibres |
| Matrix | Polymer resin |
| Composite material | Carbon fibre reinforced polymer |
|---|---|
| Reinforcement | Carbon fibres |
| Matrix | Polymer resin |
| Composite material | Chipboard |
|---|---|
| Reinforcement | Wood chips |
| Matrix | Resin glue |
It is often possible to separate the reinforcement from the matrix by physical processes. For example, concrete can be broken up using machinery. This is one stage in recycling the components of concrete.
Reinforced concrete
The properties of concrete can be improved by reinforcing it with steel rods or mesh. The compressive strengthA measure of how well a material resists being crushed when a force is applied. of concrete is higher than its tensile strengthThe tension a material can withstand without breaking., but the tensile strength of steel is higher than its compressive strength. The combination of the two creates a material that is strong in tension and in compressionBeing squashed.. This allows reinforced concrete to be strong and slightly flexible, which is important when constructing large buildings and structures.
Fibre reinforced plastics
Fibres are embedded in a polymer matrix. The fibres can be made of glass (fibreglass), aramid (Kevlar) and carbon (graphiteA form of pure carbon in which all the atoms are bonded to three others in giant sheets which can slide over each other.). These composites are often used for sporting equipment such as tennis rackets and hockey sticks.
The fibresLong, thin strands. in these composite materials have a low densityA measure of compactness and the ratio of mass to volume. It is usually measured in kilograms per metre cubed (kg/m3) or grams per centimetre cubed (g/cm3).. They are strong in tensionPulling force exerted by each end of an object such as a string or rope., so they are not easily stretched, but they are flexible. The polymer resinRaw plastic, especially when in semi-liquid form., which binds the fibres together, is not strong but it is stiff. The composite materials show a combination of these properties. They are strong, stiff and lightweight.