A composite material combines two or more distinct constituent materials to produce properties that the constituents cannot achieve as effectively alone. Composites are used because their properties can be tailored for requirements such as high strength, low mass, stiffness, durability, or corrosion resistance.
How a composite works
Most composites contain a matrix and a reinforcement. The matrix surrounds the reinforcement, maintains the product’s shape, protects the reinforcement, and transfers forces to it. The reinforcement, often fibres or particles, usually provides much of the strength or stiffness.
The constituents remain physically distinct within the finished material. This distinguishes a composite from an alloy, in which elements are combined at the atomic level.
| Composite | Constituents and their functions | Reason for use |
|---|---|---|
| Glass-fibre-reinforced polymer (GFRP) | Polymer matrix with glass-fibre reinforcement | Strong, lightweight, corrosion-resistant, and relatively economical |
| Carbon-fibre-reinforced polymer (CFRP) | Polymer matrix with carbon fibres | Very high strength-to-weight and stiffness-to-weight ratios |
| Reinforced concrete | Concrete matrix with steel reinforcement | Concrete resists compression; steel resists tension |
| Plywood | Timber veneers bonded with alternating grain directions | Improved dimensional stability and strength in multiple directions |
Designers select composites to create synergistic properties, meaning the combined performance is better suited to the design specification than either constituent alone. For example, CFRP is used in bicycles and aircraft because reducing mass can improve efficiency while the fibres maintain strength and stiffness.
A common misconception is that composites are always stronger than conventional materials. Their performance depends on reinforcement type, fibre orientation, matrix choice, manufacturing quality, loading direction, cost, repairability, and end-of-life impact.
IB exam technique
For A3.1 Material classification and properties, define a composite, identify its matrix and reinforcement, and link each constituent to a specific property. When explaining selection, connect properties directly to a product requirement rather than merely stating that the material is “better.”