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This lesson covers composite materials — materials made by combining two or more different materials to produce a new material with enhanced properties. Composites are an important topic in AQA GCSE Design and Technology (8552), Section 3.1.3.
A composite is a material made from two or more constituent materials with significantly different physical or chemical properties. When combined, they produce a material with characteristics different from — and usually superior to — the individual components.
Most composites consist of:
| Component | Role | Example |
|---|---|---|
| Matrix | Binds the reinforcement, transfers loads, protects fibres | Polyester resin, epoxy resin, cement |
| Reinforcement | Provides strength, stiffness or other mechanical properties | Glass fibres, carbon fibres, steel bars, wood particles |
The diagram below shows how the matrix and reinforcement combine to form four common composites studied in AQA D&T:
graph TD
M["Matrix\n(binder)"] --> C["Composite Material"]
R["Reinforcement\n(strength)"] --> C
C --> GRP["GRP\n(polyester + glass fibres)"]
C --> CFRP["CFRP\n(epoxy + carbon fibres)"]
C --> CON["Concrete\n(cement + sand/gravel + steel rebar)"]
C --> MDF["MDF\n(urea formaldehyde + wood fibres)"]
GRP (commonly called fibreglass) is a composite made from glass fibres embedded in a polyester resin matrix.
| Property | Detail |
|---|---|
| Strength-to-weight ratio | Excellent — strong but lightweight |
| Corrosion resistance | Does not rust or corrode; unaffected by seawater |
| Mouldability | Can be formed into complex shapes using moulds |
| Electrical insulation | Does not conduct electricity |
| Durability | Resistant to weathering and UV degradation |
| Application | Why GRP Is Used |
|---|---|
| Boat hulls | Lightweight, corrosion-resistant, can be moulded to complex curves |
| Car body panels | Lightweight (improves fuel efficiency), resistant to rust |
| Roofing sheets | Translucent panels allow light through; waterproof |
| Storage tanks | Chemical resistance; does not corrode |
| Playground equipment | Tough, weatherproof, low maintenance |
AQA Exam Tip: GRP is one of the most commonly examined composites. Remember: matrix = polyester resin, reinforcement = glass fibres. A common exam question asks you to name the two components of GRP and explain the role of each.
CFRP is a composite made from carbon fibres embedded in an epoxy resin matrix. It is one of the highest-performance engineering materials available.
| Property | Detail |
|---|---|
| Strength-to-weight ratio | Outstanding — stronger than steel at a fraction of the weight |
| Stiffness | Very high — resists bending and flexing |
| Fatigue resistance | Excellent — performs well under repeated loading |
| Corrosion resistance | Does not rust or degrade in most environments |
| Thermal stability | Retains properties at elevated temperatures |
| Application | Why CFRP Is Used |
|---|---|
| Formula 1 cars | Monocoque chassis provides extreme strength with minimal weight |
| Aircraft (Boeing 787, Airbus A350) | Reduces aircraft weight by up to 20%, saving fuel |
| High-end bicycles | Ultra-lightweight frames for racing |
| Tennis rackets | Stiff, lightweight frames for power and control |
| Prosthetic limbs | Strong, light, comfortable for the user |
| Disadvantage | Explanation |
|---|---|
| Expensive | Carbon fibre costs £10–50+ per kg; steel costs ~£0.50/kg |
| Brittle failure | CFRP can shatter rather than deform — no warning before failure |
| Difficult to recycle | Epoxy resin matrix does not melt; recycling requires energy-intensive processes |
| Labour-intensive manufacture | Laying up carbon fibre by hand is skilled, slow work |
Concrete is a composite made from cement, sand (fine aggregate), gravel (coarse aggregate) and water. It is the most widely used construction material in the world.
| Component | Role |
|---|---|
| Cement | Binder — reacts with water to form a hard paste |
| Sand | Fine aggregate — fills gaps between gravel particles |
| Gravel | Coarse aggregate — provides bulk and compressive strength |
| Water | Activates the cement (hydration reaction) |
| Property | Detail |
|---|---|
| Compressive strength | Excellent — withstands heavy loads pushing down |
| Tensile strength | Poor — weak when pulled or bent (this is why steel reinforcement is added) |
| Durability | Very long-lasting; resistant to fire and weathering |
| Mouldability | Can be poured into moulds of any shape |
| Cost | Relatively cheap and abundant raw materials |
Plain concrete cracks under tension (pulling forces). To overcome this, steel reinforcing bars (rebar) are embedded in the concrete. The steel resists tension while the concrete resists compression — together they form a much stronger material.
AQA Exam Tip: Remember that concrete is strong in compression but weak in tension — this is why it is reinforced with steel. This fact appears frequently in exam questions.
MDF is a composite made from wood fibres (from softwood waste) bonded together with urea formaldehyde resin under heat and pressure.
| Property | Detail |
|---|---|
| Smooth, uniform surface | No grain pattern — ideal for painting and veneering |
| Easy to machine | Can be cut, routed, drilled and sanded with standard tools |
| Consistent density | No knots, splits or warping |
| Affordable | Cheaper than solid timber |
| Available in large sheets | Standard sheet size: 2440 × 1220 mm |
| Disadvantage | Explanation |
|---|---|
| Swells with moisture | MDF absorbs water and swells permanently — not suitable for outdoor use unless sealed |
| Dust hazard | Fine dust produced during cutting is a health hazard (urea formaldehyde is a carcinogen) — must use dust extraction and a mask |
| Heavy | Denser and heavier than most natural timbers |
| Screws do not hold well | The fibrous structure can crumble; pilot holes and specialist screws are recommended |
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