A3.1.7 Composites Notes

Composites: Enhancing Material Properties Through Combination

1. Typically made of:
   1. A matrix (binder) that holds everything together
   2. A reinforcement that provides strength or structure

Why Combine Materials?

1. Combine the best properties of different materials
2. Increase strength-to-weight ratio
3. Improve durability, corrosion resistance, or toughness
4. Tailor performance to specific contexts (e.g. sports, aerospace)

Common Composites Materials

Carbon Fibre Reinforced Polymer (CFRP)

1. Matrix: Epoxy resin (lightweight, mouldable)
2. Reinforcement: Carbon fibre (strong, stiff)
3. Result: A strong, lightweight, and durable material used in:
   1. Aerospace structures
   2. Sports equipment (e.g. racing bike frames, tennis rackets)
   3. Car components in high-performance vehicles

Example

Carbon Fibre Reinforced Polymer (CFRP)

• Matrix: Epoxy resin (lightweight, mouldable)
• Reinforcement: Carbon fibre (strong, stiff)
• Result: A strong, lightweight, and durable material used in:
  • Aerospace structures
  • Sports equipment (e.g. racing bike frames, tennis rackets)
  • Car components in high-performance vehicles

Fibre Glass (Glass Fibre Reinforced Plastic – GFRP)

1. Matrix: Polymer resin (e.g. polyester)
2. Reinforcement: Fine glass fibres
3. Result: Lightweight, corrosion-resistant, and flexible, used in:
   1. Boat hulls
   2. Car body panels
   3. Safety helmets and water tanks

Reinforced Concrete

1. Matrix: Concrete (strong in compression)
2. Reinforcement: Steel bars or mesh (strong in tension)
3. Result: High overall strength and structural stability, used in:
   1. Bridges
   2. Buildings
   3. Pavements and tunnels

Kevlar®

1. Matrix: Epoxy or thermoplastic resin
2. Reinforcement: Kevlar fibres (high tensile strength, low weight)
3. Result: Exceptional toughness and impact resistance, used in:
   1. Bulletproof vests
   2. Military helmets
   3. Sports protective gear

Sheet-Based Composites (e.g. Plywood, Laminates)

1. Matrix: Adhesive resin
2. Reinforcement: Layers of wood veneer or fabric
3. Result: Improved stability, reduced warping, and strength in multiple directions, used in:
   1. Furniture and cabinetry
   2. Flooring and construction panels
   3. Skateboards and low-cost boats

Example question

List two mechanical properties that make carbon fibre suitable for a high-performance bicycle frame. (2 marks)

Solution

Answers may demonstrate:
Award [1] for the relevant point, up to [1 max].

Tensile strength: the ability to resist pulling forces without breaking.

Stiffness: the resistance to deformation under applied force.

Compressive strength: the ability to withstand squashing forces without buckling.

Toughness: the ability to absorb energy and resist fracture under impact

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