- Composites mix together two or more materials so that the properties of each material are enhanced and used.
- For example – Adding strands of glass (fibres) to polyester resins, a very tough, rigid, lightweight, material is formed – GLASS REINFORCED PLASTIC – GRP – FIBREGLASS.
Two main groups of composites
1) Fibre Reinforced Composites
- Natural woods
- Polymers mixed with fibres
- GRP – Plastic Laminates – Carbon Fibre
- Elastomers mixes with fibres
- Concretes mixed with fibres
2) Particle Based Composites
- Cermet’s (ceramic & metal)
- Tungsten and Titanium carbide
- Concrete & Tarmac
Wooden Composite Materials
Advantages of man-made boards
- Increased stability against warping
- Equal strength in all directions – unlike natural wood
- Available in large sheets
Fibre reinforced composite materials
- A strong, lightweight and weatherproof material (Drawing below)
- Kevlar has long chain molecules which run parallel along the length of the fibres
Arrangement of Kevlar Fibres
- This makes it very strong.
- Weight for weight Kevlar is x5 stronger than steel
- And is ½ the density of fibreglass
- Kevlar fibres are woven into a ‘cloth’
- Made into protective clothing it works like a net absorbing the force of a football on impact
- Uses include bullet proof vests – skis – helmets – racquets – windsurfing sails – run flat tyres – cut proof gloves
Particle Based Composites
Pre-Tensioned Reinforced Concrete -
- Ordinary concrete is strong under compression. Foundation beams may crack under tension.
- The surface may crack with ordinary reinforced concrete.
- Pre tensioned reinforcing bars will greatly reduce any cracking.
- A mixture of metal & ceramics
- Tungsten Carbide
- A mix of the ceramic tungsten carbide & the metal cobalt
- Used for cutting tools, both hand & machine.
- Keeps its sharp edge very well