Composites

Composites

When two or more materials are combined by bonding, a composite material is formed.
A composite has improved mechanical, functional and aesthetic properties
Glass Reinforced Plastic (GRP)
1. Made of Polyester or epoxy resin reinforced by fine fibres of glass in the form of a woven matting.
2. By combining the 2 materials GRP has both compressive and tensile strength.
  1. The plastic resins are strong in compressive strength but relatively weak in tensile strength.
  2. Glass fibres are very strong in tensile strength, but have no compressive strength.
3. The resin exists in a liquid form and has a catalyst or hardener added to become a solid.
4. The glass fibre strands provide the basic structure, while the resin with its additives, bonds the fibres together and provides a lightweight rigid structure.
5. The extremely smooth GRP finish seen on boats and some cars is achieved by a highly polished surface on the mould used and careful application of the first layer, known as the gel coat. The glass matting which is laid on top of the gel coat to provide the basic structure leaves a very rough finish.Therefore, one surface of GRP is highly polished whilst the other is extremely rough.
6. Applications
  1. Rotor blades of wind turbines
  2. Canoes
  3. fish ponds
  4. vehicle bodies
  5. fairground rides
7. Advantages
  1. Excellent strength to weight ratio
  2. Resistant to corrosion
  3. Water resistant
  4. Ideal for external shell structures
  5. Can be easily repaired
  6. Wide range of colours as pigments can be added to resin
8. Disadvantages
  1. Expensive material
  2. Specialised manufacturing process
  3. High quality mould needed
Carbon fibre
1. This carbon composite is made up of carbon fibres, which take tensile loads, set into a polymer resin matrix that takes the compressive loads
2. Carbon fibre is a filament material incorporating thousands of filaments that are woven to form a fabric. However, this fabric only has strength in tension.
3. So the fabric is placed in different directions to cover different tensile loads in all directions.
4. Carbon fibres are much stronger than GRP and are ideal for high performance structural applications in aircraft, sports equipment and F1 racing car manufacture.
5. Applications
  1. Sports Equipment
    1. Bike frames and wheels
    2. Fishing rods
    3. tennis racquets
  2. Aircraft and vehicle components
6. Advantages
  1. Excellent strength to weight ratio
  2. Better tensile strength then steel alloys
  3. Can be engineered to be fabric orientated in different directions to provide strength in specific areas of construction
  4. Can be formed into complex and aerodynamic structures
7. Disadvantages
  1. Very expensive material
  2. Only available in black
  3. Highly specified manufacturing processes needed
  4. Cannot be easily repaired as structure loses integrity
  5. Cannot be easily recycled
Medium Density Fibreboard (MDF)
1. Made from wood waste in the form of wood chips, which are subjected to heat and pressure in order to soften the fibres and produce a fine, fluffy and lightweight pulp. The pulp is then mixed with a synthetic resin adhesive to bond the fibres and produce a uniform structure and heat pressed to form a fine textured surface.
2. MDF can be worked like wood, with the added advantage that it has no grain. It also finishes well with is variety of surface treatments and is available with a veneered surface for decorative effect.
3. Advantages
  1. Less expensive than natural timbers
  2. Available in large sheet sizes and range of thickness
  3. Isotropic (no grain), so no tendancey to split
  4. Consistent strength in all directions
4. Disadvantages
  1. Heavier (the resins are heavy)
  2. Requires appropriate finishes to seal surface fibres
  3. Swells and breaks when waterlogged
  4. Warps or expands if not sealed
  5. Contains urea-formaldehyde which may cause eye and lung irritation when cutting and sanding
  6. Dulls blades more quickly than many woods
5. Applications
  1. Flat pack furniture
  2. General joinery work
  3. moulds for forming processes

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	Created by Poppy Venables over 11 years ago