Mats 301 Flashcards
What is a composite?
A material that consists of two or more constituent parts. The material is different to its individual components, but they remain separate and distinct.
Dispersed phase (composites)
Particles or fibres.
Matrix phase (composites)
Continuous phase that surrounds the dispersed phase.
Glass fibre production process
- Liquid glass is formed by blending quarry products and heating the mixture in a furnace at very high temp.
- Liquid glass is passed through a platinum bushing with very fine holes.
- The resulting fibres are cooled using water spray, then drawn together using a ‘size’ to provide filament cohesion, and to protect the glass from abrasion.
Three categories of glass fibre
- E-glass (electrical) - lower alkali content, reasonably good tensile and compressive strength.
- C-glass (chemical) - resistant to chemical attack, used in pipes and tanks.
- S-glass - higher tensile strength and modulus than E-glass, achieved by using smaller fibre diameter.
Five advantages of using glass fibres
- Low cost
- Relatively high strength
- Heat resistant
- Insensitive to moisture
- Electrical insulator
Three disadvantages of using glass fibres
- Low stiffness
- Attacked by acids
- Relatively poor fatigue resistance
Aramid fibres (kevlar) production process
- Solid fibres are extruded from a liquid chemical blend using a spinneret.
- Fibres are washed in a neutralising bath, then dried and stretched at 500°C to improve their molecular alignment.
Three advantages of aramid fibres
- High specific tensile strength
- High impact and abrasion resistance
- High fatigue resistance
Three disadvantages of aramid fibres
- Poor in compression
- Attacked by acids and UV light
- Low temperature resistance
Carbon fibre production process
- Produced by the controlled oxidation, carbonisation and graphitisation of carbon-rich organic precursors which are already in fibre form, the most common being PAN.
- PAN fibres are greatly stretched to improve molecular alignment, then oxidised in air at 300°C.
- They’re then carbonised at 1500°C to improve crystallinity (nitrogen released) then finally graphitised by heating and stretching at 3000°C
Three advantages of carbon fibres
- High strength and modulus
- High creep and fatigue resistance
- Good energy absorption
Three disadvantages of carbon fibres
- High cost
- Poor impact resistance
- Electrical conductor
Polyester fibres
Low density fibre with good impact resistance, but low modulus.
Polyethylene fibres
Drawing procedure orientates the molecules, giving a very high tensile strength.
Quartz fibres
Very high silica version of glass fibres, with much higher mechanical properties and excellent resistance to high temperatures.
Boron fibres
Carbon or metal fibres coated with a layer of boron. Strong, stiff and light.
Ceramic fibres
Very high temperature resistance, but low impact resistance.
Natural fibres
Fibrous plant material, e.g. coconut.
Five functions of the matrix phase
- Bind fibres together
- Transmit applied load to fibres
- Add ductility/toughness to the composite
- Prevent propagation of cracks
- Protect the fibres from damage
Resin
Refers to a man-made polymer
Resin criteria
The resin must be able to deform to at least the same extent as the fibre, otherwise the full mechanical properties of the fibre component won’t be achieved. Must also have good environmental and stress cycling resistance.
Toughness
The area under a stress-strain curve. It’s a combination of strength and ductility.
Why is high adhesion between resin and fibres important?
To ensure that the loads are transferred efficiently, and to prevent cracking or fibre/resin de-bonding when stressed.