Composites
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What are the two components of a composite?
• The reinforcement - The matrix
What is the role of the matrix
The matrix is a continuous phase. To protect the reinforcement and give environmental tolerance
What is the role of the reinforcement?
The reinforcement is a dispersed phase. Supports structural load. Gives the composite component its shape and determines the surface quality
What materials are most commonly used in the matrix phase?
The matrix binds the fibre reinforcement. Bulk materials e.g. metals, ceramics, polymers
What materials are most commonly used in the reinforcement
Fibres and other particulates e.g. glass, carbon, boron, ceramic, metallic, silicon carbide
What ways can the fibres be oriented?
• Short fibres 2. Aligned fibres such as in “Advanced composites”. This is unidirectional reinforcement.
Methods of reinforcing in composite materials
Particles Short or long fibres Flakes Layers of unidirectional continuous fibres are assembled into a laminate structure
Three examples of reinforcing fibres
Glass fibres, carbon fibres, aramid fibres
Properties of glass fibres
Cheap, properties vary from low to medium, good impact properties, low electrical conductivity, higher failure strains than carbon
Properties of carbon fibres
Lightweight, high performance, high strength, high electrical and thermal conductivity, relatively brittle
Properties of aramid fibres
High tensile strength at low weight, high toughness, high modulus, flame and cut resistance.
Application of aramid fibres
Anti-bullet and stab-proof vests
The properties of composites
They have intermediate strength. Composites have similar strengths to alloys but a lower density. High specific modulus and high specific strength for their normalised density
Rank the reinforcement fibre, polymer and polymer matrix composite in terms of strength
Polymer - Polymer matrix - Reinforcement Fibre
Which classes of polymers are used for composites?
• Thermosetting polymers 2. Thermoplastic polymers
Compare the thermosetting and thermoplastic polymers used in composites?
Thermosetting polymers have lower viscosities in the uncured state and require lower pressures to mould Thermoplastic polymers have higher viscosities and these require higher pressures to mould.
The stages in the chemical curing of thermoset resins
Monomers–> Viscosity increase (liquid) —> Gelation (Sol and Gel) —> Vitrifcation (Glass)
Describe the chemical curing of thermoset resins
Combination of heat , pressure and time needed to cure the resin. This is called a “Cure Cycle” - takes a long time to process structures.
Give an example of thermoset resins
Polyester (cheap and widest use), phenolics (fire resistant)
Give examples of thermoplastic polymers
Polypropylene - cheapest, mainly with glass fibres and nylons - industrial uses - some with carbon fibres
Applications of composites - aircraft and aerospace
Space (antenna, satellite dishes etc.) Military Aircraft (wings, fuselage etc.) Civil Aircraft ( control surfaces, floor beams, empennage) New civil aircraft ( wings, fuselage)
Specific components in aerospace that are composites
CF/ epoxy spoilers Quartz fibre radome
Aircraft with composites
A-380 “Super - Jumbo” Jet including horizontal tail plane, J-nose, outer flaps, vertical tail plane Boeing 787 - fuselage, composite materials allow bigger windows, higher cabin pressure, higher humidity
Advantages of composites against aluminium in aircraft
Composites have a similar strength to aluminium and a lower density. This then increases fuel efficiency The composites don’t fatigue or corrode like aluminium Composite design also lasts longer than aluminium so there are fewer maintenance and service costs Composites have a low thermal conductivity which makes them ideal for doors and windows which must withstand severe weather conditions.