Composites Flashcards
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.
Disadvantages of composites against aluminium in aircraft
The production of composites is still not fully automated.
Because composites do not break easily - it is hard to tell if the interior has been damaged or not (i.e. difficult to detect structural damage)
High initial cost
Applications of composites - automotive
The BMW i3 and i8
The body is produced by high pressure resin transfer moulding of carbon fibre preforms with epoxy.
Tough and potentially recyclable
Again low density, high strength
Applications of composites - wind energy
Can be used on onshore and offshore wind sites. Blades are made up to 88 m long and made of glass fibre epoxy. The blades for offshore sites are 50 - 60 m. Carbon fibre is used for the stiffness, durability, resistance to fatigue, processed rapidly and cost effectively
Other application of composites in renewable energy
Composites in tidal turbines
Describe the process of resin transfer moulding
- Create the preform - matrix already in the shape of the finished product into which the resin will be injected.
- Once preform of reinforcement is created, it is packed into mold cavity that ahs shape of desired part.
- Mold cavity is closed and clamped, mold cavity allows control of part thickness
- Catalysed low viscosity is pumped into heated mold under pressure and the mold is filled.
- Curing starts –> Resin to rigid plastic
How does vacuum assisted resin transfer moulding differ?
Larger parts can be made with bagging film around a hard tool. With VARTM one of the tools is replaced by a flexible vacuum bag. Vacuum pumps are used to cause the resin to flow through the reinforcement.
What is high pressure resin transfer moulding?
HPRTM is being used to produce the new series of i-cars. injection moulded thermoplastic skins for toughness.
