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Materials Science and Engineering > Composites > Flashcards

Composites Flashcards

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1
Q

What are the two components of a composite?

A
  • The reinforcement

- The matrix

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2
Q

What is the role of the matrix

A

The matrix is a continuous phase. To protect the reinforcement and give environmental tolerance

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3
Q

What is the role of the reinforcement?

A

The reinforcement is a dispersed phase. Supports structural load. Gives the composite component its shape and determines the surface quality

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4
Q

What materials are most commonly used in the matrix phase?

A

The matrix binds the fibre reinforcement. Bulk materials e.g. metals, ceramics, polymers

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5
Q

What materials are most commonly used in the reinforcement

A

Fibres and other particulates e.g. glass, carbon, boron, ceramic, metallic, silicon carbide

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6
Q

What ways can the fibres be oriented?

A
  1. Short fibres

2. Aligned fibres such as in “Advanced composites”. This is unidirectional reinforcement.

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7
Q

Methods of reinforcing in composite materials

A

Particles
Short or long fibres
Flakes
Layers of unidirectional continuous fibres are assembled into a laminate structure

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8
Q

Three examples of reinforcing fibres

A

Glass fibres, carbon fibres, aramid fibres

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9
Q

Properties of glass fibres

A

Cheap, properties vary from low to medium, good impact properties, low electrical conductivity, higher failure strains than carbon

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10
Q

Properties of carbon fibres

A

Lightweight, high performance, high strength, high electrical and thermal conductivity, relatively brittle

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11
Q

Properties of aramid fibres

A

High tensile strength at low weight, high toughness, high modulus, flame and cut resistance.

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12
Q

Application of aramid fibres

A

Anti-bullet and stab-proof vests

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13
Q

The properties of composites

A

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

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14
Q

Rank the reinforcement fibre, polymer and polymer matrix composite in terms of strength

A

Polymer - Polymer matrix - Reinforcement Fibre

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15
Q

Which classes of polymers are used for composites?

A
  1. Thermosetting polymers

2. Thermoplastic polymers

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16
Q

Compare the thermosetting and thermoplastic polymers used in composites?

A

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.

17
Q

The stages in the chemical curing of thermoset resins

A

Monomers–> Viscosity increase (liquid) —> Gelation (Sol and Gel) —> Vitrifcation (Glass)

18
Q

Describe the chemical curing of thermoset resins

A

Combination of heat , pressure and time needed to cure the resin. This is called a “Cure Cycle” - takes a long time to process structures.

19
Q

Give an example of thermoset resins

A

Polyester (cheap and widest use), phenolics (fire resistant)

20
Q

Give examples of thermoplastic polymers

A

Polypropylene - cheapest, mainly with glass fibres and nylons - industrial uses - some with carbon fibres

21
Q

Applications of composites - aircraft and aerospace

A

Space (antenna, satellite dishes etc.)
Military Aircraft (wings, fuselage etc.)
Civil Aircraft ( control surfaces, floor beams, empennage)
New civil aircraft ( wings, fuselage)

22
Q

Specific components in aerospace that are composites

A

CF/ epoxy spoilers

Quartz fibre radome

23
Q

Aircraft with composites

A

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

24
Q

Advantages of composites against aluminium in aircraft

A

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.

25
Q

Disadvantages of composites against aluminium in aircraft

A

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

26
Q

Applications of composites - automotive

A

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

27
Q

Applications of composites - wind energy

A

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

28
Q

Other application of composites in renewable energy

A

Composites in tidal turbines

29
Q

Describe the process of resin transfer moulding

A
  1. Create the preform - matrix already in the shape of the finished product into which the resin will be injected.
  2. Once preform of reinforcement is created, it is packed into mold cavity that ahs shape of desired part.
  3. Mold cavity is closed and clamped, mold cavity allows control of part thickness
  4. Catalysed low viscosity is pumped into heated mold under pressure and the mold is filled.
  5. Curing starts –> Resin to rigid plastic
30
Q

How does vacuum assisted resin transfer moulding differ?

A

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.

31
Q

What is high pressure resin transfer moulding?

A

HPRTM is being used to produce the new series of i-cars. injection moulded thermoplastic skins for toughness.

Materials Science and Engineering (6 decks)

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