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MEC207 > Composites 2 > Flashcards

Composites 2 Flashcards

1
Q

What must the fibre and matrix be maintained at throughout the process and part?

A

The correct shape, temp and pressure

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2
Q

What must be considered about reinforcements in processing? (6)

A 
Type: fibres/particulates
Continuous or discontinuous 
Random or oriented 
Sizing, coupling agent, surface treatment 
Fibre volume fraction 
Safety
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3
Q

What must be considered about the matrix in processing? (9)

A 
Thermoset/thermoplastic
Shrinkage
Moisture 
Reinforcement compatibility 
Additives, fillers
Void volume fraction
Reaction chemistry (curing factors)
Viscosity, gelation time (how long before setting) 
Safety
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4
Q

What must be considered about the component in processing? (4)

A

Size, thickness, cross-section, curvature
Surface finish
Dimensional tolerance
Holes/fixings/strong points/inserts

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5
Q

What must be considered about cost in processing? (5)

A 
Equipment 
Moulds
Materials
Labour
Energy
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6
Q

What must be considered about the process itself? (5)

A 
Automation, rate
Machining, trimming, static electricity build up
Heat transfer
Mould fabrication
Reinforcement draping
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7
Q

What is wet lay-up and what are the two kinds?

A

Liquid resin is applied to reinforcement layer as part of the lay-up procedure
Hand (manual) lay-up
Spray lay-up

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8
Q

What is the process of hand lay-up?

A 
Apply release agent to mould
Apply gel coat to mould (surface finish, protection)
Lay fibre mat into mould
Apply prepared matrix to mat, work in 
Repeat until desired thickness
Cure
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9
Q

How can matrix be worked in in hand lay-up?

A

Stipple with a brush (contact)

Roll with roller (consolidate)

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10
Q

Give a brief overview of hand lay-up

A

Fibre/fabric mats laid down into one sided mould and manually infused with resin

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11
Q

What curing temperatures are used in hand lay-up and why?

A

Room temp: cheaper

High temp: more expensive but better properties

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12
Q

What curing pressures are used in hand lay-up and why?

A

Vacuum bag improves consolidation

Vacuum bag + extra pressure gives best results

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13
Q

Which materials are usually used in hand lay-up?

A

Any, most most common is glass fibre/unsat polyester

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14
Q

Applications of hand lay-up

A

Automotive (shells, hulls)
Construction parts
Pipes, storage tanks
Bath tubs/showers

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15
Q

Advantages of hand lay-up

A 
Cheap
Versatile
Simple
Good for prototypes/short runs
Simple moulds (if not applying pressure)
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16
Q

Disadvantages of hand lay-up

A 
Poor properties
Labour intensive
Relatively slow
Quality constancy varies
One moulded surface 
Safety issues
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17
Q

What is the process of spray lay-up?

A

Chopped glass fibre and resin is sprayed onto the mould and rolled

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18
Q

How does spray lay-up compare to hand lay-up?

A

Reduced labour cost but more expensive equipment

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19
Q

Disadvantages of spray lay-up

A

Messy
Short fibres
Poor mechanical properties

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20
Q

Advantages of spray lay-up

A

Better quality consistency

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21
Q

What is the fibre volume fraction for hand layup?

A
  1. 2-0.3 for mats

0. 4 for fabrics

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22
Q

What is the fibre volume fraction for spray layup?

A

0.2-0.3

23
Q

What is the process of compression moulding?

A

A moulding compound is forced to take the shape of a two part cavity mould
Apply weighted charge to mould
Close mould and apply heat to cure

24
Q

Give details on the mould in compression moulding

A

Moulds held in hot press

Press and mould are VERY EXPENSIVE

25
Q

How does compression moulding work?

A

Curing is through the mould

High pressure compresses voids

26
Q

What materials are compression moulding used with and why?

A

Putty-like material: 25% unsat polyester, 20% chopped E glass fibre, 55% filler (CaCO3 or MgO)- very cheap
Sheet moulding compound (SMC)- reduced reorientation of fibres
Bulk moulding compound (BMC)

27
Q

Applications of compression moulding

A

Automotive (bodies, spoilers, interior panels)
Containers
Electrical housings

28
Q

Advantages of compression moulding

A 
Any geometry (without overhangs/undercuts)
Versatility
Two good surfaces 
Can be automated (but expensive)
Good quality consistency
29
Q

Disadvantages of compression moulding

A

Poor properties (mostly filler)
Can’t mould holes so versatility still limited
Medium capital investment
Size is limited

30
Q

What is the fibre volume fraction of compression moulding?

A

0.1-0.2 (BMC), 0.2-0.3 (SMC)

31
Q

What is liquid moulding a generic term for?

A

When liquid resin is transferred into a closed mould and cured

32
Q

What are the two main types of liquid moulding?

A

Unreinforced resin + dry fibre preform in mould (RTM, VARTM)

Short fibre reinforced resin + empty mould

33
Q

What is liquid moulding an intermediate process in terms of?

A

Cost, volume and properties

34
Q

What materials work with resin transfer moulding (RTM?

A

Any typical fibre/resin combination

35
Q

What is the process of RTM?

A

Place reinforcement in mould and close
Pump liquid resin into mould
Cure

36
Q

How are reinforcements treated in RTM?

A

Hand laid or as a pre-form

Preformed are tightly packed fibres aiming for ff=0.7 (same value as autoclaves)

37
Q

What are the key factors in resin in RTM?

A

Low viscosity

Curing is room or elevated temp- directly through mould or in oven

38
Q

Describe the moulds in RTM

A

2 part rigid cavity

Lower pressures used so cheaper mould materials eg Al

39
Q

Applications of RTM

A

Interior panels, propellers

Construction

40
Q

Advantages of RTM

A 
Versatile
Any size
Good surfaces
Relatively automated (gets more expensive)
Quality consistency very good
41
Q

Disadvantages of RTM

A

Movement of fibres as resin is injected
Medium-large capital investment- must have high runs
Requires low viscosity resins

42
Q

How does vacuum assisted RTM compare to RTM?

A

A vacuum helps draw resin into the mould

43
Q

What is the process of VARTM?

A

Run resin through 1 part open mould until filled

Heating is from one side of mould

44
Q

Advantages of VARTM

A

High quality finish

Inexpensive equipment

45
Q

Disadvantages of VARTM

A 
Finish on only one surface 
Heat from one side of mould 
Lower ff (not bad, just lower than RTM)
Higher void content 
Higher operator skill level
46
Q

What is the fibre volume fraction of RTM?

A

0.5-0.6

Very good

47
Q

What is the fibre volume fraction of VARTM?

A

0.4

48
Q

What are RTM preforms?

A

Dry fibres arranged into correct shape, size thickness and fibre orientation prior to resin injection

49
Q

Describe the purpose of each type of preform

A

Winding: dry filament winding for simple hollow preforms
Weaving: woven fabrics can be stacked
Stitching: woven or non-woven fabrics can be stitched together
Braiding: tubular/more complex hollow preforms
Knitting: complex geometry

50
Q

What effect does crimping have?

A

Introduces stress

51
Q

What is overbraiding?

A

Braid fibres over a reciprocating core

52
Q

What are the pros and cons of overbraiding?

A

Excellent properties
Delamination resistant
Suffers crimping issues
High equipment cost

53
Q

Overbraiding applications

A

High-end: aerospace ie ducts, landing gear

MEC207 (21 decks)

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