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Mod 6 > Composites > Flashcards

Composites Flashcards

1
Q

What are the elements that make up a composite material?

A

Matrix

Reinforcing material

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2
Q

What are the advantages of composites?

A

High strength to weight ratio
Reduces need for fasteners
Reduction of wear
Corrosion resistance

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3
Q

What are the disadvantages of composites?

A

Very expensive

Not easy to repair- needs specialists normally

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4
Q

What is Nomex?

A

Wholly aromatic polymer with high thermal stability, flame resistance, and radiation resistance

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5
Q

What is fibreglass?

A

Small strands of silica that is spun and woven into a cloth.

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6
Q

What are the two types of fibreglass that are commonly used?

A

E-glass, high resistance

S-glass, very high tensile strength

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7
Q

What makes fibreglass different to most other fibres?

A

Weighs more

Less strength

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8
Q

Why is fibreglass commonly used?

A

Wide range of applications

Low cost compared to other composites

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9
Q

Properties of fibreglass

A 
Low density
High strength
High fracture toughness
Smooth and circular cross section
Good wet out
Doesn’t absorb water
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10
Q

What is aramid short for?

A

Aromatic-polyamide

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11
Q

What is aramid?

A

Yellow fibres that are light weight and have a high tensile strength

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12
Q

What is Kevlar?

A

A man made organic fibre with properties such as high tensile strength and flexibility.

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13
Q

What company has developed Kevlar, Aramid, and Nomex?

A

DuPont

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14
Q

What are the main disadvantages of Kevlar?

A 
Easily absorbs water
Sensitive to the environment
Poor compressive properties
Difficult to cut- specialist tooling
Sensitive to UV- turns brown as its effected
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15
Q

What is the positive characteristics of carbon fibre?

A 
High strength
High E modulus
Low density
High resistance to temperature
Longitudinal thermal expansion almost 0
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16
Q

What are the negative effects of carbon fibre?

A

Electrically conductive
Will wear out high speed cutters quickly
Low fracture resistance

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17
Q

What is the difference between Kevlar and graphite?

A

Graphite has more compressive strength, but is more brittle

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18
Q

What is the downside to graphite?

A

Corrosive when in bonded with aluminium so a layer of fibreglass is needed

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19
Q

What is the warp of a fabric?

A

Length off the roll.

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20
Q

What is the weft/fill?

A

Dimension perpendicular to the warp.

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21
Q

What is the selvage edge?

A

Edge parallel to the warp that keeps the edge from unraveling

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22
Q

What is the bias?

A

Runs at 45 degrees to the warp, is what the fabric is manipulated on

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23
Q

What are unidirectional fibres?

A

Fibres run along the warps with occasional transverse threads to hold it together

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24
Q

What are bidirectional fibres?

A

Fibres run in two directions, typically more fibres on the warp for increased strength in that direction

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25
Q

What is are mats?

A

Chopped areas of fabric with little strength than unidirectional or bidirectional fibres

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26
Q

why are fabric weaves better?

A

More resistant to breakout,delamination, and damage compared to unidirectional.

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27
Q

What are the two types of resins?

A

Thermoset

Thermoplastic

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28
Q

What is a thermoset resin?

A

Heated to form then permanently retain that shape when cooled, this is mainly used in structural composites

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29
Q

What is a thermoplastic resin?

A

A resin that can be reformed by heating

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30
Q

What type of resin is an epoxy resin?

A

Thermoset

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31
Q

What are prepreg fabrics?

A

Fabrics that are pre impregnated with resin, they are kept in large rolls and need to be stored in a freezer.

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32
Q

What are the main types of core materials?

A

Foam
Honeycomb
Honeycomb core

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33
Q

What are the types of honeycomb fabrication?

A

Corrugation

Expansion

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34
Q

What are the main ways to dissipate charge?

A

Flame spray
Bonding jumpers
Aluminium wires woven into top layers
Aluminium foil bonded to top area

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35
Q

Why is paint used?

A

To seal against moisture

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36
Q

What is MSDS?

A

Material safety data sheets

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37
Q

What information is found on an MSDS?

A

Health precautions
Flammability
Ventilation requirements
Information for health professionals

38
Q

What is polymerisation?

A

A chemical reaction that creates a long chain of double bonded molecules

39
Q

Is there any by products made from polymerisation?

A

No

40
Q

What is polycondensation?

A

A chemical reaction between 2 similar of dissimilar basic units with at least 2 functional groups.

41
Q

What is polyaddition

A

Reaction of 2 different types of molecules when reactive groups are brought together.
No byproducts are produced

42
Q

What are some key polycondensation polymers?

A

Polyester
Polyamides (nylon)
Phenol-formaldehyde (Bakelite)

43
Q

What are some key polyaddition polymers?

A

Epoxies

Polyurethanes

44
Q

What are the benefits of adhesives?

A

Moisture and corrosion resistant
Eliminate need for fasteners
Distribute stress at the bonding points

45
Q

What are the main types of adhesives?

A 
Synthetic
Thermosetting
Thermoplastic resins
Elastomeric
Contact
Solvent
Dispersion
Film
Foaming adhesive films
46
Q

What are thixotropic agents?

A

Thickening agents to the resins

47
Q

What are the 2 common types of thixotropic agents?

A

Aerosil

Micro-ballons

48
Q

How should a resin be mixed?

A

In a wax free container with the accelerator added to the base

49
Q

What will happen to a resin when a catalyst is added to it?

A

The pot life is reduced

50
Q

Where are thermoplastic resins very unlikely to be used?

A

In composite structures

51
Q

What are the two main thermosetting resins used for structures and why?

A

Epoxy- external components, good mechanical strength

Phenolic- cabin due to low toxicity and fire resistance

52
Q

How can the mechanical properties of plastics be improved?

A

By bonding fibres to the plastic

53
Q

What are the key features of a good polymer?

A

Easy to use
Coat every fibre and bond to them
Have the correct mechanical properties

54
Q

What are the 4 most common resins in fibre reinforced polymers?

A

Polyester
Epoxy
Vinyl Ester
Phenolic

55
Q

What must never be done with a catalyst for a resin?

A

Mix accelerator and catalyst to avoid an exothermic reaction

56
Q

What are the disadvantages of epoxy resin?

A

Low pot and shelf life
Moderate to high costs
Toxicity

57
Q

What are the positive characteristics of epoxy resins?

A 
Low shrinkage when cured
High adhesion
Great cohesive strength when cure- can cause stress
100% solid- no byproducts
Resistance to moisture and adhesives
58
Q

What are the positive factors for surface wetting?

A

Removal of surface contamination
Viscosity reduction through heat or solvent
Time
Pressure

59
Q

What factors have negative effects on surface wetting?

A 
Leaving fingerprints
Residues left on surface
Incorrectly aligned glue lines
Low temperatures
Incorrect pretreatment
60
Q

What are the important aspects for durable adhesives?

A

Mechanical hooking

Surface wettting

61
Q

What are the pretreatment procedures for bonding?

A

Degrease only
Degrease, abrade, and remove loose particles
Degrease and chemically pretreat

62
Q

What are the aim contamination causes for pretreatment?

A 
Fingerprint
Cloths not fully clean
Poor degreasing
Contaminated abrasives
Chemical solutions
Other work in bonding area
63
Q

Where would repair procedures be for structure?

A

SRM (structure repair manual)

64
Q

What are the 3 damage levels?

A

Allowable
Repairable
Not repairable

65
Q

What would be classed as skin not perforated damage?

A 
Abrasion
Scratches
Gouges
Dents
Nicks
Debonding
Delamination
66
Q

What is classed as skin perforated damage?

A

Lightning strike
Holes
Impact by foreign object

67
Q

What is BVID?

A

Barely visible impact damage

68
Q

Is water absorption allowable?

A

No

69
Q

What causes chemical degradation?

A

Accidental contact with aggressive chemical products

70
Q

How are dents and depression inspected?

A

NDT

71
Q

What are the different types of NDT?

A 
Tap test
Visual
Radiography
Thermography
Holography
Bond tester
Acoustic emissions
72
Q

What is holography?

A

Overlaying an image of what the surface should look like on top of the actual surface. Gets inspection done fast

73
Q

What are the disadvantages of holography?

A

Tedious to set up

Difficult to get a good display of the overlay

74
Q

What is an ultrasonic NDT?

A

Ultrasonic waves are transmitted onto the structure, which then bounces off and returns to the receiver

75
Q

Why is ultrasonic used?

A

Quick

Not expensive

76
Q

What waves are used for radiography?

A

X-rays

Gamma rays

77
Q

How does radiography work?

A

By creating a photographic image from the em rays onto the film behind the area being tested

78
Q

What are the 3 types of repairs?

A

Temporary
Permanent Cosmetic
Permanent structural

79
Q

How should all surface protection be removed?

A

By mechanical means only

80
Q

How can chemical strippers affect any composite surface?

A

It can cause the resin to deteriorate

81
Q

What is scarfing?

A

The removal of layers one at a time with mechanical sanding tools

82
Q

What should be done to damaged core material?

A

The damaged core must be removed fully and replaced with a suitable filler material to restore the full strength

83
Q

What is wet lay up?

A

The application of multiple layers of hand pre-impregnated fabrics to restore the damaged skin

84
Q

What is important to remember with resins and catalysts?

A 
Mix properly for full strength
Weigh each part of the resin first
Advanced composites are very exacting
Use a wax free container
3-5 minutes mixing usually
Don’t mix too fast
Do a drop test for the the viscosity
85
Q

What is pot life?

A

Amount of time you have to work with the resin

86
Q

What is shelf life?

A

The amount of time a resin can be stored in an unopened container

87
Q

What is resin rich and how does it affect a composite?

A

There is too much resin

Increases the weight and makes it brittle

88
Q

What is resin starved and how does it affect the composite?

A

Not enough resin

Can’t transfer stresses to the fibres

89
Q

What should be done when working resins into fibres?

A

Ensure that the weave is not distorted

90
Q

What are the two lay up methods?

A

Wet application

Pre-preg

91
Q

What is vacuum bagging used for?

A

To hold parts such as thermo couple in lace during curing
To use atmospheric pressure to consolidate layers in a repair
To produce a desired surface finish
To remove trapped air or gasses during curing

Mod 6 (8 decks)

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