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CAT B- Mod 6 Materials and Hardware > 6.3 Aircraft Materials Composite > Flashcards

6.3 Aircraft Materials Composite Flashcards

1
Q

Some modern aircraft have what percentage of composite structure?

A

50%

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2
Q

What does the term composite mean?

A

Two or more materials combined to make one much stronger material.

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3
Q

What is the simplest composite composed of?

A

Matrix- bonding
Reinforcing material

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4
Q

What third material can sometimes be added?

A

A core material such as honeycomb

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5
Q

What is the tensile strength of composite compared to steel or ally?

A

4-6x

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6
Q

What is the primary load carrying element of composites?

A

The fibre

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7
Q

What are some of the most common fibres used?

A

Fibreglass
Aramid
Carbon fibre
Boron
Ceramic

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8
Q

Is fibreglass a conductor?

A

Yes

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9
Q

What are the two most common types of fibreglass?

A

E glass
S glass

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10
Q

What is E glass fibreglass?

A

Used for electrical applications due to its huge resistance to flow and is the most common fibreglass.

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11
Q

What is S glass fibreglass?

A

High strength

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12
Q

What does Aramid stand for?

A

Aromatic Polyamide Polymer

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13
Q

What is aramid more widely known as?

A

Kevlar

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14
Q

What are the two most common aramids used?

A

Kevlar 49 and Kevlar 29

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15
Q

Where is aramid used to be a benefit?

A

Areas where impact resistance is req.

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16
Q

What is the density of aramid?

A

1.35g/cm

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17
Q

What is the heat resistance of aramid?

A

260 degrees c

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18
Q

What is the negative of aramids?

A

They can absorb liquids

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19
Q

What happens when aramid is exposed to UV?

A

It turns brown.

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20
Q

What is the differences between aramid and carbon fibre?

A

CF has stronger compressive strength but is more brittle than aramid.

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21
Q

To what metal is carbon fibre galvanic?

A

Aluminium, a sheet of fibreglass must be used to isolate them.

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22
Q

How are boron fibres made?

A

Applying a small amount of vaporised boron onto thin tungsten or carbon wire.

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23
Q

What is the most common use for boron?

A

Used to repair cracked aluminium parts and panels.

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24
Q

Where are ceramic fibres used?

A

High temps up to 1200 degrees c

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25
Q

What is the warp?

A

Lengthwise threads

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26
Q

Is the fabric normally stronger in the warp or weft?

A

Warp

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27
Q

What is the weft?

A

Width

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28
Q

What is the selvedge edge?

A

Tightly woven edge that runs down the warp to prevent unravelling

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29
Q

What happens to the selvedge edge before the fabric is used?

A

It is removed

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30
Q

What is the bias?

A

The diagonal, facilitates manipulation of the fabric

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31
Q

What four different styles of lay up are used?

A

Unidirectional
Bidirectional
Quasi-isotropic
Mats

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32
Q

What are unidirectional fibres?

A

The major fibres run in the warp direction with only occasional traverse threads to hold it together.

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33
Q

What are some examples of unidirectional lay up?

A

Glass fibres
Carbon fibres
Aramid fibres

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34
Q

What are bidirectional fibres?

A

Where the threads run in two directions. Warp normally outnumbers the weft threads.

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35
Q

What is a quasi-isotropic lay up?

A

When the layers are at 45 degrees to the previous layer, such as carbon fibre.

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36
Q

What are some of the most common weaves?

A

Plain
Twill
Satin

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37
Q

What does twill weave provide?

A

Superior wet out

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38
Q

Why are polyester resins not suitable for any loads?

A

Too brittle

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39
Q

What is the modern resin matrix?

A

Epoxy

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40
Q

Resin matrix systems are a type of plastic, what two types are there?

A

Thermoplastic
Thermosetting

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41
Q

What is an example of thermoplastic parts?

A

Windshields and side windows

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42
Q

What is key about anything made in a thermosetting process?

A

It is irreversible.

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43
Q

Are epoxy resins thermosetting or thermolastics?

A

Thermosetting

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44
Q

When unmixed what is the shelf life of epoxy resin?

A

One year at 22 degrees c

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45
Q

What do prepreg fabrics help eliminate?

A

Error during mixing and application process

46
Q

Although prepreg has lots of pros what are some of the cons?

A

Must be stored frozen
Full rolls must be purchased
More expensive

47
Q

What are the two ways to construct fibre reinforced composite?

A

Laminate
Sandwich

48
Q

What is an interply hybrid?

A

When two different fabrics are used in a laminate to combine their characteristics.

49
Q

What is a sandwich construction?

A

When the core is bonded with two thin fibreglass sheets.

50
Q

What is the benefit of sandwich construction?

A

It is approx 10 times stronger than laminate and only 6 times heavier

51
Q

What are the two most common core materials?

A

Honeycomb and foam

52
Q

What is honeycomb normally made from?

A

Aramid paper

53
Q

Most honeycombs are hexagonal but what two other forms are available?

A

Flexi core and over expanded core

54
Q

What are some foam cores made of?

A

Polystyrene
Polyvinyl Chloride
Polyurethane

55
Q

What range of uses do plastics have?

A

Structural components to decorative trim to windows.

56
Q

What is polyetherketone (PEEK)?

A

Semi-crystalline organic polymer

57
Q

What are some of the characteristics of PEEK?

A

Superior mechanical and thermal properties
Creep resistance
Low flammability

58
Q

What is the operating temp of PEEK?

A

Up to 232 degrees c

59
Q

What is thermosetting polyimide used for?

A

Stand offs, and a variety of moulded parts

60
Q

Where is PAI (polyamide-imide) used?

A

Aircraft thrust reverser assemblies due to its high mechanical strength which it keeps up to 260 degrees c

61
Q

What two forms can transparent plastic be formed in?

A

Monolithic
Laminated

62
Q

What is a monolithic plastic sheet?

A

Made in a single layer

63
Q

What are clear laminated plastic sheets bonded with?

A

Layer of clear resin material.

64
Q

How are thermoplastics marked?

A

Heated dyes

65
Q

What is heated dye marking not suitable for?

A

Tubular sections
Celluloid and vinyl acetates

66
Q

How are thermosetting plastics marked?

A

Vibro-etching (preferable)
White paint and marking ink

67
Q

How are transparent plastics marked?

A

Ideally not at all.

68
Q

What two forms are sealant available in?

A

One part
Two part to be mixed

69
Q

What are some of the applications of sealant?

A

Fuel tanks
Skin joins
Aerodynamic smoothing

70
Q

What is film adhesive?

A

It pre-blends the resin and catalyst on a film of plastic.

71
Q

What are adhesive films used for?

A

Bond patches to a repair area.

72
Q

What is another form of adhesive primarily used to bond foam to honeycomb?

A

Foaming adhesive, can also be used to permanently install fasteners.

73
Q

Where is detection of defects in composite started?

A

Manufacturing process

74
Q

How is a resin starved areas identified?

A

Fibres showing on the surface.

75
Q

What can delaminations form?

A

Matrix cracks

76
Q

What does the severity of delam depend on?

A

Dimensions
Number of delams at location
Location
Loads

77
Q

Honeycomb structures have face sheets which are subject to three categories of defect, what are they?

A

Low resistance to impact
Liquid ingression
Erosion

78
Q

Damage that goes unchecked to a honeycomb structure can lead to what?

A

Liquid ingress into the core

79
Q

When a core has water ingress what is required before carrying out a repair?

A

Drying cycle to completely remove any moisture.

80
Q

When a core has skydrol ingress what is required before carrying out a repair?

A

Complete removal of contaminated core as it cannot be dried.

81
Q

What are some of the typical types of visual damage?

A

Scorch
Stain
Dent
Penetration
Abrade
Chip

82
Q

How are internal defects inspected?

A

NDT

83
Q

What is the most common test for detecting delam?

A

tap/coin testing

84
Q

What four ultrasonic techniques are used?

A

Through transmission
Pulse echo
Ultrasonic bond
Phased Array

85
Q

What is x-ray best at detecting?

A

Flaws parallel to the beams centreline.

86
Q

As most composites are transparent to x-rays what is used?

A

Low energy rays

87
Q

What is thermography most affective for?

A

Thin laminates or defects near the surface

88
Q

Ife dye penetrant sits on composite too long what happens?

A

The fibres can absorb the dye.

89
Q

How does a moisture meter work?

A

The meter measures the RF power loss caused by the presence of water.

90
Q

What are the three damage classifications to composite?

A

Negligible
Repairable
Non-repairable

91
Q

What is BVID?

A

Barely visible impact damage

92
Q

What are the five basic types of composite repairs?

A

Pre-cured patches
Potted
Resin Injection
Laminate repair (one surface or through part)

93
Q

What are bolted and bonded repairs?

A

Temporary

94
Q

What are resin injection and potted repairs for?

A

Repair small holes or voids.

95
Q

What steps are required to prepare a surface for repair?

A

Solvent degreasing
Water break test

96
Q

What is the water break test?

A

A test to see what the surface tension of the water is.

97
Q

How long must the water remain on the surface in a water break test?

A

30 seconds

98
Q

What are the 8 basic steps when assessing damage for repair?

A

Find
Assess
Define SRM
Prepare
Lay up
Clean
Inspect
Document

99
Q

How does a potted repair, repair a hole?

A

Filler is used instead of new core material.

100
Q

What is the maximum size for a potted repair?

A

2.5cm

101
Q

What are the two most common honeycomb repairs?

A

Puncture
Honeycomb core

102
Q

If honeycomb damage is more than one inch, a potting repair can’t be used, what can be done instead?

A

A honeycomb plug cut and bonded in place.

103
Q

What are the two common solvents used to clean composite?

A

MEK
Acetone

104
Q

What types of plastic wear are there?

A

Crack, degradation, distortion and aesthetic alteration.

105
Q

What are the four types of plastic failure?

A

Environmental
Thermal
Chemical
Mechanical

106
Q

What are the rules for cleaning an externally exposed surface?

A

Flush the surface with water and use a hand to remove all the dirt. Sponge with hot water and soap, dry.

107
Q

What are the rules for cleaning an internal plastic surface?

A

Dust the surface, use a damp cloth and dry. Use approved plastic cleaner/polish.

108
Q

What is crazing?

A

Small surface fissures, can lead to major cracking.

109
Q

How can scratches be removed?

A

Buffing
Sanding

110
Q

What can be done to cracks in plastic?

A

They can be stop drilled , but the component must still be replaced at next check.

CAT B- Mod 6 Materials and Hardware (14 decks)

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