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Materials And Hardware > Composites And Non-metallic Structures > Flashcards

Composites And Non-metallic Structures Flashcards

1
Q

What is a composite?

A

When two or more materials combine to form a stronger structure

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2
Q

What are some advantages of composites?

A

High strength to weight ratio
Reduction of parts and fasteners
Reduction of wear
Corrosion resistance

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3
Q

What are some disadvantages of composites?

A

Relatively expensive
Not easy to repair
Trained staff and equipment required

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4
Q

What does reinforcing materials do?

A

It gives major strength to the reinforcing component when combined with a matrix

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5
Q

Name a type of composite

A

Nomex

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6
Q

Name some properties of nomex?

A

It is manufactured only as a fibre
It has high thermal stability
It is flame resistant

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7
Q

How is fibre glass made?

A

It is manufactured from molten silica glass and spun together then woven into a cloth

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8
Q

Name one advantage and disadvantage of fibre glass

A

Advantage - low cost

Disadvantage - weighs more than other fibres

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9
Q

The simplest composite is made of two elements. What are they?

A

The matrix - adhesives or resins

The reinforcing material - fabric

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10
Q

What are the two types of fibreglass most commonly used in the aerospace sector?

A 
E Glass (highly resistant to electricity)
S Glass (very high tensile strength)
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11
Q

What are some characteristics of Aramid fibres?

A 
Yellow in colour
High strength to weight ratio
High Tensile strength
Heat resistant up to 260C 
Low density
Abrasion resistant
Chemical resistant
Non flammable and non fusible
High toughness
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12
Q

What is Kevlar?

A

A man made organic fibre with high tensile strength and flexibility

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13
Q

What is Kevlar used for?

A

Bullet proof vests, cables and reinforced composites for aircraft panels

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14
Q

How does Kevlar work?

A

NOT COMPLETED

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15
Q

What are some disadvantages of Kevlar

A

Difficult to cut

Absorbs up to 8% of moisture

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16
Q

What are some characteristics of Carbon Fibre?

A 
High E modulus
High strength
Low density
Low fracture resistance
Thermal extension in longitudinal direction in the fibre close to 0
High resistance against temp
Electrically conductive
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17
Q

What does CFRP stand for?

A

Carbon Fibre Reinforced Plastic

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18
Q

What are the different Fibre Orientations?

A

Warp
Weft/fill
Selvage edge
Bias

Uni directional Fibre
Bi directional Fibre

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19
Q

What is Warp?

A

The threads that run along the edge of the fabric

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20
Q

What is the weft/fill?

A

The fibres that run perpendicular to the warp fibres

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21
Q

What is the Selvage Edge?

A

The tightly woven edge that runs perpendicularly to the warp edges

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22
Q

Wha is the Selvage Edge used for?

A

Used to prevent unravelling edges

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23
Q

What is the Bias?

A

The thread that runs 45 degrees to the warp threads

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24
Q

What does the Bias do?

A

It allows manipulation of the material to create complex contours

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25
Q

What is Uni Directional?

A

When the threads are straight and go in one direction only

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26
Q

What are Bi directional fibres?

A

When the threads go in 2 or more different directions

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27
Q

What do Bi Directional Fibres provide more of?

A

Strength

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28
Q

What is the matrix?

A

Usually the wet form of the composite

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29
Q

What does a newer matrix material have?

A

Better stress distributions

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30
Q

What are some matrix characteristics?

A

Heat resistant
Chemical resistant
Durable

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31
Q

What can you use for a matrix?

A

Resins or adhesives

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32
Q

2 part systems include?

A

A matrix and a hardener

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33
Q

What do you need for a 2 part system between a resin and a hardener?

A

A catalyst acting agent

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34
Q

Resins are split into two categories, what are they?

A

Thermoplastics

Thermosets

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35
Q

What is the difference between a thermoplastic and a thermoset?

A

A thermoplastic uses heat to form a part into a specified shape and it is NOT permanent

A thermoset uses heat to form itself and then it is set permanently. It cannot be reformed

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36
Q

What temperature can a thermoplastic not exceed?

A

750F

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37
Q

Name an example of a thermoset resin

A

Epoxy resin

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38
Q

What are the characteristics of an epoxy resin?

A

Good adhesion
Good strength
Moisture and chemical resistant
Good for bonding NON-POROUS and DISSIMILAR metals

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39
Q

What is epoxy resin widely used in?

A

Resins for prepreg materials and structural adhesives

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40
Q

What do you refer to for composite safety?

A

MSDS - Material Safety Data Sheet

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41
Q

What does prepreg stand for and what does it mean?

A

Pre- impregnated

They are fabrics that have already been impregnated with resin

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42
Q

What type of construction is used when a core material is bonded between two thin face sheets ?

A

Sandwich construction

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43
Q

What is the honeycomb structure and what does it provide?

A

It takes the shape of a natural honeycomb and it provides strength

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44
Q

What are the 2 types of honeycomb Fabrication method?

A

Corrugation process

Expansion process

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45
Q

What materials can be converted in the corrugation process?

A

Metals
Plastic
Plastic reinforced glass
Paper

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46
Q

What is the Expansion process?

A

Where the bonds are made simultaneously

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47
Q

What are the different ways used to dissipate electrical charge on composite components?

A

Flame spray
Bonding jumpers
Aluminium wires

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48
Q

What safety precautions must always be taken?

A

Gloves at all times
Hands washed before and after
Wear masks and a gown

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49
Q

What is polymerisation?

A

A process carried out with the presence of a catalyst and it creates a chemical reaction where polymers are then created from monomers

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50
Q

What is an advantage for polymerisation?

A

There are no waste by-products

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51
Q

What are examples of polymers?

A

Polyethene, polystyrene

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52
Q

What is polycondensation?

A

A chemical reaction between two similar or dissimilar units which have at least two functional groups

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53
Q

Give examples of polymers formed by polycondensation

A

Bakelite

Polyester

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54
Q

What is polyaddition?

A

The reaction of 2 different types molecules when reactive groups are brought together

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55
Q

Name examples of polymers formed by polyaddition

A

Polyurethane

Epoxies

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56
Q

Give the 2 examples of bonding agents

A

Adhesives and resins

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57
Q

What is an adhesive?

A

A substance used to bond two or more surfaces together

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58
Q

What are some advantages of using adhesives?

A

Economical
Distribute stress at the bonding point
No need for fasteners
Depending on its factors, it is moisture and chemical resistant

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59
Q

What does the effectiveness of the adhesive depend on?

A

Resistance to shrinkage and slippage
Malleability
Cohesive strength
Surface tension - determines how far the adhesive penetrates the tiny depressions in the binding surfaces

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60
Q

What are the different types of Adhesives?

A 
Synthetic
Thermosetting
Thermoplastic
Elastrometric
Contact
Solvent
Dispersion
Resin
Film
Foaming Adhesive Film
Plastic Foams
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61
Q

What are synthetic adhesives used for?

A

Used either alone or as modifiers of natural adhesives for better performance and better range of applications than the natural products.

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62
Q

What are thermosetting adhesives used for?

A

Used for structural functions as bonding metallic parts of aircraft and space vehicles

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63
Q

How is a thermoset transformed into a tough, heat resistant solid?

A

Through the addition of a catalyst or the application of heat

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64
Q

What use do thermoplastic resins have?

A

Used to bond wood, glass, rubber, metal and paper products

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65
Q

What are examples of elastomeric adhesives?

A

Synthetic or natural rubber cements

66
Q

What do elastomeric adhesives do?

A

Join dissimilar metals without producing galvanic corrosion

Distributes stress more evenly throughout the body

67
Q

What are contact adhesives?

A

The use of atmospheric pressure to press two solids together if there is no air between the two plane parallel surfaces

68
Q

What do solvent adhesives contain?

A

Plastic or resins dissolved in a solvent

69
Q

What must the solvent do to cure the adhesive?

A

It must evaporate

70
Q

What do dispersion adhesives contain?

A

They contain resins dissolved in water solution

71
Q

How are resin adhesives cured?

A

By chemical reaction

72
Q

What do resin adhesives contain?

A

2 or more components

73
Q

What are film adhesives?

A

Film adhesives are similar to prepegs.
They are used to bond metal to metal and sandwich the core to the skin
GFRP, AFRP, CFRP

74
Q

What does GFRP stand for?

A

Glass fibre reinforced polymer

75
Q

What does AFRP stand for?

A

Aramid Fibre Reinforced Plastic

76
Q

What does CFRP stand for?

A

Carbon Fibre Reinforced Plastic

77
Q

What do supported films contain?

A

A woven nylon carrier

78
Q

At what temperature does a film adhesive have to be stored?

A

-18 degrees C

79
Q

What are Foaming Adhesive Films?

A

An adhesive in sheet form which expands during the curing cycle to fill gaps and adhere strongly to all parts of the structure it comes into contact with

80
Q

What are Foaming Adhesive Films mainly used for?

A

The repair of the honeycomb sandwich panels

81
Q

What are plastic foams?

A

Plastic foams are either produced with closed or open pores and as either preformed rigid sheets or as fluids for injections into cavities

82
Q

What are thixotropic agents?

A

Thickening agents

83
Q

Why do we use thixotropic agents?

A

Some plastic resins are extremely sensitive to temperature and may run

84
Q

How many thickening agents are used in aircraft maintenance and what are they?

A

2

Micro-balloons
Aerosil

85
Q

What are microballoons?

A

Micro-balloons are made up of hollow phenolic balls with a range of diameters.
A paste of light consistency is made up and trowelled onto the surface where it cures into a hard, light-weight filler

86
Q

What is aerosil?

A

Aerosil is a very light, white powder, which is a product of combustion

87
Q

What are the two types of resin adhesives?

A

Thermoplastic

Thermosets

88
Q

What do resins do?

A

Resins ensure the cohesion of the composite material

89
Q

What are most of the mechanical performances of a composite given by?

A

The fibres and their orientation

90
Q

Where should resins always be mixed?

A

In a wax free container

91
Q

How do you get a wax free container?

A

By adding accelerator to the resin base

92
Q

How long should the mixing process take?

A

3-5 minutes

93
Q

What will the addition of too much accelerator do to the mixture?

A

Decrease the strength of the final mix

Exothermic reactions will take place and the resin may spontaneously combust

94
Q

What are two main types of resin used for composite structures?

A

Epoxy

Phenolic

95
Q

Why are epoxy resins used for external components?

A

Good mechanical properties

96
Q

Why are Phenolic resins used for cabin furnishing?

A

They have good fire resistance and low toxicity

97
Q

What happens to thermoplastic resins when it is heated?

A

It becomes a plastic

98
Q

What are thermoplastics rarely used in?

A

Composite structures

99
Q

What are the main features of a good polymer resin?

A

Must have the correct mechanical properties
It must coat every single and bond well to them
Must be fairly easy to use

100
Q

What are the four most commonly used resins in fibre reinforced composites?

A

Polyester resin
Epoxy resin
Vinyl ester resin
Phenolic resin

101
Q

When is polyester resin typically used?

A

Used with glass fibres to form a strong durable material

102
Q

What do epoxy resins do?

A

Provide excellent adhesive strength and can be used for gluing metals together

103
Q

What are characteristics of the vinyl ester resins?

A

Tough resins with high resistance to corrosion

104
Q

What are characteristics of phenolic resins?

A

Good resistance to smoke generation in fires

105
Q

What can the wrong amount of hardener or resin do?

A

Unreacted resin in the final cured resin

Unreacted harder in the final cured resin

106
Q

How are polyesters cured?

A

By chain reactions, linking resin molecules to hardener molecules

107
Q

What are some disadvantages of using epoxy hardeners?

A

Its toxicity can cause dermatitis
It has a moderate to high cost
They have a low pot and shelf life

108
Q

What are epoxy resin characteristics?

A

Adhesion - sticks to most metals, glass and ceramics

Cohesion - material usually fades before resin

100% solution - no by products, cures without releasing water or other condensation products

Low shrinkage - cure with only a fraction of shrinkage of vinyl type adhesives

Resistance to moisture and solvents - effective barrier to heat and electric current

109
Q

What is one of the most important factors of bonding?

A

Surface wetting

110
Q

What are some positive effects of surface wetting?

A

No surface contamination
Viscosity reduction
Time
Pressure

111
Q

What are some negative effects of surface wetting?

A

Fingerprints
Incorrect alignment of glue
Low temperature
Incorrect surface pre-treatment

112
Q

What are the two important aspects of a durable adhesive joint?

A

Mechanical hooking

Surface wetting

113
Q

What is mechanical hooking?

A

Takes into account that the adhesive must penetrate into cavities before curing, otherwise trapped air will decrease the strength of the joint

114
Q

What are the pre-treatment procedures for bonding?

A

Degrease only
Degrease, abrade and wipe
Degrease and chemically pre-treat

115
Q

How can contamination occur during pre treatment?

A 
Fingerprints
Dirty cloths
Poor degreasing techniques
Poor chemical solution
Other tasks happening in the vicinity
116
Q

How many levels of composite damage are there and what are they?

A

3 levels

Allowable
Repairable
Non-repairable

117
Q

What does SRM stand for and what is it used for?

A

Structural Repair Manual

Used to determine whether a part is repairable or not and the applicable type of repair that needs to be done

118
Q

In the SRM, damage is divided into 2 categories, what are they?

A

Skin not-perforated damage

Skin perforated damage

119
Q

What sort of damage would go under skin not perforated damage?

A 
Abrasions
Scratches
Dents
Erosion
Debonding/delamination
Gouges
120
Q

What types of damages would go into the skin perforated damages?

A

Lightening strikes
Holes
Impact from another object

121
Q

What is delamination?

A

When reinforced materials separate from each other in the matrix

122
Q

What is debonding?

A

When two materials stop adhering to one another

123
Q

What is BVID?

A

Barely Visible Impact Damage

When the outer skin looks undamaged but there is a loss of skin bonding to core bonding which reduces the overall strength

124
Q

When may galvanic corrosion occur?

A

When an aluminium alloy is in direct contact with a Carbon Fibre material in the presence of a corrosive environment

125
Q

What material used on an aircraft is conductive?

A

Carbon fibre

126
Q

If erosion erosion is undetected or unrepaired, what can it generate?

A

Composite deterioration

127
Q

Where may erosion occur most on an aircraft?

A

The leading edges

128
Q

Why must repairs be made when water absorption is present?

A

To avoid any material delamination during heat application

129
Q

What must be repaired if chemical degradation is present?

A

The entire contaminated area

130
Q

What is required if a dent or depression is found?

A

Further NDT to detect delamination or debonding.

If it is a sandwich structure, the honeycomb structure is usually damaged and requires repairs

131
Q

What does NDT/NDI stand for?

A

Non-Destructive Testing

Non-Destructive Inspections

132
Q

What are some examples of NDI tests?

A 
Tap testing
Visual/optical
Holography
Ultrasonic
Radiography

Thermography
Acoustic emission
Bond tester/ resonator

133
Q

What does tap testing do?

A

Detects debonding or trapped water quickly

134
Q

How does tap testing work?

A

Tapping method using a coin/light hammer that creates a woodpecker effect. Places with debonding or trapped watter will give a flat/dead sound

135
Q

What is visual/optical testing?

A

A visual / optical inspection to quickly locate SURFACE flaws/damages

136
Q

What does visual/optical testing not locate?

A

It does not locate internal damages

137
Q

What can you use to look for glass fibre component damages?

A

A strong light

138
Q

How do you know delamination has occurred when doing a visual test with a strong light?

A

Delamination is indicated by a change in colour

139
Q

What do holography testings do?

A

Locate small surface defects

140
Q

What do ultrasounds do?

A

Locate internal defects

141
Q

What are ultrasounds most commonly used for?

A

Laminates

142
Q

What do ultrasounds rely on?

A

Surface cleanliness

143
Q

What does radiography testing do?

A

Locates internal defects and surface defects

144
Q

What are the 2 processes of radiography ?

A

X-ray

Gamma

145
Q

What is a disadvantage and advantage of using radiography?

A

Disadvantage - highly radioactive

Advantage - produces a photographic record

146
Q

How many types of repairs are there and what are they?

A

3 types of repair

Temporary
Permanent cosmetics
Permanent structural

147
Q

Where are repair instructions found?

A

SRM

148
Q

Before any repairs can be done, what must be done first?

A

Ensure the surface of the repair area has been prepared properly

149
Q

When removing surface protection, what methods must be used?

A

Mechanical methods

150
Q

Why cant chemical methods be used to remove the surface protection?

A

Can cause deterioration of the resin

151
Q

What is a wet lay-up?

A

The application of several layers of fabric material impreganted with resin onto the repair surface in order to restore the damaged skin

152
Q

What happens if the mixture is not mixed well?

A

It will not provide adequate strength

153
Q

How long are you meant to mix components?

A

3-5 minutes

154
Q

What are the two methods used for lay up operation?

A

Pre preg

Wet application

155
Q

Why is the vacuum bag technique used in advanced composite repairs?

A

To use atmospheric pressure to consolidate the layers in the laminated repair
To remove trapped air and gases during curing
To hold heater blankets, thermocouples and other materials in place during the curing cycle
To produce the required surface finish on the repair

156
Q

What are the two main principles that must be obeyed when doing a vacuum bagging repair?

A

The air and gases inside the vacuum bag must have an easy path to the vacuum pump over the entire repair surface

Amount of resin lost from the repair plies must be kept to a minimum

157
Q

What is the term for removing one layer at a time?

A

Scarfing

158
Q

What is one advantage of scarfing?

A

It is a safe way of cutting out damage of composite materials

159
Q

Where should thermocouples be placed when using the vacuum bagging method?

A

Positioned under the heating mats in order to accurately monitor the repair temperature

160
Q

What thermocouples are most commonly used for hot bonding?

A

J type

161
Q

What are the most common factors for temperature variation with thermocouples?

A

Variation of thickness of the component
External draughts
Inaccuracy of thermocouples

Materials And Hardware (6 decks)

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