M6.3 Composites Flashcards
1
Q
What is a composite
A
Two or more materials combined to make it stronger than they would be on their own
2
Q
What is the role of the matrix and what does it do?
A
. Bonds to fibre
. Transfers stress
. Adds strength to fibre
3
Q
What are the parts of a 2 part matrix mix?
A
Resin, hardener
4
Q
What are the 2 main elements that make up a composite (plus sometimes 3rd)
A
Matrix (bonding)
Reinforcing material (fabric)
Core (sandwich construction)
5
Q
What are the 2 categories of a matrix?
A
. Thermoplastics
. Thermoset
6
Q
What’s a thermoplastic?
A
Non permanent change and can be reversed
7
Q
What are a few advantages of composites
A
Longer service life than metals
Higher corrosion resistance
High strength to weight ratio
Fibre to fibre transfer of stress
8
Q
What is a Thermoset?
A
Permanent change and cannot be reversed
9
Q
What’s a thermoset?
A
Permanent change and cannot be reversed
10
Q
What are some disadvantages of composites
A
Inspections difficult to conduct
High cost production and repair
Lack of knowledge
Often toxic and hazardous
11
Q
Describe epoxy resin?
A
. Most common
. Thermoset
. Bond almost any materials together
12
Q
What is fibreglass
A
Small strands of silica glass and the spun into woven cloths
13
Q
What are the two types of fibreglass
A
E glass
S glass
14
Q
What are some advantages of fibreglass
A
Low density
Hugh strength
Good wet out💦💦💦💦💦
Does not absorb water
Not ductile
15
Q
What is pre-preg? 😩🧐😉
A
. Controlled amount of resin added to a material to prevent errors
16
Q
What are the properties of Aramid (Kevlar)
A
Yellow colour
Lightweight
Can repair with fibreglass
17
Q
What is Kevlar used for
A
Belts for radial tyres
Bullet proof vests
18
Q
What are the disadvantages of Kevlar
A
Very difficult to cut
Special cutters needed
Poor compressive properties
UV sensitive (turns brown)
19
Q
What is CFRP
A
Carbon fibre (black graphite)
20
Q
Where do you store pre-preg materials and how do you monitor it?
A
In a freezer and calculate time out of freezer with freezer log
21
Q
What are some advantages of Carbon Fibre
A
Very strong and stiff
High resistance to temperatures
Stronger than Kevlar but more brittle
22
Q
Disadvantages of pre-preg 😳🥵🤪😱🫠🥱🫶🏿
A
. Short life span
. Very expensive
23
Q
What composite is corrosive with aluminium
A
Carbon fibre
24
Q
What is carbon fibre used for on an aircraft
A
Primary structures
Ribs
Floor beams
25
What are some disadvantages of carbon fibre
Wears out tooling
Very conductive
26
Why is boron not commonly used
Expensive
Hazardous
27
What is laminate made of?
2 or more layers of reinforcing material bonded together with matrix
28
When would you use ceramic composites
For high temperature applications
29
What is a sandwich (not the food kind Sean 💀)?
. Core bonded between 2 thin fibreglass sheets
. High strength:weight
30
How much stronger is sandwich than laminate?
10x
31
What is the warp
Runs along the length of the fabric as it comes off a roll (0^)
32
What is the weft
Runs perpendicular to the warp (90^)
33
What is the Bias
Runs 45^ to warp
34
What is the selvedge edge
Prevents material from fraying or unravelling. Tightly woven edges run parallel to warp threads
35
What are examples of things a sealant seals?
Fuel tanks, skin joints, structures
36
What are the 2 core materials?
Honeycomb, Foam
37
What are the 4 styles of fabric
Unidirectional
Bidirectional fibre
Mats
Quasi-isotropic
38
What is unidirectional fabric style
Fibres run in single direction of the warp
39
What is bidirectional fibre style
Fibres run in 2 or more different directions
40
What are the advantages of plastic?
. Lightweight
. Cheap
. Corrosion resistant
. Durable
. Impact resistance
. Chemical resistance
41
What is mats style of fabric
Chopped fibres, offers little strength
42
What are the advantages of PTFE?
. Electrical insulator
. Low flammability
. Tear resistant
43
What is quasi-isotropic fabric style
Lay ups stacked in 90^, 45^, 90^ sequence
Or 0^, -60^, 60^
Provides strength and stiffness in all directions
44
What are the 3 types of fabric weave
Plane
Twill
Satin
45
What is plain weave
Simplest form
Very stable
Difficult to cover complex shapes, won’t drape
Lowest mechanical properties
46
What is twill weave
Good wet out and cover properties
Flatter and offers superior mechanical properties
47
How do you identify a thermoplastic?
. Heated dies
48
How do you identify thermosetting plastics?
White paint or ink
49
What is satin weave
Modified twill with fewer intersections
Flat, covers well, good wet out
Often used for repairs
However,
Difficult to handle
50
How do you identify transparent plastics?
Mark on metal bit or sand blasting
51
Where do you store film adhesive to slow resins cure rate
A freezer
52
What is a one part sealants?
Ready for application as packaged
53
What do two part sealant require in packaging?
Require separate packaging to prevent curing prior to application
54
What happens to film adhesive at room temp?
The resin starts to cure
55
What happens to foam adhesive under heating
Expands into crevices
56
What are foam adhesives used for?
Bond new honeycomb core segments to existing cores
57
What do in service defects include?
Impact strength
Environmental degradation
Cracks from load overload
Fatigue
58
What are the three categories of damage to composites
Negligible
Repairable
Non repairable
59
What are cosmetic defects
Defects on the outer surface, does not involve damage to structural reinforcing fibres
60
What does BVID mean
Barley visible impact damage - due to being difficult to see and deftest
61
What is delamination
Separation of the fabric layers of on a laminate
Due to impact, moisture or lightening strikes
62
What do erosion prone areas require?
Coatings and protection
63
When would a dye penetrant be used?
When called upon by manufacturer
64
What does a visual inspection consist of looking for?
Scorching
Stains
Dents
Penetration
Chips
65
What is disbonding
separation of the composite material from another material to which it has been bonded to
separation between the skin and core of a composite sandwich structure is called core disbond
Caused by poor adhesion impact damage
66
How can cracks be detected
Visually or by NDT
Thorough inspection
67
How can you inspection if there has been water ingress ion
Weight gain
Contamination of bond
Expansion/contraction (Therese thaw)
68
How does hole damage arise
Impact, over torquing, lightning strike pin holes
69
Can x rays detect delamination
No
70
What must be done in preparation to before bonding
Solvent Degreasing and de oiling
71
How is a surface checked to see if it has been properly prepared before bonding is applied
A water break test it carried out (if beads then it’s been done incorrectly)
72
What are the parts of a truss type wing?
Main and rear spar
Compression strut
Drag wires (drag and anti drag)
73
What are the parts of a truss type wing?
Main and rear spar
Compression strut
Drag wires (drag and anti drag)
74
How does the box spar help the wing?
Takes all of the torsional and bending load
75
What are the types of wood that could be used for an aircraft structure?
. Solid wood
. Laminate wood
. Plywood
. High density wood
76
What are the 3 preferred wood types for aircraft?
. Spruce
. Douglas Fir
. Noble Fir
77
What are the 5 types of composite repairs
Pre cured patches
Potted
Resin injection
Laminate repair (one surface)
Laminate repair (through part)
78
What’s the negatives of pre cured patches
Doesn’t provide the same aerodynamic properties
79
What’s potted repairs
Where a small hole is filled with foam filler instead of having a core
80
What do you asses in a wood inspection? (Pre plane built)
. Way it’s cut
. It’s grains
. Wood growth ring
. Grains slope
81
What’s the negatives of potted repairs
They can be dangerous as they make it heavier
82
What is solvent degreasing
Removes contaminates from surface, if not removed could effect bonding
83
What causes wood to decomposed?
Moisture, temperature, sunlight
84
What kind of hangars should wooden aircraft be stored in?
Well ventilated hangars, out of sunlight,
85
What could be used to preserve wooden structure?
Chemical preservatives
86
What is a water break test
To verify surface cleanliness
87
What does interior finishing do?
Protect against moisture using coatings
88
How’s resin injection carried and why is it carried out
Carried out when delamination occurs and it’s done by injecting the area with resin and clamped
89
What is exterior finishing in wooden aircraft?
Weathering protection, smooth surface as needs to be aerodynamic
90
What needs to happen before you make repairs to wooden structure?
. Degrease
. Remove sawdust
. Controlled temperature
. Seal bolt holes
91
What MSDS stand for
Material safety data sheet
92
What is a knot is wood?
. Where old branch grew
. Weakens wood
93
What is a pitch pocket in wood?
. Small opening in wood , fill with resin
94
What’s contained on the MSDS
PPE
ventilation
Fibre protection
Solvents safety
Material storage
95
How is compression wood formed?
. Leans one side during growth
. Rings out of sync
. Makes wood weaker
. Falls on slope or another log
Can’t use on aircraft’s
96
What is compression failure?
When a tree falls on uneven ground
97
Describe stained wooden structure?
. Has stains caused by decay
. Reduces toughness/strength
. Cannot be used
98
What’s happens if crazing isn’t detected
Can lead to cracking and failure
99
What is dry rot and what’s it caused by?
. Caused by fungi
. Has minimum moisture
100
Where should wooden structures be kept?
A well ventilated hangar
101
What part of the wooden wing takes all of the structural loading
The spar
102
How is the majority of wood damaged?
Moisture, temperatures, sunlight (UV)
103
What is the main characteristic of resorcinol glue?
Most water resistant
104
What separates the leading and trailing edge of the wing
Compression struts
105
Where would you use a pre cured patch repair
a temporary repair can be performed to cover holes or deep scratches by using a pre-cured patch installed with blind fasteners
Yet, does not produce same structural strength as original
106
How is wood testing done?
Test of joining technique
107
What prevents the leading edge of a wooden wing from collapsing
The drag wire
108
What things would you look for on the wood when you inspect it for damage?
Decay, splitting or cracks, bond failure, finish failure, stress damage
109
What prevents the trailing edge from collapsing forward
Anti drag wire
110
H
111
What does the box spar do
Takes all bending and torsional load
112
What wood is most commonly used for aircraft structure
Silka spruce
113
How many screws and nails per spar
No more than 2
114
Why should drain holes be kept clear
Because it can cause rotting of wood id not due to moisture being held in wind
115
How is a wood test sample performed?
. Wood glued together put in vice
. Hit apart with device of some sort
. The fractured face must have at least 75% wood to show a good joint glued
116
What size hole is a fabric patch repair used for
Up to 1 inch
117
What’s the limit of age rings that can be in 1 inch
6
118
What size hole for surface patched repair
Between 1 inch and 50inchs😏
119
What is a potted repair
Used for smaller holes up to 2.5cm and scratches. Filler is used instead of a new core.
Restricted to honeycomb core sandwich structure
120
What is a plug patch repair held in by?
Held in by a round or oval shaped ring called the doubler
121
What area of the part is plug patch repair done on
Only skin repair, only for damage not involving the supporting structure
122
What is the negative of nitrate dope
Extremely flammable
123
What defects in wood can’t be used in aircraft structures
Spiked knots and compressed wood
124
What is a resin injection used for
Minor internal delamination can be repaired by injecting a resin mix into delaminated area.
Have to check structural repair manual for limitations.
125
What types of
126
What is added to butyrate dopes to stop UV damage
Aluminium
127
What does stained wood indicate
Indicates that rotting has occurred
128
What are laminate repairs
Repairs damage on one side of the surface that does not penetrate the part.
Cut out the damage and replace with new material
129
Before joint two pieces of wood what process must it go have gone through before hand
Must have been left in the same temp for previous 24 hrs so that it can gain the same moisture levels
130
Can you do a laminate repair for damage that has gone through the part
Yes, can be repaired using a step cutting from both sides and meeting in the middle and the replaced.
Check AMM for limitations
131
What does MSDS mean
Material safety data sheets
132
What stitch is used to repair straight cut or tear
Ladder/baseball stitch (Herringbone stitch)
133
When testing bonding techniques between two pieces of wood what percentage of fibres must be on the piece of wood
75%
134
How is a good fit of a fabric achieved
Hot ironing
135
How’s solid wood repaired
By splicing
136
What is included within the MSDS requirements
PPE
Ventilation- proper ventilation, respirators provided
Fire protection- spark proof tools, eliminate fire hazards
Solvents Saftey
Material storage
137
What are the two most common solvent used
MEK (carcinogen) and acetone
138
Where should fabrics be stored?
At 20 degrees (68f) in dry clean condition away from direct sunlight
139
What’s the restriction related to splicing solid wood
No more than 2 per spar
140
What things would you look for in a fabric inspection?
Loose tape
Chafing under fairings
Brittleness
Tears
141
What are the 5 types of plastic failure
Environmental failure
Chemical failure
Mechanical failure
142
What’s used for wing rib repairs
Small sprite strips
143
What are 3 commonly inspected panels
Wood frames
Zip panels
Spring panels
144
What’s the restrictions for in which fabric patch repairs can be done.
Can’t be done on leading edge
145
How is fabric attached to the wood
Using dope
146
2 types of fabric testing devices
Seyboth punch tester- goes all the way through
Maule punch tester- doesn’t puncture , better as it doesn’t make hole
147
What’s the negative of using dope
It’s very flammable
148
When would darning be used?
Hole is no more than 50mm wide at any point (2inchs😏)
149
What is crazing
Internal cracking, can’t be removed or fixed as it’s separation of the material.
If left then could become extensive deep crack.
Prevention is paramount
150
What’s added to make dope less resistant to uv
Alluminium
151
When would an insertion be used for repair?
Damage over 100m (4inch😉)
152
When would an insertion be used for repair?
Damage over 100m (4inch😉)
153
How are fabric wings inspected
Using inspection panels
154
How can you get rid of scratches
Buffing or sanding
It is easier to prevent than remove
Refer to AMM for limitations
155
What are the three panels installed in wings
Spring, wooden frames and zip panels
156
What are the two tools used to measure tension of fabric
Seyboth and maule
157
What does cracking cause and how can you prevent it from getting worse
Renders the plastic beyond repair.
Can be stopped drilled to prevent further damage.
Will require replacement at some point.
Refer to AMM
158
Which one of the two devices that test tension are better
Maule is better and the seyboth punctures a hole in the fabric
