Module 6.3.1 Composites Flashcards
1
Q
What is the definition of a composite material?
A
Two or more materials that when combined create a much stronger material that each one by themselves.
2
Q
What are the two components of a composite?
A
- The matrix, hardener
- The fabric/reinforcing material
3
Q
What type of structure are modern composites used on in aircraft?
A
Primary structures.
4
Q
List 3 advantages of composites.
A
- High strength to weight ratio
- Stress transferred through the fibres
- Longer service life than metal
- High corrosion resistance
- 4x strength of steel
- 6x strength of aluminium
- Greater design flexibility
- No joints or fasteners needed
5
Q
List 3 disadvantages of composite materials.
A
- Difficult to inspect
- lack of long term data
- High production and repair costs
- Processing equipment is expensive
- Lack of repair knowledge
- Materials used are often hazardous
- Lack of standard methods
6
Q
Name all 5 reinforcing fibres used for composite materials.
A
- Carbon fibre
- Kevlar/aramid
- Fibreglass
- Ceramic
- Boron
7
Q
What colour is aramid?
A
Yellow/gold
8
Q
What colour does aramid go when exposed to UV rays?
A
Brown
9
Q
How can aramid be protected from lightning strikes?
A
A conductive weave in the fibres.
10
Q
List 3 advantages of aramid.
A
- Low density
- Very flexible
- High tensile strength
- Heat resistant up to 260C
- Not flammable or fusible
- Good chemical and abrasion resistance
- High toughness
11
Q
What type of strength is weak aramid?
A
Compressive
12
Q
List the disadvantages of aramid.
A
- Poor compressive properties
- Difficult to reshape
- Wears out cutters
- UV susceptible
13
Q
What is the carbon fibre also referred to as?
A
Black graphite
14
Q
List 3 advantages of carbon fibre.
A
- Low density
- High strength
- Low fracture resistance
- close to zero thermal extension
- High temp resistance
- Good electrical conductor
15
Q
List the disadvantages of carbon fibre.
A
- Wears out cutters
- Brittle
- Corrosive with aluminium
16
Q
Why is boron not commonly used on aircraft?
A
- Very expensive
- Hazardous
17
Q
Why would boron be used on aircraft? (4)
A
- High tensile strength
- High stiffness
- Very hard wearing
- Excellent compressive strength
18
Q
What applications are ceramics used in?
A
High temperature
19
Q
Where would ceramics be found on an aircraft?
A
Firewalls
20
Q
What temperature do ceramics maintain their strength too?
A
1200C
21
Q
What are the 4 keys terms in fabric orientation?
A
- Warp
- Weft
- Bias
- Selvedge edge
22
Q
What orientation does the warp run in?
A
‘Wrap’ length ways as the material is unrolled.
23
Q
At what angles do the warp, weft and bias run?
A
0, 90, 45 respectively.
24
Q
What is the purpose of the selvedge edge?
A
Tightly woven edge running parallel to the warp. Stops fibres from unravelling.
25
Is the selvedge edge used in the final hardened product?
The selvedge edge gets cut off.
26
Why is a quasi-isotropic lay up is used?
To distribute forces evenly through many different angles.
27
What weave has the lowest crimp?
Satin weave
28
What weave has the highest crimp?
Plain weave
29
How are mats produced?
Chopped fibres pressed together. A light adhesive may be used. Not as strong as uni or bi-directional fibres.
30
What are the two general plastic categories?
- Thermosetting
- Thermoplastic
31
Can thermoplastics be reheated and remoulded?
Yes they can.
32
Can thermosets be reshaped?
No they can’t.
33
What are Pre-pregs?
Pre-pregs come from the manufacturer and already have the correct amount of resin mixed.
34
What precautions must be taken when using pre-pregs?
Must be stored in a freezer to prevent curing. Must be warmed to room temperature before use. The out-of-freezer time must be recorded.
35
Why is pre-preg expensive?
Manufacturers only sell it in large quantities.
36
What are the two types of reinforced composites?
Laminated and sandwich
37
What is a laminated composite?
Multiple layers of reinforcing material bonded together and embedded in a resin matrix. Multiple layers are used to get desired thickness. Often at angles to each other. Can be made up of two or more different composite fibres.
38
What is a sandwich composite?
A core bonded between to fibreglass sheets.
39
Is the sandwich composite stronger than the laminated composite?
Yes it is. 10x stronger for only 6x the weight.
40
What are the two most common types of core material in sandwich composites?
Honeycomb and foam.
41
Why mustn't plastic pipes be marked with heated dyes?
Pipes are already thin. By applying heated dyes you run the risk of melting the outer wall.
42
Can one part sealants be used straight from the manufacturer?
Yes they can.
43
How are thermosetting plastics marked?
They are marked using vitro-etching, white paint or ink.
44
How should transparent plastics be marked?
Marking should be avoided. If there is a metal outer housing then it should be marked there. If not then a stencil and light sand-blasting should be used.
45
How can thermoplastics be marked?
Heated dyes
46
How do you make two part sealants ready for use?
Mix the base and accelerator in equal quantities.
47
Where must film adhesives be stored?
In a freezer.
48
Why must film adhesives be stored in the freezer?
As they will cure if left at room temperature.
49
What is disbonding?
Separation of two elements. Can lead to delamination.
50
What is delamination?
Forms on the boundary layer between different layers and causes layer separation.
51
What are the 7 types of NDT?
- Visual inspection
- Audible testing
- Ultrasonic inspection
- Radiography
- Thermographs
- Dye penetrants
- RF detector
52
What problems can occur with tap testing?
Not even pressure of taps, so areas may sound different.
53
In tap testing, what must the tester know about the area?
- What it should sound like.
- Position of structural supports.
54
What are the 4 types of ultrasonic inspections?
- Through transmission
- Pulse-echo
- Ultrasonic bond tester
- Phased array
55
In radiography, what area of the material appears white?
High density areas.
56
How is a thermograph test conducted?
By passing heat from, to or through the tea object and measuring/mapping the differences in conductance.
57
How is a dye penetrant test conducted?
Apply the dye all over the area. Then wipe off and spray with a dry talcum powder. This draws out the dye and reveals where the micro cracks are.
58
Can dye penetrant tests be used on composites?
No they can't, unless stated by the AMM.
59
How does an RF test work?
Measures Rf power loss caused by the presence of water.
60
Damage can be classified into 3 categories what are they?
- Negligible
- Repairable
- Non-repairable
61
Where can water ingress be a problem?
Inside the honeycomb cores
62
How can a surface be tested to see if it has been sufficiently cleaned?
Water-break test
63
Where can the procedure for a structural repair be found?
In the Structural Repair Manual SRM
64
Do fastened repairs restore the same structural strength?
No they don't. It also worsens streamlining.
65
What fasteners are used in a fastened repair?
Blind fasteners
66
What overlap should be given in a fastened repair?
1 inch
67
In a potted repair what should the overlap be?
1 inch
68
In a potted repair what should the undercut be?
1/8 inch
69
Where should resin injection repairs be used?
In areas of minor delamination
70
When doing laminate repairs what should the step cut overlap be?
1/2 inch
71
When doing laminate repairs what should the top layer overlap be?
1 inch
72
What is crazing?
When plastic is under load small surface fissures can occur.
73
How do you restore surface finish on plastics after scratches?
Polishing, buffing.
74
How can further propagation of cracks be halted?
Stop drilling
