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Mod 6 > Composites > Flashcards

Composites Flashcards

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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
What is are mats?
Chopped areas of fabric with little strength than unidirectional or bidirectional fibres
26
why are fabric weaves better?
More resistant to breakout,delamination, and damage compared to unidirectional.
27
What are the two types of resins?
Thermoset | Thermoplastic
28
What is a thermoset resin?
Heated to form then permanently retain that shape when cooled, this is mainly used in structural composites
29
What is a thermoplastic resin?
A resin that can be reformed by heating
30
What type of resin is an epoxy resin?
Thermoset
31
What are prepreg fabrics?
Fabrics that are pre impregnated with resin, they are kept in large rolls and need to be stored in a freezer.
32
What are the main types of core materials?
Foam Honeycomb Honeycomb core
33
What are the types of honeycomb fabrication?
Corrugation | Expansion
34
What are the main ways to dissipate charge?
Flame spray Bonding jumpers Aluminium wires woven into top layers Aluminium foil bonded to top area
35
Why is paint used?
To seal against moisture
36
What is MSDS?
Material safety data sheets
37
What information is found on an MSDS?
Health precautions Flammability Ventilation requirements Information for health professionals
38
What is polymerisation?
A chemical reaction that creates a long chain of double bonded molecules
39
Is there any by products made from polymerisation?
No
40
What is polycondensation?
A chemical reaction between 2 similar of dissimilar basic units with at least 2 functional groups.
41
What is polyaddition
Reaction of 2 different types of molecules when reactive groups are brought together. No byproducts are produced
42
What are some key polycondensation polymers?
Polyester Polyamides (nylon) Phenol-formaldehyde (Bakelite)
43
What are some key polyaddition polymers?
Epoxies | Polyurethanes
44
What are the benefits of adhesives?
Moisture and corrosion resistant Eliminate need for fasteners Distribute stress at the bonding points
45
What are the main types of adhesives?
``` Synthetic Thermosetting Thermoplastic resins Elastomeric Contact Solvent Dispersion Film Foaming adhesive films ```
46
What are thixotropic agents?
Thickening agents to the resins
47
What are the 2 common types of thixotropic agents?
Aerosil | Micro-ballons
48
How should a resin be mixed?
In a wax free container with the accelerator added to the base
49
What will happen to a resin when a catalyst is added to it?
The pot life is reduced
50
Where are thermoplastic resins very unlikely to be used?
In composite structures
51
What are the two main thermosetting resins used for structures and why?
Epoxy- external components, good mechanical strength | Phenolic- cabin due to low toxicity and fire resistance
52
How can the mechanical properties of plastics be improved?
By bonding fibres to the plastic
53
What are the key features of a good polymer?
Easy to use Coat every fibre and bond to them Have the correct mechanical properties
54
What are the 4 most common resins in fibre reinforced polymers?
Polyester Epoxy Vinyl Ester Phenolic
55
What must never be done with a catalyst for a resin?
Mix accelerator and catalyst to avoid an exothermic reaction
56
What are the disadvantages of epoxy resin?
Low pot and shelf life Moderate to high costs Toxicity
57
What are the positive characteristics of epoxy resins?
``` Low shrinkage when cured High adhesion Great cohesive strength when cure- can cause stress 100% solid- no byproducts Resistance to moisture and adhesives ```
58
What are the positive factors for surface wetting?
Removal of surface contamination Viscosity reduction through heat or solvent Time Pressure
59
What factors have negative effects on surface wetting?
``` Leaving fingerprints Residues left on surface Incorrectly aligned glue lines Low temperatures Incorrect pretreatment ```
60
What are the important aspects for durable adhesives?
Mechanical hooking | Surface wettting
61
What are the pretreatment procedures for bonding?
Degrease only Degrease, abrade, and remove loose particles Degrease and chemically pretreat
62
What are the aim contamination causes for pretreatment?
``` Fingerprint Cloths not fully clean Poor degreasing Contaminated abrasives Chemical solutions Other work in bonding area ```
63
Where would repair procedures be for structure?
SRM (structure repair manual)
64
What are the 3 damage levels?
Allowable Repairable Not repairable
65
What would be classed as skin not perforated damage?
``` Abrasion Scratches Gouges Dents Nicks Debonding Delamination ```
66
What is classed as skin perforated damage?
Lightning strike Holes Impact by foreign object
67
What is BVID?
Barely visible impact damage
68
Is water absorption allowable?
No
69
What causes chemical degradation?
Accidental contact with aggressive chemical products
70
How are dents and depression inspected?
NDT
71
What are the different types of NDT?
``` Tap test Visual Radiography Thermography Holography Bond tester Acoustic emissions ```
72
What is holography?
Overlaying an image of what the surface should look like on top of the actual surface. Gets inspection done fast
73
What are the disadvantages of holography?
Tedious to set up | Difficult to get a good display of the overlay
74
What is an ultrasonic NDT?
Ultrasonic waves are transmitted onto the structure, which then bounces off and returns to the receiver
75
Why is ultrasonic used?
Quick | Not expensive
76
What waves are used for radiography?
X-rays | Gamma rays
77
How does radiography work?
By creating a photographic image from the em rays onto the film behind the area being tested
78
What are the 3 types of repairs?
Temporary Permanent Cosmetic Permanent structural
79
How should all surface protection be removed?
By mechanical means only
80
How can chemical strippers affect any composite surface?
It can cause the resin to deteriorate
81
What is scarfing?
The removal of layers one at a time with mechanical sanding tools
82
What should be done to damaged core material?
The damaged core must be removed fully and replaced with a suitable filler material to restore the full strength
83
What is wet lay up?
The application of multiple layers of hand pre-impregnated fabrics to restore the damaged skin
84
What is important to remember with resins and catalysts?
``` 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
What is pot life?
Amount of time you have to work with the resin
86
What is shelf life?
The amount of time a resin can be stored in an unopened container
87
What is resin rich and how does it affect a composite?
There is too much resin | Increases the weight and makes it brittle
88
What is resin starved and how does it affect the composite?
Not enough resin | Can’t transfer stresses to the fibres
89
What should be done when working resins into fibres?
Ensure that the weave is not distorted
90
What are the two lay up methods?
Wet application | Pre-preg
91
What is vacuum bagging used for?
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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