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M6 Mac > 6.3 Composite And Non Metalic > Flashcards

6.3 Composite And Non Metalic Flashcards

1
Q

What is the definition of composite

A

Two or more materials that are combined to form a much stronger structure than either material by itself

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2
Q

Most simple composites consist of what 2 simple elements

A
  • A matrix which serves as a bonding substance (adhesives or resin)
  • A reinforcing material (fabric)
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3
Q

What are the advantages of composite materials

A
  • High strength to weight ratio
  • Reduction of parts and fasteners
  • Reduction of wear
  • Corrosion resistance
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4
Q

What are the disadvantages of composites

A
  • Generally expensive

- Not easy to repair, well trained staff, tools, equipment, facilities are required to repair composite components

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5
Q

What are the most common reinforcing fibres

A

Kevlar and graphite

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6
Q

What is nomex

A
  • Very high thermal stability
  • Temperature and flame resistant
  • Radiation resistance is good
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7
Q

What is fibre glass

A

Made from stands of molten silica glass and spun together nod woven in to a cloth.

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8
Q

What are the most common forms of fibreglass used

A

E glass - Highly resistant to electricity

S glass - Very high tensile strength

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9
Q

What are the characteristics of glass fibre

A
  • Low density
  • High strength
  • Height fracture toughness
  • circular cross section and smooth surface
  • Good wet out
  • Does not absorb water or humidity
  • Not ductile
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10
Q

Where does the name aramid come from

A

Aromatic polyamide

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11
Q

What are the characteristics of aramid

A
  • Light weight and excellent tensile strength
  • Heat resistance up to 260°c
  • Non flammable and non fusible
  • Good chemical resistance
  • Very good resistance against abrasion
  • High toughness
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12
Q

What is Kevlar

A

A man made fibre with properties such as high tensile strength and flexibility

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13
Q

Where would aramid be used

A

Rotor blades and bullet proof vests

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14
Q

Where would Kevlar be used

A

Bullet proof vests, radial tyres, cables, reinforced composites for aircraft panels

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15
Q

What are the disadvantages of Kevlar

A
  • The fibres absorb moisture
  • Compressive properties are poor
  • Very difficult to cut (special scissors are required)
  • UV light sensitive (turns brown when affected by sunlight)
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16
Q

What are the characteristics of carbon fibre

A
  • High strength
  • High E module
  • Low density
  • Low fracture resistance
  • Thermal expansion in longitudinal direction of the fibre is close to 0
  • High resistance against temperates
  • Electrical conductivity
  • Quickly wear out steel cutters
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17
Q

What must be used when bonding carbon fibre to aluminium

A

It has a problem of being corrosive when bonded to aluminium and so a layer of fibreglass is used to isolate the two materials

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18
Q

What is a matrix

A

The bonding material the completely surrounds he fibre to give strength no transfer the stress to the fibre

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19
Q

What are the characteristics of matrix materials

A
  • Good stress distribution
  • Heat resistance
  • Chemical resistance
  • Durable
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20
Q

Resins used as a matrix are two part systems consisting of what?

A

Resin and a hardener (catalyst) which acts as a curing agent

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21
Q

Resins are a type of plastic and are broken down in to what 2 categories

A
  • Thermoplastics

- Thermoset

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22
Q

What are thermoplastics

A

Thermoplastic resins use heat to form the part in to a specified shape and this shape is not permanent.

If heat is added again it will flow in to another shape

Example - plexiglass/acrylic

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23
Q

Where can thermoplastics be used

A

Can only be used in areas where temperatures do not exceed 750°f

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24
Q

What are thermosets

A

Use heat to form and set the shape permanently

Even with addition on heat they cannot be reformed (most composites are made from these)

Example - Bakelite

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25
Q

What are epoxy resins

A

One type of thermosetting plastic resin

They are used to bond non porous and dissimilar materials like metal to composite

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26
Q

What is prepreg

A

Prepreg is the abbreviation of pre impregnated

They already have resin in them

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27
Q

How should prepreg materials be stored

A

In a freezer to prevent the resin from curing at room temperature

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28
Q

What is honeycomb

A

Type of material that has the shape of natural honeycomb

Has excellent strength to weight ratio

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29
Q

What are the 2 methods of honeycomb fabrication

A

Corrugation process - material which can be converted using this process include metals, plastics, plastic reinforced glass and paper

Expansion process

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30
Q

What is the corrugation process

A

Corrugation process - material which can be converted using this process include metals, plastics, plastic reinforced glass and paper

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31
Q

What is the expansion process

A

All bonds are made simultaneously ( the corrugation process is essentially one layer at a time operation)

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32
Q

What are other core materials used other than honeycomb

A

Styrofoam, urethane, wood and several other materials are also used as core materials

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33
Q

What are the different methods used by manufacturers to dissipate the electrical charge on composite components

A
  • Flame spray
  • Bonding jumpers
  • Aluminium wires woven in to the top layer
  • Thin aluminium foil bonded to the top layer
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34
Q

What is the MSDS

A

Material Safety Data Sheet

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35
Q

What type of details can be found on the MSDS

A
  • Health precautions
  • Flammability of the material
  • Ventilation requirements
  • Information for health professionals in the event of an accident
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36
Q

What is polymerisation

A

A chemical reaction, generally carried out in the presence of a catalyst, which combines small molecules (monomers), containing a double bond, into a long chain of molecules

37
Q

What type of by products are produced during polymerisation

A

No byproducts are created

38
Q

What type of monomer molecules are there

A
  • Ethylene polymerising to polyethylene (PE)
  • Styrene polymerising to Polystyrene (PS)
  • Vinylchloride polymerising to polyvinyl-chloride (PVC)
39
Q

Other than polymerisation what are the other types of reactions used to make polymers or giant molecules

A
  • Polycondensation

- Polyaddition

40
Q

What is polycondensation

A

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

41
Q

What are the most important commercial polymers made by polycondensation

A
  • Phenol-formaldehyde (Bakelite) resins (typical thermosets)
  • Polyamides (nylon)
  • Polyester
42
Q

What is polyaddition

A

A reaction of two different types of molecules when reactive groups are brought together. No by products are produced

43
Q

What two types of important plastics made by polyaddition

A
  • Polyurethanes

- Epoxies

44
Q

What is an adhesive

A

A substance used to bond two or more surfaces together

45
Q

What are the advantages of adhesives

A
  • Economical
  • Distribute stress at the bonding point
  • Eliminate need for fasteners
  • Moisture and corrosion resistant
46
Q

What factors does the effectiveness of adhesives depend on

A
  • Resistance to slippage or shrinkage
  • Malleability
  • Cohesive strength
  • Surface tension
47
Q

What are thermosetting adhesives

A

Transformed in to tough, heat resistant solids by the addition of a catalyst or application of heat

48
Q

What are thermoplastic resins

A

Can be softened by heating, used for bonding wood, glass, rubber, metal and paper products

49
Q

Hat is aerosil

A

Very light white powder which is a product of combustion

Used as a thixotropic agent

Can find in a combination with resins, lacquers and even toothpaste and sauces

50
Q

What are elastomeric adhesives

A

Synthetic or natural rubber cements

51
Q

What are contact adhesives

A

Atmospheric pressure will press two solids together if there is no air between the two plane parallel surfaces

52
Q

What are solvent adhesives

A

Contain plastics or resins dissolved in a solvent. The solvent has to evaporate to cure the adhesive

53
Q

What are dispersion adhesives

A

Contain resins dissolved in water solution, such as wood glue or wood paste

54
Q

What are resin adhesives

A

Cure by a chemical reaction. They contain two or more components

55
Q

What are film adhesives

A

Similar to prepregs. Used for bonding metal to metal

56
Q

What are foaming adhesive films

A

In adhesive in sheet form which expands during the curing cycle to fill gaps and adhere strongly to all parts of the structure which it will come in contact

57
Q

What are thixotropic agents

A

A type of thickening agent

58
Q

What are the two most commonly used thixotropic agents

A
  • Micro balloons

- Aerosil

59
Q

How should resins be mixed

A
  • In a wax free container
  • Process should take between 3-5 mins
  • Always measured by weight
60
Q

What are the 4 most commonly used resins in fibre reinforced composites

A
  • Polyester resin
  • Epoxy resin
  • Vinyl ester resins
  • Phenolic resins
61
Q

What are the disadvantages of epoxy resins

A
  • Toxicity
  • Low pot and shelf life
  • Moderate to high cost
62
Q

What are the 3 levels of category for assessing damage

A
  • Allowable
  • Repairable
  • Not repairable
63
Q

For assessing damage on composite components what are the two main categories used

A
  • Skin not perforated

- Skin perforated

64
Q

What is BVID

A

Barely Visible Impact Damage

65
Q

What is chemical degradation

A

Normally affects the resin in a structure and is generally due to accidental contact with aggressive chemical liquids or products

66
Q

What does NDI stand for

A

Non Destructive Inspection

67
Q

What equipment or methods are used for NDI

A
  • Tap testing
  • Visual or optical inspection
  • Bond tester
  • Thermography
  • Holography
  • Acoustic emission
  • Ultrasonics
  • Radiography
68
Q

What is tap testing used for

A

Used for quick evaluation of any accessible aircraft surfaces to detect the presence of debonding or entrapped water

69
Q

What is holography used for

A

The rapid assessment of flaws In surfaces of composite structures

70
Q

What is the ultrasonic method of NDI

A

Quick and inexpensive evaluation of flaws in composite parts

71
Q

What is the radiography method of NDI

A

Widely used for quick and low cost inspection of composite structures

Small parts to relatively large parts

72
Q

What are the 3 repair types

A
  • Temporary repairs
  • Permanent cosmetic repairs
  • Permanent structural repairs
73
Q

What is scarfing

A

To remove damaged layers from a composite material it is necessary to remove one layer at a time

74
Q

When cleaning and degreasing what must be remembered

A

Spray on rag first then apply, do not supply straight to structure

75
Q

What is wet lay up

A

Consists of applying several layers of fabric material impregnated with resin on to the repair surface in order to restore the damaged skin

76
Q

What things must be remembered when working with resins and catalysts

A
  • Mix resin properly, inadequate mixture will result in poor strength
  • Must be weight before mixing
  • 3-5 mins for thorough mixing
  • Do not mix too quickly as air bubbles will form and will be detrimental to strength
77
Q

What are the two methods that can be used for the lay up application

A
  • Prepreg

- Wet lay up

78
Q

Why is vacuum bagging used

A

In advanced composite repairs

  • Remove trapped air and gasses during the curing process
  • To hold thermocouples and heater blankets in place
  • Provide desired surface finish
79
Q

What is peel ply

A

Also known as release fabric

A thin woven nylon or polyester fabric which has a non stick coating. It can be used instead of or underneath a perforated parting film

It’s main effect is on the surface finish of the repair

80
Q

What are the 2 potential disadvantages of using a peel ply

A
  • It absorbs some resin and may lead to a resin starved repair
  • It may contaminate the repair surface with its non stick coating
81
Q

What is a bleeder cloth

A

Also known as a surface bleeder or bleeder fabric

Used to provide an easy path for air to escape and to absorb any resin which comes through the holes in the perforated parting film

82
Q

What is a caul plate

A

Also Known as a pressure plate or pressure intensifier

A thin metal plate which is placed between the breather fabric and the heater blanket

83
Q

What is the purpose of the caul plate

A
  • To help even out temperature over the entire repair
  • To help even out the pressure over the whole repair
  • To improve the flatness of the surface of the repair
84
Q

What should caul plates not be used for

A

Complex shapes, they are designed for flat single curvature panels

85
Q

What is a heater blanket

A

Also known as a heater mat

A silicone rubber pad which contains an electrical heating element

86
Q

What is a heater mat used for

A

To control the temperature of the repair during the warm up, cure and cool down stages of a repair

87
Q

How are thermocouples identified

A

K type, j type etc

88
Q

What are the most commonly used thermocouples for hot bonding

A

J type

M6 Mac (11 decks)

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