Engineering 2

Question 1

Dye Penetration Pros and Cons

Answer 1

Pros:
Almost all materials
Cheap
Quicker
Good for small parts
Doesn’t require professional trianing

Cons:
No info o the dept of the cracks
Only surface cracks
Rough surfaces are hard to test.

Question 2

Magnetic Particle Inspection

Answer 2

Surface and near-surface cracks
1. Creates a magnetic field: uses magnets or an impressed current
2. magnetic particles suspended in kerosene are applied
3. Particles concentrate in perpendicular cracks: UV light improves visability

Question 3

Composites

Answer 3

Mechanically bonded

Question 4

Manufacturing methods of compostires

Answer 4

Hand lay-up
Spray-up
Vacuum lay-up
Filament winding

• chopped fibre composited can be manufactured with compression molding.

Question 5

Three types of corrosion

Answer 5

Stress
Wet
Dry

Question 6

Dry corrosion causes and accellerants

Answer 6

A chemical reaction between metal and oxygen, makes a metal oxide (can be porous or non-porous)

Accelerated by high temperatures, hot gases and some chemical in fuel
e.g. sulfer (all found in jet engines)

Question 7

Porous vs non-porous oxides

Answer 7

Porous allows for corrosion of underlying membrane
- brittle, flakey
vs
Non-prous: impermeable and act as a protective layer

Question 8

Wet corrosion corrosion

Answer 8

A reduction oxidation occus in three conditions:
1. An electrolyte e.g. water
2. An anode and a cathode (differentual electrolye concentrations [concentration cell corrosion] or different metals [galvanic])
3. Electrical contact between anode and cathode

Question 9

Concentration cell corrosion

Answer 9

1. Greater oxygen on the outside forms a cathode, anode in the centre
   Centre corrodes

Question 10

Crevice corrosion

Answer 10

Waer is trappen in crevices e.g. under loose paint

• oxygen cannot be easily replenished in crevice: outside becomes cathode, inside becomes
  anode.

Difficult to detect and aggressive.

Question 11

Pitting Corrosion

Answer 11

Occurs when the protective surface coating on metal is damages.
- more common with metals that form a protective oxide layer e.g. Al, stainless steel

Leads to cavities that penetrate deeply

Question 12

Galvanic Corrosion

Answer 12

Dissimilar metals come into contact in an electrolyte: form an electrolytic cell
More reactive = anode
- the further apart the reactivity of metals, the more corrosion

Question 13

Stress Corrosion Cracking

Answer 13

1. a corrosive environment must exist
2. The material must be susceptible to attack e.g. austenitic stainless steels and Al
3. A static residual or applied stress must be present.

Can come from welding or coldworking/pressure.

Question 14

Intergranular corrosion

Answer 14

A phenomenon related to SCC.

Grain boundaries are high stress and so will corrode first.

IN STEEL:
- corrosion happens anodic ferrite grains and cathodic cementite grans instead of at grain boundaries

Question 15

Exfoliation Corrosion

Answer 15

A severe form of intergranular corrosion that typically occurs along the elongated grain boundaries of wrought Al, etc.

Appearance of flaking or delamination.

Commonly occurs in aircraft body and wing skins.

Question 16

True length diagram types

Answer 16

1. Layout method: open box shapes
2. Rollout method: prisms or cylinders
3. Radial Method: shapes with an apex e.g cones.
4. Triangulation method: transition pieces: not all lines are ‘true length’.