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Engineering > Materials > Flashcards

Materials Flashcards

1
Q

Ceramics (Properties)

A

Properties: -BRITTLE
-resistant to corrosion/environmental degradation = long lifespan,
- hard, strong in compression:
- high stiffness (Young’s mod)
- high melting temp
- thermally and electrically insulating
- low thermal shock resistance
- resistant to vibrations
good for CIVIL STRUCTURES

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2
Q

Ceramics: What are they?

A

Compounds of: Metals and non-metals thru ionic bonding, non-metals via COVALENT bonding

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3
Q

Ceramics: common types

A

Stone
Clay ceramics
Cement
Glass

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4
Q

Stone types

A

Igneous: volcanic prosses (e.g. Basalt for asphalt and road bases, Granite for masonry)

Metamorphic: High pressure (e.g. slate in roofing, Marble for decoration)

Sedimentary: Deposition (e.g. Limestone for cement, Sandstone for masonry)

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5
Q

Stone properties

A

Weak in tension, strong in compression, low toughness (brittle)
- easy to chisel/hand carve (masonry)
Usually rough finish

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6
Q

Clay ceramics:

A

KAOLINITE: plate-like structure: absorbs water well: plastic and slippery (easy to form)
- can have other additives e.g. quartz to reduce shrinkage, alter plasticity, reduce firing temp

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7
Q

Clay firing:

A

DrDeOV
Drying (>150): evaporation of water between platelets, loss of plasticity
Dehydration: (400-600) Dehydration of kaolinite
Oxidation:(300-700)
Vitrification (>900) Formation of mullite clusters with a glassy matrix: severe shrinkage

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8
Q

Cement (definition, composition and 2 types)

A

A binding agent made of limestone and clay, good adhesive properties yet weaker than cement and prone to cracking (Romans, not used widely until 19th century)

Alumina, soda and lime are reacted at high temperatures.

Non-hydraulic: set when exposed to air
Hydraulic: set due to a chemical reaction with water (can be used underwater)

setting is EXOTHERMIC

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9
Q

Cement properties

A

Strong in compression, weak in tension and low toughness. similar to stone with properties by is able to be cast

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10
Q

Cement powder formation

A
  1. Limestone and shale mixed together and ground
  2. Heated in kiln to fuse and form clinker
  3. ground clinker mixed with gypsum (slows setting time)
    4.Reground and mixed
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11
Q

Lime Mortar (and making process)

A

Non-hydraulic,

  1. made by mixing limestone and silica, alumina and iron
  2. Firing at 1000 (LASI)
  3. adding water makes hydrated/slaked lime
  4. This mixed with sand is lime mortar: used historically in brick and stone buildings.
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12
Q

Gypsum

A

Non-hydraulic: when made by hydrating calcium sulphate to form a semi hydrate, it is PLASTER of Paris
- soft, porous, water-soluble
- USES: art and building lining

OR when heating cal. sulf. to form anhydrate: Keene’s cement
- hard, strong, insoluble
- used in exposed surfaces, imitation marble

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13
Q

Pozzolana

A

Siliceous material used in making Roman Hydraulic cement
- naturally occurring (volcanic)

Made from silica, alumina and iron oxide

  • Cement is made with pozzolana, lime and water (heated and ground into powder)
  • mixed with water and aggregate to make concrete
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14
Q

Glass (structure and how to make)

A

AMORPHOUS structure silica: made by adding a network modifier, e.g. soda and lime to quartz-based sand

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15
Q

Glass properties

A

Transparent due to loose structure, crystallized glasses are TOUGHER but less optical clarity.
Unfavourable to machining due to lack of slip planes: must be done at high temperatures where viscosity is reduced

  • brittle, low toughness, weak in tension
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16
Q

Types of Glass modification:

A
  • Chemically: addition of oxides e.g. boron, coloured pigments, modifiers e.g. lead
  • Mechanically: lamination with polyvinyl butyl (laminated glass has an interlayer of polymer to prevent penetration, breaks on impact, keep shards intact etc.): CARS
  • Heat treatment: soften and releases internal stresses to produce toughened glass: outside cooled, inside cools slower and thus shrinks, leaving the outside in compression.
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17
Q

Types of glass

A

annealed glass, breaks easily in long, sharp shards: soaked at 470 then cooled slowly
Heat strengthened glass: resistant breakage ~2x stronger
Fully tempered glass: resistant to breakage, ~4x as strong as tempered, shatters in small pieces
lamination with polyvinyl butyl (laminated glass has an interlayer of polymer to prevent penetration, breaks on impact, keep shards intact etc.)

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18
Q

Composites (Defininition)

A

Consists of two or more materials joined mechanically: creates properties unattainable from the original materials.

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19
Q

Composites classifications:

A

Natural (timber, some stone)
Fibre-reinforces (fibreglass, carbon fibre and geotextiles)
Particle reinforced (concrete)
Dispersion-strengthened: (precipitation hardened, sintered metals)
Laminated (wood products with metal/plastic laminates)

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20
Q

Concrete composition

A

Composite of cement, sand, aggregate

Role of aggregate (sand + Water) is to:
- Resist applied loads and abrasion
- Provide a filler for cement to bind
- Reduce volume changes when setting

Role of cement-water paster:
- lubricate concrete mix
- fill voids between aggregate
- strengthen the concrete

Dry concrete mix in a 4:2:1 ration

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21
Q

Concrete MACROSTUCURE

A

heterogeneous microstructure:

BIG grey: angular coarse aggregate
Small grey: angular fine aggregate
Fine sand particles within cement paste

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22
Q

Concrete characteristics:

A

Advantages:
- high compressive strength
- moldable
- durable against corrosion and rot
- fire resistance
- heat + noise insulating
- low cost
- can be reinforces
- can be precast or formed on site

Disadvantages:
- heavy
- labour intensive
- slow to set and cure
- can spall, crack or experiences chemical deterioration
- Low toughness and tensile strength

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23
Q

Crack formation and growth

A

Higher Strain energy = more chance for crack formation (cracks release strain energy which concentrates the bottom of the tip: thus crack growth accelerates with time
- method of brittle failure

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24
Q

Critical Crack length

A

Once this length is achieved, the crack will continue until failure.

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25
Q

Destructive testing Types:

A

Compressive: concrete: subjected to testing across different time intervals. Load applied is measure, as well as the way the concrete destructed
Transverse: (bending and shear)
Torsion: (twisting forces e.g. couples)
Tensile: Applying a tensile force until necking and then fracture.

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26
Q

Elastic vs Plastic deformation

A

Elastic: Metallic bonds stretch but do not break
Plastic: applied force is enough to break metallic bonds: Permanently deform along a slip plane

(NOTE: BCC cells have more slip planes the FCC)

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27
Q

How does Work Hardening work?

A

Work hardening moves dislocations through the lattice structure, increasing the amount of dislocations and thus making it less ductile more brittle.

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28
Q

How to grain boundaries form?

A

Through the random nature of cooling, unit cell lattices will grow and then merge to create grain boundaries

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29
Q

3 Non-destructive testing types:

A
  1. X-ray testing:
    - observe cavities and cracks
  2. Dye penetration test:
    - See cracks existing on the surface. Area is prepped by removing surface contaminatnts e.g. oil, then heated. Dye is applied, excess whiped off. A developer is appplied, then cooled. (squeezes out dye from cracks from shrinkage)
  3. Ultrasonic testing:
    - similar to x-ray, expect radio waves instead. Waves sent out, reflected to transmiter. (Early waves = cavity)
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30
Q

Slump Test

A

Measures workability, compacts a sample into a metal cone which is tempered multiple times, before lifting and measuring how far the concrete collapses. The greater the slump, the increased workability. However, collapse = too wet, crumbling = too dry

High slump = narrow or complex structures, low slump = larger structures

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31
Q

Strain energy

A

The amount of energy stores in a material that has undergone strain (e.g. tensile, compression, torsion, bending)
SE=1/2 stress x strain

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32
Q

Tranverse bend/beam testing

A

Three or four point loading (^—v—-v—^ vs ^—-v—-^)
measures flexural strength or modulus of rupture

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33
Q

Types of Cast Iron:

A
  1. White cast iron
  2. Grey cast iron
    3.Malleable cast iron
  3. Ductile/nodular/spheroidal cast iron
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34
Q

White Cast Iron

A

Low carbon, <1% silicon (graphite cannot form)
- dendrites of pearlite in a cementite matrix
- Hard, brittle, good castiblility

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35
Q

Grey cast iron

A
  • High carbon, enough silicon to make graphtite
  • Graphite flakes (make it prone to fracture) in a pearlite/ferrite mixture
  • lower tensile strength, vibration dampening self-lubricating, resistant to corrosion
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36
Q

Malleable cast iron

A
  • High carbon and silicon
  • Graphite rosettes in pearliitic/ferritic matrix (made by heat-treating WCI)
  • Soft, malleable, ductile, tough, machinable
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37
Q

Ductile/nodular/spheroidal cast iron

A

Highest carbon and silicon, some magnesium or cerium
- Graphitic spheroids in a pearlitic/ferritic matrix
- Soft, malleable, tough, machinable

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38
Q

Types of Imperfections in lattice structures:

A
  1. Point defects
  2. Dislocations
  3. Planar imperfections (e.g. grain boundaries)
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39
Q

What is Cast Iron and properties?

A

2-4% carbon content, usually brittle especially under tension, with high compressive strengths.
- cheap in production
- Good wear resistance and hardness
- Typically manufactured in a mold

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40
Q

Cracking Prevention and fixing for ceramics, metals and polymers

A

If metallic: welding
- repairs crack, however other microstructural changes weaken material (potential point of stress concentration)
- must be then heat treated

Polymeric materials:
- adhesives, polymer welding (thermoplastic)

Ceramic materials:
- drill a hole to release strain energy buildup

PREVENT: don’t use sharp corners, add interfaces (prevents critical crack length)

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41
Q

Timber composition and types

A

Consists of cellulose fibers/tracheids, held together in a lignin resin.

Hardwood vs softwood: pored vs non-pored

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42
Q

Timber Properties

A

High specific strength (strength/weight ratio), reasonable at bending

Good Young’s modulus

Adversely affected by weather, susceptible to attacks by pests. (not long-lasting)

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43
Q

Concrete reinforcement:

A

Reinforced concrete: Reinforces with steel rods/mesh that takes tensile load.

Pre-stressed reinforced concrete: tensioned beams in concrete, which when released, place in compression

Post-tensioned: wires are pulled thru slab

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44
Q

Spalling and prevention

A

Steel inside corrodes: expands, cracks concrete: prevented by ensuring correct water ration, vibrate concrete to reduce porosity

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45
Q

Asphalt composition and properties

A

Good for road surfaces: made with hard aggregate (often slag or basalt) and bitumen as matrix.

Tough, crack-resistant but hard-wearing. Impervious to contamination by oil. Can deal with slight movements in road.

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46
Q

Laminates: what and examples

A

Varying materials sandwiched together

Plywood:
= timber with grain structure and 90 degree angles.
Laminated veneer lumber (LVL): stronger then timber, less susceptible to shrinkage or warping
Laminated glass: shatter resistant
Bimetallic strips: two metals back to back (thermostats, protection circuits)

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47
Q

Geotextiles: what and properties/uses

A

Woven polymers (usually polypropylene, polyester or ceramic fibers)

Stabilising road bases (under asphalt, often contaminated by earth underneath): makes layer between base and subsoil

Filters for drainage systems, stop dirt from getting into storm water runoff.

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48
Q

Corrosion: (dry and wet)

A

Chemical deterioration of a material (‘reverse refinement”)

Dry:
- chemical reactions with gases in furnaces at high temps e.g. steam locomotive boilers, water tubers.

Wet:
- metal is placed in a fluid usually electrolyte.

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49
Q

Wet corrosion types: (uniform and galvanic)

A

Uniform attack:
- placed in electrolyte, some parts cathodic, some anodic (constantly changing)

Galvanic:
1. corrosion: dissimilar metals placed together, more anodic will corrode.
2.Concentration cells: difference in concentration of electrolyte e.g. trapped water.
3. Stress cells: high residual stress in parts of metal object. (high stress = anodic) e.g. grain boundaries

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50
Q

Oxidisation and reduction

A

O: loses electrons at anode
R: gains electron at cathode

The more cathodic = more stable e.g. platinum.

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51
Q

Passivity

A

When a metal forms a protective film from corrosion, e.g. aluminum, titanium, chromium.

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52
Q

Rust

A

Needs water and oxygen: continually flakes off to expose metal underneath

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53
Q

Protecting against corrosion (5 types)

A

Painting the steel: provides protective layer

Galvanising: dipping steel into molten zinc: protects from corrosion for far longer. Other products can then be added on top to further this effect.

Cathodic Protection: object made cathode to prevent corrosion

ICCP systems: use a current to reverse standard electrical flow: steel becomes cathode (found in pipelines, long structures, etc)

Sacrificial Anodes:
- using blocks of more anodic metals bolted nearby (steel becomes cathodic): e.g. ship hulls.

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54
Q

Steel Properties

A

Cost effective, tough, strong in tensile and compression, ease of fabrication, hard, ductilie
- properties are manipulatable

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55
Q

Train environmental factors

A

Still use a lot of pollution HOWEVER better then individual transport options
- Train lines are use far less land then roadways

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56
Q

4 Testing processes for hardness

A

Brinell: Hardened steel ball impressed into surface, SA measured.

Vickers: Square pyramid, (V is POINTY) Formula with load and area (better for thin metals)

Rockwell: smaller diamond cone or sphere pressed into surface, DEPTH

Shore Scleroscope: a small striker in a tube: height it rebounds is measured.

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57
Q

4 Types of Steel: (alloys)

A

Carbon steel
Stainless steel
Alloy steel
Tool steel

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58
Q

Impact tests: what do they measure? 3 Types?

A

They measure notch toughness (ability for material to absorb shock energy)

Izod: large pendulum raised to give it PE, then struck against the test piece, losing KE and thus not reaching as high. The height reached is recorded. Sample has v shaped notch to promote crack propagation
|
|
<
——

Charpy: nv`n held horizontally, notch away from pendulum.

Hounsfield: Smaller, transportable: uses two pendulums

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59
Q

Process Annealing:

A

Heating steel with <0.3% C to a temp ~ 550-650. Relieves stress from distorted grains e.g. after cold working, deformation. Cooled in still air. FERRITE UNSTRESSED, PEARLITE STRESSED

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60
Q

Full Annealing

A

Heat hypo-eutectoid or eutectoid steels to AUSTENITE or 40 degrees above upper critical temperature (UCT). Cooled in furnace. All grains unstressed.

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61
Q

Austenite

A

FCC structure, only occurs at high temperatures.

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62
Q

Normalising

A

Heating to austenite region far above UCT. Cooled in still air.

Shorted the annealing, finer grain structure and thus stronger steel.

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63
Q

Spheroidising

A

Medium to high carbon steels: high cementite = hard to machine

Heating to 650-700, holding it there. Cementite in pearlite makes spheroids: much easier to machine

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64
Q

Steel ranges and properties (low, mild, medium, high, ultra high)

A

Low carbon: up to 0.15%.
- soft, ductile, malleable
- Sustain cold-working
- Equiaxed ferrite grains, some pearlite
- Rivets, car bodies, chains e.t.c.

Mild: 0.15-0.3%
- “”
- structural steels

Medium: 0.3-0.6%
- Tough, hard, machinable
- small equiaxed ferrite, mostly pearlite
- shafts, axels, gears, etc.

High carbon: 0.6-0.9%
- Brittle, hard, poor machinability, high tensile strength
- pearlite with cementite at grain boundaries
- high strength and wear resistance in non-cutting tools

Ultra-high (1-2%)
- cutting tools
- High strength and hardness

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65
Q

UCT (Upper critical temperature)

A

Point at which steel becomes completely austenite.

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66
Q

Martensite:

A

When rapidly quenched, carbon attempt to go from FCC to BCC but gets trapped, causes internal stresses.

forms BCT structure. Sharp points have a build up of stress

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67
Q

Quench Hardening

A

Only done to steels above mild grade (enough carbon content to form martensite)
- high brittleness, hard, good wear resistant

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68
Q

Air hardening

A

Done with steels with some nickel and chromium (<5%) (NiCr)
- heated to red hot and cooled in still air.

Molybdenum usually added to reduce brittleness.

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69
Q

Tempering

A

Sacrifice some hardness with great increase in toughness

Hardened steel heated to between 200-600, (more temp = more tough)

Needle structure of martensite with some shading of acicular martensite being broken down into ferrite and cementite.

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70
Q

Austempering

A

Austenitic steal quenches to around 400, held until consistant temp, then queched to room temp

Forms BAINITE: similar to tempered martensite, but more resiliant.

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71
Q

Banite

A

Formed through austempering
similar to tempered martensite, but more resiliant.
formed when quench rate is not fast enough for martensite

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72
Q

4 Surface hardening techniques and why

A

Harder outside for scratches, etc, yet tougher inside

Case Hardening (carburisation)
Nitriding
Flame Hardening
Induction hardening

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73
Q

Case Hardening/Carburising

A

Heating and soaking steel in a carbon rich atmosphere. Increases carbon content on surface, hardness and tensile strength.

  • Further heat treatment is difficult, however normalising and hardening of surface possible
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74
Q

Nitriding

A

Alloy steal heated in furnace with nitrogen present. Performed at 500 for 40-100 hours.

This reacts with alum., chrom, or vanadium.

High hardness, corrosion resistant surface.

Initially costly, and properties lost if heated beyond 500.

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75
Q

Flame Hardening

A

Applies a flame to localised area then quenched. Mechanised with flame and water jet holder on same assembly

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76
Q

Induction hardening

A

Similar to flame hardening except using an induction coil. Quenched.

good for camshafts

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77
Q

Austempered Ductile Irons (ADIs)

A

Austempered spheroidal cast iron/ductile cast iron.

Acicilar ferrite within austenite structure.

Excellent tensile strength, easier to cast, lighter, less affected by sub-zero temperatures, work harden, better damping capacity.

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78
Q

3 ways of changing properties of Steel

A
  1. Heat treating
  2. Alloying
  3. Carbon content
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79
Q

Manufacturing processes

A

Forming
Casting
Molding
Joining
Machining
Additive

FCmmJA
For cults, make many acidic juices

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80
Q

Forming: what is, types

A

Applying forces or pressure to PLASTICALLY deform material
- used for metals, hot or cold working

Forging
Extrusion
Rolling

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81
Q

Casting

A

Die casting
Sand
Investment

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82
Q

Molding

A

Used for PLASTICS
injection
Compression
Blow

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83
Q

Joining

A

Welding
Soldering
Fastening

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84
Q

Machining

A

Turning
Drilling
Reaming

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85
Q

Additive

A

3D printing
Laser sintering
Vat photopolymerisation

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86
Q

Hot vs Cold rolling: what, benefits

A

Hot: above recrystallisation temperature, grains can re-nucleate and grow annealed grains
- easier to plastically deform
- ductile and malleable: unstressed:
- not as dimensionally accurate, bad finish
Cold: below
- increases strength and hardness of material, requires more force to extrude
- more dimensionally accurate, better finish
- more costly (heavier machinery)

BOTH:
- good mechanical properites
- can be fully automated
- high tooling costs
- can’t form complex shapes

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87
Q

Forging: What and properties

A

hot or cold

better mechanical properties as grainflow follows shape of object
- worse tolerances
- expensive equipment

Closed die/impression forging: placed between two dies, then hammered into shape.

88
Q

Extrusion: 3 types

A

Hot metal in a chamber, using a ram to force it through a die

Indirect, direct, impact extrusion
Uses: pipes, rod, tubing, fencing, thermoplastic coatings, wire insulation.

89
Q

Indirect vs direct extrusion

A

Only can form 2D shapes, hot working process

Direct (more common): uses more force, thus usually done with more ductile materials, cheaper

Indirect: alloys with lower ductility, yet more expensive

90
Q

Impact extrusion

A

Cold forming process

Hammer ‘punches’ blank into die, material is forced to flow up the sides
- cans, short tubes

91
Q

Drawing vs Upsetting (forging)

A

Drawing: increasing length, smaller cross sectional area
Upsetting: reverse

92
Q

Hot vs Cold working uses

A
  • sheets, strips, bars, etc
93
Q

Casting

A

Pouring molten metal into a mold, allowing it to solidify
PRIMARY forming process (often requires further refining for surface finish)
- used for metals

94
Q

Die casting process

A

Placed in hopper, released into shaft which is then, through a ram, is forced into the reusable die. Removed once solidified

  • non-ferrous metals e.g. aluminium, zinc
  • good surface finish
  • tight tolerances
  • high start-up cost.
95
Q

Die casting/permanent mold casting + 2 types

A

Uses a permanent mold: more environmentally friendly, cheaper for long-term manufacturing, good surface finish
GRAVITY:
- automotive parts e.g. pistons
PRESSURE:
- higher denisty
- lower melting-point alloys e.g. aluminium and zinc (cheaper)
- GRAPHITE dies needed for ferrous alloys
- gear box casings

96
Q

Sand casting process, pros and cons, uses

A
  • common
  1. “Drag” is placed on board, Sand with binder (green sand: can be reused) has pattern of finished product (in two halves)
  2. Drag inverted, top box ‘cope’ placed on top.
  3. Cope, drag separated, patter, riser and runner puns removed.
  4. Molten metal poured in until riser and runner filled.
  5. soldification: shrinkage alleviated by excess in riser pin
  6. halves removed, pins ground off.
  • can be automated, cheap, good grain structure, wide range of metals, large and complex parts
  • BUT poor surface finish, inaccurate: further machining is required for higher precision

e.g. automative fields such as engine blocks and heads.

97
Q

Investment casting/Lost wax casting: pros, cons, process and uses

A
  • high quality, dimensional accuracy, high surface finish, cast metal alloys too hard to machine.
  • new mold made each time: costly, time consuming.
  1. wax patterns attacted to a ‘sprue’ to for a tree
  2. dipped into slurry, make ceramic mold.
  3. Heat melts out max, leaving mold. Molten metal is then poured in
  4. Ceramic is removed through vibrations
  • rocker arms for automotive engines, transport systems, turbine blades, dropouts for bikes.
98
Q

Ingot casting

A

Intially cast into a large block/ingot that can then be further processed.

Molten metal poured into large, tapered mould.

Outdated: now mechanised continuous casting.

99
Q

Continuous casting

A

Rapid production of simple cross-section products e.g. bars, strips

Molten metal poured in water-cooled ingot with sliding bottom
- once solidified, this moves down continuously, etc.
- long metal strip formed, then cut to required length

  • cost effective for large runs
  • rapid speed
100
Q

Shell moulding: pros and cons, process

A
  • similar to sand casting: better surface finish, closer tolerances the die casting.
  • more expensive
  1. starts with heated pattern plate (partially sets resin, binding sand together) and frame in oven
  2. cope and drag sit side by side
  3. Burners heat pattern to ~315 to fully cure resin
  4. cured half ejected off by pins
  5. two halves bolted together, placed in box, molten metal poured in. Once solidified, removed.
101
Q

Centrifugal casting

A

Metal is spun in a mold and forced into shape of hollow cylinder
- useful for pipes, piston rings

102
Q

Full mold process

A

similar to investment, but used for one-offs/prototypes e.g. suspension systems

  1. pattern made with runner from polystyrene
  2. placed in box, surrounded by sand with thermosetting resin
  3. metal poured in, melts foam.
103
Q

Powder Forming/metallurgy process

A
  1. Metal is made into power by grinding, atomising chemically, or electrolytically
  2. Then blended with stearate based dry lubricants and pressed into mold (cold welding
    • pressure compacts particles together
  3. Sintered in a furnace: homogenous grain structure
104
Q

What is made with powder forming? (4 groups)

A

Porous metals:
- using larger powder sizes, metal with porous properties and can be impregnated with oil for lubrication e.g. bearings in bike suspensions, electric motor bearings

Complex articles:
Some shapes too difficult/costly to cast and machine

products difficult to machine: too hard to machine e.g. tungsten cemented carbides

composites: cannot be alloyed, so formed together to maintain individual properties e.g. copper/silver with tungsten/nickel for electric contacts

105
Q

Power metallurgy pros and cons

A

Allows for products otherwise too difficult to make
BUT: expensive to set up fascilities, still limited shapes
Not as strong

106
Q

Welding types, description

A

Fusion:
- done WITHOUT filler material (base material is melted together

Pressure:
- done with filler

Joining process, better for low-carbon steels (high carbon = martensite, slow cooling necessary)
don’t recommend with stainless steels unless with very low carbon (prevents oxide layer)

107
Q

Butt Welding

A

Pressure

Metal is butted together at ends and current melts metal.

  • joining tubes
107
Q

Spot Welding

A

Pressure welding.

Electric current melts metal sheets, joining it in ‘spots’

Used in car manufacturing

108
Q

Seam Welding

A

Pressure:

Metal moved through rotating wheels that pass electric current
- melts, then joins

  • tubes for cheap bikes
108
Q

Oxy-acetylene Welding

A

Fusion
- Metal is metled by oxy-acetylene flame, filler metal added.
- used in repairs, more home-style DIY repairs

109
Q

Bronze Welding

A

Fusion/alloying

A flame heats parent metal, bronze filler is added. (different from oxy-acetylene as little to no melting of parent metal)
- lower-temperature projects

110
Q

Electric arc welding

A

Fusion

  • melted by an electrode (also filler metal)
  • electrode covered in flux to prevent oxidisation
  • electrode must be changed periodically
111
Q

Metal inert gas (MIG) welding

A

Fusion
- replaces electrode of Electric arc welding with continuous feed of wire (quicker)
- flux replaced by inert gas

  • good for automation, used in car and bike manufacturing
112
Q

Tungsten inert gas (TIG) welding

A

Fusion

Similar to MIG but replaces wire with a tungsten electrode and filler rod fed by operator.
- similar to MIG, argon shield used to protect weld

  • good for stainless steel, aluminum and titanium alloys
113
Q

Plasma arc welding

A

Fusion

A gas e.g. argon passed through electric arc. gas IONISES electrons and positive ions
- called plasma
- ions recombines, make hot flame
- used with high refractory metals e.g. tungsten and molybdenum

114
Q

Stainless steel properties

A
  • add chromium and sometimes nickel
  • CORROSION resistantHigh tensile strength.
    Very durable.
    Temperature resistant.
    Easy formability and fabrication.
    Low-maintenance (long-lasting)
    Attractive appearance.
    Environmentally friendly (recyclable)
115
Q

Tool steel

A

High carbon content with vanadium, tungsten, chromium, etc

Wear resistance, heat resistance, toughness

116
Q

HAZ and welding structure:

A

Heat affected zone: part that has not melted yet still experiences changes in structure: weaker then parent metal

Original cold rolled structure -> recystalisation -> grain growth -> chill crystals -> columnar grains -> equaixed grains

117
Q

Aluminium properties, uses

A
  • lightweight
  • extremely reactive
  • low strength, hard to weld
  • more costly then mild steel
  • ductile
  • low specific gravity
  • easily fabricated

BUT
- good specific strength
- corrosion resistant
- electrical conductivity

Wiring, cooking pots and pans, foil, alloying

118
Q

Aluminium alloys: (2 types)

A

Wrought:
- heat treatable and non-heat treatable
- mechanical working

Casting:
- good for casting

119
Q

Non- heat treatable aluminium alloys:

A

1xxx, 3xxx, 5xxx

120
Q

1xxx aluminium

A

Pure aluminium with small amounts of iron and silicon
- used for sheet metal work

121
Q

3xxx

A

Manganese alloyedm solid solution strengthening

  • used for pressure vessels, chemical equiptment, sheet metal
122
Q

5xxx

A

Magnesium, (5052 is most important industrial alloy)

  • sheet metal work, truck and marine applications
123
Q

Heat Treatable alloys:

A

2xxx, 6xxx, 7xxx

124
Q

2xxx

A

Copper: strengthened by solid solution strengthening and precipitation hardening

e.g. duralumin

  • aircraft structures (high tensile strengths)
125
Q

Solid solution hardening

A

introduction of solluble elements to distort lattice

126
Q

6xxx

A

Two primary alloying elements: magnesium and silicon
- strengthened through precipitation hardening
- good corrosion resistance and strength

  • bike frames, truck and marine uses
127
Q

7xxx

A

Zinc, but also other allows of magnesium and copper
- strengthened through precipitation hardening (alloy elements allow denser precipitates -> stronger alloy)

  • aircraft structures, quality bike parts
127
Q

Casting alloys choice of manufacturing

A

Sand-casting, gravity or pressure die-casting

127
Q

Aluminium Lithium alloys

A

used in bikes and aviation
- better fatigue life, better strength
- replaced CFRP

127
Q

Aluminium casting alloys system

A

ACSSMZTO
All cookie snacks should make zebras totally obese
(al, Cu, Si +cu/mg, si, mg, zn, sn, other)

127
Q

Casting alloys:

A

most contain silicon (5-12%)
- lower melting point for alloy (fluidity improved)
- strengthens alloy
- manganese and copper also added to improve strength and hardening

127
Q

Important aluminium alloy in transport industry

A

aluminium/silicon/magnesium/iron alloy
- used in wheels

127
Q

Cartridge Brass

A

70/30 brass
- ductile
- was used in making cartridges for bullets
- higher ductility then Cu
- good for deep-drawing operations

128
Q

Copper alloys

A

Used in electrical industries, cost effective
- used in railway overhead wiring

128
Q

Brass alloy

A

Copper and zinc (COUSIN = CuZn)
- Commercial rarely contains over 40% zinc: becomes brittle, of little use
- up to 35% zinc is single-phase alloys (fully soluble together)

128
Q

Types of Brass alloys (5)

A

Cartridge brass
Standard
Muntz metal
Naval Brass
High tensile Brass

129
Q

Standard Brass

A

Only 25% zinc: good quality, cold-working alloy
- stampings and limited deep drawing

130
Q

Muntz Metal

A

two-phase brass
- 40% zinc
- brittle phase in microstructure
- hot-worked
- rods and bars, can also be cast e.g. tap bodies
- can be heat-treated

131
Q

Naval Brass

A

37% zinc, 1% tin, corrosion resistance in seawater (shipbuilding)

132
Q

High-Tensile Brass or manganese bronze

A

36% zinc, with small bits of Mn, Al, Pb, Fe, Sn
- tensile strength, less ductility

  • used for stampings and pressings
  • also marine propellers and rudders
133
Q

Bronze and types

A

copper and tin alloy
Low tin
High tin
Admiralty gunmetal
Leaded gunmetal
Phosphor bronze
Aluminium bronze

LLAAHP
Less legs also adds health points

134
Q

Low tin bronze

A

3.75% tin
- good elastic properties and corrosion resistance
- good for springs

135
Q

High tin bronze

A

18%: heavy load applications e.g. slewing turntables on large cranes

136
Q

Aluminium Bronze

A

Cu alloy with primary alloying element Al.
- good corrosion resistance, tensile strength
- marine and chemical applications
- casting is hard (oxidisation of Al)

  • hardenable through heat treatment
137
Q

Leaded Gunmetal/red brass

A

85% Cu, 5% Sn, Zn, 1% Pb
- reduced ductility
- but increased durability: good for pressure vessels

138
Q

Admiralty Gunmetal

A

885 Cu, 10% tin, 2% zinc, some Ni
Zn makes allow more fluid, good for casting
- pumps, valves, marine castings (good corrosion resistance in salt water)

139
Q

Phosphor Bronzes

A

Bronze with phosphorous added
- higher tensile strength, corrosion resistance
- lower μ, good for bearings

140
Q

Structure of non-ferrous alloys

A

Second harder phase: reduces ductility, e.g. Muntz metal

141
Q

Heat treatment of non-ferrous alloys

A

Annealing
Precipitation hardening

142
Q

Precipitation hardening: metal

A

Duralumin and similar aluminium alloys, etc.
- after being cold-worked: have primary and secondary phase (usually at grain boundaries): hard and brittle

143
Q

Precipitation hardening steps

A
  1. Alloy heated to 530, b phase dissolved to produce a homogenous single-phase alloy. Cooled. Then soaked.
  2. quenched to room temperature: single phase microstructure of equiaxed a grains

AGING:
1. trapped beta phase precipitates out, restricts movements of dislocations and strengthening of alloys (natural aging)
OR
artificial aging:
- accelerates precipitation by heating alloy to 150. (CAREFUL: too long = overaged, brittle)

144
Q

Ceramic uses

A

Alumina is used as insulatiion in spark plugs

145
Q

4 Glass types

A

High silica glass
Soda Lime Glass
Borosilicate glass
Lead Glasses

146
Q

High Silica Glass:

A

Refined from borosilicate glass
-very clear
- good against elevated temperatures: excellent resistance to thermal shock (missile nose cones, space vehicle windows)

147
Q

Lead Glasses

A

Contain up to 40% Pb.
- Lowers softening temperature
- high refractive index: optically clear
- good for optical glass, thermometer tubes, tableware

148
Q

Soda Lime Glass

A

Common
- soda prevents devitrification (crystallisation)
- makes it water soluble (however lime alleviates this)
- easy to form when hot, cost effective, water resistant
- windows, plate glass, bottles, electric light bulbs

149
Q

Borosilicate glass (Pyrex)

A

Glasses with 20% boron and silica
- chemical resistance, low thermal expansion (resistant to fraction at high temps)
- electrical insulation, gauge glasses, domestic cooking

150
Q

Thermoplastic structure

A

Strong primary covalent bonds, weak secondary bonds (Van der Waal’s forces)
- flexible, transparent, recyclable
- low tensile strength
- ductile

151
Q

Thermoplastic examples

A

Polyethylene
Polystyrene
Polytetrafluoroethylene (PTFE)
Polymethylmethacrylate (Acrylic)
Polypropylene
Polyvinyl chloride (PVC)
acrylonitrile butadiene styrene (ABS)

152
Q

Themoplastic uses

A
  • cable coating for bikes, car parts e.g. grills, badges, door handles, window winders
153
Q

Thermosets structure

A

Undergoes a chemical change when under heat (non-reversible)
- has a network structure with strong covalent primary and secondary bonds
- resistant against deformation (tough)

154
Q

Laminated glass:

A
  • uses a small sheet of PVB
  1. layers assembled in area of low humidity and temoperature
  2. passed thorugh heaters and rubber rollers to achieve preliminary adhesion
  3. high pressure and temps are applied: final adhesion and even thickness
  4. then cooled gently
155
Q

Thermal toughing of glass

A

cooled very quickly: outside in compression, inside in tension

156
Q

Chemical toughening (Glass)

A

Submersed in a bath of potassium nitrate at 300.
- sodium ions on surface replaced by potassium ions (LARGER)

  • surface in compression, core in tension
  • Thus stronger, BUT cannot be cut or shaped afterwards
    -used in protective glass applications e.g. phones, cameras
157
Q

Fracture patterns

A

Untreated: ///-/|/\/: long, sharp sharsd emanating from centre

Toughened: oooo: shaatters into small pieces

Laminated: spider web, glass intact afterward

158
Q

Hooke’s Law property

A

Elasticity

159
Q

Generator

A

Converts Kinetic energy into Electric

160
Q

Form of energy sources

A

Coal/gas powered turbines
Petrol and diesel endinges
Wind
Hydro
Tidal

161
Q

Environmental impacts of hydro

A

Impacts on irrigation/farming
Deforestation
Disruption of natural waterways: wildlife

162
Q

What type of electricity is generated

A

All create AC except for solar farms (DC)

163
Q

Frequency of AC power

A

50Hz (Aus)

60Hz (America)

164
Q

Why 3 Phase?

A

Single phase varies with time: ok for small household devices, however not for large machinery

Thus, 3 phase (shifted by 120) provides CONSTANT power: causes less stress to mechanical components of generators and motors.

165
Q

Advantages of 3 phase

A

more efficient against resistive losses

Long-distance tranmission can be done without a neutral conductor (reduces size and weight

Higher Voltages eaily obtained by combining 2 or 3 phase

166
Q

TPS Power cable

A

Thermoplastic sheathed copper cabling
- used in residential and light industrial applications

166
Q

3 types of power cbles

A

Low voltage: Copper with PVC insulation
High Voltage: copper or Al, polyethelene insulation
Extra High Voltage: aluminium with steel core, not insulation

More cases: wire is stranded rather than solid.

167
Q

TPS cables properties

A

Some flat cables, but usually round
Solid or stranded wires
Each wire is separately insulated

168
Q

Four-core armoured cable

A

Three live wires and a neutral
Used in low voltage outdoor applications
Each is insulated separately
Armour later provides mechanical protection

169
Q

High Voltage Cables

A

Aluminium or copper
Stranded, may have steel core

Insulation is ethylene propylene rubber EPR or crosslinked-polyethylene (XLPE): thick
Copper screen acts as earth, drains leakage currents
Mechanical protection by Al or Pb sheath
Jacket may be PVC ,HDPE or polypropylene

170
Q

The skin effect

A

Tendency of AC to flow along the SURFACE of the conduction
- decreases and frequency increases (about 8mm at 50Hz)
- more important in large diameter cables
- stranded wire allows for steel reinforcement is centre, which no current passes through

171
Q

Aluminium conductor steel reinforced powerlines (ACSR)

A

Lines are stranded
Al better then Cu (density, price)
- steel core for mechanical strength
- lines are not always insulated

172
Q

Rectification

A

Because of transmission losses: power generated at power stations is AC, but DC is needed

Rectifir uses DIODES and CAPACTATORS to go from AC-Dc

173
Q

Diodes

A

Only allow current to flow in one direction

174
Q

Rectifier Types

A
  1. Half wave
  2. Full wave (bridge)
    - both may be filtered (smooth)
175
Q

Capacitator

A

Stores electric charge (e.g. camera flash), blocks DC, passes AC

176
Q

Diode symbol

A
  • |>|-
177
Q

Capacitator symbol

A
  • | |-
178
Q

Resistor symbol

A

-vvvvv-

179
Q

Half wave recitification

A
  • Only one diode is used
  • removes one half of current flow
    n_n_n
180
Q

Filtered half wave

A

Uses a diode, with capicator is parallel

-n~~n~~n~~

181
Q

Full wave rectification

A

Allows for ALL of the current to pass
- slight ripple in resultant dc current
- looks like a square

uses a smoothing capacitation, with 4 diodes (used in modern engines)

-n~n~n~ with smaller ripples as more frequent peak

182
Q

Diesel vs electrical train

A

Modern and urban: electric: electrified in the 1920s (used 1500V supply)
Rural: diesel

183
Q

Historical use of motors in trains

A

1920s: DC motors for high starting torque, variable speed
AC motors are better improved now and are smaller, more efficient
BUT cost of replacing is expensive

184
Q

Powering of trains

A
  1. 33kV AC power
  2. 33 -> 1500 DC for CATENARY lines
  3. Pantograph transfers power from Cat. lines to train carriages
  4. DC power is used by older trains or converted to AC (newer AC induction motors)
  5. Current returns to ground via. Wheels in train tracks (live)
185
Q

Control systems

A

uses a mechanism, a computer and sensor to measure info about the mechanism and communicate it to the computer
Makes a descision based off this
- input is binary (0s and 1s)

186
Q

Amp Hours

A

(Ah) A measurement of charge that gives the amount of current drawn in an hour

187
Q

Watt hours

A

(Wh), a measurement of power that gives the amount of Watts used in an hour

  • Can be found by multiplying Ah by voltage (P=IV)
188
Q

Batteries in Series

A
  • Voltages add up, capacity (Ah) remains the same as individual cell
189
Q

Batteries in Parallel

A

Capacities add, voltage remains same as individual cell.

190
Q

3 Types of Motors

A

DC
AC
Special

191
Q

2 Types of DC motors

A

Brushed
Brushless: BLDC and stepper motors

192
Q

Types of AC motors

A

Induction (asynchronous) motors (single or 3 phase) -
Synchronous

193
Q

Special motor types

A

Universal
Servomotor
Stepper

194
Q

Variable resistor symbol

A
  • |__/`__|-
195
Q

3 Phase AC induction motors

A

Heavy applications e.g. trains, cranes
- 3 electromagnet pairs, creates a rotating electric field
- Slight lag between stator and rotor: called SLIP. (difference in rotational speed)

196
Q

DC motor control

A

speed is prop, to current and voltage
- current can be increased by reducing resistance
- to reduce resistance continuous, a variable resistor (potentiometer) can be used.
- Pulse-width modulation alters voltage (modern: supply switched on and off rapidly, experiences AVERAGE rather then peak)

197
Q

Aluminium joining techniques

A

Riveting bolting and TIG welding, easily extruded

198
Q

Strengthening Aluminium

A

solid solution hardening, age hardening, work hardening

199
Q

Solid solution hardening types

A

Substitutional (atoms of similar size) vs interstitial (atoms of different sizes) - e.g. steel

200
Q

Super saturated alloys

A

The increase in strength depends on concentration and the difference in size between solute and solvent.

201
Q

Solution hardening

A

For 5000-series Al with Mg, it can be heated to 450 so the Mg is dissolved, increasing the concentration and thus strength: quickly cooled to prevent precipitation
- also used for Ti alloys and Mg alloys.

202
Q

Age hardening process/precipitation

A

1Heat, the quenching.
2. Hold at lower temperature to age harden and thus create precipitates.

HOWEVER: must be careful of over-aging: brittle, prone to cracking

203
Q

Age-hardenable Alloys

A

Al in the 2,6, and 7000 series,
Ti and Mg alloys, but to a lesser extent.

204
Q

Over aging alternate causes

A

e.g. supersonic flight: air resistance
2. resistance heating in fastening Al cables
3. welding Al

instead: Ti has better thermal stability.

Engineering (7 decks)

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