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
2
Q
Ceramics: What are they?
A
Compounds of: Metals and non-metals thru ionic bonding, non-metals via COVALENT bonding
3
Q
Ceramics: common types
A
Stone
Clay ceramics
Cement
Glass
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)
5
Q
Stone properties
A
Weak in tension, strong in compression, low toughness (brittle)
- easy to chisel/hand carve (masonry)
Usually rough finish
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
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
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
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
10
Q
Cement powder formation
A
- Limestone and shale mixed together and ground
- Heated in kiln to fuse and form clinker
- ground clinker mixed with gypsum (slows setting time)
4.Reground and mixed
11
Q
Lime Mortar (and making process)
A
Non-hydraulic,
- made by mixing limestone and silica, alumina and iron
- Firing at 1000 (LASI)
- adding water makes hydrated/slaked lime
- This mixed with sand is lime mortar: used historically in brick and stone buildings.
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
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
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
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
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.
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.)
18
Q
Composites (Defininition)
A
Consists of two or more materials joined mechanically: creates properties unattainable from the original materials.
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)
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
21
Q
Concrete MACROSTUCURE
A
heterogeneous microstructure:
BIG grey: angular coarse aggregate
Small grey: angular fine aggregate
Fine sand particles within cement paste
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
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
24
Q
Critical Crack length
A
Once this length is achieved, the crack will continue until failure.
25
Destructive testing Types:
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.
26
Elastic vs Plastic deformation
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)
27
How does Work Hardening work?
Work hardening moves dislocations through the lattice structure, increasing the amount of dislocations and thus making it less ductile more brittle.
28
How to grain boundaries form?
Through the random nature of cooling, unit cell lattices will grow and then merge to create grain boundaries
29
3 Non-destructive testing types:
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)
30
Slump Test
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
31
Strain energy
The amount of energy stores in a material that has undergone strain (e.g. tensile, compression, torsion, bending)
SE=1/2 stress x strain
32
Tranverse bend/beam testing
Three or four point loading (^---v----v---^ vs ^----v----^)
measures flexural strength or modulus of rupture
33
Types of Cast Iron:
1. White cast iron
2. Grey cast iron
3.Malleable cast iron
4. Ductile/nodular/spheroidal cast iron
34
White Cast Iron
Low carbon, <1% silicon (graphite cannot form)
- dendrites of pearlite in a cementite matrix
- Hard, brittle, good castiblility
35
Grey cast iron
- 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
36
Malleable cast iron
- High carbon and silicon
- Graphite rosettes in pearliitic/ferritic matrix (made by heat-treating WCI)
- Soft, malleable, ductile, tough, machinable
37
Ductile/nodular/spheroidal cast iron
Highest carbon and silicon, some magnesium or cerium
- Graphitic spheroids in a pearlitic/ferritic matrix
- Soft, malleable, tough, machinable
38
Types of Imperfections in lattice structures:
1. Point defects
2. Dislocations
3. Planar imperfections (e.g. grain boundaries)
39
What is Cast Iron and properties?
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
40
Cracking Prevention and fixing for ceramics, metals and polymers
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)
41
Timber composition and types
Consists of cellulose fibers/tracheids, held together in a lignin resin.
Hardwood vs softwood: pored vs non-pored
42
Timber Properties
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)
43
Concrete reinforcement:
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
44
Spalling and prevention
Steel inside corrodes: expands, cracks concrete: prevented by ensuring correct water ration, vibrate concrete to reduce porosity
45
Asphalt composition and properties
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.
46
Laminates: what and examples
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)
47
Geotextiles: what and properties/uses
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.
48
Corrosion: (dry and wet)
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.
49
Wet corrosion types: (uniform and galvanic)
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
50
Oxidisation and reduction
O: loses electrons at anode
R: gains electron at cathode
The more cathodic = more stable e.g. platinum.
51
Passivity
When a metal forms a protective film from corrosion, e.g. aluminum, titanium, chromium.
52
Rust
Needs water and oxygen: continually flakes off to expose metal underneath
53
Protecting against corrosion (5 types)
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.
54
Steel Properties
Cost effective, tough, strong in tensile and compression, ease of fabrication, hard, ductilie
- properties are manipulatable
55
Train environmental factors
Still use a lot of pollution HOWEVER better then individual transport options
- Train lines are use far less land then roadways
56
4 Testing processes for hardness
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.
57
4 Types of Steel: (alloys)
Carbon steel
Stainless steel
Alloy steel
Tool steel
58
Impact tests: what do they measure? 3 Types?
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
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Charpy: n`````v``````n held horizontally, notch away from pendulum.
Hounsfield: Smaller, transportable: uses two pendulums
59
Process Annealing:
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
60
Full Annealing
Heat hypo-eutectoid or eutectoid steels to AUSTENITE or 40 degrees above upper critical temperature (UCT). Cooled in furnace. All grains unstressed.
61
Austenite
FCC structure, only occurs at high temperatures.
62
Normalising
Heating to austenite region far above UCT. Cooled in still air.
Shorted the annealing, finer grain structure and thus stronger steel.
63
Spheroidising
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
64
Steel ranges and properties (low, mild, medium, high, ultra high)
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
65
UCT (Upper critical temperature)
Point at which steel becomes completely austenite.
66
Martensite:
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
67
Quench Hardening
Only done to steels above mild grade (enough carbon content to form martensite)
- high brittleness, hard, good wear resistant
68
Air hardening
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.
69
Tempering
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.
70
Austempering
Austenitic steal quenches to around 400, held until consistant temp, then queched to room temp
Forms BAINITE: similar to tempered martensite, but more resiliant.
71
Banite
Formed through austempering
similar to tempered martensite, but more resiliant.
formed when quench rate is not fast enough for martensite
72
4 Surface hardening techniques and why
Harder outside for scratches, etc, yet tougher inside
Case Hardening (carburisation)
Nitriding
Flame Hardening
Induction hardening
73
Case Hardening/Carburising
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
74
Nitriding
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.
75
Flame Hardening
Applies a flame to localised area then quenched. Mechanised with flame and water jet holder on same assembly
76
Induction hardening
Similar to flame hardening except using an induction coil. Quenched.
good for camshafts
77
Austempered Ductile Irons (ADIs)
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.
78
3 ways of changing properties of Steel
1. Heat treating
2. Alloying
3. Carbon content
79
Manufacturing processes
Forming
Casting
Molding
Joining
Machining
Additive
FCmmJA
For cults, make many acidic juices
80
Forming: what is, types
Applying forces or pressure to PLASTICALLY deform material
- used for metals, hot or cold working
Forging
Extrusion
Rolling
81
Casting
Die casting
Sand
Investment
82
Molding
Used for PLASTICS
injection
Compression
Blow
83
Joining
Welding
Soldering
Fastening
84
Machining
Turning
Drilling
Reaming
85
Additive
3D printing
Laser sintering
Vat photopolymerisation
86
Hot vs Cold rolling: what, benefits
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
87
Forging: What and properties
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
Extrusion: 3 types
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
Indirect vs direct extrusion
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
Impact extrusion
Cold forming process
Hammer 'punches' blank into die, material is forced to flow up the sides
- cans, short tubes
91
Drawing vs Upsetting (forging)
Drawing: increasing length, smaller cross sectional area
Upsetting: reverse
92
Hot vs Cold working uses
- sheets, strips, bars, etc
93
Casting
Pouring molten metal into a mold, allowing it to solidify
PRIMARY forming process (often requires further refining for surface finish)
- used for metals
94
Die casting process
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
Die casting/permanent mold casting + 2 types
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
Sand casting process, pros and cons, uses
- 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
Investment casting/Lost wax casting: pros, cons, process and uses
- 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
Ingot casting
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
Continuous casting
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
Shell moulding: pros and cons, process
- 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
Centrifugal casting
Metal is spun in a mold and forced into shape of hollow cylinder
- useful for pipes, piston rings
102
Full mold process
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
Powder Forming/metallurgy process
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
What is made with powder forming? (4 groups)
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
Power metallurgy pros and cons
Allows for products otherwise too difficult to make
BUT: expensive to set up fascilities, still limited shapes
Not as strong
106
Welding types, description
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
Butt Welding
Pressure
Metal is butted together at ends and current melts metal.
- joining tubes
107
Spot Welding
Pressure welding.
Electric current melts metal sheets, joining it in 'spots'
Used in car manufacturing
108
Seam Welding
Pressure:
Metal moved through rotating wheels that pass electric current
- melts, then joins
- tubes for cheap bikes
108
Oxy-acetylene Welding
Fusion
- Metal is metled by oxy-acetylene flame, filler metal added.
- used in repairs, more home-style DIY repairs
109
Bronze Welding
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
Electric arc welding
Fusion
- melted by an electrode (also filler metal)
- electrode covered in flux to prevent oxidisation
- electrode must be changed periodically
111
Metal inert gas (MIG) welding
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
Tungsten inert gas (TIG) welding
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
Plasma arc welding
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
Stainless steel properties
- 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
Tool steel
High carbon content with vanadium, tungsten, chromium, etc
Wear resistance, heat resistance, toughness
116
HAZ and welding structure:
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
Aluminium properties, uses
- 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
Aluminium alloys: (2 types)
Wrought:
- heat treatable and non-heat treatable
- mechanical working
Casting:
- good for casting
119
Non- heat treatable aluminium alloys:
1xxx, 3xxx, 5xxx
120
1xxx aluminium
Pure aluminium with small amounts of iron and silicon
- used for sheet metal work
121
3xxx
Manganese alloyedm solid solution strengthening
- used for pressure vessels, chemical equiptment, sheet metal
122
5xxx
Magnesium, (5052 is most important industrial alloy)
- sheet metal work, truck and marine applications
123
Heat Treatable alloys:
2xxx, 6xxx, 7xxx
124
2xxx
Copper: strengthened by solid solution strengthening and precipitation hardening
e.g. duralumin
- aircraft structures (high tensile strengths)
125
Solid solution hardening
introduction of solluble elements to distort lattice
126
6xxx
Two primary alloying elements: magnesium and silicon
- strengthened through precipitation hardening
- good corrosion resistance and strength
- bike frames, truck and marine uses
127
7xxx
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
Casting alloys choice of manufacturing
Sand-casting, gravity or pressure die-casting
127
Aluminium Lithium alloys
used in bikes and aviation
- better fatigue life, better strength
- replaced CFRP
127
Aluminium casting alloys system
ACSSMZTO
All cookie snacks should make zebras totally obese
(al, Cu, Si +cu/mg, si, mg, zn, sn, other)
127
Casting alloys:
most contain silicon (5-12%)
- lower melting point for alloy (fluidity improved)
- strengthens alloy
- manganese and copper also added to improve strength and hardening
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Important aluminium alloy in transport industry
aluminium/silicon/magnesium/iron alloy
- used in wheels
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Cartridge Brass
70/30 brass
- ductile
- was used in making cartridges for bullets
- higher ductility then Cu
- good for deep-drawing operations
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Copper alloys
Used in electrical industries, cost effective
- used in railway overhead wiring
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Brass alloy
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)
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Types of Brass alloys (5)
Cartridge brass
Standard
Muntz metal
Naval Brass
High tensile Brass
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Standard Brass
Only 25% zinc: good quality, cold-working alloy
- stampings and limited deep drawing
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Muntz Metal
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
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Naval Brass
37% zinc, 1% tin, corrosion resistance in seawater (shipbuilding)
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High-Tensile Brass or manganese bronze
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
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Bronze and types
copper and tin alloy
Low tin
High tin
Admiralty gunmetal
Leaded gunmetal
Phosphor bronze
Aluminium bronze
LLAAHP
Less legs also adds health points
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Low tin bronze
3.75% tin
- good elastic properties and corrosion resistance
- good for springs
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High tin bronze
18%: heavy load applications e.g. slewing turntables on large cranes
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Aluminium Bronze
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
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Leaded Gunmetal/red brass
85% Cu, 5% Sn, Zn, 1% Pb
- reduced ductility
- but increased durability: good for pressure vessels
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Admiralty Gunmetal
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)
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Phosphor Bronzes
Bronze with phosphorous added
- higher tensile strength, corrosion resistance
- lower μ, good for bearings
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Structure of non-ferrous alloys
Second harder phase: reduces ductility, e.g. Muntz metal
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Heat treatment of non-ferrous alloys
Annealing
Precipitation hardening
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Precipitation hardening: metal
Duralumin and similar aluminium alloys, etc.
- after being cold-worked: have primary and secondary phase (usually at grain boundaries): hard and brittle
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Precipitation hardening steps
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)
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Ceramic uses
Alumina is used as insulatiion in spark plugs
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4 Glass types
High silica glass
Soda Lime Glass
Borosilicate glass
Lead Glasses
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High Silica Glass:
Refined from borosilicate glass
-very clear
- good against elevated temperatures: excellent resistance to thermal shock (missile nose cones, space vehicle windows)
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Lead Glasses
Contain up to 40% Pb.
- Lowers softening temperature
- high refractive index: optically clear
- good for optical glass, thermometer tubes, tableware
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Soda Lime Glass
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
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Borosilicate glass (Pyrex)
Glasses with 20% boron and silica
- chemical resistance, low thermal expansion (resistant to fraction at high temps)
- electrical insulation, gauge glasses, domestic cooking
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Thermoplastic structure
Strong primary covalent bonds, weak secondary bonds (Van der Waal's forces)
- flexible, transparent, recyclable
- low tensile strength
- ductile
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Thermoplastic examples
Polyethylene
Polystyrene
Polytetrafluoroethylene (PTFE)
Polymethylmethacrylate (Acrylic)
Polypropylene
Polyvinyl chloride (PVC)
acrylonitrile butadiene styrene (ABS)
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Themoplastic uses
- cable coating for bikes, car parts e.g. grills, badges, door handles, window winders
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Thermosets structure
Undergoes a chemical change when under heat (non-reversible)
- has a network structure with strong covalent primary and secondary bonds
- resistant against deformation (tough)
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Laminated glass:
- 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
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Thermal toughing of glass
cooled very quickly: outside in compression, inside in tension
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Chemical toughening (Glass)
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
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Fracture patterns
Untreated: ///-/\|/\/: long, sharp sharsd emanating from centre
Toughened: oooo: shaatters into small pieces
Laminated: spider web, glass intact afterward
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Hooke's Law property
Elasticity
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Generator
Converts Kinetic energy into Electric
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Form of energy sources
Coal/gas powered turbines
Petrol and diesel endinges
Wind
Hydro
Tidal
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Environmental impacts of hydro
Impacts on irrigation/farming
Deforestation
Disruption of natural waterways: wildlife
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What type of electricity is generated
All create AC except for solar farms (DC)
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Frequency of AC power
50Hz (Aus)
60Hz (America)
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Why 3 Phase?
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.
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Advantages of 3 phase
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
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TPS Power cable
Thermoplastic sheathed copper cabling
- used in residential and light industrial applications
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3 types of power cbles
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.
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TPS cables properties
Some flat cables, but usually round
Solid or stranded wires
Each wire is separately insulated
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Four-core armoured cable
Three live wires and a neutral
Used in low voltage outdoor applications
Each is insulated separately
Armour later provides mechanical protection
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High Voltage Cables
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
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The skin effect
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
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Aluminium conductor steel reinforced powerlines (ACSR)
Lines are stranded
Al better then Cu (density, price)
- steel core for mechanical strength
- lines are not always insulated
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Rectification
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
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Diodes
Only allow current to flow in one direction
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Rectifier Types
1. Half wave
2. Full wave (bridge)
- both may be filtered (smooth)
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Capacitator
Stores electric charge (e.g. camera flash), blocks DC, passes AC
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Diode symbol
-|>|-
177
Capacitator symbol
-| |-
178
Resistor symbol
-vvvvv-
179
Half wave recitification
- Only one diode is used
- removes one half of current flow
n_n_n
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Filtered half wave
Uses a diode, with capicator is parallel
-n~~n~~n~~
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Full wave rectification
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
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Diesel vs electrical train
Modern and urban: electric: electrified in the 1920s (used 1500V supply)
Rural: diesel
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Historical use of motors in trains
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
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Powering of trains
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)
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Control systems
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)
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Amp Hours
(Ah) A measurement of charge that gives the amount of current drawn in an hour
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Watt hours
(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
Batteries in Series
- Voltages add up, capacity (Ah) remains the same as individual cell
189
Batteries in Parallel
Capacities add, voltage remains same as individual cell.
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3 Types of Motors
DC
AC
Special
191
2 Types of DC motors
Brushed
Brushless: BLDC and stepper motors
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Types of AC motors
Induction (asynchronous) motors (single or 3 phase) -
Synchronous
193
Special motor types
Universal
Servomotor
Stepper
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Variable resistor symbol
-|__/`__|-
195
3 Phase AC induction motors
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)
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DC motor control
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)
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Aluminium joining techniques
Riveting bolting and TIG welding, easily extruded
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Strengthening Aluminium
solid solution hardening, age hardening, work hardening
199
Solid solution hardening types
Substitutional (atoms of similar size) vs interstitial (atoms of different sizes) - e.g. steel
200
Super saturated alloys
The increase in strength depends on concentration and the difference in size between solute and solvent.
201
Solution hardening
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.
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Age hardening process/precipitation
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
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Age-hardenable Alloys
Al in the 2,6, and 7000 series,
Ti and Mg alloys, but to a lesser extent.
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Over aging alternate causes
e.g. supersonic flight: air resistance
2. resistance heating in fastening Al cables
3. welding Al
instead: Ti has better thermal stability.
