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Module 2 Personal and Public transport - Coggle Diagram
Module 2 Personal and Public transport
Mechanics
Friction & normal Forces
Graphical
Use μ as a fraction of the Normal as landmark point and use resultant and then connect line between normal and end of resultant
Analytical
Friction: The force that opposes the motion of two bodies in contact
F = uN
The coefficient of static friction is larger than kinetic friction
μ = F/N
Laws of Friction
Acts along contacting surface between two bodies
Works to oppose motion
if in equilibrium Ff= F applied
ratio of Magnitude of Limiting friction to Normal force is constant
Limiting friction is independent of area
Angle of static friction
The angle between the Normal and Reaction (resultant of Normal and friction) forces
The angle of a slope is angle of inclination
Angle of Repose
The angle for which a body is on the point of sliding and the friction becomes limiting
When Angle of static friction is equal to angle of inclination
tanΦ = F/N = μ
Normal: the Reaction force that acts perpendicular to a surface
Energy, work and Power
Work = Fs = Fscosθ where θ is angle between line of action and displacment
Energy the capacity to do work
Mechanical energy
movement energy
Kinetic
1/2mv^2
Potential
mgh
Strain Energy
SE = W = 1/2Fe
Springs
Line up to elastic limit is the spring constant
k=F/e
F=ke
W = 1/2ke^2
Used to store energy that can then produce work
Conservation of Energy
A body in motion under external forces has constant energy in system
For free falling body - Sum of KE and PE = Constant
But if constant speed down slope it due to negative work
Power
P= W/t = Fs/t =Fv
If constant speed Friction = P/v
Efficiency
η = Output/Input = Brake power / Indicated power
Machines/pulleys
VR= dE/dL
Efficiency η = MA/VR
MA = L/E
Pulleys
Single Fixed
T=L
Single moveable
2T=L
With Each addition of the moveable pulley the MA and VR double
If L & E in same direction MA=VR = Number of pulleys
If L & E are in opposite direction MA = VR = Number of pulleys + 1
Gear Trains
VR = Teeth on driven/ Teeth on driver
Inclined plane
VR = dE along plane /dL upwards
Screw Threads
Can be used for work
The pitch of the thread is distance the load moves
Then one full revolution times the jack is the distance the effort moves
Development
Issues
Social
populations beginning to lean towards bicycle use
due to increased social awareness of environmental impact and increase urban density
also due to cheaper costs of bicycles compared to personal cars
Noise
transport creates noise which can hurt both humans and environment
mitigation
isolation of transport system
or choosing quieter transport eg trams or electric cars
Environmental
Air pollution
Leads to global warming
Sources
Cars
help reduce impact
car pooling
try and ward off car users
increase cost, inconvience etc
Electric trains and light rail
good for high density urban areas
less impact per person
most have regenerative braking system so even more power saved
accessible for senior and disabled peoples
Hybrid cars
struggle as they need to be charged regularly
batteries are also big and heavy
car also cost a lot
Equity
Rural areas cut off from rest of country via the reduction of train, bus and truck use
but 'too' costly to continue for such little people
Safety
Bicycles
barely any safety features
except from mandated helmets
Cars
Passive safety features
Seat belts
Air bags
Crumple zones
Active safety features
Anti lock breaking systems
4WD
traction control
Adaptive headlights
Planes
Are pretty safe
Systems
Includes all elements associated with moving goods or peoples from one place to another
Personal
anu form of transport that offers a high degree of say in where and when
advantages
on demand
convient
prestige
higher level of comfort and security
disadvantages
owner responsible for costs
stricter laws regarding use
greater chance of accident
greater air pollution
Public
transport that is shared across multiple users and generally ran by government departments
Advantages
No license or training required
reduced chance of accident
Cheaper to use
lesss airpollution
can transport peoples unable to utilize personal transport
Disadvantages
little control over route and timetable
increase transport and wait time
taxpayer money used to subsidize cost of running system
high initial construction cost
Bicycles (personal)
Evolved over time
to improve speed
by reducing weight and altering shape
to improve personalisation
by introducing multiple variations of bicycle models
To improve comfort
by increasing stability
to improve control
by adding brakes and handlebars
Materials and Manufacture
Testing
Non Destructive
Tests that don't damage the material
Destructive
Tensile Tests
Attached on one side while a tensile load is applied on the other side
Stress/strain Graph
Notched Bar Impact Tests
A pendulum is raised so knock and cause failure in a specimen
A scale reads the energy of pendulum before and after
therefore the energy absorbed to cause failure
Izod
Standard 10mm specimen with notch in bottom of piece facing towards pendulum
Charpy
Piece is situated with notch away from specimen and notch pointing inwards toward spot of impact
Fatigue tests
A specimen may fail due to fatigue if a stress is repeated or sustained for prolong amounts of time.
Wohler Test
A revolving specimen experiences a fluctuating bending stress
Hardness Tests
REFER TO YEAR ELEVEN
Cantilevered tests
tests bending stress
Metals
Ferrous
Manufacture processes
Welding
uses electric arcs to melt and join metals
TIG
Non consumable tungsten electrode and then a filler matierial
Suitable for stainless, aluminium and exotic of thin materials
due to the high control given by TIG
MIG
Continuos wire electrode and gas shield
For aluminum and stainless steel
High welding speed
Microstructure
The Heat affected Zone (HAZ) is the area with changed grains
Closer to the weld big and larger grains and further out more fine grains
Columnar grains at outer edge
Casting
Die casting
high costs for dies and only used for zinc & aluminium alloys
bike components, gear boxes and carburettors
improved dimensional accuracy, excellen surface finish, high output rate and uniform microstructure
Investment casting
high cost and labor, and only for small shapes
turbine blades and any small components
accurate intricate shapes without forging
Sand Casting
Intricate shapes slow cooling and cheap
labour intensive and good packing is essential
Engine and rolling blocks
Shell Casting
good surface finish & dimensional accuracy, relatively defect free and less labor than sand casting
high initial costs
car crankshafts and exhausts manifolds
Hot & cold working
Hot - Above recrystallisation temperature
Causes uniform equiaxed grains
stronger tougher more ductlie
But poor surface finish and dimensional accuracy
Examples
Rolling
rolled between rollers
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Forging
Smashed really hard
Extrusion
pushed through die really hard
Piercing
Piece is rolled through with a skewer pushing into the middle
Cold- Below recrystallisation temperature
Good
increased strength
only way to harden mild steel and non ferrous metals
Good dimensional accuracy and better surface finish
produces directional properties
Bad
needs More powerful equipment
may produce undesirable directional properties
needs to be oxide free
Examples
upsetting
forging but for nuts
extrusion
rolling
Drawing
pulled really hard through die
only suitable for ductile materials
Recrystallisation
After cold working the lattice is distorted and thus stressed
if heated above recrystallisation temperature stress free equiaxed grains form out of the stressed grains
Generally resulting in higher electrical conductivity and ductility
Powder forming
Powder manufacture - metals and powders are disintegrated into super fine particles and then blended
Pressing - Powder put into die and crushed, strength of press decides porosity of material
sintering- heated in furnace so that certain metals may melt and bind the components
Good for
Very hard and complex pieces
composites that don't normally bind
Heat Treatment
The controlled heating and cooling of a material to obtain desired properties
Carbon in the microstructure fills the spaces in Iron lattice
Heat treatment occurs due to change in allotrope at 910C
Body centered cubic structure --> Face centered cubic structure
0.008% carbon dissolved --> 2% Carbon dissolved
Ferrite
Iron with 0.008%C
Cementite
Iron with 6.67%C
Methods
Annealing
Full
Heat to 900C until all Iron in FCC
Slow cooled in furnace or insulator
Returns grain structure to equilibrium with unstressed grains, inducing electrical and magnetic properties and softness
Process
Suitable for softening coldwork low carbon steels and other steels that are mostly ferrite
Full annealing at 500-600C to recrystallise ferrite but leave stressed ferrite grains
Normalising
Full annealing but higher temperature and cooled in still air
Slightly faster cooling rate caused finer equiaxed grains
therefore higher UTS Yield strength, impact strength in tests and hardness but less ductility
Hardening
depends on solubilities of Carbon
If carbon given insufficient time to move to FCC structure it distorts the structure creating stress
Tempering
Heated to specific temperature and air cooled
If need hardness
240C
If toughness needed
300C
Surface hardening
Nitriding
Heat specimen in nitrogen rich environment at 500C for 40-100 hours
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Selective hardening
Rapidly heating parts to 900C and then quenching
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Carburising
Carbon rich atmosphere as flames heat metal 950C that is water jet cooled right after to create hard outer layer
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Examples
Dead Mild
Large ferrite grains with little pearlite
Ductile, malleable & can be cold worked
Body panels
0.05-0.1C
Mild
Smaller Ferrite Grains more pearlite 1:1
Doesn't Quench harden, Weldable & can be cold worked
Nuts n Bolts
0.1-0.3C
Medium Carbon
Minimal Ferrite grains mostly pearlite matrix
Can be hot or cold worked and Suitable for forging and Heat treatment
Brake cables and train axles
0.3-0.6C
High Carbon
All pearlite
High strength and hardness, Heat treatable
Suspension springs
0.6-0.9C
Carbon Tool
Big Pearlite grains with ferrite matrix
High Wear resistance
Ball bearings
0.9-1.5C
Cast Irons
White
hard and brittle
intermediate stage in production of malleable cast iron
Medium Pearlite grains with Fe3C matrix
Grey
Small-Med ferrite grains with pearlite matrix and graphite flakes
Weak in tension, strong in compression and brittle
Engine Blocks
Malleable
medium pearlite grains with ferrite matrix and graphite nodules
Brake rotors and drums
excellent casting properties and improved strength and ductility
Misc Alloy steels
Stainless Steel
if >12% chromium present a corrosion resistant, strong and hard film forms
Chrome Molybdenum
0.3%Carbon + 1% chromium and 0.25% molybdenum
Good hardening properties, ductility and weldability
Low carbon steel + 12-25% chromium
cant be hardened but can be cold worked
Medium carbon steel + 12-18% chromium
can be quench hardened
A metal that contains Iron as a major Element
Non Ferrous
Heat Treatment
Cold working
one of the only things that can increase strength in most non ferrous metals
as it distorts lattice
Annealling
Cooling rate of non ferrous metals does not matter as the carbon in iron does not distort lattice in non ferrous materials
Tempering
Precipitation hardening
Certain non ferrous materials when cooled under equilibrium conditions harden and become brittle
due to the total precipitation of a metal compound
The metal is then reheated back into single phase structure that is quenched to prevent precipitation
Eventually (1 week) submicroscopic particles precipitate out, thus distorting the structure
hardening and improving strength
Artificial aging
Left in low temperature oven for long time
Normallising
special process
Recovery
Stress in microstructure is slightly relieved
Examples
Chromium
hard with a clear oxide layer
Bronzes
Any copper alloy except the brasses
Tin Bronzes10% Tn
Tough ductile and can be coldworked
Aluminum bronzes
Cold worked 5%Al
Hot worked 10% Al
Examples
80% Bronze
suitable for casting and forging, can be hardened and tempered, good strength and hardness
95.5% Bronze
Can be cast, cold worked, good strength and corrosion, fatigue and wear resistance
used for dies and sand casting
Titanium
Light, strong, impact resistant, non corrosive
Brass (70% Cu and 30% Zn)
Corrosion resistant, soft, can be cold worked
Other brasses
Alloys of Copper with up to 45% Zinc
Up to 37% Zn
Suitable for cold working by pressing extrusion and drawing
tough ductile
has single alpha phase
Depending on cooling rate for equilibrium temperature
alpha phase can become cored with copper if faster
More than 37%
brittle beta phase presnet
Examples Cu/Zn
Muntz Metal 60/40
Corrosion resistant, high strength and excellent hot working properties
extruded tubes hot rolled plates
High tensile brass 58/28 +Mn
High strength and wear resisitance
pressings forging and stamps
Cartridge brass 70/30
Cold rolled sheets, wire and electrical contacts
Brazing alloys 50/50
Hard and brittle
filler rod as low temp joining
Aluminium
Corrosion resistant, soft, can be cold worked
Alloys
Zinc
High strength to weight ratio
Silicon
Low MP at 9-13%Si
Wrought
good forgeability and low coefficient of thermal expansion
Cast
used for general purpose casts
Silicon-magnesium
Wrought
Excellent corrosion resistance and workability
Cast
good castability strength and corrosion resistance
Copper
2.5% and 5%Cu (Duralumin) can precipitation hardened
4%Cu
brittle and lack strength
GENERAL PROPERTIES
Good formability
Corrosion resistant
Low density
poor weldability
high thermal and electrical conductivity
Polymers
Soft Vs Hard
ThermoSoftening
Based Covalent bonded chains
Can have branches causing further rigidity
Structure looks like spaghetti
Properties
Low softening temperature
Transparent Vs Opaque
Only amorphous polymers can be transparent
different sized chains don't cause alignment allowing for light through
Crystalline polymers are opaque
Generally same chains all in alignment thus no light through
Strength
If simple chains stronger along chains
Elastometers
Thermosoftening structure but with multiple bond present in structure
Natural rubber items will become distorted under tensile load
can be mitigated by vulcanisation
the controlled breaking of spare bonds and then reforming covalent bonds between the chains
therefore will not completely soften
Sulfur is added as Vulcanizing agent
Filler such as carbon and silica can be added to improve abrasion resistance
Properties
good abrasion resistance
Electrical insulator
High Elastic limit
Examples
Butyle rubber
good resistance to ozone and holds gas and air well
bike tyers and inner tubes
Vulcanized rubber
low cost, tough and flexible
Car tires and brake blocks
Examples
Polyethylene
Low Melt temperature, tough, flexible , low density has branched chains, high density is linear
Coating bike gears and cables
PVC
electrical covering and bike grips
Rigid, tough, insulator and hard
Perspex
Helmets outers and chrome plated body trims
transparent, excellent optical properties and weather resistant
Thermosetting
Strong covalent bonds in all directions along chains
Fillers like mica or glass fibre can be added to improve strength or electrical resistance
Other additions
Pigments
Plasticizers to improve flexbility
Stabilizers to prevent damage from UV
Examples
Polyurethane foam
Excellent electrical resistance and traps oxygen in structure
Silicone
Resists oxidation and is excellent electrical insulator
Forming processes
Polymerization
Addition
Simple monomers that form together to form a complex polymer that leaves no waste
Copolymerization
Two different polymers form together to form a more complex polymer
Themorsetting
Condensation
Differing polymers form together to produce a complex polymer and water
Manufacture processes
Compression molding
Granules place at bottom of mold and then stamped with high force and heat to form productc
car tyres
Extrusion
Thin films or bags
Heated and screwed and rolled out in continuous profile
Can also be blown into a film by cold air pumps
Blow molding
Polymer glob pushed into mold with blow pin inserted that ejects high pressure air into glob into it covers the shell of the mold.
Bottles and fluid reservoirs
Injection molding
polymer granules are screwed and injected into a mold
Pedals grips and reflectors
Calendering
Viscous polymer is spread onto a fabric material
For upholstery in cars
Rotational molding
Melted polymer is rotated around a big drum to form a skin and then cooled
Casting
poured into big mold
A compound with a structure that is characterized by several long molecular chains
Can be enbrittled by oxygen oxidizing into the structure
Textiles
Certain polymers and textiles are composited together for applications
But generally vandalised in most applications
so a non rip tough textile needs to be used
Electronics
DO AFTER EXAM