engineering studies – personal and public transport

BRYAN HO ENGINEERING STUDIES – PERSONAL AND PUBLIC TRANSPORT

PERSONAL AND PUBLIC TRANSPORT

HISTORICAL AND SOCIETAL INFLUENCE

Historical Development of the Bicycle

1791 De Sivrac developed a 2 wheeled wooden horse

Front wheel was fixed = No steering, no brakes

Used by nobility for leisure

Made entirely from timber

1817 Von Drais developed the ‘Draisienne’ (hobby horse)

Front wheel had a pivoted steering fork

Wooden frame, wrought iron forks, large spoked wrought iron rim wheels (strength and

abrasion resistance), a saddle, armrest (for pushing and comfort)

Not made after 1830 (lack of interest)

1821 Louis Gompetz fitted a ‘swinging arc’ ratchet drive on the front wheel so that the rider

could pull on the steering handle to assist his feet

1839 Kirkpatrick Macmillon developed the first pedal operated bicycle

Wooden wheels with iron tyres, frame consisted of a wooden bar extending in a curve from

the top of the front wheel to the hub of the rear wheel

Added cranks to the rear wheel of a steerable velocipede, with connecting rods coming

forward to swinging pedals. Both axles ran in brass bearings

Originator of true bike

1861 Boneshaker. Pierre Michaus developed first bicycle with crank + pedals on front wheel,

also known as the velocipede.

Frame was of solid wrought iron, timber wheels with iron tyres

Saddle is mounted on a plate spring support

Brake was developed, applied to the back wheel by a cord tightened by rotating handle bar

1870 1. J. Starley. “lever tensioned” spoke wheels

2. J Moore. Ball bearings made from wrought iron and case hardening

1870-80 Penny Farthing. Developed in many countries by inventors such as Magee, Starley,

Reynolds and Kelly

Large front wheels (speed, absorb greater shock), frame was a single metal tube, solid

rubber tyres, brakes available for both wheels

1877 J Lawson developed the safety cycle

Rider sits between 2 medium sized wheels

First chain driven rear wheel bicycle. Didn’t catch on; costly, heavy, complex than P.F.

1885 The Rover Safety cycle. Starley produced first commercially successful design

Chain drive, rubber tyres, wire spoke wheels, brakes applied by hand levers

1889 Pneumatic tyres introduced by Dunlop

During the 1900s, this basic design was further refined.

Stronger and lighter metals. Hollow steel tube design (double diamond)

Gear change mechanisms, derailleur, cadence (speed, comfort)

Back pedal brakes

Bowden brake cables

Electric Lighting (safety)


1950s. Drop down handle bars basically force the rider into a crouched position which reduced wind

resistance and enabled a more efficient use of arm and leg muscles. Also, new materials (eg light Al

alloys) were used where available, but high costs restricted it to high level racing bikes

1970s. BMX. Originally designed to imitate Moto-cross. Used for tricks, freestyle, therefore they have

low gear ratio/no gear system.

Features: CroMo frame, gyro headset braking system (handlebars have 360 motion w/o cables restricting

motion), ABS spokes and rims, slick tyres (reduce rolling resistance)

1980s. Mountain bikes. Fat tyres, straight handlebars. Generally thicker and heavier frame. Modern

mountain bike is utilises lighter and stronger materials (eg carbon fibre, aluminium)

Features: Shock absorbers, knobbly tyres for better grip, high tensile steel frame.

Effects of Bicycle Innovation on People’s Lives.

Pedal powered velocipede (1839) greatly improved usability of bike

Penny Farthing – faster transport than velocipede but dangerous to ride (higher centre of gravity)

Rover Safety Cycle (1885) – safer transport with similar speeds

1889 – Dunlop’s pneumatic tyres – more comfortable ride

Early 1900s – mass production of the bike. Improved mobility

High strength steel alloys eg Reynolds 531– Bikes became lighter

Recumbent bikes offered better comfort but outlawed from racing (speed) – stalled development

Lightweight Al alloys and reliable derailleur gears – improved traditional design of RSC

After WWII – cycle usage declined as cheap cars available – subsequent pollution not considered.

BMX – small wheels, off road, popular with children

1980s. Growth of mountain bike. Most popular. Many specialised components developed.

Recumbent bikes regrew in popularity – good for long-distance touring as it was easier on the body

1990s. More exotic materials. Greater weight savings = Improved performance

Construction and Processing Material over Time

Material Properties Application

Timber Formability, strength:weight ratio,

availability, low cost of manufacture

Used in early bike due to a lack of suitable

alternatives. Shaped pieces in frame and wheels

Iron Superior to timber in almost every

mechanical property but a bit more costly

Initially as a tyre on wooden wheels and in

early frames

Steel Good strength with relatively low weight,

cold drawn steel tubes are best for frames

Ease of fabrication

Cost Effective

Steel wheels with thin steel spokes were used.

Joined by lug brazing. Only cheaper frames

were welded. Used extensively in brake and

gear construction before Al alloys were used.

Still used in chain, gear clusters, cheaper bikes

Stainless

Steel

Good corrosion resistance Widely used in components such as cable,

brake/gear pins

Steel Alloys CroMo steel. Superior S:W, can be welded,

which is quicker, lighter and cheaper to

fabricated than lug frames

Air Hardening Steel. Steel hardens in air

around welded joint to maintain strength

and S:W approaching to that of Al/Ti alloys

High performance bikes, ie racing or touring

applications


Aluminium

Alloys

Lighter, but weaker

Must be welded

Relatively corrosion resistant

Tubes are oval to increase resistance to

bending. Used in brake/gear parts due to light

weight. Most brake levers and arms are pure

Al, whilst derailleurs and hubs use Al alloys.

Titanium

Alloys

Excellent stiffness, S:W, but very expensive Titanium sprockets instead of steel cogs. High

cost, only for best racing bikes

Not much advantage over steel alloys

Carbon

Fibre

Excellent S:W, stiffness. Frame is moulded,

not fabricated. Tough, but failure is sudden

and catastrophic

Excellent alternative to Al or steel alloy frames.

Only used for competitions

Rubber Light, moderate springing (provides comfort

and improves suspension), self-damping.

Solid rubber tyres used to replace iron tyres.

1889. Pneumatic tyres = Greater comfort. Also

used in suspension

Polymers Lightweight. Flexible. Good resistance to

weather and UV deterioration.

Polymer sheaths are placed over cables

(Bowden cables), also in pedal construction.

Used in cycle lights and finishing pieces.

Environmental Effects of Transport Systems - Bicycle

Possible solution to pollution, Greenhouse effect. Very energy - efficient way to travel (non-polluting,

human power is renewable).

Still not as popular as other modes of transport due to factors such as speed, weather issue (increased

risk in wet weather), fear on roads (cars, road rage, no dedicated paths)

Environmental Implications from Material Use in Transport

Timber

Used as sleepers (railways) and fuel source as well as in the physical structure of the transport.

Result: Global warming, local climate change. . Large deforestation reduces habitat for local fauna.

Steel

In plain carbon and alloyed forms. Demand = Large steelworks, which affects local atmosphere with

pollutants produced in working and refining.

Requires much iron, so iron ore must be mined, often open-cut, which has large environmental impacts

Coal and limestone also needed. Coal has to be mined and refined to coke.

Cast Iron

Similar impact to steel, but used less in modern times.

Aluminium

Refined from bauxite, mined in open cut, affects local landscape and environment

Production process uses coal generated electricity.

Polymer

Lightweight, and so transporting and production requires less fuel and energy

Must be backed up by recycling old equipment as polymers contribute greatly to landfill


ENGINEERING MECHANICS AND HYDRAULICS

Simple Machines

These devices change the direction or magnitude of a force, often providing mechanical advantage. They are:

1. Lever

2. Wheel and axle

3. Pulley

4. Inclined plane

5. Wedge

6. Screw

Friction

When 2 surfaces are in contact and tending to move relative to one other, tangential forces will develop

between them. These are frictional forces and they always act parallel to the surfaces and oppose movement

between the surfaces. Friction is generally accepted to be the result of irregularities on the surfaces in

contact and to a lesser extent, molecular attraction.

Maximum/Limiting Friction

The magnitude of the friction force increases from zero to a max value (Fm). 4

situations can occur when two surfaces are in contact

1. When P = 0, there is no tendency to move, therefore no friction

2. As P increases, it is still too small to move the object. Friction will develop to just balance P.

3. At the point of moving, pushing force is equal to maximum friction, ie . Most questions will

ask you to find this case. Take care to remember that N is equal to the reaction of net vertical forces.

4. If P > Fm and the body will move and accelerate to the left. Friction will be capped at

Coefficient of Friction

The magnitude of the friction force, F, is proportional to the normal reaction, N. The constant for any pair of

surfaces is called their coefficient of friction (μ). Friction is independent of surface area.

Angle of Repose and Static Friction

Repose: The maximum angle before which the

object on the slope will begin sliding: .

Static Friction: In the case of a block on a flat, horizontal floor, consider the

normal and (maximum) friction force combined into one resisting, resultant

force at an angle from the vertical. In this case as well:

(NOTE that I haven’t found angle of static friction to be useful, but simply just to

consider ie and go from there. Or )

Work, Energy and Power

Work (vector quantity) Energy Power

Occurs when a force causes

motion. Measured in Joules/ Nm.

Energy is an object’s ability to do

work. Measured in Joules/Nm.

Power is the rate at which work

is done. Measured in Watts

W = Fs PE = mgh

KE = ½mv2

(Mech) P = Fs/t = Fv

(Elec) P = EI


ENGINEERING MATERIALS (PPT)

Testing of Materials

Compression Test

This test is used to determine the strength properties of brittle materials since

such materials are used in compression rather than in tension (eg cast iron,

concrete, mortar, brick, ceramics, wood)

Transverse Tests

These are used on structural members which may experience tensile and compressive stresses, at the one

time, when loaded. Such members are in “bending”. Transverse tests assess the strength of the material in

this situation.

Shear Tests

These tests involve applying a load to a given test piece which acts parallel to a

given plane. Must consider what is the area (perimeter of cut/punch * thickness)

Ultimate Shear Strength =

Notched Bar Impact Test

The Izod and Charpy impact tests are used to measure the

capacity of a material to resist shock loadings, that is, its

toughness. These tests will show the brittleness of a

material. The Charpy test is more widely used.

Hardness Testing

3 methods of measuring the hardness of materials:

Brinell. 10mm steel/carbide ball.

Vickers. Diamond pyramid.

Rockwell. Diamond cone.

Each test forces an indenter into the material’s surface and a number is derived depending on how far the

indenter sank into the material.


Heat Treatment of Ferrous Metals (Steel)

Hardening, or Quenching is the process used to increase the hardness of a material by heating a

material above the UCT then dropping it in water, brine or oil. (eg/ gears, shafts)

The atoms have no time to grow and realign themselves, rendering the material hard and brittle.

Highly stressed material. New microstructure is martensite.

Stainless steel will have air hardening properties. Forms martensite in air. Molybdenum added to

reduce brittleness.

Carbon Carburising or case hardening. Steel heated in the presence of another material liberates

carbon to the surface, thus when quenched, the high carbon content surface becomes hard.

o Core is soft and tough as pearlite whilst case is hard as martensite

o Increase in hardness, wear resistance, fatigue/tensile strength

Tempering is the process used to toughen a, usually, hardened material by removing internal stresses.

By heating it below recrystallisation temp (LCT) the atoms can realign themselves slightly,

becoming tougher and more ductile with only a small trade-off in hardness as well as improving

malleability. This is done predominantly with brittle martensite, as the carbon atoms of the distorted

microstructure can rearrange becoming more useful in toughness and ductility. The microstructure

doesn’t change, because not heated past LCT.

Low tempering temp – High hardness and moderate toughness. High temp has opposite effect

Annealing is the process of heating a material then slowly cooling it inside the furnace.

Long time to recrystallise = large, equiaxed grains. Increases ductility, toughness, softens material,

and relieve internal stresses. Improves cold working properties.

Full annealing. Heat just above UCT. Result is

a softer, larger grained steel. Not often used,

high temperature is costly

Process annealing. Just below LCT, so only a

portion recrystallises, in this case, it happens to

the distorted ferrite grains, which are a majority

of the microstructure. Pearlite doesn’t change.

Normalising is an annealing process in which a

material is cooled in (jets of) air to relieve stress whilst

it is still in the austenite region.

Smaller grains than annealing are produced, resulting in a harder and tougher material w/o the

maximum ductility achieved through annealing. Heated just above UCT.


Structure/Property Relationship in Manufacturing Processes

Forging is the shaping of a metal through the use of force.

Forge about recrystallisation temp (LCT) = LCT. Below = Cold or pressing.

Increase length, reduce cross sectional area = Drawing

Reduce length, increase cross sectional area = Upsetting

Force metal into dies to take required shape = Drop forging

All methods, if hot worked, produce grain flow in the metal that follows object profile. Improves strength of

finished article, whereas the grain flow of a machined part may cause planes of weakness

Rolling

Hot Rolling

Used extensively in production of sheets, strips, bars and rods

Ingots are passed through successive roles to produce required thickness

When passed through, the metal’s crystal structure is deformed

As above LCT, it recrystallises into an unstressed form

Advantages

Less stress on machinery

Unstressed finished product

Disadvantages

Less dimensionally accurate

Black oxide layer over product

Cold Rolling

Rollers and machinery are more heavily built as larger forces are required

Distorted grain structure produces a harder and stronger final product, at the expense of ductility and

malleability

Advantages

Harder final product that is more dimensionally accurate

Good surface finish due to lack of oxides

Disadvantages

Greater cost due to heavier machinery

Casting involves the pouring of molten metal into a prepared mould cavity which has the shape of the

article to be made. Advantage: No directional properties so less internal weak points

In general, casting is more economically desirable.

Metal to be cast must be melted cleanly and economically.

Mould cavity must allow for the escape of gases

Must be able to remove the solidified casting form the mould cavity.

Large

equiaxed

grains

Small

equiaxed

grains


Ingot Pour molten metal into large tapered metal mould

and then shape.

Continuous Allows for rapid production of simple cross-section

products such as bars, rods, and strips. Can be

vertical or horizontal.

1. Poured into water-cooled ingot with a sliding

bottom.

2. Once bottom solidifies, base moves down at a

rate that allows metal above to solidify.

3. Result is a long metal strip.

Method is used in large plants due to rapid speed

and cost effectiveness on large runs

Sand 1. Sand with binder (green sand) is packed around

pattern of finished product.

2. Mould is in 2 halves so it can be removed.

3. Cavity is left for molten metal. Once metal

solidifies, sand is removed and reconstituted,

ready to be reused.

Defect may occur as gas porosity

Shell Similar to sand casting, but uses resin in the sand.

Offers closer tolerances than die casting and better

surface finish than sand casting. Costs more and

high dimensional accuracy needs metal pattern

plates, which are expensive

Die Unlike sand casting, this uses a permanent mould

which is not remade every time

Gravity die casting. On long runs, cost is less than

sand casting and has better surface finish. Eg/

pistons, other automotive parts

Pressure die casting. Denser casting than gravity.

Good surface finish, cost effective. Primarily used

with lower melting point alloys (eg Al alloys) as

dies for high temp ferrous alloy are expensive (use

graphite dies). Eg/ gearbox castings.

Investment Pattern is expendable. Excellent dimensional

accuracy and surface finish.

eg/ turbine blades for aircraft

Centrifugal Useful in creating pipes. Eg/ piston rings for cars.

Produce a cylinder then cut rings off it.


Extrusion

Direct and Indirect Extrusion

Metal is forced through a die so it takes the shape of the die

through which it passes. Direct requires more effort, so it is used with

more ductile materials. Indirect, where the ram and die are one part, is

used in extrusion of less ductile alloys, but as it is more expensive,

direct is used where possible. Both are hot working processes.

Tubing may be made through extrusion by a mandrel placed in centre

of die to create hole.

Impact Extrusion involves the use of a hammer impact to extrude a

shape.

Cold forming process. Material blank is forced from the die around

the punch.

Eg/ cans, short tubes

Powder Forming

After the powders are prepared, they must be stored in dry conditions

prior to use. Just before use, they must be carefully blended in correct

proportions, pressed at the optimum pressure and sintered to promote

adhesion between all of the particles.

Pressing

Reduces the porosity of mass (particles forced together). Causes particle

deformation, causing increased mechanical strength.

In general, a fine powder requires a higher pressure to give it the

necessary strength and density than a coarser powder. Powders of hard metals give weaker and less

dense compacts than do those of softer metals if both types are subjected to the same pressure.

Sintering is the process whereby cohesion is promoted in a powder compact by heating it in a controlled

atmosphere.

If the compact is sintered for too long, grain growth may increase to the point where the grain

coarseness will weaken the material.

Advantages Disadvantages

Less machining Less strength

High production rates High die cost and material cost

Complex shapes Design limitations (not much more than planar)

Various compositions properties Density variations = property variations

Less scrap

Excellent surface finish

Fine tolerance


Non Ferrous Metals and Alloys

Usually good formability

Low density

High thermal and electrical conductivity

Corrosion resistance

Low strength compared to steel

Poor weldability

α phase = soft, ductile

β phase = increased strength, reduced ductility

γ phase = hard, brittle

Pure Aluminium

Lightweight

Extremely reactive

Relatively low strength

Ductile

Low specific gravity

Easily fabricated

More difficult to weld than ferrous alloys

More costly than mild steel

Good S:W

Corrosion resistance (oxide film)

Good electrical conductivity

(60% of copper’s conductivity

Aluminium alloys (below contains more information that will be reasonably tested, but for completeness it has

been included. Phrases regarding aluminium alloys that have been emboldened are potentially more relevant)

Wrought Alloys - Used for mechanical working.

Non-heat treatable alloys

1xxx Primarily pure Al with small amounts of Fe and Si. Used mainly for sheet

metal work

3xxx Al – Mn. Provides solid solution strengthening. Used for pressure vessels,

chemical equipment and sheet metal work

5xxx Al – Mg. 5052 (2.5%Mg, 0.2%Cr). Used for sheet metal work, particularly

for truck bodies and marine applications

Heat treatable alloys

2xxx Al – Cu. Duralumin (2017, 4%Cu), Strengthened by solid solution

strengthening and precipitation hardening. Primarily for aircraft because of

high tensile strengths (4x that of mild steel)

6xxx Al – Si, strengthened by precipitation hardening, good corrosion resistance

and strength. Used in bike frames, truck and marine structures

7xxx Al – Zn, little Mg and Cu. Alloy strengthened through precipitation

hardening. Alloy elements allow denser precipitates; produce a stronger alloy

w/ strengths up to 500MPa. Used in aircraft structures and high quality bike

frames

Casting alloys.

Most Al alloys are cast, using sand casting, gravity or pressure die-casting. Most contain silicon (5-12%) to

produce a lower alloy melting point and improve strength and fluidity of molten alloy. Manganese and

copper may be added to improve strength and hardening.

eg/ Al/Si/Mg/Fe alloy. Used in the manufacture of alloy wheels in cars.

Aluminium Lithium Alloys.

Used in bike manufacture. Reynolds is marketing an Al/Li alloy that offers a 100% better fatigue life and

50-100% better strength than 6061 Al alloy tubing.


Aluminium Zinc Alloys

Mainly extracted from sphalerite/zinc blend

Fairly soft, brittle at room temp. High corrosion resistance, so used to galvanise

Mainly used in die cast industry due to low melting point (420), low cost, high dimensional stability

Copper, Brass and Bronze (below contains information of various types of copper, brass or bronze. It is not

expected of the student to remember every type, but to recognise that many types exist and their common applications)

Copper

Good electrical conductivity, excellent formability, high corrosion resistance.

Cu + Zn = brasses, Cu + Sn = bronzes, with Ph/Al = other bronzes

3rd

most used metal. Extensively used in electrical industries.

2nd

best conductor (only to silver). Far more cost effective as a conductor than silver

Brass

Commercial brasses rarely contain more than 40% Zn as then the alloy becomes brittle.

Cartridge brass. 70/30 brass (30% Zn). Quite ductile. Formerly used in bullet cartridges. Higher

ductility than copper, hence perfect for deep drawing operations

Standard brass. 25% Zn. Good quality, cold working alloy where the ductility of cartridge brass is not

required. Used for stampings and limited deep drawing

Muntz metal. 40% Zn. Due to brittle phase in microstructure it is usually hot-worked to shape. Eg/ rods

and bars. It may also be cast eg/ tap bodies. Muntz metal can be heat treated to change its properties

Naval Brass. 37% Zn, 1% Sn. Zn adds corrosion resistance in seawater

High Tensile Brass (Manganese bronze) is a Cu (58%), Zn (~36%) alloy with small additions (<1.5%)

of Mn, Al, Pb, Fe and Sn. = Improve the tensile strength over other brasses, at the expense of ductility.

Eg/ stampings and pressings, propellers and rudders

Bronze

Good tensile strength, corrosion resistant, used in marine and chemical applications

Low tin bronze. 3.75% tin. Good elastic properties and corrosion resistance. Eg/ springs

High tin bronze. 18% tin. Heavy load applications, such as slewing turntables on large cranes.

Admiralty gunmetal. Bronze with 88% cu, 10% Sn and 2% Zn and some nickel. Zinc makes the alloy

more fluid in liquid state, which suits casting. Used for pumps, valves and especially marine castings as

it has good corrosion resistance in saltwater

Leaded gunmetal (red brass). 85%Cu/5%Sn but also 5%Zn/5%Pb, which reduces ductility and makes it

more suitable than Admiralty gunmetal for pressure vehicles

Phosphor bronzes. Deliberate amounts of phosphorous added as opposed to trace amounts left over

from refining. Tend of have higher tensile strength and corrosion resistance than standard tin bronzes.

Importantly, they have a lower coefficient of friction, thus suitable for bearing applications.

Aluminium Bronze - Cu/Al (11%)

Good tensile strength, corrosion resistant, used in marine and chemical applications

Casting is difficult due to oxidation of aluminium. Hardenable through heat treatment.


Heat Treatment of Non-Ferrous Alloys

Annealing is done to remove stress that may result from cold working the alloy when producing sheet, plate

or bar metals. Each alloy will have varying optimum annealing temp.

Solid Solution Strengthening/Hardening is done on many alloys to

improve its overall strength and hardness.

Alloy is heated so that a homogenous structure is formed

It is then quenched to retain that homogenous structure

Submicroscopic particles of other material/additive are

precipitated and locked in the grain boundaries

This resists internal slippage and distortion, resulting in an increase in strength and hardness.

Corresponding decrease in ductility/malleability

The aging part means to simply let the material rest and can be done in two ways:

o Natural Ageing: stand alloy at room temperature for a long time (at least few days)

o Artificial Ageing/Precipitation Hardening: alloy is slightly heated and left for several hours

Age over a longer period of time = Increase corrosion resistance and slightly improves mechanically

Precipitation is more commonly done because it takes less time. However, if the material is left to

over-age, it can soften as the necessary bonds may break and reduce the quality of the material.

Ceramics and Glasses

Ceramics

Can withstand higher temp than metal alloys, then they can run at higher operating temperatures without

cooling systems, which accounts for a motor’s 20% loss in heat energy, thus improved thermal

efficiency and fuel efficiency would be in a ceramic motor, but most ceramics are brittle

Modern ceramics (eg Zirconia) aren’t as brittle as common ceramics such as porcelain/china. They are

strong enough to withstand forces and shockwaves developed in an internal combustion engine.

Alumina (insulator of spark plug) offers insulation, thermal stability and resistance to vibration

Glass is an inorganic fusion product that did not crystallise when solidified (amorphous structure)

(NOTE: Below, only soda lime glass is really needed as it is the most common by far, but again, know that other types exist)

When glass is deformed, it is unable to dissipate the applied forces through a slip/dislocation mechanism,

so once bond resistance is exceeded, the structure factures rapidly.

High Silica

Refined from borosilicate glass, nearly entirely silica.

Almost perfectly clear. Used in situations of elevated temp (eg/ missile nose cones)

Soda Lime

Most common type of glass

Soda prevents devitrification/crystallisation; however it makes the glass water-soluble. Addition of

lime alleviates this.

Softens at ~850°C, easily formed when hot, will not recrystallise, water resistant and cost effective.

Eg/ windows, bottles, light bulbs, windscreens

Laminating and Heat Treatment of Glass: See Laminated Glass and Toughened Glass (CIVIL)


Borosilicate

Up to 20% boron and silica.

Good levels of chemical resistance and low thermal expansion = high resistance to fracture at

elevated temperatures.

Used in electrical insulation, gauge lab glasses, cooking and ovenware (eg Pyrex)

Lead

Up to 40% lead. Lowers softening temp of regular soda lime glass.

High refractive index, thus optically clearer, hence used for optical glass, thermometer, crystal

tableware

Polymers (NOTE: For this section, as many different polymers exist and it is easy to get confused between them,

I recommend researching at least 3 polymers (1 thermoplastic, thermosetting and a resin) and write down their

mechanical and chemical properties and their physical applications. This should fill a single sheet.)

Thermoplastics (or thermosoftening polymers)

Softens on the application of heat, can be remelted and reformed.

Usually flexible and often transparent.

Under tension, they stretch readily (little resistance to chains straightening/sliding)

Eg/ polyethylene (plastic bags), polystyrene (plastic cups), PVC (piping), polypropylene (house base

liner). Used in cable coating on bikes. Car door handles.

Thermosets (or thermosetting polymers)

Will not soften when reheated. Heating will char and burn.

Under tension, cross-linking resists deformation, therefore less flexible.

Eg/ epoxy resin (joining aircraft panels), polyurethane (lacquer). Used in switches.

Rubber

Natural polymer. In synthetic form, it has great use in transport, especially vulcanised rubber

Vulcanised rubber is the addition of sulphur, which improves cross-linking, thus improves durability

To increase rigidity, tyres are usually constructed from a composite of rubber with cotton strands, while

radial tyres for cars use steel wire and polyester cord.

Engineering Textiles are polymer resins that are drawn into threads then woven into cloth-like sheets. They

are synthetic polymers offering vast improvements over natural fibres

Polyester Strong and resilient. Hydrophobic (resistant to water absorption)

Eg/ helium airships, manufacture of some tyres, car fan belts, radiator hoses

Nylon Used as dry lubrication. High elongation. Melts instead of burning. Excellent

abrasion resistance. Now replaced by PTFE. Resistant to acids, bases and oil.

Aramid Fibres Eg/ Nomex and Kevlar. Excellent strength qualities, but limited to low temp uses.

Used in aircraft manufacture, bullet proof vests.

Eg/ Modern bikes - reinforce carbon fibre forks - protect against the sudden CF

failure.

Olefins Polyethylene/polypropylene fibres shaped into sheets

Waterproof, eg / tents

PTFE (Teflon) Fire resistant. Stop water vapour, but not water. Eg/ engine filters, cooking pans


Manufacturing Process for Polymer Components

Compression

moulding (TS) Heat + pressure forms the shape & polymerise

the polymer

Eg/ plugs, switches and casters

Transfer moulding

(TS) Applies pressure to force die via sprue into

adjacent cavity. Allows for more intricate

designs.

Blow Moulding (TP) Air forces polymer tube to the shape of the mould

Used to make plastic bottles and containers

Extrusion (TS) Polymers granules are melted and the molten

material is forced through a die.

Hopper feeds into heated chamber and die may

be water cooled to speed production

Eg/ polymer tubing. Outer covering of bike

cables.

Thermo-forming (TP) Heated thermoplastic sheets are placed over dies

to produce required shape. Eg/ containers

Forming can be done using matching dies, a

vacuum or air pressure.

Using gravity would be inaccurate Calendaring (TP) Poured between two possibly embossed rollers

Eg/ tiles, films, curtains

It’s like rolling, but with

patterns on the rollers

Rotational Moulding Centrifugal force throws molten polymer to the

mould walls to form a hollow article

Injection Moulding Most common procedure.

Molten polymer is inject into a cavity in the

shape of the finished product

Mass production. Used in manufacture of small

thermoplastic mouldings for cars/bikes


ENGINEERING ELECTRICITY/ELECTRONICS

Power Generation/Distribution

Generation

Coal

o Most common. Produce steam to drive turbine to produce electricity.

o Readily available resource. But it produces large amounts of CO2 greenhouse effect

Hydroelectric

o Water’s potential energy is converted to kinetic energy, to drive turbine and generator in power station.

o Water is fed back into water system for irrigation

o “clean”, but impacts surrounding environment. Only possibly in mountainous regions. Eg/ Snowy

Mountains. Increased salinity levels due to irrigation and farming in formerly dry regions

Wind Power

o While truly clean, many turbines are needed to power larger cities, hence much land clearance.

o Wind is also intermittent and unreliable. They also generate a lot of noise.

Nuclear Power?

o Doesn’t contribute to global warming. A bit of nuclear fuel produces large amounts of heat

o By-products are often contaminated for thousands of years, hence not completely safe.

Distribution

In recent years, smaller power stations have closed and replaced by larger ones in more remote locations.

eg/ none in Sydney/Wollongong areas, but in Bathurst, Snowy Mountains

Power lines: Steel cored Al/Cu. Steel core provides strength to let wire support itself. Al/Cu provides

electrical conductivity.

Aluminium is used instead of copper as it is lighter. If copper is used, more poles are required.

To reduce resistive loss in Al cable, power is transmitted at very high voltages.

Power loss is directly proportional to the voltage and the current squared. Raising the voltage reduces the

current for the same amount of power, thus reducing the resistive loss in cable.

Ploss = IR2 , P=VI , P is constant.

Given that power loss is directly proportional to current, it would be beneficial for electricity to be

distributed with high voltage/low current. Therefore, transformers are used change voltage level in the

transmission of electricity. High voltage is easier and more efficient to send a long distance (as there is

less loss), but low voltage is easier and safer to use at home/office. Transformers can only work in AC.

Simple Circuits

With simple circuits, it is much like having a basic electricity experiment

at school, with a power source, wiring and some components, such as a

lamp, LED or motor, for example. Basic knowledge of circuits is assumed

and expected from year 11, such as of parallel and series circuits, and the

corresponding effects on voltage, current and resistance in those circuits.


Components

Cell Device used to produce electricity, possible form chemical reaction

Battery A group of cells connected together

Resistor Electronic device that provides resistance to a circuit

Diode Only allows current to flow in one direction, often used as a protective measure

LED Diode that emits light (light emitting diode)

Capacitor Device capable of showing electric charge

Transistor Acts like a switch or amplifier

AC/DC Circuits

AUS AC mains power = 50Hz. AC should be rectified for use in DC

mechanisms.

Rectification is the conversion of AC to DC.

Half wave rectification = one diode is used. Eliminates the

current flowing the opposite way, so blocks the negative

part of the waveform

Full wave rectification = 4 diodes. Allows all of the sine

wave to pass, but all waves on the positive side = same

direction for load. The final wave form is not a true DC,

but a varying DC.

Not ideal for most DC equipment. To achieve better

waveform, a smoothing capacitor is added to circuit. It stores

energy that can be used when the wave form reduces in

voltage. The result is a nearly flat wave form, with the capacitor

smoothing out the trough.

There is a slight voltage rise when T1 becomes positive again,

which is minimized by ensuring the capacitor value times the

resistor value is larger than the cycle of AC. For efficient

smoothing:

C1 x R1 > 0.02

Electric Motors used in Transport Systems

DC Motors

Shunt wound motors are rarely used in locomotives. They have constant speed but low starting torque,

therefore not suitable if there is a lot of stopping/starting

Series wound motors offer excellent torque at low speeds and will operate at high speed under light load.

This makes them excellent for use in trains, hence widely used

Compound motors combine good features of both. Good starting torque and will not run away under no-

load conditions


AC Motors

Generally induction motors used in trains. Lack of commutator and brushes, which wear out over time.

Rely on the frequency of electricity and magnetic induction for their power.

Function is aided by alternators, which produce AC, replacing generators on diesel electric trains

On English Channel Tunnel, locomotives are powered by single phase AC voltage, which is rectified to

DC, passed through a control circuit. The voltage is converted into AC for the motors.

Advantages over DC motors: no brushes, no need to rectify

Control Technology is the use of some type of mechanism or circuit to control the operation of an item

eg// float arm of toilet controls water delivery

Can be simple mechanical linkage, digital Y/N circuit, or complex circuit that reads various inputs to

produce various outputs. Enhances comfort and safety in transport.

Earliest governor on steam engines. Centrifugal forces caused arms to rise. This controlled a throttle

system, which maintained the engine at constant speed under varying loads

Cars electronic cut-outs that sense the speed of crankshaft and cut fuel supply if car revs too fast.

Trialled on car suspension, trying to reduce the compromise by engineers between ride and handling,

which exists in conventional suspension systems

Control technology is used to trigger safety devices such as ABS. When wheel begins to lock, computer

reduces brake pressure, prevent wheel from locking and the car from skidding out of control.

Semiconductors are essentially poor/non conductors.

Made up of insulating material doped with another atom to give it a

surplus/deficiency in electrons.

Silicon and germanium compounds – most common SC materials - both have 4

electrons in outer shell.

Boron – 3 electrons – creates positive “holes” = P TYPE

Phosphorous – 5 electrons – creates surplus electrons = N TYPE

P-N JUNCTION. P type layer on a one way component is created, allowing

electricity to flow only one way.

This is due to DEPLETION zone, which is the gap between the bulk of the

positive and negative charges of the semiconductor materials. If current flows in

one direction the unlike particles attract, reducing the depletion zone and current flows. This is called

forward bias. If current flows the other way, charges repel, the depletion layer grow and current doesn’t

flow. This is called reverse bias.

Double p-n junction = Transistor. By applying a current to the sandwiched material allows current to

flow between the other materials, with the middle layer acting as a gate. NPN or PNP

Smaller, cheaper, often used for control technology.

Electrical Safety

Electric Shocks. Whilst current is the killer (small currents can trigger fibrillation in the heart) but still

requires sufficient voltage to cause the electricity to arc. Mains power (240V) is sufficiently dangerous

Take care that appliances are earthed or doubly insulated to prevent short circuiting

Overloaded systems can catch fire. Fuses or circuit-breakers can prevent this by cutting the circuit.

engineering studies – personal and public transport

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