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Michael McElroy Year 12 Engineering Studies

Engineering HSC Syllabus Summary

Civil Structures

Engineering mechanics and hydraulics Stress and Strain

- Strain › The proportional change in length caused when a specimen is under load

› Strain ( ε )= e(extensionm)L(original lengthm)

› No units (ratio)

- Shear stress› A measure of the internal reaction that occurs in response to an externally applied

load

› Stress (σ Pa )= P(Load N)A(Aream2)

- Engineering and working stress› Engineering stress – the original C.S.A is used to calculate the stress for every value

of the applied force› Working stress – The actual or constantly changing C.S.A value is used to calculate

the stress - Yield stress, proof stress, toughness, Young’s Modulus, Hooke’s law, engineering

applications› Yield stress - the stress where there is a marked increase in strain without an

increase in stress. Yield stress is always greater than the elastic limit, but less that the UTS

› Proof stress - used as a measure on materials that do not show a marked yield point. Usually a set amount of strain is given to the material, usually 15 or 2% and the amount of stress can be calculated

› Toughness - indicated by the area under the curve in a stress/strain diagram. Ability of a material to absorb energy

› Young’s Modulus - Measure of the stiffness of a material. Applies up to the elastic limit of a material. The gradient of the straight line in section of the graph indicates YM.

› Hooke’s law - the amount of elastic deformation that a material can sustain in tension or compression before it undergoes permanent plastic deformation.

- Factor of safety

› For ductile materials – FOS= Yield stressmax .allowable stress

› For brittle materials - FOS= UTSmax . allowable stress


- Stress/strain diagram

Truss analysis- Method of joints


- Methos of sections

Bending stress induced by point loads only

- Concept of shear force and bending moment› Shear force

A shear force causes one part of a material to slide past the adjacent part of the material


› Bending momentThe bending moment is the amount of bending that occurs in a beam

- Shear force and bending moment diagrams


- Concept of neutral axis and outer fibre stress› As a beam bends, the concave side will compress and set up compressive forces

within the beam› The convex side of the beam will stretch, producing tensile forces› In between, there exists a plane where the fibres in the beam are not subjected

to tensile or compressive forces. This plane is called the neutral axis› The fibres furthest away from the neutral axis will be subjected to maximum

stress

- Bending stress calculation (second moment of area given)› To calculate the bending stress (σ ) at any section of the beam.

σ= MyI

Where: σ = bending stress (Pa)M = max. bending moment (Nmm)Y = distance from neutral axis (mm)I = second moment of area of the cross section of the beam (mm4)


Uniformly distributed loads- Unlike a point load, UDL is a load that is spread across a beam

Crack theory- Crack formation and growth

› Cracking begins with micro cracks (crack initiation phase)› Cracking then leads to crack propagation, that phase in which the crack grows in

size under cyclic loading to ultimate part failure› Crack initiation can be long and develops from repetitive stresses at stress

concentrations› Dependant on material and method of component manufacture› Surface cracks can be detected using visual inspection techniques such as

magnetic particle add dye penetration tests› Sub surface cracks require ultrasonic or radiographic methods to be detected

- Failure due to cracking› Cracking can occur at stresses below yield stress, known as fatigue› Fatigue fracture begins as small crack, that grows in size from repeated stress› As a crack expands, the load carrying cross-section of the component is reduced,

with the result that the stress on this section is raised- Repair and/or elimination of failure due to cracking

› For metallic materials: welding can repair crack. However doing this will repair crack but micro structural changes will appear around the weld and weaken the material, with weld being a point of stress concentration. Heat treating the material after welding will avoid this


› For polymers: adhesives can be used to repair crack. This cannot be done for thermosets, instead it must be replaced

› For ceramics: usually can’t be repaired – need to be replaced › Prevention: designing item without sharp corners will reduce cracks from

forming as stress can be concentrated at these points

Engineering mechanics and hydraulics

Testing of materials- Compressive testing

› Used to determine the compressive strength of materials› Test piece is compressed and load deformation is recorded

- Transverse beam testing› Many materials used are not only in compression or tension at the same time. They

can be exposed to bending stresses› Used to determine bending and shear in materials › Transverse beam testing involves placing a test piece between two› supports and then gradually applying a load

- Concrete testing› The water/cement ratio in concrete effects the workability of the mix and also the

final strength of the concrete› Slump test – measures the workability of concrete. Wet concrete is placed in a

mould. When the mould is removed, the amount of deformation of the shape is measures and is used to describe the workability of the concrete

› Compression test – compression testing of concrete is measured after 28 days. This is done to test the strength of the concrete.

Ceramics- Structure property relationships, applications

› Hard, brittle, chemically inert, electrical/thermal insulation, durable› Compressive strength

- Glass› Non-crystalline ceramics› 3 basic ingredients are: silica, limestone, soda ash› Soda-lime glass: accounts for 90% of glass – windows, bottles etc.› Borosilicate glass: used for ovenware, telescopes › Lead glasses: optical components, radiation shielding › Main properties: transparent, brittle, compressive strength › Properties can be improved by: thermal toughening (air quenching), chemical

toughening, laminating- Cement

› Bonding material› Compressive strength› Low toughness


› Easily casted› Excellent workability

Composites- Timber

› Organic materials› Structure: cellulose tubes bounded together by glue lignin (wood grain)› Factors affecting strength of timber: loading duration, moisture content, defects

(within grain)› Exposure to chemicals

- Concrete (reinforced and pre-stressed)› Concrete is a compound of sand, gravel, cement and water› Reinforced concrete: steel bars imbedded in concrete to add tensile strength› Pre-stressed: concrete is poured over steel wires or cables that are placed in

tension. After concrete is hardened, tensile stress on cables is released - Asphalt

› Consists of aggregate, bitumen and air voids› Aggregate held together with bituminous binder› Adding small amounts of materials, such as rubber, alter asphalt properties› Toughness› Durability › Resistance to moisture, heat etc. (weather resistant)

- Laminates› Consists of materials that are sandwiched together› Plywood: layers of timber with adhesive› Laminated glass: two layers of glass with PVB polymer in middle – adds strength› Fibre glass: glass fibres bonded with polymer resin

- Geotextiles› Woven polymers or ceramic fibres› Used to stabilise road base, geotextile is placed underneath asphalt – prevents

potholes Corrosion

- Corrosive environments› Availability of oxygen to enable reactions to proceed› Temperature

- Dry corrosion, wet corrosion, stress corrosion› Dry corrosion – occurs through chemical reactions with gases, at high

temperatures i.e. in furnaces› Wet corrosion – occurs when material is in contact with fluid or moisture› Stress corrosion – when a material is subjected to stress (i.e. cyclic loads) and

cracks begin to form. The material will eventually degrade due to fatigue

Recyclability of materials- Steel


› B.O.F (basic oxygen furnace) – 25% recycled steel possible› E.A.F (electric arc furnace) – 100% recycled steel possible

- Concrete› Recycled concrete weaker that original product› Usually used as rubble› Concrete is crushed/broken down and re-used

- Wood› Can be recycled for basic uses i.e. furniture, pallets etc.› Dependant on type of wood› Used as chips for garden mulch, playground covering› Smaller chips to form wood composites› Recycled as paper or cardboard

- Asphalt › Limited uses for recycled products› Usually crushed and refined with other materials added to reproduce asphalt

again- Glass

› Can be reused to produce glass again

Personal and Public Transport

Engineering mechanics and hydraulics

Static friction- Concept of friction and its use in engineering

› Friction is the resistance to motion and efficiency › Friction always acts opposite to the direction in which the body moves› Static friction – frictional force present when two bodies are at rest› Limiting friction - frictional force present when two bodies are at the point of

moving› Dynamic friction – frictional force while a body is moving

- Coefficient of friction → amount of friction that materials develops between them (μ)

› μ=FF

RN= Frictin force

Normal reaction› Normal force

Reaction force Always perpendicular to supporting surface Equal to, but opposite direction to weigh force Balances out forces

› Friction force Force that prevents movement Force that is exerted between contacting surfaces Always opposes direction of motion


Increases as applied force increases› Angle of static friction (φ)

Resultant force (of friction force and normal force) makes with the normal

The angle that the resultant force makes with the normal reaction tan φ=μ

› Angle of repose The angle when the angle of static friction will equal the inclination of

the plane When the gravitational force down an inclined slope equals the frictional

force, i.e. the system is an equilibrium - Energy, power

› Potential energy Stored energy within an object with the ability to do work The PE is equal to the work done in lifting a body’s weight (mg) through

a vertical height (h). PE =mgh Hydro electricity uses PE

› Kinetic energy Energy a body possess due to its motion KE = Energy a body possess due to its motion

KE = 12 mv2

› Work W=∆KE or W=Fs or W=Fscosθ When a force causes motion Total work – multiple forces acting on a body

› Power The rate at which work is done P=w/t = Fs/t = Fv

Engineering materials

Testing of materials

- Visual testing› Dye penetration

Dye or coloured liquid is placed on the surface of a component and excess is wiped clean

Any cracks or imperfections on surface of component will be highlighted by the dye remaining

Fast, simple, inexpensive Used for small specimens and various materials Difficult to detect small cracks UV light is also used to help show up any imperfections


› Magnetic particle testing Component is placed on a conducting rod, that produces a magnetic field

about the component Fluorescent liquid of charged particles is sprayed over component Fluorescent magnetic particles are drawn to the cracks by the conducting

rod, highlighting surface imperfections

- Radiographic examination› X-Rays

Favourable because a photo film is produced, for close analysis Detects sub-surface defects Radiation is used to penetrate the item, with any voids allowing the rays to

pass through more easily, resulting in a dark area of film Used on large objects Longer/more expensive than visual testing Exposure to radiation can be harmful to humans

› Gamma Rays Effective when testing thick structures, i.e. steels Can be used to examine joining methods, i.e. welds Exposure to radiation can be harmful to humans

- Ultrasonic testing› Detects sub-surface defects› A probe transmits high frequency vibrations throughout the component as it

passes over the surface of a component› Any imperfections within the component causes the vibration to be reflected

without travelling to the bottom› Results are displayed on detection machine

Heat treatment of ferrous metals- Heat treatment of steels

› Heat treatment used to give steel to alter their properties. Heat treatment involves 3 main processes

1. Heating of metal to pre-determined temp.2. Soaking (holding) of metal at that temp. until heat becomes uniform

throughout 3. Cooling of metal at pre-determined rate such that is will cause formation of,

or will maintain desirable structures within the metal- Annealing

› Process annealing Heat steel to temp. Between 550 and 650˚CRelieve internal stresses from within materialAir cooled


Complete recrystallisation of the metal› Full annealing

Heated above 923˚CSoakedCooled within furnace – slow processProduces softer steel

- Normalising› Heating to higher temps. than annealing

SoakedAir cooledProduces fine grain structure – stronger materialIncrease in UTS, hardnessDecrease in ductility

- Hardening and Tempering› Hardening

Hardening steel depends on carbon contentHeat above 800˚CSoakQuench (cool very quickly) – water, oil, brine can be usedQuenching causes stress to build up in steel – becomes extremely hardQuenching produces martensite – hard + brittle material that needs further treatment to increase toughness

› Tempering Remove internal stresses from material that have been quenched (martensite)Retains hardness and replaces brittleness with toughnessHeat steel between 200 - 600˚CSoakCool in airTempered martensite produced

- Structure property relationships› Annealed → coarse grain structure → soft with moderate strength

Normalised → fine grain structure → higher strength Hardening → stressed grain structure → hardness + brittlenessTempering → very fine grain structure → toughness + hardness

Structure/property relationship in the material forming processes- Forging

› Shaping a metal through use of force› Can be done above recrystallisation temp. (hot forging) or below (cold forging)› Extrusion› Drop forging – technique that uses hydraulic pressure to operate a hammer that

shapes metalo Dimensional accuracy not goodo Grain flow/direction is major advantage – grain flow follows profile of part,

no points of weakness. Contrasting to machined part where grain flow does not follow profile and provides points of weakness


- Rolling › Metal pressed into shape between rollers› Can be done as hot or cold rolling› Cold rolling

o Compressed grains result in specific directional propertieso High strengtho Grains in material remain stressedo Increased harness

› Hot rollingo Unstressed finished producto Easily performed than cold rollingo Favourable directional grain flow

- Casting› Pour molten metal into a mould to form a specific shape› Good dimensional properties → close to finished product› Cheap› Can effect physical properties of metal – depending on material mould is made

from› Sand casting

o Mould made form sando Chill grains form on surface of metalo Larger columnar grains form within metal → present weakness in metal

– allows for metal to shear along the grain boundaries› Shell moulding

o Form of sand mouldingo High dimensional accuracyo Fine clean sand with thermosetting binder

› Die castingo Metal forced into mould cavity under pressureo Excellent surface finish

› Centrifugal castingo Molten metal injected into spinning mouldo Centrifugal force forces molten metal to stick to interior of the mould

- Extrusion› Metal forced through die so it takes shape of the die it passes

- Powder forming› Metal power is mixed with other desired materials and put into mould in room

temperature› Mixture is then pressed into mould to form desired shape› Pressure compacts particles together› Pressed item is sintered in controlled atmosphere furnace› Heated to temp. Where atoms are allows to diffuse between grains, producing

uniform grain structure


› Used to form brake pads → materials with different properties mixed together to give superior final product

› Difficult to produce certain shapes Non-ferrous metals- Aluminium

› Non-corrosive› Lightweight› Good strength to weight ratio› Easily fabricated› Very good electrical conductivity› Ductile

o Aluminium siliconGood casting propertiesMore corrosive than pure aluminium

o Aluminium copperHigh strengthGood electrical conductivityMore corrosive than pure aluminiumHard

o Aluminium silicon-magnesiumMedium strength WeldableCar doors

- Brass› Alloy of copper and zinc› Corrosion resistance› Cannot spark › Low coefficient of friction

- Bronze› Alloy of copper and tin› Excellent corrosion resistance→ from oxidization › Hard› Brittle

- Structure/property relationship- Annealing, strengthening

Ceramics and glasses- Semi-conductors

› Operates on the basis of the deficiency/surplus of electrons within a material › Semi conductors are a unique group of materials that, when subjected to a certain

type of energy (i.e. thermal, electrical), can act either as conductors or insulators. The properties of these materials make them highly favourable in the electronics industry.

o Diodes


- Form the basis of rectifiers, which allow the conversion of AC power to DC. Allows an electric current to pass in one direction, while blocking current in the opposite direction. Rectifiers are used to function battery charges in most transportation vehicles.

- Used to extract modulation from radio signals in radio receivers that can be found in various transportation vehicles such as cars, trains, aeroplanes and even motorcycles.

- Used to produce light in LED’s (light emitting diode) that can be found in the instrument panels and consoles of various transportation vehicles. Also used in some modern day headlamps on vehicles such as cars and motorcycles.

o Transistors- Enables the amplification of current or voltage, or acts as a switch. These qualities are

present in practically all electronic devices found in the control systems of transportation vehicles.

- Allows for the miniaturization of electronic components which are essential in the electrical equipment found in cars, trains and aeroplanes.

- Featured within microprocessors, located in computing systems such as GPS devices, speech recognition technology and various on-board technologies found within modern day cars and aeroplanes.

- Overall, transistors are fundamental components to all electronic devices. It can be understood that virtually all electronic devices and equipment found in transportation systems feature transistors.

- Justify appropriate choices of ceramics and glasses used in transportation parts and systems

› Ceramics – car brake pads → high heat resistance, durability› Glasses – laminated glass → car/train windows for safety reasons

Multi-laminated glass → planes - to cope with pressurised cabin, protect against substances such as moisture and salts from occurring between glass layers, safety, strength

- Laminating and heat treatment of glass› Heat treatment

Tempered glass - Heat treatment of glass increases resistance to fracture by creating compressive surface layer

Glass heated to around 650˚C Subjected to air quench → rapidly cools surface Cooling surface contracts → placed under compression

› Laminated glass Consists of a sandwich of two layers of glass and a polymer interlayer of PVB

joined under heat and pressure

Polymers- Structure/property relationships and applications

› Basic structure consists of molecules composed of repeating atoms of the same element that are joined together by chains.


› The basic unit of any polymer is the carbon atom - forms the backbone of the polymer chain.

› Different polymers with different properties can be produced when replacing the hydrogen atom with another element.

› Thermoplastics - covalent bonds (atoms sharing same electrons and hence fusing them together) form the polymer chains but only weak secondary bonds between the chains →elastic, malleable

› Thermosets - covalent bonds (atoms sharing same electrons and hence fusing them together) form both the polymer chains and secondary bonds between the chains →rigid, strong, less elastic

› Applications – thermoplastics - In transportation systems, thermoplastics are mainly used as interior components (dashboards, linings etc.)

› Applications – thermosets - In transportation systems, thermosets are mainly used as interior components and textiles, however in some modern transportation systems composite thermosets (more than 2 substances combined) can be used to make exterior parts such as body panels. Exterior components of boats → waterproof, rigid, buoyant, hard, tough

- Engineering textiles› Thermosets act as binder for textiles → adds tensile and compressive strength

and durability to textile- Manufacturing processes for polymer component

› Injection moulding - plastic is heated from granular form and melted into resin form and then injected through a die by way of a ram into a cavity or cast → usually thermoplastics

› Extrusion - plastic is heated from granular form and melted into resin form and then injected through a die by way of a ram onto a conveyer belt to cool

› Compression moulding – in granular form, plastic is placed in mould where heat and pressure is applied to melt the plastic allowing it to flow within cavities → used for thermosets

Engineering electricity/electronics

Power generation/distribution

Power generation

To produce electricity and power, generators are used to convert the mechanical energy of rotation into electrical energy. In Australia, electricity can be produced in a number of ways that include:

› Steam - Takes place in a coal fire power station- This production process includes burning finely crushed coal in a furnace. The heat

generated from this heating process is used boil pure fresh water, which produces high pressure steam and turns a series of turbines that are connected to generators.

- The steam used to rotate the turbines can reach 540˚C

Industry

Industry


- Steam pressure turns the generator shaft at up to 50rps (=50hz – AC frequency in domestic power supply)

- Advantages: coal is an abundant, relatively cheap and an easily transportable substance. Production process re-uses the steam (or rather the water that is boiled)

- Disadvantages: mining the coal damages the environment greatly, burning the coal produces polluting gases (i.e. sulphur dioxide), releases mass amounts of greenhouse gases which contribute to global warming

› Hydro-electric- Involves harnessing the potential energy of dammed water by allowing the water to run

through a water turbine and generator. - Advantages: does not produce atmospheric pollution, renewable energy source (sources

that are naturally replenished)- Disadvantages: expensive production method (i.e. erecting infrastructure), affects

surrounding environment, only possible in particular areas (such as mountainous regions)

› Wind- Involves using the wind to turn large blades which turn turbines connected to generators.- Advantages: does not produce atmospheric pollution, renewable energy source (sources

that are naturally replenished)- Disadvantages: high initial costs (to erect infrastructure), to produce high amounts of

electricity; a lot of wind turbines are needed, consumes large amounts of land.

› Nuclear Power - Involves using the heat from a nuclear reaction to drive a steam turbine. The turbine

connects to a generator that is spun, producing electricity. - Advantages: efficient production method, doesn’t contribute to global warming- Disadvantages: produces very harmful by-products to the environment, nuclear waste

disposal is an issue.

Power distribution

From the generation of electricity at a large scale, a number of processes occur during the distribution to the consumer to provide safe and manageable amounts. These processes include:

20 kV supply

(generating station)

500 kV(district

transformer station)

132 kV(Local

transformer station)

66 kV(substation)

11 kV(Pole or

undeground transformer

415/240 kV

(Consumer)


The transmission lines used for distribution consist of high-tension galvanised steel core aluminium cables. The steel core adds for better support and strength of the wires, with aluminium more favourable over copper for its high conductivity and low density.

AC/DC Circuits

AC- AC (alternating current) is where they electrons oscillate back and forth in the circuit –

meaning the current direction alternates- The rate of oscillation is called the frequency- The current from the power outlet in a domestic home has a frequency of 50hz

(changes directions 50 times per second or 3000 times per minute (rpm))

DC- DC (direct current) always flows in the same direction (put in AC terms: a current

with 0hz)- DC power mainly comes from a battery- DC is used in applications where we need to control the speed of electric motors e.g.

electric trains

Single phase and three phase system

Single phase

- The distribution of AC in which the power supply varies over time (i.e. at some instances power is at max and other instances it is at 0)

- Has an average output of 50%- Does not produce a consistent power output, instead has power lapses (when the current is

alternating)- Used when loads are most likely heating, and not heavy loads such as machinery and electric

motors etc.- Ideal for residential consumers and not the industry- Common in rural areas

Three phase

- Makes use of three wires to deliver three independent alternating electrical currents at different time intervals

- Removes any moment of 0 power and maintains max power average (100%) rather than the average of 50%

- Produces a stable flow of electricity - Desirable for electric motors as a magnetic field can be more effectively produced and

maintained as oppose to single-phase


- Can still power a single phase circuit- Used in the industry

Rectification

- Rectification is the process of converting AC to DC- Rectification is achieved with the use diodes, which allows for only certain waveforms to

pass through, blocking the others (i.e. allowing positive, but blocking negative)- Half wave rectification is achieved with one diode in a circuit and blocks current flowing in

one direction, so only the negative waveform direction is blocked.- Full wave rectification is achieved with four diodes, which allows the entire wave to pass

through but only on the positive side. This produces a varying DC current.- The varying DC produced by these rectifiers does not produce true DC current and is not

ideal for most DC equipment. However, adding a capacitor to the circuit will get a better waveform.

- The capacitor stores energy that can be used when the wave form reduces in voltage, resulting in a nearly flat waveform with the capacitor smoothing out the troughs.

- When the potential (voltage) falls at any time during the propagation, the capacitor releases a charge that causes the voltage to rise again.

Electric motors used in transport systems

Principles

- DC electric motor


A DC electric motor works by passing a DC electric current through the rotor (coils) that produces a magnetic field. When this rotor is placed within an external magnetic field, the magnetic field from the rotor interacts with the external magnetic field, causing either a force of repulsion or a force of attraction on the rotor, causing it to rotate. This rotation is known as torque. To maintain this torque and produce constant rotation, a commutator is used to change the current supply into the rotor after every half turn. This changing current will in turn produce a changing magnetic field from the rotor and alternate its polarity. This reversed magnetic field will ultimately change the forces produced due to the field interactions and cause constant rotation (when this process is repeated).

- AC electric motor An AC electric motor works on the same principle as a DC electric motor, in that current through the rotor causes rotation when in an external magnetic field, however in this case an AC electric currant is provided as oppose to DC. The supply of an AC electric current into the rotor means that the current will already be alternating, therefore eliminating the need for a commutator. The input of AC will cause for the current through the rotor to alternate at 50 times per second and therefore causing the magnetic field produced by the rotor to alternate also. This changing current and magnetic field means that constant torque and rotation is produced.

› Induction motor Induction motors are the most popular type of AC motors. The principle behind the AC induction motor is in the opposite to the generic AC motor (torque is caused from alternating current passing through rotor in a stationary magnetic field) in that is consists of a rotating magnetic field that exerts a torque on a stationary coil. In an induction motor, electromagnets in the stator produce a changing magnetic field (from the AC current, the oscillation of the current will cause the electromagnets to change polarities) that induces an electric current within the rotor (from electromagnetic induction). This induced current within the rotor will in turn produce its own magnetic field. The interaction between the two magnetic fields will cause the rotor to rotate. When the electromagnets in the stator are connected in single phase, the rotor’s initial torque is low. Three phase on the other hand produces a much better torque due to the timing of the three electromagnets. In three phase, the stator simulates rotation because the rapid switching of current through the magnets one after the other simulates motion of one pair of magnets spinning. This ultimately increases the rate of change of magnetic flux in the motor and increases the induced current within the rotor.

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