ENGINEERING STUDIES NOTESHSC Engineering Course

Enjoy cunt! Please remember that these notes are based around the theory parts of the course and not the mechanics. Please refer to your provided text book, your engineering teacher and any other sources that you locate.

Created in 2011

CIVIL STRUCTURES

STRESS & STRAIN

SHEAR STRESS: It is a measure of the internal reaction of a shearing force.

If the shear plane runs perpendicularly across the object, the shear area will be the cross-sectional area. But if the shear force punches a hole through the object, the area used will be the circumference of the circle/s multiplied by the thickness of the material.

fs= P/A

f=shear stressP=load

A= shear area

ENGINEERING AND WORKING STRESS:

Engineering stress is calculated with the load always divided by the original cross sectional area. This stress does not take into account the falling cross-sectional area.

Working stress is usually less than the yield stress and UTS. The ratio of working stress to one of the other two values is called the Factor of Safety and it is an important consideration in designing equipment. Safe working stress is always less than the elastic limit of the material.

Yield stress is the stress where there is a marked increase in strain without corresponding increased in stress. It is always greater (though by a small amount) than the elastic limit, but less than the UTS.

Proof stress is the amount of stress necessary to bring about a certain amount of permanent strain in a material. Used as a measure of a yield on materials that does not show a yield point.

Toughness is the measure of the ability of a material to absorb energy. They are the opposite of brittle materials and can be found by the area under the curve (i.e. larger the area, the tougher the material).

Hooke’s Law may be stated as follows “Stress is proportional to strain up to the elastic limit”. It simply means that any increase in stress will bring about a proportional amount of strain.

E=f/e E=constant f= stress e=strainFactor of Safety:

Factor of Safety is the ratio of Safe Working stress to either the yield stress or UTS depending on the type of material.

For ductile materials:

FofS= yield stress/maximum allowable stress

For brittle materials:

FofS= UTS/maximum allowable stress

Factor of Safety has a large impact on the design of an object. In buildings and bridges the FofS is usually a large ratio to ensure there is no chance of failure in the structure.

Crack Theory

Crack Formation and Growth:

Crack formation and growth is a method of brittle failure. When a crack forms, the strain energy held in the entire object will be retained but it is released from the area adjacent to the crack.

Failure due to cracking:

Some materials are more likely to crack than others. The more brittle the material, the shorter the critical crack length will be. Once the critical crack length has been exceeded then failure is inevitable if stress levels are maintained.

Repair and/or Elimination of Failure Due to Cracking:

Repair:

For a metallic material welding is a solution but this solution as problems. Even though the weld will repair the crack, changes in the microstructure will occur resulting in a weakened material. It may require heat treatment to resolve any microstructural problems.

In polymeric materials, it is possible to use adhesives for repair. If the failure is in a thermoset and adhesives are unavailable, replacement of the material is the answer. Polymer welding is another solution, which offers strengths close to the parent metal.

In ceramic materials such as stone and concrete, repairs are very difficult. Replacement of the material is often required.

Elimination:

One solution is to design the item without sharp corners, which tend to concentrate stress within that point.

Another solution is the placing of an interface for the material. It is an area within a material, weaker than the surrounding area that runs perpendicularly to the expected growth of a crack. When a crack travels through the material, it will be blocked and possibly never reach the critical crack length.

Engineering Materials

Non-destructive testing:

X-ray testing

X-rays are passed through the object and expose a photographic film on the opposite side. This method is designed to expose cavities that may be present within the component.

Dye penetrant testing

This is used to find small cracks in the surface by placing a dye on the surface and examining the surface, after cleaning, under UV light.

Ultrasonic testing

High frequency radio waves are sent via a transmitter, through the component. Reflected signals are recorded and will determine if a cavity or cavities are present.

Destructive:

Test Type UseTensile Destructive Used to determine the

tensile strength of materials used. Test piece is stretched and load and extension are recorded.

Compressive Destructive Used to determine the compressive strength of a material. Test piece is compressed, load and deformation are recorded.

Transverse Destructive Used to determine a materials performance when undergoing bending and shear.

Torsion Destructive Determines how well a material will cope with twisting forces (couples)

Ceramics

Stone

Stone is weak in tension, strong in compression and low in toughness i.e. brittle.

Glass

Found immensely in civil structures especially modern buildings. Glass has low toughness (therefore brittle) and weak in tension.

Common window glass is made of silica, soda and lime.

Toughened glass is a heat treated glass that increases the toughness of a glass pane.

Cement

Cement is a ceramic material formed by complex reactions when alumina, soda and lime are reacted at high temperatures.

Cement is strong in compression, weak in tension and exhibits low toughness. But unlike stone, cement can be cast into almost any shape required.

Composites

Timber

There are two types of wood; hardwood (pored) and softwood (non-pored).

Even though there are more favourable materials, timber does uphold desirable properties. Timber has an excellent strength-to-weight ratio and reasonable performance in bending.

It does however, have weakness such as being adversely affect by weather and susceptible to attacks from pests e.g. termites.

Mortar

Mortar is the material used between bricks in buildings. It consisted of slaked lime, sand and water.

It was replaced by Portland cement.

Concrete

Concrete is a composite material consisting of cement, sand and aggregate.

Concrete offers far greater strength than cement and is cheaper, so it is used extensively.

Pre-tensioned (pre-stressed) concrete is created when the concrete is cast over a series of steel rods or cables that have been tensioned prior to pouring.

Post-tensioned (post-stressed) concrete is formed when concrete is cast with tubes running through the slab. After setting and curing, wires are pulled through the slab and anchored to plates at one end and tensioned at the other. When a compressive stress is gained and the tension is gained, the cables are left in this state and cement slurry is injected into the tubes to stop corrosion of the steel.

Both methods assist in increasing the concretes tension.

Concrete cancer is when the reinforcing steels corrode. When steel corrodes it expands which causes the concrete to crack, which makes the structure unstable and dangerous.

Asphalt

It is generally used for the surfacing of the roads. It is a composite consisting of hard aggregate and bitumen as a matrix. Asphalt is advantageous for roads as it is crack resistant and tough. It also cannot be contaminated by oil and hard wearing due to the aggregate.

Laminates

They are materials that consist of varying materials sandwiched together.

Plywood is an example of a laminate and is used where the grain structure of timber causes weakness.

Laminated glass is used when shatter-resistant glass is needed.

Bimetallic strips use two metals back to back. One metal has a different thermal expansion rate than the other which makes it useful for thermostats and protection circuits in gas systems.

Geotextiles

Geotextiles are woven polymers or ceramic fibres that are used for a wide variety of civil based purposes. Such examples include the stabilisation of a road base and also used for filters in drainage systems.

Corrosion

Corrosive environments

Oxidisation occurs when the metal loses electrons, and it occurs at the anode.

Reduction is the consumption of electrons and occurs at the cathode.

(OILRIG=Oxidisation Is Loss, Reduction Is Gain)

Dry corrosion

Dry corrosion occurs through chemical reactions of metals or alloys with gases, in furnaces at high temperatures.

The primary cause is a reaction of the metal with oxygen and other molecules in flue gases.

Wet corrosion

Wet corrosion occurs when a metal is placed into a fluid, usually an electrolyte

Uniform attack is when a metal is placed within an electrolyte and some parts become anodic and the other cathodic.

Galvanic corrosion occurs when dissimilar metals are placed together in the presence of a corrosive environment.

Protecting civil structures

One method is painting the surface of the material. Another is galvanising, which involves dipping the material in molten zinc, which then covers the steel and protects it from corrosion by forming a passive layer.

PUBLIC TRANSPORT

Construction and Processing Materials over Time

Cycle

Timber

Used for earlier bicycles. Often used for the frame and wheel construction.

Iron

Iron was initially used as a tyre on wooden wheels. It was eventually replaced by steel frames and rubber tyres.

Steel

Steel was produced in large numbers as it was the material chosen for bicycle frames and wheel spokes (earlier times).

Nowadays, steel has been replaced by aluminium alloys but remains the primary material choice for chains and gear clusters.

Alloy steels

Alloys steels were more superior to plain steels, as it was identified that alloys steels offered a better strength to weight ratio in comparison to plain steels.

Examples of alloy steels used in bicycle construction include; manganese-molybdenum and chromium-molybdenum (Cro-Mo). Both of these examples were used in bicycle frames.

Stainless steel

This high alloy steel was not used for frame construction (except Moulton bikes). Instead was heavily used in bike components such as cables, pins for breaks and gears. Its corrosion resistance made this material quite desirable.

Aluminium alloys

Aluminium alloys are very widely used in bicycle construction. These materials offer excellent corrosion resistance and are more workable than other heat-treated alloys. In addition to this, they are lightweight but weaker which is why many of these bicycle frames are oval in shape.

Aluminium is also used for both brake and gear components.

Titanium alloys

Titanium alloys are used in bicycle frames and gear components. Titanium is also very expensive and in relation to frames and offer little over aluminium alloys and steel alloys.

Carbon fibre

Carbon fibre has an excellent strength to weight ratio and is very desirable in racing bikes.

Unfortunately when this material fails, it does so suddenly without warning. This is the reason why this material is only used in racing bicycles.

Rubber

Solid rubber tyres replaced iron tyres. Rubber is lighter and provided moderate springing. In 1888, John Boyd Dunlop developed pneumatic tyres which made bicycle riding more pleasant and comfortable. Rubber is also used for suspension.

Heat Treatment of Ferrous Metals

Annealing

Process annealing relieves any stress from distorted grains caused by cold working or deformation.

Full annealing makes the steels have a softer, coarser grain structure than previously existed.

Normalising

Involves heating the steel up to the austenite region and after it is cooled in still air, produces a finer grain structure and hence a stronger steel.

Structure/Property Relationship in the Material Forming processes

TYPE METHOD APPLICATIONForging It is essentially shaping a

metal through the use of a force. Example; a blacksmith with an anvil.

Produces a stronger component as the grain flow coincides with the shape of the object.

Hot Rolling The ingots of the required metal are passed through rollers to produce the required thickness. The metal’s temperature is above the recrystallisation temperature.

Produces an unstressed finish product.

Cold Rolling This is the same but the metal’s temperature is below the recrystallisation temperature. Also heavier machinery is needed.

Produces are more dimensionally accurate product, with elongated coarse grains. It is also more presentable due to

lack of oxides.Ingot casting It is done by pouring molten

metal into a large tapered metal mould. Upon solidification, the mould is lifted away and the ingot is ready for shipment.

Prepares metals for another material forming process e.g. Rolling

Continuous casting The molten metal is poured into a water-cooled ingot with a sliding bottom. Once the bottom has solidified, the base moves down at a rate that allows the molten metal above to solidify. The resulting long strip is cut to the required length.

Used in large plants because of is rapid speed and cost effectiveness.

Sand casting Sand is packed around a pattern of the finished product. The mould is in two halves to allow the pattern to be removed. Once removed, and the two halves are assembled a cavity is left for the molten metal. Once metal solidifies, sand is removed, reconstituted and ready for use again.

Useful for engine blocks and heads. A disadvantage would be that the final surface finish is poor and inaccurate.

Shell moulding 1. A heated plate is placed over a dump box.

2. The dump box is inverted and the sand and resin mix drops over the heated pattern plate.

3. The half mould and pattern plate are then heated in an oven to 315 degrees to ensure resin is fully cured.

4. The cured half mould is ejected off the pattern by small ejector pins.

More expensive than sand casting but is more dimensionally accurate.

5. The two half moulds are then placed together; they may be bolted or screwed together.

6. The mould is placed in a box surrounded by metal shot, ready to receive the molten charge. Upon solidification of the casting, the mould is separated.

Centrifugal casting Utilises a centrifugal force to spin the metal into the shape.

Useful for making pipes, pistons, etc.

Permanent mould Uses a permanent mould and is not remade all the time.

Generally used for automotive parts e.g. pistons, gearboxes, etc

Investment casting 1. A pattern of the item is made from wax and a refractory ceramic is then poured over the material and allowed to set.

2. The wax is drained out by heating the mould, leaving a cavity that is a perfect replica of the item to be cast.

3. Molten metal is poured in and allowed to solidify.

4. The mould is broken away from the cast article.

Large runs can be costly because new moulds are needed with every cast. It does however, has a good surface finish and is dimensionally accurate.

Used for rocker arms in automotive engines. Turbine blades from planes are made this way.

Direct and indirect extrusion

It is essentially when a metal is forced to go through a die so it takes the shape of the die.

Direct is where the ram pushes the metal into the die from the other side.

Direct extrusion requires more effort and is used with more ductile materials.

Indirect is used for alloys.

Both are hot working processes.

Indirect is when the ram and die are one part.

Impact extrusion This is a cold working process that involves the use of hammer impact to extrude the shape.

The punch goes into the die and the material is forced from the die around the punch.

Used to make cans and short tubes.

Powder forming This involves getting the metal into powder form. Once in powder form, the powders are blended with stearate based dry lubricants, to get the required mix. They are then pressed into the mould to form the shape required. The pressure used is enough to compact the particles together and give them sufficient strength to be handled. After the item is sintered at a temperature to allow atoms to diffuse between grains, producing a homogeneous grain structure. This gives the final strength.

Used for bearings.

Non-Ferrous Metals and Alloys

Aluminium

low strength ductile easy to fabricate good strength to weight ratio good corrosion resistance

Due to its low strength, most engineering applications use aluminium alloys.

Non-heat treatable alloys

1xxx- Primarily pure aluminium with small amounts of iron and silicon. Used mainly for sheet metal work.

3xxx- Manganese is the main alloying element, provides solid solution strengthening. Used for pressure vessels, chemical equipment and sheet metal work.

5xxx-Maganese is the primary alloying element. Used for sheet metal work, particularly for truck and marine applications.

Heat treatable alloys

2xxx- Primary alloying element is copper. Primarily used for aircraft structures because of its high tensile strengths.

6xxx- Has two primary elements magnesium and silicon. Used for bicycle frames, truck and marine structures.

7xxx- The primary element is zinc but may have additions of magnesium and copper. Used in aircraft structures and good quality bike frames.

Brass

Brass is an alloy of copper and zinc.

Cartridge brass

This brass contains 30% zinc. This brass is ductile and is predominately used for cartridges for bullets.

Standard brass

Contains 25% zinc. This is a good quality, cold working alloy. It is used for stampings and limited deep drawing.

Muntz metal

It is a two phase brass, contains 40% zinc and is usually hot worked when shaped. It is used in the manufacture of rods and bars. It may also be cast. Muntz metal can be heat treated to change its properties.

Naval brass

This contains 37% zinc and 1% tin. Tin is used for its corrosion resistance to saltwater. This is important for the manufacture of ships.

High tensile brass

This alloy contains copper (58%), zinc (36%) and small additions (<1.5%) of manganese, aluminium, lead iron and tin. These improve tensile strength whilst sacrificing ductility. Used for stampings and pressings, but also for marine propellers and rudders.

Bronzes

Bronze is an alloy consisting of copper and tin.

Low tin bronze

Only contains 3.75% tin. Demonstrates good elastic properties and corrosion resistance. It is used for springs (suspension).

High tin bronze

Contains 18% tin. It is used in heavy load applications, such as slewing turntables on large cranes.

Admiralty gunmetal

It is a bronze containing 88% copper, 10% tin and 2% zinc and some nickel. It is used for pumps, valves and especially marine castings, as it has good corrosion resistance. Good material to be cast.

Leaded gunmetal

This has 85% copper and 5% tin, but also 5% zinc and 5% lead. This reduces ductility and makes it suitable for pressure vessels.

Phosphor bronze

These are bronzes with phosphorous. This material tends to have higher tensile strength and better corrosion resistance than standard bronze. Importantly, they have a lower coefficient of friction, which makes this material suitable for bearing applications.

Aluminium bronze

Aluminium is the primary alloying element with amounts of 11%. Aluminium bronze offers good corrosion resistance and good tensile strength. This material can be hardened through heat treatment. Their corrosion resistance is used in marine and chemical applications.

Structure/Property Properties

The microstructure has a large impact on the properties of many non-ferrous alloys. In many cases, a second harder phase is often present which reduces ductility.

The white phase, which is not pure copper, is ductile, whilst the dark phase contributes to the brittleness of the alloys.

Heat Treatment of Non-Ferrous Metals

Annealing

Annealing is used to relieve any internal stress in a cold worked alloy. This results in an equiax grain structure.

Precipitation hardening

Step 1-Solution Treatment: The alloy is heated to 530 degrees until the β phase dissolves to produce a homogenous sing phase alloy. It’s then quenched to room temperature.

Step 2-Aging: Over time the trapped β phase precipitates out on stress planes within the quenched phase, thus restricting dislocations and strengthening the alloy.

Ceramics and Glasses

Semiconductors

they are essentially poor conductors but they will allow a current to flow past N-type semiconductor-an excess of electrons P-type semiconductor-a deficiency of electrons

Semiconductors are most important for the use of a p-n junction. This is where a layer of p-type and a layer of n-type are butted against each other. What this does is form a one-way gate for electricity to flow through.

Extra shit: This is accomplished due to the depletion zone. This is a gap between the positive and negative charges of the semiconductor material. If the current flows in one direction, the unlike particles attract, which reduces the depletion zone and allows current to flow.

Ceramics

There’s research suggesting that the use of ceramic materials instead of metal alloys, will improve the overall efficiency of a motor vehicle engine. Ceramics have a greater tolerance to heat than metallic alloys. This means, if used, engines will not require a cooling system which is responsible for the loss of 20% of the heat energy the motor uses. Ceramics may lead to improved thermal efficiency and better fuel efficiency.

Glass

High silica glass

Refined from borosilicate glass and is nearly entirely silica. These glasses are perfectly clear, and are used in situations that experience great heat. Such examples of these applications include; missile cones and space vehicle windows.

Soda lime glass

This is the most common glass, consisting soda and lime. It will not recrystallise, water resistant and is cost effective. It is used for window and plate glass, bottles, tableware, electric light bulbs and windscreens.

Borosilicate glass

It is made up of 20% boron and silica. This imparts in good chemical resistance and low thermal expansion. This type of glass is extensively used in electrical insulation, gauge glasses for laboratory ware, and domestic cooking and ovenware.

Lead glasses

These contain 40% lead. They have a high refractive index, which makes them optically clearer which means they are used extensively for optical glass. They are also used for thermometer tubes and tableware.

Laminating and Heat Treatment of Glass

Glass is rarely used in its normal condition in transport devices because of their brittleness to resist projectiles. Laminating and heat treatment of glass eliminates this so that they may be used in transport devices.

Polymers

Thermoplastics

This polymer softens with the application of heat, but can also be re-melted and reformed. They find its use n cable coating for bicycles and for car parts such as grilles, badges, door handles and window winders.

Thermosets

This type of polymer undergoes a chemical change when heat is applied and this change is irreversible. Epoxy resins are an example and are used in the aircraft industry for joining panels, and the silicones are often used in gasket manufacture for cars.

Rubber

This is a natural polymer but its synthetic variant is used in transport. They are used for the tyres in bicycles and cars.

Manufacturing Processes for Polymer Components

Transfer moulding

Similar to compression moulding but instead of polymerising happening in the mould, it happens in the adjacent cavity. This is used for thermosets.

Blow moulding

This is used to shape thermoplastics. A polymer tube is lowered into a mould, and air forces the tube to the shape of the mould. It is used to make plastic bottles and containers.

Extrusion

Polymers, like metals, can be extruded to take shape of the die. The polymer granules are melted and the molten material is forced into the die. This is only suitable for thermosoftening material and is used to make tubing for example, the tubing for bicycle cables.

Thermoforming

This is used to make various thermoplastic containers. Heated thermoplastic sheets are placed over dies to produce the required shape.

Calendaring

A thermoplastic is poured into a cavity between two rollers, and the plastic is squeezed through the rollers. Tiles, films and curtains can be made this way.

Rotational moulding

The molten polymer is poured into a mould and the centrifugal force throws the polymer to the walls of the mould, forming a hollow article.

Injection moulding

This is one of the most commonly used methods. Molten polymer is injected into a cavity in the shape of the finished article. When polymer solidifies, is it ejected and the procedure starts again. This process is used for small thermoplastic mouldings for cars and bicycles.

Engineering Textiles

Polyester

It is a synthetic fibre that is strong and resilient. It is hydrophobic (resistant to water absorption). Used in helium airstrips and in the manufacture of some tyres. It is also used in the manufacture of various car parts, like fan belts and radiator hoses.

Nylon

This is used in the engineering world in dry lubrication. It has been replaced by PTFE. It is resistant to acids, bases and oils.

Aramid

These types of fibres exhibit excellent strength properties but are limited to low temperature uses. They are used in aircraft manufacture and in bullet-proof vests. The Moulton bicycle company has used aramid fibres to reinforce carbon fibre front forks, to protect from the sudden failure of carbon fibre.

Olefins

This textile is a number of polyethylene or polypropylene fibres shaped into sheets. They are waterproof and find use in the manufacture of collapsible shelters and buildings.

PTFE (Teflon)

These fibres are fire resistant and will stop water vapour, but not water. They are used for filters in cars.

Power Generation/Distribution

Generation

Coal

Most common method of electricity generation Coal is used to produce steam that drives a stream turbine As it is known, this produces high levels of carbon dioxide and this contributes to the

greenhouse effect

Hydroelectric systems

Generates electricity without atmospheric pollution Uses water held in dams above the power station The waters kinetic energy is used to turn the turbine, which then produces electricity Has large impacts on the environment as it involves damming and diverting of rivers Only possible in mountainous regions

Wind power

Uses wind to drive the turbine (obviously) The turbine drives a generator and electricity is produced It is ‘clean’ for the environment, but would be required in large numbers in order to

power large towns and cities Large tracts of land are needed for these projects Causes noise pollution to neighbouring citizens

Nuclear power

Uses heat from a nuclear reaction to turn a turbine Does not pollute the atmosphere The by-products of nuclear power are a problem as they are contaminated for thousands

of years

Distribution

Power lines used to carry electricity are made of steel cored aluminium. Steel provides strength whilst aluminium provides conductivity

High voltages are used to reduce power loss (Power loss is proportional to voltage over the current squared)

AC/DC

DC has a constant potential and AC has a constantly varying voltage In Australia, the AC mains power varies from 0 to +240V, to 0 and -240V, 50 times a

second (50Hz)

Rectification

Rectification is the conversion of AC to DC.

Half wave rectification occurs when one diode is used. This eliminates the current flowing the opposite way, so blocks the negative part of the waveform.

Full wave rectification can be achieved by using four diodes. This will allow all of the sine wave to pass but it will have all the waves on the positive side, so they will travel in the same direction. The final waveform is not true DC, but a varying DC.

A varying DC is not ideal for most DC equipment, so a capacitor is used to achieve a better waveform.

Electric Motors used in Transport Systems

DC Motors

Shunt wound motors are rarely used in locomotives. They have a constant speed but low starting torque (therefor not suitable for stopping and starting)

Series wound motors offer excellent torque at slow speeds and will operate at high speed under light load. They are an excellent choice for trains and are why they are extensively used.

Compound motors combine the best features of the other two. Good starting torque and will not run away under no-load situations.

AC Motors

The AC motors used are induction motors. They do not require a commutator and brushes which wear out over time. They are reliant on the frequency of electricity and magnetic induction for their power. Their function is helped by generators being replaced alternators on diesel electric trains. Alternators produce AC so one would assume the use of an AC motor would be easier.

Control Technology

Digital Technology

Unlike an analogue system, digital technology is based around the binary system (1s and 0s)

They work with transistors as they act as an electronic switch Technology used for engine management is based around digital technology Bicycles use digital technology for speedometers

LIFTING DEVICES

Historical and Societal Influences

Engineering Innovation in Lifting Devices and their effect on people’s lives

The crane allows ships to be loaded and unloaded more quickly, requiring less time in transit for supplies.

Large block-setting cranes allow bigger harbours and breakwaters to be built around the world, making it easier for shipping

Cranes relieve workers from lifting heavy weights. They also make it possible to build things that could not have been built before (skyscrapers, etc.)

Cranes made work on aircraft easier in WW2. They meant that repair was quicker which got planes back into the air faster

Cranes made job sites safer, as they are more able to support a load than a worker using a block and tackle

Cranes have made large-scale civil engineering faster and safer

Archimedes’ and Pascal’s Principles

Archimedes’ principle explained buoyancy. If an object is placed in water and “weighed” it will register a smaller value than if weighed in air. This is because the water provides an upward force that partially balances the weight force.

This explains as follows:

A body wholly or partially submerged in a fluid is buoyed up by a force equal to the weight of the fluid displaced by the body.

Basically, as I understand it, buoyancy comes from displaced fluid. When you place an object in the water, water is moved. The mass of the “moved” water applies an upward force to the object. Buoyancy is accomplished.

Pascal’s principle

It has been established that pressure at the bottom of any container is greater than the pressure at the top, and is independent of the shape of a container. It can be further stated that pressure is the same at all points at the same depth. If we increase the pressure at the surface, then the increase is the same throughout the liquid.

It is explained as follows:

Pressure applied to an enclosed liquid is transmitted undiminished to every point in the fluid and to the walls of the container.

Hydrostatic Pressure

When an object is placed in a fluid, the fluid pressure will act upon the entire surface of the object at right angles the surface.

The cross sectional size or shape of the container does not affect hydrostatic pressure, but depth does. The deeper something is under the surface of the fluid, the greater the pressure created.

Applications to Lifting Devices

Hydrostatic pressure is also important in relation to hydraulic systems. For example, a hydraulic ram usually consists of a cylinder with a moving piston. If hydrostatic pressure is applied to the cylinder, the pressure is applied will act at right angles to every surface within the cylinder, including the piston.

Some hydraulic rams are termed two-way; this means that they provide movement and force in two directions. One-way rams are used in hoists, truck tippers and small car jacks. They can only provide a lifting force and rely on the weight of the raised object to force the fluid from the ram.

Backhoes, excavators, telescopic cranes and all terrain extension forklifts use two-way rams. Some forklifts, trucks, jacks and car hoists use one-way rams.

Testing of Materials used in Lifting Devices

Note: Tensile and compressive tests were covered earlier.

Hardness

Hardness Test OperationBrinell A hardened steel ball is forced into an object

under specified load conditions. The diameter of the ball is dependent on the test piece’s thickness. The hardness number is determined by measuring the depth and surface area of the impression and using a formula.

Vickers A small square pyramid is forced into a test piece under specified load conditions; the hardness number is derived from a formula that contains the load and area of the indention.

Rockwell A diamond cone (or sphere) is forced into a test piece under specified load conditions and a reading is displayed on the dial.

Shore scleroscope This test involves a small striker in a tube. The tube is placed over an item and the striker is dropped, the height the striker rebounds from the item is a measure of the hardness. (i.e. soft items will absorb more of the energy of the falling striker giving a lower rebound than hard materials).

Impact tests

Determines the notch toughness of a material. This is done by subjecting the material to a concentrated shock load (tough materials will not break as easily as a brittle material)

The two most common methods are the Izod and Charpy tests, both tests are essentially the same except the test pieces are held in the device differently.

The tests involves a large pendulum that is swung, using its kinetic energy, it breaks the test piece.

The height of which the pendulum was held prior to the test is recorded.

The Hounsfield test uses two pendulums; one solid and the other hollow. The result is double the impact that would be had with a single pendulum.

Heat treatment processes and Forming processes were covered earlier. Check it out because there’s no fucking way I’m re-writing that….uMad?

Applications found in appropriate lifting devices

Motor control

DC motors are essentially controlled by the amount of electricity allowed to flow through them. Controllers can be as simple as variable resistors. On electrical forklifts the accelerator may be a type of variable resistor.

Electrical safety

Many lifting devices use DC motors which reduces the risk of electrocution Batteries and power cables are always remained away from the operator Recharging facilities should also be simple, using sockets instead of direct access to

batteries Circuit breakers or fuses should be used to avoid the causing of fires from overloads Warning notices also should be used for the general public to stop them from accessing

electric systems

Engineering report

A crane company needs to investigate the use of a forged hook versus a cast hook. You decide which is better choice. Once decided, also decide on the appropriate material and justify your choices. (examination favourite)

Aeronautical Engineering

Scope of the Profession

Nature and Scope of the Aeronautical Engineering profession

They are responsible for the design and development of new aircraft They are also employed to modify and improve existing aircraft designs Aeronautical engineers often have set requirements and develop an aircraft that can

perform according to the design specifications

Current projects

They are constantly engaged in the design of new aircraft to improve air travel and air defence.

Aeronautical engineers often work with material engineers in an attempt to reduce the weight of aircraft with improvements to material choices.

If needed, a recent development is the A380 Airbus. This is a double decker that can seat up to 555 people.

Health and Safety matters

Aeronautical engineers are always exposed to dangers like other engineers. They may be exposed to machinery as they are overseeing manufacture or they may be

exposed to risks if doing fieldwork If the engineer works in a design office, risks and dangers are greatly minimised.

Training for the Profession

If aeronautical engineering is a possible career choice, a HSC student should be studying; mathematics, physics chemistry and engineering studies

University of Sydney, UNSW, etc. offers courses in this profession They will learn about physics, aerodynamics and materials required by modern aircraft

Career prospects

Australia has a great need for aircraft so therefore aeronautical engineers are needed The Defence Forces are the greatest employer for aeronautical engineers, as they need

these engineers to modify and improve the various aircraft used.

Unique Technologies in the Profession

The development of the turbine has been a technology that has remained unique to aircraft and aeronautical engineers.

There are four key material properties looked for in aeronautical engineering; strength to weight ratio, formidability, and durability and corrosion resistance. In terms of engine design, stability in high temperatures is another important feature for materials to have, titanium alloys and Nimonic alloys are examples of these.

The use of composites and adhesive technology has been developed. This is because composites offer good specific strengths and can be readily joined by adhesives.

Legal and Ethical implications

This is most likely a topic that won’t be examined. If you read the right side of the syllabus, there’s nothing asking you to do something in regards to this information. Please refer to your provided text book for information.

Engineers as managers

Engineers are managers as they oversee the development of a project and also they may be responsible in coordinating teams of people working on the project.

In terms of aeronautical engineering, engineers have different roles. Some are responsible for materials, some avionics and others power plants (engines).

Some engineers are good managers of companies, as they have good problem solving skills and common sense. In aircraft companies, there’s a balance of engineers on the management team to ensure that the company doesn’t lose it way in terms of aircraft development.

Relations with the Community

Aeronautical engineers have a good relationship with the community as they provide safe, fast transport.

Noise pollution was a problem for neighbouring communities, but due to a recent development there has been a noise reduction in modern commercial aircraft of approximately 10%.

Historical and Societal Influences

I apologise but I refuse to cover all the information in terms of the history of flight as it is way too much information. Just read it yourself, cheers.

The effects of Aeronautical Engineering on people’s lives and living standards

Here’s a list of effects…

Aircraft:

o Have made travel more accessible to people who have time constraints on holidays.o Jets have made overseas commerce much quicker.o Allow families who live overseas to be brought closer together.o Have reduced time of overseas postal and freight services.o For military purposes, have developed to a point where they may be used instead of

ground troops (less casualties)o Act as ambulances which save lives as they transport patients to hospitals more quickly.o May be used to fight bushfires, hence protecting properties and people.o Are used to gather images for news services quickly and efficientlyo Are used to transport people into and out of isolated areas that otherwise are difficult to

reach.o Have boosted tourism, particularly to isolated countries like Australia

Environmental implications of Flight

Pollution

o Exhaust gases from both piston and turbine aircraft engines.o Fuel dumping o Noise pollution which is a problem for an urban area near an airport (they’re pretty

fucking loud aye cunts)

Insect spraying

The insecticides protect crops but also disturb the natural food chain. Concentrations of these poisons increase as we go up the food chain leading to a particular concern for the food we eat.

Destruction

Destruction caused by aircraft was generally caused through aerial bombings during war conflicts. An example could be the Vietnam conflict, where saturation bombing with chemicals saw huge areas of forest destroyed to ‘flush out’ Viet Cong troops.

Of course, lives have been taken especially the atomic bomb bombings in Japan.

Bernoulli’s Principle

Bernoulli's Principle is a physical phenomenon that was named after the Swiss scientist Daniel Bernoulli who lived during the eighteenth century. Bernoulli studied the relationship of the speed of a fluid and pressure.

The principle states that "the pressure of a fluid [liquid or gas] decreases as the speed of the fluid increases." Within the same fluid (air in the example of aircraft moving through air), high-speed flow is associated with low pressure, and low-speed flow is associated with high pressure.

Propulsion Systems

Jet

1. Inlet- air enters and is compressed slightly2. Compressor- sets of turning blades which compress the air, hence heating it3. Combustor/Burner- fuel is injected into the combustion chambers where it is mixed with

the compressed air and burned4. Turbine- burnt gases expand through the turbine stages, which are rotated by the gas

flow. The turbine is connected on the same shaft as the compressor and provides the energy to drive the compressor. The turbine only extracts enough energy to keep the compressor going.

5. Nozzle- the gas is expanded through the nozzle and exits the engine as very hot, very fast gas which provides thrust

Turboprop

These engines have the same operation as the turbojet but with an important distinction where the turbine is used to power the compressor and drive the propeller. The majority of the energy of the gas is used to drive the turbine leaving only a very small amount of the exhaust energy to provide thrust.

Fluid Mechanics

Hydrostatic and Dynamic pressure

Hydrostatic pressure is pressure that results from static fluid. A still gas or fluid will produce a static pressure, either due to the mass of the fluid acting on the container or through the random movement of molecules, as in gas.

Dynamic pressure is what occurs in a moving fluid. This moving fluid tends to create pressure because of ordered velocity. With dynamic pressure the movement is ordered, and we consider the velocity of the fluid and its density to determine the dynamic pressure.

Applications to Aircraft Components

All aircraft are subjected to dynamic pressure. The airframes of supersonic aircraft in particular, are subjected to very large amounts of dynamic pressure because of their high speed.

Jet engines are subjected to large amounts of dynamic pressure through the intake of air and thrust produced. Many jet aircraft use reverse thrust vanes, which guide the jet thrust forward to aid in braking following landing.

Applications to Aircraft Instruments

Aircraft indicators rely on the principles of aerodynamics to convey flight information to the pilot.

Airspeed Indicator

They are actually mechanical devices where in such a device, the total pressure entering the pilot tube acts on the inside of a diaphragm. The diaphragm is connected to a linkage that controls the airspeed indicator. The diaphragm positions itself according to the difference between the total pressure and static pressure i.e. the dynamic pressure.

Altimeter

This is used to measure the altitude of the aircraft and it works on the principle of having a small expandable vessel of air, which is called an aneroid, surrounding by the static air pressure. As the aircraft ascends, the static pressure falls which in turn, allows the aneroid to expand. This expansion controls the needle to the altimeter.

Specialised Testing of Aircraft Materials

The X-ray, ultrasonic and dye penetrant testing methods were covered earlier.

Magnetic Particle Method

This is used to find cracks in a component

The piece of metal is placed across two magnetic poles, or a magnetic field is induced in it, and it is then sprinkled with a magnetic powder. Excess powder is removed and cracks are revealed by magnetic powder sticking to the area each side of the crack (each side of the crack becomes a magnetic pole).

Its major limitation of this method is that it will only work with magnetic materials, which makes it useless with aluminium and titanium alloys, which are materials extensively used in this field.

Aluminium and its alloys used in Aircraft

Aluminium and its alloys are desired in aircraft due to their low density The precipitation hardening of duralumin is an important alloy for aeronautical

engineering. Pure aluminium and duralumin can be rolled together and pressure welded so that

duralumin can gain the corrosion resistance that aluminium offers.

Polymers

Polymers are used as a solution to reduce the weight of the aircraft.

Composites

Carbon Fibre

It is lightweight, has very high specific strength and a high modulus of elasticity. It is also used for its resistance to cyclic stress that carbon fibre exhibits An example of its use may include the Boeing 737 and A330 Airbus for control surfaces

and wingtips Its disadvantage is failure is sudden and often catastrophic.

Aramid Fibre

Often referred as Kevlar, it is more impact resistant in comparison to carbon fibre. It is important in battle situations as shrapnel and debris has the potential to cause

damage to the aircraft.

Metal Matrix Composites

Used to simply improve the property of a material for example, boron fibre aluminium is used to improve tensile strength

They are difficult to manufacture Capable of withstanding high temperatures

Adhesives

Epoxy adhesives are used to join composite aircraft surfaces to the base structures.

Corrosion

Corrosion poses as a large problem in aircraft design as the frames and skin of the aircraft already stressed, so weakening via corrosion is a major concern

Composites offer resistance to electrochemical corrosion, UV light and the weather may degrade them.

Pit and Crevice Corrosion

this is a concentration cell that occurs because of different oxygen levels at the top and bottom of a crevice

Moisture forms in these gaps each time the aircraft passes what is known as a dew point, which is a particular combination of pressure, temperature and moisture content in the air.

Aircraft are always having moisture of them because:

o Condensation on the airframe from temperature changes in atmosphereo Airborne moisture accumulatingo Rain

Telecommunications

Scope of the Profession

Nature and Scope of the profession

Telecommunication engineers are responsible for the design and development of communication equipment and infrastructure. They are also employed to improve and modify existing designs. The telecommunication engineer is responsible for developing equipment that makes use of the various communication technologies to improve communication for society.

Health and Safety matters

Much of their work is carried out in office locations, where occupation and safety concerns relating to the ergonomics, lighting and good housekeeping are a priority.

Sometimes in their work, it may take them to the manufacturing industry where hazards associating with machinery and electrocution may present themselves as hazards.

Training for the Profession

HSC students looking at this for a career path should choose 2 unit math, physics, chemistry and engineering studies as their subjects.

During university study, students will learn about electronics, computers and also must be familiar with networks and associated equipment.

Career Prospects

Australia is always looking for newer industries such as telecommunications to become a core industry.

With technology and communication, Australia will need trained engineers in this field to ensure it does not fall behind the rest of the developed World.

There are always new opportunities for telecommunication engineers.

Relations with the Community

Due to the wide acceptance of technology within Australia, telecommunications engineers have a good relationship with the community. This is because the infrastructure developed by telecommunication engineers is design to provide services to the consumer that probably far exceed the needs of most people.

There has been controversy in relation to the radiation made from satellites and mobile phones are said to cause tumours and cancer.

Technologies Unique to the Profession

The use of semiconductor technology which is used in digital television, FM radio and mobile telephones.

Satellite technology is exclusively used by the telecommunications industry Fibre optic cables are used in medical examinations, TV cameras and its use for carrying

communication signals.

Engineers as managers

They are the managers of the design process, overseeing the design and development of a project.

They also coordinate teams of engineers for a particular project. The establishment of a telecommunication network or a satellite design often have these

engineers take on manager roles in a team structure. They also should have a logical method of dealing with problems, good problem-solving

skills and good communication skills.

Current Projects and Innovations

One of the most important projects is the mobile network as it is continually expanding to cover more and more of Australia.

The Iridium satellite telephone system is a clever technology that takes mobile telephones to the next step.

Engineering Materials

Voltage, Current and Insulation

A material resistivity must be assessed and checked before its use High resistivity=insulator, low resistivity=conductor Allowing a current with a certain potential difference is a method of assessing the

material, this and the use of Ohm’s Law, telecommunications engineers can find information about length and cross-sectional area of a conductor.

Multimeters and Cathode Ray Oscilloscopes are used to test electrical quantities.

Copper and its Alloys, used in Telecommunications

Copper in terms of conductivity, is second only to silver but it’s much more cost effective.

Pure Copper

Pure copper is an excellent conductor but impurities may lower this trait. So keeping impurities low is essential.

Copper Cadmium Alloy

Has good wear resistance and greater strength than pure copper which reduces the number of support towers per kilometre of overhead cable.

The microstructure of annealed Copper Cadmium is an equiax single-phase structure where all the Cd (cadmium) is dissolved in the solid copper.

Semiconductors

Diodes

Used in devices as one-way components. Zener diodes that act as a one-way component up to a certain voltage. Beyond this voltage, current begins to flow both directions through the diode.

Light emitting Diodes (LEDs)

These diodes give off light, and are extensively used as indicators doe telecommunication equipment.

The current can only flow in one direction and a visible radiation is emitted. They offer greater reliability and less power consumption than conventional lamps.

Transistors were covered earlier. Check it out.

Integrated circuits

They are a complex miniaturised circuit containing various semiconductors and other electronic components. Various types are available, each with a differing function.

Lasers

These are a type of semiconductor where; by creating to pn junctions, and passing a large forward bias current through them, the electrons hols recombine and give off photons. These are used in CD players and signal transmitters for fibre optic systems.

Polymers

Polymers find extensive use in telecommunications Used for insulation and casings for various devices. Manufacturers make extensive use of polymer casings for mobile and fixed telephones. Polymers offer insulation, shock resistance and also lend themselves to mechanised

production by injection moulding.

Fibre Optics

They function around the concept of transmitting electronic information, encoded onto a light beam.

A fibre optic system consists of three parts: a device to convert electric current into light, the cable to carry the light and a receiver to convert the light back into electric current.

Fibre optic cables are lighter and less expensive than copper cables, and are less affected from interference.

The primary reason for their use is that it can carry hundreds of times more information than can be carried on a copper wire.

Types and Applications

Single mode- it means a more narrows cable diameter. It is more favoured for long distance telecommunications as it has the highest bandwidth and suffers the least from losses of light. It is also more costly to manufacture.

Multimode – These cables have a larger inner core diameter. There’s two types; graded-index and stepped index. With a larger diameter core, light waves can take differing paths, which in turn means they take different times to reach their destination. Graded-index uses a refractive index which allows the cable to flow through the cable instead of reflecting along it.

Telecommunications

Analogue and Digital Systems

Digital data can be converted into binary numbers, and these can be transmitted as digital electrical signals. Digital systems are extremely effective in data transmission and for computerised systems; unfortunately many of the inputs or outputs required must be analogue. Converters are needed to turn one signal into the other.

A true advantage of digital signals is that they can be more easily compressed than analogue systems, which means more information can be carried on the signal.

Modulation and Demodulation

Modulation is the process of using the sine wave to transmit information. Once the signal is sent, it is necessary to demodulate the signal back to the original form. Here a demodulator reverts the modulated sine wave back to its original form and the signal is separated from it, before converting it back to sound waves.

There are three types of modulation: Pulse modulation (PM), Amplitude modulation (AM) and Frequency modulation (FM).

Multiplexing is the process of placing multiple signals along a single communication channel. This allows an increase in the amount of information carried. Once the signal is received, a demultiplexer separates the multiple signals from one another.

Radio transmission

Amplitude modulation

It is used for some radio stations and for transmitting the visual signal for television. A disadvantage of AM is that induced noise reduces the signal quality. The noise is

unwanted signal such as that induced by electrical storms.

When the AM waves are sent by the transmitter they are eventually received by a radio receiver. To receive the required signal, the radio must be tuned to the required carrier frequency. The radio wave is detected and passed through a demodulator, which removes the carrier frequency waves while the signal remains. The signal is then amplified and fed into the loud speaker. The variations in amplitude are converted into sound by the loudspeaker.

Frequency modulation

This is a more common method of radio transmission. The FM system modulates the frequency of the carrier wave and not the amplitude. An advantage of FM over AM is that the quality of the signal is not affected as much by

induced noise. They too are received by the aerial, amplified, detected, demodulated to remove the

carrier frequency, then amplified and sent to the loudspeaker. The difference is the variations in frequency are converted into sound.

Television Transmission

Black and White Television

Black and white camera uses optics and electronics to display variations in brightness. The vidicom tube fires electrons at a screen, which varies in resistance, depending on the amount of light present.

The heart of the television is the cathode ray tube (CRT). It works by firing electrons from the cathode at an anode placed behind the glass screen. When the electrons strike the anode, the phosphor glows, creating a bright part.

The recording sound system produces an audio signal that is modulated, sent to the transmitter, received, demodulated and reproduced by the television’s sound system.

Colour television

Instead of a single electron beam found in black and white televisions, colour televisions features three beams that react on red, blue and green phosphors.

Other colours are produced by varying combinations of the three.

In addition to this there is a mask which has millions of holes. This mask determines the position of the dot pattern for each phosphor.

Telephony- Fixed and Mobile

Fixed telephones

The mouthpiece is a microphone whilst the ear-piece is a simple loudspeaker. The current is fed down the telephone line to the exchange, then on the receiver’s

telephone.

Transmission Media

Cables

Oxygen free, high conductivity copper and high conductivity tough pitch (or copper alloy) cabling is used in many of the telecommunication systems.

They are now being replaced by optic fibre which are cheaper, have greater bandwidth and are unaffected by magnetic induction.

Microwave

Microwave transmission makes use of microwaves for transcontinental communication They were originally used with analogue transmissions and is now used with digital. Used extensively in communication satellites

Fibre optics

It has revolutionised telecommunications as it allows a greater information carrying capacity (due to its bandwidth).

Used in computer and telephone communication networks. They have also improved the operation of cable television systems.

UHF Cable Systems

They use a copper conductor surrounded by an excellent insulating polymer UHF cables, with encoded sound and television signals are used to route cable television

from transmission centres to people’s home.

Satellite communication systems

There are three main types of satellite orbits: geostationary, asynchronous and polar. Nowadays communication satellites are active where they capture a signal, amplify it and

relay it back to earth. They may also relay it to another satellite, which relays it back to earth.

A ground station sends a signal in the form of low frequency microwaves, as there are less affected by the ionosphere and weather than high frequency microwaves. The satellite receives these microwaves, and then uses a transponder to boost the signal strength, before relaying it to either another satellite or ground station.

Used for broadcasting television, international telephone calls and mobile international calls.