HSC Engineering Studies Notes¶

Civil Structures¶

Historical and societal influences¶

Syllabus Excerpt

historical developments of civil structures
engineering innovation in civil structures and their effect on people’s lives
construction and processing materials used in civil structures over time
environmental implications from the use of materials in civil structures

Engineering mechanics¶

Syllabus Excerpt

truss analysis
- actions (loads)
- reactions
- pin jointed trusses only
- method of joints
- method of sections
bending stress induced by point loads only
- concept of shear force and bending moment
- shear force and bending moment diagrams
- concept of neutral axis and outer fibre stress
- bending stress calculation (second moment of area given)
uniformly distributed loads
stress and strain
- shear, compressive and tensile stress
- engineering and true stress
- yield stress, proof stress, toughness, Young’s modulus, Hooke’s law, engineering applications
- factor of safety
- stress/strain diagram

Truss Analysis¶

Bending Stress Induced By Point Loads¶

Uniformly Distributed Loads¶

Stress and Strain¶

Shear, Compressive and Tensile Stress¶

Compressive forces are forces which squeeze an object, and will reduce the length. Tensile forces are forces which stretch and will lengthen the object. Shear forces are forces acting along the cross section of an object (highlighted in red).

Stress and strain are calculated with the following formulae:

\[\begin{array}{ll} \sigma = \frac{F}{A} & \varepsilon = \frac{e}{L} \end{array}\]

\[\begin{split}\begin{array}{llll} \sigma & \text{stress (MPa)} & \varepsilon & \text{Strain (unitless)} \\ F & \text{Force (N)} & e & \text{Elongation (mm)} \\ A & \text{Area ($\text{mm}^2$)} & L & \text{Original Length (mm)} \\ \end{array}\end{split}\]

Tensile

Compressive

Shear

$A = \pi{}r^2$

$A = \pi{}r^2$

$A = \pi{}d{h}$

$A = \pi{}r^2$

Engineering and True Stress¶

Engineering / nominal stress is the stress when the diameter of the material is assumed to be constant, i.e. the same size as it was before the beginning of uniform reduction in area of test specium or necking. This is easier to work with and is (mostly) the same in the elastic zone - which engineers try to stay within regardless.

True / Working stress is the actual stress the material experiences. As the material reduces in area, the stress increases.

During plastic deformation, fatigue occurs and the material has weakened even after the force is removed.

Stresses, Toughness, Young’s Modulus, Hooke’s Law, Engineering Applications¶

Yield Stress

The point after which their is an increase in strain without increase in stress. Located just after the straight line line section on the graph.

Proof Stress

A type of stress used when their is no definite yield point in a material e.g. aluminium / rubber.
You allow some percentage of strain (e.g. 0.1% - 0.2%).
Allows the materials to be “safely” used with a higher amount of stress
- tradeoff is that they need to be replaced often due to creep.
- Used for aluminium as it has low elastic limit; thus allows much higher safe loads with weight savings.

Toughness

A measure of the impact resistance of a material. Represented as the area under the stress/strain graph. Is measured with an izod or charpy machine.

Young’s Modulus

Material stiffness. Measured as the gradient of the straight line section.

\[E = \frac{\sigma}{\varepsilon}\]

\[\begin{split}\begin{array}{ll} E & \text{Young's Modulus (GPa)} \\ \sigma & \text{Stress (MPa)} \\ \varepsilon & \text{Strain (unitless/percentage)} \\ \end{array}\end{split}\]

Hooke’s Law: $F=-kx$ It tells us that elastic deformation is a straight line gradient. $k$ would be Young’s Modulus.

Factor of Safety¶

Materials are never entirely perfect and it is diffficult to accurately determine the working loads
The factor of safety allows for defects in the materials or manufacturing
The factor of safety changes with the relevant risk:
- In bridges and planes, the risk is much higher: factory of safety is often 4-5x
- In bikes, the risk is lower, and so the factory of safety maybe be only 2x.

Stress/Strain Diagram¶

Tensomers measure force and elongation; not stress and strain. This creates a load-extension diagram, not a stress-strain diagram. Load-extension is specific to specimen, stress-strain is not.

Engineering materials¶

Syllabus Excerpt

testing of materials
- specialised testing of engineering materials and systems
- X-ray
testing of concrete
crack theory
- crack formation and growth
- failure due to cracking
- repair and/or elimination of failure due to cracking
ceramics
- structure/property relationships and their application to civil structures
- glass
- cement
- bricks
composites
- timber
- concrete (reinforced, pre- and post- tensioned )
- asphalt paved surface
- laminates
- geotextiles
corrosion
- corrosive environments
- dry corrosion, wet corrosion, stress corrosion, galvanic corrosion
recyclability of materials

Communication¶

Syllabus Excerpt

Australian Standard (AS 1100)
orthogonal assembly dimensioned drawings
freehand pictorial drawings
graphical mechanics
- graphical solutions to engineering problems
computer graphics
- Computer Aided Drawing (CAD)
- applications for solving problems
collaborative work practices
Engineering Report writing

Personal and Public transport¶

Historical and societal influence¶

Syllabus Excerpt

historical developments in transport systems
effects of engineering innovation in transport on society
construction and processing materials used over time
environmental effects of transport systems
environmental implications from the use of materials in transport

Engineering mechanics¶

Syllabus Excerpt

simple machines
static friction
- concept of friction and its application in engineering
coefficient of friction
- normal force
- friction force
- angle of static friction
- angle of repose
basic calculations for work, energy and power
- potential energy
- kinetic energy

Engineering materials¶

Syllabus Excerpt

testing of materials
- hardness
- impact
heat treatment of ferrous metals
- annealing
- normalising
- hardening and tempering
- changes in macrostructure and microstructure
- changes in properties
manufacturing processes for ferrous metals
- forging
- rolling
- casting
- extrusion
- powder forming
- welding
changes in macrostructure and microstructure of ferrous metals
changes in properties of ferrous metals
manufacturing processes for non-ferrous metals
- alloying
- annealing
- solid solution hardening
changes in macrostructure and microstructure of non-ferrous metals
changes in properties of non-ferrous metals
ceramics and glasses
- as an insulation material
- laminating and heat treatment of glass
- structure/property relationship and their application
thermo softening polymers
- engineering textiles
- manufacturing processes
  - extrusion
  - injection moulding
  - blow moulding
- structure/property relationships and application

Testing of Materials¶

Heat Treatment of Ferrous Metals¶

Manufacturing Processes for Ferrous Metals¶

Forging¶

Where metal is deformed due to compressive or high impact forces
Forged objects are stronger than machined objects as it creates grainflow
Functions that can be performed by forging are:
- Upsetting
  - Flattening the metal
  - Increases cross-sectional area by reduces length
- Drawing
  - Metal drawn out by hammering along sides
  - Increases length by reducing cross-sectional area

Hot Forging¶

The metal is heated to above recrystallisation temperature and then worked at the temperature
After working it is left to cool
Much easier to change the shape of the metal as it becomes malleable
(heating) will relieve internal stresses, increasing toughness and durability but decreases the hardness
- prevents strain hardening
- FCC not BCC is formed
- due to heating, the material can warp due to thermal contraction/expansion -> low dimensional accuracy and poor surface finish

Cold Forging¶

Large amounts of force are applied to the metal at (mostly) room temperature
usually for softer metals
retains dimensional acccuracy and surface finish
However, creates residual stresses which leads to lower ductility and toughness, but harder
Can often be accompanied by later annealing to relieve stresses

Rolling¶

Metal is passed through a set of rolls, which exert a compressive force on the sheet. This creates a reduction thickness an extension in length.

Hot Rolling¶

Done at temperatures above recrystallisation
Produces fine, equiaxed, and unstressed grains
Requires less force
Not dimensionally accurate or good surface finish
Can form an oxide layer

Cold Rolling¶

Produces elongated and stressed grains
Harder and stronger final product
Better surface finish
Less ductile
Elongated grains -> only strong in two dimensions
Requires high amounts of form

Casting¶

A general category involving pouring molten metal into a mould. Most of the difference comes in how the mould is made.

The solidification of pure metals has a defined temperature at which the metal transitions from liquid to solid. This causes a solidification front to move through the material, from the outer walls into the centre. Non-pure metals have a range of temperatures where the metal solidifies, this is the ‘mushy’ region.

At the mould walls, the metal cools rapidly and creates an outer shell of equiaxed grains. Grains will then grow opposite direction of heat transfer, forming columnar grains inwards on the material. Further away from the walls, the grains grow slower and are able to become equiaxed and course. The addition of nucleating agents (see (c)) creates course grains throughout. In alloys, dendrites form of the material with a higher freezing point.

_images/wall-grain-growth.png — From Manufacturing Engineering & Technology [6 ed], pg. 241¶

_images/square-mould-cast-structures.png — From Manufacturing Engineering & Technology [6 ed], pg. 239¶

Slower cooling creates coarser structures, and faster cooling creates finer dendritic structures.

Smaller grain size increases strength and ductility. Lack of uniform grain structures create anisotropic properties (not uniform in all directions).

Convection within the metal promotes the formation of the outer chill zone and the transition from columnar to equiaxed grains. Reducing convection creates more columnar structures.

Sand Casting¶

A pattern (made from wood or other material) is made from a design by a skilled pattern maker; in two parts, the cope and the drag [top and bottom] and mounted on plates
The cope pattern is placed within a flask, alongside a pattern for a sprue (for adding metal) and riser. It is then filled with sand that is then rammed to compact it.
This is repeated with the drag, except there is no sprue or riser.
The patterns are then removed.
The cope and drag are assembled together.
Metal is then poured into the sprue via the pouring basin
- The pouring basin is used to ensure consistent flow of metal
The metal is then allowed to cool and then the cope and drag are separated. The excess parts created by the runner and riser are then machined off.
The sand can then be reused

Advantages of sand casting:

Cost effective
Relatively simple to do
Suitable for small or large production runs

Disadvantages:

Poor surface finish -> fatigue cracking
Poor dimensional tolerance and stability
Grains are often columnar
- Properties become anisotropic
- Large grains reduce ductility
- Weakness where columnar grains meet equiaxed grains
- Resolved with the addition of innoculants, which encourage nucleation (formulation of new crystals)

_images/innoculants.png — From Materials Engineering Online Tutorials: Casting¶

Shell Moulding¶

A metal (usually cast iron) pattern is made by hand and is then heated to ~200-300C
Fine silica sand combined with ~5% thermosetting phenotic resin is then dumped onto the metal pattern, and left to cure for a few minutes.
The pattern + sand are then inverted, allowign the excess (non-cured) sand to drop free. This leaves a 10-20mm shell.
The pattern + sand are then placed in an oven to finish curing.
The shell is then removed from the pattern via a removing pin, and combined with #. the other half of the shell by clamping/gluing/adhsive, forming a mold.
The shell is then placed in a flask filled with shot or sand.
Metal can then be poured into the shell and left to set.
The shell is then removed and discarded.

Advantages:

can be completely automated
law labour cost
efficient
very good surface finish and dimensional tolerance
relatively short lead time (~weeks)
large and complex parts can be produce (similar to sand casting)

Disadvantages:

the initial cast iron pattern is moderately expensive to make and hence requires long runs to be economical
the dumping / shell moulding machine is expensive
can be highly porous
part size limited

Permanent Metal Mould / Gravity Die Casting¶

_images/gravity-die-cast.jpg — From OpenLearn: Gravity die casting¶

A die is made from steel. This is very expensive and can take a while to make. It integrates the sprue and riser as part of the mould.
The die must be able to be separated along one plane
Metal can be poured into the mould, left to cool, then the mould is pulled apart

Advantages:

good dimensional accuracy and surface finish
high production rate

Disadvantages:

high die cost
limited part size
long lead time
limited to nonferrous metals e.g. aluminium as the melting point needs to be lower than that of the die itself

Pressure Die Casting¶

Similar to gravity die casting but is done under high pressure.

Advantages:

excellent dimensional acuracy and surface finish (pressure forces into surface)
high production rate

Disadvantages:

lead time of up to a few months
very expensive die cost

Lost Foam Casting¶

_images/lost-foam.png — From Manufacturing Engineering & Technology [6 ed], pg. 271¶

A pattern is made from polystyrene by heating polystyrene beats containing pentane inside of an aluminium die, which is then separated
The polystyrene foam is then placed in a box with fine sand which is then compacted.
Molten metal is poured in and vapourises the foam pattern.

Advantages:

simple process as no parting lines, risers, or cores
minimal cleaning and finishing operations necessary

Disadvantages:

die cost is expensive
metal cools faster as energy is taken out through vapourisation of foam * formation of more columnar structures rather than equiaxed
patterns low strength

Investment Casting¶

A pattern is created of wax through moulding or other techniques
The wax patterns are often joined together in large trees, then covered in a fine silica and binders
Once dried, it is then repeatedly coated in more sand to increase the strength of the mould
The mould is then heated (~150C) to melt out the wax
It is then fired at 600-1000C to burn out any remaining wax or chemicals
Molten metal is then poured into the mould and then the mould is broken up to reveal castings

Can be used for manufacture of orthopedic replacements e.g. the knee. Suitable for use with titanium, chrome, or cobalt alloys.

Advantages:

excellent surface finish and dimensional accuracy
very high production rates
can cast high melting point alloys
removes the need for most finishing or machining processes, which can reduce cost
creates equiaxed grains through the mould, leading to better properties
thin walls (1.5mm) can be created

Disadvantages:

expensive tooling cost, lead time of a few weeks * creation of both wax mould and then this secondary mould
part size limited (up to ~35kg)

Engineering electricity/electronics¶

Syllabus Excerpt

power generation/distribution
- electrical energy and power
- simple circuits
electric motors used in transport systems
- principles
- applications
control technology
electrical safety

Communication¶

Syllabus Excerpt

freehand sketching, design and orthogonal drawings
sectional views
Australian Standard (AS 1100)
computer graphics, computer aided drawing for orthographic projection
collaborative work practices
Engineering Report writing

Aeronautical Engineering¶

Scope of the profession¶

Syllabus Excerpt

nature and scope of the aeronautical engineering profession
current projects and innovations
health and safety issues
training for the profession
career prospects
unique technologies in the profession
legal and ethical implications
engineers as managers
relations with the community

Historical and societal influences¶

Syllabus Excerpt

historical developments in aeronautical engineering
the effects of aeronautical innovation on people’s lives and living standards
environmental implications of flight

Engineering mechanics and hydraulics¶

Syllabus Excerpt

fundamental flight mechanics
- relationship between lift, thrust,
- weight and drag
- lift to drag ratio
- effect of angle of attack
Bernoulli’s principle and its application to
- venturi effect
- lift
bending stress
- airframes
propulsion systems including
- internal combustion engines
- jet including turbofan, ram and scram
- turboprop
- rockets
fluid mechanics
- Pascal’s principle
- hydrostatic and dynamic pressure
- applications to aircraft components and instruments

Engineering materials¶

Syllabus Excerpt

specialised testing of aircraft materials
- dye penetrant
- X-ray, gamma ray
- magnetic particle
- ultrasonic
aluminium and aluminium alloys used in aircraft including aluminium silicon, aluminium silicon magnesium, aluminium copper
structure/property relationship and alloy applications
- changes in macrostructure and microstructure
- changes in properties
heat treatment of applicable alloys
thermosetting polymers
- structure/property relationships and their application
- manufacturing processes
- compression moulding
- hand lay-up
- vacuum lay-up
- modifying materials for aircraft applications
composites
- types including reinforced glass fibre, Kevlar, carbon fibre and Fibre Metal Laminate (FML) as used in aircraft construction
- structure/property relationships and their application in aircraft
corrosion
- common corrosion mechanisms in aircraft structures
- pit and crevice corrosion
- stress corrosion/cracking
- corrosion prevention in aircraft

Communication¶

Syllabus Excerpt

freehand and technical drawing
- pictorial and scaled orthogonal drawings
Australian Standard (AS 1100)
developments
- transition pieces
graphical mechanics
- graphical solution to basic aerodynamic problems
computer graphics, computer aided drawing (CAD)
- 3D applications
collaborative work practices
Engineering Report writing

Telecommunications Engineering¶

Scope of the profession¶

Syllabus Excerpt

nature and scope of telecommunications engineering
health and safety issues
training for the profession
career prospects
relations with the community
technologies unique to the profession
legal and ethical implications
engineers as managers
current applications and innovations

Nature and Scope¶

Telecommunication Engineers are responsible for:

Equipment: design, build, maintain, repair
Transmission Media (copper, optic fibre, radio waves): design, build, maintain, repair, evaluate, control, write software to control and manage

Nature

Training - university + postgraduate
Systems Analyst - identifying faults & correcting them in systems

Health and Safety Issues¶

In the past, chemical and waste from materials used, e.g. fumes from soldering
Now, only (untrue) concerns about radiowaves

Training for the Profession¶

Trade skills for installation and maintenance
University Training in engineeering, mathematics, physics, IT software/hardware, design, manufacture, and materials
Graduate + Postgraduate Training is often necessary for jobs
On-job training
As a growing field, so the training is often growing and rapidly developing alongside

Career Prospects¶

40% of ASX companies have engineer-trained managers
Many jobs will exist that do not exist yet
Can be government or private companies
- Smaller companies are at the forefront of innovation as they are agile and can innovate rapidly

Relations with the Community¶

Generally quite good as people like phones & the benefits it provides
BUT:
- visual pollution from wires + infra
- Annoyance due to delays in installation & management
- Quality & speed of the Transmission
- Radiowave safety

Technologies Unique to the Profession¶

Legal and Ethical Implications¶

Engineers as Managers¶

Current Applications and Innovations¶

Historical and societal influences¶

Syllabus Excerpt

historical development within the telecommunications industry
the effect of telecommunications engineering innovation on people’s lives
materials and techniques used over time and development of cathode ray television including B/W and colour

Engineering materials¶

Syllabus Excerpt

specialised testing
- voltage, current, insulation
- signal strength and testing
copper and its alloys used in telecommunications including copper beryllium, copper zinc, electrolytic tough pitched copper
- structure/property relationships and their application
semiconductors such as transistors, zener diodes, light emitting diodes and laser diodes
- uses in telecommunications
polymers
- insulation materials
fibre optics
- types and applications
- materials

Engineering electricity/electronics¶

Syllabus Excerpt

telecommunications including:
- analogue and digital systems
- modulation, demodulation
- radio transmission (AM, FM, digital)
- digital television transmission and display media such as plasma, LED, LCD, 3D
- telephony: fixed and mobile
- transmission media
  - cable
  - wireless
  - infrared
  - microwave
  - fibre-optic
satellite communication systems, geostationary, low orbit satellite and GPS
digital technology (AND, NAND, NOR, OR GATES)

Communication¶

Syllabus Excerpt

freehand and technical pictorial drawing, graphical design drawings
computer graphics; computer aided drawing (CAD)
- graphical design
- in the solution of problems
collaborative work practices
Engineering Report writing

Glossary¶

toughness: Resistance to impact
hardness: Resistance to permanent deformation
anisotropic: Having a different value when measured in different directions