Engineering

Five Properties of Metals

- Lustrous- Solid at Room Temp- Malleable- Ductile- Good Conductors

Four Properties of Non-Metals

- Dull- Brittle- Non-conductors- Cant Form Alloys

Organic Materials

Derived from carbon

Biological Materials

Derived from organism-live cycle

Ferrous Alloys

Alloys that contain greater than 50% iron

Polymers

Organic materials heavily modified to produce desirable properties

4 Properties of Ceramics

- Hard and brittle- High compressive low tensile strength- Low conductivity- Chemically inert

Composite Materials

Bonding of two or more materials

Ductility

Can be stretched into a wire without fracturing

Malleability

Can be flattened by a compressive force without failing

Hardness

Can resist scratching and indentation

Elasticity

Can return to original position after deformation

Toughness

Can withstand impact force and deform plastically before fracturing

Strength

Can withstand load force without failure

Brittleness

A material that under stress breaks without much plastic deformation

Primary Atomic Bonds

Strong - ionic, covalent and metallic

Ionic Bonds

Transfer of electrons between atoms with matching valencies results in attracting ions e.g. ceramics

Covalent Bonds

Sharing of outer electrons between non-metals to achieve outer shell

Metallic Bonds

Valence electrons condense into a sea of electrons

Secondary Atomic Bonds

Weak - Van der Waals, Hydrogen bonds

Van der Waals/Molecular Bonds

Negative electrons concentrate on one side of atom - attracts to sides of other atoms

Hydrogen Bonds

Hydrogen atoms attracted to each other due to dipoles

Dipole Molecules

Molecules which have an unbalanced distribution of charge

Metal Structures

- Body Centered Cubic- Face Centered Cubic- Close Packed Hexagonal

Body Centered Cubic Properties

Less dense, low ductility

Face Centered Cubic Properties

More dense, high ductility

Close Packed Hexagonal Properties

More dense, lower ductility

Polymorphism

A material with more than one crystalline structure

Elastic Deformation

Atoms do not permanently move from their original position

Plastic Deformation

Atoms move into a new permanent position

Slip Planes

Rows of atoms sliding along a specific plane in plastic deformation

Dislocations

Holes or defects in a uniform grain

Work Hardening

Working a material, moving dislocations until movement impeded. Increases hardness, strength and brittleness

Three Steps of Grain Growth

1. Solidification into structure begins at nucleation points2. Grain dendrites grow (tree like)3. Grain boundaries form

Slow Cooling Result

Produces fewer nucleation points resulting in larger grains, softer and weaker material

Equiaxed Grains

Grains of roughly similar proportions

Concurrent Force System

All forces pass through a common point

Co-linear Force System

All forces act along the same line of action

Force Equation

F=ma

Scalar Quantity

Units, Magnitude

Vector Quantity

Units, Direction, Magnitude

Vector Addition Methods

Polygon of Forces, Vector Components

Three Force Rule

If 3 forces are acting on a body that is in equilibrium all forces will be concurrent

Moment Equation

M=Fd

Couple

Two parallel forces of equal magnitude and opposite direction acting on a body - produces rotation

Moment of Couple Equation

Magnitude of one force * perp distance between forces

Stress/Strength/Pressure

The intensity of a load

Tensile Stress

Stress that lengthens an object

Compressive Stress

Stress that shortens an object

Shear Stress

One surface moving over another acting parallel to the area of the shear

Strain

Deformation of a material due to a stress

Strain Equation

0

Hooke's Law

Stress and strain are proportional up until the elastic limit

Yield Point

Market increase in strain without increase in load - dip in curve after proportionality results

Yield Stress

The maximum amount of stress applied to which the object will still elastically deform

Calculating Toughness from a Diagram

Area under the curve

Youngs Modulus

A measure of the stiffness of a material

PLEA Formula

ΔL=(PLo)/(E*Ax )

Factor of Safety

Reflects the confidence the designer has in the materials and design

Working Stress Equation

WS = YS/FS

Disadvantage of Iron

Very Soft, Easily Corroded - Little to no commercial use

Two Alloys of Iron (C)

Steel - <2%Cast Iron - 2-4%

Two Alloys of Steel

Plain Carbon SteelAlloy Steel

Five Alloys of Plain Carbon Steel

Low Carbon SteelMild SteelMedium Carbon SteelHigh Carbon SteelUltra-High Carbon Steel

Eight Elements of Alloy Steel

- Nickel- Chromium- Manganese and Silicon- Molybdenum- Tungsten- Vandium- Stainless Steels- High Speed Tool Steels

Low Carbon Steel (C)

<0.15% e.g. fence wire, car bodies, rivets

Mild Steel (C)

0.15-0.3% Carbon; very commonly used for structural steels

Medium Carbon Steel (C)

0.3-0.6% Carbon e.g. Shafts, axles

High Carbon Steel (C)

0.6-1% Carbon; High wear resistance and strength e.g. hammers, spanners, cables

Ultra-high Carbon Steel (C)

1-2% Carbon used as tool steels e.g. files, knives, drills

Plain Carbon Steel (C)

<1.2% Carbon - may contain manganese and silicon

Alloy Steel

Contains significant amounts of other elements

Nickel Alloy

Increases toughness and fatigue resistance e.g. high strength structural work

Chromium

Wear resistance specifically case hardening

Manganese and Silicon

Used for strengthening and toughening

Molybdenum

Increases high temperature hardness and strength e.g. aircraft structures

Tungsten

High temperature wear resistance e.g. tool steels

Vanadium

Strong cementite former and limits grain growth e.g. high toughness for springs, crankshafts

Stainless Steels

>10% Chromium - Produces surface layer of chromium oxide which provides excellent corrosion resistance

High Speed Tool Steels

Contain most of steel alloying elements in varying amounts e.g. lathe tools, milling cutters, drills

Ferrite

Pure BCC iron <0.04% Carbon

Austenite

Grain that forms when steel is at red heat <2% Carbon FCC meaning its soft and ductile. Turns into Pearlite when cooled.

Cementite

Created from excess carbon the Ferrite couldn't absorb. Compound Fe3C and is extremely hard and brittle

Carbide

Molecule Fe3C

Pearlite

Layers of Ferrite and Cementite

Point of Pure Pearlite

0.8% Carbon

Silicon in Steel (%)

>1.5% used to aid formation of graphite

Three Features Grey Cast Iron

- Graphite present as flakes- Stress concentrations occur at sharp ends- Graphite voids allow easy machining and damping properties

Nodular/Spheroidal (SG) Graphite Cast Iron

- Small amounts of magnesium/cerium added to form graphite nodules- No stress concentrations = greater tensile strength and ductility

White Cast Iron (%)

<1% Silicon - All carbon forms carbide; hard and brittle material

Malleable Cast Iron

- Head white cast iron to 900 degrees then slow cool then reheat for 12 hours- Graphite clusters resulte.g. axle housing, manhole covers

Four Cast Irons

- Grey Cast Iron- Nodular/Spheroidal (SG) Graphite Cast Iron- White Cast Iron- Malleable Cast Iron

Annealing

Heating and cooling of a metal to produce the softest state. Used to relieve internal stresses, and for working or machining

Four Annealing Processes

- Full Annealing- Process Annealing- Normalising- Spheroidising Annealing

Full Annealing

Heating steel to red heat until all grains are austenite, then slow cooling to room temperature in furnace

Process Annealing

Heating steel below red heat at slow cooling to room temperature. Ferrite equiaxes but not pearlite.

Normalising

Heating steel to Austenitic Range, then cooled in still air to room temperature. Used to refine grain structure for forgings and castings

Spheroidising Annealing

Soaking steel in 700 degrees for several hours. Cementite forms in spheres, then slow cooled. Result is very easy to machine.

Hardening (%)

Heating >0.3% Carbon steel to austenitic range then quenching. Forms Martensite instead of Ferrite. Needs to be tempered to be used commercially

Martensite

Body centred Tetragonal structure which is extremely hard and brittle

Tempering

Soaking in 500-600 degrees to remove internal stresses. Atoms trapped in martensite diffuse to form fine cementite

Case Hardening

Producing a hardened, wear resistant surface with a softer tough inside.

Carburising (%)

Case Hardening method for metals with <0.2%C. Soak metal at austenitic range in a high carbon material. Creates 0.8% carbon case.

Nitriding

Diffusion of nitrogen into steel creates tough outer compound NH3

Flame and Induction Hardening

Case Hardening method for metals with >0.3% Carbon. Outside is heated to austenitic range then quenched.

Recrystallisation Zone

550-650 degrees, metal forms new equiaxed grains which relieves stresses

Waste Reduction

Achieved by changing base materials or product e.g. steel to aluminum cans

Waste Reusing

Using base materials or entire product for new applications

Waste Recycling

Collection, separation and clean-up of waste material

Recyclable Materials

Plastics, Glass, Metals

3 Benefits of Waste Management

Reduction in landfill, reduced energy consumption from production, reduced use of new resources - less depletion

2 Costs of Waste Management

Reduced income from less demand on natural resources, Unsightly recycling areas

Destructive Testing

Test results in destroyed test piece

Non-destructive Testing

Test piece can be used after testin

Tensometer

Tests tension and compression; results recorded on a load-extension diagram

Brinell Hardness Test

A tungsten carbide ball is forced into the surface

Vickers Hardness Test

Diamond pyramid forced into the surface

Rockwell Hardness Test

Uses either diamond pyramid or ball indenters

Notched-bar Impact Tests

Notch is cut into material, hammer swings to knock the top part of the material off

Izod Impact Test

Vertical test piece {I for Izod}

Charpy Impact Test

Horizontal test piece {H for cHarpy}

Bend Tests

Test for materials that cannot be used because of preparing suitable test pieces

5 Crack Detection Tests

Dye Penetrant Inspection (DPI), Magnetic Particle Testing, Eddy Current Testing, Ultrasonic Testing, Radiography

Dye Penetrant Inspection (DPI)

Part is dipped in dye then washed away, developer is added leaving visible dye filled cracks - only for surface cracks

Magnetic Particle Testing

Fine magnetic particles are applied to surface. Part is magnetised to reveal surface and shallow defects because of stray EMF

Eddy Current Testing

Detects variation in an induced electromagnetic field

Ultrasonic Testing

Transmitter vibrations are sent through material, flaws or cracks reflect a portion of the vibrations

Radiography

High energy x-rays pass through object and impinge on sensitive film. Darker areas are formed by internal flaw because more radiation is let through

Converting Load Extension Diagram to Stress Strain Diagram

Divide load axis by cross-sectional areas to get stress. Strain can be expressed as a percentage of the original length

Stress Equation

Stress = Load (P)/Area (Ax)

Stress Symbol and Unit

σ - sigma, MPa

Strain Symbol and Units

ε - epsilon, % of original length

Strain Equation

Change in length (ΔL)/Original lenght (Lo)

3 Advantages of Non-Ferrous Alloys

Greater ductility, lower density, higher thermal and electrical conductivity

Brass

Alloy of Copper and Zinc

Cartridge Brass

70% Copper 30% Zinc - soft and ductile - used for tubes, wire, cartridge cases

High Tensile Brass

60% Copper 40% zinc - high tensile strength - used for propellers and shafts

Muntz Metal

60% Copper 40% zinc - high tensile strength - used for propellers and shafts

4 Properties of Aluminum Alloys

Corrosion Resistance, Electrical Conductivity, Low Mass, Non-toxic oxides

Duralumin

Alloy of aluminum and 4% copper

3 Properties of Titanium Alloys

High specific strength, melting point and excellent corrosion resistance

2 Properties of Zinc Alloys

Low melting point and high corrosion resistance

Precipitation Hardening

Hardening or strengthening of an alloy by heating and quenching to form zones of material precipitate which distort bonds

Natural Ageing

During precipitation hardening, aterial is left at a room temperature over a period of days

Artificial Ageing

During precipitation hardening, aterial is heated slightly to speed hardening process

Homogeneous Structure

Uniform composition and properties throughout a material

Why Does Alloying Strengthen Materials

Disruptions in uniform atomic structure block slip planes

Work

An object is displaced in the direction of force

Work Units

Joules (J)

Work Equation

U=Fd

Energy

The capacity to do work

Potential Energy Equation

PE = mgh

Kinetic Energy Equation

KE = 1/2mv^2

Conservation of Energy

No energy is lost during work; it is transformed to different states e.g. heat to light

Power

The rate of doing work

Power Units

Watt (W) or J/s

Mechanical Power Equation

P = work (U)/ time (t)

Electrical Power Equation

P = VI

Mechanical Advantage

The ratio of the output force to input force in a machine

Mechanical Advantage Equation

MA = f(out)/f(in) = load/effort

Velocity Ratio Equation

VR = d(in)/d(out) = De/Dl

Efficiency

A measure of how much work or energy is conserved in a process

Efficiency Symbol

η - eta

Efficiency Equation

η = MA/VR

Lever

A rigid bar that rotates about a fulcrums

Lever Order Mnemonic

FLE 123

Pulley Velocity Ratio Equation

VR = v(in)/v(out) = r,d or c of B/ r,d or c of A

Gear Velocity Ratio Equation

VR = v(in)/v(out) = r,d,c or teeth of output gear/ r,d,c or teeth of input gear

Inclined Plane Velocity Ratio Equation

VR = l/h = 1/sin⁡θ

Wedge

Wedge moves into position and effort is applied to vertical face

Lead (Screw)

The distance the nut moves along the shaft in one revolution

Pitch (Screw)

The lead for a single helix

Screw Velocity Ratio Equation

VR = circumference (πD)/pitch (P)

Hydraulics

Work done using liquids

Hydrostatic Pressure

The pressure of a stationary fluid due to the force of gravity

Hydrostatic Pressure Equation

P= ρgh

Absolute Pressure Equation

P = Po + ρgh

Buoyancy

An upwards force acting on all floating and submerged object by the fluid

Pascal's Law

Pressures on input and output cylinders are the same at equal heights

Pascal's Law Equation

F(in)/A(in) = F(out)/A(out)

Hydraulic System Velocity Ratio Equation

VR = Load piston ∅^2/Effort piston ∅^2

3 Advantages of Hydraulic Systems

Extremely efficient and reliable, Self-lubrication results in less maintenance and higher reliability

3 Disadvantages of Hydraulic Systems

Requires reservoir of liquid to use -needs to be refilled. Brake booster is needed for brakings systems to get the required force to operate

Pneumatics

Work done using gases

3 Advantages of Pneumatic Systems

Freely available and clean source - atmospherePneumatic leaks to not pollutePneumatic machines have a lower mass due to lower operating pressures

2 Disadvantages of Pneumatic Systems

Reduced precision of movement due to compressible natureLower available pressures

Voltage

The electrical potential difference between two points in a circuit

Current

A measure of the charge passing a point in a circuit

Conductors

Materials that have many free electronics through which a stream of electrons can flow

Insulators

Materials that have few free electrons and as such a small flow of electrons can pass

Semiconductors

Materials that exhibit characteristics of conductors and insulators

Resistance

The opposition to the flow of electrons a substance exhibits

Total Resistivity Equation

R = ρl/A ρ = resistivity in Ωm, l = length, A = cross-sectional area

Total Resistance in Series

Rt = R1 + R2...

Total Resistance in Parallel

1/Rt = 1/R1 + 1/R2 ...

3 Safety Devices

Earth wires, Double insulation, Circuit breakers

Generators

Large quantities of conductor spinning fast in a magnetic field to produce current

Direct Current

Current flows continually in one direction around a circuit

Alternating Current

Changes direction many times per second. A sign wave of current draw is produced

Alternator

AC generators are less costly and more efficient than DC generators

Electric motors

Converts electrical energy into mechanical energy

Universal Electric Motors

Stationary field coil windings (stator) around a rotating coil (armature)

3 Advantages of Universal Motors

High power and torque for size, run on AC and DC and can run at high speeds

Disadvantage of Universal Motors

Brushes create ozone and noise

Induction Motors

3 phase AC current creates 'moving' electric field that rotor chases

2 Advantages of DC Motors

Inexpensive and convenient

2 Disadvantages of DC Motors

Brushes create ozone, Brushless requires complex drive electronics

Printed Circuit Motor

Windings in each layer of the PCB create moving magnetic field when powered

3 Advantages of Printed Circuit Motors

Very efficient, lightweight, and small

2 Disadvantages of Printed Circuit Motors

Expensive to produce, only applicable for low torque applications

Stepper Motors

Move single steps as opposed to continuous rotation.

3 Advantages of Stepper Motors

Remains in position when not powered, high torque, and precision

2 Disadvantages of Stepper Motors

Inefficient and requires complex input

Regenerative braking

When braking, the kinetic energy of the wheels are converted into electrical energy -> DC motor used as a generator

Kinetic Energy Recovery System (KERS)

Type of regenerative braking consisting of a device such as a flywheel or battery that stores kinetic energy from braking

3 Advantages of Electric Motors in Transport

No pollution at point of use, higher efficiency, can use regenerative braking

Control technology

Use of controls such as microcontrollers to produce desired outcomes e.g. field coils of electric motor are reversed to allow for regenerative braking

PWM Signals

a type of digital signal used to give analogue style variable signal strength

Duty Cycle

The time a PWM signal is on over one cycle

Thermistor

A resister which varies resistance according to its temperature - higher temp higher resistance

Light Dependent Resistor

A resistor which varies resistance according to light measure - bright light lower resistance

Trimpots

Small variable resistors for PCB's that can be adjusted with a screwdriver

Slider/Rotary Pots

Variable resistors that are adjusted by turning or sliding a knob e.g. stereo volume knob

Dry Cell

A battery cell that contains a dry paste

Wet Cell

A battery cell that contains an electrolytic liquid

Lithium-Ion Batteries

Rechargeable batteries used in consumer electronics -> high energy density and low loss of charge

Capacitor

Stores potential energy in an electric field

Variable Capacitor

Used to tune radio signals by changing resonant frequency

Transformer

Use of electromagnetic inductance to step up and down current. Primary winding it input and secondary is output

Diode

A device that lets current flow in a single direction

Photodiode

A light-sensitive diode

Rectifier

Convert AC to DC using an arrangement of diodes to produce a steady voltage

Voltage Regulator

Remove voltage fluctuations that impact circuit function

Zener Diode

Passes current in both directions but retains constant voltage

Transistor

An electronically operated switch that makes up the most electronics systems

Integrated Circuits (IC's)

A microscopic array of electronic circuits printed onto a single wafer for ease of use in complex circuitry

Logic Gate

Electronic circuits designed to perform a logical operation from one or more inputs

AND Gate

Only outputs 1 if both inputs 1

NAND Gate

Only outputs 0 if both inputs 1

OR Gate

Outputs 1 unless both inputs 0

NOR Gate

Outputs 0 unless both inputs 0

Truth Table

Describes the behavior of a logic gate by listing all possible combinations of inputs

Friction

The force that resists motion when two surfaces are in contact

Normal Force (Fn)

a force proportional to the force of friction - acts perpendicularly to the two surfaces

Coefficient of Friction

the ratio of the force of friction between the two bodies

Coefficient of Friction Equation

Ff = μFn where μ = coefficient of friction

Angle of Repose

The angle an inclined plan when slide on the plane begins

Angle of Repose Equation

tan⁡α = μ where α=angle of repose and μ=coef. of friction

Casting

Heating up a material and pouring into a mould

Moulding

Casting for polymers

Rolling

Changing the thickness and cross-section of a material by passing it through rollers. In can be done at a high temperature (Hot Rolling) or at close to room temperatures (Cold Rolling).

Extruding

Metals pushed through a die at an elevated temperature

Spot Welding

Electric current melts sheets under pressure in spots; used for joining sheet metal

Butt Welding

Metal butted together at ends; current melts metal; used for joining tubes

Seam Welding

Metal moved through rotating disks; current melts metal; used for manufacturing pipes

Oxy-acetylene Welding

Metal melted by oxy-acetylene flame and filler metal added; used for joining small parts

Bronze Welding

Metal heated up and bronze filler added; little to no melting of the parent metal

Electric Arc Welding

Metal melted by electrode acting as filler metal; covered in flux to prevent oxidation; used for joining steel

Metal Inert Gas (MIG) Welding

Electrode is replaced with continuous wire feed; facilitates faster welding; gas acts as flux; can be more automated

Tungsten Inert Gas (TIG) Welding

Tungsten rod acts as an electrode; fed by the operator; used for joining aluminium and stainless steel

Plasma Arc Welding

Gas passed through an electric arc which ionises and forms a plasma; specialty use due to expense

Soldering

A tin-lead alloy is melted to join two metals together

Turning

Working is rotated; tool piece removes unwanted material; lathe

Grinding

Unwanted material removed by abrasive material

Sawing

Material remove by saw tearing

Drilling

Drill piece removes metal to produce a hole

Reaming

Burr removing

Interior Grinding

Reaming but using abrasive tool vs cutting

Shaping

Tool is moved horizontally across workpiece which is moved after each pass

Milling

Using rotary cutters to remove material by feeding the cutter into the workpiece in a certain direction

1st Angle Projection

The Vertical Plane is behind the object and the Horizontal Plane is underneath the object

3rd Angle Projection

The Vertical Plane

Oblique Drawing

...

Heat Affected Zone (HAZ)

Area of the parent metal affected by the weld. Elongated grains of parent metal become equiaxed

Columnar grains

Elongated grains in the weld microstructure that run in opposite direction to heat flow

Sand Casting

A process of pressing moist sand around a pattern to make a mold. The pattern is removed, leaving a cavity in the sand. The cavity is the mold that will be filled with liquid metal. The result will be a casting that is identical in shape to the original pattern.

Riser (sand casting)

A hole in the top of the mould that allows exit of trapped air

2 Advantages of Sand Casting

- Inexpensive and quick- Useful for forming special alloys

3 Disadvantages of Sand Casting

- Thin and projecting sections are difficult to cast- Poor surface finish- Tendency for defects to occur

Shell Moulding

Heating a metal replica of desired part and pushing into sand mixed with the thermosetting polymer. The result is half of the shell mould which is baked then glued to other half. Used for small mass production of components

Die Casting

Permanent metal moulds are used for large number of castings. Moulds have usually been machined

Gravity Die Casting

Molten metal is poured into cast under gravitational force - used only for simple shapes

Pressure Die Casting

Molten metal injected into mould and pressurised.

Full Mould Casting

Artificial polystyrene pattern of the part is constructed.

1st Angle Projection

The Vertical Plane is behind the object and the Horizontal Plane is underneath the object

3rd Angle Projection

Vertical is the top of the object, right is the front side

1st Angle Projection

Vertical is the bottom of the object, right is the back side

Hot Rolling

Produces no work hardening due to higher temperatures - refined, unstressed strain structure.

Cold Rolling

Produces cleaner, smooth and more accurate finish. Harder, stronger and less ductile product

Extrusion

Metal being forced under pressure to flow through a die. Increased hardness, strength and toughness