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/sinθ
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
tanα = 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