Engineering Fundamentals (1)

Historical and Societal Influences

• Suspension Bridge : Wrought iron

• Steel: Henry Bessemer developed “Bessemer converter”

• Aliminium Smelting

• Helicopter

Effect of Engineering on Peoples lives

• Engineering improves people’s lives by providing safe infrastructure, transport, communication, and medical technology. It also makes daily life safer, easier and more comfortable

Sine Rule

A/ sin a= B/ sin b = C/ sin c

Cosine Rule

a²= b²+c²-2bc Cos A

Newtons Law of Motion

1. A body will remain at rest unless acted upon by an unbalanced force

2. F= MA

3. To every action there is an equal and opposite reaction

Force

• Push or Pull on a body

Gravity

10m/s²

Weight

• Mass x Gravity

• W = MG

Concurrent force

• Forces that pass through the same point

Non- Concurrent Force

• Intersect various points

Co-Linear Force

• Act along the same line

Classifaction of Materials

• Elements: Cannot be broken down into simple material

• Solutions: Where one substance dissolves in another, Sugar in Tea

• Compounds: Two or more elements that combine chemically

• Mixtures: 2 or more pure substances, elements or compounds mixed together, Salt and Pepper

Physical Properties

• Density: The amount of matter packed into a given volume

• P= M/V…. Density= Mass divided by volume (Kg/m³)

• Porosity: How many holes a material has

• Moisture content: Measure of amount of moisture

Mechanical Properties

• Strength: Ability of a material to withstand applied loads without failure

• Hardness: Ability of a material to withstand scratching or dents

• Elasticity: Return to its original shape

• Stiffness: Ability of a material to resist elastic deformation

• Plasticity: Ability of a material to undergo some degree of damage ( Glass has no plasticity as it easily breaks)

• Malleability: Ability to be rolled into thin wire

• Ductility: Ability to be drawn flat into thin wire

• Fatigue: Tendency of a material to breal

• Notch Toughness: Measure of the amount of energy recquired to cause failure
  

Thermal Properties

• Thermal conductivity: Ability of a material to conduct heat

• Heat resistance: How well a material can resist hear

Magnetic Materials

• Diagmagnetic

• Paramagnetic

• Feromagnetic

Atomic Structure

• Neutrons

• Protons

• Electrons

Neutrons

• Have no charge

• Located in nucleus

Protons

• Have a single positive charge

• Located in nucleus

• Have a mass 0.992x of a neutron

Electrons

• Negative charge

• Electrons outer shell called “Valence”

• 2,8,8,18

Bonding

• Ionic

• Covalent

• Metallic

Ionic Bonding

• Metal and Non Metal ( Ceramics)

• Transfer of one or more electron ( Electrostatic action)

Electrical Insulator

Covalent Bond

• Non metals (Polymers)

• Share valence electrons

• Insulators

Metallic Bond

• Valence electrons form a sea of eletrons

• Metal atoms

• Electical conductors

Intermolecular forces

• Van der Waals forces

• Very weak

• Always in covalent bond

Polymorphosim

• Exist in more than one crystal structure

Crystal Structure

• BCC ( Body centred cube)

• FCC (Face centered cube)

• HCP ( Hexagonal close packed)

BCC

• Room temperature

• Atoms at each corner of a cube

• One atom in the centre of the cube

FCC

• Very ductile (easy to bend and shape)

• Atoms at each corner

• Atoms in the centre of each face

• GOLD, SILVER, ALIMINUIM, PLATINUM

HCP

• Heat treatment

• Atoms arranged in hexagon layers

Non- Crystalline (Amorphous)

• Polymers and Ceramics in their solid state

• Glass

Metals

• Ferrous Metals

• Non Ferrous Metals

Ferrous Metals

• Have iron as a PRIMARY constituent

• Iron, cast iron, carbon steel

Mild Steel

• Eaily formed, machined and welded

• Ductile- Into thin wire

• Scews, bolts

• Easily corrodes, must be painted, electroplated, galvanised

Stainless Steel

• 10 percent of chromium added

Non ferrous

• May contain Iron, but not primary constituent

• Copper: High electrical conductivity, corrostion resistance, electrical wiring

• Brass: 70 copper, 30 zinc, corrosion resistance, switch gears

• Bronze: Copper and Tin

Vulcanised rubber tyre

• Alimnium bronze: Excellent corrosion resistance

Basic Forming Processes

• Casting

• Rolling

• Extruding

• Joining

• Cutting

• Fabricating

Casting

• Involves heating up a material such as a metal alloy, then placing into a mould

• Investment casting- Lost wax casting

• Polymer - Moulding NOT CASTING, blow moulding

Rolling

• Pass a metal through a roller to form a circular or square bar

• Hot rolling- Easier, less dimensionally accurate

• Cold Rolling- Harder- More dimensionally accurate

Extruding

• Passed through a die at an elevated temperature

• Aliminium alloy window frame

Joining

Metallurgical Methods

• Welding

• Soft soldering

• Brazing

• Silver soldering

Mechanical Joining

Welding

• Spot Welding: Joining sheetmetal

• Butt Welding: Joining tubes

• MIG Welding: Can weld aliminum

• TIG Welding: Joining aliminum and stainless steel

Soft Soldering

• Join 2 metals using tin alloy

• EG Joining electrical wires together, 60 percent tin, 40 percent lead

Brazing

• Brass that is melted onto a ferrous temperature at 860 degrees

Silver soldering

• Joining dissimilar parent metals

Mechanical Joining

• Mechanical joining is a method of fastening two or more materials together using physical devices — instead of melting (welding)

• Screws, bolts, nuts, studs

Cutting

• Removal of unwanted material

Fabricating

• Assembling an item from various components

Polymers

• Plastics, manufactured from crude oil

Formation of Polymers

• Polymers are formed by linking together small molecules called monomers

• Addition Polymerisation

• Condensation Polymeriasation

Addition Polymerisation

• 2 or more monomers to form polymer

Condensation Polymerisation

• Monomers join to form a by-product

• Eg- Phenol formaldehyde ( Bakelite)

Polymer structure

• Thermoplastics ( Thermosoftening)

• Thermosetting

Thermosoftenning

• Can be resoftened by heat or rehardned by coolness

• Covalent bonds and Weak secondary bond

• HORIZONTAL STRONG BOND, VERTICAL WEAK BOND!!!

Examples

• ABS: Lego bricks

• Nylon: Clothing

• Polycarbonate: Glass

• Polyethylene: Water pipes

Thermosetting

• Cannot be re-softened by heating

• Better rigidity and less elasticty

• Epoxy or GRP

ALL COVALENT BONDS!!!

Ceramics

• Clay Body

• Glass

• Refractories

• Clay body ceramics

• Porcelain and China

• Low porosity

• Good thermal and electrical insulator

Glass

• Soda Lime Glass

• Amorphous ( Non crystallisation)

• Good mechanical strength

• GORILLA GLASS- ALKALI ALUMNIOSILICATE

Refractories

• Stable at high temperatures

• Oven and Furnaces

Forming and Shaping ceramics

• Slip casting technique- Toilets

• Glass Sheets- Windows

• Hot Isostatic Pressing (HIP)- Medical implants

Composites

• Materials made from different materials combined together

• TIMBER

• CONCRETE

Timber

• Natural composie that is composed of cellulose fibres, the tracheids and lignin

• Excellent strength and reasonable peformance

• Affected by weather and prone to pests

Concrete

• Consists of sand, cement and aggregrate

• 4 aggregrate : 2 sand: 1 cement

• Portland cement

• Good in compression, weak in tension