Materials Notes (T1) - 11 Engineering Studies

7/30/2019 Materials Notes (T1) - 11 Engineering Studies

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Engineering Notes 11ES (Beginner: Term 1)

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Effects of Engineering Innovations

20th

century

Electronics: used in information/signal processing

Advantages:- Convenience instantaneous information processing- Extreme accuracy e.g. aided in work in many professions and in sensitive volatile markets like in

finance

- Large storage capacity, aided by search engines, databases, scanners- Fast communications revolution, in text, speech, or video replaces traditional forms of mail

(snail mail)

- Automation of tasks: robotics and microwave ovens less knowledge is required to performfundamental activities

- Lifesaving technologies e.g. bionic eye, pacemaker- Entertainment, such as music, film, and computer games (video game culture)- Cheaper costs of previous technologies like in photography expanding consumer markets

Disadvantages:

- Dependency lifestyle factors change, including poorer health from excessive computer usage(eye/muscle strain, joint problems, blood circulation) and television (obesity)

- Mental laziness lower problem solving ability e.g. calculator replaces thinking developmentdone by the young

- Addictive content e.g. internet/gaming addiction- Abnormal sleeping patterns (change in melatonin) from bright computer screens- Excessive electricity consumption drains resources, damages environment (pollution, global

warming, e-waste)

Agricultural mechanisation: any form of machine used to perform agriculture tasks, including planting,

cleaning, applying fertiliser/pesticide, and harvesting. Substituted human and animal (horses, oxen)

labour

Advantages:

- Increase in agricultural production change in lifestyle from subsistence to commercial farming,greater profits for farmers, society benefits from more food

- Efficiency of machines lowers labour and fuel costs while maximising production- Automated processes provide convenience and reliability e.g. water sprinklers- Less reliance on animals space allocated for living and food (grass) can be used for more crops

and produce more food

- Ability to do tasks human labour cannot, including lifting heavy objects- Fewer complaints from workers over repetitive work- Promote growth in rural communities modern farming equipment = modern development

Disadvantages:

- Loss of jobs- High costs debt- Pollution from diesel

21st

century


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Space Exploration: process of exploring and discovering space, beginning from WW2

Advantages:

- Research for future generations and for unlikely warnings of meteor strikes/showers- Application of space technology to other areas e.g. solar energy, robotics, water purification

systems, high density batteries- Satellite imaging to record physical changes on Earth and GPS- More accurate weather forecasts- Aesthetics and art- Space tourism education, research, recreation (economy)- Potential future mining resolves non-renewable resource issue

Disadvantages:

- Expensive funded by government money and tax (unfair usage does not improve quality oflife within that area)

- Space competition promotes aggression e.g. Space War during Cold War, along with spacetechnology potentially used for military purpose

Virtualisation: virtual simulation of computer infrastructure

Advantages:

- Maximises efficiency of underutilised servers/hardware- Fewer physical servers more space, less equipment, saves energy- Faster establishment and configuration (software only, not hardware)- Ability to move virtual severs from hardware to hardware backup, portability- Security if virtual server fails, it is a software issue only- Lack of dependency on specific hardware no compatibility issues- Compatible with older software

Disadvantages:

- Greater dependency on less hardware failure of multiple virtual servers if hardware fails- Strain on hardware- Capable hardware required if too much is needed to be replaced, virtualisation is not worth the

costs and e-waste

- Usage of VPNs for unfair purposes e.g. geo-blocking online to restrict who can purpose products- Problems with virtual servers more difficult to diagnose and fix- Increased training expertise

Virtual Reality: interaction with natural senses/movements and software, OR creation of new virtual

worlds.

Advantages:

- Real-time information distribution (internet) Google Glasses- Realistic simulations aid in industries, casual usage, entertainment (games), fitness (e.g. Wii Fit)

Disadvantages:

- Psychological problems virtual worlds allow escapism from reality dangerous e.g. Second Life- Google Glasses potentially limited to those with good eyesight discrimination- Health issues e.g. Wii Fit people see no need


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Types of Engineering

- Chemical engineering:o Materials

- Civil engineering:o Environmentalo Geotechnical, Mining

- Electrical engineering:o Computer, Software, Hardwareo Electronic, Telecommunications

- Mechanical engineering:o Aerospace/aeronauticalo Vehicle, Automotive

- Other (specialised fields):o Agriculturalo Biological, Genetico Industrial, Safety

o Mechatronicso Nuclearo Petroleum

Fields of Engineering:

- Electrical: deals with electrical machines (generators, motors, transformers) and powertransmission high voltage

o Bachelor of Engineering degreeo Fields: construction, power generation/distribution, telecommunications and

broadcasting, computing, manufacturing, electronics, transport, defence, aerospace,

research/education

- Environmental: aims to find sustainable solutions to improve conditions in natural/humanenvironments (pollution, waste disposal, land/resource management, sustainable energy,

global warming)

o High school diploma, but associate's/bachelor's degree preferred, OR civilengineering degree

o Fields: construction, mining, process engineering, energy industries, air/waterquality control and soil testing, noise control, waste disposal

Engineering Mechanics

Scalar and vectors:- Scalars: defined by magnitude (number) only

o E.g. distance (20m), time (30s), mass (22kg), speed (100km/h)- Vectors: defined by magnitude and direction (+ point of application and sense)


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Mass and Force:

- Mass: amount of matter in a body SI unit: kg (kilogram). This is typically constant.- Force: defined a push or pull SI unit: N (newton)- Gravity: acceleration towards the centre of a body gravity of earth: 9.8m/s2- Weight: force of gravity acting on a mass

o W = mg, where weight in N, mass in kg, gravity is 9.8m/s2- Lift: a mechanical aerodynamic force caused by interactions with a fluid (liquid/gas). In

simple terms, when a wing deflected air downwards, reaction forces push the wing up.

o Lift can occur in any direction e.g. horizontally on a sail, down on a race car- Thrust: a mechanical force that is opposite of the acceleration of a mass

o Thrust to move the aircraft forward is caused by reaction forces from accelerating amass of gas (fluid) through a propulsion system (propellers)

- Drag: a mechanical force that acts opposite to the movement of an object through a fluid(air/fluid resistance) resists the movement of an object

o Unlike friction, drag force increases as the object moves faster

- Downforce: downwards thrust/lift created by aerodynamics (front wings) of car verticalforce on tires creates more grip

- Friction: an opposing force that acts to stop the movement between two touching objectso Static friction: strong enough to stop movemento Kinetic friction: not strong enough to stop all motion

- Buoyancy: force on an object making them move upwards opposes gravity. Caused bydiffering pressure the fluid/air places on the object.

o Net buoyancy equals the weight of fluid that has been displaced by the objecto E.g. used in boats, ships, balloons, blimps

- Normal force: a force that prevents any object from sinking/penetrating into its restingsurface

Other Forces:

- Stress: a physical quantity that expresses the internal forces that particles of an object exerton one another. These internal forces are a result of the actions of external forces.

o Measured by [force/unit area], e.g. Newtons/m2 (Pascals) SI unit for pressure- Compression: external pushing forces acting to compress/collapse an object

o Buckling: an object's ability to endure compression forces- Tension: internal pushing forces within an object, attempting to expand it


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o Snapping: when tension surpasses an object's ability to handle the lengthening forceo This dealt with by dissipating or transferring the force

- Torsional: twisting motion shear stress (any stress not in a straight line)Mechanics

- Mechanics: the study of the behaviour of a body under the influence of a force or a systemof forces

o Statics: concerns the body at equilibrium (at rest)o Dynamics: concerns the body in motion (due to a system of unbalanced forces)

Kinematics: considers the motion of a body without consideration thecauses for the motion no reference to the forces acting on it

Considers aspects of motion excluding mass and force Kinetics: considers the motion of a body with reference to the forces

Considers the forces and energy associated with it- Newton's Laws:

1. Inertia: when forces are balanced, there is no acceleration (constant velocity) or theobject is at rest

2. F = ma: external forces are dependent on mass and acceleration. This equation onlyapplies when the mass is constant, if it is not there is a second portion of this equation

involving momentum (as a decrease in mass causes acceleration, e.g. deflated balloon)

3. Reaction forces: for every action force, there is an equal and opposite reaction force.Energy is defined by the ability to do work. Work is a change in energy caused by an applied force

moving an object a distance. W = Fs*cos (work in joules, force in newtons, distance in metres)

- cos: where is the angle between the force vector and the direction of movement.- When a force moves an object in exactly the same direction, cos = 1 and is not considered.

SixClassical Simple Machines

Force-Distance Trade-offs

Lever: a force is applied over a distance to magnify the user's effort (e.g. crowbar) or magnify the

distance the effort carries (e.g. fishing rod)

- Construction: a beam where the effort, load, and pivot point (fulcrum) are placed.- In each class, each one of these (L, E, F) exists on the left, centre, and right portions of the

beam.

- Mechanical advantage: an input produces an amplified output (the law of the lever)

Class 1 Class 2 Class 3

Magnifies force OR distance,

depending on which side of the

arm is longer.

Magnifies force when distance

(of arm) is increased.

Magnifies movement when

force is increased.

E.g. see-saw E.g. wheelbarrow E.g. arm, sweeping of a broom


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Inclined Plane: a ramp. Distance is extended to decrease the effort required to move a load.

- It is easier to raise something progressively than to lift it up the same distance in one hit.- On an inclined plane, W = mg*sin, where sin is angle of the ramp off the ground/resting

surface.

Screw: an inclined plane wrapped around a shaft (a long narrow beam)

- Screws magnify effort, but distance is greatly increased.Wedge: two inclined planes joined back to back. The two planes meet to form a sharp edge.

- Used to push two objects apart (including slicing through a surface)- Mechanical advantage is determined by the ratio of the length of its slope to its width. Short

wedges with wide angles do jobs faster but require more force. (length/width)

Wheel and axle: a large wheel/crank is connected to an axle, allowing heavy objects to be moved

more easily.

- The wheel reduces the amount of friction to the ground (as opposed to the flat surface of anobject)

o A larger wheel converts to a more powerful motion at the axle- It also acts as a lever:

o Force arm: radius of the wheelo Resistance arm: radius of the axleo Fulcrum: the axis of the axle (the line where the body rotates)

- Mechanical advantage is found in the ratio of the radial dimensions of the wheel and theaxle (wheel radius / axle radius).

o Bigger wheel -> more distance travelled -> more force.- Wheels are different to a rolling object: wheels require an axle.

Pulley: a wheel used to transmit force through the use of a belt/rope/cable

- Allows a change in direction of a forceo E.g. a rope is pulled down (rather than up) to move a load upo E.g. a vehicle (horizontal movement) pulls something out of the ground (vertical m.)

- Block and tackle: an arrangement of pulleys and rope, allowing a trade of force for distance.o Also transfers rotational movement from one shaft to anothero In simple calculations, friction and elasticity is not considered.o More pulleys mean more mechanical advantage, but there will also be more friction

and thus more resistance.


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Simple Machines continuum

Gears: circular devices with teeth that intermesh with one another

- Allows rotational motion to be transferred from shaft to shafto No. of gear teeth is proportional to radius of its circle.

This allows the gears to roll without slipping.

- Speed reducer: if the input gear (GA) has fewer teeth than theoutput gear (GB), GA must fully rotate more often to make one

full rotation of GB.

- Speed amplifier: if the input has more teeth than the output, then the output magnifies theinput torque.

- Types of gears:o Peg wheel gear: rounded pegs act as teeth. Uneven gaps cause a constant

acceleration and deceleration.

o Spur gear: small, straight teeth with slanted edgeso Helical gear: small, straight teeth that are cut an angle to the face of the gear

(slanted) diagonal rather than vertical teeth

o Bevel gears: straight/spiral teeth that allow gears to be well-connected atperpendicular angles. (shaped like a mushroom)

o Worm gear: used to create gear reductions. Worms can turn gears, but gears cannotturn worms due to its shallowness, causing friction. (a long cylindrical shape, shaped

like a screw's shaft)

o Rack and pinion gears: converts rotational movement into linear movement (shapedlike a tenon saw-blade)

- Involute: a special tooth profile that allows a constant speed ratio. The contact pointbetween teeth starts at the middle of one tooth and goes to its tip. During this, the other

gear's tooth contacts from the tip to the middle.

Mechanism: a device that transforms input forces into a desired set of output forces and movement

Materials

ENGINEERING VIEWPOINT: structure -> properties -> uses

Classification of Materials: classified by their properties, in terms of their natural occurrence (iron

ore), preparation (mild steel), atomic/crystal structure (thermoset), or in industrial applications.

-

Element: most simple material (cannot be further broken down). These simple matterscompose all matter, and often do not exist purely in their natural form.

- Solution: one substance dissolves into another. Exist as solids/liquids.- Compound: two or more elements chemically combined in fixed proportions- Mixture: two or more pure substances (element/compound) mixed mechanically without

any regard of fixed proportions

Metals and Non-metals

Metals Non-metals

Usually solid at room temp. (except Mercury, Hg) Solid/liquid/gas at room temp.

Lustrous (when freshly cut) Dull (if solid, except diamond)

Malleable, ductile Brittle (generally)


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Thermal/electrical conductivity (generally) Thermal/electrical insulators (usually)

Forms alloys May form compounds (not alloys)

Types of Materials

- Metals: most exist as ores and then refined to their pure form. Most are used as alloys(mixtures with at least one metal component)

o Natural occurring: e.g. gold, silver, copper, platinumo Ore-refinement: e.g. iron, aluminium, copper, lead, titaniumo Alloys: steel (iron, carbon), brass (copper, zinc), bronze (copper, tin), aluminium

bronze (copper, aluminium) duralumin (aluminium, copper), solder (tin, lead)

- Ceramics: naturally occurring materials (rocks) that are often used where metals are suitable(e.g. furnace linings, turbine/diesel engine).

o Igneous (volcanic rock): graniteo Sedimentary (compacting sediment): sandstone, shaleo Metamorphic (any rock converted to another structure by extreme

temperature/pressure): slate, marble

o Clayso Synthetic ceramics: requires purification/mixing/firing e.g. clay-body, glass,

refractories (non-metallic materials that retain strength at high temperatures),

cement

- Polymer: organic materials containing carbon as the primary constituento Natural polymers: shellac (resin organic secretion from plant/animal that is sticky,

flammable, insoluble in water), natural rubber, cellulose fibres

o Synthetic polymero Consider: Bakelite

- Biological: materials that are the result of plants/animals (organic, carbon-based)o Natural: wood, wax, leather, limestone (fossils, shells, sedimentary), diatomite (soft,

silicon dioxide sedimentary rock)

o Manufactured: paper, seasoned timber, wood products, lime, diatomite brickso Biofuelso Wool, silk, cotton

- Composite: different materials combined togethero Fibreglass: thermosetting matrix (main material) with glass fibres that offer tensile

strength.

o Carbon fibre: polymer with carbon fibreo Concrete: cement, water, aggregate (rocks)o Asphalt: mineral aggregate and bitumeno Cermet: ceramic (cer-) and metallic (-met) materials, e.g. used in electronics that

experience high temperatures

o Galvanised steel: iron (strength), zinc (sacrificial protection)


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o Plywood: natural and synthetic composite (laminate, glue, differing layers of woodveneers placed with grains placed perpendicularly)

Advantages: resistance to cracking, shrinking, splitting, twisting/warping,and high strength

o Laminex/HPDL: plastic laminate (paper), plastic resin. Applied on woodso Fibreboard (MDF): wood fibres combined with wax, resin binder (adhesive) no

grain pattern

o Particle board/chipboard: wood chips, sawmill shavings, saw dust combined withpressure and glue resin

o Geotextiles: permeable fabrics made from polymer (geo-)grids, used inenvironmental engineering

o Cemented tungsten carbide: carbide aggregate and metal matrix compositeo Bone: calcium phosphate (mineral) in a collagen (protein) matrix

Engineered product: any man-made product (does not necessary contain a simple machine)

- Polymers: any synthetic- Composites: fibreglass, carbon fibre

Properties of Materials

- Mechanical: mechanical testing, resistance to mechanical loadingo Strength: ability to withstand applied loads without failure

Compressive, tensile, shear, torsional.o Hardness: resistance to scratches, abrasion, indentiono Elasticity: ability to return to original shape and dimensions after subjected to a loado Stiffness: ability of material to resist elastic deformation under a loado Plasticity: ability to undergo some degree of permanent deformation without

rupture

o Malleability: ability of a material to be hammered and rolled (shaped)o Ductility: ability to be drawn into a thin wireo Fatigue: tendency for a material to break when subject to stresso Notch Toughness: measure of energy required to cause failure

- Chemical: chemical reactionso Metals: knowledge of alloying elements and impurities

Naturally exist as oxides, sulphides, carbonates metastable in metallicform

Revert to stable forms when exposed to aqueous solutions and atmosphericgases corrosion

o Polymers and ceramics: chemical breakdown from UV light- Physical: measured in terms of physical science

o Density: amount of matter packed per given volume (mass/volume) [kg/m3] Symbol of density () given by Greek letter rho Measures how heavy something is

o Porosity: measure of no. of voids/pores in a material Natural: timber Manufactured: porous bearings made by powder metallurgy


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o Moisture content: moisture present in the material's structure Moisture has effect on strength and thermal and electrical conductivity

- Thermal: thermal properties (note conductivity is only one property)o Conductors: metalso Insulators: non-metals

- Electrical: electrical propertieso Conductors: metals, carbono Insulators: air, glass, polymers, ceramicso Semiconductors: manufactured as poor conductors only allow small amounts of

current through. Silicon/germanium is infused with boron/arsenic, and produces a

deficiency [holes] or surplus of electrons to allow low current flow.

- Magnetic: magnetic behaviour from unpaired electrons. When electrons are paired the spinin opposite directions and their magnetism is cancelled.

o Diamagnetic: ionic/molecular materialso Paramagnetic: materials with a single valence electron (one outer shell electron)o Ferromagnetic: materials with large amounts of unpaired electrons, becoming

permanent magnets

Only iron, nickel, cobalt exist in this groupAtom Structure

- Electrons: smallest particle (mass)o Single negative chargeo Orbit the nucleus in shells (1st shell: 2 electrons, 2nd onwards: 8 electrons, although

more can exist in sub-shells)

o Valence electrons are used inbonding to make full shells

- Neutrons: heaviest particle (mass)o No chargeo Located in the nucleuso Creates isotope atoms if the regular

number of neutrons is different

- Protons:o Single positive chargeo Located in the nucleuso Mass 0.992 times that of a neutron

Atom Equations

- Atomic number: no. of protonso In a neutral atom: no. of protons = no. of electrons

- Mass number: no. of protons and neutronsSolids/Liquids/Gases

- Solid: ordered atomic structure, low energy level (lack of atom movement)o

Incompressibleo Slow diffusion (spreading)

oDefinite shape and volume

o Crystalline


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- Liquid: random atomic arrangement with no order, high energy levelo Minimally compressibleo Fast diffusion

o Takes shape of its container- Gas: random arrangement, very high energy level

o Compressibleo Rapid diffusion

o Expands to the limits of asealed container

Bonding: where electrons attempt to lost/found in order to create full shells

- Noble gases: atoms with full shells unreactive at normal temp/pressure- Primary bonds: metallic, ionic, or covalent- Secondary bonds: van der Waals- Metallic:

o Occurs between atoms with 1-3 valence electrons (metals). Bonding occurs (creatingpositive ions) and all valence electrons form an 'electron cloud'. The positive ion

(surface) repels each other but is held together by attraction to the electrons. This

equilibrium causes a crystalline structure (from three-dimensional bonding).

o Free electrons good thermal/electrical conductivity, and light photons are repelledgiving metals an opaque colour

o Differing forms of bonding causes malleability Carbon content adds strain cannot readjust, adds strength and brittleness

- Ionic:o Occurs between atoms with large differences in valence electrons (metals and non-

metals). Bonding creates a compound with an ordered structure from electrostatic

attraction (attraction between atoms of opposite charge).

o Donor atom: loses electrons, removing its outer shello Recipient atom: gains electrons, creating an outer shello Three dimensional bonding creates a lattice structureo E.g. ceramics (including glass) electrical insulators (no free electrons)

- Covalent:o Occurs between non-metals. Valence electrons are shared and both atoms receive a

full outer shell.

o E.g. polymers- Inter-molecular forces: van der Waals

o Imbalance in electron distribution to one sidecauses a weak charge in the overall atom

o Van der Waals are weak: 1% strength of aprimary bond

o London Dispersion Force: classifies all non-covalent van der Waals, such as in individual

atoms. This occurs because electron

movement is rarely in a balanced formation.

o Especially seen in dipoles: there are twopoles from unevenly distributed molecules two electrical charges (positive and

negative) e.g. H2O (water)

o Any van der Waal force containing hydrogen is also known as a stronger hydrogenbond, because the hydrogen atom only has one electron


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Strength and type of bonds:

1. London Dispersion (temporary)2. Dipoles (permanent)3. Hydrogen Bonds (permanent)

As order decreases:

- Higher molecular strength- Higher boiling point (more energy is required to

break bonds)

- Polymorphism (allotropes): for any material that can exist in many different crystalstructureso Can be vastly different in strength and behaviouro E.g. tin: soft metal at 13+ degrees Celsius, and a grey powder below this temp.o E.g. carbon: graphite (brittle, soft, self-lubricates), diamond (hardest substance)

Crystal structures:

- Crystalline materials: any structure with a regular ordered patterno E.g. all metals, some polymers, most ceramics, most mineralso Body Centred Cubic (BCC)o Face Centred Cubic (FCC)o Hexagonal Close Packed (HCP)

BCC FCC HCP

- Non-crystalline material:o When a material's solid state is non-crystalline/amorphouso Often unstableo E.g. sine polymers, ceramics, glass (cooled to rigidness without crystallising)

Metals

- Period table: 92 elements, 70 metalsFerrous material: contains iron as the primary constituent (as the main element)

- E.g. iron, cast iron (iron, carbon, silicon) , carbon steel, stainless steel (iron, chromium metal)- Also classifies pure iron (rarely used) and steels- Steels can also be grouped by carbon content- Mild steel: commonly used in domestic homes 0.15-0.25% carbon & manganese

o Easily formed, machined, and welded. Does not harden much. Ductile.o Uses in appliances: power plugs, screws (assembly), motor shafts (non-corrosive

environments), housing sheet steel appliances

- All steels (except stainless) will corrode (for ferrous materials, this is known as rusting).o Rust (metal oxide) is flaky (porous), causing further corrosion


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- Painting or electroplating is required for steels exposed to fluids, acidic/salty foods, unlessstainless steel or tin plating is used

Ferrous Metal What? (Content) Where? (Application) Why?

Cast Iron 2-4% carbon White C.I: for abrasion andwear resistance

Grey C.I: castings

White: hard, cheaper than

malleable iron

Grey: flows easily into complex

shapes

Wrought Iron 0.1% carbon (or less)1-2% slag

Ornamental ironwork, e.g.

fences, handrails

Easily welded and painted, slow

rust factor, tough and malleable

Low carbon Steel Up to 0.3% carbon Iron sheeting (due to easywelding and tooling)

Soft, ductile, easily machined

and welded, easily case/surface

hardened, worked hot or cold

Medium carbon Steel 0.3-0.5% carbon Machining and forging of parts Surface hardness and strength

High carbon Steel 0.5-1.05% carbon Machine and hand tools Withstands high shear stressand wear

Tool Steel 0.9-1.7% carbon Manufacturing of chisels,blades, taps, tools, razors

High hardness required to

maintain sharp cutting edges

High-speed Steel? Cutting tools Hard at high temperatures,

allowing deeper cuts

Alloy Steels Various elementsbetween 1-50%

Many uses, both as low- and

high- alloy

Hardness, toughness,

machinability, etc.

Table Summary:

- All steels are an alloy of iron and carbon. They are called carbon steelor simply steel.o Alloy steel: refers to a steel that is further made a new alloy with one or more other

elements added

E.g. tungsten -> tungsten steelor tungsten alloy- Pattern: steel contains less than 2% carbon, while cast iron contains more than 2%

Properties of Metals (applicable to any material): refer back to Mass and Force, and Mechanics

- Tensile Strength: resistance to being pulled by opposing forces- Shear Strength: resistance to opposing forces not acting in a straight line, e.g. scissors

o Controlled by the hardness of the metal- Compressive Strength: ability to withstand pressures acting on it in a given plane- Elasticity: ability of a metal to return to its original shape after forces have been applied on it

(stretching/pulling out of shape)

- Ductility: ability of a metal to be drawn or stretched permanently without rupture/fractureo Metals lacking ductility crack and break before bending

- Malleability: ability of a metal to be hammered, rolled, or pressed into a shape withoutrupture/fracture

- Toughness: ability of a metal to resist fracture, and failure when damage has beguno Tough metals can withstand stress either slowly or suddenly applied. They will

deform before failure.

- Hardness: ability of a metal to resist penetration and wearo Can be controlled by heat treatmento Greater hardness means machining the metal becomes more difficulto As hardness increases, toughness decreases, and thus, brittleness increases

- Machinability and Weldability: Ease or difficulty a metal can be machined or weldedo Interlinked with toughness

- Corrosion resistance: resistance to wearing away from exposure to air, moisture, agents


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- Heat and electrical conductivity: ease of heat and electrical transfer- Brittleness: tendency of a metal to fracture or break with little or no deformation, bending

or twisting. This is not a desired mechanical property.

o Usually, a harder material means a more brittle materialMethods of Marking Metals

- Stencilling: a stencil is a sheet with cut-out holes that make up text and images. Paint is usedto quickly mark this information on a metal surface (the paint only passes through the holes).

- Stamping: used only when stencilling not applicable. A portion of metal is cut out to indentthe required markings. Waste material should be kept at a minimum.

Non-ferrous material: where iron is not a primary constituent. (note it can contain iron)

- Copper:o High electrical conductivity good for electronics (second to silver)o Red-orange colouro High ductility and malleabilityo Good corrosion resistance

- Brass: (copper and zinc)o Can contain up to 40% zinc, but beyond this, it becomes brittle

Cartridge brass: 70% copper/ 30% zinc Muntz steel: 60/40

o All brasses are corrosion-resistanto Electrical appliances: switch gears, brass contactso Harder than copper, more durable in certain applications

- Bronze: (copper and tin)o An alloy of copper, tin and additions to improve corrosion resistanceo Used as commuters in motors, low maintenance bearings (using bronze powder)o Phosphorus phosphor bronze: 0.1-1% phosphorous additive, used for spring and

switch contacts

- Aluminium and its alloys:o Lightweighto Corrosion-resistant under most conditions (due to layer of aluminium oxide)o Can be cast-forged, machined, and easily welded

- Aluminium bronzes: excellent corrosion properties at room temp, good wearing prop,golden colour. Used as brush holders in electric motors, gear wheels, moving contacts.

- Magnesium: strength, lightweight, shock/vibration resistance, good machinability- Lead: low strength, heavy weight. Used in electrical equipment, various chemical

compounds, X-ray protection (radiation shields).

- Tin: Can be die cast (see below), cold worked, machined, soldered, but cannot be welded.Used to coat steel or as an alloying element (bronze [copper-tin], solder [tin-lead]).

Basic forming processes

Casting: melting (furnace) -> pouring (moulding) -> cleaning (inspection) -> finishing

(machining/cutting, heat treatment, painting/coating, assembly)


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- Material, such as a metal alloy, is heated up. This is placed in a mould made of metal or sand(expendable moulds), either by gravity pouring or through pressure.

- Die casting uses permanent moulds and is used in non-ferrous alloy casting. Molten metal isforced into the mould cavity at high pressure.

- Investment casting/lost-wax casting is an old technique. A wax model is made and then aceramic shell is formed around it. The wax is then melted and the hollow shell is left behind,

for casting.

Polymers are also formed in their molten state, but this is called moulding, not casting.

- Injection: material injected into a mould and forced to cool.- Blow (for hollow containers): plastic is melted within a sealed mould and compressed air is

passed in, pushing the plastic to the edges of the mould.

- Extrusion: plastic is melted through a screw and forced out through a hole (die), beforecooled to shape the final product.

Extrusion: in a water-cooled mould, metals at an elevated temperature are passed out a die and

form a final tube-structure in the shape of the die.

- A ram applies the compressive force that forces out the metal- No tensile forces mean high deformations without the risk of fracturing the extruded

material. Gives the desired cross-sectional area and a good surface finish, meaning no

machining is required.

- E.g. aluminium alloy window constructionRolling: metal is passed through smooth rollers to change its thickness and cross-section into longer

lengths, before it is then water cooled with spray.

- Rolling changes casted ingots/bars into more useful forms, e.g. short rectangular bars intolong circular cross-sections

- Hot rolling: rolling done at high temp.o Easier to do, resultant bar is unstressed by deformation.o Dimensions are less accurate and often covered in scale and oxide (that forms at the

elevated temperature)

- Cold rolling: rolling done at a slightly elevated temperatureo Harder to do, resultant bar stressed by deformationo Better surface finish and dimensional accuracy

Cutting: see Joining and Cutting Methods

Joining: see Joining and Cutting Methods

Fabricating: the process of assembling an item from various components

- This is used when casting of an item is too difficult/impossible- E.g. welding of mild-steel components

Joining and Cutting Methods

Metallurgical Methods:

- Soft soldering: tin-lead alloy (probably out-dated) joins two pieces of metal together, withlittle microstructural change.


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o Solder melts at 183 degrees Celsiuso 60% tin, 40% lead: solder optimised for joining electrical wires

More tin, more expensiveo Provides joint strength, optimised with a flux (cleaning agent) e.g. resin. Solder in

wire form places resin at the centre of the wire to wet the joint and clean it

- Brazing/silver soldering: stronger joints than soft soldering, but requires higher temp. Stillrequires a flux to alloy at the interface.

o Brazing: brass melted onto a ferrous metal, at 860 degrees Celsius. Surfaces must beclean and the joint design must use capillary action (molten filler metal is drawn into

a small gap) to draw the molten brazing alloy into the joint and maximise joint

strength.

o Silver: similar to brazing, allows the molten alloy to flow more smoothly. Melts at620-750 degrees Celsius. Used to join dissimilar parent metals.

- Welding: similarities are colour-codedMethod Type Method Uses

Spot welding PressureElectrical current melts metal sheets

under pressure and makes spots.

Joining sheet-metal

cases

Butt welding

(butted -> joined)Pressure

Electrical current welds two metal

sheets by their edges instantaneously.Joining tubes

Seam welding Pressure

Electrical current welds two metal

sheets by their edges progressively.

(uses rotating wheels)

Manufacturing pipes

Oxy-acetylene welding Fusion

Metal melted by an oxy-acetylene

flame and a filler metal added.

(now rarely used for appliances)

Joining steel fan cages

Bronze weldingFusion

Alloying

A flame (usually oxy-acetylene) heatsthe parent metal, and a bronze filler

metal is added into the joint.

(parent metal not melted, unlike oxy-

acetylene welding)

(similar to brazing)

Like oxy-acetylene

welding, used in low

strength applications

Electric arc welding Fusion

Filler metal is melted by an

electrode's arc (electrical spark) into

the joint of another metal. Flux

prevents the weld metal oxidising

when melted.

Joining steel in thick

sections, in small run

appliances.

Metal Inert Gas (MIG) Fusion

Filler metal is melted by a continuousfeed wire into another metal's joint.

Inert gas protects from oxidation.

(quicker welding)

Welds aluminium.

(more automated

process)

Tungsten Inert Gas

(TIG)Fusion

Filler metal is melted by a tungsten

electrode and filler rod into another

metal's joint. Inert gas protects from

oxidation.

Welds aluminium and

stainless steel

(cross of electric arc

and MIG welding)

Plasma arc welding Fusion

(Argon) gas is passed through an

electric arc and ionises electrons and

positive ions (creating plasma). The

ions recombine and cause a hotflame. (used for refractory metals)

Speciality use, due to

metals and costs


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Mechanical joining: used instead of metallurgical joining when structural change (in melting the

metal) is to be avoided

- Fastening of metals: bolts and nuts, screws, studs and rivets (types of bolts)- Special types of nuts and washers (metal rings) resist being undone- Drawback: metals are weakened due to drilling. Greater possibility of corrosion from

exposure and from usage of dissimilar metals.

Cutting methods: the removal of unwanted material

Operation Outline of processes Machines used

TurningRotation of work piece and a tool piece removes

unwanted material.Lathe

Grinding Abrasive wheel removes unwanted material Grinder

Sawing Saw tears/cuts material away

Hacksaw

Bandsaw

Cold cut-off saw

Drilling Drill piece creates a hole in the material Drill press

Boring Modified cutting piece creates a hole in the materialLathe

Boring mill

ReamingRemoval of burrs (ragged edge)/scratches from a drilled

hole, using a cutting tool

Lathe

Drill press

Boring mill

Interior grinding Removal of burrs/scratches from a drilled hole using anabrasive tool

Cylindrical grinder

ShapingA machine moves a tool horizontally across a stationary

work piece. After each pass the work piece is moved.Shaper

Milling

Slab milling: a tool removes waste from a horizontal

work moving into a spinning cutterMilling machine

Face milling: a tool removes waste from a work piece by

using a spinning tool with a cutting tip

Polymers (plastics)

Polymer:

Rivets


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- Solid materials made from long molecular chains composing smaller molecules connectedtogether

o Many (poly-) small repeating units (-mer) connected together- Usually covalently bonded, as a result they are good insulators of electricity and heat, but

low temperature stability

Formation of Polymers

- Addition polymerisation: monomers combine together using heat, pressure, or a catalyst.Unsaturated bonds (repeated bonds with themselves e.g. double bonds) are broken and re-

formed

- Condensation polymerisation: monomers combine together but small molecules are lost inthe process to condense and form a by-product

Polymer Structures

- Thermoplastics: (thermosoftening polymers)o Simple additional structureso Covalent bonds form the polymer chains, and weak van der Waals form the

secondary bonds between the chains

o Can be resoftened by heat, where the weak secondary bonds break. Thermoplasticbecomes viscous (thick and sticky, between solid and liquid)

o E.g. polyethylene, PVC, acrylic, PTFE/Teflon and ABS- Thermosets: (thermosetting polymers)


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o Cross-linking covalent bonds occur for both the polymer chains and the secondarybonds

o These covalent bonds cannot be reheated and reshaped the energy required tobreak these bonds would char the material

o Controlling the cross-linking in thermosets, with heat/pressure or catalysts (coldsetting), can create differing properties

o E.g. Bakelite (first synthetic thermoset), or epoxy, GRP, polyester resins

Polymer Properties Uses

Acrylonitrile butadiene styrene

ABS

Good tensile strengthCan be chrome (electro-) plated

for corrosion protection or

increasing surface hardness

Good impact resistance

Motorcycle helmets

Mobile phone casing

Car fixtures (bumpers)

Lego bricks

Nylon

High elongation (lengthening)

Good specific strength

Abrasion resistant

Rope

Airbags, seatbelts

Clothing, stocking/hosiery

Polycarbonate

High impact resistance

Low hardness

Good optical properties

Screens, glasses, bottles

Windows (for impact strength)

Mobile phones

PolyethyleneChemical resistanceModerate strength

Available in different densities

Bottle capsFuel containers, water pipes

Garbage bins, plastic bags

Polymethylmethacrylate

Acrylic

Good optical properties

Good strength

Poor impact resistance

Reading glasses

Signs

Skylights

Polypropylene

Good formability

Tough

Resistant to cyclic loading

Packaging

Textiles

Kettles

Polytetrafluroethylene

TeflonLow coefficient of friction

Non-stick surfaces

High temperature plastics

Polyvinyl chloride

PVC

Good strength

Rigid

Durable fabric with plasticisers

(additives that increase

plasticity/fluidity)

Electrical insulation

Seat coverings

Flexible (with plasticisers)

Ceramics

- Ceramics are no longer extensively used in appliances replaced by polymerso Electrical and thermal insulation propertieso Resistance to chemicals

Types Used


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- Clay body ceramics: wet clay is moulded to its required shape, then fired (with glaze) to ahigh temperature until they melt together on a molecular level.

o Porcelain/china: kaolin (clay) fired to 1400 degrees Celsius 1% porosity usage in chinaware Electric insulation material Building material (tiles)

- Glass: made primarily from silicon oxide. It is an inorganic fusion product where molten glassis cooled without crystallising (making it non-crystalline/amorphous)

o Better scratch and stain resistanto More expensive than other ceramicso Soda-lime glass: used as flat glass (windows) and container glasso Glass-ceramic: produced through controlled crystallisation of base glass.

Medium alumina/silica glass (90% crystalline, pore-free) is added with anucleation agent (promotes crystallisation) like TiO2, and then heat-treated

to promote recrystallisation. Properties:

Good mechanical strength and toughness (durable, impact resistant) Low thermal expansion rate (withstands sudden temperature

changes)

Uses: ceramic-glass cooktop- Refractories: materials with stability at high temperatures. Most refractories are ceramics.

o Used in ovens, furnaces.Composites

Timber:

- A naturally occurring composite made up of a lignin (organic polymer) matrix and reinforcedby cellulose (glucose) fibres.

- It makes up many other composites, called engineered (manufactured) woods, includingplywood, fibreboard, and particleboard (unlike fibreboard, it is grainier/lower quality)

(see previous section)

- Uses: wood fuel, construction (housing frames, support materials, boats), furniture, utensils(wooden spoon, chopsticks), sports equipment (cricket bat)

- Reasons for usage: natural (non-toxic, biodegradable), renewable, low in production energy,insulation, easily available and worked (light, simple equipment)

Concrete

- Composite of aggregate, cement, water- Uses: architecture and foundations/walls, pavements, dams/pools, fences and poles, boats- Reasons for usage: withstands compression, workable, durable, mouldable, cheap, corrosion

resistant (silo production, etc.) abrasive resistance

o Disadvantage: weak under tensionDrawings:


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Isometric Oblique

- Pictorial: three dimensional images in one view- Orthographic: two dimensional images showing a variety of views

E.g. view from left, is on the right. E.g. view from left, is on the left.

FAP-O:first angle is the opposite TAP-S: third angle is the same (easier to read)


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Others:

- Perspective: uses points in the distance rather than in isometric and oblique drawings- Sectioned view: a drawing of the object cut in half. Can be considered a cross-section- Exploded view: components are shown separated rather than combined- Freehand drawing: conveys ideas in an impromptu manner. Can be done without usage of

any drawing instruments.

o Start with light construction outlines and then continuous lines to firm ino Always look where you are drawingo To draw freehand circles, start drawing radiuses from the centre with dashes to mark

distance, before joining the dashes together

Documents

Materials Notes (T1) - 11 Engineering Studies