1 - Engineering Materials

strength

the ability of a material to resist an applied force

tensile strength

the maximum pulling/stretching force a material can withstand before failure

yield strength

the amount of stress at which the material will start to permanently deform

ultimate tensile stress (UTS)

the stress at which the material eventually breaks

compressive strength

the resistance of a material under a compressive/pushing force

ductility

the amount a material can be deformed when applying tensile force

malleability

the ability of a material to be deformed without rupturing or splitting

hardness

the ability of a material to resist wear and abrasion

toughness

the ability of a material to withstand an impact without breaking

brittleness

the potential for a material to shatter when it experiences an impact

stiffness

the ability of a material to resist bending

how is stiffness measured?

with young’s modulus

young’s modulus

young’s modulus = stress/strain

E = σ/ε

metal

a type of material typically made by processing an ore that has been mined/quarried

ore

an oxide of a metal, in the form of a rock

alloy

a mixture of two or more metals

ferrous

a material that contains iron

non-ferrous

a material that doesn’t contain iron

characteristics of cast iron (elements, properties, typical uses)

elements - 3-3.5% carbon

properties -

• good compressive strength

• hard, difficult to machine

• suitable for casting

• rusts easily

• relatively low cost

uses - anvils, engineering vices, engine blocks

characteristics of low-carbon steel (elements, properties, typical uses)

elements - less than 0.3% carbon]

properties -

• lower strength than other steels

• stronger than most non-ferrous materials

• tough and relatively low cost

uses - nails, screws, car bodies

characteristics of high-carbon steel (elements, properties, typical uses)

elements - 0.8-1.4% carbon

properties -

• strong and hard

• not as tough as low-carbon

• difficult to form

uses - saw blades, hammers, chisels

characteristics of stainless steel (elements, properties, typical uses)

elements - at least 11.5% chromium

properties -

• strong and hard

• difficult to machine

• good corrosion resistance

• relatively expensive

uses - knives and forks, medical equipment, sinks

characteristics of aluminium and its alloys (properties, typical uses)

properties -

• light

• ductile

• malleable

• good conductor

• corrosion resistant

uses - aircraft bodies, saucepans, cooking utensils, foil, cans

characteristics of copper [pure metal] (properties, typical uses)

properties -

• malleable

• ductile

• tough

• good conductor

• easily joined

• corrosion resistant

uses - electrical wire, hot-water tanks, printed circuits

characteristics of brass [65% copper, 35% zinc] (properties, typical uses)

properties -

• corrosion resistant

• good conductor

• easily joined

• casts well

uses - castings, forgings, ornaments, boat fittings

characteristics of bronze [90% copper, 10% tin] (properties, typical uses)

properties -

• tough

• hardwearing

• corrosion resistant

uses - bearings, castings for statues, coins, water and steam valves

characteristics of lead [pure metal] (properties, typical uses)

properties -

• malleable

• heaviest common metal

• corrosion resistant

• low melting point

• easy to work

uses - soft solders, roof coverings, protection against radiation

characteristics of zinc [pure metal] (properties, typical uses)

properties -

• poor strength-weight ratio

• low melting point

• extremely corrosion resistant

• easily worked

uses - galvanising

cold working

repeatedly bending or hammering a metal

work hardening

an increase in the strength and hardness of a metal due to cold working

annealing

a heat treatment that makes a metal softer and easier to work

quenching

the rapid cooling of a hot metal by immersing it in a liquid, often oil or brine

tempering

a heat treatment to remove some of the brittleness in a hardened steel at the cost of some hardness

hardening

a heat treatment that increases the hardness and strength of a metal due to a change in the arrangement of the atoms

carburising

the addition of carbon to the surface of a low carbon steel to improve hardness and strength

corrosion

a reaction between the surface of a metal and its environment that eats away some of the material

hardening step by step

1. heat metal to cherry red

2. put in powder for 10 minutes

3. repeat 1 and 2 three times

4. clean off carbon with wire brush

5. heat to cherry red

6. quench in water

polymer

a type of material made from a large number of similar, smaller chemical units that are bonded together

thermoplastic

a type of polymer that can be reshaped when heated

thermosetting polymer

a type of polymer with crosslinks between the polymer chains; it cannot be reshaped when heated

name 5 thermoplastics

ABD, acrylic, nylon, polycarbonate and polystyrene

name 5 thermosetting polymers

epoxy, polyester resin, melamine resin, polyurethane and vulcanised rubber

name four ferrous alloys

cast iron, low-carbon steel, high-carbon steel, and stainless steel

name six non-ferrous alloys

aluminium (and its alloys), copper, brass, bronze, lead and zinc

characteristics of abs [acrylonitrile butadiene] (properties, typical uses)

properties-

• strong

• rigid

• twice the price of polystyrene

uses - plastic pipes, children toys, keyboard key caps

characteristics of acrylic (properties, typical uses)

properties -

• good optical properties (can be transparent)

• hard wearing

• will not shatter

uses - plastic windows, bath tubs, machine guards

characteristics of nylon (properties, typical uses)

properties -

• good resistance to wear

• low friction qualities

• ductile

• durable

uses - gear wheels, bearings

characteristics of polycarbonate (properties, typical uses)

properties -

• high stress and toughness

• heat resistant

• excellent dimensional and colour stability

uses - safety glasses, DVD's exterior lighting fixtures

characteristics of polystyrene (properties, typical uses)

properties -

• good toughness and impact strength if high grade

• good for vacuum forming, injection moulding or extrusion

characteristics of epoxy (properties, typical uses)

properties -

• high strength

• stiff and brittle

• excellent temperature, electrical and chemical resistance

characteristics of polyester resin (properties, typical uses)

properties -

• good strength and stiffness

• brittle

• good temperature, chemical and electrical resistance

• lower cost than other resins

uses - bonding/encapsulation of other materials, suitcases/luggage

characteristics of melamine resin (properties, typical uses)

properties -

• stiff

• hard

• strong

• resistant to some chemicals and stains

uses - laminate coverings for kitchen worktops, impact-resistant plastic plates

characteristics of polyurethane (properties, typical uses)

properties -

• hard with high strength

• flexible and tough

• low thermal conductivity

uses - foam insulation panels, hoses, surface coatings and sealants

characteristics of vulcanised rubber (properties, typical uses)

properties -

• higher tensile strength

• elastic

• resistant to abrasion and swelling

uses - tyres, shoe soles, bouncing balls

difference between a thermoplastic and a thermosetting polymer

a thermoplastic can be reheated whist a thermosetting polymer cannoy

composite

a type of material made by combining two or more different types of material which remain physically distinct within its structure

reinforcement

the particles or fibres within a composite matrix that increases its strength

matrix

holds the reinforcement, making it rigid

thermosetting polymers are normally found as…

liquids or granules that will form the polymer when mixed together

which type of polymer can be recycled?

a) thermoplastics

b) thermosetting polymers

thermoplastics

common types of reinforcement

• fibres or strands

• layers of material (plies or laminates)

• particles

characteristics of carbon-fibre reinforced polymer [CRP] (description, properties, typical uses)

description - carbon fibres in a resin matrix

properties -

• extremely high strength and rigidity

• low density

• expensive to produce

uses - racing bicycles, helmets

characteristics of glass-reinforced plastic [GRP] (description, properties, typical uses)

description - glass fibres in a resin matrix

properties -

• high strength

• low density

• good chemical resistance

• lower cost than CRP but weaker

uses - canoes, water tanks

characteristics of plywood (description, properties, typical uses)

description - made from layers of wood bonded to each other at 90º using adhesive

properties -

• smooth even surface

• good strength

• may be covered in veneer

uses - furniture, exterior grades used for boat building

characteristics of medium-density fibreboard [MDF] (description, properties, typical uses)

description - manufactured from wood fibres and an adhesive matrix

properties. -

• smooth, even surface

• easily machined and lower cost than plywood

• can be painted or veneered

uses - internal panels for furniture

characteristics of oriented strand board [OSB] (description, properties, typical uses)

description - manufactured from strands of wood compressed with adhesive matrix

properties -

• same as plywood but more uniform and lower cost

uses - roof decking

characteristics of structural concrete (description, properties, typical uses)

description - concrete reinforced with steel bars

properties -

• better tensile strength than ‘pure’ concrete

uses - high-rise buildings

if all the reinforcement is aligned in the same direction then..

the strength will be stronger in that direction and weaker in others

timber

wood; a type of material obtained from trees

properties of ceramics

• good strength in compression

• low tensile strength

• very low ductility

• brittle

• excellent resistance to corrosion

• very hard

ceramic

a type of material that is typically an oxide, nitride or carbide of a metal

form

shape and dimension of a material

renewable

a sustainable resource that is either not consumed as quickly as it’s used or is quickly replaced

non-renewable

a finite resource that is consumed as quickly as it’s used, and is not quickly replaced

why are standard material bought rather than made in the exact size needed?

it’s cheaper as they would need additional matines and skill

why is copper used over gold for electrical wiring?

gold has a higher electrical conductivity, however is way more expensive than copper

why is low-carbon steel used for scaffolding over structural timber?

although structural timber has a lower weight per volume, higher strength to wait ratio costs less, and is easier to attach together, it softens and rots when used outside, compared to steel that rusts way more slowly and can be reused.

why aren’t ceramics like tungsten carbide used over steel for cutting tools in machining centres?

although ceramics are harder than steel, so they offer better resistance to wear, they are more expensive and can be brittle and may shatter if accidentally driven into the material being machined

fossil fuels - a+d

advantages -

• reliable technology

• energy can be produced as needed

disadvantages -

• creates pollution/gases that contribute to global warming

• price may increase as they’re used

nuclear energy - a+d

advantages -

• produces continuous supply of electricity at low cost

• can respond to changes in demand

disadvantages -

• materials cause damage if released into environment

• waste produced remains hazardous for hundreds of years

• expensive to build due to number of safety systems needed

wind power - a+d

advantages -

• produces electricity at very low costs

• only cost is to produce and maintain turbines

disadvantages -

• depends on wind so energy needs to be stored

• unaesthetic and spoils landscape

tidal power - a+d

advantages -

• more consistent than wind power as tide is always moving

disadvantages -

• expensive

• may have adverse effect on local ecosystem

solar power - a+d

advantages -

• sustainable

disadvantages -

• cannot generate electricity at night

• a large area is need to generate power; cost of land is an important factor

biomass - a+d

advantages -

• sustainable

• much of biomass used for fuel would be wasted if not use

disadvantages -

• less efficient than fossil fuels

• by-products include gases that contribute to global warming

engineered lifespan

the amount of time a product is designed to last

planned obsolescence

designing a product so it’ll have a limited lifespan

sealed parts

parts enclosed in compartments that cannot be easily accessed, so the whole product must be replaced

maintenance

activities which extend the life of a product

reactive maintenance

repairing broken parts

proactive maintenance

carrying out actions that will prevent a product from failing

lubrication

using a fluid or other substances to reduce friction and wear between moving parts

ways to avoid/prevent corrosion

• regular cleaning to remove materials and chemicals

• applying protective coating (paint, oil)

compensating for wear

adjusting the position of some parts to allow for wear, especially in products with complicated moving parts

EOL disposal and recovery

replacing parts before they fail (eg batteries when they reach a certain charge level, so device that they’re powering never fails)

how are statistics used in maintenance

to predict service intervals and lifespans of components, to see how long they'll work before needing replacement

how is cost affected?

• limits on the material (trade restrictions)

• greater demand than supply

• supplier has gone out of business

how does user requirements affect material choice and manufacturing process?

users might want a certain look or material (eg using materials with higher strength and lower weight) which affects the manufacturing process