Module ME2019
Engineering Materials
Second Semester 2016-2017
Lecture 2
The ‘family’ of engineering
materials
Richard T Booth
30 January 2017
The engineering materials ‘family’



Metals
Polymers
Elastomers




Both above include
natural and
synthetic
materials
Ceramics
Glasses
Hybrids (combinations
of materials; definitions
vary)



What they are made of?
Much more importantly,
what are their properties?
Leading to:
 What are their
strengths and
weaknesses when
used for ‘engineering’
components,
products, and
structures?
The engineering materials family (simplified)
Reproduced from Ashby et al
Simplified
version
What’s
missing?
stiffness
& density
not the
whole
story: see
Ashby
Materials and products

Three questions:
1.
2.
3.


What are the properties I am looking for?
What classes of materials are most likely to deliver what
I am looking for?
What is the detailed chemical composition – how does
the composition affect the properties?
Question 1 more important than 2. Question 3:
does it matter? Yes, but just for materials scientists
What makes me incredulous:



Huge range of materials available
Wide range of products that can be made from specific
materials, or classes of materials
Same products: choice of widely-different materials
Materials and products

Five minute ‘brainstorming’ question:

Write down all the material properties you
can think of





In addition to stiffness and density
By yourself or with your neighbours (all make
notes)
Quick feedback
Don’t throw away your list (added to from
feedback)
If a few send their list to me, I will prepare a
consolidated slide (structured like mine). Though
some item on your list might be left out
Metals

Pure crystalline solids

Many metals are alloys, ie, a combination of a pure metal
and other elements (eg, iron and carbon)

Pluses: stiffness, ductility, ‘strength’, good conductors

Minus: corrosion; ‘heavy’
Polymers (‘plastics’)




Organic solids –
long chains of
carbon (usually)
Pluses: strength /
weight,
manufacturing
ease
Minus:
temperature
effects and range
Are some natural
materials polymers
(or hybrids)?
Elastomers




Polymers but those with
mega low stiffness
Pluses: elasticity (eg, rubber
bands)
Minuses: As polymers plus
‘perishing’ in storage
Ceramics





Non metallic inorganic solids
Both ‘solid’ and porous
Pluses: stiff, hard, abrasion-resistant, high
compressive strength, good insulators,
solid at high temperatures
Minus: highly brittle; low tensile strength
https://en.wikipedia.org/wiki/Ceramic
Glasses

Non-crystalline
ceramic




Soda-lime and
borosilicate
Pluses: hard,
corrosion-resistant,
insulators,
transparent; flavour
retained in drinks
Minus: highly brittle
(no crystal structure
so ‘zero’ ductility)
Topic for mini project
What are ‘natural’ materials?





Many sources say ‘Polymers’
Ashby describes them all as ‘Hybrids’ (bones certainly
are)
What matters is that natural materials are originally
‘alive’, eg, can repair (skin lesions and bone fractures in
particular)
What matters more are the properties of natural
materials in practical applications:
 Wood; wool; leather; silk (parachutes); rubber
Don’t let semantic distinctions ‘get in the way’
it’s what different materials can do that counts
Hybrids

Usually combination of two or more of
the other materials


Glass (below) and carbon fibre reinforced
plastics (GFRP; CFRP)
Natural materials are strictly hybrids. They
are not just polymers (see above)
Hybrids

Pluses:


Optimum combinations
of combined properties
Minuses:

Often expensive,
manufacturing of
hybrids problems
Carbon fibre (right)
Wood (next slide)

Wood pluses



Usually cheap
Sustainable
Hugely versatile
Wood
Royal Theatre, Windsor: fall from height

Theatre refurbishment

Open trapdoor covered by
strong multi-ply plywood

Someone replaced
plywood with weak fibre
board (similar dimensions)

IP fell through trap door
and landed on stage
 Did ‘someone’ think
that fibre board as
strong as plywood?
 Or indifferent?
Motor bike and pedal cycle materials:
Mini project 1
Screen
Fuel tank
Seat
Mirror
Brakes
Fairing
Frame
Chain and
sprockets
Tyres
Reproduced from Ashby et al
Mini-project 1

For a high performance motor bike AND pedal
cycle

AND for a ‘basic’ motor bike AND pedal cycle

Overall design criteria: USPs and market?

What materials have or might have been chosen for
specific components (see next page)? And WHY?

What are the properties of these materials that have
led to their possible adoption – and conflicts?

Key failure modes of all materials considered?
Materials and Components

Choose three parts (m/b) two parts (p/c) from:



Frame
(Fuel tank)
(Engine component, eg: cylinder block; cylinder
head; valves; crankshaft)

(Spark plug)

(Exhaust system / silencer)
Suspension
Chain and sprockets
Brakes (‘disc’ and pad)




Note that electrically-assisted push bike adds to
above categories – notably electric motor and
battery materials
Materials and Components

Choose two parts from:








Rear tyre
(Fairing)
(Windscreen)
Lights and reflectors
‘Mudguards’
Seat
Crash helmet
Protective clothing
Mini-project 1






Work in teams (up to six – self-select)
Contact me (with ppt) if you would like to
present your views
Target for reports: Thursday 23 February; but
later submissions OK
Will give brief feedback only
But will try and give more feedback for all
prospective presentations
A closely-related question will be in the exam
Mini-project 1



Alternatives to motor bikes OR push bikes (by
arrangement only)
Open-top car (three years ago)
Other form of transport (with wheels)
Material failure case studies
Hatfield Train Crash
Rail buckling
Flixborough Explosion
Liberty Ships
Concluding remarks
Port Talbot blast
furnace + explosion
Port Talbot blast
furnace explosion –
the aftermath
53
Concluding remarks