ENMAT101A Engineering Materials and
Processes
Associate Degree of Applied Engineering
(Renewable Energy Technologies)
Lecture 2 – Material Properties
www.highered.tafensw.edu.au
TAFE NSW -Technical and Further Education Commission
Properties of Materials
Reference Text
Section
Higgins RA & Bolton, 2010. Materials for Engineers and Technicians
Ch 2
Additional Readings
Section
Sheedy, P. A, 1994. Materials : their properties, testing and selection
Ch 3, Ch5
Callister, W. Jr., 2010, Materials Science and Engineering
Ch7
EMMAT101A Engineering Materials and Processes
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Properties
A property is characteristic of a material. It should be
about the same for any piece of the material.
PROPERTY
NOT A PROPERTY
Density
Mass
Stiffness
Length
Hardness
Wear
Strength
Force
Some properties can be measured easily, others
may require breaking a specimen.
EMMAT101A Engineering Materials and Processes
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Example Properties
• Hardness: Diamond, Hardened Steel
• Density: Plutonium, Lead
• Toughness: Mild Steel, Kevlar
• Elasticity: Rubber, steel, glass(!)
• Ductility: Plastics, Nickel, Copper,
• Conductivity: Silver, Copper, Aluminum
• Resistivity: Plastics, Glass, Ceramics
• Linear Expansion Coeff: Polyethylene
• Corrosion Resistance: Ceramics, titanium, polymers
HARDNESS
Ball Bearing SKF
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Classes of Properties
• Mechanical properties: most are related to forces applied to the
material, e.g. strength, stiffness, hardness, toughness…
• Electrical properties: resistivity, conductivity
• Magnetic properties:
• Thermal properties: expansion, heat capacity.
• Optical properties: transparency, refractive index.
• Aesthetic properties: appearance, texture.
• Chemical properties: reactivity, corrosion resistance, chemical
compatibility, degradation.
EMMAT101A Engineering Materials and Processes
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Basic Formulas 1
Density (kg/m3) = Mass (kg) / Volume (m3)
r=m/V
Varies with temperature;
• Slightly for solids.
• About x10 for liquids.
• By gas law for gases.
Material
ρ (kg/m3)
Air
1.2
Styrofoam
75
Cork
240
Ice
916.7
Water (fresh)
1,000
Aluminium
2,700
Titanium
4,540
Iron
7,870
Lead
11,340
Tungsten
19,300
EMMAT101A Engineering Materials and Processes
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Basic Formulas 1
Density (kg/m3) = Mass (kg) / Volume (m3)
r=m/V
Varies with temperature;
• Slightly for solids.
• About x10 for liquids.
• By gas law for gases.
DENSITY INCREASES AS VOLUME DECREASES
Tim Lovett
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission
Basic Formulas 2
Stress (MPa) = Force (N) / Area (mm2)
s=F/A
Tensile Stress: Pulling
Compressive Stress: Squashing
Shear Stress: Sliding
Tensile Stress
Tim Lovett
EMMAT101A Engineering Materials and Processes
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Basic Formulas 3
Strain () = Elongation (mm) / Original Length (mm)
e = e / Lo
Strain has no units.
Low elastic strain in metals.
Elongation
Tim Lovett
Elongation
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Basic Formulas 4
Stiffness (Mpa) : Stress (Mpa) / Strain ()
E=s / e
Many names;
• Young’s Modulus
• Modulus of Elasticity
• Stiffness Modulus
• Modulus !
•Usually a BIG number (GPa)
Higgins 2.2.1 Table 2.1
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Mechanical Properties
Strength: Ability to endure stress – the
intensity of force.
Stress (Pa) = Force (N) / Area (m2)
s =F/A
• Ultimate Strength: Highest stress
without breakage.
• Yield Strength: Highest stress without
deformation.
TENSILE STRESS
TL
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Mechanical test of the strength of mild steel.
Stress / Strain Curve for Mild Steel
www.nmu.edu
Tim Lovett
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission
Mechanical test of the strength of mild steel.
Ultimate
Tensile
Strength
UTS
Yield
Strength
YS
Stress / Strain Curve for Mild Steel
Tim Lovett
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Alternative to Yield Point
Yield point. A levelling off on the stressstrain curve as plastic deformation
begins.
1.True elastic limit: The first hint of
atomic slip. Hard to measure because
some atoms move easily.
2. Proportionality limit: End of straight
line (Hooke's law).
3. Elastic limit (yield strength) Where
permanent deformation will occur. The
lowest stress at which permanent
deformation can be measured. This
requires a manual load-unload procedure,
and the accuracy is critically dependent
on equipment and operator skill.
4. Proof Stress (Offset yield point).
When a yield point is not easily defined.
Alternative Yield definitions for materials that do
not exhibit a well-defined yield point.
Wikipedia
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Proof Stress (Offset yield point)
Some materials do not show an
obvious yield point. E.g. high
strength steels and aluminium.
In this case, an offset yield point is
used, with an offset of 0.1 or 0.2% of
the strain.
The real elastic limit…
You have an unknown material and a
tensile tester. How do you find the
yield point.
Proof Stress as alternative to Yield Stress
Tim Lovett
EMMAT101A Engineering Materials and Processes
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Stress grade 8.8
embossed on bolt head.
Hydraulic tensioning of
foundation bolts of wind
turbine tower.
Nut torquing
www.torcup.com
Grade 8.8 Bolt
Hebei Saite Fastener Co., Ltd.
EMMAT101A Engineering Materials and Processes
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Stress grade 8.8
embossed on bolt head.
4.6 = 400 Mpa and 60% YS
8.8 = 800 Mpa and 80% YS
10.9 = 1000 Mpa and 90% YS
12.9 = 1200 Mpa and 90% YS
Grade 8.8 Bolt
Hebei Saite Fastener Co., Ltd.
EMMAT101A Engineering Materials and Processes
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Stress grades of bolts.
4.6 = 400 Mpa and 60% YS
8.8 = 800 Mpa and 80% YS
10.9 = 1000 Mpa and 90% YS
12.9 = 1200 Mpa and 90% YS
Higher grade bolts have
lower ductility.
Grade 8.8 Bolt
Hebei Saite Fastener Co., Ltd.
Tim Lovett
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission
Tensile Strength (UTS)
values for different materials.
Higgins 2.2.1 Table 2.1
Tensile Test on Plastic
Intertek Plastics: http://www.ptli.com
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Tensile tests are usually done on
prepared specimens.
A narrowed section is where the stress is
calculated, otherwise the specimen will
break where it is gripped.
“Necking” occurs on ductile materials
after reaching the UTS.
“Cup and cone” fracture indicates ductility
Tensile Test specimens
metassoc.com
EMMAT101A Engineering Materials and Processes
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Comparison of Tensile Strength of Steels (UTS)
As steels get stronger they get more brittle.
American Iron and Steel Institute: AISI
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Typical materials
diagram by Ashby.
(c) Copyright Granta
Design Ltd,
Cambridge, England
www.grantadesign.c
om.
Reproduction
Permission?
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Stress/Strain curve showing elastic and plastic regions.
Typical curve
for mild steel.
This curve
shows
engineering
stress – based
on original
cross-sectional
area.
Stress / Strain Curve for Mild Steel showing elastic/plastic regions.
EMMAT101A Engineering Materials and Processes
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True stress (B) is higher than
engineering stress (A). Due to
decreasing area.
True Stress = Force / Actual
area
Engineering usually based on
original area because this will
determine strength in service.
1 = UTS Ultimate Tensile Strength
2 = YS Yield Strength
3 = Engineering fracture Stress
4 = Work Hardening
5 = Necking
Wikipedia.
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Factor of Safety
How many times you could multiply
the working stress before it breaks.
FS = ultimate strength / working stress
Use High FS when: Dangerous,
unknown loads. E.g. Lifting gear.
Low FS: Very accurate knowledge
of problem, optimum weight / cost /
size. E.g. Bridge.
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28kN carabiner designed to
hold a human (100kg).
FS = 24 !
Extremely high FS accounts
for shock loading.
Force ratings engraved on Aluminium karabiner.
28kN closed, 10kN open, 8kN sideways
Wind Turbine Repair
wwww.ropepartner.com
Karabiner Edelrid.de
EMMAT101A Engineering Materials and Processes
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A European standard shows minimum force.
20kN closed, 7kN open, 7kN sideways. (UIAA 121)
Edelrid: 28kN closed, 10kN
open, 8kN sideways
Karabiner Edelrid.de
UIAA standards for the minimum strength of a carabiner
http://www.crabdev.co.uk/comp%20introduction.htm
EMMAT101A Engineering Materials and Processes
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Force increased beyond ultimate stress of turbine blades,
causing catastrophic failure.
Turbine
Collapse
Wind Turbine Collapse
www.spiegel.de
EMMAT101A Engineering Materials and Processes
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Bolted joints in critical
applications in a wind turbine.
Bolts are designed for a certain
stress.
Torque rating (Nm) used to
convert to pulling force
(clamping force) of bolt.
Torqup.com
EMMAT101A Engineering Materials and Processes
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Stiffness
Stiffness (Mpa) = Stress (Mpa) / Strain ()
E=s / e
Many names;
• Young’s Modulus
• Modulus of Elasticity
• Stiffness Modulus
• Modulus !
Carbon fibre is very light and
stiff. This bike fork uses carbon
and magnesium. A carbon crown
and steerer with a carbon fibre
wrapped magnesium lower.
www.bikerumor.com
EMMAT101A Engineering Materials and Processes
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Stiffness E
Stiffness: The stress that will stretch a material by a certain amount.
Stiffness is defined in the elastic region (before the yield point), as the slope of the
stress/strain curve. Since strain has no units, stiffness is same as stress (MPa)
Engineering materials frequently have a
modulus of the order of 1000 000 000 Pa,
i.e. 109 Pa.
This is generally expressed as GPa,
with 1 GPa = 109 Pa.
Higgins 2.2.1 Table 2.1
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Stiffness is the slope of the Stress/Strain
curve – up to the yield point.
Stiffness = Stress / Strain
= 500 / 0.25%
= 200000 Mpa
= 200 GPa
Stiffness is a reliable and
predictable property.
Steels are all about
200GPa regardless of
strength or hardness.
Stress / Strain Curve for Mild Steel
Tim Lovett
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission
Stiffness vs Density.
Stiff materials tend to be
heavy.
Composites have fairly
high stiffness but almost
as light as polymers.
Stress / Strain Curve for Mild Steel
Tim Lovett
http://wwwmaterials.eng.cam.ac.uk/mpsite/int
eractive_charts/stiffnessdensity/basic.html
EMMAT101A Engineering Materials and Processes
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Ductility
Ductility: this is the ability of a material to deform without breaking.
The opposite to ductile is Brittle. (Like glass)
Ductility allows forming processes (like pressing, wire drawing)
Measured as percent elongation: How far it has stretched compared to the
original length.
% elongation = L x 100 / Lo
Tim Lovett
EMMAT101A Engineering Materials and Processes
TAFE NSW -Technical and Further Education Commission
Ceramics are brittle – zero elongation, which means they have no plastic
deformation.
Plasticity: permanent deformation
Ductility: tensile plasticity
Malleability: compressive plasticity
Some plastics have % elongation of
500% or more.
Higgins Table 2.3
EMMAT101A Engineering Materials and Processes
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Toughness
Energy to break. (Joules)
Charpy Impact Test measures
energy absorbed by impact and
breaking of specimen.
A brittle material will hardly slow
down the hammer, a tough
material will almost halt it.
Toughness usually decreases at
lower temperatures.
Toughness usually decreases
with higher impact speed.
CHARPY IMPACT TEST: Tim Lovett
EMMAT101A Engineering Materials and Processes
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Toughness
Type
Aluminum alloy (7075)
Energy to break.
(Joules)
A tough material:
• resists a crack running
through the material
(fracture toughness).
• absorbs more energy as
crack runs through it.
• will have ductility
KIc (MPa · m1/2)
Material
Metals
Ceramic
Polymer
Composite
Steel alloy (4340)
50
Titanium alloy
44–66
Aluminum
14–28
Aluminium oxide
3–5
Silicon carbide
3–5
Soda-lime glass
0.7–0.8
Concrete
0.2–1.4
Polymethyl methacrylate
0.7–1.6
Polystyrene
0.7–1.1
Mullite-fibre composite
1.8–3.3
Silica aerogels
0.0008–0.0048
Fracture Toughness: Wikipedia
EMMAT101A Engineering Materials and Processes
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Toughness/Strength
For the engineering
materials, increasing the
strength tends to
DECREASE toughness.
The ultimate engineering
material has both strength
and toughness.
This is why composites
appear in the high
performance areas:
Tough, Strong and Light.
http://www-materials.eng.cam.ac.uk
EMMAT101A Engineering Materials and Processes
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Composites used for toughness, strength and light weight.
Record 75m long turbine blade: Siemens press picture.
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Hardness
Resistance to indentation or abrasion. (no units)
There are several types of hardness tests:
• Brinell (Ball indentor. Measure diameter of dent)
• Vickers (Pyramid diamond indentor. Measure dent)
• Rockwell…
VICKERS: www.twi.co.uk
BRINELL: www.twi.co.uk
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Rockwell Hardness Test
• Fast and simple test.
• Various scales for
hard/soft materials
ROCKWELL
HARDNESS TEST:
Tim Lovett
ROCKWELL HARDNESS TEST:
Tim Lovett
EMMAT101A Engineering Materials and Processes
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Mechanical Properties Summary
Strength (Mpa) : Ability to endure stress – the intensity of force.
Strain () Elastic = Elongation (mm) / Original Length (mm)
Elongation (%) Plastic = Elongation (mm) / Original Length (mm)
Stiffness (Mpa) : Stress to cause strain = Stress (Mpa) / Strain ()
Toughness (J) : Energy to break
Hardness () : Resistance to indentation / abrasion.
EMMAT101A Engineering Materials and Processes
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Mechanical Properties Definitions
• Ductility: The ability of a material to deform plastically before fracture.
• % Elongation: Plastic deformation determined after fracture by realigning
and fitting together the broken ends of the specimen.
• Engineering strain: Change in length / original length
• Strength: Ability to endure stress – the intensity of force.
• UTS Ultimate tensile strength or tensile strength: The maximum tensile
stress that a material is capable of sustaining. (original area)
• Yield strength: The engineering stress at which, by convention, it is
considered that plastic elongation of the material has commenced.
• Stiffness: Stress required to give a certain strain.
• Toughness (J) : Energy to break
• Hardness () : Resistance to indentation / abrasion.
EMMAT101A Engineering Materials and Processes
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Information that can be determined from the Stress/Strain curve…
1. Ductility
2. Elongation
3. Engineering
strain
4. Strength
5. UTS
6. YS
7. Stiffness
Toughness
8. Hardness?
Not directly, but
correlates with
strength. E.g.
High strength
steels are
harder.
Stress / Strain Curve for Mild Steel showing elastic/plastic regions.
EMMAT101A Engineering Materials and Processes
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Electrical Properties
Resistivity (ohm.m): r is an electrical property defined by the equation;
where R = resistance (ohms), L = length (m), A = sectional area (m2)
• An electrical insulator, (e.g. ceramic) has high resistivity. (1010 Wm)
• An electrical conductor, (e.g. copper), has low resistivity, (10"8 Wm).
• Conductivity is the reciprocal of resistivity.
EMMAT101A Engineering Materials and Processes
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Resistivity (ohm.m):
Ceramics and polymers
are insulators.
Metals are conductors
Higgins
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Thermal Property a
The coefficient of linear expansion (a): The proportion a material
expands with temperature. (mm/mmK)
e
=
a DT
DT = change in temperature
e = strain (thermal)
a = coefficient of thermal expansion
Bridges expand
with temperature,
so an expansion
joint is needed on
one end.
Sydney Harbour Bridge
EMMAT101A Engineering Materials and Processes
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Thermal Property c
• Specific Heat Capacity (c): The amount of heat needed to heat 1 kg of
the material by 1 K. (J/kgK)
c = H / (m DT)
DT = change in temperature (K)
m = mass (kg)
H = heat (Joules)
Radiator: Water has a high
Specific Heat which is why it is
used as the basis of cooling fluid.
hgvdirect.co.uk
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The term Thermal Mass can also mean heat capacity.
Reverse Brick Veneer:
A traditional brick veneer building
has a brick wall on the outside and
a stud wall inside. The insulation
is inside the wall lining
(plasterboard).
With reverse brick veneer, the
thermal mass (heat capacity) of
the brickwork moderates the
internal temperature without the
impacts of the external weather
conditions.
ruralbuilding.com.au
EMMAT101A Engineering Materials and Processes
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Hydrogen has a very high c = 14.8. It is used as the working fluid in this Stirling
engine generator. These generators achieved 31% solar-to-grid efficiency.
However, there are more working parts than a photovoltaic system. sandia.gov
EMMAT101A Engineering Materials and Processes
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Demonstration: Low temperature Stirling engine.
Working fluid = air.
Friction is very low, so it can run on small
temperature difference. For higher power (to run
something useful) needs a higher temperature
difference such as solar concentrator (below).
solarthermalmagazine.com
Low Temp Stirling Engine: ministeam.com
EMMAT101A Engineering Materials and Processes
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Thermal Property l
Thermal conductivity l : the ability to conduct heat.
Defined as Heat flowrate / temp gradient.
W / (mK): Watts per metre-Kelvin
Aluminium Heat sink: High thermal
conductivity. Wikipedia
Insulation: Glass has a low thermal
conductivity. roofperf.com.au
EMMAT101A Engineering Materials and Processes
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Thermal Properties Summary
Summary of thermal
properties.
For metals, good thermal
conductors tend to be good
electrical conductors. (E.g.
copper)
Higgins
EMMAT101A Engineering Materials and Processes
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Ashby Charts
•
•
•
•
•
•
•
•
•
•
•
•
Select chart:
Young's modulus - Density
Young's Modulus - Cost
Strength - Density
Strength - Toughness
Strength - Elongation
Strength - Cost
Strength - Max service temperature
Specific stiffness - Specific strength
Electrical resistivity - Cost
Recycle Fraction - Cost
Energy content - Cost
TAFE NSW -Technical and Further Education Commission
http://www-materials.eng.cam.ac.uk
Online Properties Resources.
Searchable listing of material properties.
Graphical comparison of materials properties.
Testlopedia: Testing of plastics
Wikipedia: Materials properties
• Composite carabiner study: http://www.crabdev.co.uk/comp%20introduction.htm
EMMAT101A Engineering Materials and Processes
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GLOSSARY
Strength
Stiffness
Toughness
Elongation
Strain
Malleability
Ductility
Resilience
Yield Strength
Ultimate Tensile Strength
Factor of Safety
Hardness
Coeff of thermal expansion
Specific Heat Capacity
Thermal Conductivity
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QUESTIONS
1. Discuss the variables that control the heat transfer through a solid material.
2. Why are long steam supply lines built with a loop at regular intervals along their
length? What other methods could be used?
3. Explain what is meant by high thermal mass.
4. What is a refractory material? Give examples.
5. What is the effect of temperature on the resistivity of a conductor?
6. What are wind turbine blades made of? Explain why this material is used. List
some alternatives.
7. Explain the concept of reverse brick veneer. List advantages/disadvantages.
What alternatives could achieve a similar outcome?
8. Give examples of components of a wind turbine that require properties of:
strength, toughness, hardness, stiffness.
9. Give examples of components of a solar Stirling engine generator that require
properties of: strength, toughness, hardness, thermal conductivity, heat capacity,
electrical conductivity.
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