Engineering Materials and Processes Lecture 2 – …learneasy.info/MDME/focus/materials/enmat/LECTURES/... Engineering Materials and Processes Lecture 2 – Material Properties Prescribed

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Engineering Materials and ProcessesLecture 2 – Material Properties

PresenterPresentation NotesPrescribed Text: Ref 1: Higgins RA & Bolton, 2010. Materials for Engineers and Technicians, 5th edition, Butterworth Heinemann. ISBN: 9781856177696 Readings:Callister: Callister, W. Jr. and Rethwisch, D., 2010, Materials Science and Engineering: An Introduction, 8th Edition, Wiley, New York. ISBN 9780470419977Ashby 1: Ashby, M. & Jones, D., 2011, Engineering Materials 1: An Introduction to Properties, Applications and Design, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN: 9780080966656Ashby 2: Ashby, M. & Jones, D., 2011, Engineering Materials 2: An Introduction to Microstructures and Processing, 4th edition, Butterworth-Heinemann, Oxford UK. IBSN: 9780080966687 Lecture (2 hrs): Ref 1, Ch 1: Engineering materials;Ref 1 Ch 2: Properties of materials. Laboratory 1 (2 hrs): Hardness testReadings: Callister: Ch 1, 2, 18-21Ashby 1: Ch 1, 2 Ashby 2: Ch 1

Properties of Materials

EMMAT101A Engineering Materials and Processes

Reference Text SectionHiggins RA & Bolton, 2010. Materials for Engineers and Technicians

Ch 2

Additional Readings SectionSheedy, P. A, 1994. Materials : their properties, testing and selection

Ch 3, Ch5

Callister, W. Jr., 2010, Materials Science and Engineering Ch7

PropertiesA property is characteristic of a material. It should be about the same for any piece of the material.

Some properties can be measured easily, others may require breaking a specimen.


PROPERTY NOT A PROPERTYDensity MassStiffness LengthHardness WearStrength Force

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


HARDNESSBall Bearing SKF

PresenterPresentation NotesHiggins RA & Bolton, 2010. Materials for Engineers and Technicians, 5th edition, Butterworth Heinemann. Ch 1.2.1

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.



Basic Formulas 1Density (kg/m3) = Mass (kg) / Volume (m3)

ρ = 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 75Cork 240Ice 916.7

Water (fresh) 1,000Aluminium 2,700Titanium 4,540

Iron 7,870Lead 11,340

Tungsten 19,300


http://en.wikipedia.org/wiki/Airhttp://en.wikipedia.org/wiki/Styrofoamhttp://en.wikipedia.org/wiki/Cork_(material)http://en.wikipedia.org/wiki/Icehttp://en.wikipedia.org/wiki/Waterhttp://en.wikipedia.org/wiki/Aluminiumhttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Ironhttp://en.wikipedia.org/wiki/Leadhttp://en.wikipedia.org/wiki/Tungsten

Basic Formulas 1Density (kg/m3) = Mass (kg) / Volume (m3)

ρ = m / V


Varies with temperature;• Slightly for solids.• About x10 for liquids.• By gas law for gases.

DENSITY INCREASES AS VOLUME DECREASESTim Lovett


Basic Formulas 2Stress (MPa) = Force (N) / Area (mm2)

σ = F / A

Tensile Stress: PullingCompressive Stress: SquashingShear Stress: Sliding


Tensile StressTim Lovett


Basic Formulas 3Strain () = Elongation (mm) / Original Length (mm)

ε = e / Lo

Strain has no units.Low elastic strain in metals.


Elongation

ElongationTim Lovett


http://www-materials.eng.cam.ac.uk/mpsite/properties/non-IE/elongation.html

Basic Formulas 4Stiffness (Mpa) : Stress (Mpa) / Strain ()

E = σ / ε

Many names; Young’s Modulus Modulus of Elasticity Stiffness Modulus Modulus !

Usually a BIG number (GPa)


Higgins 2.2.1 Table 2.1


Mechanical PropertiesStrength: Ability to endure stress – the intensity of force.

Stress (Pa) = Force (N) / Area (m2)

σ = F / A

Ultimate Strength: Highest stress without breakage. Yield Strength: Highest stress without deformation.


TENSILE STRESSTL



Mechanical test of the strength of mild steel.

Stress / Strain Curve for Mild SteelTim Lovett

www.nmu.edu




Yield StrengthYS

Ultimate Tensile StrengthUTS

Mechanical test of the strength of mild steel.



Alternative to Yield PointYield point. A levelling off on the stress-strain 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



Proof Stress as alternative to Yield StressTim Lovett

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.


Stress grade 8.8 embossed on bolt head.


Hydraulic tensioning of foundation bolts of wind turbine tower.

Nut torquingwww.torcup.com

Grade 8.8 BoltHebei Saite Fastener Co., Ltd.


Stress grade 8.8 embossed on bolt head.


4.6 = 400 Mpa and 60% YS8.8 = 800 Mpa and 80% YS10.9 = 1000 Mpa and 90% YS12.9 = 1200 Mpa and 90% YS



Stress grades of bolts.


4.6 = 400 Mpa and 60% YS8.8 = 800 Mpa and 80% YS10.9 = 1000 Mpa and 90% YS12.9 = 1200 Mpa and 90% YS


Higher grade bolts have lower ductility.

Tim Lovett



Tensile Strength (UTS) values for different materials.

Higgins 2.2.1 Table 2.1 Tensile Test on PlasticIntertek Plastics: http://www.ptli.com



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 specimensmetassoc.com



Comparison of Tensile Strength of Steels (UTS) As steels get stronger they get more brittle.

American Iron and Steel Institute: AISI



Typical materials diagram by Ashby. (c) Copyright Granta Design Ltd, Cambridge, Englandwww.grantadesign.com. Reproduction Permission?


http://www.grantadesign.com/


Stress/Strain curve showing elastic and plastic regions.

Stress / Strain Curve for Mild Steel showing elastic/plastic regions.

Typical curve for mild steel.

This curve shows engineering stress – based on original cross-sectional area.



Wikipedia.

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 Strength2 = YS Yield Strength3 = Engineering fracture Stress4 = Work Hardening5 = Necking


Factor of SafetyHow 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.

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

Karabiner Edelrid.de

Wind Turbine Repair wwww.ropepartner.com



A European standard shows minimum force. 20kN closed, 7kN open, 7kN sideways. (UIAA 121)

Karabiner Edelrid.de UIAA standards for the minimum strength of a carabinerhttp://www.crabdev.co.uk/comp%20introduction.htm

Edelrid: 28kN closed, 10kN open, 8kN sideways



Force increased beyond ultimate stress of turbine blades, causing catastrophic failure.

Turbine Collapse

Wind Turbine Collapse www.spiegel.de

http://www.youtube.com/watch?v=CqEccgR0q-o


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

StiffnessStiffness (Mpa) = Stress (Mpa) / Strain ()

E = σ / εMany 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



Stiffness EStiffness: 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



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.



Stiffness vs Density.

Stiff materials tend to be heavy. Composites have fairly high stiffness but almost as light as polymers.


http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/basic.html


DuctilityDuctility: 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


Ceramics are brittle – zero elongation, which means they have no plastic deformation.


Higgins Table 2.3

Plasticity: permanent deformationDuctility: tensile plasticityMalleability: compressive plasticity

Some plastics have % elongation of 500% or more.


ToughnessEnergy 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

ToughnessEnergy 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

Fracture Toughness: Wikipedia

Type Material KIc (MPa · m1/2)

Metals

Aluminum alloy (7075)Steel alloy (4340) 50Titanium alloy 44–66Aluminum 14–28

Ceramic

Aluminium oxide 3–5Silicon carbide 3–5Soda-lime glass 0.7–0.8Concrete 0.2–1.4

Polymer Polymethyl methacrylate 0.7–1.6

Polystyrene 0.7–1.1Composit

eMullite-fibre composite 1.8–3.3

Silica aerogels 0.0008–0.0048

http://en.wikipedia.org/wiki/Aluminumhttp://en.wikipedia.org/wiki/Steelhttp://en.wikipedia.org/wiki/Titaniumhttp://en.wikipedia.org/wiki/Aluminium_oxidehttp://en.wikipedia.org/wiki/Silicon_carbidehttp://en.wikipedia.org/wiki/Soda-lime_glasshttp://en.wikipedia.org/wiki/Concretehttp://en.wikipedia.org/wiki/Polymethyl_methacrylatehttp://en.wikipedia.org/wiki/Polystyrenehttp://en.wikipedia.org/wiki/Mullitehttp://en.wikipedia.org/wiki/Aerogel


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


Composites used for toughness, strength and light weight.

Record 75m long turbine blade: Siemens press picture.

http://www.siemens.com/press/en/presspicture/?press=/en/presspicture/pictures-photonews/2012/pn201204.php

HardnessResistance 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…

BRINELL: www.twi.co.ukVICKERS: www.twi.co.uk

PresenterPresentation NotesIndentation (plastic deformation)Abrasion (brittle materials – ceramics)

Rockwell Hardness Test


• Fast and simple test.• Various scales for hard/soft materials

ROCKWELL HARDNESS TEST: Tim Lovett

ROCKWELL HARDNESS TEST: Tim Lovett

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.



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.




Information that can be determined from the Stress/Strain curve…

Stress / Strain Curve for Mild Steel showing elastic/plastic regions.

1. Ductility2. Elongation3. Engineering

strain4. Strength5. UTS6. YS7. Stiffness

Toughness

8. Hardness? Not directly, but correlates with strength. E.g. High strength steels are harder.


Electrical PropertiesResistivity (ohm.m): ρ 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 Ωm)

An electrical conductor, (e.g. copper), has low resistivity, (10"8 Ωm).

Conductivity is the reciprocal of resistivity.



Resistivity (ohm.m):


Higgins

Ceramics and polymers are insulators.

Metals are conductors

PresenterPresentation NotesHiggins RA & Bolton, 2010. Materials for Engineers and Technicians, 5th edition, Butterworth Heinemann. Ch 2.4

Thermal Property αThe coefficient of linear expansion (α): The proportion a material expands with temperature. (mm/mmK)

ε = α ∆T∆T = change in temperature

ε = strain (thermal)α = coefficient of thermal expansion


Bridges expand with temperature, so an expansion joint is needed on one end.Sydney Harbour Bridge


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 ∆T)∆T = change in temperature (K)

m = mass (kg)Η = heat (Joules)


Radiator: Water has a high Specific Heat which is why it is used as the basis of cooling fluid.hgvdirect.co.uk


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



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



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).

Low Temp Stirling Engine: ministeam.comsolarthermalmagazine.com

PresenterPresentation NotesDemonstration: Low temperature Stirling engine. Explain how power related to temp difference.

http://www.youtube.com/watch?v=n-mKP9E6a6I

Thermal Property λThermal conductivity λ : the ability to conduct heat.Defined as Heat flowrate / temp gradient.

W / (mK): Watts per metre-Kelvin


Insulation: Glass has a low thermal conductivity. roofperf.com.au

Aluminium Heat sink: High thermal conductivity. Wikipedia


Thermal Properties SummarySummary of thermal properties.

For metals, good thermal conductors tend to be good electrical conductors. (E.g. copper)


Higgins


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

http://www-materials.eng.cam.ac.uk

http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-density/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/stiffness-cost/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-density/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-toughness/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-ductility/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-cost/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-temp/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/spec-spec/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/resistivity-cost/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/recycling-cost/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/energy-cost/default.htmlhttp://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-density/NS6Chart.html


Online Properties Resources.

Testlopedia: Testing of plastics

Graphical comparison of materials properties.

Wikipedia: Materials properties

• Composite carabiner study: http://www.crabdev.co.uk/comp%20introduction.htm

Searchable listing of material properties.

PresenterPresentation Noteshttp://www.matweb.comShow this website on screen. Will be using this later.

http://www.matweb.com/http://www-materials.eng.cam.ac.uk/mpsite/interactive_charts/strength-density/NS6Chart.htmlhttp://www.ptli.com/list.asphttp://en.wikipedia.org/wiki/List_of_materials_properties

GLOSSARYStrengthStiffnessToughnessElongationStrainMalleabilityDuctilityResilienceYield StrengthUltimate Tensile StrengthFactor of SafetyHardnessCoeff of thermal expansionSpecific Heat CapacityThermal Conductivity

PresenterPresentation Noteshttp://www.youtube.com/watch?v=1GFst2IQBEM

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.

PresenterPresentation Noteshttp://www.youtube.com/watch?v=1GFst2IQBEM

Engineering Materials and Processes�Lecture 2 – Material PropertiesProperties of MaterialsPropertiesSlide Number 4Classes of PropertiesBasic Formulas 1Basic Formulas 1Basic Formulas 2Basic Formulas 3Basic Formulas 4Mechanical PropertiesSlide Number 12Slide Number 13Slide Number 14Slide Number 15Slide Number 16Slide Number 17Slide Number 18Slide Number 19Slide Number 20Slide Number 21Slide Number 22Slide Number 23Slide Number 24Factor of SafetySlide Number 26Slide Number 27Slide Number 28Slide Number 29StiffnessSlide Number 31Slide Number 32Slide Number 33DuctilitySlide Number 35ToughnessToughnessSlide Number 38Slide Number 39HardnessSlide Number 41Mechanical Properties SummaryMechanical Properties DefinitionsSlide Number 44Electrical PropertiesSlide Number 46Thermal Property aThermal Property cSlide Number 49Slide Number 50Slide Number 51Thermal Property lThermal Properties SummaryAshby ChartsSlide Number 55Slide Number 56Slide Number 57

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Engineering Materials and Processes Lecture 2 – …learneasy.info/MDME/focus/materials/enmat/LECTURES/... Engineering Materials and Processes Lecture 2 – Material Properties Prescribed