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MECH3100 2007

Materials Selection in Mechanical Design

Lecture 1

Exploring the world of materialsIntroduction to Material Indices

A./Prof. Carlos H. Caceresc.caceres@minmet.uq.edu.au

Room 405

Frank White Bldng. (#43)

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TEXTBOOK:

Ashby, M.F., Materials selection in mechanical design , 3rdedition, Butterworth-Heinemann, Oxford,(2005)

TA403.6 .A74 2005

PDF files of Materials Selection Charts and lectures notes in

Mech Eng web sitehttp://www.mech.uq.edu.au/courses/mech3100

CES software and data base, available at 50-N301

Computer room, Hawken Bldng

http://library.uq.edu.au/search/cTA403.6+.A74+2005/cta++403.6+a74+2005/-3,-1,,E/browsehttp://www.mech.uq.edu.au/courses/mech3http://www.mech.uq.edu.au/courses/mech3http://library.uq.edu.au/search/cTA403.6+.A74+2005/cta++403.6+a74+2005/-3,-1,,E/browse

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The evolution of materials (Ashby, 2005)

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The World of Engineering Materials

Composites

Sandwiches

HybridsLattices

Segmented

PE, PP, PCPS, PET, PVC

PA (Nylon)

PolymersPolyester

PhenolicEpoxy

Soda glassBorosilicate

GlassesSilica glass

Glass ceramic

IsopreneButyl rubber

ElastomersNatural rubber

SiliconesEVA

AluminaSi-carbide

CeramicsSi-nitrideZiconia

SteelsCast ironsAl -alloys

Metals, alloysCu-alloysNi-alloys

Ti-alloys

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Materials and design (Ashby, 2005)

The goal of design: To create products that perform their function effectively, safely,at acceptable cost and environmentally sound. What do we need to know to do this?More than just test data.

Test Test data

Data

capture

Statistical

analysis

Allowables

Mechanical PropertiesBulk Modulus 4.1 - 4.6 GPaCompressive Strength 55 - 60 MPaDuctility 0.06 - 0.07Elastic Limit 40 - 45 MPaEndurance Limit 24 - 27 MPaFracture Toughness 2.3 - 2.6 MPa.m1/2

Hardness 100 - 140 MPaLoss Coefficient 0.009- 0.026Modulus of Rupture 50 - 55 MPaPoisson's Ratio 0.38 - 0.42Shear Modulus 0.85 - 0.95 GPa

Tensile Strength 45 - 48 MPaYoung's Modulus 2.5 - 2.8 GPa

Successfulapplications

$

Economic , environmental and

business caseSelection of

material and process

Potentialapplications

Characterisation Selection and implementation

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Mechanical properties illustrated (Ashby, 2005)

StiffStrong

Tough

Light

Not stiff enough (need bigger E)

Not strong enough (need bigger

y )

Not tough enough (need bigger Kic)

Too heavy (need lower )

All OK !

Need to improve onthe selection of

materials

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Organising information: the MATERIALS TREE

Kingdom

Materials

Family

Ceramics& glasses

Metals& alloys

Polymers& elastomers

Hybrids

Class

Steels

Cu-alloys

Al-alloys

Ti-alloys

Ni-alloys

Zn-alloys

Member

1000

2000

3000

4000

5000

6000

7000

8000

A material record

Attributes

DensityMechanical props.

Thermal props.

Electrical props.

Optical props.

Corrosion props.

Supporting information

-- specific

-- general

Density

Mechanical props.

Thermal props.

Electrical props.

Optical props.

Corrosion props.Supporting information

-- specific

-- general

Structured

information

Unstructured

information

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Structured information for ABS* (CES database)

General PropertiesDensity 1.05 - 1.07 Mg/m^3

Price 2.1 - 2.3 US $/kg

Mechanical PropertiesYoung's Modulus 1.1 - 2.9 GPa

Elastic Limit 18 - 50 MPa

Tensile Strength 27 - 55 MPa

Elongation 6 - 8 %

Hardness - Vickers6 - 15 HV

Endurance Limit 11 - 22 MPa

Fracture Toughness 1.2 - 4.2 MPa.m1/2

Thermal PropertiesMax Service Temp 350 - 370 K

Thermal Expansion 70 - 75 10-6/K

Specific Heat 1500 - 1510 J/kg.K

Thermal Conductivity 0.17 - 0.24 W/m.K

Acrylonitrile-butadiene-styrene (ABS) - (CH2-CH-C6H4)n

Electrical PropertiesConductor or insulator? Good insulator

Optical PropertiesTransparent or opaque? Opaque

Corrosion and Wear Resistance

Flammability AverageFresh Water Good

Organic Solvents Average

Oxidation at 500C Very Poor

Sea Water Good

Strong Acid Good

Strong Alkalis Good

UV Good

Wear Poor

*Using the CES Level 2 DB

+ links to processes

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Unstructured information for ABS* (CES database)

What is it?ABS (Acrylonitrile-butadiene-styrene ) is tough, resilient, and easily molded. It isusually opaque, although some grades can now be transparent, and it can be given vivid colors.ABS-PVC alloys are tougher than standard ABS and, in self-extinguishing grades, are used for the

casings of power tools.

Design guidelines. ABS has the highest impact resistance of all polymers. It takes colorwell. Integral metallics are possible (as in GE Plastics' Magix.) ABS is UV resistant for outdoorapplication if stabilizers are added. It is hygroscopic (may need to be oven dried beforethermoforming) and can be damaged by petroleum-based machining oils.

ABS can be extruded, compression moulded or formed to sheet that is then vacuum thermo-formed. It can be joined by ultrasonic or hot-plate welding, or bonded with polyester, epoxy,isocyanate or nitrile-phenolic adhesives.

Technical notes.ABS is a terpolymer - one made by copolymerising 3 monomers: acrylonitrile, butadiene and syrene. The acrylonitrilegives thermal and chemical resistance, rubber-like butadiene gives ductility and strength, the styrene gives a glossy surface, ease of machiningand a lower cost. In ASA, the butadiene component (which gives poor UV resistance) is replaced by an acrylic ester. Without the addition ofbutyl, ABS becomes, SAN - a similar material with lower impact resistance or toughness. It is the stiffest of the thermoplastics and hasexcellent resistance to acids, alkalis, salts and many solvents.

Typical Uses. Safety helmets; camper tops; automotive instrument panels and other interior components; pipe fittings; home-securitydevices and housings for small appliances; communications equipment; business machines; plumbing hardware; automobile grilles; wheelcovers; mirror housings; refrigerator liners; luggage shells; tote trays; mower shrouds; boat hulls; large components for recreational vehicles;weather seals; glass beading; refrigerator breaker strips; conduit; pipe for drain-waste-vent (DWV) systems.

The environment. The acrylonitrile monomer is nasty stuff, almost as poisonous as cyanide. Once polymerized with styrene it becomes

harmless. ABS is FDA compliant, can be recycled, and can be incinerated to recover the energy it contains.

*Using the CES Level 2 DB

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Relationships, perspective and comparisons

Metals Polymers Ceramics Hybrids

PEEK

PP

PTFE

WC

Alumina

Glass

CFRP

GFRP

Fibreboard

Young

sm

odul u

s ,

GPa

Steel

Copper

Lead

Zinc

Aluminum

Material bar-charts

Material property charts

Data sheets do not allow comparison,

perspective. For these we need

E

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Bar- chart created with CES(Level1)

Bar Charts allow exploring relationships Bar Charts allow selection and sorting

UntitledMaterials:\MET ALS Materials:\POLYMERS Materials:\CERAMICS and GLASSES Materials:\COMPOSITES

Young'sModulus(GPa)

1e-004

1e-003

0.01

0.1

1

10

10 0

1000

Low alloy steel

Mg-alloys

Al-alloysZn-alloys

Ti-alloys

Cu-alloys

Stainless steel

High carbon steel

Acetal, POM

Polyurethane

EVA

IonomerPTFE

WC

Alumina

Glass Ceramic

Silica glass

Soda-Lime glassPolyester, rigid

PC

PS

PUR

PE

ABS

PP

BC

SiCAl-SiC Composite

CFRP

KFRP

GFRP

Plywood

Neoprene

Natural Rubber (NR)

CompositesPolymersMetals Ceramics & glass

Youngs

modulus

(G

Pa)

Metals Polymers Ceramics Hybrids

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Material property- charts: modulus - density

0.1

10

1

100

Metals

Polymers

Elastomers

Ceramics

Woods

Composites

Foams

0.01

1000

1000.1 1 10

Density (Mg/m3)

Youngsmod

ulusE,

(GPa

)

E

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Thermal properties (CES chart, pdf file)

Choke for carburator

Thermal

expansion

Thermal

conduct.

Ceramic insert for piston

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Materials that are stiff?

Charts offer both Methods and Tools

At this stage you have a selection tool.

Materials with low expansion?

Charts help developing a perspective

with high conductivity?

Materials that are light and compliant?

Materials that are light and stiff?

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A method for systematic selection:

Material Selection Indices

(a crash course)

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Example 1: Materials for a stiff tie-rod of minimum mass

Minimise mass m:

m = A L

Length L is specified

Must not deflect more thanunder load F

Material Cross section area A

Equation for constraint on : = L = L /E = L F/(A E)

Chose materials with largest M =

E

MaterialIndex

=

E

FLm

2

Constraints

What can be variedto meet the goal ?

Performance

metric: mass

Goal

{

{

EliminateA

L

FF

AreaA

Tie-rod

m = mass

= densityE = Youngs modulus

= deflection

Function

Minimise mass? Maximise Material Index !

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Example 2: Materials for a stiff, light beam

=

2/1

2/15

EC

LS12m Chose materials with largest M=

2/1E

Material

Index Material choiceArea = b2

What can bevaried ? {

I = second moment of area:12

bI

4

=

Beam (solid square section)

b

b

L

F

Function

m = mass A = area

L = length = densityb = edge length

S = stiffness

I = second moment of area

E = Youngs modulus

Stiffness of the beam, S:

3L

IECS =

FS=

Constraint

== LbLAm 2Minimise mass, m, where:Goal

Eliminateb

Minimise mass? Maximise Material Index !

Get these equations

from the textbook, or

pdf file Useful

Solutions

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Elastic Bending of Beams and Panels; p. 479 or useful solutions pdf file

3

1

L

EICFS ==

3L

IECS=

12

bI

4

=

FS=

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Moments of Sections; p 477, or Useful Solutions file

12

bI

4

=

E l 3 M i l f iff li h l

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m = mass

w = width

L = length

= densityt = thickness

S = stiffness

I = second moment of area

E = Youngs modulus

Panel, width w and length L specified

Stif fness of the panel, S

I is the second moment of area:

3L

IECS =

12

twI

3

=

tw

=

3/1

2

3/12

E

L

C

wS12m

L

F

== LtwLAm

Minimise mass, m

Chose materials with largest M=

3/1E

FS =

Example 3: Materials for a stiff, light panel

MaterialIndex

Function

Goal

Constraint

Material choice.

Panel thickness t

What can be

varied ? { Eliminatet

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Material Indices for Minimum Mass

Function Stiffness

Same Volume

Tension (tie)

Bending (beam)

Bending (panel)

E/

/E1/2

E1/3

/

1/

Objective: minimisemass for given stiffness

Objective: minimise mass

Minimise mass? Maximise Material Index !

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Ranking Materials using Charts

CE

=

2/1

CE

=

CE

=

3/1

1

2

3

E

metals

ceramics

composites& polymers

foams

Selection l inefor tie rodsSelection linefor beams

Selection linefor panels

For beams and panels a low density

is more important than a high

modulus. This is why foams are

ignored for tie rods, but are preferredfor beams and more so for flat panels

Better this way

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The EndLecture 1