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Materials Selection for Mechanical Design:
Exploring the World of Materials
Background: the motivation
History – the evolution of materials
Materials and their attributes
The nature of materials data
ME 474-674 Winter 2008 Slides 1 Intro -2
Introduction
Design is…“…the process of translating a new idea or a market need into detailed
information from which a product can be manufactured.”
M. F. Ashby, “Materials Selection in Mechanical Design”,
Idea or Need ProductDesignInventionMarket need
Engineering DesignIndustrial Design
ME 474-674 Winter 2008 Slides 1 Intro -3
Types of Design
Original DesignNew idea or working principle
e.g. CD replacing magnetic tape
Adaptive or Development DesignTakes existing product and seeks an incremental advance in performance through a refinement in working principle.
e.g. beverage cans, automobiles,…
Variant DesignChange in scale/dimension without change of function
e.g. desktop to laptop computer
ME 474-674 Winter 2008 Slides 1 Intro -4
Vocabulary of Design
Design problems are open ended - no single correct answer
Design is an iterative process
Products are technical systems composed of assemblies and components
The design objective must be formulated as a “need statement”
“A device for performing task x is needed”But must not specify a way of satisfying the need
“Must be solution neutral”
ME 474-674 Winter 2008 Slides 1 Intro -5
Example
Design objective:“A device is needed to pull the cork from wine bottle”
Not solution neutral – pulling specifies the solution
Need
ME 474-674 Winter 2008 Slides 1 Intro -6
Possible solutions
Revised Design Objective:
“a device is required to allow access to wine in a corked bottle with convenience, at modest cost, without contaminating wine…”
Screw to transmit prescribed load to cork
Slender elastic blade that will not buckle when driven between the cork and the bottle-neck
Thin, hollow needle, stiff and strong enough to penetrate corkConcepts
ME 474-674 Winter 2008 Slides 1 Intro -7
Possible solutions
Embodiments
Direct pull Levered pull Spring assisted pullGeared pull
Embodiments of one concept
ME 474-674 Winter 2008 Slides 1 Intro -8
One solution
ME 474-674 Winter 2008 Slides 1 Intro -9
Other Concepts
ME 474-674 Winter 2008 Slides 1 Intro -10
Air pressure cork popper
Air Pressure Bottle Opener -Automatic Cork Popper
No tugs, no pulls, no corkscrews - no groans! This advanced approach to uncorking wines is almost effortless. Just push the needle into the cork, pump and... pop! The injected air causes the cork to lift itself right out of the bottle
ME 474-674 Winter 2008 Slides 1 Intro -11
Butler’s friend
This device consists of a pair of thin, narrow, flexible metal blades mounted in parallel to a flattened loop of a handle.In storage the blades are protected by a metal or plastic sheath.Remove the sheath, and you'll notice that one blade is slightly longer than the other.Insert the longer blade first between cork and glass (about 1/4 inch); then insert the shorter blade opposite.Rocking the handle back and forth, you gently push down each blade in turn about 1/4 inch at a time until the frame of the handle rests on the top of the cork. Then simply twist and lift.The cork comes out with ease and can be removed from between the puller's blades in one motion--no need to untwist as from a helix.
ME 474-674 Winter 2008 Slides 1 Intro -12
Why Materials and Process Selection In Design?
Engineers make things to make life better.
They make them out of materials using processes.
Materials have played a role in human life since the beginning of civilization.
The progress of civilization has been recorded by the materials.
Stone age, bronze age, iron age etc.
At this time we have over 160,000 materials available to us.
Materials selection is a systematic elimination of those that are not suitable to arrive at an optimum material for the particular application.
Materials selection is an integral part of any design processes
The transition from the conceptual design to physical reality.
ME 474-674 Winter 2008 Slides 1 Intro -13
Materials and Process Selection In Design
What do engineers need to know to do this successfully?
A perspective of the world of materials and processes
An understanding material properties and their origins
An ability to select those that best meet requirements of a design
Access to information and tools for comparison and selection
ME 474-674 Winter 2008 Slides 1 Intro -14
General Classification of Materials
MetalsIron, Copper, Aluminum, Zinc, Nickel, Titanium, Silver, Gold, etc. and their alloys Steel, Brass, Bronze, etc.
CeramicsPorcelain, China, Glass, Silicon Carbide, Boron Nitride, Aluminum Oxide, etc.
PolymersPolyethylene, PVC, Teflon, Nylon, Plexiglas, Bakelite, Epoxy, Polyesters, Melamine, Neoprene, Silicone
Electronic MaterialsSilicon, Germanium, Gallium-Arsenide
CompositesConcrete, FRP, MMC, CMC, Asphalt, Wood
ME 474-674 Winter 2008 Slides 1 Intro -15
The world of structural materials
CompositesSandwiches
HybridsLattices
Segmented
PE, PP, PCPS, PET, PVC
PA (Nylon)
PolymersPolyesterPhenolic
Epoxy
Soda glassBorosilicate
GlassesSilica glass
Glass ceramic
IsopreneButyl rubber
ElastomersNatural rubber
SiliconesEVA
AluminaSi-carbide
CeramicsSi-nitrideZiconia
SteelsCast ironsAl-alloys
Metals, alloysCu-alloysNi-alloysTi-alloys
ME 474-674 Winter 2008 Slides 1 Intro -16
History – the evolution of materials
ME 474-674 Winter 2008 Slides 1 Intro -17
Comparison of Materials
Metals
ME 474-674 Winter 2008 Slides 1 Intro -18
Metals
DisadvantagesFailure by fatigue
Most susceptible to environmental attack
(corrosion and oxidation)
AdvantagesRelatively high moduli (stiff)
Can be made strong by alloying or working
Nominally ductile
Relatively high toughness
Paramagnetic or ferromagnetic
Good electrical conductors
Bonding: Metallic bonds – Delocalized electronsStructure: Crystalline
ME 474-674 Winter 2008 Slides 1 Intro -19
Metals
Aerospace, currencyNickel AlloysPressure vessels, fittingsBrass
Heat exchangers, chemical industry, maritime industry
BronzeElectrical conductorsCopperCopper AlloysAerospace, chemical industryTitanium AlloysAerospace, automotive, sporting equipmentMagnesium Alloys
Aerospace, construction, transport, packaging, electrical conductors
Aluminum AlloysLight Alloys
Cylinders, pistons, motor blocks, construction, wear resistant materials
Cast Irons
Off shore drilling rigs, naval construction, chemical transport, food preparation, medical instruments
Stainless Steels
Utensils, construction, automotive, transmission towers …
Carbon SteelsFerrous MetalsExamples of applicationMetal
ME 474-674 Winter 2008 Slides 1 Intro -20
Ceramics and Glasses
ME 474-674 Winter 2008 Slides 1 Intro -21
Ceramics and Glasses
AdvantagesHigh moduli (stiff)
High strength
Abrasion resistant
High melting point
Resist corrosion and oxidation
Transparent
Good electrical insulators
DisadvantagesBrittle
Statistical spread in strength
Strength in compression ~ 15x strength in tension
Notch sensitive
More difficult to design with than metals or polymers
Bonding: Ionic & Covalent Bonding – Directional & StrongStructure: Crystalline or amorphous
ME 474-674 Winter 2008 Slides 1 Intro -22
Ceramics and Glasses
Windows, food preparationGlasses
High temperature furnaces, heat shields
Alumina, SiliconNitride, SiliconCarbide…
Industrial CeramicsCutting wheels, polishing clothsAbrasive Particles
Reinforcements in polymer and metalComposites
Particles(alumina, siliconcarbide, magnesia)
Reinforcements in polymer compositesFibers (glass, carbon …)Ceramic fibers and powders
Construction, electrical insulators, hygienic applications, household
Fired ceramics (pottery, bricks …)
ConstructionRocks
ConstructionHydrated ceramics(cement, plaster…)
Bulk CeramicsExamples of applicationCeramics
ME 474-674 Winter 2008 Slides 1 Intro -23
Polymers and Elastomers
ME 474-674 Winter 2008 Slides 1 Intro -24
Polymers and Elastomers
AdvantagesCan have high strength
High elastic deformation (flexible)
Low coefficient of friction
Corrosion resistant
Easy to form
Can be colored
DisadvantagesCreep at room temp.
Properties change a great deal with temperature
Low melting points
Low moduli
Difficult to recycle
Bonding: Covalent and secondary bondingStructure: Amorphous or partially crystalline
ME 474-674 Winter 2008 Slides 1 Intro -25
Polymers and Elastomers
Thermal or acoustic insulatorsElastomeric Foams
Shock absorbers, thermal insulatorsRigid Foams
Automotive interiorsFlexible FoamsFoams
Shock absorbersPolyurethane
Medical equipmentEthyl vinyl acetate
TiresPolyethylene Chloride
Tires, jointsButyl Elastomers
Electrical applications, structural applications (< 200ºC)Silicone
Integrated circuit supportsPolyamides
FabricsPolyesters
Electrical componentsPhenols
Glue, connectors, moldingEpoxyThermosets
Credit cards, plumbing, window sashes…Polyvinylechloride (PVC)
Microwave oven dishesPolyether ether ketone (PEEK)
Windows, food storagePolycarbonates
Clothing, strong fabricsPolyamide (Nylons)
Overhead transparenciesCellulose Acetate
Clothing, household appliancesAcrylobutadiene styrene (ABS)Thermoplastics
Examples of ApplicationsPolymers
ME 474-674 Winter 2008 Slides 1 Intro -26
Composites
ME 474-674 Winter 2008 Slides 1 Intro -27
Composites
AdvantagesCombine attractive qualities of other materials
Properties can be engineered to demand
LightStiffStrong
DisadvantagesExpensive
Difficult to join
Often difficult to fabricate
Bonding: Various bondingStructure: Inhomogeneous and anisotropic structure
ME 474-674 Winter 2008 Slides 1 Intro -28
Composites
Cutting tools, polishing materialsCermets
High temperature mechanical applications
Alumina Matrix Ceramic Matrix High strength electrical conductorsCopper Matrix Aerospace turbinesTitanium Matrix
Aerospace, sporting equipment, electronic packaging
Aluminum Matrix Metal Matrix TiresElastomer Matrix Aerospace, spoting equipmentThermoset Matrix
Mechanical components, protection screens
Thermoplastic MatrixPolymer MatrixExamples of ApplicationComposites
ME 474-674 Winter 2008 Slides 1 Intro -29
Natural Materials
ME 474-674 Winter 2008 Slides 1 Intro -30
Natural Materials
AdvantagesHighly Recyclable
Often high strength
Variety of physical and mechanical properties
DisadvantagesLarge variability in properties
Difficult to control
Renewable?
Variety of bonding at different levels
ME 474-674 Winter 2008 Slides 1 Intro -31
Summary of Structural materials
Broadly the “material kingdom” has 6 basic families
As designers we need to familiarize ourselves with the range of properties available from each class
Each class of material has advantages and disadvantages
Application of material depend on their properties
ME 474-674 Winter 2008 Slides 1 Intro -32
Materials information for design
The goal of engineering design: “To create products that perform their function effectively, safely, at acceptable cost”. What do we need to know to do this? More than just test data.
Test Test data
Data capture
Statisticalanalysis
Allowables
Mechanical Properties
Bulk 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 GPaTensile Strength 45 - 48 MPaYoung's Modulus 2.5 - 2.8 GPa
Successful applications
$
Economic analysisand business case
Selection ofmaterial and process
Potential applications
Characterization Selection and implementation
DATA INFORMATION KNOWLEDGE
ME 474-674 Winter 2008 Slides 1 Intro -33
Approaches to Materials Selection
Traditional approachMost design within an organization, or for a particular class of applications is with a limited number of materials.
Materials selection is based on what we are already comfortable with.
This approach is suitable in applications that are highly codified.
The introduction of a new material would require approval from governmental or standards organizations.e.g. Critical aircraft components, highway bridges require lengthy approval or certification processes
ME 474-674 Winter 2008 Slides 1 Intro -34
Approaches to Materials Selection
Optimization approachThis approach is promoted by Ashby, involves selecting a material based on critical properties, with multiple constraintsimposed on the selection process.
The approach requires the definition of a “performance index” for combining and quantifying the various requirements and constraints.
Single properties are rarely the basis of materials selection.Mechanical design may require materials with a combination of strength, stiffness, density, corrosion resistance, weldability, etc.
Master charts showing the properties of all materials, relevant to this performance index, are used to down-select from the tens of thousands of materials that are available down to a few that would work the best
ME 474-674 Winter 2008 Slides 1 Intro -35
Example: Electrical Transmission Wire
Select a material that has lowest transmission losses
Transmission Loss – heat generated due to electrical resistance of the wire
Minimize Resistance R
What about cost?
RIW 2=ALR ρ
=
66027k102,7002.9x10-8Aluminum9624 M40010,4901.47x10-8Silver108066k7.58,8901.72x10-8Copper
Melting Point(°C)
Cost($/m3)
Cost ($/kg)
Density(kg/m3)
Electrical Resistivity, ρ, (Ωm)
Material
ME 474-674 Winter 2008 Slides 1 Intro -36
Materials Selection in Product Development
Dieter
ME 474-674 Winter 2008 Slides 1 Intro -37
Factors Involved in Materials Selection
Properties
There are literally dozens of properties that a material could have.
Mechanical: Strength, stiffness, ductility, fracture toughness, fatigue strength, creep strength, etc
Thermophysical: Density, thermal conductivity, color, transparency, electrical conductivity, magnetic susceptibility, etc.
Chemical: Corrosion resistance, bonding, composition, etc.
Other: Cost
Availability
An issue that is taken into consideration in material selection is the availability of the material
is it available at handdoes it need to be ordered from a warehouse, does it need to be specially made for the application
Budinski
ME 474-674 Winter 2008 Slides 1 Intro -38
Factors Involved in Materials Selection
Economics
How many parts are to be made?a few, a few hundred or millions per yearThe economy of scale may dictate one material over another, or one
process over another.Business and Environmental Issues
Is recycleability an issue?
Are the materials hazardous or subject to environmental and other regulations?
Is there a liability issue related to a particular material?
Budinski
ME 474-674 Winter 2008 Slides 1 Intro -39
Materials Selection
In summary, a designer assumes certain properties when creating a new design or modifying an existing one.
The designer is not is not interested in the material per se, but the properties.
There are thousands of materials, each of which has a specific set of attributes or properties.
Materials selection is the process of identifying the optimum material for a particular design or application
ME 474-674 Winter 2008 Slides 1 Intro -40
Finding Information for Materials Selection
Material properties are generally available in a database. These properties may be classified and tabulated in different ways.
If a particular application requires both high impact strength and highstiffness then
Impact strength requirement eliminates ceramics.
The stiffness requirement further eliminates polymers since theyhave very low elastic moduli.
This may limit the selection to a few metals; copper, titanium, steels, stainless steels or nickel based alloys.
At this point, the engineer may look back at the experience in the company and select an alloy steel, 4140 in particular, for a part that is being designed.
Does this approach give the best material for the application?
ME 474-674 Winter 2008 Slides 1 Intro -41
Finding information
Handbooks, compilations (see Appendix D of The Text)
Suppliers’ data sheets
The Internet : www.matweb.comwww.matdata.net
Finding data using the EduPack
Browse: locate candidate on MATERIALS or PROCESS TREE and double click,
Search: enter name or word string name (trade-name, or application)
3 levels of data, with increasing content
Level 1: 64 materials 75 processes
Level 2: 94 materials 107 processes
Level 3: 2916 materials 233 processes
Tables or compilation of data but no comparison or perspective