Materials Selection for Mechanical Designcecs.wright.edu/~rsrin/Courses/ME474-674/Winter 2008... · · 2008-01-08M. F. Ashby, “Materials Selection in Mechanical Design”, Idea

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


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


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”


Example

Design objective:“A device is needed to pull the cork from wine bottle”

Not solution neutral – pulling specifies the solution

Need


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


Possible solutions

Embodiments

Direct pull Levered pull Spring assisted pullGeared pull

Embodiments of one concept


One solution


Other Concepts


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


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.


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.


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


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


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


History – the evolution of materials


Comparison of Materials

Metals


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


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


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



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


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



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


Composites


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


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


Natural Materials


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


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


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


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


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


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


Materials Selection in Product Development

Dieter


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


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


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


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?


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



Tables or compilation of data but no comparison or perspective

Documents

Materials Selection for Mechanical Designcecs.wright.edu/~rsrin/Courses/ME474-674/Winter 2008... · · 2008-01-08M. F. Ashby, “Materials Selection in Mechanical Design”, Idea