material selection 1-5

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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef

MaterialSelectionCharts


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Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefAin Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

Lecture 1: Introduction to Material Selection

in Mechanical DesignThe Design Process

COMPETITIVE DESIGN of new products is the key capability that companies must masterto remain in business. It requires more than good engineering, it is fraught with risks andopportunities, and it requires effective judgment about technology, the market, and time.

The concept and configuration development process:

Activ it ies occur throughout product development

The process starts with identifying the customer population for the product and developing arepresentation of the feature demands of this group. Based on this representation, afunctional architecture is established for the new product, defining what it must do. The nextstep is to identify competitive products and analyze how they perform as they do. Thiscompetitive benchmarking is then used to create a customer-driven specification for theproduct, through a process known as quality function deployment. From this specification,different technologies and components can be systematically explored and selected throughfunctional models. With a preliminary concept selected, the functional model can be refinedinto a physically based parametric model that can be optimized to establish geometric and

physical targets. This model may then be detailed and established as the alpha prototype ofa new product.

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Customer Needs & Problem Definition:

In the early 1980s, Sony offered an improved magnetic videotape recording technology, theBetamax system. Although it offered better magnetic media performance, it did not satisfycustomers, who rather were more concerned with low cost, large selection of entertainment,and standardization.

In 1996, both Ford and Toyota launched new family sedans. Three years earlier, each hadtorn apart and thoroughly analyzed each other's cars. Ford decided to increase the optionsin its Taurus, matching Toyota's earlier Camry, while Toyota decided to decrease the optionsin its Camry, matching Ford's earlier Taurus.

Note how the design depends on the viewpoint of the individual who defines the problem

As Proposed by Project Sponsor As Specified in the Project Request As designed by the senior designer

As producer by manufacturing As installed at the users site What the user wanted

Task ClarificationConceptual and configuration design ofproducts begins and ends with customers,

emphasizing quality processes and artifactsthroughout. We thus initiate the conceptualdesign process with task clarification:understanding the design task and mission,questioning the design efforts andorganization, and investigating the businessand technological market. Task clarificationsets the foundation for solving a design task,where the foundation is continually revisited tofind weak points and to seek structuralintegrity of a design team approach. It occursnot only at the beginning of the process, butthroughout.

2Lecture 1 [Introduction to Material Selection in Mechanical Design]


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Mission Statement and Technical QuestioningA mission statement and technical clarification of the task are important first steps in theconceptual design process. They are intended to:

Focus design efforts

Define goals

Define timelines for task completion

Provide guidelines for the design process, to prevent conflicts within the design team andconcurrent engineering organization

The first step in task clarification is usually to gather additional information. The followingquestions need to be answered, not once but continually through the life cycle of the designprocess:

What is the problem really about?

What implicit expectations and desires are involved?

Are the stated customer needs, functional requirements, and constraints trulyappropriate?

What avenues are open for creative design?

What avenues are limited or not open for creative design? Are there limitations on scope?

What characteristics/properties must the product have?

What characteristics/properties must the product not have?

What aspects of the design task can and should be quantified?

Do any biases exist in the chosen task statement or terminology? Has the design taskbeen posed at the appropriate level of abstraction?

What are the technical and technological conflicts inherent in the design task?

For further information about the design process, reviewASM Handbook, Volume 20, Materials Selection and Design

Relation of Materials Selection toDesign:

An incorrectly chosen material canlead not only to failure of the part butalso to unnecessary cost.

Selecting the best material for a partinvolves more than selecting amaterial that has the properties toprovide the necessary performance inservice; it is also intimately connectedwith the processing of the materialinto the finished part.

A poorly chosen material can add tomanufacturing cost and unnecessarilyincrease the cost of the part.

Also, the properties of the material can be changed by processing (beneficially ordetrimentally), and that may affect the service performance of the part.



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The Place of Materials Selection in the Design ProcessMaterials selection should contribute to every part of the whole design process. This isbecause it is hardly possible to proceed very far with a genuinely innovative design without

taking account of all the materials and manufacturing methods that are available for use.Any technical system consists of assemblies and components, put together in a way thatperforms a function. It can be described and analyzed in more than one way based on theideas of systems analysis-thinks of the flows of information, energy and materials into andout of the system. The system transforms inputs into outputs.

Analysis of a technical system

Component 1.1Assembly[1]

Component 1.2

Component

4

The figure illustrates the analysis of a technical system as a breakdown of the system into

assemblies and components. Each component is made of a material, differentcomponents of different materials .

Material selection is at the component level. Some components are standard,common to many designs: a wood screw, for instance; but even amongstandards there is a choice of material (the screw could be of brass, or mildsteel, or stainless steel). Some are specific, unique to the design: then thedesigner must select the material, the shape, and the processing route.

ComponentAssembly[2]

Technical

System Component

Component

ComponentAssembly[3]

Component

Component


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The Design Flowchart

Design is an iterative process. The starting point is a market need or an idea; the end point isa product that fills the need or embodies the idea. A set of stages lie between these points:

the stages ofconceptual design, embodiment design and detailed design, leading to aset of specifications the production information, which define how the product should bemade.

Design flow chart

The design flow chart shows how design tools and materials selection enter the procedure.Information about materials is needed at each stage, but at very different levels ofbreadth and precision.

At the conceptual design stage all options are open: the designer considers the alternativeworking principles or schemes for the functions which make up the system, the ways inwhich sub functions are separated or combined, and the implications of each scheme forperformance and cost.

Embodiment design takes a function structure and seeks to analyze its operation at anapproximate level, sizing the components. And selecting materials, which will performproperly in the ranges of stress, temperature and environment suggested by the analysis.The embodiment stage ends with a feasible layout that is passed to the detailed designstage.

At the detailed design stage, specifications for each component are drawn up. Criticalcomponents may be subjected to precise mechanical or thermal analysis using finite elementmethods. Optimization methods are applied to components and groups of components tomaximize performance; materials are chosen the production route is analyzed and thedesign is costed. The stage ends with detailed production specifications.



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Function, Material, Shape and Process Interactions

Function, material, shape and process interact:

Function dictates the choice of material. The shape is chosen to perform the function using the material.

Process is influenced by material properties: by formability, machinability,weldability, heat-treatability and so on.

Process obviously interacts with shape. The process determines the shape,the size, the precision and of course the cost.

The interactions are two-way.

Specification of shape restricts the choice of material, so does specificationof process.

The more sophisticated the design, the tighter the specifications and thegreater the interactions.

The figure shows the central problem of material selection in mechanical design, which is theinteraction between function, material, process and shape.

MATERIAL

PROCESS

SHAPE

FUNCTION

Transmit loads,

heat, contain

pressure, store

energy, etc.

Interaction of function, material, process and shape

The interaction between function, material, shape and process lie

at the heart of the Design process.

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Motivations for Material Selection Forces for Change: [1] Market Competition & Cost Reduction

The creation of a completely new product should commence with a clearly defined objective,

derived from market research in the case of a component for sale, and associated costaccountancy and with a time scale which should allow an optimum choice to be made. Forsuch a venture to be successful a program for market entry in relation to the cost ofdevelopment and getting into production has to be fulfilled.

However, markets will change, new competitors will arise and to some extent knowncompetitors may change their approach also. A new venture in an engineering product willalways be something of a gamble.

However, for the maximum chance of success, the choice of materials will be a key decisionin terms of 'value for money' in service and the impact on the market. Also, since the choicemay well control the method of fabrication, it will influence the whole production line

specification involving a very large capital investment, which cannot always accommodate asubsequent change of material.

The design process must continually operate even in an established manufacturingoperation. The figure below illustrates the product lifetime.

Here we see that each product offered in the market place has a life-cycle. Research anddevelopment (R&D) enables its introduction to be effected, prior to the period of growthduring which the product finds acceptance.

After a while, it becomes mature, either through built-in obsolescence or as a result of newdevelopments; by this time the far-seeing company will have replacement products alreadyin the R&D stage.

Inevitably (and this may occupies a period of months or of decades), the product will go intomarket decline. Decisions must be made as to whether any of the design features can beretained to produce a new revitalized product, or whether the operation has to be closeddown to make way for an entirely new family of products.

Technical

decision

ConceptMarket screening

Design feasibility pro-production

ProductionModification to

broaden productfamily

Cost reduction

Phase-out ObsolescenceCut-off point

Return oninvestment

Introduction Growth Maturity Decline

Types of corporatedecision

Capital investmentRecruitment of newemployees

Change of priceExpansion ofproduction

New marketstrategiesChanges in productdesign

Extend marketto overseasReduce theproduct price

Time

ProfitResearch &development

Sales volume

The life cycle of a product

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Forces for Change: [2] The Design Status of the Product

The terms dynamic and static are used to describe the type of change in the product

design. Dynamic product is a product where design changes are innovative, the concept

is likely to change, and Static Product is a product where design changes are incrementalor non-existent, the concept is unlikely to change.

Factors that create or retain aSTATIC plateau

Improving environment for theexisting design

Factors that cause a product tobecome DYNAMIC

Commodities and resources

Government action or legislation Customers not willing tochange

Changing environment User familiarity

Commodities and resources Stable technology

Customers willing to change Conformance standards

Technical advancement Stable or decreasing numberof producers

No conformance standards Few large producers

Many small producers(increasing)

Product available for a longtime

No infrastructure Existing infrastructure

Balance diagram of the macro factors that change / maintain a product status.

Factors that create or retain aSTATIC plateau

Insufficient design resources

Poor market research

Restricted design

Product interfaces with existingdesign

Rationalization or commonalityof parts

Assembling component madeby others

Using experience in design

Factors that cause a product tobecome DYNAMIC

More process design thanproduct design

Management committed todeign

Management not committed todeign

Changing PDS Stable effective PDS

Process design small Restricted PDS

Adequate time for design Limited Design time

Wide effective market research Limitation

Companies seeking newconcepts

Automation CAD

Flexible machinery subcontract,manufacture

Purchasing new machinery(dedicated)

Balance diagram of the micro factors that change / maintain a product s tatus.

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Lecture 1 [Introduction to Material Selection in Mechanical Design] 9

Forces for Change: [3] The Science-Push: Curiosi ty-driven ResearchCuriosity is the life-blood of innovative engineering. Technically advanced countries sustainthe flow of new ideas by supporting research in three kinds of organization: universities,government laboratories and industrial research laboratories.

Some of the scientists and engineers working in these institutions are encouraged to pursueideas, which may have no immediate economic objective, but which can evolve into thematerials and manufacturing methods of the next decade. Numerous now-commercialmaterials started in this way.

Forces for Change: [4] Energy and Environment: Green Design

There is a growing interest in reducing and reversing the environmental damage. Thisrequires processes, which are less toxic and products, which are easier to recycle, lighter,and less energy-intensive; and this must be achieved without compromising product quality.New technologies must be developed which can allow productivity without cost to the

environment.Concern about environmental friendliness must be injected into the design process, taking alife-cycle view of the product, which includes manufacture, distribution, use and finaldisposal.

All materials contain energy. Energy is used to mine, refine, and shape metals; it isconsumed in the firing of ceramics and cement; and it is intrinsic to oil-based polymers andElastomers.

When we use a material, we are using energy, and energy carries with it an environmentalpenalty: CO2, oxides of nitrogen, sulphur compound, dust, and waste heat. The energycontent is only one of the ways in which the production of materials pollutes, but it is the one,

which is easier to quantify than most others are.

Forces for Change: [5] The Pressure to Recycle and Reuse:

Discarded materials damage the environment; they are a form of pollution. Materialsremoved from the manufacturing cycle must be replaced by drawing on a natural resource.And materials contain energy, lost when they are dumped.

Recycling is obviously desirable. But in a market economy it will happen only if there is profitto be made. To allow this we have to look first, at where recycling works well and where itdoes not.

Primary scrap-the turnings, trimmings and tailings, which are a by-product of manufacture-

has high value: it is virtually all recycled. That is because it is uncontaminated and because itis not dispersed.

Secondary scrap has been through a consumption cycle-a newspaper, a beer can, or anautomobile; the other materials to which it is joined; by corrosion products; by ink and paintcontaminate it; and it is dispersed. It is worth little or nothing or less than nothing meaningthat the cost of collection is greater than the value of scraps itself.

Newsprint and bottles are common examples: in a free market it is not economic to recycleeither of these. Recycling does take place, but it relies on social conscience and good will,encouraged by publicity. It is precarious for just those reasons.


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Main Situations for Material Selection:The decision-making process of materials selection may be initiated for a variety of reasonsand several situations.

The three main situations are:1 The introduction of a new product, component or plant, which is being produced or builtfor the first time by the organization concerned.

2 A desire for the improvement of an existing product, or a recognition of over designwhere economy can be effected, which may be considered as an evolutionary change.

3 A problem si tuation , due for example to the failure of components leading to rejectionby customers, failure of supplies, or failure of in-house manufacturing plant, necessitatinga change in material use.This is the area where the metallurgist must be employed, for investigating a failure, andon determination of the cause, suggesting a change of design or of the materialemployed.

Materials Selection Objectives:

The selected material should be:1 Readily available.

2 Can be formed into the desired shape with the required dimensional tolerances.

3 After getting the shape, will perform the designed functions of the product.

4 Will continue performing the functions satisfactorily for the required lifetime of the product.

5 Can be disposed of, or recycled, in the way, which is environmentally acceptable.

Note that:

The selected material should achieve these objectives at a cost, which permit the product

to be offered at a price that attracts customers and gives a profitable return to themanufacturer.

Among the material selection many objectives, there is a main objective, which is failureprevention.

Material Failure Modes

The different material failure modes are listed in following table as classified by Collinos,

Each failure mode has:

a failure mechanism

material selection

guide lines material selection rules

to prevent the failuremode from takingplace.

1. Elastic deformation2. Yielding3. Brinelling4. Ductile failure

5. Brittle fracture6. Fatiguea. High-cycle fatigueh. Low-cycle fatiguec. Thermal fatigued. Surface fatiguee. Impact fatiguef. Corrosion fatigueg. Fretting fatigue9. Impacta. Impact fractureb. Impact deformationc. Impact wear

d. Impact frettinge. Impact fatigue

8. Corrosiona. Direct chemical attackb. Galvanic corrosionc. Crevice corrosion

d. Pitting corrosione. Intergranular corrosionf. Selective leachingg. Erosion-corrosionh. Cavitationi. Hydrogen damagej. Biological corrosionk. Stress corrosion9. Weara. Adhesive wearb. Abrasive wearc. Corrosive weard. Surface fatigue wear

e. Deformation wearf. Impact wearg. Fretting wear

10. Frettinga. Fretting fatigueb. Fretting wearc. Fretting corrosion

11. Galling and seizure12. Scoring13. Creep14. Stress rupture15. Thermal shock16. Thermal relaxation17. Combined creep andfatigue18. Buckling19. Creep buckling20. Oxidation21. Radiation damage22. Bonding failure

23. Delamination24. Erosion


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Investigations about the frequency of failure causes in some engineering industries indicatethat the main cause for failure is improper material selection.

Origin %Improper material selection 38Fabrication defects 15

Faulty heat treatments 15

Mechanical design fault 11

Unforeseen operating conditions 8

Inadequate environment control 6

Improper or lack of inspection and quality control 5

Frequency of Causes of Failurein Some Engineering IndustriesInvestigations:

Material mix-up 2

Origin %Corrosion 29Fatigue 25

Brittle fracture 16

Overload 11

High temperature corrosion 7

Stress corrosion / corrosion fatigue / hydrogenembrittlement

6

Creep 3

Frequency of Failure Modes inSome Engineering IndustriesInvestigations.

Wear, abrasion, and erosion 3

Failure experience matrix

Collins suggested a failure experience matrix,which is an attempt to place failure analysis on afirm analytical basis by classifying each failure withrespect to failure mode, the elemental function thatthe component provided, and the corrective actionthat should be taken recurrence of the failure. Thusthe failure experience matrix is a three dimensionalassemblage of information cells. Corrective action

is defined as any measure or steps taken to returnfailed component or system to satisfactoryperformance.

Three dimensional experience matrixassemblage of information cells

Elemental Mechanical Function

Failure Mode

Corrective Action

Dieter stated that if there ware a computerized database that encompassed a nationalinventory of failures, it would have a great use in engineering design. An engineer whoneeded to design a critical component would enter the matrix with elemental mechanicalfunction and learn about failure modes that likely to occur as well as the corrective actionsmost likely to avoid failure.


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Some of elemental mechanical functions and the corrective actions of failure experiencematrix in a study on 500 failed parts from U.S. army helicopters

Elemental mechanical functions:1. Supporting 36. Permanent fastening 71. Force sensing2. Attaching 37. Pressure increasing 72. Spacing3. Motion constraining 38. Streamlining 73. Temporary supporting4. Force transmitting 39. Motion reducing 74. Gas switching5. Sealing 40. Filtering 75. Electrical transforming6. Friction reducing 41. Lighting 76. Power absorbing7. Protective covering 42. Pumping 77. Information attaching8. Liquid constraining 43. Gas transferring 78. Sound absorbing9. Pivoting 44. Aero. force transmitting 79. Constraining10. Torque transmitting 45. Motion transmitting 80. Flexible coupling11. Pressure supporting 46. Signal transmitting 81. Removable coupling12. Oscillatory sliding 47. Motion damping 82. Damping13. Shielding 48. Force distributing 83. Electrical distributing14. Sliding 49. Reinforcing 84. Load distributing15. Energy transforming 50. Pressure sensing 85. Gas guiding16. Removable fastening 51. Information transmitting 86. Pressure indicating17. Limiting 52. Coupling 87. Electrical insulating18. Electrical conduction 53. Displacement indicating 88. Sound insulating19. Contaminant constraining 54. Clutching 89. Temporary latching20. Linking 55. Fastening 90. Force limiting21. Continuous rolling 56. Information indicating 91. Force maintaining22. Liquid transferring 57. Position indicating 92. Variable position maintenance23. Force amplifying 58. Movable lighting 93. Liquid pumping24. Power transmitting 59. Partitioning 94. Electrical reducing25. Covering 60. Position restoring 95. Rolling26. Oscillatory rolling 61. Flexible spacing 96. Position sensing27. Energy absorbing 62. Electrical amplifying 97. Energy storing28. Light transmitting 63. Adjustable attaching 98. Liquid storing29. Viewing 64. Shape constraining 99. Flexible supporting30. Energy dissipating 65. Deflecting 100. Switching31. Guiding 66. Disconnecting 101.Pressure to torque transmitting32. Latching 67. Electrical limiting 102. Electrical transmitting33 electrical switching 68. Motion limiting 103. Flexible motion transmitting34. Stabilizing 69. Pressure limiting 104. Flexible torque transmitting35. Gas constraining 70. Sensing 105. Torque limiting

Corrective actions for failure-experience matrix:Direct replacement Changed vendor Improved instructions to userChange Of material Changed dimensions Design change to improve partSupplement part Improved quality control Changed mechanism of operationAdded adhesive Changed lubricant type Improved run-in procedureProvided drain Improved lubrication Changed manufacturing procedureAdded sealant Applied surface coating Changed mode of attachmentRepositioned part Applied surface treatment Changed method of lubricationRepaired part More easily replaceable part Added or changed locking featureReinforced part Changed to correct part Revised procurement specificationEliminated part Made part interchangeable Provided for proper inspection

Strengthened part Changed loading on part Changed electrical characteristicsAdjusted part Relaxed replacement criteria


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Review question:

What is the meaning of Task Clarification & Mission Statement?

Explain how the Information about materials is needed at each design stage.

Discuss the different forces for change, which motivate the material selection process.

Discuss the interaction between Function, Material, Shape and Process.

Explain the Main Situations for Material Selection.

What are the main Materials Selection Objectives?

What is the meaning of Failure-experience matrix?

Text Book:

M. F. Ashby, (1992), Materials Selection in Mechanical Design, Pergamon Press.

References:

J.A. Charles, FAA Crane, (1989), Selection and Use of Engineering Materials, ButterworthsHeinemann.

E.H. Cornish, (1987) Materials and The Designer, Cambridge University Press

Bill Hollins, and Stuart Pugh, (1990), Successful Product Design, Butterworths.

J. A.Collins, (1981) Failure of Materials in Mechanical Design, Wiley-Inter-science.

George Dieter, (1983) Engineering Design, A Materials and Processing Approach, McGraw-Hill.

ASMMetals Handbook, (1999), Volume 20, Materials Selection and Design, AmericanSociety for Metals, Metals Park, Ohio, USA.


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Ain Shams University Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefFaculty of EngineeringDesign & Prod. Eng. Dept.

Lecture 2 [Engineering Materials & Their Properties]

Lecture 2:Engineering Materials & Their PropertiesClasses of Engineering Materials:

Metals

They have relatively high elastic moduli. They can be made strong by alloying,

mechanical working, and heat treatment.

They show good ductility. This allowsthem to be formed by deformation

processes.

They typically yield before fracturing. They are prone to fatigue failure. Relative to other material classes they are

not very resistant to corrosion.

Ceramics and Glasses:

They have too high elastic moduli, butunlike metals they are brittle. Because

ceramics have no ductility, they have a

low tolerance to stress concentrations or

for high contact stresses.

Their strength in compression is about 15times larger than their strength in tension.

Brittle materials always show a wide

scatter in strength.

They are stiff hard and abrasion resistant,hence their use in bearing and cutting

tools.

They retain their strength to hightemperatures.

They are resistant to corrosion.Polymers & Elastomers:

They have low elastic moduli, about 50times less than those of metals. However,

some polymers can be very strong

nearly as strong as metals. As aconsequence, the elastic deflections can

be large.

Polymers creep even at room temperature.Very few polymers having useful strength

above 250C.

When specific properties, e.g. strength perunit mss, are important, then some

polymers are as good as metals.

They are easy to shape. Polymers are corrosion resistant. They have a low coefficient of friction.

Composites:

They combine attractive properties ofother classes of materials while avoiding

some of their drawbacks.

They are light, stiff and strong, and theycan also be tough.

Most currently available composites havepolymer matrices epoxy or polyester,

usually enforced by fibers of glass,

graphite, or Kevlar. They cannot be used

above 250C because of the polymer

matrices.

Composite components are expensive, andmanufacturing processes are not well

developed. They are also difficult to join.

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Lecture 2 [Engineering Materials & Their Properties] 2

Material classes, generic members, and abbreviated names:

Class Members Short nameEngineering alloys

(The metals and alloys of engineering)Aluminium alloysCopper alloys

Lead alloysMagnesium alloysNickel alloysSteelsTin alloysTitanium alloysZinc alloys

Al alloys

Cu alloysLead alloysMg alloysNi alloysSteelsTin alloys

Ti alloysZn alloys

Engineering polymers

(The thermoplastics and thermosets of engineering)EpoxiesMelamines

PolycarbonatePolyesters

Polyethylene, high density

Polyethylene, low densityPoly formaldehydePoly methyl metha crylate

PolypropylenePoly tetra fluor ethylene

Polyvinyl chloride

EPMEL

PCPESTHDPE

LDPEPFPMMA

PP.PTFEPNC

Engineering ceramics

(Fine ceramics capable of load bearing application)

Alumina

DiamondSialonsSilicon CarbideSilicon nitrideZirconia

Al2O3

CSialonsSiCSi3N4ZrO2

Engineering composites

(The composites of engineering practice)A distinction is drawn between the properties of a ply UNIPLY and of a laminate LAMINATES

Carbon fiber reinforced polymer

Glass fiber reinforced polymerKevlar fiber reinforced polymer

CFRP

GFRPKFRP

Porous ceramics

(Traditional ceramics, cement, rocks, & minerals)BrickCementCommon rocks

ConcretePorcelainPottery

Brick

CementRocks

ConcretePclnPot

Glasses

(Ordinary silicate glass)Borosilicate glassSoda glassSilica

B-glassNa-glassSiO2

Woods

Separate envelopes describe properties parallel to the grainand normal to it, and wood products)

Ash

BalsaFir

OakPineWood products

Ash

BalsaFir

OakPineWood products

Elastomers

(Natural and artificial rubbers)Natural rubberHard butyl rubber

PolyurethaneSilicone rubberSoft butyl rubber

RubberHard butylPUSiliconeSoft butyl

Polymer foams

(Foamed polymers of engineering)CorkPolyesterPolystyrene

Polyurethane

CorkPESTPS

PUNote that abbreviated names as used in material selection charts developed by M.F. Ashby.


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[2] Material Properties:

Each material has a set of attributes (properties). The designer seeks a specific combination of these attributes (a property profile).

The material name is the identifier for a particular property profile. The properties themselves are standard, density, strength, toughness, etc.

Design Limiting Material Properties

Class Property Symbol Units

General Relative Cost CR ---Density Mg/m 3

Mechanical Elastic Modulus E, G, K GPaStrength (yield / ultimate / fracture) f MPaToughness G c KJ/m

2Fracture Toughness KIC MPa m

1/2

Damping Capacity ------Fatigue Ratio f ------

Thermal Thermal Conductivity W/m KThermal Diffusivity a m 2/sSpecific Heat CP J/Kg KMelting Point T m KGlass Temperature T g KThermal Expansion Coefficient K-1Thermal Shock resistance T KCreep Resistance ----- ------

Wear Archard Wear Constant KA MPa-1

Corrosion / Corrosion Rate ----- ------Oxidation Parabolic rate constant KP m

2/s

Elastic Modulus Shear Modulus Bulk Modulus

E= 3G/(1+G/3K) G= E/2(1+) K= E/3(1-2) =1/3f= KIC / (C) KIC the resistance to the propagation f a crack.


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Ain Shams University Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefFaculty of EngineeringDesign & Prod. Eng. Dept.Material Mg/m3Density,

Mass per unit volume, Mg/m3

Iron, Steels

Titanium alloysAluminium alloys

Magnesium alloys

Polycarbonate

7.8

4.52.7

1.7

1.2

Material E, GPa Stiffness, Elastic MODULUS, E

Slope of the liner elastic part of the

stress-strain curve, GN/m2

= GPa

Poissons ratio,

= lateral / axial

Iron, Steels

Titanium alloys

Aluminium alloys

Magnesium alloys

Polycarbonate

RubbersSilicon

SiC

200

116

70

43

2.6

0.01-0.1160

410

0.27

0.34

0.33

0.35

0.4

0.490.22

0.3

For isotropic materials:

E Youngs Modulus Poissons ratioG= E/2(1+) Shear ModulusK= E/3(1-2) Bulk ModulusTypically

1/3, G 3/8 E KEElastomers are exceptional:

1/2, G 1/3 E K>>E

Strength, f, MN/m2 = MPa.Strength requires careful definition and usually defined differently for different materials and mode of

loading.

Material y, MPaMetalsfis identified with the 0.2% offset yield strength y.It is the stress level the application of which has caused

dislocations to move large distances through the crystals

of the metal, so that upon unloading from this stress level

there is a measurable permanent plastic strain of 0.2%.y in compression y in tension

Steels

Titanium alloys

Aluminium alloys

Magnesium alloys

200-2000

800-1200

200-500

100-200

4Lecture 2 [Engineering Materials & Their Properties]


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Ceramics & GlassesStrength for ceramics and glasses depends strongly

on the mode of loading. In tension, strength means

the fracture strength, ft. In compression it meansthe crushing strengthfC, which is much larger,typically

fC in compression 15ft in tensionModulus of Rupture, MOR MPa

If the material is difficult to grip, as is the casewith ceramics, its strength can be measured in

bending.

The Modulus or Rupture, MOR, is the maximum

surface stress in a bent beam at the instant of

failure.

In ceramics MOR 1.3ft in tension

Polymers:

fis identified as the stress y at whichthe stress strain curve has become

markedly non-linear- typically a strain

of 1%. Yield mechanisms: shear

yielding, crazing.

Material y, MPaPolymers are a little stronger 20% in compression thanin tension.y in compression 1.2 y in tension PolycarbonatePMMA 80100Composites:

The strength of a composite is typically defined by a set deviation e.g. 0.5% from linear elastic

behaviour.

The strength of long fibre composites is approximately 30% lower in compression than in tension,

because in compression the fibres buckle.

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Ultimate tensile strength,u- MPaThis defined as the maximum engineering stress that can be achieved in an un-notched round bar of

the material loaded in tension. For brittle solids ceramics, glasses and brittle polymers it is the same

as fin tension. For metals, ductile polymers and most composites it is larger than f, by factor ofbetween 1.1and 3. In metalsu is higher than y because of work hardening.Hardness, H MPa:

The hardness of material is a crude

measure of its strength. It is

measured by pressing a point

diamond or hardened steel ball into

the surface of the material. It is

defined as the indenter force divided

by the projected area of the indent.

H 3 fResilience, R- J/m

3

This measure the

maximum elastic strain

energy per unit volume

stored in a material. It is

the area under the elastic

part of the stress straincurve.

R = f fR = f2 / 2EMaterials with large

values of R are suitable

for good springs

Fracture Toughness, KIC- MPa mThe fracture toughness of a material is a

measure of the resistance of the material to

failure by parting of the solid into two or

more pieces by the propagation of a macro

crack.

Where;

KIC is the critical stress intensity factor,

material property, and 2c= crack length.

KIC = c

6


21/45



Material KICMPa mFracture Criterion:

KI < KIC No Fracture

KI >= KIC Fracture

Rule of thumb:Avoid materials with fracture toughness less than 15MPa m

Most metals have values ofKIC in the range 20 100MPa m

Engineering ceramics have values ofKIC - 1 5MPa mTherefore, engineers view them with great suspicion.

Steels

Titanium alloys

Aluminium alloysEpoxies

Polystyrene

Polycarbonate

PMMA

PETP

Soda-Lime Glass

Al2O3

Si3N4

SiC

Al2O3, 15% ZrO2

50-200

20-75

20-400.3-0.5

0.5

2.5-3.8

1.2-1.7

3.5-6.0

0.7

3.0-5.0

4.0-5.0

3.5

10.0

Loss coefficient The loss coefficient ,

measures the fractional energy dissipated in

a stress-strain cycle.

D= U/U specific damping capacity = D / 2 = U/ 2 The loss coefficient

Thermal ConductivityThermal

conductivity measures the flux of heatdriven by a temperature gradient dT/dX.q= (dT / dX)

7


22/45


Linear thermal ExpansionThe linear-

thermal expansion coefficient a measures

the change in length, per unit length, when

the sample is heated.


= (1/L) (d/dT)

T m, melting temperature

T g, glass temperature, is a property of non-crystalline solids, which do not have a sharp meltingpoint; it characterizes the transition from true solid to a very viscous liquid.

T max is the maximum service temperature, at which the material can be used reasonably withoutoxidation, chemical change or excessive creep becoming a problem.

T s is the softening temperature, which is needed to make the material flow easily for forming andshaping.

The thermal shock resistance is the maximum temperature difference through which a material can

be quenched suddenly, without damage.

The thermal shock resistance and creep resistance are important for high temperature design.

CreepCreep is the slow time dependent

deformation, which occurs when materials

are loaded above 1/3 T m or 2/3 T g. it ischaracterized by a set of creep constants:

n, creep exponent (dimensionless)

Q, activation energy (KJ/mole)

A, kinetic factor (s-1

)o, reference stress (MPa)The strain rate oo = A [ /o ]n * exp [Q/RT]

Wear & Corrosion:

Wear, oxidation and corrosion are harder to quantify, partly because they are surface, not bulk,

phenomena, and partly because they involve interactions between two materials, not just the property

of one.


23/45

Ain Shams University Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefFaculty of EngineeringDesign & Prod. Eng. Dept.WearWear is the loss of material from

surfaces when they slide. The wear

resistance is measured by the Archard wear

constant KA (m2/MN or MPa-1)

W/A = KA P

Where;

W, wear rate (volume of weight lost per

unit distance slid)

A, area of the surface.

P, normal pressure.

Data ofKA is available, but it must be

interpreted as the property of the sliding

couple, not of just one member of it.

Corrosion


Corrosion is the surface reaction

of the material with gases or liquids.

Sometimes a simple rate equation can be

used but normally the process is too

complicated to allow this.

Dry corrosion, oxidation behavior is

characterized by the parabolic rate constant

for oxidation KP (m2/s).

Wet corrosion is much more complicated,

and cannot be captured by rate equations, itis more useful to catalogue corrosion

resistance by a simple scale such as A (very

good) to E (very bad).

Summary

There are six important classes of materials for mechanical design: Metals, polymers, ceramics,

glass, and composites.

Within a class there is certain common ground:

Ceramics as a class are hard, brittle, and corrosion resistant. Metals as a class are ductile, tough, and electrical conductors. Polymers as a class are light, easily shaped, and electrical insulators.This is makes the classification of materials into classes useful.

Importance of material properties versus material classes:

Each material has some attributes, its properties, e.g. density, modulus, strength, toughness,thermal conductivity, etc.

A designer does not seek a particular material, but a specific combination of these attributes: aproperty-profile.

The material name is merely the identifier for a particular property-profile


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Ain Shams University Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefFaculty of EngineeringDesign & Prod. Eng. Dept.Lecture 3: The Performance Maximizing Indices

Material Selection has 4 basic steps:1. Translation of design requirements into a material specification2. Screening out of materials that fail constraints3. Ranking by abili ty to meet objectives; material indices4. Search for supporting information for promising candidates

Note that: the task is explained in the following three lectures as follows;

Step 1 Lecture 3 Performance maximizing indices

Step 2 Lecture 4 Material selection charts

Step 3 & 4 Lecture 5 Formalization of material selection

Analysis of design requirements:

The analysis of design requirements and development of performance index steps are:

Identify function, constraints, objective and free variables, (list simple constraints for limit-stage).

Write down equation for objective -- the performance equation .

If it contains a free variable other than material identify the constraint that limi ts it .

Use this to eliminate the free variable in performance equation.

Read off the combination of material properties that maximise performance.

The concept is illustrated in more details in the next page.

1Lecture 3 [Performance Maximizing Indices]


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Lecture 3 [Performance Maximizing Indices] 2

Performance Maximizing Indices:

Three things specify the design of a structural element, the functional requirements, the geometry, and

the properties of the material of which it is made. The performance of the element is described by an

equation of the form:

P= f (F, G, M)Where:

F is functional requirements,

G is geometric parameters, and

M is material properties.

P describes some aspect of performance of the components: its mass, or volume, or cost, or life forexample.

Optimum design is the selection of the material and geometry, which maximize or minimize P,

according to its desirability. The three groups of parameters can be separable, P can be written as

follow P= f1 (F)* f2 (G)* f3 (M), Where f1, f2, and f3 are functions.

When the groups are separable, the optimum choice of material becomes independent of the details of

the design; it is the same for all the details of F and G. This enables enormous simplification; the

performance for all F and G is maximized by maximizing f3 (M), which is called the performance

index. Experience shows that he groups are usually separable.

Procedure for driving a Performance Index:

1 Identify the attribute to be maximized or minimized (weight, cost, stiffness, strength, etc.).

2 Develop an equation for this attribute in terms of functional requirements, the geometry andthe material properties (the objective function).

3 Identify the free (unspecified) variables.

4 Identify the constraint; rank them in order of importance.

5 Develop equation for the constraints (no yield, no fracture, no buckling, max heat capacity,cost below target, etc.).

6 Substitute for the free variables from the constraints into the objective function.

7 Group the variables into three groups: functional requirements, F, geometry, G, and materialproperties, M, thus: ATTRIBUTE< f (F, G, M)

8 Read the performance index, expressed as a quantity M to be maximized.

9 Note that a full solution is not necessary in order t o identify the material property group.


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Lecture 3 [Performance Maximizing Indices] 3

Example 1: Performance Index for a Light Strong Tie

A material is required for a solid cylindrical tie rod of length L, to carry a tensile force F with safety

factor Sf; it is to be of minimum mass.

The mass is:

Where A is the cross sectional area, is the densitym= A L

To carry the tensile load FF/A = f/ S f

Eliminating A between the two equations.

The first bracket contains the functionalrequirement that is the specified load is safely

supported.

The second bracket contains the specifiedgeometry (the length of the tie).

The last bracket contains the material properties.

m= (Sf F ) (L) ( / f)

The lightest rod, which will safely carry the load F

without failing is that with the largest value of the

performance index:

M = [ f / ]

Example 2: Performance Index for a Light Stiff Column

A material is required for a solid cylindrical column of length L, to carry a compressive force F with

safety factor Sf; it is to be of minimum mass.

The mass is:

Where A is the cross sectional area, is

the density

m= A L

The column will buckle elastically when

the Euler load, Fcrit, is exceeded.

The design is safe if:

n is a constant that depends on the endsconstraints.

F


27/45




28/45




29/45


This simplified material selection chart explains the use of selection guidelines of the previous three

examples for Screening out of materials that fail the selection constraints.

Attachments:

Performance maximizing Property Groups table in 2 pages as carried out by M. Ashby.



30/45

Ain Shams University

Faculty of Engineering

Material & Process Selection

Summary of Lecture Notes

Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.

Lecture 4 [Material Selection Charts]

Lecture 4: Material Selection Charts

Material Selection has 4 basic steps:1. Translation of design requirements into a material specification2. Screening out of materials that fail constraints3. Ranking by abili ty to meet objectives; material indices4. Search for supporting information for promising candidates





Material Selection Charts:

The use of graphical relationship approach from the data is ideally engineer-friendly and particularly

effective in the initial sorting stages of a selection procedure.

Ashby has described such a graphical approach for materials selection in conceptual design, i.e. the

first stages of design, choosing from the vast range of engineering materials, an initial subset on which

design calculations can be based.

In this approach the data for the mechanical and thermal properties of all materials are presented as a

set of Materials Selection Charts. The axes are chosen to display the common performance-limiting

properties: modulus, strength, toughness, density, and thermal conductivity wear rate etc. The,logarithmic scales allow performance-limiting combinations of to be examined and compared.

List of material selection charts proposed by Ashby:1. Youngs' Modulus v Density2. Strength v Density3. Fracture Toughness v Density4. Young's Modulus v Strength5. Specific Modulus v Specific Strength6. Fracture Toughness v Young's Modulus7. Fracture Toughness v Strength8. Loss Coefficient v Young's Modulus9. Thermal Conductivity v Thermal Diffusivity10.Thermal Expansion Coefficient v Thermal Conductivity11.Thermal Expansion Coefficient v Young's Modulus12.Normalized Strength v Thermal Expansion Coefficient13.Strength v Temperature14.Young's Modulus v Relative Cost15.Strength v Relative Cost16.Wear Rate v Hardness17.Young's Modulus v Energy Content18.Strength v Energy Content

1


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Design & Prod. Eng. Dept.



Dr. Ahmed Farid A. G. Youssef

Lecture 4 [Material Selection Charts] 2

Using Material Selection Charts

There are three main things to think about when choosing materials

(in order of importance):1.Will they meet the performance requirements?

2.Will they be easy to process?

3.Do they have the right 'aesthetic' properties?

So that leaves us with performance requirements...

Most products need to satisfy some performance targets, which wedetermine by considering the design specification. e.g. they must be cheap,

or stiff, or strong, or light, or perhaps all of these things...

Each of these performance requirements will influence which materials we

should choose - if our product needs to be light we wouldn't choose lead and

if it was to be stiff we wouldn't choose rubber!

So what we need is data for lots of material properties and for lots of

materials. This information normally comes as tables of data and it can be a

time-consuming process to sort through them. And what if we have 2

requirements - e.g. our material must be light and stiff - how can we trade-

off these 2 needs?

The answer to both these problems is to use material selection charts.

Here is a materials selection chart for 2 common properties: Young's

modulus (which describes how stiff a material is) and density.


32/45





Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.

On these charts, materials of each class (e.g. metals, polymers) form

'clusters' or 'bubbles' that are marked by the shaded regions. We can see

immediately that:

Metals are the heaviest materials, Foams are the lightest materials, Ceramics are the stiffest materials.

Selection charts are really useful is in showing the trade-off between 2

properties, because the charts plot combinations of properties. For instance if

we want a light and stiff material we need to choose materials near the top

left corner of the chart - so composites look good.

3Lecture 4 [Material Selection Charts]


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Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.Consider a design problem where the specification is for a component that is

both light and stiff (e.g. the frame of a racing bicycle).

What can we conclude?

The values of Young's modulus for polymers are low, so mostpolymers are unlikely to be useful for stiffness-limited designs.

Some metals, ceramics and woods could be considered butcomposites appear best of all.

Note that the values for Young's modulus cover a huge range and wehave therefore used a logarithmic scale.



34/45





Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.It is unlikely that only 2 material properties matter, so what other properties

are important? Let's consider strength and cost - these properties are plotted

as another chart.


The strength of ceramics is only sufficient for loading in compression -they would not be strong enough in tension, including loading in

bending.

Woods may not be strong enough, and composites might be tooexpensive.

Metals appear to give good overall performance5Lecture 4 [Material Selection Charts]


35/45





Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.Selection charts can also be used to select between members of a given class

by populating it with the main materials. For instance, we can do this for

metals in the stiffness-density chart.


Some metals look very good for light, stiff components - e.g. magnesium,

aluminum, titanium, while others are clearly eliminated - e.g. lead.

Steels have rather a high density, but are also very stiff. Given their high

strength and relatively low cost, they are likely to compete with the other

metals.



36/45



Design & Prod. Eng. Dept.



Dr. Ahmed Farid A. G. Youssef

Lecture 4 [Material Selection Charts] 7

Summary:

By considering 2 (or more) charts, the properties needed to

satisfy the main design requirements can be quickly assessed.

The charts can be used to identify the best classes of

materials, and then to look in more detail within these

classes.

There are many other factors still to be considered,

particularly manufacturing methods.

The selection made from the charts should be left quite broadto keep enough options open.

A good way to approach the problem is to use the charts to

eliminate materials, which will definitely not be good

enough, rather than to try and identify the single best

material too soon in the design process.


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Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.Example: Materials for Lightweight Table LegsSolved by Cambridge material Engineering Selector software CES Courtesy M. F. Ashby

The selection methodology used in CES Materials can be encapsulated by developing a case

study. Here, we will use the design of a simple table to illustrate the development of someselection criteria; we will apply them and plot them on some selection stages by using CES.

The Design Problem

Luigi Tavolino, furniture designer, conceives of a lightweight table of daring simplicity: a flat

sheet of toughened glass supported on slender, cylindrical legs. The legs must be solid (to

make them thin) and as light as possible (to make the table easier to move). They must support

the tabletop and whatever is placed on it without buckling. What materials could one

recommend?

Design Requirements

We must first identify the Function, Objective and Constraints of our problem.

FUNCTION Column (support compressive loads)OBJECTIVE Minimize mass

CONSTRAINTS Must not buckle

The Model

Figure 1 - A lightweight table with slender cylindrical legs

The performance-maximizing index

M1 = [E1/2/]



38/45





Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.The SelectionWe can now plot the material properties of our Performance Index using the CES software. In

order to identify which materials maximize the performance index, we need to plot a line

representing it on the graph. We use logarithmic axes on the graph and note that a simpleperformance index typically has the form:

M = P1/P2n

Taking logs of this equation gives:

log P1 = n log P2 + log M

So, if P1 and P2 are plotted on logarithmic scales, the equation describes a line of slope n on

the plot, with its position determined by the value of M. We are seeking to maximize the value

of M, so our selection is optimised by moving the line to the highest value of M, which still

leaves a viable subset of materials exposed above the line.

For the table, we are seeking the subset of materials which have high values of E1/2

/ , so we

plot a line of slope 2 on our graph.

Figure 2 shows the appropriate chart: Young's Modulus plotted against the density. The

guideline is displaced upwards (retaining the slope) until a reasonably small subset of

materials is isolated above it; it is shown in the position M1 = 6 GPa1/2

/(Mg/m3). Materials

above this line have higher values of M1. They are identified on the figure.

The thinnest legs is that made of the material with the largest value ofM2 =E

Figure 2 Materials for light slender legs



39/45





Dr. Ahmed Farid A. G. YoussefDesign & Prod. Eng. Dept.Woods meet the criteria and so do composites such as CFRP. Certain of the engineering

ceramics also meet the stated design goals. However, ceramics, we know, are brittle they

lack fracture toughness. Table legs are exposed to abuse - they get knocked and kicked;

common sense suggests that an additional constraint is required - that of adequate fracturetoughness. A Selection stage that takes this into account is shown in Figure 3.

Figure 3 A Protective Selection Stage to eliminate brittle and expensive materials

ResultsMaterial M1

(GPa

m3/Mg)

M2

(GPa)

Comment

Woods 5-8 4-20 Outstanding M1, Poor M2, Cheap,

traditional, reliable.

CFRP 4-8 30-200 Outstanding M1, and M2, but

expensive.

GFRP 3.5-5.5 20-90 Much cheaper than CFRP, but not so

good.

Ceramics 4-8 150-1000 Outstanding M1, and M2, eliminated by

brittleness.So, woods and CFRP make good materials for table legs - although the cost of CFRP may cause Snr

Tavolino to reconsider his design. If (improbably) the goal were to design a light slender-legged table

for use at high temperatures, then ceramics would have to be reconsidered. The brittleness problem

can be designed around by protecting the legs or by pre-stressing them in compression.

Review the material selection charts at:

M. F. Ashby, (1992), Materials Selection in Mechanical Design, Pergamon Press. Chapter 5.



40/45


Lecture 5 [Formalization of Material Selection]

Lecture 5: Formalization of Material Selection

Material Selection has 4 basic steps:1. Translation of design requirements into a material specif ication2. Screening out of materials that fail constraints3. Ranking by ability to meet objectives; material indices4. Search for supporting information for promising candidates





Formalization of Material Selection:Formalization of material selection is the third step after defining one or two material groups by

applying a selection criterion (performance index) and a corresponding selection chart, as previously

explained.

The aim here is to define the optimum material name within the proposed material group.

1


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Lecture 5 [Formalization of Material Selection] 2

Formalization of Material Selection Procedure

Illustrative Example of Material Selection Formalization By: J.A. Charles & FAA Crane

In selecting a material for a given application the materials engineer is faced with an almost endless

number of possibilities. If the choice is to be made economy of time and effort, but also with theassurance that no possibilities are overlooked, some systemization of procedures is essential.

The basis for materials selection is a shopping list of design requirements and the selection

procedure should be as numerate as possible. However the extent to which this can be achieved varies

from one design requirement to another

A useful reduction in the initial number of candidate materials can be obtained by establishing the

outset of upper and lower bounds for the various design requirements. On the basis that every design

requirement must be present to an acceptable degree, the costs will increase if the design requirements

present to a greater extent than is strictly necessary. The following table illustrates the concept of

material selection procedure in detailed six steps example.

1st. Step is drawing up a table summarizing the merits and demerits of the contenders so as to permit

early elimination of unsuitable materials. Considerable knowledge and experience are required to

reject a material at this stage, because materials properties can be varied widely during manufacture

and processing, and so also can the costs.

A material would not necessarily be rejected because it was unsatisfactory in respect of a single

secondary design requirement, or even a primary one, if there were scope for ameliorating the

disadvantage during design and manufacture. Whether or not over-provision of some property is cause

for rejection depends upon the effect on cost.

Excessive cost is always a cause for rejection but cost is also a function of processing. Clearly, any

version of a basically expensive material, such as titanium, will be costly but whereas steels aremostly cheap, they become expensive when highly alloyed or manufactured to tight tolerances or

compositional limits. It is likely that any class of material, which passes this initial stage of selection,

will produce three or more competing variants of the same material to be considered at a later stage.

1st

. Step U = under provision, O= over provision, E = excessive, a= acceptableDesign requirements

Materials Primary Secondary Cost DecisionDR1 DR2 DR3 DR4 DR5

M1 a O a a a E RejectM2 a a a O a aM3 U a a a a a RejectM4 a O a a O a

M5 a a a a a E RejectM6 a a a U a a

2nd. Step is refining the table by replacing the simple go/no-go criteria of satisfactory and

unsatisfactory by varying degrees of merit. For properties that are not reliably quantifiable, more-or-

less vague terms such as poor, fair, excellent, etc. are best abandoned in favour of numerical ratings

of, 1 to 5 in ascending order of merit.2

nd. Step

Material Heatresistance

Rigidity Resistance tostress cracking

Mould-ability

Overall rating(Max. =20)

M1 4 3 3 3 13/20=0.65M2 2 3 4 3 12/20=0.60M3 5 4 1 1 11/20=0.55

M4 1 1 4 3 09/20=0.45M5 4 5 1 3 13/20=0.65M6 3 2 5 5 15/20=0.75


42/45



3rd. Step is obtaining an overall numerical rating, when individual merits ratings are totalled.

Clearly, in the example shown in table, that overall superiority of the material M6 is derived from its

maximum ratings in respect of stress cracking and mouldability, but what if heat resistance and

rigidity were the properties more urgently required? This might be so, since although the life of thecomponent could be determined by its resistance to stress cracking, but its resistance to heat and its

rigidity could determine whether or not it could do the job at all.

(Mouldability is important mainly through its influence on costs.). The relative importance of the

various properties therefore depends upon the nature of the application and this can only be assessed

in the mind of the designer. He can exercise his judgment in this respect by assigning weighting

factors to the various properties.

3rd

. step


X 5

Rigidity

X 5

Resistance tostress cracking

X 2

Mould-abilityX 3


M1 20 15 6 9 50/75=0.67M2 10 15 8 9 42/75=0.56M3 25 20 2 3 50/75=0.67M4 5 5 8 9 27/75=0.36M5 20 25 2 9 55/75=0.73M6 15 10 10 15 50/75=0.67

4th. Step is assigning weighting factors to the various properties. The choice now moves to M5, see

the table, which means that a short-life material has been preferred to a long-life material. This

emphasizes that weighting factors must be used cautiously, since by their use small changes in heavily

weighted properties can mask the effects of large changes in more lightly weighted properties.

Materials selection is more effective, when it can be carried out in terms of precisely defined

quantitative property parameters. The example shown in table is dealing with materials, which mightbe considered for use in an airplane wing. The values of cost/ton given are illustrative only, and must

not be taken as definitive. Price instability will bring change of magnitude and possibly even

relationships.

4th

. Step

Material YS(MPa)

KIc(MPa m

1/2)

(ton/m

3)

E(GPa)

Cost($/ton)

Aluminum alloy 1 350 45 2.7 70 590Aluminum alloy 2 550 25 2.7 70 700

Titanium alloy 880 60 4.5 110 5500Stainless steel 900 100 7.8 200 500

5th. Step is assigning the performance maximizing indices. The data cannot be used in raw form,firstly, because the significance of the individual properties varies from one part of the structure to

another, and secondly, because the units are variegated.

The first point can be dealt with by combining units appropriately in the performance maximizing

indices; the second by expressing the data in each column as proportions of the largest figure

appearing in that column.

In the shown example in table, the results of this calculation are not highly informative since it could

have been anticipated that the high price of titanium would force it to the bottom of the list. This,

together with the high density of the steel, leaves the aluminum alloys as the main contenders. If,

however, the airplane were to be a military supersonic aircraft it might be appropriate to downgrade

the importance of cost by the use of suitable weighting factors. It is then necessary to include data forresistance to elevated temperature since this is an important requirement for high-speed flight.


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5th

. Step

Material YS/ [KIC/YS]2 E

1/3/ Cost Overall rating

Abs. Rel.= A Abs. Rel.= B Abs. Rel.= C Abs. Rel.= D A+B+C+(1-D)4Aluminum alloy 1 130 0.64 16.5 1.00 1.50 1.0 590 0.11 0.88Aluminum alloy 2 204 1.00 2.1 0.13 1.50 1.0 700 0.13 0.75

Titanium alloy 193 0.96 4.6 0.27 1.06 0.71 5500 1.00 0.49Stainless steel 115 0.56 12.3 0.75 0.75 0.50 500 0.09 0.68

6th. Step is calculating overall ratings by using weighting factors. In the shown example weighting

factors of 10 for the mechanical properties, 20 for temperature resistance and unity for cost were used.

The overall ratings obtained thereby correlate to some extent with experience since stainless steels and

titanium alloys have been used in prototype aircraft.

6th

. Step


1/3/ Temp. Limit

(C)

Cost Overall rating

Abs Rel.= A

Abs Rel.= B

Abs Rel.= C

Abs Rel.= D

Abs Rel.= E

10A+10B+10C+20D+(1-E)

51Al-alloy 1 130 0.64 16.5 1.00 1.50 1.0 150 0.38 590 0.11 0.68Al-alloy 2 204 1.00 2.1 0.13 1.50 1.0 150 0.38 700 0.13 0.58

Ti-alloy 193 0.96 4.6 0.27 1.06 0.71 300 0.75 5500 1.00 0.67St-St. 115 0.56 12.3 0.75 0.75 0.50 400 1.00 500 0.09 0.76

It is instructive to observe the magnitude of the weighting factors required for achieving such

correlation. Clearly, however, the results are distorted by the fact that some properties are over-

provided for.

For example, the highest speed for a supersonic aircraft is Mach 3, which corresponds to a saturationtemperature of (200 C). This figure should therefore be used as the basis for the relative temperature-

resistance column so that stainless steel does not benefit from a degree of temperature-resistance,

which cannot be used.

Again, the first aluminium alloy benefits excessively from its high toughness. Now, toughness and

strength are conceptually different in that increasing strength is always beneficial because it allows

progressively less material to be used, whereas toughness need be provided only in sufficient quantity

to allow satisfactory service at a given level of stress. It may be adequate, therefore, to account for

toughness only as a lower bound and not incorporate it into the overall rating. On the other hand, since

for any material toughness and strength are inversely related, there exists the possibility of mutual

optimisation.This detailed formalization, which have been suggested and adopted in many references, indicates that

the selection process is mainly two tasks. The design engineer task is to define the design

requirements and their weighting factors, and the materials engineer task is to define the optimum

material. The work in the present thesis is concerning with carrying out the second task.

The example is collected in one page table (next page) for easier review

Remember that:

Step 4: Search for supporting information for promising candidatesOne step is still needed, which is the last step, which can be carried out by collecting supporting

information (structured and unstructured data) about the proposed material to ensure the suitability of

the selection by considering the other fine details.


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Here is the example collected in one page table for easier review:Illustrative Example of Material Selection Formalization By: J.A. Charles & FAA Crane1

st. Step U = under provision, O= over provision, E = excessive, a= acceptable

Design requirements

Materials Primary Secondary Cost DecisionDR1 DR2 DR3 DR4 DR5

M1 a O a a a E RejectM2 a a a O a aM3 U a a a a a RejectM4 a O a a O aM5 a a a a a E RejectM6 a a a U a a

2nd

. Step


Rigidity Resistance tostress cracking

Mould-ability


M1 4 3 3 3 13/20=0.65M2 2 3 4 3 12/20=0.60M3 5 4 1 1 11/20=0.55M4 1 1 4 3 09/20=0.45M5 4 5 1 3 13/20=0.65M6 3 2 5 5 15/20=0.75

3rd

. step


X 5

Rigidity

X 5

Resistance tostress cracking

X 2

Mould-abilityX 3


M1 20 15 6 9 50/75=0.67M2 10 15 8 9 42/75=0.56M3 25 20 2 3 50/75=0.67M4 5 5 8 9 27/75=0.36

M5 20 25 2 9 55/75=0.73M6 15 10 10 15 50/75=0.67

4th

. Step

Material YS(MPa)

KIc(MPa m

1/2)

(ton/m

3)

E(GPa)

Cost($/ton)

Aluminum alloy 1 350 45 2.7 70 590Aluminum alloy 2 550 25 2.7 70 700

Titanium alloy 880 60 4.5 110 5500Stainless steel 900 100 7.8 200 500

5th

. Step


1/3/ Cost Overall rating

Abs. Rel.

= A

Abs. Rel.

= B

Abs. Rel.

= C

Abs. Rel.

= D

A+B+C+(1-D)

4Aluminum alloy 1 130 0.64 16.5 1.00 1.50 1.0 590 0.11 0.88Aluminum alloy 2 204 1.00 2.1 0.13 1.50 1.0 700 0.13 0.75

Titanium alloy 193 0.96 4.6 0.27 1.06 0.71 5500 1.00 0.49Stainless steel 115 0.56 12.3 0.75 0.75 0.50 500 0.09 0.68

6th

. Step


1/3/ Temp. Limit

(C)Cost Overall rating

Abs Rel.= A

Abs Rel.= B

Abs Rel.= C

Abs Rel.= D

Abs Rel.= E

10A+10B+10C+20D+(1-E)

51Al-alloy 1 130 0.64 16.5 1.00 1.50 1.0 150 0.38 590 0.11 0.68Al-alloy 2 204 1.00 2.1 0.13 1.50 1.0 150 0.38 700 0.13 0.58

Ti-alloy 193 0.96 4.6 0.27 1.06 0.71 300 0.75 5500 1.00 0.67St-St. 115 0.56 12.3 0.75 0.75 0.50 400 1.00 500 0.09 0.76


45/45


Material Selection Software List:The following list contains some of the most common material selection software. The prices vary widely. Four price groups are given: free,modest (less than $1000), expensive (between $1000 and $10,000) and very expensive (more than $10,000).CMS: Cambridge Materials Selector(l992) Cambridge University Engineering Department, Cambridge, UK (Tel: 0223 334755; Fax: 0223

332797). All materials, PC formats. Allows successive application of up to six selection stages. (Modest-price).Mat.DB (1990) (replacing METSEL 2) Materials Database; ASM International, Metals Park, Ohio 44073, USA. (Tel: 216 338 515 I; Fax:216 338 4634). PC formats. Databases of property and processing (of metals and some polymers) are now available; more are inpreparation. Selection based on user-defined target values. Expensive, and cumbersome.PERITUS Matsel Systems Ltd., 6th Floor, Cunard Building, Water St, Liverpool L3 IEG, UK (Tel: 051 227 5080; Fax: 051 236 1934). PCformats. A database for metals, polymers and ceramics, aimed at materials and process selection. Selection based on requesting "high","medium or "low values (or given properties rather than numerical values; a display shows the match between candidate materials andthe target profile. Typical uses are given. (Expensive), (An educational version, Peritus-ED, is more modestly priced)PLASCAMS 220: Plastics Materials Selector (1998) RAPRA Technology Ltd., Shrewsbury, Shrewsbury SY4 4NR, UK. PC formatsPolymers only. Mechanical and processing properties of polymers, thermoplastics and Thermosets. Easy to use for data retrieval, withmuch useful information. Selection procedure cumbersome and not design-related. Modest initial Price plus annual maintenance fee.Updated regularly.DataPLAS: Plastics Information System (1990) Modern Plastics, 43rd Floor, 1221 Avenue of the Americas, New York, NY 10020, USA(Tel: 1 800 845 5056; Fax: 212 512 6111). PC formats. Properties, processing and Producer information for 1000 high-performancethermoplastics available from US suppliers. Updated regularly, (Expensive).CAMPUS, Computer Aided Material Pre-selection by Uniform Standards (1988) Hoechst Aktiengesellschaft, Verkauf Kunststoffe, D-6320

Frankfurt am Main 80, Germany. PC formats. A collection of four databases of Hoechst, BASF, and Bayer and Huels thermoplasticpolymers, containing information on modulus, strength, viscosity and thermal properties. Regularly updated, but limited in scope. Free.EPOS, Engineering Plastics on Screen (1989) ICI Engineering, Plastics Sales Office, PO Box 90, Wilton, Middlesborough, Cleveland TS68JE, UK (Tel: 0642 454144 or 0707 337852). PC formats. The software lists general and electrical properties of ICI polymer products, witha search facility. Updated periodically. Free.MATUS: Materials User Service Engineering Information Company Ltd., 15/17 Ingate Place, London SWS 3NS UK. An on-line data bank ofUK material suppliers, trade names and properties for metals polymers and ceramics, using data from suppliers' catalogues and datasheets. A stand-alone system that can be customized to the users needs is now available. Expensive.M-VISION (1990) PDA Engineering, 2975 Redhill Avenue, Costa Mesa, CA 92626, USA (Tel: 714 540 8900; Fax: 714 979 2990). Requiresa workstation. An ambitious image and database, with flexible selection procedures. Data for aerospace alloys and composites. Veryexpensive.IMAMAT: Institute of Metals and Materials, Australia, PO Box 19, Parkville 3052, Vic, Australia (Tel: 03 347 2544; Fax: 03 348 1208). Priceand functionality not known.THERM: Thermal Properties of Materials; Rob Bailey, Lawrence Livermore Laboratory, Materials Laboratory, PO Box 808, Livermore, Ca94550, USA (Tel: 415 422 8512). Very simple but useful PC-based compilation of thermal data for materials: specific heat, thermalconductivity. Density and melting point. Free.

STRAIN: Plastic Properties of Materials; Rob Bailey, Lawrence Livermore Laboratory, Materials Laboratory, PO Box 808, Livermore, Ca94550, USA (Tel: 415 422 8512). Very simple but useful PC-based compilation of room-temperature mechanical properties of ductilematerials. Free.CopperSelect: Computerized System for Selecting Copper Alloys: Copper Development Association Inc, Greenwich Office, Park No 2,Box 1840, Greenwich CT 06836, USA (Tel: 203 625 8210; Fax: 203 625 0174). PC formats. A database of properties and processinginformation for wrought and cast copper alloys. Free.DESIGN DATA-CAST IRON: BCIRA, the Cast Metals Technology Center, Alvechurch, Birmingham B48 7QB, UK (Tel: 0527 66414; Fax:0527 585070). PC system, which retrieves the physical and mechanical properties of ductile, gray and malleable, cast irons. Modest price.PM Selector: Structural Powder Metallurgy Materials Selector (1990) MPR Publishing Services Ltd., Old Bank Buildings, Bellstone,Shrewsbury SY1 1HU, UK (Tel: 0743 64675; Fax: 0743 62968). A PC-based selector for powder metallurgical materials for structural use.Modest price.UNSearch: Unified Metals and Alloys Composition Search; ASTM, 1916 Race Street, Philadelphia, PA 19103, USA. PC system whichretrieves information about composition, US designation and specification of common metals and alloys. Modest price.CUTDATA: Machining Data System; Metcut Research Associates Inc, Manufacturing Technology Division, 11240 Cornell Park Drive,Cincinnati, Ohio 45242 USA (Tel: 513 489 6688). A PC-based system, which guides the choice of machining conditions: tool materials,geometry, feed rates, cutting speeds, and so forth. Modest price.

SteCal: Steel Heat-Treatment Calculations; ASM International, Metals Park, Ohio 44073, USA. (Tel: 216 338 5151; Fax: 216 338 4634).PC formats software, which computes the properties resulting from defined heat treatments of low-alloy steels, using the composition asinput. Modest price.STEELMASTER: Schwing UK Ltd., Summerton Road, Oldbury, Warley, West Midlands B69 2KL, UK (Tel: 021 511 1203). PC formats. Adatabase of compositions, properties, trade names and heat treatment procedures for steels. Expensive.ELBASE: Metal Finishing/Surface Treatment Technology (1992) Metal Finishing Information Services Ltd., PO Box 70, Stevenage, HertsSG1 4DF, UK (Tel: 0438 745115). PC formats. Comprehensive information on published data related to surface treatment technology.Regularly updated. Modest price.EASel: Engineering Adhesives Selector Program (1986) The Design Center Bookshop, Haymarket, London SW1Y 4SU, UK. PC and Appleformat. A knowledge-based program to select industrial adhesives for joining surfaces. Modest price.PAL: Permabond Adhesives Locator (1990) Permabond, Woodside Road, Eastleigh, Hants SOS 4EX, UK (Tel: 0703 629628; Fax: 0703629629). A knowledge-based, PC system for adhesive selection am

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