material selection 1-5
TRANSCRIPT
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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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Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefAin Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.
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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Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefAin Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.
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.
3Lecture 1 [Introduction to Material Selection in Mechanical Design]
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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]
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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Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefAin Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.
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.
5Lecture 1 [Introduction to Material Selection in Mechanical Design]
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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]
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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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]
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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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]
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 1 [Introduction to Material Selection in Mechanical Design] 10
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 1 [Introduction to Material Selection in Mechanical Design] 11
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 1 [Introduction to Material Selection in Mechanical Design] 12
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 1 [Introduction to Material Selection in Mechanical Design] 13
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 2 [Engineering Materials & Their Properties] 3
[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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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]
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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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]
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
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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]
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)
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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Linear thermal ExpansionThe linear-
thermal expansion coefficient a measures
the change in length, per unit length, when
the sample is heated.
Lecture 2 [Engineering Materials & Their Properties] 8
= (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.
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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
Lecture 2 [Engineering Materials & Their Properties] 9
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
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
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4Lecture 3 [Performance Maximizing Indices]
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5Lecture 3 [Performance Maximizing Indices]
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Ain Shams University Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. YoussefFaculty of EngineeringDesign & Prod. Eng. Dept.
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.
6Lecture 3 [Performance Maximizing Indices]
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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
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
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
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Ain Shams University
Faculty of Engineering
Design & Prod. Eng. Dept.
Material & Process Selection
Summary of Lecture Notes
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.
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Material & Process Selection
Summary of Lecture Notes
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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Material & Process Selection
Summary of Lecture Notes
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.
4Lecture 4 [Material Selection Charts]
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Material & Process Selection
Summary of Lecture Notes
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.
What can we conclude?
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]
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Material & Process Selection
Summary of Lecture Notes
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.
What can we conclude?
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.
6Lecture 4 [Material Selection Charts]
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Faculty of Engineering
Design & Prod. Eng. Dept.
Material & Process Selection
Summary of Lecture Notes
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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Faculty of Engineering
Material & Process Selection
Summary of Lecture Notes
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/]
8Lecture 4 [Material Selection Charts]
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Material & Process Selection
Summary of Lecture Notes
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
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Material & Process Selection
Summary of Lecture Notes
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.
10Lecture 4 [Material Selection Charts]
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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
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
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.
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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
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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 5 [Formalization of Material Selection] 3
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
Material Heatresistance
X 5
Rigidity
X 5
Resistance tostress cracking
X 2
Mould-abilityX 3
Overall rating(Max. =75)
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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Ain Shams UniversityFaculty of EngineeringDesign & Prod. Eng. Dept.Material & Process SelectionSummary of Lecture NotesDr. Ahmed Farid A. G. Youssef
Lecture 5 [Formalization of Material Selection] 4
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
Material YS/ [KIC/YS]2 E
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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Lecture 5 [Formalization of Material Selection] 5
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
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=0.55M4 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
Material Heatresistance
X 5
Rigidity
X 5
Resistance tostress cracking
X 2
Mould-abilityX 3
Overall rating(Max. =75)
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
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
Material YS/ [KIC/YS]2 E
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
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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