Material Selection 1-5

Ain Shams University Faculty of Engineering Design & Prod. Eng. Dept.

Material & Process Selection Summary of Lecture Notes Dr. Ahmed Farid A. G. Youssef

Material Selection Charts

Ain Shams University Faculty of Engineering Design & Prod. Eng. Dept.

Material & Process Selection Summary of Lecture Notes Dr. Ahmed Farid A. G. Youssef

Lecture 1: Introduction to Material Selection in Mechanical Design The Design Process COMPETITIVE DESIGN of new products is the key capability that companies must master to remain in business. It requires more than good engineering, it is fraught with risks and opportunities, and it requires effective judgment about technology, the market, and time. The concept and configuration development process:

Activities occur throughout product development The process starts with identifying the customer population for the product and developing a representation of the feature demands of this group. Based on this representation, a functional architecture is established for the new product, defining what it must do. The next step is to identify competitive products and analyze how they perform as they do. This competitive benchmarking is then used to create a customer-driven specification for the product, through a process known as quality function deployment. From this specification, different technologies and components can be systematically explored and selected through functional models. With a preliminary concept selected, the functional model can be refined into 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 of a new product. Lecture 1 [Introduction to Material Selection in Mechanical Design]

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Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept.

Customer Needs & Problem Definition: In the early 1980s, Sony offered an improved magnetic videotape recording technology, the Betamax system. Although it offered better magnetic media performance, it did not satisfy customers, 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 had torn apart and thoroughly analyzed each other's cars. Ford decided to increase the options in its Taurus, matching Toyota's earlier Camry, while Toyota decided to decrease the options in 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 user’s site

What the user wanted

Task Clarification Conceptual and configuration design of products begins and ends with customers, emphasizing quality processes and artifacts throughout. We thus initiate the conceptual design process with task clarification: understanding the design task and mission, questioning the design efforts and organization, and investigating the business and technological market. Task clarification sets the foundation for solving a design task, where the foundation is continually revisited to find weak points and to seek structural integrity of a design team approach. It occurs not only at the beginning of the process, but throughout.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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

Mission Statement and Technical Questioning A mission statement and technical clarification of the task are important first steps in the conceptual 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 and concurrent engineering organization The first step in task clarification is usually to gather additional information. The following questions need to be answered, not once but continually through the life cycle of the design process: • What is the problem really about? • What implicit expectations and desires are involved? • Are the stated customer needs, functional requirements, and constraints truly appropriate? • 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 task been 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, review ASM Handbook, Volume 20, Materials Selection and Design Relation of Materials Selection to Design: • An incorrectly chosen material can lead not only to failure of the part but also to unnecessary cost. • Selecting the best material for a part involves more than selecting a material that has the properties to provide the necessary performance in service; it is also intimately connected with the processing of the material into the finished part. • A poorly chosen material can add to manufacturing cost and unnecessarily increase the cost of the part. • Also, the properties of the material can be changed by processing (beneficially or detrimentally), and that may affect the service performance of the part.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept.

The Place of Materials Selection in the Design Process Materials selection should contribute to every part of the whole design process. This is because 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 that performs a function. It can be described and analyzed in more than one way based on the ideas of systems analysis-thinks of the flows of information, energy and materials into and out of the system. The system transforms inputs into outputs. Assembly [1]

Component 1.1 Component 1.2

Component

Technical System

Assembly [2]

Component Component Component

Assembly [3]

Component Component Component

Analysis of a technical system 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, “different

components 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 among standards there is a choice of material (the screw could be of brass, or mild steel, or stainless steel). Some are specific, unique to the design: then the designer must select the material, the shape, and the processing route.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept. The Design Flowchart

Design is an iterative process. The starting point is a market need or an idea; the end point is a product that fills the need or embodies the idea. A set of stages lie between these points: the stages of conceptual design, embodiment design and detailed design, leading to a set of specifications the production information, which define how the product should be made.

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 of breadth and precision. At the conceptual design stage all options are open: the designer considers the alternative working principles or schemes for the functions which make up the system, the ways in which sub functions are separated or combined, and the implications of each scheme for performance and cost. Embodiment design takes a function structure and seeks to analyze its operation at an approximate level, sizing the components. And selecting materials, which will perform properly 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 design stage. At the detailed design stage, specifications for each component are drawn up. Critical components may be subjected to precise mechanical or thermal analysis using finite element methods. Optimization methods are applied to components and groups of components to maximize performance; materials are chosen the production route is analyzed and the design is costed. The stage ends with detailed production specifications. Lecture 1 [Introduction to Material Selection in Mechanical Design]

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Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept.

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 specification of process. • The more sophisticated the design, the tighter the specifications and the greater the interactions. The figure shows the central problem of material selection in mechanical design, which is the interaction between function, material, process and shape.

FUNCTION Transmit loads, heat, contain pressure, store energy, etc.

MATERIAL

SHAPE

PROCESS

Interaction of function, material, process and shape

The interaction between function, material, shape and process lie at the heart of the Design process.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept. 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 cost accountancy and with a time scale which should allow an optimum choice to be made. For such a venture to be successful a program for market entry in relation to the cost of development and getting into production has to be fulfilled. However, markets will change, new competitors will arise and to some extent known competitors may change their approach also. A new venture in an engineering product will always be something of a gamble. However, for the maximum chance of success, the choice of materials will be a key decision in terms of 'value for money' in service and the impact on the market. Also, since the choice may well control the method of fabrication, it will influence the whole production line specification involving a very large capital investment, which cannot always accommodate a subsequent change of material. The design process must continually operate even in an established manufacturing operation. The figure below illustrates the product lifetime. Here we see that each product offered in the market place has a life-cycle. Research and development (R&D) enables its introduction to be effected, prior to the period of growth during which the product finds acceptance. After a while, it becomes mature, either through built-in obsolescence or as a result of new developments; by this time the far-seeing company will have replacement products already in the R&D stage. Inevitably (and this may occupies a period of months or of decades), the product will go into market decline. Decisions must be made as to whether any of the design features can be retained to produce a new revitalized product, or whether the operation has to be closed down to make way for an entirely new family of products. Technical decision

Concept Market screening Design feasibility proproduction

Production Modification to broaden product family Cost reduction

Phase-out

Obsolescence Cut-off point

Introduction

Growth

Maturity

Decline

Sales volume Return on investment Profit

Research & development

Time Types of corporate decision

Capital investment Recruitment of new employees

Change of price Expansion of production

New market strategies Changes in product design

Extend market to overseas Reduce the product price

The life cycle of a product Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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

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 incremental or non-existent, the concept is unlikely to change.

Factors that cause a product to become DYNAMIC Government action or legislation

Factors that create or retain a STATIC plateau Improving environment for the existing design Commodities and resources

Changing environment

Customers not change User familiarity

willing

to

Commodities and resources

Stable technology

Customers willing to change

Conformance standards

Technical advancement No conformance standards

Stable or decreasing number of producers Few large producers

Many small producers (increasing) No infrastructure

Product available for a long time Existing infrastructure

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

Factors that cause a product to become DYNAMIC Management committed to deign Changing PDS Process design small Adequate time for design Wide effective market research Companies seeking new concepts Flexible machinery subcontract, manufacture

Factors that create or retain a STATIC plateau Insufficient design resources Poor market research Restricted design Product interfaces with existing design Rationalization or commonality of parts Assembling component made by others Using experience in design More process design than product design Management not committed to deign Stable effective PDS Restricted PDS Limited Design time Limitation Automation CAD Purchasing (dedicated)

new

machinery

Balance diagram of the micro factors that change / maintain a product status. Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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

Forces for Change: [3] The Science-Push: Curiosity-driven Research Curiosity is the life-blood of innovative engineering. Technically advanced countries sustain the 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 pursue ideas, which may have no immediate economic objective, but which can evolve into the materials and manufacturing methods of the next decade. Numerous now-commercial materials 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. This requires 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 a life-cycle view of the product, which includes manufacture, distribution, use and final disposal. All materials contain energy. Energy is used to mine, refine, and shape metals; it is consumed in the firing of ceramics and cement; and it is intrinsic to oil-based polymers and Elastomers. When we use a material, we are using energy, and energy carries with it an environmental penalty: CO2, oxides of nitrogen, sulphur compound, dust, and waste heat. The energy content 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. Materials removed 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 profit to be made. To allow this we have to look first, at where recycling works well and where it does not. Primary scrap-the turnings, trimmings and tailings, which are a by-product of manufacturehas high value: it is virtually all recycled. That is because it is uncontaminated and because it is not dispersed. Secondary scrap has been through a consumption cycle-a newspaper, a beer can, or an automobile; the other materials to which it is joined; by corrosion products; by ink and paint contaminate it; and it is dispersed. It is worth little or nothing or less than nothing meaning that 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 recycle either 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.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

9

Material & Process Selection Summary of Lecture Notes

Ain Shams University Faculty of Engineering

Dr. Ahmed Farid A. G. Youssef

Design & Prod. Eng. Dept. Main Situations for Material Selection:

The decision-making process of materials selection may be initiated for a variety of reasons and several situations. The three main situations are: 1 The introduction of a new product, component or plant, which is being produced or built for the first time by the organization concerned. 2 A desire for the improvement of an existing product, or a recognition of over design where economy can be effected, which may be considered as an evolutionary change. 3 A problem situation, due for example to the failure of components leading to rejection by customers, failure of supplies, or failure of in-house manufacturing plant, necessitating a change in material use. This is the area where the metallurgist must be employed, for investigating a failure, and on determination of the cause, suggesting a change of design or of the material employed.

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 the manufacturer. • Among the material selection many objectives, there is a main objective, which is failure prevention.

Material Failure Modes The different material failure modes are listed in following table as classified by Collinos, 1. Elastic deformation 8. Corrosion 10. Fretting Each failure mode has: • a failure mechanism • material selection guide lines • material selection rules to prevent the failure mode from taking place.

2. Yielding 3. Brinelling 4. Ductile failure 5. Brittle fracture 6. Fatigue a. High-cycle fatigue h. Low-cycle fatigue c. Thermal fatigue d. Surface fatigue e. Impact fatigue f. Corrosion fatigue g. Fretting fatigue 9. Impact a. Impact fracture b. Impact deformation c. Impact wear d. Impact fretting e. Impact fatigue

a. Direct chemical attack b. Galvanic corrosion c. Crevice corrosion d. Pitting corrosion e. Intergranular corrosion f. Selective leaching g. Erosion-corrosion h. Cavitation i. Hydrogen damage j. Biological corrosion k. Stress corrosion 9. Wear a. Adhesive wear b. Abrasive wear c. Corrosive wear d. Surface fatigue wear e. Deformation wear f. Impact wear g. Fretting wear

Lecture 1 [Introduction to Material Selection in Mechanical Design]

a. Fretting fatigue b. Fretting wear c. Fretting corrosion 11. Galling and seizure 12. Scoring 13. Creep 14. Stress rupture 15. Thermal shock 16. Thermal relaxation 17. Combined creep and fatigue 18. Buckling 19. Creep buckling 20. Oxidation 21. Radiation damage 22. Bonding failure 23. Delamination 24. Erosion

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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

Investigations about the frequency of failure causes in some engineering industries indicate that the main cause for failure is improper material selection. Frequency of Causes of Failure in Some Engineering Industries Investigations:

Origin Improper material selection Fabrication defects Faulty heat treatments Mechanical design fault Unforeseen operating conditions Inadequate environment control Improper or lack of inspection and quality control Material mix-up

% 38 15 15 11 8 6 5 2

Frequency of Failure Modes in Some Engineering Industries Investigations.

Origin Corrosion Fatigue Brittle fracture Overload High temperature corrosion Stress corrosion / corrosion fatigue / hydrogen embrittlement Creep Wear, abrasion, and erosion

% 29 25 16 11 7 6 3 3

Failure experience matrix Collins suggested a failure experience matrix, Three dimensional experience matrix which is an attempt to place failure analysis on a assemblage of information cells firm analytical basis by classifying each failure with respect to failure mode, the elemental function that • Elemental Mechanical Function the component provided, and the corrective action that should be taken recurrence of the failure. Thus • Failure Mode the failure experience matrix is a three dimensional • Corrective Action assemblage of information cells. Corrective action is defined as any measure or steps taken to return failed component or system to satisfactory performance. Dieter stated that if there ware a computerized database that encompassed a national inventory of failures, it would have a great use in engineering design. An engineer who needed to design a critical component would enter the matrix with elemental mechanical function and learn about failure modes that likely to occur as well as the corrective actions most likely to avoid failure.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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

Some of elemental mechanical functions and the corrective actions of failure experience matrix in a study on 500 failed parts from U.S. army helicopters Elemental mechanical functions: 1. Supporting 2. Attaching 3. Motion constraining 4. Force transmitting 5. Sealing 6. Friction reducing 7. Protective covering 8. Liquid constraining 9. Pivoting 10. Torque transmitting 11. Pressure supporting 12. Oscillatory sliding 13. Shielding 14. Sliding 15. Energy transforming 16. Removable fastening 17. Limiting 18. Electrical conduction 19. Contaminant constraining 20. Linking 21. Continuous rolling 22. Liquid transferring 23. Force amplifying 24. Power transmitting 25. Covering 26. Oscillatory rolling 27. Energy absorbing 28. Light transmitting 29. Viewing 30. Energy dissipating 31. Guiding 32. Latching 33 electrical switching 34. Stabilizing 35. Gas constraining

36. Permanent fastening 37. Pressure increasing 38. Streamlining 39. Motion reducing 40. Filtering 41. Lighting 42. Pumping 43. Gas transferring 44. Aero. force transmitting 45. Motion transmitting 46. Signal transmitting 47. Motion damping 48. Force distributing 49. Reinforcing 50. Pressure sensing 51. Information transmitting 52. Coupling 53. Displacement indicating 54. Clutching 55. Fastening 56. Information indicating 57. Position indicating 58. Movable lighting 59. Partitioning 60. Position restoring 61. Flexible spacing 62. Electrical amplifying 63. Adjustable attaching 64. Shape constraining 65. Deflecting 66. Disconnecting 67. Electrical limiting 68. Motion limiting 69. Pressure limiting 70. Sensing

71. Force sensing 72. Spacing 73. Temporary supporting 74. Gas switching 75. Electrical transforming 76. Power absorbing 77. Information attaching 78. Sound absorbing 79. Constraining 80. Flexible coupling 81. Removable coupling 82. Damping 83. Electrical distributing 84. Load distributing 85. Gas guiding 86. Pressure indicating 87. Electrical insulating 88. Sound insulating 89. Temporary latching 90. Force limiting 91. Force maintaining 92. Variable position maintenance 93. Liquid pumping 94. Electrical reducing 95. Rolling 96. Position sensing 97. Energy storing 98. Liquid storing 99. Flexible supporting 100. Switching 101.Pressure to torque transmitting 102. Electrical transmitting 103. Flexible motion transmitting 104. Flexible torque transmitting 105. Torque limiting

Corrective actions for failure-experience matrix: Direct replacement Change Of material Supplement part Added adhesive Provided drain Added sealant Repositioned part Repaired part Reinforced part Eliminated part Strengthened part Adjusted part

Changed vendor Changed dimensions Improved quality control Changed lubricant type Improved lubrication Applied surface coating Applied surface treatment More easily replaceable part Changed to correct part Made part interchangeable Changed loading on part Relaxed replacement criteria

Improved instructions to user Design change to improve part Changed mechanism of operation Improved run-in procedure Changed manufacturing procedure Changed mode of attachment Changed method of lubrication Added or changed locking feature Revised procurement specification Provided for proper inspection Changed electrical characteristics

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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

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, Butterworths Heinemann. 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, McGrawHill. ASM Metals Handbook, (1999), Volume 20, Materials Selection and Design, American Society for Metals, Metals Park, Ohio, USA.

Lecture 1 [Introduction to Material Selection in Mechanical Design]

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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 2: Engineering Materials & Their Properties Classes 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 allows them 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, but unlike 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 15 times 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 high temperatures. • They are resistant to corrosion. Polymers & Elastomers: • They have low elastic moduli, about 50 times less than those of metals. However, some polymers can be very strong – nearly as strong as metals. As a consequence, 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 per unit 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 of other classes of materials while avoiding some of their drawbacks. • They are light, stiff and strong, and they can also be tough. • Most currently available composites have polymer 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, and manufacturing processes are not well developed. They are also difficult to join.

Lecture 2 [Engineering Materials & Their Properties]

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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

Material classes, generic members, and abbreviated names: Class Members Engineering alloys (The metals and alloys of engineering)

Engineering polymers (The thermoplastics and thermosets of engineering)

Engineering ceramics (Fine ceramics capable of load bearing application)

Engineering composites (The composites of engineering practice) A distinction is drawn between the properties of a ply – UNIPLY – and of a laminate – LAMINATES Porous ceramics (Traditional ceramics, cement, rocks, & minerals)

Glasses (Ordinary silicate glass) Woods Separate envelopes describe properties parallel to the grain and normal to it, and wood products)

Elastomers (Natural and artificial rubbers)

Polymer foams (Foamed polymers of engineering)

Short name

Aluminium alloys Copper alloys Lead alloys Magnesium alloys Nickel alloys Steels Tin alloys Titanium alloys Zinc alloys Epoxies Melamines Polycarbonate Polyesters Polyethylene, high density Polyethylene, low density Poly formaldehyde Poly methyl metha crylate Polypropylene Poly tetra fluor ethylene Polyvinyl chloride Alumina Diamond Sialons Silicon Carbide Silicon nitride Zirconia Carbon fiber reinforced polymer Glass fiber reinforced polymer Kevlar fiber reinforced polymer

Al alloys Cu alloys Lead alloys Mg alloys Ni alloys Steels Tin alloys Ti alloys Zn alloys EP MEL PC PEST HDPE LDPE PF PMMA PP. PTFE PNC Al2O3 C Sialons SiC Si3N4 ZrO2 CFRP GFRP KFRP

Brick Cement Common rocks Concrete Porcelain Pottery Borosilicate glass Soda glass Silica Ash Balsa Fir Oak Pine Wood products Natural rubber Hard butyl rubber Polyurethane Silicone rubber Soft butyl rubber Cork Polyester Polystyrene Polyurethane

Brick Cement Rocks Concrete Pcln Pot B-glass Na-glass SiO2 Ash Balsa Fir Oak Pine Wood products Rubber Hard butyl PU Silicone Soft butyl Cork PEST PS PU

Note that abbreviated names as used in material selection charts developed by M.F. Ashby. Lecture 2 [Engineering Materials & Their Properties]

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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

[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

General

Relative Cost Density

Mechanical

Elastic Modulus Strength (yield / ultimate / fracture) Toughness Fracture Toughness Damping Capacity Fatigue Ratio

Thermal

Thermal Conductivity Thermal Diffusivity Specific Heat Melting Point Glass Temperature Thermal Expansion Coefficient Thermal Shock resistance Creep Resistance

Wear

Archard Wear Constant

Corrosion / Oxidation

Corrosion Rate Parabolic rate constant

Elastic Modulus E= 3G/(1+G/3K)

σf = KIC /√ (πC)

Shear Modulus G= E/2(1+ν)

CR ρ

Units

--Mg/m 3

E, G, K GPa MPa σf Gc KJ/m 2 KIC MPa m 1/2 -----η f -----λ a CP Tm Tg α ΔT -----

W/m K m 2/s J/Kg K K K K-1 K ------

KA ----KP

MPa -1 -----m 2/s

Bulk Modulus K= E/3(1-2ν)

ν =1/3

KIC the resistance to the propagation f a crack.

Lecture 2 [Engineering Materials & Their Properties]

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Ain Shams University Faculty of Engineering Design & Prod. Eng. Dept. Density, ρ

Material & Process Selection Summary of Lecture Notes Dr. Ahmed Farid A. G. Youssef Mg/m3 7.8 4.5 2.7 1.7 1.2

Material

Mass per unit volume, Mg/m

3

Stiffness, Elastic MODULUS, E Slope of the liner elastic part of the stress-strain curve, GN/m2 = GPa Poisson’s ratio, ν

ν = ε lateral / εaxial

Iron, Steels Titanium alloys Aluminium alloys Magnesium alloys Polycarbonate Material Iron, Steels Titanium alloys Aluminium alloys Magnesium alloys Polycarbonate Rubbers Silicon SiC

E, GPa 200 116 70 43 2.6 0.01-0.1 160 410

ν 0.27 0.34 0.33 0.35 0.4 0.49 0.22 0.3

For isotropic materials: E

ν

Young’s Modulus

Poisson’s ratio G= E/2(1+ν) Shear Modulus K= E/3(1-2ν) Bulk Modulus Typically ν ≈ 1/3,

G ≈ 3/8 E

K≈E

Elastomers are exceptional: ν ≈ 1/2, G ≈ 1/3 E K>>E

Strength, σf, MN/m2 = MPa.

Strength requires careful definition and usually defined differently for different materials and mode of loading.

Metals

σf is identified with the 0.2% offset yield strength σy. 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%.

Material Steels Titanium alloys Aluminium alloys Magnesium alloys

σy, MPa 200-2000 800-1200 200-500 100-200

σy in compression ≈ σy in tension

Lecture 2 [Engineering Materials & Their Properties]

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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

Ceramics & Glasses Strength for ceramics and glasses depends strongly on the mode of loading. In tension, strength means t the fracture strength, σf . In compression it means C

the crushing strength σf , which is much larger, typically

σfC in compression ≈ 15 σft in tension Modulus of Rupture, MOR – MPa If the material is difficult to grip, as is the case with 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 ≈ 1.3 σft in tension

Polymers:

σf is identified as the stress σy at which the stress strain curve has become markedly non-linear- typically a strain of 1%. Yield mechanisms: shear yielding, crazing.

Polymers are a little stronger ≈ 20% in compression than in tension.

σy in compression ≈ 1.2 σy in tension

Material Polycarbonate PMMA

σy, MPa 80 100

Composites: 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. Lecture 2 [Engineering Materials & Their Properties]

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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

Ultimate tensile strength, σu - MPa This 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

σf in tension. For metals, ductile polymers and most composites it is larger than σf, by factor of between 1.1and 3. In metals σu is higher than σy because of work hardening.

as

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 σf Resilience, R- J/m3 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 strain curve.

R = ½ σf εf R = σf2 / 2E

Materials with large values of R are suitable for good springs

Fracture Toughness, KIC- MPa √m The 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 = σ√πc

Lecture 2 [Engineering Materials & Their Properties]

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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

Fracture Criterion:

KI < KIC KI >= KIC

No Fracture Fracture

Rule of thumb: Avoid materials with fracture toughness less than 15 MPa √m Most metals have values of KIC in the range 20 – 100 MPa √m Engineering ceramics have values of KIC - 1 – 5 MPa √m Therefore, engineers view them with great suspicion.

Material Steels Titanium alloys Aluminium alloys Epoxies Polystyrene Polycarbonate PMMA PETP Soda-Lime Glass Al2O3 Si3N4 SiC Al2O3, 15% ZrO2

KIC MPa √m 50-200 20-75 20-40 0.3-0.5 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 η, measures the fractional energy dissipated in a stress-strain cycle.

D= ΔU/U specific damping capacity η = D / 2π The loss coefficient η = ΔU/ 2π

Thermal ConductivityThermal conductivity λ measures the flux of heat driven by a temperature gradient dT/dX.

q= λ (dT / dX)

Lecture 2 [Engineering Materials & Their Properties]

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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

Linear thermal ExpansionThe linearthermal expansion coefficient a measures the change in length, per unit length, when the sample is heated.

α = (1/L) (dδ/dT)

T m, melting temperature T g, glass temperature, is a property of non-crystalline solids, which do not have a sharp melting point; 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 without oxidation, 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 and shaping.

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 is characterized by a set of creep constants: n, creep exponent (dimensionless) Q, activation energy (KJ/mole) A, kinetic factor (s-1) σo, reference stress (MPa) o The strain rate ε

εo = A [σ /σo ]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.

Lecture 2 [Engineering Materials & Their Properties]

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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

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 of KA is available, but it must be interpreted as the property of the sliding couple, not of just one member of it. CorrosionCorrosion 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, it is 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: a property-profile. • The material name is merely the identifier for a particular property-profile

Lecture 2 [Engineering Materials & Their Properties]

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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 3: The Performance Maximizing Indices Material Selection has 4 basic steps: 1. Translation of design requirements into a material specification 2. Screening out of materials that fail constraints 3. Ranking by ability to meet objectives; material indices 4. 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 limits 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.

Lecture 3 [Performance Maximizing Indices]

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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

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 for example. 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 2 3 4 5 6 7 8 9

Identify the attribute to be maximized or minimized (weight, cost, stiffness, strength, etc.). Develop an equation for this attribute in terms of functional requirements, the geometry and the material properties (the objective function). Identify the free (unspecified) variables. Identify the constraint; rank them in order of importance. Develop equation for the constraints (no yield, no fracture, no buckling, max heat capacity, cost below target, etc.). Substitute for the free variables from the constraints into the objective function. Group the variables into three groups: functional requirements, F, geometry, G, and material properties, M, thus: ATTRIBUTE< f (F, G, M) Read the performance index, expressed as a quantity M to be maximized. Note that a full solution is not necessary in order t o identify the material property group.

Lecture 3 [Performance Maximizing Indices]

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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

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:

m= A L ρ

Where A is the cross sectional area, ρ is the density To carry the tensile load F

F/A = σ f / S f

Eliminating A between the two equations.

m= (Sf F ) (L) (ρ / σ f )

•

The first bracket contains the functional requirement that is the specified load is safely supported.

•

The second bracket contains the specified geometry (the length of the tie).

•

The last bracket contains the material properties.

The lightest rod, which will safely carry the load F without failing is that with the largest value of the performance index:

M = [σ f / ρ]

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, ρ is the density The column will buckle elastically when the Euler load, Fcrit, is exceeded. The design is safe if:

m= A L ρ F