24 Chapter 2 The design process the first three concepts: in the first, a screw is threaded into the cork to which an axial pull is applied; in the second, slender elastic blades inserted down the ides of the cork apply shear tractions when pulled; and in the third the cork is arced by a hollow needle through which a gas is pumped to push it out igure 2.10 shows examples of cork removers using these working princi- ples. All are described by the function-structure sketched in the upper part of Figure 2.11: create a force, transmit a force, apply force to cork. They differ in the working principle by which these functions are achieved, as indicated in the lower part of the figure. The cork removers in the photos combine working rinciples in the ways shown by the linking lines. Others could be devised by making other links. Figure 2.12 shows embodiment sketches for devices based on just one some sort of mechanical advantage -levered-pull, geared pull and sprf e concept-that of axial traction. The first is a direct pull; the other three us assisted pull; the photos show examples of all of these The embodiments of Figure 2.9 identify the functional requirements of each component of the device, which might be expressed in statements like a cheap screw to transmit a prescribed load to the cork; a light lever (i.e. a beam)to carry a prescribed bending moment; e a slender elastic blade that will not buckle when driven between the cork and bottle-neck: a thin, hollow needle, stiff and strong enough to penetrate a cork and so on. The functional requirements of each component are the inputs to the materials selection process. They lead directly to the property limits and material indices of Chapter 5: they are the first step in optimizing the choice of material to fill a given requirement. The procedure developed there takes requirements such as“ light strong beam”or“ slender elastic blade” and uses them to identify a subset of materials that will perform this function particu larly well. That is what is meant by design-led materials selection 2.7 Summary and conclusions Design is an iterative process. The starting point is a market need captured in a set of design requirements. Concepts for a products that meet the need are devised. If initial estimates and exploration of alternatives suggest that the concept is viable, the design proceeds to the embodiment stage: working principles are selected, size and layout are decided, and initial estimates of performance and cost are made. If the outcome is successful, the designer proceeds to the detailed design stage: optimization of performance, full analysis of critical components, preparation of detailed production drawings (usually as a CAD file), specification of tolerance, precision, joining and finishing methods, and so forth
the first three concepts: in the first, a screw is threaded into the cork to which an axial pull is applied; in the second, slender elastic blades inserted down the sides of the cork apply shear tractions when pulled; and in the third the cork is pierced by a hollow needle through which a gas is pumped to push it out. Figure 2.10 shows examples of cork removers using these working principles. All are described by the function-structure sketched in the upper part of Figure 2.11: create a force, transmit a force, apply force to cork. They differ in the working principle by which these functions are achieved, as indicated in the lower part of the figure. The cork removers in the photos combine working principles in the ways shown by the linking lines. Others could be devised by making other links. Figure 2.12 shows embodiment sketches for devices based on just one concept — that of axial traction. The first is a direct pull; the other three use some sort of mechanical advantage — levered-pull, geared pull and springassisted pull; the photos show examples of all of these. The embodiments of Figure 2.9 identify the functional requirements of each component of the device, which might be expressed in statements like: a cheap screw to transmit a prescribed load to the cork; a light lever (i.e. a beam) to carry a prescribed bending moment; a slender elastic blade that will not buckle when driven between the cork and bottle-neck; a thin, hollow needle, stiff and strong enough to penetrate a cork; and so on. The functional requirements of each component are the inputs to the materials selection process. They lead directly to the property limits and material indices of Chapter 5: they are the first step in optimizing the choice of material to fill a given requirement. The procedure developed there takes requirements such as ‘‘light strong beam’’ or ‘‘slender elastic blade’’ and uses them to identify a subset of materials that will perform this function particularly well. That is what is meant by design-led materials selection. 2.7 Summary and conclusions Design is an iterative process. The starting point is a market need captured in a set of design requirements. Concepts for a products that meet the need are devised. If initial estimates and exploration of alternatives suggest that the concept is viable, the design proceeds to the embodiment stage: working principles are selected, size and layout are decided, and initial estimates of performance and cost are made. If the outcome is successful, the designer proceeds to the detailed design stage: optimization of performance, full analysis of critical components, preparation of detailed production drawings (usually as a CAD file), specification of tolerance, precision, joining and finishing methods, and so forth. 24 Chapter 2 The design process
2. 8 Further reading 25 Materials selection enters at each stage, but at different levels of breadth and precision. At the conceptual stage all materials and processes are potential can didates, requiring a procedure that allows rapid access to data for a wide range of each, though without the need for great precision. The preliminary selection passes to the embodiment stage, the calculations and optimizations of which require information at a higher level of precision and detail. They eliminate all but a small short-list candidate-materials and processes for the final, detailed stage of the design. For these few, data of the highest quality are necessary Data exist at all these levels. Each level requires its own data-management scheme, described in the following chapters. The management is the skill: it must be design-led, yet must recognize the richness of choice and embrace the complex interaction between the material, its shape, the process by which it is given that shape, and the function it is required to perform. And it must allow rapid iteration-back-looping when a particular chain of reasoning proves to be unprofitable. Tools now exist to help with all of this We will meet one-the CES materials and process selection platform-later in this book But given this complexity, why not opt for the safe bet: stick to what you(or others)used before? Many have chosen that option. Few are still in business. 2. 8 Further reading a chasm exists between books on design methodology and those on materials selection ach largely ignores the other. The book by French is remarkable for its insights, but the word'material' does not appear in its index Pahl and Beitz has near-biblical standing in the design camp, but is heavy going. Ullman and Cross take a more relaxed approach nd are easier to digest. The books by Budinski and Budinski, by Charles, Crane and Furness and by Farag present the materials case well, but are less good on design. Lewis lustrates material selection through case studies, but does not develop a systematic procedure. The best compromise, perhaps, is Dieter. General texts on design methodology Cross, N.(2000) Engineering Design Methods, 3rd edition, Wiley, Chichester, UK. ISBN0-471-87250-4. (A durable text describing the design process, with emphasis on developing and evaluating alternative solutions. French, M.J. (1985)Conceptual Design for Engineers, The Design Council, London, UK, and Springer, Berlin, Germany. ISBN 0-85072-155-5 and 3-540-15175-3(The origin of the "Concept-Embodiment-Detail "block diagram of the design pro- cess. The book focuses on the concept stage, demonstrating bow simple physica principles guide the development of solutions to design problems.) Pahl, G. and Beitz, W.(1997) Engineering Design, 2nd edition, translated by K. Wallace and L. Blessing, The Design Council, London, UK and Springer-Verlag, Berli
Materials selection enters at each stage, but at different levels of breadth and precision. At the conceptual stage all materials and processes are potential candidates, requiring a procedure that allows rapid access to data for a wide range of each, though without the need for great precision. The preliminary selection passes to the embodiment stage, the calculations and optimizations of which require information at a higher level of precision and detail. They eliminate all but a small short-list candidate-materials and processes for the final, detailed stage of the design. For these few, data of the highest quality are necessary. Data exist at all these levels. Each level requires its own data-management scheme, described in the following chapters. The management is the skill: it must be design-led, yet must recognize the richness of choice and embrace the complex interaction between the material, its shape, the process by which it is given that shape, and the function it is required to perform. And it must allow rapid iteration — back-looping when a particular chain of reasoning proves to be unprofitable. Tools now exist to help with all of this. We will meet one — the CES materials and process selection platform—later in this book. But given this complexity, why not opt for the safe bet: stick to what you (or others) used before? Many have chosen that option. Few are still in business. 2.8 Further reading A chasm exists between books on design methodology and those on materials selection: each largely ignores the other. The book by French is remarkable for its insights, but the word ‘material’ does not appear in its index. Pahl and Beitz has near-biblical standing in the design camp, but is heavy going. Ullman and Cross take a more relaxed approach and are easier to digest. The books by Budinski and Budinski, by Charles, Crane and Furness and by Farag present the materials case well, but are less good on design. Lewis illustrates material selection through case studies, but does not develop a systematic procedure. The best compromise, perhaps, is Dieter. General texts on design methodology Cross, N. (2000) Engineering Design Methods, 3rd edition, Wiley, Chichester, UK. ISBN 0-471-87250-4. (A durable text describing the design process, with emphasis on developing and evaluating alternative solutions.) French, M.J. (1985) Conceptual Design for Engineers, The Design Council, London, UK, and Springer, Berlin, Germany. ISBN 0-85072-155-5 and 3-540-15175-3. (The origin of the ‘‘Concept— Embodiment— Detail’’ block diagram of the design process. The book focuses on the concept stage, demonstrating how simple physical principles guide the development of solutions to design problems.) Pahl, G. and Beitz, W. (1997) Engineering Design, 2nd edition, translated by K. Wallace and L. Blessing, The Design Council, London, UK and Springer-Verlag, Berlin, 2.8 Further reading 25
26 Chapter 2 The design process Germany. ISBN 0-85072-124-5 and 3-540-13601-0. The Bible-or perhaps more exactly the Old Testament-of the technical design field, developing formal methods in the rigorous German tradition. Ulman, D G(1992)The Mechanical Design Process, McGraw-Hill, New York, USA ISBN 0-07-065739-4(An American view of design, developing ways in which an initially ill-defined problem is tackled in a series of steps, much in the way suggested by Figure 2.1 of the present text.) Ulrich, K.T. and Eppinger, S D(1995) Product Design and Development, McGraw- Hill, New York, USA. ISBN 0-07-065811-0 (A readable, comprehensible text on product design, as taught at MIT. Many belpful examples but almost no mention of materials.) General texts on materials selection in design Budinski, K.G. and Budinski, M.K. (1999)Engineering Materials, Properties and Selection 6th edition, Prentice-Hall, Englewood Cliffs, NJ, USA. ISBN 0-13-904715-8 (A well- established materials text that deals well with both material properties and pro- cesses.) Charles, J.A., Crane, F.A.A. and Furness, J.A. G. (1997) Selection and Use of engi neering Materials, 3rd edition, Butterworth-Heinemann Oxford, UK. ISBN 0-7506 3277-1.(A materials-science, rather than a design-led, approach to the selection of materials.) Dieter, G.E. (1991)Engineering Design, a Materials and Processing Approach, 2nd edition, McGraw-Hill, New York, USA. ISBN 0-07-100829-2(A well-balanced and A respected text focusing on the place of materials and processing in technical design., rag, M.M.(1989)Selection of Materials and Manfacturing Processes for Engi- neering Design, Prentice-Hall, Englewood Cliffs, NJ, USA. ISBN 0-13-575192-6 ike Charles, Crane and Furness, this is Materials-Science approach to the selection of materials.) Lewis, G. (1990) Selection of Engineering Materials, Prentice-Hall, Englewood Cliffs N. USA. ISBN 0-13-802190-2. (A text on materials selection for technical design, based largely on case studies And on corks and corkscrews McKearin, H( 1973)"On'stopping, bottling and binning", International bottler and T, 47-54 Perry, E(1980) Corkscrews and Bottle Openers, Shire Publications Ltd, Aylesbury, The Design Council (1994) Teaching aids program EDTAP DE9, The Design Council 28 Haymarket, London SWIY 4SU, UK Watney, B M. and Babbige, H.D.(1981)Corkscrews. Sotheby's Publications London UK
Germany. ISBN 0-85072-124-5 and 3-540-13601-0. (The Bible— or perhaps more exactly the Old Testament — of the technical design field, developing formal methods in the rigorous German tradition.) Ullman, D.G. (1992) The Mechanical Design Process, McGraw-Hill, New York, USA. ISBN 0-07-065739-4. (An American view of design, developing ways in which an initially ill-defined problem is tackled in a series of steps, much in the way suggested by Figure 2.1 of the present text.) Ulrich, K.T. and Eppinger, S.D. (1995) Product Design and Development, McGrawHill, New York, USA. ISBN 0-07-065811-0. (A readable, comprehensible text on product design, as taught at MIT. Many helpful examples but almost no mention of materials.) General texts on materials selection in design Budinski, K.G. and Budinski, M.K. (1999) Engineering Materials, Properties and Selection 6th edition, Prentice-Hall, Englewood Cliffs, NJ, USA. ISBN 0-13-904715-8. (A wellestablished materials text that deals well with both material properties and processes.) Charles, J.A., Crane, F.A.A. and Furness, J.A.G. (1997) Selection and Use of Engineering Materials, 3rd edition, Butterworth-Heinemann Oxford, UK. ISBN 0-7506- 3277-1. (A materials-science, rather than a design-led, approach to the selection of materials.) Dieter, G.E. (1991) Engineering Design, a Materials and Processing Approach, 2nd edition, McGraw-Hill, New York, USA. ISBN 0-07-100829-2. (A well-balanced and respected text focusing on the place of materials and processing in technical design.) Farag, M.M. (1989) Selection of Materials and Manufacturing Processes for Engineering Design, Prentice-Hall, Englewood Cliffs, NJ, USA. ISBN 0-13-575192-6. (Like Charles, Crane and Furness, this is Materials-Science approach to the selection of materials.) Lewis, G. (1990) Selection of Engineering Materials, Prentice-Hall, Englewood Cliffs, N.J., USA. ISBN 0-13-802190-2. (A text on materials selection for technical design, based largely on case studies.) And on corks and corkscrews McKearin, H. (1973) ‘‘On ‘stopping’, bottling and binning’’, International Bottler and Packer, April issue, pp 47–54. Perry, E. (1980) Corkscrews and Bottle Openers, Shire Publications Ltd, Aylesbury, UK. The Design Council (1994) Teaching aids program EDTAP DE9, The Design Council, 28 Haymarket, London SW1Y 4SU, UK. Watney, B.M. and Babbige, H.D. (1981) Corkscrews. Sotheby’s Publications, London, UK. 26 Chapter 2 The design process
Chapter 3 Engineering materials and their properties Metals Cu-aloys n-aloys Silicon carbides PA(nylons Ceramics Polymers Sandwiches Zirconias Hybrids segmented structues Weaves Glasses Elastomers Glass-ceramics Chapter contents 3.1 Introduction and synopsis 28 3. 2 The families of engineering materials 3.3 The definitions of material proper 3.4 Summary and conclusions 43 3.5 Further reading
Steels Cast irons Al-alloys Cu-aloys Zn-alloys Ti-alloys Metals Elastomers Aluminas Silicon carbides Silicon nitrides Zirconias Ceramics Composites Sandwiches Segmented structues Lattices Weaves Hybrids PE, PP, PET, PC, PS, PEEK PA (nylons) Polyesters Phenolics Epoxies Polymers Soda glass Borosilicate glass Silica glass Glass-ceramics Glasses Isoprene Neoprene Butyl rubber Natural rubber Silicones EVA Chapter contents 3.1 Introduction and synopsis 28 3.2 The families of engineering materials 28 3.3 The definitions of material properties 30 3.4 Summary and conclusions 43 3.5 Further reading 44 Chapter 3 Engineering materials and their properties
28 Chapter 3 Engineering materials and their properties 3. Introduction and synopsis Materials, one might say, are the food of design. This chapter presents the menu: the full shopping list of materials. A successful product-one that performs well, is good value for money and gives pleasure to the user-uses the best materials for the job, and fully exploits their potential and char acteristics. Brings out their flavor, so to speak The families of materials -metals, polymers, ceramics, and so forth-are introduced in Section 3. 2. But it is not, in the end a material that we seek; it is a certain profile of properties-the one that best meets the needs of the design. The properties, important in thermo-mechanical design, are defined briefly in Section 3. 3. It makes boring reading. The reader confident in the definitions of moduli, strengths, damping capacities, thermal and electrical conductivities and the like, may wish to skip this, using it for reference, when needed, for the precise meaning and units of the data in the Property Charts that come later. Do not, however, skip Sections 3. 2-it sets up the classification structure that is used throughout the book. The chapter ends, in the usual way, with a summary 3.2 The families of engineering materials It is helpful to classify the materials of engineering into the six broad families hown in Figure 3. 1: metals, polymers, elastomers, ceramics, glasses, and hybrids. The members of a family have certain features in common: similar properties, similar processing routes, and, often, similar applications Metals have relatively high moduli. Most, when pure, are soft and easily deformed. They can be made strong by alloying and by mechanical and heat treatment, but they remain ductile, allowing them to be formed by deformation rocesses. Certain high-strength alloys(spring steel, for instance) have ductil ities as low as 1 percent, but even this is enough to ensure that the material yields before it fractures and that fracture, when it occurs, is of a tough, ductile type. Partly because of their ductility, metals are prey to fatigue and of all the classes of material, they are the least resistant to corrosion. Ceramics too, have high moduli, but, unlike metals, they are brittle. Their strength"in tension means the brittle fracture strength; in compression it is the brittle crushing strength, which is about 15 times larger. And because ceramics have no ductility, they have a low tolerance for stress concentrations (like holes or cracks) or for high-contact stresses(at clamping points, for instance). Ductile materials accommodate stress concentrations by deforming in a way that redistributes the load more evenly, and because of this, they can be used under static loads within a small margin of their yield strength Ceramics cannot Brittle materials always have a wide scatter in strength and
3.1 Introduction and synopsis Materials, one might say, are the food of design. This chapter presents the menu: the full shopping list of materials. A successful product — one that performs well, is good value for money and gives pleasure to the user — uses the best materials for the job, and fully exploits their potential and characteristics. Brings out their flavor, so to speak. The families of materials — metals, polymers, ceramics, and so forth — are introduced in Section 3.2. But it is not, in the end, a material that we seek; it is a certain profile of properties — the one that best meets the needs of the design. The properties, important in thermo-mechanical design, are defined briefly in Section 3.3. It makes boring reading. The reader confident in the definitions of moduli, strengths, damping capacities, thermal and electrical conductivities and the like, may wish to skip this, using it for reference, when needed, for the precise meaning and units of the data in the Property Charts that come later. Do not, however, skip Sections 3.2 — it sets up the classification structure that is used throughout the book. The chapter ends, in the usual way, with a summary. 3.2 The families of engineering materials It is helpful to classify the materials of engineering into the six broad families shown in Figure 3.1: metals, polymers, elastomers, ceramics, glasses, and hybrids. The members of a family have certain features in common: similar properties, similar processing routes, and, often, similar applications. Metals have relatively high moduli. Most, when pure, are soft and easily deformed. They can be made strong by alloying and by mechanical and heat treatment, but they remain ductile, allowing them to be formed by deformation processes. Certain high-strength alloys (spring steel, for instance) have ductilities as low as 1 percent, but even this is enough to ensure that the material yields before it fractures and that fracture, when it occurs, is of a tough, ductile type. Partly because of their ductility, metals are prey to fatigue and of all the classes of material, they are the least resistant to corrosion. Ceramics too, have high moduli, but, unlike metals, they are brittle. Their ‘‘strength’’ in tension means the brittle fracture strength; in compression it is the brittle crushing strength, which is about 15 times larger. And because ceramics have no ductility, they have a low tolerance for stress concentrations (like holes or cracks) or for high-contact stresses (at clamping points, for instance). Ductile materials accommodate stress concentrations by deforming in a way that redistributes the load more evenly, and because of this, they can be used under static loads within a small margin of their yield strength. Ceramics cannot. Brittle materials always have a wide scatter in strength and 28 Chapter 3 Engineering materials and their properties