1. 2 Materials in design 3 procedure-one with steps that can be taught quickly, that is robust in the decisions it reaches, that allows of computer implementation, and with the ability to interface with the other established tools of engineering design. The question has to be addressed at a number of levels, corresponding to the stage the design has reached. At the beginning the design is fluid and the options are wide; all materials must be considered. As the design becomes more focused and takes shape, the selection criteria sharpen and the short-list of materials that can satisfy them narrows. Then more accurate data are required (though for a lesser number of materials)and a different way of analyzing the hoice must be used In the final stages of design, precise data are needed, but for still fewer materials-perhaps only one. The procedure must recognize the initial richness of choice, and at the same time provide the precision and detail on which final design calcula ations can The choice of material cannot be made independently of the choice of process by which the material is to be formed, joined, finished, and otherwise treated. Cost enters, both in the choice of material and in the way the material is processed. So, too, does the influence material usage on the environment in which we live. And it must be recognized that good engineering design alone is not enough to sell products. In almost everything from home appliances through automobiles to aircraft, the form, texture, feel, color, decoration of the product-the satisfaction it gives the person who owns or uses it-are important. This aspect, known confusingly as"industrial design", is one that, if neglected, can lose the manufacturer his market. Good designs work; excellent designs also give pleasure Design problems, almost always, are open-ended. They do not have a unique or"correct"solution, though some solutions will clearly be better than others They differ from the analytical problems used in teaching mechanics structures, or thermodynamics, which generally do have single, correct answers. So the first tool a designer needs is an open mind: the willingness onsider all possibilities. But a net cast widely draws in many fish. A procedure is necessary for selecting the excellent from the merely good. This book deals with the materials aspects of the design process. It develops a methodology that, properly applied, gives guidance through the forest of complex choices the designer faces. The ideas of material and process attributes are introduced. They are mapped on material and process selection charts that show the lay of the land, so to speak, and simplify the initial survey for potential candidate-materials. Real life always involves conflicting objectives-minimizing mass while at the same time minimizing cost is an example-requiring the use of trade-off methods. The interaction between material and shape can be built into the method. Taken together, these suggest schemes for expanding the boundaries of material performance by creating hybrids -combinations of two or more materials, shapes and configurat with unique property profiles. None of this can be implemented without data for material properties and process attributes: ways to find them are described The role of aesthetics in engineering design is discussed. The forces driving
procedure — one with steps that can be taught quickly, that is robust in the decisions it reaches, that allows of computer implementation, and with the ability to interface with the other established tools of engineering design. The question has to be addressed at a number of levels, corresponding to the stage the design has reached. At the beginning the design is fluid and the options are wide; all materials must be considered. As the design becomes more focused and takes shape, the selection criteria sharpen and the short-list of materials that can satisfy them narrows. Then more accurate data are required (though for a lesser number of materials) and a different way of analyzing the choice must be used. In the final stages of design, precise data are needed, but for still fewer materials — perhaps only one. The procedure must recognize the initial richness of choice, and at the same time provide the precision and detail on which final design calculations can be based. The choice of material cannot be made independently of the choice of process by which the material is to be formed, joined, finished, and otherwise treated. Cost enters, both in the choice of material and in the way the material is processed. So, too, does the influence material usage on the environment in which we live. And it must be recognized that good engineering design alone is not enough to sell products. In almost everything from home appliances through automobiles to aircraft, the form, texture, feel, color, decoration of the product — the satisfaction it gives the person who owns or uses it — are important. This aspect, known confusingly as ‘‘industrial design’’, is one that, if neglected, can lose the manufacturer his market. Good designs work; excellent designs also give pleasure. Design problems, almost always, are open-ended. They do not have a unique or ‘‘correct’’ solution, though some solutions will clearly be better than others. They differ from the analytical problems used in teaching mechanics, or structures, or thermodynamics, which generally do have single, correct answers. So the first tool a designer needs is an open mind: the willingness to consider all possibilities. But a net cast widely draws in many fish. A procedure is necessary for selecting the excellent from the merely good. This book deals with the materials aspects of the design process. It develops a methodology that, properly applied, gives guidance through the forest of complex choices the designer faces. The ideas of material and process attributes are introduced. They are mapped on material and process selection charts that show the lay of the land, so to speak, and simplify the initial survey for potential candidate-materials. Real life always involves conflicting objectives — minimizing mass while at the same time minimizing cost is an example — requiring the use of trade-off methods. The interaction between material and shape can be built into the method. Taken together, these suggest schemes for expanding the boundaries of material performance by creating hybrids — combinations of two or more materials, shapes and configurations with unique property profiles. None of this can be implemented without data for material properties and process attributes: ways to find them are described. The role of aesthetics in engineering design is discussed. The forces driving 1.2 Materials in design 3
4 Chapter I Introduction ge in the materials-world are surveyed, the most obvious of which is ealing with environmental concerns. The appendices contain useful nformation The methods lend themselves readily to implementation as computer-based tools; one, The CES materials and process selection platform, has been used for the case studies and many of the figures in this book. They offer, too, potential for interfacing with other computer-aided design, function modeling optimization routines, but this degree of integration, though under develop ment, is not yet commercially available. All this will be found in the following chapters, with case studies illustrating 1.3 The evolution of engineering materials Throughout history, materials have limited design. The ages in which man has lived are named for the materials he used: stone. bronze. iron. And when he died. the materials he treasured were buried with him: Tutankhamen in his enameled sarcophagus, Agamemnon with his bronze sword and mask of gold each representing the high technology of their day If they had lived and died today, what would they have taken with them? Their titanium watch, perhaps; their carbon-fiber reinforced tennis racquet, their metal-matrix composite mountain bike, their shape-memory alloy eye-glass frames with diamond-like carbon coated lenses, their polyether- ethyl-ketone crash helmet. This is not the age of one material, it is the age of an immense range of materials. There has never been an era in which their evolution was faster and the range of their properties more varied. The menu f materials has expanded so rapidly that designers who left college 20 years go can be forgiven for not knowing that half of them exist. But not- D-know is, for the designer, to risk disaster. Innovative design, often, means the imaginative exploitation of the properties offered by new or improved materials. And for the man in the street, the schoolboy even, not-to-know is to miss one of the great developments of our age: the age of advanced materials This evolution and its increasing pace are illustrated in Figure 1. 1. The materials of pre-history (>10,000 BC, the Stone Age) were ceramics and glasses, natural polymers, and composites. Weapons -always the peak of technology-were made of wood and flint; buildings and bridges of stone and wood. Naturally occurring gold and silver were available locally and, through their rarity, assumed great influence as currency, but their role in technology was small. The development of rudimentary thermo-chemistry allowed th GrantaDesignLtd,RustatHouse62CliftonRoadcAmbridgeCbi7eg.Uk(wWw.grantadesign.com)
change in the materials-world are surveyed, the most obvious of which is that dealing with environmental concerns. The appendices contain useful information. The methods lend themselves readily to implementation as computer-based tools; one, The CES materials and process selection platform, 1 has been used for the case studies and many of the figures in this book. They offer, too, potential for interfacing with other computer-aided design, function modeling, optimization routines, but this degree of integration, though under development, is not yet commercially available. All this will be found in the following chapters, with case studies illustrating applications. But first, a little history. 1.3 The evolution of engineering materials Throughout history, materials have limited design. The ages in which man has lived are named for the materials he used: stone, bronze, iron. And when he died, the materials he treasured were buried with him: Tutankhamen in his enameled sarcophagus, Agamemnon with his bronze sword and mask of gold, each representing the high technology of their day. If they had lived and died today, what would they have taken with them? Their titanium watch, perhaps; their carbon-fiber reinforced tennis racquet, their metal-matrix composite mountain bike, their shape-memory alloy eye-glass frames with diamond-like carbon coated lenses, their polyether– ethyl–ketone crash helmet. This is not the age of one material, it is the age of an immense range of materials. There has never been an era in which their evolution was faster and the range of their properties more varied. The menu of materials has expanded so rapidly that designers who left college 20 years ago can be forgiven for not knowing that half of them exist. But notto-know is, for the designer, to risk disaster. Innovative design, often, means the imaginative exploitation of the properties offered by new or improved materials. And for the man in the street, the schoolboy even, not-to-know is to miss one of the great developments of our age: the age of advanced materials. This evolution and its increasing pace are illustrated in Figure 1.1. The materials of pre-history (>10,000 BC, the Stone Age) were ceramics and glasses, natural polymers, and composites. Weapons — always the peak of technology — were made of wood and flint; buildings and bridges of stone and wood. Naturally occurring gold and silver were available locally and, through their rarity, assumed great influence as currency, but their role in technology was small. The development of rudimentary thermo-chemistry allowed the 1 Granta Design Ltd, Rustat House, 62 Clifton Road, Cambridge CB1 7EG, UK (www.grantadesign.com). 4 Chapter 1 Introduction
1. 3 The evolution of engineering materials 5 10000BC5000Bc 010001500180 190019401960198 990 2000 20102020 Polymers AlLithiu Development Slow Dual Phase Steels control and Skins Microalloyed Steels Processing Fibers 8 Glues New Super Alloys Rubber Super Alloys Titanium iconium Alloys aStone Modulus Pottery Cement Refractories PS: P Cement: Suied Cermets Ceramics Ceramics qiaeernLN: Psz etc 10000BC 5000BC 10001500180019001940196 20102020 DATE Figure 1. I The evolution of engineering materials with time. "Relative importance"is based on nformation contained in the books listed under "Further reading". plus, from 1960 onwards, data for the teaching hours allocated to each material family in UK and US Universities. The projections to 2020 rely on estimates of material usage in automobiles and aircraft by manufacturers. The time scale is non-linear. The rate of change is far faster today than at any previous time in history extraction of, first, copper and bronze, then iron(the Bronze Age, 4000-1000 BC and the Iron Age, 1000 BC-1620 AD)stimulating enormous advances, in technology.(There is a cartoon on my office door, put there by a student, showing an aggrieved Celt confronting a sword-smith with the words: "You sold me this bronze sword last week and now I'm supposed to upgrade to iron! ")Cast iron technology(1620s) established the dominance of metals in engineering; and since then the evolution of steels (1850 onward), light alloys (1940s)and special alloys, has consolidated their position. By the 1960s “ engineering materials” meant“ metals”. Engineers were given courses metallurgy; other materials were barely mentioned. There had, of course, been developments in the other classes of material Improved cements, refractories, and glasses, and rubber, bakelite, and poly ethylene among polymers, but their share of the total materials market was small. Since 1960 all that has changed. The rate of development of new metallic alloys is now slow; demand for steel and cast iron has in some countries
extraction of, first, copper and bronze, then iron (the Bronze Age, 4000–1000 BC and the Iron Age, 1000 BC–1620 AD) stimulating enormous advances, in technology. (There is a cartoon on my office door, put there by a student, showing an aggrieved Celt confronting a sword-smith with the words: ‘‘You sold me this bronze sword last week and now I’m supposed to upgrade to iron!’’) Cast iron technology (1620s) established the dominance of metals in engineering; and since then the evolution of steels (1850 onward), light alloys (1940s) and special alloys, has consolidated their position. By the 1960s, ‘‘engineering materials’’ meant ‘‘metals’’. Engineers were given courses in metallurgy; other materials were barely mentioned. There had, of course, been developments in the other classes of material. Improved cements, refractories, and glasses, and rubber, bakelite, and polyethylene among polymers, but their share of the total materials market was small. Since 1960 all that has changed. The rate of development of new metallic alloys is now slow; demand for steel and cast iron has in some countries 10000BC 0 1000 1500 1800 1900 1940 1960 1980 1990 2000 2010 2020 5000BC 10000BC 0 1000 1500 1800 1900 1940 1960 1980 1990 2000 2010 2020 5000BC Gold Copper Bronze Iron Cast Iron Cast Iron Wood Skins Fibres Glues Rubber Straw-Brick Straw-Brick Paper Bakerlite Bakerlite Stone Flint Pottery Pottery Glass Cement Refractories Refractories Portland Portland Cement Fused Silica PyroCeramics Ceramics Steels Alloy Steels Light Alloys Super Alloys Super Alloys Titanium Titanium Zirconium Zirconium Alloys etc Nylon PE PMMA Acrylics Acrylics PC PS PP Cermets Cermets Epoxies Epoxies Polyesters Polyesters Tough Engineering Tough Engineering Ceramics ( Al Ceramics ( Al2O3, Si3N4, PSZ etc ) , PSZ etc ) GFRP CFRP Kelvar-FRP Kelvar-FRP Composites Composites Metal-Matrix Metal-Matrix Ceramic Composites Ceramic Composites High Modulus High Modulus Polymers Polymers High Temperature High Temperature Polymers Polymers Development Slow: Development Slow: Mostly Quality Mostly Quality Control and Control and Processing Processing Glassy Metals Glassy Metals Al-Lithium Alloys Al-Lithium Alloys Dual Phase Steels Dual Phase Steels Microalloyed Steels Microalloyed Steels New Super Alloys New Super Alloys Gold Copper Bronze Iron Cast Iron Wood Skins Fibers Glues Rubber Straw-Brick Paper Bakelite Stone Flint Pottery Glass Cement Refractories Portland Cement Fused Silica PyroCeramics Steels Alloy Steels Light Alloys Super Alloys Titanium Zirconium Alloys etc Nylon PE PMMA Acrylics PC PS PP Cermets Epoxies Polyesters Tough Engineering Ceramics ( Al2O3, Si3N4, PSZ etc.) GFRP CFRP Kelvar-FRP Composites Metal-Matrix Ceramic Composites High Modulus Polymers High Temperature Polymers Development Slow: Mostly Quality Control and Processing Glassy Metals Al-Lithium Alloys Dual Phase Steels Microalloyed Steels New Super Alloys DATE Relative importance Polymers & elastomers Polymers & elastomers Composites Composites Ceramics & glasses Ceramics & glasses Metals Metals Figure 1.1 The evolution of engineering materials with time. ‘‘Relative importance’’ is based on information contained in the books listed under ‘‘Further reading’’, plus, from 1960 onwards, data for the teaching hours allocated to each material family in UK and US Universities. The projections to 2020 rely on estimates of material usage in automobiles and aircraft by manufacturers. The time scale is non-linear. The rate of change is far faster today than at any previous time in history. 1.3 The evolution of engineering materials 5
6 Chapter I Introduction actually fallen. The polymer and composite industries, on the other hand, are growing rapidly, and projections of the growth of production of the new igh-performance ceramics suggests continued expansion here also. This rapid rate of change offers opportunities that the designer cannot afford to ignore. The following case study is an example 1. 4 Case study: the evolution of materials in vacuum cleaners Sweeping and dusting are homicidal practices: they consist of taking dust from the floor, mixing it in the atmosphere, and causing it to be inhaled by the inhabitants of the house. In reality it would be preferable to leave the dust alone where it was. That was a doctor, writing about 100 years ago. More than any previous generation, the Victorians and their contemporaries in other countries worried about dust. They were convinced that it carried disease and that dusting merely dispersed it when, as the doctor said, it became yet more infectious. Little wonder, then, that they invented the vacuum cleaner The vacuum cleaners of 1900 and before were human-powered (Figure 1. 2(a) The housemaid, standing firmly on the flat base, pumped the handle of the cleaner, compressing bellows that, via leather flap-valves to give a one-way flow, sucked air through a metal can containing the filter at a flow rate of about 1 l /s The butler manipulated the hose. The materials are, by todays standards, pri- nitive: the cleaner is made almost entirely from natural materials: wood, canvas ther and rubber. The only metal is the straps that link the bellows (soft iron) and the can containing the filter(mild steel sheet, rolled to make a cylinder).It reflects the use of materials in 1900. Even a car, in 1900, was mostly made of wood, leather, and rubber; only the engine and drive train had to be metal The electric vacuum cleaner first appeared around 1908. By 1950 the design had evolved into the cylinder cleaner shown in Figure 1.2(b)(flow rate about 1 s). Air flow is axial, drawn through the cylinder by an electric fan. The fan occupies about half the length of the cylinder; the rest holds the filter. One advance in design is, of course, the electrically driven air pump. The motor, it is true, is bulky and of low power, but it can function continuously without tea breaks or housemaid's elbow but there are others: this cleaner is almost entirely made of metal: the case, the end-caps, the runners, even the tube to suck up the dust are mild steel: metals have entirely replaced natural materials Developments since then have been rapid, driven by the innovative use of new materials. The 1985 vacuum cleaner of Figure 1.2(c) has the power of roughly 16 housemaids working flat out(800 W)and a corresponding air Do not, however, imagine that the days of steel are over. Steel production accounts for 90% of all world metal output, and its unique combination of strength, ductility, toughness, and low price make Inventors: Murray Spengler and william B. Hoover. The second name has become part of the English anguage, along with those of such luminaries as john B Stetson(the hat), S.F.B. Morse(the code), Leo Henrik Baikeland(Bakelite), and Thomas Crapper(the flush toilet
actually fallen.2 The polymer and composite industries, on the other hand, are growing rapidly, and projections of the growth of production of the new high-performance ceramics suggests continued expansion here also. This rapid rate of change offers opportunities that the designer cannot afford to ignore. The following case study is an example. 1.4 Case study: the evolution of materials in vacuum cleaners Sweeping and dusting are homicidal practices: they consist of taking dust from the floor, mixing it in the atmosphere, and causing it to be inhaled by the inhabitants of the house. In reality it would be preferable to leave the dust alone where it was. That was a doctor, writing about 100 years ago. More than any previous generation, the Victorians and their contemporaries in other countries worried about dust. They were convinced that it carried disease and that dusting merely dispersed it when, as the doctor said, it became yet more infectious. Little wonder, then, that they invented the vacuum cleaner. The vacuum cleaners of 1900 and before were human-powered (Figure 1.2(a)). The housemaid, standing firmly on the flat base, pumped the handle of the cleaner, compressing bellows that, via leather flap-valves to give a one-way flow, sucked air through a metal can containing the filter at a flow rate of about 1 l/s. The butler manipulated the hose. The materials are, by today’s standards, primitive: the cleaner is made almost entirely from natural materials: wood, canvas, leather and rubber. The only metal is the straps that link the bellows (soft iron) and the can containing the filter (mild steel sheet, rolled to make a cylinder). It reflects the use of materials in 1900. Even a car, in 1900, was mostly made of wood, leather, and rubber; only the engine and drive train had to be metal. The electric vacuum cleaner first appeared around 1908.3 By 1950 the design had evolved into the cylinder cleaner shown in Figure 1.2(b) (flow rate about 10 l/s). Air flow is axial, drawn through the cylinder by an electric fan. The fan occupies about half the length of the cylinder; the rest holds the filter. One advance in design is, of course, the electrically driven air pump. The motor, it is true, is bulky and of low power, but it can function continuously without tea breaks or housemaid’s elbow. But there are others: this cleaner is almost entirely made of metal: the case, the end-caps, the runners, even the tube to suck up the dust are mild steel: metals have entirely replaced natural materials. Developments since then have been rapid, driven by the innovative use of new materials. The 1985 vacuum cleaner of Figure 1.2(c) has the power of roughly 16 housemaids working flat out (800 W) and a corresponding air 2 Do not, however, imagine that the days of steel are over. Steel production accounts for 90% of all world metal output, and its unique combination of strength, ductility, toughness, and low price makes steel irreplaceable. 3 Inventors: Murray Spengler and William B. Hoover. The second name has become part of the English language, along with those of such luminaries as John B. Stetson (the hat), S.F.B. Morse (the code), Leo Henrik Baikeland (Bakelite), and Thomas Crapper (the flush toilet). 6 Chapter 1 Introduction
1. 4 Case study: the evolution of materials in vacuum cleaners 7 Figure 1. 2 Vacuum cleaners: (a)the hand-powered bellows cleaner of 1900, largely made of wood and leather;(b) the cylinder cleaner of 1950;(c) the lightweight cleaner of 1985, almost entirely made of polymer; and(d)a centrifugal dust-extraction cleaner of 1997. flow-rate; cleaners with twice that power are now available. Air flow is still axial and dust-removal by filtration, but the unit is smaller than the old cylinder cleaners. This is made possible by a higher power-density in the motor reflecting better magnetic materials, and higher operating temperatures(heat resistant insulation, windings, and bearings). The casing is entirely polymeric and is an example of good design with plastics. The upper part is a single molding, with all additional bits attached by snap fasteners molded into the original component. No metal is visible anywhere; even the straight part of the suction tube, metal in all earlier models, is now polypropylene. The number of components is dramatically reduced: the casing has just 4 parts, held together by just 1 fastener, compared with 11 parts and 28 fasteners for the 1950 cleaner The saving on weight and cost is enormous, as the comparison in Table 1.1 shows. It is arguable that this design(and its many variants)is near-optimal for oday's needs; that a change of working principle, material or process could increase performance but at a cost-penalty unacceptable to the consumer. We will leave the discussion of balancing performance against cost to a later chapter, and merely note here that one manufacturer disagrees. The cleaner shown in Figure 1. 2(d)exploits a different concept: that of inertial separation rather than filtration. For this to work, the power and rotation speed have to be igh; the product is larger, heavier and more expensive than the competition Yet it sells -a testament to good industrial design and imaginative marketing
flow-rate; cleaners with twice that power are now available. Air flow is still axial and dust-removal by filtration, but the unit is smaller than the old cylinder cleaners. This is made possible by a higher power-density in the motor, reflecting better magnetic materials, and higher operating temperatures (heatresistant insulation, windings, and bearings). The casing is entirely polymeric, and is an example of good design with plastics. The upper part is a single molding, with all additional bits attached by snap fasteners molded into the original component. No metal is visible anywhere; even the straight part of the suction tube, metal in all earlier models, is now polypropylene. The number of components is dramatically reduced: the casing has just 4 parts, held together by just 1 fastener, compared with 11 parts and 28 fasteners for the 1950 cleaner. The saving on weight and cost is enormous, as the comparison in Table 1.1 shows. It is arguable that this design (and its many variants) is near-optimal for today’s needs; that a change of working principle, material or process could increase performance but at a cost-penalty unacceptable to the consumer. We will leave the discussion of balancing performance against cost to a later chapter, and merely note here that one manufacturer disagrees. The cleaner shown in Figure 1.2(d) exploits a different concept: that of inertial separation rather than filtration. For this to work, the power and rotation speed have to be high; the product is larger, heavier and more expensive than the competition. Yet it sells — a testament to good industrial design and imaginative marketing. 1905 1950 1985 1997 (a) (b) (c) (d) Figure 1.2 Vacuum cleaners: (a) the hand-powered bellows cleaner of 1900, largely made of wood and leather; (b) the cylinder cleaner of 1950; (c) the lightweight cleaner of 1985, almost entirely made of polymer; and (d) a centrifugal dust-extraction cleaner of 1997. 1.4 Case study: the evolution of materials in vacuum cleaners 7