Materials in design

Design is the process of translating a new idea or a market need into the detailed information from which a product can be manufactured. Each of its stages requires decisions about the materials from which the product is to be made and the process for making it. Normally, the choice of material is dictated by the design. But sometimes it is the other way round: the new product, or the evolution of the existing one, was suggested or made possible by the new material. The number of materials available to the engineer is vast: something between 40 000 and 80 000 are at his or her (from here on ‘his’ means both) disposal. And although standardization strives to reduce the number, the continuing appearance of new materials with novel, exploitable, properties expands the options further.

How, then, does the engineer choose, from this vast menu, the material best suited to his purpose? Must he rely on experience? Or can a systematic procedure be formulated for making a rational choice? The question has to be answered 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 shortlist of materials which can satisfy them narrows.  Then more accurate data are required (although for a lesser number of materials) and a different way of analysing 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, narrow this to a small subset, and 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. And -it must be recognized -good engineering design alone is not enough to sell a product. In almost everything from home appliances through automobiles to aircraft, the form, texture, feel, colour, decoration of the product- the satisfaction it gives the person who buys or uses it -are important. This aesthetic aspect (known confusingly as 'industrial design') is not treated in most courses on engineering, but it 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, although some solutions will clearly be better than others. They differ from the analrtical problems used in teaching mechanics, or structures, or thermodynamics, or even materials, 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 which, 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 which show the lay of the land, so to speak, and simplify the initial survey for potential candidate materials. The interaction between material and shape can be built into the method, as can the more complex aspects of optimizing the balance between performance and cost. 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 change in the materials world are surveyed. The Appendices contain useful information.

The methodology has further applications. It suggests a strategy for material development, particularly of composites and structured materials like sandwich panels. It points to a scheme for identifying the most promising applications for new materials. And it lends itself readily to computer implementation, offering the potential for interfaces with computer-aided design, function modelling, optimization routines and so forth.

All this will be found in the following chapters, with case studies illustrating applications. But first, a little history.

MICHAEL F. ASHBY

Department of Engineering, Cambridge University, England

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