Introduction and synopsis
‘Design’ is one of those words that means all things to all people. Every manufactured thing, from
the most lyrical of ladies’ hats to the greasiest of gearboxes, qualifies, in some sense or other, as a
design. It can mean yet more. Nature, to some is Divine Design; to others it is design by Natural
Selection, the ultimate genetic algorithm. The reader will agree that it is necessary to narrow the
field, at least a little.
This book is about mechanical design, and the role of materials in it. Mechanical components
have mass; they carry loads; they conduct heat and electricity; they are exposed to wear and to
corrosive environments; they are made of one or more materials; they have shape; and they must
be manufactured (Figure 1.1). The book describes how these activities are related.
Materials have limited design since man first made clothes, built shelters and waged wars. They
still do. But materials and processes to shape them are developing faster now than at any previous
time in history; the challenges and opportunities they present are greater than ever before. The book
develops a strategy for exploiting materials in design.
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
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
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.