Materials, bicycles, and design
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Materials, Bicycles, and Design
M.F. ASHBY
If the selection of materials is to be integrated into engineering design, a procedure is needed to identify, from among the enormous range of materials, the subset which most closely meets the design requirements. The elements of such a procedure are here described and illustrated by using it to select materials for bicycle frames. I.
INTRODUCTION
THE starting point of this article can be put in four short sentences. Materials and processes underpin all engineering design31~1 The computer (by which we mean "information technology") has revolutionized the way the geometric, thermomechanical, and manufacturing aspects of design are tackled. [5,6] But the selection of material and process is poorly integrated into this new technology. What can we do about it?
M.F. ASHBY received his Bachelors degree and Doctorate in Natural Sciences at the University of Cambridge and then joined the Institute for Metal Physics at the University of Grttingen, Germany, working with Professor P. Haasen from 1962 to 1965. From 1966 to 1973, he held the post of Professor of Applied Physics in the Division of Engineering and Applied Physics at Harvard University. Since 1973, he has been a member of the Cambridge University Engineering Department, where he holds the post of Royal Society Research Professor. Professor Ashby has been the editor of Aeta Metallurgica since 1974. His research interests include mechanisms of plasticity and fracture, methodologies for materials selection and their integration into an integrated design framework, and the modeling of material-shaping processes. The Edward DeMille Campbell Memorial Lecture was established in 1926 as an annual lecture in memory of and in recognition of the outstanding scientific contributions to the metallurgical profession by a distinguished educator who was blind for all but two years of his professional life. It recognizes demonstrated ability in metallurgical science and engineering. METALLURGICAL AND MATERIALS TRANSACTIONS B
II.
M A T E R I A L S AND THE DESIGN PROCESS
Figure 1 helps clarify the problem. The central column shows, much simplified, the stages of the design process. A market need is identified. Concepts which might meet the need are devised. The functional units of each concept are identified and their viability is examined (left-hand columns). Potentially practical concepts are selected and the design proceeds to the embodiment stage in which a layout is developed and approximate estimates of its overall performance are made. If successful, the design passes to the detail stage in which analysis and optimization lead to a set of working drawings giving the size and layout of each component; critical components are subjected to finite-element analysis; and the performance of assemblies is optimized using modeling or simulation tools, until the design is finally frozen. The output is a product specification: a set of instructions for shape, material, and technology of manufacture.t5,6] An example may help. A need is
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