Ashby6 - Materials selection 6.1 Introduction and synopsis...

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Materials selection - case studies 6.1 Introduction and synopsis Here we have a collection of case studies* illustrating the screening methods** of Chapter 5 . Each is laid out in the same way: (a) the problem statement, setting the scene; (b) the model, identifying function, objectives and constraints from which emerge the property (c) the selection in which the full menu of materials is reduced by screening and ranking to a (d) the postscript, allowing a commentary on results and philosophy. Techniques for seeking further information are left to later chapters. The first few examples are simple but illustrate the method well. Later examples are less obvious and require clear identification of the objectives, the constraints, and the free variables. Confusion here can lead to bizarre and misleading conclusions. Always apply common sense: does the selection include the traditional materials used for that application? Are some members of the subset obviously unsuitable? If they are, it is usually because a constraint has been overlooked: it must be formulated and applied. The case studies are deliberately simplified to avoid obscuring the method under layers of detail. In most cases nothing is lost by this: the best choice of material for the simple example is the same as that for the more complex, for the reasons given in Chapter 5 limits and material indices; short-list of viable candidates; and 6.2 Materials for oars Credit for inventing the rowed boat seems to belong to the Egyptians. Boats with oars appear in carved relief on monuments built in Egypt between 3300 and 3000 BC. Boats, before steam power, could be propelled by poling, by sail and by oar. Oars gave more control than the other two, the military potential of which was well understood by the Romans, the Vikings and the Venetians. * A computer-based exploration of these and other case studies can be found in Case Studies in Materials Selection by M.F. Ashby and D. Cebon, published by Granta Design, Trumpington Mews, 40B High Street, Trumpington CB2 2LS, UK ( 1996). **The material properties used here are taken from the CMS compilation published by Granta Design. Trumpington Mews, 40B High Street, Trumpington CB2 2LS , UK.
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86 Materials Selection in Mechanical Design Records of rowing races on the Thames in London extend back to 1716. Originally the competitors were watermen, rowing the ferries used to carry people and goods across the river. Gradually gentlemen became involved (notably the young gentlemen of Oxford and Cambridge), sophisticating both the rules and the equipment. The real stimulus for development of boat and oar came in 1900 with the establishment of rowing as an Olympic sport. Since then both have exploited to the full the craftsmanship and materials of their day. Consider, as an example, the oar.
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This note was uploaded on 04/26/2008 for the course M&AE 212 taught by Professor Miller during the Spring '07 term at Cornell University (Engineering School).

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Ashby6 - Materials selection 6.1 Introduction and synopsis...

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