1、 本科毕业设计（论文） 外文资料翻译 Material Selection During recant years the selection of engineering materials has assumed great importance. Moreover, the process should be one of continual reevaluation. New materials often become available and there may be a decreasing availability of others. Concerns regarding
2、environmental pollution, recycling and worker health and safety often impose new constraints. The desire for weight reduction or energy savings may dictate the use of different materials. Pressures from domestic and foreign competition, increased serviceability requirements, and customer feedback ma
3、y all promote materials reevaluation. The extent of product liability actions, often the result of improper material use, has had a marked impact； in addition, the interdependence between materials and their processing has become better recognized. The development of new processes often forces reeva
4、luation of the materials being processed. Therefore, it is imperative that design and manufacturing engineers exercise considerable care in selecting, specifying, and utilizing materials if they are to achieve satisfactory results at reasonable cost and still assure quality. The first step in the ma
5、nufacture of any product is design, which usually takes place in several distinct stages: (a) conceptual； (b) functional； (c) production design. During the conceptual-design stage, the designer is concerned primarily with the functions the product is to fulfill Usually several concepts are visualize
6、d and considered, and a decision is made either that the idea is not practical or that the idea is sound and one or more of the conceptual designs should be developed further. Here, the only concern for materials is that materials exist that can provide the desired property. If no such materials are
7、 available, consideration is given as to whether there is a reasonable prospect that new one could be developed within cost and time limitations. At the functional or engineering design stage, a practical, workable design is developed .Fairly complete drawings are made, and materials are selected an
8、d specified for the various components. Often a prototype or working modal is made that can be tested to permit evaluation of the product as to function, reliability, appearance, serviceability, and so on. Although it is expected that such testing might show that some changes may have to be made in
9、materials before the product is advanced to the production-design stage, this should not be taken as an excuse for not doing a thorough job of material selection. Appearance, cost, and reliability factors should be considered in detail, together with the functional factors. There is much merit to th
10、e practice of one very successful company which requires that all prototypes be built with the same materials that will be used in production and, insofar as possible, with the same manufacturing techniques. It is of little value to have a perfectly functioning prototype that cannot be manufactured
11、economically in the expected sales volume, or one that is substantially different from what the production units will be in regard to quality and reliability. Also, it is much better for design engineers to do a complete job of material analysis, selection, and specification at the development stage
12、 of design rather than to leave it to the production design stage, where changes may be made by others, possibly less knowledgeable about all of the functional aspects of the product. At the production design stage, the primary concern relative to materials should be that they are specified fully, that they are compatible with, and can be processed economically by, existing equipment, and that they are readily available in the needed quantities.
