As manufacturing progresses, it is inevitable that situations will arise that may require modifications of the materials being used. Experience may reveal that substitution of cheaper materials can be made. In most cases, however, changes are much more costly to make after manufacturing is in progress than before it starts. Good selection during the production design phase will eliminate the necessity for most of this type of change. The more common type of change that occurs after manufacturing starts is the result of the availability of new materials. These, of course, present possibilities for cost reduction and improved performance. However, new materials must be evaluated very carefully to make sure that all
Their characteristics are well established. One should always remember that it is indeed rare that as much is known about the properties and reliability of a new material as about those of an existing one. A large proportion of product failure and product liability! Cases have resulted from new materials being substituted before their long-term properties were really known.
Product liability actions have made it imperative that designers and companies employ the very best procedures in selecting materials. The five most common faults in material selection have been: (a) failure to know and use the latest and best information available about the materials utilized; (b) fail are to fore, and take into account the reasonable uses for the product( where possible, the designer is further advised to foresee and account for misuse of the product, as there have been many product liability cases in recent years where the claimant, injured during misuse of the product, has sued the manufacturer and won);(c) the use of materials about which there was insufficient or uncertain data, particularly as to its king term properties; (d) inadequate, and unverified, quality control procedures; and(e) material selection made by people who are complete unqualified to do so.
The Computer in Design and Graphics
Computers are widely used in engineering and related fields and their use is expected to grow even more rapidly than in the past Engineering and technology students must became computer literate, to understand the applications of computer and their advantages. Not to do so well place students at a serious disadvantage in pursuing their careers.
Computer-aided design (CAD) involves solving design problems with the help of
Computer: to make graphic images on paper with a plotter or printer, analyze design data, and store design information for easy retrieval. Many CAD systems perform these functions in all integrated manner, greatly increasing the designer's productivity.
Computer-aided design drafting (CADD), an offshoot of CAD, is the process of Generating engineering drawings and other technical documents by computer and is more directly related to drafting than is CAD. The CADD user inputs data by keyboard and/or mouse to produce illustrations on the monitor screen that can be reproduced as paper copies with a plotter or printer.
Engineers generally agree that the computer does not change the nature of the design process but is a significant tool that improves efficiency and productivity. The designer and the CAD system may be described as a design team: the designer provides knowledge, creativity, and control; the computer generates accurate, easily modifiable graphics, performs complex design analysis at great speed, and stores and recalls design information. Occasionally, the computer may augment or replace many of the engineer's other tools, but it cannot replace the design process, which is controlled by the designer.
Depending on the nature of the problem and the sophistication of the computer system, computers offer the designer or drafter some or all of the following advantages. 材料选择英文文献和中文翻译(2):http://www.751com.cn/fanyi/lunwen_62085.html