机械专英第三课翻译

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1、Lesson 3 selecting materialsWe are surrounded by materials and we rarely think about how these materials are selected我们被材料包围着,我们很少考虑这些材料是如何选定的Why was your desk made of solid wood, plywood, or plastic-laminated particleboard?为什么你的桌子是实木、胶合板、或塑料层压刨花板制造的?Why have so many plastics replaced steel and zinc

2、 in automobiles?在汽车里为什么有这么多的塑料代替了钢和锌?What is the controversy about using foamed polystyrene plastic to package fast food?有关使用发泡聚苯乙烯塑料包快餐的争议是什么?While you might take for granted the materials that make up your products, you can be sure that the designers did not.虽然你可能会把制造您的产品的材料认为是理所当然,但是可以确保的是设计师却没有。

3、People who design homes, cars, aircraft, clothing, furniture, and other products or systems devote a lot of attention to the selection of the materials they use.房子、汽车、飞机、服装、家具、其它产品或系统的设计者们投入了许多注意力在他所使用的材料 的选择上。Material selection might make or break a company.材料的选择可能成就或也可能打破一家公司。But how do the design

4、ers make that selection to arrive at the best material?但设计者如何让该到达的材料的最佳选择呢?What selection criteria are most important?什么选择标准是最重要的?The ideal material (理想的材料)1Endless and readily available source of supply无止境、随时可获得的供应来源2. Cheap to refine and produce 捉取和生产廉价3 Energy efficient 能源效率4. Strong, stiff, an d

5、imensionally stable at all temperatures 强度,刚度、尺寸的稳定性在所有温度5. Lightweight 轻量6 Corrosion resistant 耐腐蚀7. No harmful effects on the environment or people 对环境或人们无害8. Biodegradable可生物降解9. Numerous secondary uses 众多的辅助用途Obstacles to changeSwitching from traditional materials such as steel and concrete to n

6、ewer materials such as plastic-based composites seems a simple, straightforward approach for the contemporary designer.从钢铁和混凝土等传统材料切换到较新的材料,如塑料复合材料的对当代设计者是似乎简单、直接的方法。The newer materials are often superior, but sometimes there are complications较新的材料往往性能更优越,但有时有并发症。Often, lack of experience with new m

7、aterials causes hesitation by designers通常情况下,新材料与经验不足导致rti设计师设计的犹豫。Departures from tried-and-true materials may be costly.、偏离有经验的材料可能代价高昂。It requires time before both designers and fabricators gain sufficient experienceto make products or systems.它需耍设计者和加工者获得使产品或系统成为舒适与新材料及相关的流程所需的足够经验。This problem

8、is exacerbated when human life might be in jeopardy, such aswhen designing for aircraft此问题加剧时人类的生活可能陷入困境,如设计的飞机时。Consequently, new materials and processes are usually slower to enter themarketplace than might be expected因此,新的材料和工艺是进入市场上通常比预期慢These issues are all a part of engineering problem solving

9、.这些问题是工程问题需要解决的一部分Materials selection is a problem-solving issue that requires an algorithm for its solutio n材料选择是为其解决方案找到-种算法的问题Algorithm for materials selection 材料选择算法Engineering requires clearly stated, unambiguous steps for problem solving.工程 需耍解决问题的清晰、明确的步骤。Algorithms are well-defined methods f

10、or solving specific problems.算法是明确定义 的方法,解决具体问题。Computer programs are written after an algorithm has been developed to lie out clearly the steps that the program is to solve.后种算法已经发展到躺着明确的程序是解决 的步骤编写计算机程序。For example, you could write a simple algorithm to calculate the strength required of a light p

11、ole to withstand the pushing forces (compression) from a light fixture例如,您可以编写一个简单的算法来计算所需的一根路灯杆承受推力(压缩)从轻的夹具的强度。A much more complex algorithm would be required to select a piston connecting rod for an internal-combustion engine.复杂得多的算法,将要求选择的内燃机活塞连杆。The first problem requires only the selection of

12、a material of suitable size/strength to hold up the light fixture, and almost any material suffice as long as it was sufficiently strong and pleasing to the user.第一个问题需要只实力支撑灯具,合 适大小的一种材料的选择和儿乎任何材料够了,只要它是足够有力和令人愉快,给用户。On the other hand, a connecting rod will undergo many types of mechanical stress,

13、ranging from compressive to tensile to torsional to gravity forces, in addition to thermal stress from the combustion chamber.另一方面,连接杆会经过许多 类型的机械应力,从压缩到拉伸到扭重力的力量,从燃烧室内的热应力。How does the designer match component requirements with available materials.Selection tools设计器与可用的材料与组件要求冇什么匹配。To aid in the cre

14、ation of materials selection algorithms, databases must be available to answer questions on material suitability.为了帮助材料选择算法的创作中,数 据库必须可用回答有关材料适合的问题。A material database involves tables listing properties of material, such as tensile strength, hardness, corrosion resistance, and the ability to withsta

15、nd heat.材料数 据库涉及表格列出了屈性的材料,如拉伸强度、硬度、耐腐蚀性和热的承受能力。Thousands of reference books are available with such data提供此类数据与成千上力的 参考书籍。Much of these data are computerized to allow easier access.许多这些数据计算机化以 允许更容易访问。Certain graphical techniques aid the designer in materials selection某些图形技术援 助在材料选择中的设计器。Properties

16、 of materials 材料的性能Periodicals can provide current data and performance criteria that involve structural materials:当前数据和涉及结构材料的性能标准,可提供期刊:1 Strenghth (tensile, compressive, flexural, shear, and torsional)关于我们(拉伸、压 缩、弯曲、剪切、扭)2 resistance to elevated temperatures 耐高温3. fatigue resistance(repeated loading and unloading)抗疲劳(重复装载和卸载4. tough

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