【优秀毕设】机械设计制造及其自动化专业英语翻译超级大全

1、Unit 1 Metals金属The use of metals has always been a key factor in the development of the social systems of man. Of the roughly 100 basic elements of which all matter is composed, about half are classified as metals. The distinction between a metal and a nonmetal is not always clear-cut. The most basi

2、c definition centers around the type of bonding existi ng betwee n the atoms of the element, and around the characteristics of certain of the electrons associated with these atoms. In a more practical way, however, a metal can be defi ned as an eleme nt which has a particular package of properties.M

3、etals are crystalline when in the solid state and, with few exceptions (e.g. mercury), are solid at ambient temperatures. They are good con ductors of heat and electricity and are opaque to light. They usually have a comparatively high density. Many metals are ductile-that is, their shape can be cha

4、nged permanently by the application of a force without break ing. The forces required to cause this deformati on and those required to break or fracture a metal are comparatively high,在人类社会的发展中，金属的应用 起着关键性的作用。构成物质的大约100种基本兀素中，大约有一半为金属。金属和非 金属之间的区别不是特别明显。最基本的定 义集中在元素原子间存在的连接形式和与这 些原子相关联的电子的某些特性。然而，在

5、实际应用中，可以将具有某些特性集合金属 定义为某种元素。除了少数例外金属在常温下是固态 的。它们是热和电的良导体，不透光。它们 往往具有较咼的密度。 许多金属具有延展性， 也就是说，在不被破坏的情况下它们的形状 在外力的作用下可以发生变化。引起永久变 形所需的力和最终使金属断裂所需的力相当 大，尽管发生断裂所需的力远没有像所预期 的撕开金属原子所需的力那么大。从我们的观点来看，在所有的特性中结 晶性是最重要的。结晶体是这样一种结构， 组成它的原子定位在规则的三维排列中，仿 佛位于三维棋盘的方格的角上。原子间距随 着原子大小呈规律性变化，原子间距是金属 的一种特性。三维排列的轴线决定了晶体在 空

6、间中的方向。在工程实践中应用的金属由 大量的晶体组成，这些晶体称之为晶粒。在 大多数情况下，晶粒在空间中是自由排列的。 在原子范围内，晶粒之间相互接触紧密结合。 晶粒之间连接区域被称为晶界。although, the fracture forces is not nearly ashigh as would be expected from simplecon siderati on of the forces required to tear apart the atoms of the metal.One of the more significant of these character

7、istics from our point of view is that of crystallinity. A crystalline solid is one in which the constituent atoms are located in a regular three-dimensional array as if they were located at the corners of the squares of a three-dimensional chessboard The spacing ofthe atoms in the array is of the sa

8、me order as the size of the atoms, the actual spaci ng being a characteristic of the particular metal. The direct ions of the axes of the array defi ne the orientation of the crystal in space. The metals commonly used in engineering practice are composed of a large number of such crystals,called gra

9、ins. In the most general case, the crystals of the various grains are randomly orie nted in space. The grains are everywhere in in timate con tact with one ano ther and joined together on an atomic scale. The region at which they join is known as a gra in boun dary.An absolutely pure metal (i.e. one

10、 composed of only one type of atom) has n ever bee n produced. Engin eers would not be particularly interested in such a metal even if it were to be produced, because it would be soft and weak. The metals used commercially inevitably contain small amounts of one or more foreign elements, either meta

11、llic or nonmetallic. These foreign elements may be detrimental, they may be beneficial, or they may have no in flue nee at all on a particular property. If disadva ntageous, the foreig n elements tend to be known as impurities. If advantageous, they tend to be known as alloying elements Alloyi ng el

12、eme nts are commonly added deliberately in substantial amounts in engineering materials. The result is known as an alloy.The distinction between the descriptors “ metal and “ alloy is not clear-cut. The term “ metal may be used to encompass both a commercially pure metal and its alloys. Perhaps it c

13、an be said that the more deliberately an allo vina additi on has bee n made and the larger the amount of the addition the more likely 计 is that the product will specifically be called an alloy. In any event the chemical composition of a metal or an alloy must be known and con trolled with in certa i

14、n limits if consistent performa nee is to be achieved in service. Thus chemical compos it ion has to be taken into绝对纯净的金属从来也没有被生产出来 过。即使绝对纯净的金属可以生产出来，工 程师们对它们也并不会特别感兴趣，因为它 们很柔软、脆弱。实际应用中的金属往往都 包含着一定数量的一种或多种外来金属或非 金属元素，这些外来元素可能是有害的也可 能是有益的或者它们对某种特定的属性没有 影响。如果是有害的，这些外来元素被认为 是杂质。如果是有益的，它们被认为是合金 元素。在工程材料

15、中往往被特意地加入一定 数量的合金元素。得到的物质被叫做合金。金属和合金区别不大。金属这个词可以 包括工业用纯金属和它的合金。也许可以这 样说，合金元素越故意的被添加，被添加的 合金元素的量越大，那么生产出来的产品越 倾向于被称之为合金。不管怎样，如果想使 一种金属或合金在使用中表现出稳定一致的 特性，在其中添加何种化学成分，它的量多 大都应该在控制范围之内。因此，当想了解 决定金属和合金性质的因素时，应充分考虑 它们的化学组成。在50种左右的金属兀素里， 工程头践中 只有少数金属被大量生产和使用。到目前为 止最重要的是铁，以它为基础构成了处处可 见的钢和铸铁。（主要由铁和碳构成的合金）account when developing an understanding ofthe factors wh