2022年机械设计制造及其自动化专业英语翻译 .pdf
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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 ba
2、sic definition centers around the type of bonding existing between the atoms of the element, and around the characteristicsof certain of the electrons associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of properties. Met
3、als are crystallinewhen in the solid state and, with few exceptions (e.g. mercury), are solid at ambienttemperatures. They are good conductors of heat and electricity and are opaqueto light. They usually have a comparatively high density. Many metals are ductile-that is, their shape can be changed p
4、ermanently by the application of a force without breaking. The forces required to cause this deformation and those required to break or fracture a metal are comparatively high, although, the fracture forces is not nearly as high as would be expected from simple consideration of the forces required t
5、o tear apart the atoms of the metal. One of the more significant of these characteristics 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
6、of a three-dimensional chessboard. The spacing of the atoms in the array is of the same order as the size of the atoms, the actual spacing being a characteristic of the particular metal. The directions of the axes of the array define the orientation of the crystal in space. The metals 在人类社会的发展中,金属的应
7、用起着关键性的作用。构成物质的大约100 种基本元素中,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。它们往往具有较高的密度。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
8、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。精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 1 页,共 30 页commonly used in engineering practice are composed of a large numbe
9、r of such crystals, called grains. In the most general case, the crystals of the various grains are randomly oriented in space. The grains are everywhere in intimate contact with one another and joined together on an atomic scale. The region at which they join is known as a grain boundary. An absolu
10、tely pure metal (i.e. one composed of only one type of atom) has never been produced. Engineers 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 inevitablycontain small amounts of one or more foreign
11、elements, either metallicor nonmetallic. These foreign elements may be detrimental , they may be beneficial, or they may have no influence at all on a particular property. If disadvantageous, the foreign elements tend to be known as impurities . If advantageous, they tend to be known as alloying ele
12、ments. Alloying elements are commonly added deliberatelyin 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 al
13、loys. Perhaps it can be said that the more deliberately an alloying addition has been made and the larger the amount of the addition, the more likely it 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 controlle
14、d within certain limits if consistentperformance is to be achieved in service. Thus chemical composition has to be taken into account when developing an understanding of the factors which determine the properties of metals and their alloys. Of the 50 or so metallic elements, only a few are produced
15、and used in large quantities in 绝对纯洁的金属从来也没有被生产出来过。即使绝对纯洁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
16、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 种左右的金属元素里,工程实践中只有少数金属被大量生产和使用。到目前为精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 2 页,共 30 页engineering practice. The most important by far is iron , on which are based the ubiquit
17、oussteels and cast irons (basically alloys of iron and carbon). They account for about 98% by weight of all metals produced. Next in importance for structural uses (that is, for structures that are expected to carry loads) are aluminum , copper, nickel, and titanium% for all other metals. As might b
18、e expected, the remainders are all used in ratherspecial applications. For example, nickel alloys are used principally in corrosion-and heat-resistant applications, while titanium is used extensivelyin the aerospace industry because its alloys have good combinations of high strength and low density.
19、 Both nickel and titanium are used in high-cost, high-quality applications, and, indeed, it is their high cost that tends to restrict their application. We cannot discuss these more esotericproperties here. Suffice it to say that a whole complex of properties in addition to structural strength is re
20、quired of an alloy before it will be accepted into, and survive in, engineering practice. It may, for example, have to be strong and yet have reasonable corrosion resistance; it may have to be able to be fabricated by a particular process such as deep drawing, machining, or welding; it may have to b
21、e readily recyclable; and its cost and availability may be of critical importance. 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它们的重量占所有生产出来的金属重量的98%。在结构应用也就是说,可以承受载荷的结构中居于其次位置的是铝、铜、镍和钛。在所有的金属产量中,铝占0.8,铜占 0.7,剩下的占0.5。剩下的金属用于相对特殊的用途。例如,镍合金主要用于抗磨损和耐高温的用途,由于钛合金具有高强度和低密度的综合特性,钛被广泛应用于航空工业中。镍合钛有高成本和高质量的使用特性,事实上,
22、它们高的成本限制了它们的应用。我们不能在这里讨论这些深奥的特性。在合金材料被采用和应用于工程实际之前,掌握其结构强度和它的综合性质就够了。举例来说,它可以强度很高,并且有好的耐磨性;它可以被例如拉伸加工,机械加工,或焊接等特殊工艺来加工出来;它可以被循环利用;它的成本和实用性是首要的。Unit 2 Selection of Construction Materials 工程材料的选择There is not a great difference between “ this” steel and “ that ” steel; all are very similar in mechanica
23、l properties. Selection must be made on factors such as hardenability,price, and availability , and not with the idea that “ this” steel can do something no other can do because it contains 2 percent instead of 1 percent of a certain alloying element, or because it has a mysterious (神在钢之间没有太大的区别;所有的
24、钢在机械性能方面都是近似的。它们的选取标准是诸如脆硬性,价格,和可用性等。不仅仅是因为这种钢含有2的合金元素另一种钢含有1而使前者具有了后者没有的某些能力,或者是某种钢具有神奇的名字。经过热处理后, 任何一种钢都具有大范围的特性;这种性质同样在合金钢中存在。精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 3 页,共 30 页秘的,不可思议的) name. A tremendous range of properties is available in any steel after heat treatment; this is particula
25、rly true of alloy steels.Considerations in fabrication(制造 ) The properties of the final part (hardness, strength, and machinability ), rather than properties required by forging, govern the selection of material. The properties required for forging have very little relation to the final properties o
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