机械设计制造及自动化专业英语翻译超级大全

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1、 .wd.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

2、 basic definition centers around以为中心 the type of bonding existing between the atoms of the element, and around the characteristics of certain of the electrons某种电子 associated with these atoms. In a more practical way, however, a metal can be defined as an element which has a particular package of pro

3、perties.Metals are crystallineadj.晶体的 when in the solid state and, with few exceptions极少例外 (e.g. mercury), are solid at ambient周围环境的 temperatures. They are good conductors of heat and electricity and are opaque不透明的 to light. They usually have a comparatively high density. Many metals are ductile柔软的；

4、易延展的-that is, their shape can be changed permanently永久地，长期不变地 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 =far from,much less than as

5、high as would be expected from simple consideration of the forces required to tear apart the atoms of the metal.One of the more significant of these characteristics from our point of view is that of crystallinitycrystallinity ,kristlinti. A crystalline solid is one in which the constituent atoms are

6、 located in a regular three-dimensional array as if they were located at the corners of the squares of a three-dimensional chessboardn. 棋盘. 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 dire

7、ctions of the axes of the array define the orientation of the crystal in space. The metals commonly used in engineering practice are composed of a large number of such crystals, called grains晶粒. In the most general case一般情况下, the crystals of the various grains are randomly oriented in space. The gra

8、ins 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 absolutely pure metal (i.e.也就是 one composed of only one type of atom) has never been produced. Engineers would not be particularly interested

9、in such a metal even if it were to be produced, because it would be soft and weak. The metals used commercially inevitably不可防止地 contain small amounts of one or more foreign elements, either metallicmetallic mitlik, me-adj. 金属的，含金属的 or nonmetallic. These foreign elements may be detrimental有害的, they m

10、ay 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杂质. If advantageous, they tend to be known as alloying elements合金元素. Alloying elements are commonly added deliberately成心地，蓄意地 in substantialadj. 大量的

11、；实质的；内容充实的substantial evidence:实质体证据|实质性证据|实质证据substantial order:大宗订单|大订单 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 allo

12、ys. 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无论如何，不管怎样, the chemical composition of a metal or an alloy must be known and co

13、ntrolled within certain limits if consistent一致的 performance 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

14、 produced and used in large quantities in engineering practice. The most important by far is iron铁, on which are based the ubiquitous普遍的，无处不在的 steels 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 u

15、ses (that is, for structures that are expected to carry loads) are aluminum铝, copper, nickel, and titanium taiteinim, ti-n. 化钛金属元素. Aluminum accounts for about 0.8% by weight of all metals produced, and copper about 0.7%, leaving only 0.5% for all other metals. As might be expected, the remainders a

16、re all used in rather相当 special applications. For example, nickel alloys are used principally主要地 in corrosion-and heat-resistant applications, while titanium is used extensively广泛地 in the aerospace industry because its alloys have good combinations of high strength and low density. Both nickel and t

17、itanium 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 esotericadj. 秘传的；限于圈内人的；难懂的Esoteric Buddhism:密宗|密宗，特别是指xx的喇嘛教。 properties here. Suffice it to say1. Suffice it to say that you love me.只要

18、说你爱我就够了。2. Suffice it to say that the gun was his.只需说这枪是他的就够了。 that a whole complex of properties in addition to structural strength is required 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

19、 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 be readily容易地 recyclable; and its cost and availability may be of critical importance.在人类社会的开展中，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

20、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。结晶体是这样一种构造，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

21、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，晶粒之间相互接触严密结合。晶粒之间连接区域被称为晶界。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参加一定

22、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，合金元素越成心的被添加，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。到目前为止最重要的是铁，以它为根基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%。在构造应用也就是

23、说，可以承受载荷的构造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。镍合钛有高本钱和高质量的使用特性，事实上，它们高的本钱限制了它们的应用。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，掌握其构造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；它的本钱和实用性是首要的。Unit 2 Se

24、lection 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 mechanical properties. Selection must be made on factors such as hardenability ,h:dnbiltin. 可硬化性；淬硬性, price, and availability ,veilbilti是产品在被调用时能够运行即未处于失效或修复状态的概率。此量度考

25、虑了产品的可靠性多久会失效和可用性多久能被修复。 , 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 mistirisadj. 神秘的；不可思议的；难解的(神秘的，不可思议的) name. A tremendousadj. 极大的，巨大的；惊人的 range of proper

26、ties is available in any steel after heat treatment; this is particularly true of alloy steels.在钢之间没有太大的区别；所有的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。Considerations in fabrication(制造)The properties of the final p

27、art (hardness, strength, and machinability m,i:nbiltin. 切削性；机械加工性), rather than properties required by forging, govern the selection of material. The properties required for forging have very little relation to the final properties of the material; therefore, not much can be done无论做什么都是 白费力，都改变不了既定的

28、现 实 to improve its forgeability. Higher-carbon steel is difficult to forge. Large grain size is best if subsequent heat treatment will refine the grain size.关于加工的考虑最后零件的特性硬度、强度和可加工性而不是锻造特性决定了材料的选择。可锻性与材料的最后特性联系不大；因此，提高金属的可锻造性价值不大。高碳钢很难锻造。如果在随后的热处理过程进展细化，大尺寸晶粒是最好的。Low-carbon, nickel-chromium(铬) steel

29、s are just about几乎，差不多j as plastic at high temperature under a single 520-ftlb(1 ftlb=1.35582J) blowat a single blow= at one blowat a single blow:一下子|一举|一击 as plain steels of similar carbon content. Nickel decreases forgeability of medium-carbon steels, but has little effect on low-carbon steels. Ch

30、romium seems to harden steel at forging temperatures, but vanadium(钒) has no discernible(可区分的) effect; neither has the method of manufacture any effect on high-carbon steel.在高温下低碳，镍铬合金钢在受到520-ftlb的冲击下表现出与一样碳含量普通钢几乎同样的塑性。镍减少了中碳钢的可锻性，但对低碳钢影响不大。铬在锻造温度下时使钢硬化，但钒没有明显的效果；两种加工方法对高碳钢没有影响。FormabilityThe cold-

31、formability of steel is a function(功能) of its tensile strength combined with ductility. The tensile strength and yield point must not be high or too much work will be required in bending弯曲; likewise同样地, the steel must have sufficient充足的 ductility to flow to the required shape without cracking. The f

32、orce required depends on the yield point, because deformation starts in the plastic range above the yield point of steel. Work-hardening also occurs here, progressively日益增多地 stiffening使变硬 the metal and causing difficulty, particularly独特的，显著的 in the low-carbon steels.成形钢的冷成形是它的拉伸强度和延展性相结合的结果。拉伸强度和屈服点

33、不能太高否则在发生弯曲时需要做很多工作；与之相类似，钢应该有高延展性，使其在没有断裂的情况下成形。加工力的大小取决于屈服点，因为钢在屈服点之上才开场变形。与此同时，加工硬化也同时发生，金属变得越来越硬，增加加工难度，尤其在低碳钢中容易发生。It is quite interesting in this connection关于这一点，就此而论 to discover that deep draws can sometimes be made in one rapid operation that could not possibly be done leisurely缓慢地，沉着不迫地 in

34、two or three. If a draw is half made and then stopped, it may be necessary to anneal退火 before proceeding, that is换句话说, if the piece is given time to work-harden. This may not be a scientific statement, but it is actually what seems to happen.在这方面，相当有趣的是你将发现有时可通过一次快速加载完成大拉伸，但以缓慢的方式两三次加载却不能实现。如果拉伸进展了一

35、半就停顿了，那么在再加工之前应先退火，也就是说工件是否有时间进展加工硬化。这不是一种科学的表达方法，但确实是发生了。Internal stressesCold forming is done above the yield point in the work-hardening range, so internal stresses can be built up easily. Evidence of this is the springback回弹 as the work leaves the forming operation and the warpage翘曲，扭曲 in any任何一

36、种 subsequent heat treatment. Even a simple washer might, by virtue of由于，凭借(依靠) the internal stresses resulting from punching冲压 and then flattening整平, warp弯曲 severely严格地，剧烈地 during heat treating. virtue n.德行, 美德, 贞操, 优点, 成效, 效力, 英勇 believed in the virtue of prayer.相信祈祷的力量内应力在高于屈服点的加工硬化区进展冷加工很容易产生内应力。

37、例如工件停顿成型加工后会发生回弹，在随后的热处理后，工件会发生翘曲。即使是一个简单的垫圈，由于打孔和随后的平整加工中产生内应力，也会在热处理中呈现严重的翘曲。When doubt exists as to关于 whether internal stresses will cause warpage, a piece can be checked by heating it to about 1100 and then letting it cool. If there are internal stresses, the piece is likely to可能 deform. Pieces

38、that will warp severely while being heated have been seen, yet 然而the heat-treater热处理炉 was expected to有望做某事；被期待做某事 put them throughput through 完成 and bring them out better than they were in the first place.当是否内应力会引起翘曲的疑心存在时，可以通过将工件加工至1100然后进展冷却来验证。如果存在内应力，工件会发生变形。经过热处理的工件像我们看到的那样会发生严重的翘曲，但是我们仍然希望工件被扔

39、到热处理炉中被处理，这样好过它存在内应力的状态。WeldingThe maximum carbon content of plain carbon steel safe for welding without preheating or subsequent heat treatment is 0.3%. higher-carbon steel is welded every day, but only with proper preheating. There are two important factors: the amount of heats that is put in ; th

40、e rate at which it is removed.焊接不需要预热或之后进展热处理就能安全焊接的最高碳含量为0.3。高碳钢通过适宜的预热通常也可焊接。有两点值得注意：吸收热量的多少；移除速度。Welding at a slower rate puts in more heat and heats a large volume of metal, so the cooling rate due to loss of heat to the base metal is decreased(减少). A preheat will do the same thing. For example,

41、 sae4150 steel, preheated to 600 or 800, can be welded readily容易地. When the flame or arc is taken away from the weld, the cooling rate is not so great, owing to the higher temperature of the surrounding metal and slower cooling results. Even the most rapid air-hardening风硬钢 steels are weldable if pre

42、heated and welded at a slow rate.低速焊接带来了更多的热量，这对金属的大量体积进展了加热，所以冷却速度降低。预热可以取得与之相当的效果。例如当 被预热至 或 时可以很好的焊接。由于周围金属的较高温度，当焊接弧移开焊接点后，冷却速度不会太快，产生了低速冷却的结果。即使是冷作硬化速度最快的金属也可以通过预热和慢速焊接到达良好的焊接效果。MachinabilityMachinability机械加工性能 means several things. To production men it generally means being able to remove meta

43、l at the fastest rate, leave the best possible finish, and obtain the longest possible tool life. Machinability applies to应用于 the tool-work工具，零件 combination.可加工性可加工性意味着几件事情。对于加工者来说，它意味着可以快速的移除金属，取得最好的加工效果，得到最长的刀具寿命。可加工性是刀具和零件的结合。It is not determined by hardness硬度 alone, but by the toughness韧性, micro

44、structure, chemical composition成分, and tendency倾向 of a metal to harden under cold work. In the misleading expression “too hard to machine, the word “hard is usually meant to be synonymous同义的 with “difficult. Many times a material is actually too soft to machine readily. Softness and toughness may ca

45、use the metal to tear撕裂 and flow ahead of the cutting tool rather than cut cleanly. Metal that are inherently天性地，固有地 soft and tough are sometimes alloyed to improve their machinability at some sacrifice skrifais n. 牺牲；祭品；供奉All gains are made at some sacrifice.Most people might choose to divert the c

46、ourse of the train, and sacrifice only one child.牺牲 in ductility. Examples are use of lead铅 in brass黄铜 and of sulfur slf硫磺 in steel.加工性不仅仅只由硬度决定，它还由韧性，微观构造，化学成分和在冷加工下金属所呈现的硬化特性所决定。在容易混淆的表示“难加工中，“hard与“difficult同义。许多时候，因为材料过软而难于稳定加工。材料柔软性和韧性能够产生金属撕裂，使金属在完成切削前流动至刀具前端。柔软的金属往往会被参加合金从而牺牲它的延展性来提高加工性能。如黄铜中

47、参加铅钢中参加硫磺。Machinability is a term used to indicate the relative比较的 ease不费力 with which a material can be machined by sharp cutting tools in operations such as turning车, drilling钻, milling铣, broachingbuti n. 拉削；拉孔；推削；扩孔v. 钻孔；开口拉削, and reaming铰.机械加工性能是在指对工件材料使用刀具进展诸如车、钻、铣、拉削、铰加工时的难易程度。In the machining

48、of metal, the metal being cut, the cutting tool, the coolant, the process and type of machine tool机床, and the cutting conditions all influence the results. By changing any one of these factors, different results will be obtained. The criterion kraitirinn. 批评判断的标准；准则；标准；准据标准 upon which the ratings等级

49、listed are based(等级评定的标准) is the relativeadj. 相对的；有关系的；成比例的 volume of various不同种 materials that may be removed by turning under fixed conditions to produce an arbitrary任意的 fixed amount of tool wear. 在对金属进展加工时，被切削的金属，切削刀具，冷却液，使用的机床的种类，切削条件均影响着切削效果。改变任何一种均会产生不同的切削效果。切削效果评定的准则是：车削时在固定的切削条件下产生一定量的刀具磨损时，

50、被加工试件相应的材料去除量。淬透性：指在规定条件下，决定钢材淬硬深度和硬度分布的特性。即钢淬火时得到淬硬层深度大小的能力，它表示钢承受淬火的能力。钢材淬透性好与差，常用淬硬层深度来表示。淬硬层深度越大，则钢的淬透性越好。钢的淬透性是钢材本身所固有的属性，它只取决于其本身的内部因素，而与外部因素无关。钢的淬透性主要取决于它的化学成分，特别是含增大淬透性的合金元素及晶粒度，加热温度和保温时间等因素有关。淬透性好的钢材，可使钢件整个截面获得均匀一致的力学性能以及可选用钢件淬火应力小的淬火剂，以减少变形和开裂。 淬透性主要取决于其临界冷却速度的大小，而临界冷却速度则主要取决于过冷奥氏体的稳定性，影响奥

51、氏体的稳定性主要是：1.化学成分的影响 碳的影响是主要的，当C小于1.2时，随着奥氏体中碳浓度的提高，显著降低临界冷却速度，C曲线右移，钢的淬透性增大；当C大于时，钢的冷却速度反而升高，C曲线左移，淬透性下降。其次是合金元素的影响，除钴外，绝大多数合金元素溶入奥氏体后，均使C曲线右移，降低临界冷却速度，从而提高钢的淬透性。2.奥氏体晶粒大小的影响 奥氏体的实际晶粒度对钢的淬透性有较大的影响，粗大的奥氏体晶粒能使C曲线右移，降低了钢的临界冷却速度。但晶粒粗大将增大钢的变形、开裂倾向和降低韧性。3.奥氏体均匀程度的影响 在一样冷度条件下，奥氏体成分越均匀，珠光体的形核率就越低，转变的孕育期增长，C

52、曲线右移，临界冷却速度减慢，钢的淬透性越高。4.钢的原始组织的影响 钢的原始组织的粗细和分布对奥氏体的成分将有重大影响。5.局部元素，例如Mn，Si等元素对提高淬透性能起到一定作用，但同时也会对钢材带来其他不利的影响。可锻性(forgeability)金属具有热塑性，在加热状态(各种金属要求温度不同)，可以进展压力加工，称为具有可锻性。可锻性：指金属材料在压力加工时，能改变形状而不产生裂纹的性能。它包括在热态 或 冷态下能够进展锤锻，轧制，拉伸，挤压等加工。可锻性的好坏主要与金属材料的化学成分有关讨论 元素在钢中的形成物对可锻性的影响1C 与Fe形成渗碳体Fe3C，与其它合金元素形成合金渗碳体

53、(FeM)3C或合金碳化物。所有碳化物都有硬度高、塑性低、熔点高的特点，但渗碳体型碳化物在加热到锻造温度时经适当保温可大局部或全部溶入固溶体中，而合金碳化物较难溶入固溶体中，对钢的可锻性影响最大。一般高合金工具钢含碳高，故具有变形抗力大，塑性差，碳化物不易被粉碎等特点。2Mn 在钢中形成MnS以代替FeS。因MnS熔点高1620，且呈断续分布，不像FeS熔点988，呈网状分布在晶界，所以可减少热脆。锰对钢的过热性粗晶很敏感，钢锭加热温度过高，易生粗晶，使锻造困难。锰对珠光体钢的可锻性影响较小，奥氏体锰钢临界点将降低。3 Ni炼钢时有Ni极易吸收氢形成大量气泡，锻造时引起开裂。Ni与Mn的作用相

54、反，它促使硫化物成网状分布于晶界，使锻造时开裂，所以不宜在含硫的炉气中加热。珠光体Ni钢在锻造时易形成片状破裂和带状组织。为了消除这种组织可采用镦粗和拔长交织进展，或在10001100下长时期扩散退火。4 Cr铬在钢中形成较稳定的碳化物，提高碳化物在钢中的溶解温度，减慢溶解速度。铬能促进使铸锭生成大晶粒，冷却时沿晶界形成内裂。高铬钢在空气中冷却即能淬火，常在外表生裂，所以不易锻造。5 V与碳形成稳定碳化物V能使钢生成细晶组织，阻止过热，适当参加对锻性有利。6 Mo钼的熔点高，能降低钢的过热倾向它和Ni一样，使硫化物以网状分布在晶界。含有0.7%C，25%Mo的钼钢，锻造时无特殊困难。这些钢在空

55、冷时间淬火，要防止冷裂。Mo提高钢的热强性，提高变形抗力。7 W与碳形成稳定的碳化物提高钢的热强性，增大变形抗力8 Cu铜在钢中可溶于铁素体中，也可沿晶界析出游离铜铜中含0.15%Cu时，加热不当，外表易生裂纹，高温轧制时易产生热脆9 B硼能细化晶粒，能溶解在和固溶体中，与Fe化合成Fe2B钢中含B0.007%时，锻造易裂10 S在钢中形成硫化物或共晶体，如FeS、Fe的熔点为985，且成网状布于晶界显著降低可锻性红脆11 P促成偏析，使晶粒粗大，容易引起锻件外表龟裂降低可锻性Unit 3 Mechanical Properties of MaterialsThe material prope

56、rties can be classified into three major headings: (i) Physical, (ii) Chemical, (iii) Mechanical.Physical propertiesDensity or specific gravity, moisture mist n. 水分；湿度；潮湿；降雨量 content, etc., can be classified under this category.Chemical propertiesMany chemical properties come under归入 this category.

57、These include acidity sidti n. 酸度；酸性；酸过多；胃酸过多 or alkalinity,lklinti n. 碱度；碱性, reactivity化学反响的活性 and corrosion. The most important of these is corrosion which can be explained in laymans terms as the resistance of the material to decay腐朽，腐烂 while in continuous use in a particular atmosphere.Mechanica

58、l propertiesMechanical properties include the strength properties like tensile, compression, shear, torsion, impact, fatigue and creepn. 爬行；毛骨悚然的感觉；谄媚者vi. 爬行；蔓延；慢慢地移动；起鸡皮疙瘩creep:蠕变|潜变|渐变creep strength:蠕变强度|潜变强度|蠕变弱度creep strain:蠕变变形|蠕动应变|蠕变应变. The tensile strength of a material is obtained by dividi

59、ng the maximum load, which the specimen bears by the area of cross-section of the specimen.This is a curve plotted between the stress along the Y-axis(ordinate) and the strain along the X-axis(abscissabsis n. 数横坐标；横线) in a tensile test. A material tends to change or changes its dimensions when it is

60、 loaded, depending upon the magnitude大小 of the load. When the load is removed it can be seen that the deformation disappear s. For many materials this occurs up to一直到；相当于；忙于，在做；由决定的 a certain value of the stress called the elastic limit. This is depicted by the straight line relationship and a small

61、 deviation,di:vieinn. 偏差；误差；背离average deviation:平均偏差|平均差|平均偏差，均差 thereafter, in the stress-strain curve.Within the elastic range, the limiting value of the stress up to which the stress and strain are proportional, is called the limit of proportionality. In this region, the metal obeys Hookes law, w

62、hich states that the stress is proportional to strain in the elastic range of loading (the material completely regains its original dimensions after the load is removed). In the actual plotting of the curve, the proportionality limit is obtained at a slightly lower value of the load than the elastic

63、 limit. This may be attributed to the time-lag in the regaining of the original dimensions of the material. This effect is very frequently noticed in some no-ferrous有色金属铁的，含铁的 metals.While iron and nickel exhibitizibitn. 展览品；证据；展示会vt. 展览；显示；提出证据等vi. 展出；开展览会 clear ranges of elasticity, copper, zinc锌, tin锡, etc, are found to be imperfectlyimp:fiktliadv. 有缺点地；不完美地；未完成地 elastic even at relatively相当地 low values of stresses. Actually the elastic limit is distinguishable可区分的 from the proportionality比例性 limit more clearly depending upon the sensit