【優(yōu)秀畢設】機械設計制造及其自動化專業(yè)英語翻譯超級大全

1、Unit 1 Metals金屬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,在人類社會的發(fā)展中，金屬的應用 起著關鍵性的作用。構成物質的大約100種基本兀素中，大約有一半為金屬。金屬和非 金屬之間的區(qū)別不是特別明顯。最基本的定 義集中在元素原子間存在的連接形式和與這 些原子相關聯(lián)的電子的某些特性。然而，在

5、實際應用中，可以將具有某些特性集合金屬 定義為某種元素。除了少數(shù)例外金屬在常溫下是固態(tài) 的。它們是熱和電的良導體，不透光。它們 往往具有較咼的密度。 許多金屬具有延展性， 也就是說，在不被破壞的情況下它們的形狀 在外力的作用下可以發(fā)生變化。引起永久變 形所需的力和最終使金屬斷裂所需的力相當 大，盡管發(fā)生斷裂所需的力遠沒有像所預期 的撕開金屬原子所需的力那么大。從我們的觀點來看，在所有的特性中結 晶性是最重要的。結晶體是這樣一種結構， 組成它的原子定位在規(guī)則的三維排列中，仿 佛位于三維棋盤的方格的角上。原子間距隨 著原子大小呈規(guī)律性變化，原子間距是金屬 的一種特性。三維排列的軸線決定了晶體在 空

6、間中的方向。在工程實踐中應用的金屬由 大量的晶體組成，這些晶體稱之為晶粒。在 大多數(shù)情況下，晶粒在空間中是自由排列的。 在原子范圍內，晶粒之間相互接觸緊密結合。 晶粒之間連接區(qū)域被稱為晶界。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 計 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絕對純凈的金屬從來也沒有被生產(chǎn)出來 過。即使絕對純凈的金屬可以生產(chǎn)出來，工 程師們對它們也并不會特別感興趣，因為它 們很柔軟、脆弱。實際應用中的金屬往往都 包含著一定數(shù)量的一種或多種外來金屬或非 金屬元素，這些外來元素可能是有害的也可 能是有益的或者它們對某種特定的屬性沒有 影響。如果是有害的，這些外來元素被認為 是雜質。如果是有益的，它們被認為是合金 元素。在工程材料

15、中往往被特意地加入一定 數(shù)量的合金元素。得到的物質被叫做合金。金屬和合金區(qū)別不大。金屬這個詞可以 包括工業(yè)用純金屬和它的合金。也許可以這 樣說，合金元素越故意的被添加，被添加的 合金元素的量越大，那么生產(chǎn)出來的產(chǎn)品越 傾向于被稱之為合金。不管怎樣，如果想使 一種金屬或合金在使用中表現(xiàn)出穩(wěn)定一致的 特性，在其中添加何種化學成分，它的量多 大都應該在控制范圍之內。因此，當想了解 決定金屬和合金性質的因素時，應充分考慮 它們的化學組成。在50種左右的金屬兀素里， 工程頭踐中 只有少數(shù)金屬被大量生產(chǎn)和使用。到目前為 止最重要的是鐵，以它為基礎構成了處處可 見的鋼和鑄鐵。（主要由鐵和碳構成的合金）account when developing an understanding ofthe factors wh