【正文】 性變形。橄欖球運(yùn)動(dòng)員據(jù)此相信他的面罩不會(huì)裂成碎片。Materials with high densities often contain atoms with high atomic numbers, such as gold or lead. However, some metals such as aluminum or magnesium have low densities, and are used in applications that require other metallic properties but also require low weight.高密度材料通常由較大原子序數(shù)原子構(gòu)成，例如金和鉛。Some metal alloys, such as those based on aluminum, have low densities and are used in aerospace applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable.某些金屬合金，例如鋁基合金，其密度低，可用于航空航天以節(jié)約燃料。 and gold jewelry which usually contains an alloy of gold and nickel.合金包含不止一種金屬元素。在極低的溫度下，某些金屬和金屬化合物能轉(zhuǎn)變成超導(dǎo)體。 Engineering materials may be further subdivided into: ①M(fèi)etal ②Ceramics ③Composite ④Polymers, etc. 工程材料還能進(jìn)一步細(xì)分為：①金屬材料②陶瓷材料③復(fù)合材料 ④聚合材料，等等。他們也把材料分為有機(jī)材料(曾經(jīng)有生命的)和無機(jī)材料(從未有生命的)。8目錄111 For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and bee parts of products. 就工業(yè)效用而言，材料被分為工程材料和非工程材料。? Metals and Metal Alloys 金屬和金屬合金 Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility. 金屬就是通常具有良好導(dǎo)電性和導(dǎo)熱性的元素。 What is the difference between an alloy and a pure metal? Pure metals are elements which e from a particular area of the periodic table. Examples of pure metals include copper in electrical wires and aluminum in cooking foil and beverage cans. 合金與純金屬的區(qū)別是什么？純金屬是在元素周期表中占據(jù)特定位置的元素。合金的性質(zhì)能通過改變其中存在的元素而改變。許多合金還具有高斷裂韌性，這意味著它們能經(jīng)得起沖擊并且是耐用的。然而，諸如鋁和鎂之類的一些金屬則具有低密度，并被用于既需要金屬特性又要求重量輕的場(chǎng)合。 Plastic deformation is the ability of bend or deform before breaking. As engineers, we usually design materials so that they don’t deform under normal conditions. You don’t want your car to lean to the east after a strong west wind. 塑性變形就是在斷裂前彎曲或變形的能力。汽車上壓皺的區(qū)域在它們斷裂前通過經(jīng)歷塑性變形來吸收能量。It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.因?yàn)檫@些階電子吸收到達(dá)金屬的光子，所以透過金屬不可能看得見。For example, adding a small amount of iron to aluminum will make it stronger. Also, adding some chromium to steel will slow the rusting process, but will make it more brittle.例如，往鋁里加少量鐵可使其更強(qiáng)。照此定義，陶瓷材料也應(yīng)包括玻璃；然而許多材料科學(xué)家添加了“陶瓷”必須同時(shí)是晶體物組成的約定。Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials。陶瓷和玻璃都有一個(gè)主要的缺點(diǎn)：它們?nèi)菀灼扑椤Ｗ鳛樘娲?，一般采用“燒結(jié)”或“焙燒”工藝。In order for the core glass to have a higher refractive index than the cladding, the core glass is doped with a small, controlled amount of an impurity, or dopant, which causes light to travel slower, but does not absorb the light. 為了使核心玻璃有比覆層大的折射指數(shù)，在其中摻入微小的、可控?cái)?shù)量的能減緩光速而不會(huì)吸收光線的雜質(zhì)或攙雜劑。例子有聚合物/陶瓷和金屬/陶瓷復(fù)合材料。Fiberreinforced Composites Reinforcing fibers can be made of metals, ceramics, glasses, or polymers that have been turned into graphite and known as carbon fibers. Fibers increase the modulus of the matrix material. 纖維加強(qiáng)型復(fù)合材料 加強(qiáng)纖維可以是金屬、陶瓷、玻璃或是已變成石墨的被稱為碳纖維的聚合物。Fiberreinforced posites are used in some of the most advanced, and therefore most expensive sports equipment, such as a timetrial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix. 纖維加強(qiáng)型復(fù)合材料用于某些最先進(jìn)也是最昂貴的運(yùn)動(dòng)設(shè)備，例如計(jì)時(shí)賽競(jìng)賽用自行車骨架就是用含碳纖維的熱固塑料基材制成的。Particlereinforced posites Particles used for reinforcing include ceramics and glasses such as small mineral particles, metal particles such as aluminum, and amorphous materials, including polymers and carbon black.微粒加強(qiáng)型復(fù)合材料 用于加強(qiáng)的微粒包含了陶瓷和玻璃之類的礦物微粒，鋁之類的金屬微粒以及包括聚合物和碳黑的非結(jié)晶質(zhì)微粒。這種重復(fù)結(jié)構(gòu)產(chǎn)生鏈狀大分子。它們的強(qiáng)度通?？刹捎眉訌?qiáng)復(fù)合結(jié)構(gòu)來改善。這些溫度通常決定聚合物能否使用的上限。 Interchain interactions. The polymer chains can be free to slide past one another (thermoplastic) or they can be connected to each other with crosslinks (thermoset or elastomer). Thermoplastics can be reformed and recycled, while thermosets and elastomers are not reworkable. 原子鏈間的相互作用：聚合物的原子鏈可以自由地彼此滑動(dòng)(熱可塑性)或通過交鍵互相連接(熱固性或彈性)。第二單元 The understanding of heat treatment is embraced by the broader study of metallurgy. Metallurgy is the physics, chemistry, and engineering related to metals from ore extraction to the final product. 對(duì)熱處理的理解包含于對(duì)冶金學(xué)較廣泛的研究。With the proper heat treatment internal stresses may be removed, grain size reduced, toughness increased, or a hard surface produced on a ductile interior. The analysis of the steel must be known because small percentages of certain elements, notably carbon, greatly affect the physical properties.使用合適的熱處理可以去除內(nèi)應(yīng)力、細(xì)化晶粒、增加韌性或在柔軟材料上覆蓋堅(jiān)硬的表面。 The following discussion applies principally to the heat treatment of ordinary mercial steels known as plain carbon steels. With this process the rate of cooling is the controlling factor, rapid cooling from above the critical range results in hard structure, whereas very slow cooling produces the opposite effect. 下列討論主要針對(duì)被稱為普通碳鋼的工業(yè)用鋼而言。這對(duì)理解鋼的性能和處理是十分有用的。在較高溫度時(shí)，只存在奧氏體，%的碳溶解在鐵里形成固溶體。本質(zhì)上，%的碳→%的碳+%的碳。 Steels having less than the eutectoid amount of carbon (less than %) are known as hypoeutectoid steels. Consider now the transformation of such a material represented by cooling along line yy’ in . 含碳量少于共析體(%)的鋼稱為亞共析鋼。At 727℃(1341℉), the austenite is of eutectoid position (% carbon) and further cooling transforms the remaining austenite to pearlite. The resulting structure is a mixture of primary or proeutectoid ferrite (ferrite that formed above the eutectoid reaction) and regions of pearlite.在727℃(1341℉)時(shí)，奧氏體為共析組成(%)，再冷卻剩余的奧氏體就轉(zhuǎn)化為珠光體。As the carbonrich phase forms, the remaining austenite decreases in carbon content, reaching the eutectoid position at 727℃(1341℉). As before, any remaining austenite transforms to pearlite upon slow coo