【正文】 he 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(xiàn)的雜質(zhì)或攙雜劑。作為替代，一般采用“燒結(jié)”或“焙燒”工藝。陶瓷和玻璃都有一個(gè)主要的缺點(diǎn)：它們?nèi)菀灼扑?。Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials。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。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)。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(guò)金屬不可能看得見(jiàn)。汽車(chē)上壓皺的區(qū)域在它們斷裂前通過(guò)經(jīng)歷塑性變形來(lái)吸收能量。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。然而，諸如鋁和鎂之類(lèi)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。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。合金的性質(zhì)能通過(guò)改變其中存在的元素而改變。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。? 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。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。. . . .第一單元? Types of Materials 材料的類(lèi)型Materials may be grouped in several ways. Scientists often classify materials by their state: solid, liquid, or gas. They also separate them into organic (once living) and inorganic (never living) materials.材料可以按多種方法分類(lèi)。那些用于加工制造并成為產(chǎn)品組成部分的就是工程材料。許多金屬具有高強(qiáng)度、高硬度以及良好的延展性。例如電線(xiàn)中的銅和制造烹飪箔及飲料罐的鋁。金屬合金的例子有：不銹鋼是一種鐵、鎳、鉻的合金，以及金飾品通常含有金鎳合金。What are some important properties of metals?Density is defined as a material’s mass divided by its volume. Most metals have relatively high densities, especially pared to polymers.金屬有哪些重要特性？密度定義為材料的質(zhì)量與其體積之比。Fracture toughness can be described as a material’s ability to avoid fracture, especially when a flaw is introduced. Metals can generally contain nicks and dents without weakening very much, and are impact resistant. A football player counts on this when he trusts that his facemask won’t shatter.斷裂韌性可以描述為材料防止斷裂特別是出現(xiàn)缺陷時(shí)不斷裂的能力。作為工程師，設(shè)計(jì)時(shí)通常要使材料在正常條件下不變形。The atomic bonding of metals also affects their properties. In metals, the outer valence electrons are shared among all atoms, and are free to travel everywhere. Since electrons conduct heat and electricity, metals make good cooking pans and electrical wires.金屬的原子連結(jié)對(duì)它們的特性也有影響。沒(méi)有光子能通過(guò)金屬。同樣，在鋼里加一些鉻能減緩它的生銹過(guò)程，但也將使它更脆。A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous.玻璃是沒(méi)有晶體狀結(jié)構(gòu)的無(wú)機(jī)非金屬材料。 some are piezoelectric materials。Ceramics are not typically formed from the melt. This is because most ceramics will crack extensively (. form a powder) upon cooling from the liquid state.陶瓷一般不是由熔化形成的。In sintering, ceramic powders are processed into pacted shapes and then heated to temperatures just below the melting point. At such temperatures, the powders react internally to remove porosity and fully dense articles can be obtained.在燒結(jié)過(guò)程中，陶瓷粉末先擠壓成型然后加熱到略低于熔點(diǎn)溫度。Because the refractive index of the core glass is greater than that of the cladding, light traveling in the core glass will remain in the core glass due to total internal reflection as long as the light strikes the core/cladding interface at an angle greater than the critical angle.由于核心玻璃的折射指數(shù)比覆層大，只要在全內(nèi)反射過(guò)程中光線(xiàn)照射核心/覆層分界面的角度比臨界角大，在核心玻璃中傳送的光線(xiàn)將仍保留在核心玻璃中。之所以使用復(fù)合材料是因?yàn)槠淙嫘阅軆?yōu)于組成部分單獨(dú)的性能。纖維能加強(qiáng)基材的模量。Body parts of race cars and some automobiles are posites made of glass fibers (or fiberglass) in a thermoset matrix.競(jìng)賽用汽車(chē)和某些機(jī)動(dòng)車(chē)的車(chē)體部件是由含玻璃纖維(或玻璃絲)的熱固塑料基材制成的。Particles are used to increase the modulus of the matrix, to decrease the permeability of the matrix, to decrease the ductility of the matrix. An example of particlereinforced posites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer.微粒用于增加基材的模量、減少基材的滲透性和延展性。由于重量輕、耐腐蝕、容易在較低溫度下加工并且通常較便宜，聚合物是很有用的。Important Characteristics of PolymersSize. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/mol—that can be more than 2,000 repeating units depending on the polymer structure!聚合材料的重要特性尺寸：?jiǎn)蝹€(gè)聚合物分子一般分子量為10,000到1,000,000g/mol之間，具體取決于聚合物的結(jié)構(gòu)—這可以比2,000個(gè)重復(fù)單元還多。For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100℃, 212℉), and they are most useful for room temperature applications. Some specially engineered polymers can withstand temperatures as high as 300℃(572℉).例如，許多工業(yè)上的重要聚合物其玻璃狀轉(zhuǎn)化溫度接近水的沸點(diǎn)(100℃, 212℉)，它們被廣泛用于室溫下。熱可塑性材料可以重新形成和循環(huán)使用，而熱固性與彈性材料則是不能再使用的。冶金學(xué)是物理學(xué)、化學(xué)和涉及金屬?gòu)牡V石提煉到最后產(chǎn)物的工程學(xué)。因?yàn)槟承┰?尤其是碳)的微小百分比極大地影響物理性能，所以必須知道對(duì)鋼的分析。熱處理時(shí)冷卻速率是控制要素，從高于臨界溫度快速冷卻導(dǎo)致堅(jiān)硬的組織結(jié)構(gòu)，而緩慢冷卻則產(chǎn)生相反效果。The key transition described in this diagram is the deposition of singlephase austenite(γ) to the twophase ferrite plus carbide structure as temperature drops.在此圖中描述的關(guān)鍵轉(zhuǎn)變是單相奧氏體(γ) 隨著溫度下降分解成兩相鐵素體加滲碳體組織結(jié)構(gòu)。當(dāng)鋼冷卻到727℃ (1341℉)時(shí)，將同時(shí)發(fā)生若干變化。Since this chemical separation of the carbon ponent occurs entirely in the solid state, the resulting structure is a fine mechanical mixture of ferrite and cementite. Specimens prepared by polishing and etching