第一单元
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Types of Materials
材料的类型
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.
材料可以按多种方法分类。科学家常根据状态将材料分为：固体、液体或气体。他们也把材料分为有机材料(曾经有生命的)和无机材料(从未有生命的)。
For industrial purposes, materials are divided into engineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products.
就工业效用而言，材料被分为工程材料和非工程材料。那些用于加工制造并成为产品组成部分的就是工程材料。 Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product.
非工程材料则是化学品、燃料、润滑剂以及其它用于加工制造过程但不成为产品组成部分的材料。
Engineering materials may be further subdivided into: ①Metal ②Ceramics ③Composite ④Polymers, etc.
工程材料还能进一步细分为：①金属材料②陶瓷材料③复合材料 ④聚合材料，等等。
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Metals and Metal Alloys
金属和金属合金
Metals are elements that generally have good electrical and thermal conductivity. Many metals have high strength, high stiffness, and have good ductility.
金属就是通常具有良好导电性和导热性的元素。许多金属具有高强度、高硬度以及良好的延展性。
Some metals, such as iron, cobalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors.
某些金属能被磁化，例如铁、钴和镍。在极低的温度下，某些金属和金属化合物能转变成超导体。
What is the difference between an alloy and a pure metal Pure metals are elements which come 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.
合金与纯金属的区别是什么纯金属是在元素周期表中占据特定位置的元素。例如电线中的铜和制造烹饪箔及饮料罐的铝。
Alloys contain more than one metallic element. Their properties can be changed by changing the elements present in the alloy. Examples of metal alloys include stainless steel which is an alloy of iron, nickel, and chromium; and gold jewelry which usually contains an alloy of gold and nickel.
合金包含不止一种金属元素。合金的性质能通过改变其中存在的元素而改变。金属合金的例子有：不锈钢是一
种铁、镍、铬的合金，以及金饰品通常含有金镍合金。
Why are metals and alloys used Many metals and alloys have high densities and are used in applications which require a high mass-to-volume ratio.
为什么要使用金属和合金许多金属和合金具有高密度，因此被用在需要较高质量体积比的场合。
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.
某些金属合金，例如铝基合金，其密度低，可用于航空航天以节约燃料。许多合金还具有高断裂韧性，这意味着它们能经得起冲击并且是耐用的。
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 compared to polymers.
金属有哪些重要特性
密度定义为材料的质量与其体积之比。大多数金属密度相对较高，尤其是和聚合物相比较而言。
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.
高密度材料通常由较大原子序数原子构成，例如金和铅。然而，诸如铝和镁之类的一些金属则具有低密度，并被用于既需要金属特性又要求重量轻的场合。
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.
断裂韧性可以描述为材料防止断裂特别是出现缺陷时不断裂的能力。金属一般能在有缺口和凹痕的情况下不显著削弱，并且能抵抗冲击。橄榄球运动员据此相信他的面罩不会裂成碎片。
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.
塑性变形就是在断裂前弯曲或变形的能力。作为工程师，设计时通常要使材料在正常条件下不变形。没有人愿意一阵强烈的西风过后自己的汽车向东倾斜。
However, sometimes we can take advantage of plastic deformation. The crumple zones in a car absorb energy by undergoing plastic deformation before they break.
然而，有时我们也能利用塑性变形。汽车上压皱的区域在它们断裂前通过经历塑性变形来吸收能量。
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.
金属的原子连结对它们的特性也有影响。在金属内部，原子的外层阶电子由所有原子共享并能到处自由移动。由于电子能导热和导电，所以用金属可以制造好的烹饪锅和电线。
It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through.
因为这些阶电子吸收到达金属的光子，所以透过金属不可能看得见。没有光子能通过金属。
Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fracture toughness, plastic deformation, electrical conductivity and environmental degradation.
合金是由一种以上金属组成的混合物。加一些其它金属能影响密度、强度、断裂韧性、塑性变形、导电性以及环境侵蚀。
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，往铝里加少量铁可使其更强。同样，在钢里加一些铬能减缓它的生锈过程，但也将使它更脆。
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Ceramics and Glasses
陶瓷和玻璃
A ceramic is often broadly defined as any inorganic nonmetallic material． By this definition, ceramic materials would also include glasses; however, many materials scientists add the stipulation that “ceramic” must also be crystalline.
陶瓷通常被概括地定义为无机的非金属材料。照此定义，陶瓷材料也应包括玻璃；然而许多材料科学家添加了“陶瓷”必须同时是晶体物组成的约定。
A glass is an inorganic nonmetallic material that does not have a crystalline structure. Such materials are said to be amorphous.
玻璃是没有晶体状结构的无机非金属材料。这种材料被称为非结晶质材料。 Properties of Ceramics and Glasses
Some of the useful properties of ceramics and glasses include high melting temperature, low density, high strength, stiffness, hardness, wear resistance, and corrosion resistance.
陶瓷和玻璃的特性
高熔点、低密度、高强度、高刚度、高硬度、高耐磨性和抗腐蚀性是陶瓷和玻璃的一些有用特性。
Many ceramics are good electrical and thermal insulators. Some ceramics have special properties: some ceramics are magnetic materials; some are piezoelectric materials; and a few special ceramics are superconductors at very low temperatures. Ceramics and glasses have one major drawback: they are
brittle.
许多陶瓷都是电和热的良绝缘体。某些陶瓷还具有一些特殊性能：有些是磁性材料，有些是压电材料，还有些特殊陶瓷在极低温度下是超导体。陶瓷和玻璃都有一个主要的缺点：它们容易破碎。
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。因为大多数陶瓷在从液态冷却时将会完全破碎(即形成粉末)。
Hence, all the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be used for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used.
因此，所有用于玻璃生产的简单有效的—诸如浇铸和吹制这些涉及熔化的技术都不能用于由晶体物组成的陶瓷的生产。作为替代，一般采用“烧结”或“焙烧”工艺。
In sintering, ceramic powders are processed into compacted 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.
在烧结过程中，陶瓷粉末先挤压成型然后加热到略低于熔点温度。在这样的温度下，粉末内部起反应去除孔隙并得到十分致密的物品。
An optical fiber contains three layers: a core made of highly pure glass with a high refractive index for the light to travel, a middle layer of glass with a lower refractive index known as the cladding which protects the core glass from scratches and other surface imperfections, and an out polymer jacket to protect the fiber from damage.
光导纤维有三层：核心由高折射指数高纯光传输玻璃制成，中间层为低折射指数玻璃，是保护核心玻璃表面不被擦伤和完整性不被破坏的所谓覆层，外层是聚合物护套，用于保护光导纤维不受损。
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.
为了使核心玻璃有比覆层大的折射指数，在其中掺入微小的、可控数量的能减缓光速而不会吸收光线的杂质或搀杂剂。
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数比覆层大，只要在全内反射过程中光线照射核心/覆层分界面的角度比临界角大，在核心玻璃中传送的光线将仍保留在核心玻璃中。
The total internal reflection phenomenon, as well as the high purity of the core glass, enables
light to travel long distances with little loss of intensity.
全内反射现象与核心玻璃的高纯度一样，使光线几乎无强度损耗传递长距离成为可能。
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Composites 复合材料
Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composites. Composites are used because overall properties of the composites are superior to those of the individual components.
复合材料由两种或更多材料构成。例子有聚合物/陶瓷和金属/陶瓷复合材料。之所以使用复合材料是因为其全面性能优于组成部分单独的性能。
For example: polymer/ceramic composites have a greater modulus than the polymer component, but aren’t as brittle as ceramics.
Two types of composites are: fiber-reinforced composites and particle-reinforced composites. 例如：聚合物/陶瓷复合材料具有比聚合物成分更大的模量，但又不像陶瓷那样易碎。 复合材料有两种：纤维加强型复合材料和微粒加强型复合材料。 Fiber-reinforced 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.
纤维加强型复合材料
加强纤维可以是金属、陶瓷、玻璃或是已变成石墨的被称为碳纤维的聚合物。纤维能加强基材的模量。 The strong covalent bonds along the fiber’s length give them a very high modulus in this direction because to break or extend the fiber the bonds must also be broken or moved.
沿着纤维长度有很强结合力的共价结合在这个方向上给予复合材料很高的模量，因为要损坏或拉伸纤维就必须破坏或移除这种结合。
Fibers are difficult to process into composites, making fiber-reinforced composites relatively expensive.
把纤维放入复合材料较困难，这使得制造纤维加强型复合材料相对昂贵。
Fiber-reinforced composites are used in some of the most advanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix.
纤维加强型复合材料用于某些最先进也是最昂贵的运动设备，例如计时赛竞赛用自行车骨架就是用含碳纤维的热固塑料基材制成的。
Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix.
竞赛用汽车和某些机动车的车体部件是由含玻璃纤维(或玻璃丝)的热固塑料基材制成的。
机械工程英语第二版翻译
