机械工程英语翻译.docx

1、机械工程英语翻译第一单元 ：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. For industrial purposes, materials are divided into e

2、ngineering materials or nonengineering materials. Engineering materials are those used in manufacture and become parts of products. Nonengineering materials are the chemicals, fuels, lubricants, and other materials used in the manufacturing process, which do not become part of the product. Engineeri

3、ng materials may be further subdivided into: Metal Ceramics Composite Polymers, etc. 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. Some metals, such as iron, c

4、obalt and nickel, are magnetic. At low temperatures, some metals and intermetallic compounds become superconductors. 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 e

5、lectrical wires and aluminum in cooking foil and beverage cans. 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 jew

6、elry which usually contains an alloy of gold and nickel. 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. Some metal alloys, such as those based on aluminum, have low densities and are used in aerospace

7、 applications for fuel economy. Many alloys also have high fracture toughness, which means they can withstand impact and are durable.What are some important properties of metals? 金属有哪些重要特性？ Density is defined as a materials mass divided by its volume. Most metals have relatively high densities, espe

8、cially compared to polymers. 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. Fract

9、ure toughness can be described as a materials 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 wont shatter. Plastic d

10、eformation is the ability of bend or deform before breaking. As engineers, we usually design materials so that they dont deform under normal conditions. You dont want your car to lean to the east after a strong west wind. However, sometimes we can take advantage of plastic deformation. The crumple z

11、ones in a car absorb energy by undergoing plastic deformation before they break. 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

12、 good cooking pans and electrical wires. It is impossible to see through metals, since these valence electrons absorb any photons of light which reach the metal. No photons pass through. Alloys are compounds consisting of more than one metal. Adding other metals can affect the density, strength, fra

13、cture toughness, plastic deformation, electrical conductivity and environmental degradation. 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. Ceramics and Glasses 陶瓷和玻璃 A ce

14、ramic 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. A glass is an inorganic nonmetallic material that does not have a cry

15、stalline structure. Such materials are said to be amorphous.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.Many ceramics are good ele

16、ctrical 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. Ceramics are not typ

17、ically formed from the melt. This is because most ceramics will crack extensively (i.e. form a powder) upon cooling from the liquid state. Hence, all the simple and efficient manufacturing techniques used for glass production such as casting and blowing, which involve the molten state, cannot be use

18、d for the production of crystalline ceramics. Instead, “sintering” or “firing” is the process typically used. 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 p

19、orosity and fully dense articles can be obtained. 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 an

20、d other surface imperfections, and an out polymer jacket to protect the fiber from damage. 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

21、 not absorb the light. 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

22、angle. 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. Composites 复合材料 Composites are formed from two or more types of materials. Examples include polymer/ceramic and metal/ceramic composite

23、s. Composites are used because overall properties of the composites are superior to those of the individual components.For example: polymer/ceramic composites have a greater modulus than the polymer component, but arent as brittle as ceramics. Two types of composites are: fiber-reinforced composites

24、 and particle-reinforced composites.Fiber-reinforced Composites纤维加强型复合材料 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. The strong covalent bonds along the fi

25、bers 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. Fibers are difficult to process into composites, making fiber-reinforced composites relatively expensive.Fiber-reinforced composites are used in some of the most a

26、dvanced, and therefore most expensive sports equipment, such as a time-trial racing bicycle frame which consists of carbon fibers in a thermoset polymer matrix. Body parts of race cars and some automobiles are composites made of glass fibers (or fiberglass) in a thermoset matrix. Fibers have a very

27、high modulus along their axis, but have a low modulus perpendicular to their axis. Fiber composite manufacturers often rotate layers of fibers to avoid directional variations in the modulus.Particle-reinforced composites微粒加强型复合材料 Particles used for reinforcing include ceramics and glasses such as sm

28、all mineral particles, metal particles such as aluminum, and amorphous materials, including polymers and carbon black. 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 particle-reinforced comp

29、osites is an automobile tire which has carbon black particles in a matrix of polyisobutylene elastomeric polymer. Polymers 聚合材料 A polymer has a repeating structure, usually based on a carbon backbone. The repeating structure results in large chainlike molecules. Polymers are useful because they are

30、lightweight, corrosion resistant, easy to process at low temperatures and generally inexpensive. Some important characteristics of polymers include their size (or molecular weight), softening and melting points, crystallinity, and structure. The mechanical properties of polymers generally include lo

31、w strength and high toughness. Their strength is often improved using reinforced composite structures.Important Characteristics of Polymers Size. Single polymer molecules typically have molecular weights between 10,000 and 1,000,000g/molthat can be more than 2,000 repeating units depending on the po

32、lymer structure! The mechanical properties of a polymer are significantly affected by the molecular weight, with better engineering properties at higher molecular weights. Thermal transitions. The softening point (glass transition temperature) and the melting point of a polymer will determine which it will be suitable for applications. These temperatures usually determine the upper limit for which a polymer can be used.For example, many industrially important polymers have glass transition temperatures near the boiling point of water (100, 212), and they a