Е. С. Закирова, П. А. Красавин Английский язык для технических вузов
READING Exercise 10. Read the text, try to focus on its essential facts and choose the most
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- DIFFERENT KINDS OF ENGINEERING MATERIALS
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Exercise 10. Read the text, try to focus on its essential facts and choose the most suitable heading given below for each paragraph. 1) Metallic Materials 2) Ceramics 3) Various Classes of Materials 4) Polymers 5) Choosing Materials DIFFERENT KINDS OF ENGINEERING MATERIALS Materials played a major role in the development of societies. Civilizations were named by the level of their materials development, e.g. the Stone Age, the Bronze Age, and the Iron Age. The earliest humans had an access to only a very limited number of natural materials. Modern technologies have made it possible to produce new materials. We believe more than 50,000 materials with specialized properties to have been developed by now. Materials science encompasses various classes of materials, but the traditional groups of engi- neering materials are metallic materials (metals and alloys) and non-metallic materials (polymers, ceramics, etc.). Metallic materials include ferrous (those that contain iron) and non-fer- rous (those that do not contain iron) metals. It should be noted that while 128 describing alloys which are metallic materials it is possible to use the term “metals”. The most common ferrous metals are cast iron and steel, which are both alloys. Different elements in alloys influence properties of materials: large amount of carbon in cast iron increases its brittleness; stainless steels contain- ing nickel or chromium do not rust; steels, which contain tungsten or cobalt, are extremely hard, etc. We consider the most widely used non-ferrous metals to be aluminium and copper. Aluminium alloys are widely used in engineering structures and components where light weight or corrosion resistance is re- quired. Copper is a ductile, malleable metal with a very high thermal and elec- trical conductivity. It is a frequent element of various metal alloys: brass (cop- per and zinc), bronze (copper and tin/lead). Polymers are representatives of non-metallic materials. One of the best known natural polymers is rubber. However, most of the polymers used in in- dustry are not natural but synthetic; they are generally called ‘plastics’. Plastics can be divided in two categories: thermoplastics and thermosets. Thermo- plastics can be heated and moulded numerous times. Common engineering thermoplastics are ABS (acrylonitrile butadiene styrene); polycarbonate; PVC (polyvinylchloride). Thermosets can be heated and moulded only once, they cannot be remoulded. The most common engineering thermosets are epoxy resins and polyamides. The properties of plastics are indispensable: they are lightweight, hard, easy to shape and colour, flexible, non-rusting, relevantly cheap, etc. Ceramic materials are inorganic, non-metallic materials which are formed by the action of heat and subsequent cooling. Clay was one of the earliest ma- terials used to produce ceramics, but many different ceramic materials are now being used in domestic and industrial products. Ceramics tend to be strong, stiff, brittle, chemically inert. They are non-conductors of heat and electricity, but still their properties vary widely. For example, porcelain is widely used to make electrical insulators, but some ceramic compounds made from a metal and a non-metal are superconductors. Thus, at present a lot of engineering materials are available to engineer, who has to choose the one best suited to serve the given purpose. жүктеу/скачать 4,38 Mb. Достарыңызбен бөлісу:
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