Готовые работы → Английский язык

Прочитать и перевести все тексты. 1. ADVANCED COMPOSITE MATERIALS Composite materials are among the oldest and newest of structural materials. Men discovered early that when two or more materials are used together as one, the combination often behaves better than each of the materials alone. Fol¬lowing this principle they combined clay and straw to make bricks. Then with some notable exceptions, the further poten¬tialities of composite materials remained virtually untapped for centuries while monolithic materials, such as iron and copper, served the major needs of an advancing technology. E

2013

С условиями соглашения согласен (согласна)

Скачать методичку, по которой делалось это задание (0 кб)

Содержание

Прочитать и перевести все тексты.

1. ADVANCED COMPOSITE  MATERIALS

Composite materials are among the oldest and newest of structural materials. Men discovered early that when two or more materials are used together as one, the combination often behaves better than each of the materials alone. Fol­lowing this principle they combined clay and straw to make bricks. Then with some notable exceptions, the further poten­tialities of composite materials remained virtually untapped for centuries while monolithic materials, such as iron and copper, served the major needs of an advancing technology. Even in the more recent times with the coming of reinforced concrete, linoleum, plasterboard and plywood panels were somewhat out of mainstream of materials development and technology.

During the 1930's and 1940's, however, light-weight hon­eycomb structures, machine parts made from compressed metal powders and plastic reinforced with glass fibers be­came commercial realities. These developments marked the be­ginning of the modern era of composite engineering materials. The use of composite materials has been steadily growing. The consumption of the fiber reinforced plastics, for example, has been increasing at the phenomenal rate of 25 per cent annually. Nevertheless, the emergence of a strict discipline and technology of composite materials is barely 20 years old.

There are two major reasons for the current interest in composite materials. The first is simply the demand for ma­terials that will outperform the traditional monolithic mate­rials. The second, and the more important in the long run, is that composites offer engineers the opportunity to design totally new materials with the precise combination of proper­ties needed for a specific task. Although the new compo­sites are usually, more costly than conventional materials, they can be used more sparingly, because of their superior qualities.

2. MAN-MADE  DIAMONDS

The new industries of today are in great need of super-hard materials, diamonds in particular. One could even say that the level of the technical development of a country is largely determined by the number of diamonds used for bore­hole drilling, for the machining of super-hard and refractory materials, and for the setting of grinding wheels, stone saw­ing,   wire  drawing,   etc.

There are not enough natural diamonds to meet all these needs. Therefore, people have learned to manufacture artifi­cial ones. Over a decade ago, Soviet scientists discovered how to synthesize diamonds.

A diamond, just like common graphite, is almost pure carbon. Thus, it turns out that graphite and diamond are two forms of the same substance. Their properties differ, how­ever. Graphite is a black, non-transparent and light-weight substance and a good conductor of electricity, whereas a dia­mond is colourless, transparent, extremely hard and a non­conductor. This is explained by the difference in the struc­tures of their crystals. It takes a very high pressure (tens of thousands of atmospheres) and a high temperature to com­press the waywar-d carbon atoms into a diamond. Soviet scien­tists were' among the first to achieve this. They worked out the diamond production processes, designed the necessary equipment and handed over the results of their work to a number of research organizations and industrial enterprises which are introducing synthetic diamonds into the country's national economy on a wide scale.

Graphite or any other carbonaceous substance is placed in a special chamber where the necessary pressure and temper­ature are built up. The reaction usually takes a few minutes, but may vary from a few seconds to a few hours. The whole mass is then cooled to room temperature under a very high pressure. When the pressure is down to that of the atmosphere, the chamber is opened, and the diamonds are separated from the non-converted mass.

Artificial diamonds are about 50-66 per cent cheaper. Tests revealed that abrasive tools using artificial diamonds are stronger than those using natural ones. Man-made dia­monds are not substitutes—they are exactly like the diamonds found  by  geologists   in  kimberlite  pipes.

Soviet scientists are not content with what they have al­ready achieved. Scientific quests in the field of synthesis continue. This work has already brought results. Of late we have synthesized new polycrystals. This is a very rare form of crystal which hardly ever occurs in nature. The synthesized polycrystallic diamond possesses extremely valuable proper­ties and is successfully used in many fields of science and tech­nology. The new material is much easier and cheaper to make, and its field of application is much broader than that of natu­ral diamonds. A number of foreign firms—American and Jap­anese,   in particular—have   already applied  for  licences.

The institute has succeeded in making large stones from a new material called "elbor", which is analogous to the dia­mond in structure. Elbor has quite a few advantages over the diamond. Diamonds are known to be very hard; if heated to a certain temperature, however, they lose this property and turn back into soft graphite. This happens to the new material, too, but at a temperature which is 2,000 higher. The new stones are more stable and possess high chemical inertness.

Machine tools with cutters made of the new material can work hard-tempered steel. This is an unprecedented case in world practice. Usually, steel parts are worked first and tempered later. Hard-alloy cutters have to be changed every 1 or 2 minutes, while elbor cutters are capable of working for a whole hour without re-sharpening. An fnteresting point is that the higher the cutting speed, the higher the cutter's wear  resistance.

High-pressure physics is a comparatively young but very promising science. It is not only an efficient tool for studying the physical properties of solids in a state of high density, but also a powerful means of creation. Using it, we can make a variety of materials man may need.

3. THE UNCERTAIN FUTURE OF THE AMERICAN  SKYSCRAPER

Just at a time when the building of skyscrapers is moving ahead, attacks on these "megastructures" are spreading on a wide variety of fronts.

In San Francisco, officials set a 40-foot height limit on buildings in more than 95 per cent of residential areas in the city.

In Washington, efforts by builders to raise a height limit of 130 feet have been unsuccessful.

Tallest of the new "spacescrapers" are the twin towers of the World Trade Centre in New York City, which opened recently. But these 1,350-foot buildings will be short-lived. The Sears, Roebuck Tower in Chicago will rise to 1,450 feet when finished.

And the owners of the 40-year-old Empire State Building are going to add 11 storeys to make it once again the world's tallest building.

Other high-rise structures are under way in Boston, Atlan­ta, Philadelphia, San Francisco, Detroit, Dallas, Miami, Oklahoma City and others.

200 Storeys? Many builders are convinced that high-rise structures are an economic necessity in cities because of space shortage.

Engineers believe that tall buildings will rise to 200 storeys or more. In Chicago the Hancock Centre — or "Big John" as it's known among architects—is a 95-million-dollar verti­cal city 1,127 feet high. Its 100 storeys contain department and grocery stores, 705 apartments, office space for 4,000 workers, restaurants, bank and recreational and parking facil­ities.

The management says its "megastructure" provides a com­plete living arrangement for more than 1,700 tenants—a place where people can live comfortably, without ever leaving the house. But some residents have complained of tedious elevator delays, "living above the weather", and "a sense of isolation from street   life."

"You wake up literally on top of the clouds while back down on earth it's raining," said one.

"It's all so artificial," said another. "You can't open a win­dow, only a slot. Everything is done by push button. You feel like you're living in a space station. And you just have to get on the ground for a while."

Experts in the field agree there are no structural limits to the potential height of buildings.

"We could start erecting a mile-high structure next year," they say in the New York engineering firm. "But do we really want to? The question is not can such a building be built, but should it be built."

Effects on People. Some scientists think that the sway

'and vibrations caused in the upper storeys of tall buildings

by high winds or minor earthquakes—cause discomfort and

tension. Some tall buildings sway as much as 15 inches in

strong winds.

Another structural problem has been to provide adequate foundation support for massive buildings.

What effect a tall building will have on the rest of a city is a question city planners should ask themselves before the building goes up. Architects and engineers should enter the political arena where questions about a building's effect on the ecology and the environment are asked. "Too often we get into the picture after it is too late," said one of the statesmen.

In Chicago, the gigantic new Sears tower threatened to distort television reception for estimated 62,500 households because it would intercept signals from antennas mounted atop the Hancock buildings, causing double images on TV screens.

Fire and Crime. The most immediate menaces to high-rise workers and' dwellers are fire and crime, which take a heavy toll in lives and dollars.

When flames break out in a modern skyscraper, they may quickly spread to combustible carpeting and furniture stuffed with polyurethane foam. Smoke and lethal gases are channel­led through air-conditioning ducts, mail chutes, elevator shafts and stair wells, rising between the steel and concrete walls as if in a chimney. Most persons killed In fires In tall buildings  die  from  smoke.  

Many skyscrapers are also proving an easy mark for crimi­nals—in fact, urban crime is moving into the office buildings, luxury apartment complexes and low-income housing from small stores,  alleys and parks.

Most recent evidence of this trend were the results of a three-year study by New York University which showed that the taller a building was, the higher its rate of crime.

The research, conducted in 100 public-housing projects in New York City, indicated that the crime rate in high-rise buildings was more than twice that in walk-up buildings. In some Chicago offices, employers are providing armed guards to escort women to and from their jobs even in daytime.

Now many people are beginning to feel that skyscrapers should not be considered the only option available in growing cities because skyscrapers have always been put up for reasons of advertisement and publicity.

4. SPECIAL  STRUCTURES

Power stations, factories, airports—these are some of the special buildings that every modern community needs. And so very special are structures of this type—so specific in their function—that we can generally recognize their purpose from their design. This is true, for example, of television masts or of the huge concrete water-cooling towers that are an essen­tial feature of many modern power stations.

If we examine any building that needs large, uninterrupt­ed areas of floor space—for instance, an aircraft hangar, exhibition hall, traffic terminal, or factory—we can see that its very construction must depend on the intelligent use of steel and concrete. These days, buildings with immense spans are commonplace; concrete and steel have made them so. This is only one instance of the way in which many of today's basic structures have been made possible through new develop­ments in building materials and methods. New technological developments (and, of course, earlier scientific research) have also helped improve the services provided by recently con­structed concert halls, stadiums, theatres, shops, and garages. To take just one obvious example: Studies in acoustics have helped architects to design concert halls whose shape, assisted by skilfully positioned sound-absorbing and sound-reflecting materials makes for nearly perfect hearing in all parts of the hall. The view of the theatre stage is far better than it used to be, too, because balconies need no longer be propped up by view-obstructing supports. There are no visible supports at all if the cantilever style of construction is adopted. And air conditioning, good lighting, and better-than-adequate sanitation are amenities (all developed in our own time) that most modern community buildings.are sure to incorpo­rate.

Temples and palaces used to be the outward signs of a community's development. As such they have been replaced by imposing atomic-power stations, concert halls, airports, radio and television towers, multistory car parks, and shop­ping centres

5. CONCRETE

These days, a building's framework is as likely to be of reinforced concrete as of structural steel. Conrete is made by mixing together small stones, sand, cement, and wat­er in rotating drums. The mixture is tipped or piped into forms (wooden molds) of the shape required. The coarse stones used in the mix give the concrete its strength; the sand is needed to fill the gaps between the stones; and the cement (mixed with just enough water to make it into a paste) covers the surfaces of all solids and binds the entire mixture into a single mass.

The less water that is used in mixing the concrete, the denser and stronger it is when it has set. The difficulty here is that a dryish mix is not so easy to stir as one that is fairly wet and sloppy. So where a really strong concrete is essential, it is mixed with the necessary minimum of water, placed in the forms, and then vibrated, before it sets, by slowly "comb­ing" it with electrically vibrated bars. This both drives out any lingering pockets of air and ensures that the mix is thor­oughly even.

To make the concrete resistant to bending, engineers rein­force it. They do this by putting bars of steel or miniature steel frameworks into the forms—before the concrete mixture is poured—in just those places where the stress will be greatest. Hence the name "reinforced concrete". With such mate­rial an infinite variety of constructional shapes can be pro­duced, including "shells" and roofs in the shape of hyperbolic paraboloids. For these very modern structural items reinfor­ced- concrete is used in thin sheets.

In an ordinary reinforced concrete beam, much of the concrete does little more than hojd the steel in place. It can be used more effectively if, before the external load comes on, stresses are put into it. For instance, suppose that a rein­forced beam could be bent out of the straight by an inch, either upward or downward, before it developed serious cracks. Then, if we tighten up the reinforcement before any load comes . on so as to bend the beam an inch upward, it would take twice as much load as before to bend it an inch downward. In other words, we can, by prestressing it in reverse, prepare the con­crete in advance to withstand the pressures and pulls that the external  load will  cause.

Concrete can be prestressed in two'ways. In the first meth­od, the concrete is cast around stretched steel wires. When the concrete has set, the wires are released and compress the concrete as they contract. Such a method of prestressing pro­duces pretensioned concrete.

The other method is called post-tensioning. In the case of a beam, for example, the concrete is cast around polythene tubes through which, after the concrete has set, steel cables are drawn. These cables are anchored at one end of the beam, stretched by jacks, and then fixed at the other end of the beam, In their stretched po'sition they give a built—in stress to the beam; and this too will be cancelled out when a load is applied.

In constructing a building, it is possible to cast the floors and walls as well as the framework directly on the spot where they are to stand. The building then forms a monolith-one large artificial stone composed entirely of concrete that has been shaped within wooden molds that fit together per­fectly. Thus, no sections have to be joined together later on. To cast all the parts in place, the builder has, of course, to use a great many forms; these are removed as soon as the concrete has set. And the concrete of each story must be given plenty of time to harden "before work on the next story can begin.

In order to save time, the builder may prefer to use a num­ber of standardized concrete units. These can then be made in advance—that is, either the individual members can be pre­cast (and possibly prestressed), or whole sections of the build­ing can be prefabricated.

Precasting and prefabrication have made possible the speedy erection of buildings designed to use a great'many standardized parts (such as window frames).

6. SPECIAL-PURPOSE GLASS

Most people over the age of 50 would have a hard time reading this page with the naked eye. But they can read even smaller print easily with the help of lenses. Spectacles were first made in the late 13th century; and with the invention of printing their use became widespread. We now have many uses for lenses that are made of a hard, clear glass, called opti­cal glass; we find them in microscopes, for instance, and in telescopes and cameras.

The development of optical glass is closely connected with advances in chemistry; and the story of optical technology actually began only when scientists found that they could alter the amount of refraction (bending of light waves) by adding small amounts of other compounds to plain glass.

Chemists, working hand in hand with glass makers, have also found ways to make glass that will absorb certain light rays while letting others pass through. For instance, we now have glass that allows the passage of very short invisible rays such as X-rays; and we also have glass that does the very opposite: it absorbs X-rays and the. shorter gamma rays from nuclear reactions. Still another type of glass transmits invisible infra-red rays, which can penetrate haze; used as a camera lens, it greatly extends the range of long-distance photography.

Another important result of applying chemistry to glass manufacture was the American invention, in 1916, of Pyrex, an immensely strong glass containing a high percentage of boric oxide. Because it can withstand sharp temperature changes without cracking, Pyrex is widely used in baking dishes and frying pans that can be put directly over a naked flame. But it has an important industrial use as well: Large-diameter Pyrex pipes are used for conveying chemicals through a series of continuous processes. Pyrex is highly resistant to attack by corrosive chemicals; and, because it is transparent, the pro­cesses can be watched through all the stages of certain kinds of manufacture.

There are many other types of modern glass, of course. Two that are worth mentioning here because they are vital to present-day motoring and flying are both safety glasses. The first is Triplex, so called because the French inventor— E. Benedictus—produced in 1909 a three-part "sandwich" consisting of two sheets of glass glued to an in-between layer of celluloid. Used as a windshield in place of plate glass, Triplex has saved many lives because, in the event of an accident, the glass does not break up into sharp-edged fragments but sticks to the celluloid. On the Triplex principle, modern aircraft carry windshields up to 1.5 inches thick, with as many as nine layers of alternate glass and plastic sheet.

The other safety glass is called toughened glass. It is made by heating glass sheet up to the softening point; then both sides of the sheet are suddenly cooled by a blast of compressed air. The outside solidifies at once; and the sudden colding and consequent contraction pulls the inner film into a state of high compression. This has the effect of making the whole sheet immensely strong. Furthermore, because of the intense internal stresses, such glass is so very brittle that, if it does get broken, it breaks into tiny fragments—too tiny to cause injury. That is why it has come into common use for car windshields.

Все темы готовых работ →

Другие готовые работы по теме «английский язык»