Part II. stress at which a material first deforms plastically

stress at which a material first deforms plastically. For a metal the yield strength may be less than the fracture strength, which is the stress at which it breaks. Many materials have a higher strength in compression than in tension.

Ductility is the ability of a material to deform with­out breaking. One of the great advantages of metals is their ability to be formed into the shape that is needed, such as car body parts. Materials that are not ductile are brittle. Ductile materials can absorb energy by deforma­tion but brittle materials cannot.

Toughness is the resistance of a material to breaking when there is a crack in it. For a material of given tough­ness, the stress at which it will fail is inversely propor­tional to the square root of the size of the largest defect present. Toughness is different from strength: the toughest steels, for example, are different from the ones with highest tensile strength. Brittle materials have low toughness: glass can be broken along a chosen line by first scratching it with a diamond. Composites can be designed to have considerably greater toughness than their con­stituent materials. The example of a very tough compos­ite is fiberglass that is very flexible and strong.

Creep resistance is the resistance to a gradual per­manent change of shape, and it becomes especially im­portant at higher temperatures. A successful research has been made in materials for machine parts that oper­ate at high temperatures and under high tensile forces without gradually extending, for example the parts of plane engines.

Vocabulary

ability [a'biliti] — способность amount [a'maunt] — количество

Unit3

absorb [ab'zo: b] — поглощать

amount [a'maunt] — количество

application [aspli'keijbn] — применение

brittle ['britlj — хрупкий, ломкий

car body — кузов автомобиля

constituent [kgn'stitjusnt] — компонент

crack [krask] — трещина

creep resistance — устойчивость к ползучести

definition [defi'ni/эп] — определение

density ['densiti] — плотность

ductility [dAk'tiliti] — ковкость, эластичность

failure ['feilja'] — повреждение

gradual ['graedjusl] — постепенный

permanent ['psimsnant] — постоянный

rigid ['nd3id] — жесткий

to sink [sink] — тонуть

square root ['skwea 'ru: t] — квадратный корень

stiffness ['stifnis] — жесткость

strain [strem] — нагрузка, напряжение, деформация

strength [strcn0] — прочность

stress [stres] — давление, напряжение

tensile strength — прочность на разрыв

toughness [tAfnis] — прочность, стойкость

yield strength [ji: ld] — прочность текучести

Young modulus — модуль Юнга

General understanding:

1. What is the density of a material?

2. What are the units of density? Where low density is needed?

3. What are the densities of water, aluminium and steel?

4. A measure of what properties is stiffness? When stiffness is important?

Part II

5. What is Young modulus? 6.-What is strength?

7. What is yield strength? Why fracture strength is always greater than yield strength?

8. What is ductility? Give the examples of ductile materials. Give the examples of brittle materials.

8. What is toughness?

9. What properties of steel are necessary for the manufacturing of: a) springs, b) car body parts, c) bolts and nuts, d) cutting tools?

10. Where is aluminium mostly used because of its
light weight?

Exercise 3.3. Find the following words and word combinations in the text:

1. количество массы в единице объема

2. килограмм на кубический метр

3. мера сопротивления деформации

4. отношение приложенной силы на единицу пло­щади к частичной упругой деформации

5. жесткая конструкция

6. прочность на сжатие

7. способность материала деформироваться не раз­рушаясь

8. поглощать энергию путем деформации

9. обратно пропорционально квадрату размера де­фекта

10. постепенное изменение формы

11. повышенные температуры

12. высокие растягивающие усилия

Exercise 3.4. Translate into English the following:

1. Плотность измеряется в килограммах на куби­ческий метр.

Unit 3

2. Большинство материалов имеют более высокую плотность, чем вода и тонут в воде.

3. Плотность материала очень важна, особенно в авиации.

4. Модуль Юнга — отношение приложенной силы к упругой деформации данного материала.

5. Чем более металл жесткий, тем менее он дефор­мируется под нагрузкой.

6. Когда металл растягивают, он сначала течет, то есть пластически деформируется.

7. Свинец, медь, алюминий и золото — самые ков­кие металлы.

8. Сопротивление ползучести является очень важ­ным свойством материалов, которые используются в авиационных моторах.

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«FAMOUS PEOPLE OF SCIENCE AND ENGINEERING»

> ■ -<

Sikorsky Igor Ivanovich was a well-known aircraft engineer and manufacturer.

Sikorsky was born in 1889 in Kiev, in the Ukraine, and got his education at the naval college in St. Peters­burg, and later in Kiev and Paris. He was the first to make experiments in helicopter design. In 1913 he designed, built, and flew the first successful aeroplane. Later he built military aircrafts for Russia and France.

In 1919 Sikorsky moved to the United States and later helped to organize an aircraft company that produced a series of multiengine flying boats for commercial serv­ice. Sikorsky became an American citizen in 1928. In the late 1930s he returned to developing helicopters and pro­duced the first successful helicopter in the west. Heli­copters designed by Sikorsky were used mostly by the US