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Text В: «Mechanical Properties of Materials»




Density (specific weight) is theamount of mass in a unitvolume. It is measured in kilograms per cubic me­tre. The density of water is 1000 kg/ m3 but most mate­rials have a higher density andsink in water. Aluminium alloys, with typical densities around 2800 kg/ m3 are con­siderably less dense than steels, which have typical den­sities around 7800 kg/ m3. Density is important in any application where the material must not be heavy.

Stiffness (rigidity) is a measure of the resistance to deformation such as stretching or bending. The Young modulus is a measure of the resistance to simple stretch­ing or compression. It is the ratio of the applied force per unit area (stress) to the fractional elastic deforma­tion (strain). Stiffness is important when a rigid struc­ture is to be made.

Strengthis the force per unit area (stress) that a ma­terial can support without failing. The units are the same as those of Stiffness, MN/m2, but in this case the deformation is irreversible. Theyield strength is the 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 theirabilityto be formed into the shape that is needed, such ascar body parts. Materials that are not ductile are brittle. Ductile materials canabsorb 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 agradual 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 — способность

amount — количество

absorb — поглощать

amount — количество

application — применение

brittle —хрупкий, ломкий

car body — кузов автомобиля

constituent — компонент

crack — трещина

creep resistance — устойчивость к ползучести

definition — определение

density — плотность

ductility — ковкость, эластичность

failure — повреждение

gradual — постепенный

permanent — постоянный

rigid — жесткий

to sink — тонуть

square root — квадратный корень

stiffness — жесткость

strain — нагрузка, напряжение, деформация

strength — прочность

stress — давление, напряжение

tensile strength — прочность на разрыв

toughness — прочность, стойкость

yield strength — 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?

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.

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.

«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 Army Air Forces during World War II. He died in 1972 at the age of 83.

Tupolev Andrey Nikolayevich, famous aircraft de­signer, was born in 1888. He graduated from the Moscow Higher Technical School, where he designed the first Russian wind tunnel. He helped to found the Central Aerohydrodynamics Institute in 1918 and later worked as the head of its design bureau. During his career he directed the design of more than 100 military and com­mercial aircraft, including the TU-2 and TU-4 bombers used in the World War II. In 1955 he designed the TU-104, the first passenger jet airliner. His TU-144 su­personic jet liner began its commercial passenger flights in 1977.



 

UNIT 7

MACHINE-TOOLS

I. Text A: «Machine-tools», Text B: «Lathe»,

Text C: «Milling, boring, drilling machines. Shapers and Planers», Text D: «Dies»

II. Famous people of science and technology: George Stephenson, Robert Slephenson.

Text A: «MACHINE-TOOIS»

Machine-tools are used toshape metals and other ma­terials. The material to be shaped is called theworkpiece.Most machine-tools are nowelectrically driven. Ma­chine-tools with electrical drive are faster and moreac­curate than hand tools: they were an important element in thedevelopment of mass-production processes, as they allowed individual parts to be made in large numbers so as to beinterchangeable.

All machine-tools havefacilities for holding both the workpiece and the tool, and for accurately controlling the movement of the cutting toolrelative to the workpiece. Most machining operations generate largeamounts of heat, and use coolingfluids (usually a mixture of water and oils) for cooling andlubrication.

Machine-tools usually work materials mechanically but other machining methods have been developed lately. They include chemical machining,spark erosionto machine very hard materials to any shape by means of a continuous high-voltagespark (discharge) between an electrode and a workpiece. Other machining meth­ods includedrilling using ultrasound, and cuttingby means of a laserbeam. Numerical control of machine-tools andflexible manufacturing systems have made it possible for complete systems of machine-tools to be used flexibly for the manufacture of arange of pro­ducts.

Vocabulary:


machine-tools — станки

electrically driven — с электроприводом

shape — форма

workpiece — деталь

accurate — точный

development — развитие

to allow — позволять, разрешать

interchangeable — взаимозаменяе­мый

facility — приспособление

relative —относительный

amount — количество

fluid — жидкость

to lubricate — смазывать

spark erosion — электроискровая об­работка

discharge — разряд

by means of — посредством

beam — луч

drilling — сверление

flexible — гибкий

range — ассортимент, диапазон


Text B: «LATHE»

Lathe is still the most important machine-tool. It pro­duces parts ofcircular cross-section by turning the workpiece on its axis and cutting itssurface with a sharp stationary tool. The tool may be movedsideways to pro­duce a cylindrical part and moved towards the workpiece to control thedepth of cut. Nowadays all lathes are power-driven by electric motors. That allows continuous rotation of the workpiece at a variety of speeds. The mod­ern lathe is driven by means ofa headstock supporting a hollowspindle on accurate bearings and carrying either achuck or a faceplate, to which the workpiece is clamped. The movement of the tool, both along thelathe bed and at right angle to it, can be accurately controlled, soena­bling a part to be machined to closetolerances. Modern lathes are often under numerical control.

Vocabulary:


lathe — токарный станок

circular cross-section — круглое попереч­ное сечение

surface — поверхность

stationary — неподвижный, стационар­ный

sideways — в сторону

variety — разнообразие, разновидность

depth — глубина

headstock — передняя бабка

spindle — шпиндель

chuck — зажим, патрон

faceplate — планшайба

lathe bed — станина станка

to enable — давать возможность

tolerance — допуск


General understanding:

1. What are machine-tools used for?

2. How are most machine-tools driven nowadays?

3. What facilities have all machine-tools?

4. How are the cutting tool and the workpiece cooled during machining?

5. What other machining methods have been devel­oped lately?

6. What systems are used now for the manufacture of a range of products without the use of manual labor?

7. What parts can be made with lathes?

8. How can the cutting tool be moved on a lathe?

9. How is the workpiece clamped in a lathe?

10. Can we change the speeds of workpiece rotation in a lathe?

11. What is numerical control of machine tools used for?

 

Exercise 4.1. Find English equivalents in the text:


1. обрабатываемый материал

2. электропривод

3. более точный

4. отдельные детали

5. процесс массового производства

6. приспособления для держания резца и детали

7. операции по механической обработке детали

8. высоковольтный разряд

9. сверление ультразвуком

10. резание с помощью лазерного луча

11. гибкие производственные системы

12. детали круглого сечения

13. поворачивать деталь вокруг ее оси

14. двигать в сторону, двигать по направлению к детали

15. глубина резания

16. непрерывное вращение детали

17. движение резца вдоль станины


Exercise 4.2. Translate into English:

1. Токарный станок позволяет производить детали круглого сечения.

2. Деталь зажимается в патроне или на планшайбе токарного станка.

3. Резец может двигаться как вдоль станины, так и под прямым углом к ней.

4. Современные токарные станки часто имеют циф­ровое управление.

Text С: «MILLING MACHINE»

In a milling machine thecutter (фреза) is a circular device witha series of cuttingedges on itscircumfer­ence. The workpiece is held on a table that controls the feed against the cutter. The table has three possible movements:longitudinal, horizontal, andvertical; in some cases it can also rotate. Milling machines are the mostversatile of all machine tools.Flat or contouredsurfaces may be machined with excellent finish and ac­curacy.Angles, slots, gear teeth and cuts can be made by using various shapes of cutters.





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