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Text В: «Mechanical Properties of Materials»Density (specific weight) is the amount of mass in a unit volume. It is measured in kilograms per cubic metre. The density of water is 1000 kg/ m3 but most materials have a higher density and sink 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. Strength is 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. The yield 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 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 — 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.'>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 4 |