I. Text A: Materials science and technology,
Text B: Mechanical Properties of Materials.
II. Famous people of science and technology: Igor Sikorskly, Andrey Tupolev.
Text A: MECHANICAL PROPERTIES Of MATERIALS
Materials Science and Technology is the study of materials and how they can be fabricated to meet the needs of modern technology. Using the laboratory techniques and knowledge of physics, chemistry, and metallurgy, scientists are finding new ways of using metals, plastics and other materials.
Engineers must know how materials respond to external forces, such as tension, compression, torsion, bending, and shear. All materials respond to these forces by elastic deformation. That is, the materials return their original size and form when the external force disappears. The materials may also have permanent deformation or they may fracture. The results of external forces are creep and fatigue.
Compression is a pressure causing a decrease in volume. When a material is subjected to a bending, shearing, or torsion (twisting) force, both tensile and compressive forces are simultaneously at work. When a metal bar is bent, one side of it is stretched and subjected to a tensional force, and the other side is compressed.
Tension is a pulling force; for example, the force in a cable holding a weight. Under tension, a material usually stretches, returning to its original length if the force does not exceed the material's elastic limit. Under larger tensions, the material does not return completely to its original condition, and under greater forces the material ruptures.
Fatigue is the growth of cracks under stress. It occurs when a mechanical part is subjected to a repeated or cyclic stress, such as vibration. Even when the maximum stress never exceeds the elastic limit, failure of the material can occur even after a short time. No deformation is seen during fatigue, but small localized cracks develop and propagate through the material until the remaining cross-sectional area cannot support the maximum stress of the cyclic force. Knowledge of tensile stress, elastic limits, and the resistance of materials to creep and fatigue are of basic importance in engineering.
Creep is a slow, permanent deformation that results from a steady force acting on a material. Materials at high temperatures usually suffer from this deformation. The gradual loosening of bolts and the deformation of components of machines and engines are all the examples of creep. In many cases the slow deformation stops because deformation eliminates the force causing the creep. Creep extended over a long time finally leads to the rupture of the material.
Vocabulary
bar ,
completely ,
compression
creep
cross-sectional area
cyclic stress
decrease
elastic deformation
elastic limit
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exceed
external forces
fatigue
fracture ,
loosen ,
permanent deformation
remaining
shear
simultaneously
to stretch
technique
tension
to propagate
to bend ,
to extend ,
to meet the needs
to occur
to respond
to suffer
torsion
twisting ,
volume ,
rupture
General understanding:
1. What are the external forces causing the elastic deformation of materials? Describe those forces that change the form and size of materials.
2. What are the results of external forces?
3. What kinds of deformation are the combinations of tension and compression?
4. What is the result of tension? What happens if the elastic limit of material is exceeded under tension?
5. What do we call fatigue? When does it occur? What are the results of fatigue?
6. What do we call creep? When does this type of permanent deformation take place? What are the results of creep?
Exercise 3.1. Find the following in the text:
1.
2.
3.
4. , , , ,
5.
6.
7.
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9.
10.
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14.
Exercise 3.2. Translate into English the following sentences:
1. , , , , , .
2. .
3. .
4. , .
5. .
6. , - .
7. .
Text : 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.
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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
amount
absorb
amount
application
brittle ,
car body
constituent
crack
creep resistance
definition
density
ductility ,
failure
gradual
permanent
rigid
to sink
square root
stiffness
strain , ,
strength
stress ,
tensile strength
toughness ,
yield strength
Young modulus
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.
2.
3.
4.
5.
6.
7.
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9.
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12.
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Exercise 3.4. Translate into English the following:
1. .
2. , .
3. , .
4. .
5. , .
6. , , .
7. , , .
8. , .
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
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 to shape metals and other materials. The material to be shaped is called the workpiece. Most machine-tools are now electrically driven. Machine-tools with electrical drive are faster and more accurate than hand tools: they were an important element in the development of mass-production processes, as they allowed individual parts to be made in large numbers so as to be interchangeable.
All machine-tools have facilities for holding both the workpiece and the tool, and for accurately controlling the movement of the cutting tool relative to the workpiece. Most machining operations generate large amounts of heat, and use cooling fluids (usually a mixture of water and oils) for cooling and lubrication.
Machine-tools usually work materials mechanically but other machining methods have been developed lately. They include chemical machining, spark erosion to machine very hard materials to any shape by means of a continuous high-voltage spark (discharge) between an electrode and a workpiece. Other machining methods include drilling using ultrasound, and cutting by means of a laser beam. Numerical control of machine-tools and flexible manufacturing systems have made it possible for complete systems of machine-tools to be used flexibly for the manufacture of a range of products.
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Vocabulary:
machine-tools
electrically driven
shape
workpiece
accurate
development
to allow ,
interchangeable
facility
relative
amount
fluid
to lubricate
spark erosion
discharge
by means of
beam
drilling
flexible
range ,
Text B: LATHE
Lathe is still the most important machine-tool. It produces parts of circular cross-section by turning the workpiece on its axis and cutting its surface with a sharp stationary tool. The tool may be moved sideways to produce a cylindrical part and moved towards the workpiece to control the depth 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 of a headstock supporting a hollow spindle on accurate bearings and carrying either a chuck or a faceplate, to which the workpiece is clamped. The movement of the tool, both along the lathe bed and at right angle to it, can be accurately controlled, so enabling a part to be machined to close tolerances. Modern lathes are often under numerical control.
Vocabulary:
lathe
circular cross-section
surface
stationary ,
sideways
variety ,
depth
headstock
spindle
chuck ,
faceplate
lathe bed
to enable
tolerance
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.
2.
3.
4.
5.
6.
7.
8.
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10.
11.
12.
13.
14. ,
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17.
Exercise 4.2. Translate into English:
1. .
2. .
3. , .
4. .
Text : MILLING MACHINE
In a milling machine the cutter () is a circular device with a series of cutting edges on its circumference. The workpiece is held on a table that controls the feed against the cutter. The table has three possible movements: longitudinal, horizontal, and vertical; in some cases it can also rotate. Milling machines are the most versatile of all machine tools. Flat or contoured surfaces may be machined with excellent finish and accuracy. Angles, slots, gear teeth and cuts can be made by using various shapes of cutters.
