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Task 2. Can we change the properties of engineering materials? How?

Task 3. Read and translate the text:

Properties of engineering materials are known to affect manufacture and application of them. While using engineering materials we must know their physical characteristics. All engineering materials have definite characteristics which determine their abilities to assume external loads because of which materials change their shape. Metals are known to be subjected to the influence of external forces when they are treated. These forces are called "loads" and may have different characteristics: according to their value they may be small or large; according to the duration and character of their action they may be constant and impact. According to the influence of the load upon the metal causing different changes of its shape, loads are distinguished as compression, tensile, torsion, shearing and bending ones. By testing a metal under a load one can define what mechanical properties it has. In order to have a clear conception of the metal properties it is subjected to tests on special devices and machines. The determination of these properties is made in the laboratory using a specimen of the metal to be tested.

In studying engineering processes an engineer who is to build a machine must select suitable materials for each machine member. One must know the characteristics of engineering materials. These are as follows: strength, stiffness, ductility, toughness, elasticity, plasticity, fatigue resistance, shock resistance, corrosion resistance, wear resistance, hardness, frictional qualities, machinability, casting and forging properties. They depend upon the chemical composition and the physical structure of the material.

Strength is the property of hard materials to be subjected to the influence of external forces without incurring damage, without changing their shape. The ultimate tensile strength of a material is that unit stress developed in the material by maximum slowly applied load that material can resist without rupturing in a tensile test.

Special machines, called "rupture machines", are used to test metals for strength. When testing a specimen, the upper clamp remains fixed and the lower one is being slowly lowered, thus causing the extension of the specimen. The load upon the specimen may be easily determined at any moment by means of pointer indications on the dial.

Elasticity is the ability of a material to change its shape under the influence of external loads and return to its original form upon removal of the loads. All materials are elastic but the range of elasticity varies for different materials. Elasticity is evaluated by means of the modulus of elasticity. The modulus of elasticity is considered to be the ratio of the unit stress to the unit deformation within the proportional limit of the material to be tested. A rupture machine may be used to determine the elasticity of metals.

Plasticity is the property of a material when under the influence of loads, specimens of different materials may elongate while their cross-section decreases. Plasticity is the opposite of elasticity. So, plasticity is the ability of material to change its form without breaking under the influence of load and preserve this changed form after removal of the load. For determining the plasticity of metals a rupture machine may be used too.

There are some processes changing and improving the properties of metals. Heat-treatment is the process of controlled heating and cooling of metals to change their structural arrangement and to ensure certain desirable properties. Annealing consists of heating the metal to a temperature slightly above the critical temperature and then cooling slowly to produce an even grain structure, reduce the hardness, and increase the ductility. Normalising is a form of annealing in which the material is cooled in the air. Quenching or rapid cooling from above the critical temperature by immersion in bold water or some other cooling medium is a hardening treatment. Tempering consists of reheating the quenched metal to restore ductility to some extent and reduce the brittleness.

Task 4. Find in the text equivalents to the following words and expressions:

, , , , , , , , , , , , , , , .

Task 5. Make word combinations from the words in column A and column B, translate them into Ukrainian:

  A   B
controlled a) machines
special b) materials
unit c) resistance
engineering d) heating
rupture e) loads
wear f) strength
external g) devices
tensile h) stress

Task 6. Translate into Ukrainian the following words and word combinations:

strength, stiffness, ductility, toughness, elasticity, plasticity, fatigue resistance, shock resistance, corrosion resistance, wear resistance, hardness, frictional qualities, machinability, casting and forging properties, annealing, normalising, quenching, tempering.

Task 7. Fill in the gaps with the verbs given below. Put them in proper tense form. Translate the following sentences into Ukrainian:

to be, to calculate, to be identical, to determine, to keep, to undergo

1. Elasticity _______ by means of the modulus of elasticity.

2. Tempering consists of reheating the quenched metal _______ ductility to some extent and reduce the brittleness.

3. In order to have a clear conception of the metal properties it _______ to tests on special devices and machines.

4. Viscosity _______ a measure of the resistance of a fluid to deform under shear stress.

5. By testing a metal under a load one _______ what mechanical properties it has.

6. The average density of an object _______ to its total mass divided by its total volume.

Task 8. Complete the sentences using the given words:

Strength   quality of being easily made into any shape, and of staying in that shape until something changes it.
Elasticity   making metal hard by heating it and then slowly letting it get cold in the air.
Plasticity   a way of treatment by immediate cooling in corresponding media.
Heat-treatment is property of hard materials to resist external forces.
Annealing   second heating for changing material properties.
Normalising   making metal hard by heating it and then slowly letting it get cold.
Quenching   the ability of the material to stretch and go back to its usual length or shape.
Tempering   the processing of material with the help of controlled heat.

Task 9. Translate next sentences into English:

1. , .

2. , .

3. , .

4. 䳺 ().

5. -- , .

6. - .

Task 10. Find in the text synonyms to the following words:

form ,distinct characteristics, steady, to choose, sample

Task 11. Memorize the following words and word combinations:

1. annealing
2. to assume ,
3. bending
4. clamp ,
5. corrosion resistance 糿
6. device
7. ductility ,
8. duration
9. external forces
10. fatigue resistance
11. frictional qualities
12. hardness
13. heat-treatment
14. machinability
15. physical characteristics
16. quenching
17. shearing
18. shock resistance
19. specimen ,
20. stiffness
21. tensile ,
22. tempering ,
23. torsion
24. toughness ,
25. wear resistance

 

Unit 10

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