Properties of engineering materials

Task 1. What are the most important properties of engineering materials?

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:

певні характеристики, змінювати форму, зовнішні сили, обробляти, тривалість, пружність, згинання, прилад, примірник, показник ступеня гнучкості, властивість, зберігати, визначення пластичності металу, покращувати властивості металу, тепло обробка, охолодження

Task 5. 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 6. Make word combinations from the words in column A and column B, translate them into Ukrainian:

	A		B
1	controlled	a)	machines
2	special	b)	materials
3	unit	c)	re­sistance
4	engineering	d)	heating
5	rupture	e)	loads
6	wear	f)	strength
7	external	g)	devices
8	tensile	h)	stress

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. При обробці, метали піддаються впливу зовнішніх сил.

2. Щоб чітко визначити властивості матеріалу, його слід перевірити різними приладами та інструментами.

3. Будуючи машину, інженер має обрати правильний матеріал з потрібними властивостями та характеристиками.

4. Пластичність – це властивість матеріалу змінювати форму під дією зовнішніх сил та зберігати її (форму).

5. Тепло-обробка - це процес контрольованого охолоджування і нагрівання металів, з метою зміни їх структури і отримання певних властивостей.

6. Еластичність - це властивість матеріалу змінити свою форму під впливом зовнішніх сил і повернутися до його первинного виду.

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	відпал
2.	to assume	приймати, брати на себе
3.	bending	згинання
4.	clamp	затиск, клема
5.	corrosion resistance	стійкість до корозії
6.	device	прилад
7.	ductility	ковкість, тягучість
8.	duration	тривалість
9.	external forces	зовнішні сили
10.	fatigue resis­tance	втомна стійкість
11.	frictional qualities	якості тертя
12.	hardness	твердість
13.	heat-treatment	тепло обробка
14.	machinability	здатність до обробки
15.	physical characteristics	фізичні характеристики
16.	quenching	закалювання
17.	shearing	нарізання
18.	shock resistance	ударопрочність
19.	specimen	зразок, примірник
20.	stiffness	жорсткість
21.	tensile	розрив, розтягнення
22.	tempering	відпуск, пом’якшення
23.	torsion	кручення
24.	toughness	пружний, гнучкий
25.	wear re­sistance	зносостійкість

Lesson 10.