2.16. Read and translate the following text. Talk about the properties of engineering materials in your own words.

Vocabulary

determine v	—	устанавливать, определять
girder n	—	балка
durability n	—	долговечность
density n	—	плотность
specific weight	—	удельный вес
amount n	—	количество, величина
alloy n	—	cплав
stiffness (rigidity) n	—	жесткость
malleability n	—	ковкость, пластичность
roll v	—	прокатывать
copper n	—	медь
strength n	—	прочность
yield strength	—	предел текучести
ductility n	—	пластичность
ability n	—	способность
advantage n	—	преимущество
draw v	—	волочить
fracture v, n	—	ломаться, излом
absorb v	—	поглощать
toughness n	—	1. вязкость 2. жесткость, прочность, крепость
tensile strength	—	предел прочности на растяжение
scratch v , n	—	царапать, царапина
composite n	—	композит, композитный материал
Constituent a	—	образующий, составляющий
fiberglass n	—	стекловолокно
hardness n	—	твердость
Indentation n	—	вдавливание
creep resistance	—	сопротивление ползучести

Engineering materials and their properties (Part II)

It is important to know the properties of engineering materials for they determine their use. For example, steel is used for making girders because it is an elastic material. Under normal conditions, glass shows high durability and so do plastics. A durable material does not corrode easily. Among the metals, chromium is extremely durable and so is platinum. Gold is quite durable. Cast iron is not very durable and nor is steel.

In any application where the material must not be heavy its density is important. Density (specific weight) is the amount of mass in a unit volume. The density of water is 1000kg/m³ but most materials have a higher density and sink in water. Steels, which have typical densities of 7800kg/m³, are considerably denser than aluminium alloys with densities of 2800kg/m³.

Stiffness (rigidity) is a measure of the resistance to deformation such as stretching or bending. Stiffness is important when a rigid structure is to be made. The opposite of stiffness is malleability. It is possible to roll gold into very thin sheets because gold is extremely malleable. Copper and lead are also malleable. Cast iron is not at all _malleable.

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 (meganewton per square metre), but in this case the deformation is irreversible. The yield strength is the stress at which a material first deforms plastically. 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 required. Aluminium and copper are very ductile, and it is easy to draw them. Steel is not very ductile and nor is lead. It is very difficult to draw lead into thin wire because it fractures easily. Materials that are not ductile are brittle. Ductile materials can absorb energy by deformation but brittle ones cannot.

Toughness is the resistance of a material to breaking when there is a crack in it. Toughness is different from strength: the toughest steels, for example, are different from the ones with the highest tensile strength. Brittle materials have low toughness: glass can be broken along a chosen line by 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.

Hardness may be defined as the resistance of a material to deformation, particularly permanent distortion, by indentation or scratching.

Creep resistance is the resistance to a gradual permanent change of shape, and it becomes especially important at higher temperatures.

2.17. Add one more sentence to each one below the picture to make a conclusion.

Example: (a) This material is hard. You cannot pierce it.

This material is hard.

This material is tough.

This material is flexible.

This material is combustible.

This material is soft.

This material is brittle.

This material is rigid.

This material is non-combustible.

2.18. Name at least three materials for each sentence.

Example: (a) Paper, wood and oil.

(a) You can burn it.	(e) It is non-combustible.
(b) It is brittle.	(f) You can bend it easily.
(c) You cannot scratch it easily.	(g) It is very hard.
(d) It is very tough.	(h) It is rigid.

2.19. Find the English equivalents to the following words and word combinations.

в высшей степени чугун упругая деформация подверженный растягивающее напряжение внешняя сила первоначальная форма долговечный материал циклическое напряжение ковкий материал

а) durable material b) cast iron c) malleable material d) cyclic stress e) original shape f) subjected (to) g) external force h) elastic deformation i) tensile stress j) extremely

2.20. Form the adjectives from the following nouns:

malleability, ductility, elasticity, brittleness, toughness, stiffness, hardness, refractoriness, corrodibility, strength

Notes

refractoriness n – огнеупорность, тугоплавкость

corrodibility n – способность подвергаться коррозии

2.21. Complete descriptions 1– 4 with the words from the verb list according to the model.

break, change, regain, withstand

Model: The opposite of durable is corrodible.

A corrodible material does not withstand corrosion well.

1. The opposite of hard is soft. A soft material … abrasion well.

2. The opposite of elastic is ductile. A ductile material … its shape easily.

3. The opposite of malleable is stiff. A stiff material … its shape easily.

4. The opposite of brittle is tough. A tough material … easily.

Notes

withstand v – противостоять, сопротивляться

abrasion n – истирание

2.22. Match each property in column a with an appropriate expression from column b. Make sentences according to the model.

Model: Flexibility of a material means that it will bend easily.

a	b
1. softness	a) will not bend easily
2. rigidity	b) will resist abrasion, deformation and indentation
3. plasticity	c) will resist wear
4. elasticity	d) will regain its original dimensions after the forces which have caused deformation are removed
5. brittleness	e) will bend easily
6. flexibility	f) will tend to fracture under impact loads
7. toughness	g) will not return its original dimensions after the forces which have caused deformation are removed
8. corrodibility	h) will not fracture when indented or scratched
9. corrosion resistance	i) will resist fracture when subjected to an impact load
10. hardness	j) will resist corrosion
11. wear resistance	k) will withstand tension
12. tensile strength	l) will not withstand corrosion well

Notes

bend v – гнуть, сгибаться

corrosion resistance – коррозионная стойкость

wear resistance – износостойкость

_{2.23. Examine the table and make sentences according to models a and b. In model b to speak about similar properties of metals, you will have to use so in positive and nor in negative sentences. After these words (and some others) you should put an auxiliary verb before the subject, that is, use inversion.}

Metal	Malleability	Ductility	Durability
Copper	****	*****	****
Aluminium	***	*****	***
Tin	****	****	****
Nickel	***	***	***
Cast iron	*	*	**
Lead	****	**	***
Steel	***	**	**
Chromium	***	***	*****
Zinc	****	***	****
Brass	***	***	****
Bronze	***	***	*****

_***** – extremely, _**** – very, _*** – quite

_** – not very, _* – not at all

_{a) Model:}

1. _{Copper is very malleable and durable, and it is extremely ductile.}

2. _{Lead is very malleable and quite durable but it is not very ductile.}

3. _{Cast iron is not very durable, and not at all malleable and ductile.}

_{b) Model:}

_{1. Malleability: copper and lead.}

_{Copper is very malleable and so is lead.}

_{2. Ductility: glass and cast iron.}

_{Glass is not at all ductile and nor is cast iron.}

_{Ductility: aluminium and tin; steel and lead.}

_{Malleability: copper and zinc; bronze and brass.}

_{Durability: steel and cast iron.}

2.24. Test yourself. Choose the best answers from a­–d for the questions in the tests below.