Unit 4 Ductility and Brittleness

1. Pronounce the words correctly:

brittleness; extrusion; rupture; ductile; annealed; yield; strain; barrel; fibrous; magnesium, appreciable, exceed, iron, subsequent.

2. Memorize the following terminological words:

ductility	- эластичность
ductile	- эластичный
brittleness	- хрупкость
drawing	- волочение, протяжка
bending	- гибкая
cross-sectional area	- зона поперечного сечения
extrusion	- выталкивание, вытеснение
rupture	- разрыв, пролом
anneal	- отжигать, прокалывать, обжигать
yield	- текучесть (металла)
strain	- натяжение, растяжение, (тех.) деформация
barrel	- баррель (мера жидких, сыпучих тел)
fibrous	- волокнистый, жилистый

3. Read and translate the text. Ductility and Brittleness

The ability of material to acquire large permanent deformations without fracture is known as ductility. The property of ductility is of prime importance in such processes as extrusion, drawing, bending, etc. The measure of ductility is the percentage elongation at rupture. Highly ductile materials include annealed copper, aluminium, brass, low-carbon steel, etc. Duration and bronze are less ductile. Slightly ductile materials include many alloy steel.

A property opposite to ductility is brittleness, i.e., the ability of a material to fracture without any appreciable permanent deformation. Materials possessing this property are called brittle. For such materials, the amount of elongation at rupture does not exceed 2 to 5 per cent, and in some cases it is expressed by a fracture of one per cent. Brittle materials include cast iron, high carbon tool steel, brick, stone, etc. The tension test diagram for brittle materials has no yield point or strain zone.

Ductile and brittle materials behave differently in compression tests as well. As already mentioned, the compression test is conducted on short cylindrical specimens, placed between parallel plates. On the yield point can be observed with subsequent transition to the zone of strain hardening. However the load does not fall, as in tension, but increases abruptly. This is due to the fact that the cross-sectional area of the compressed specimen increases; the specimen takes a barrel-like shape due to friction at the ends. It is practically impossible to bring the specimen of a ductile material to fracture. The test cylinder is compressed into a thin desk and testing is limited by the capacity of the machine. Hence, the ultimate compressive strength cannot be found for materials of this kind.

Brittle materials behave in a different way in compression tests.

There are materials that are capable of sustaining larger loads in tension than in compression. These are generally materials having fibrous structure, such as wood and various plastics. Some metals as magnesium possess thus property.

This division of materials into ductile and brittle is purely conventional not only because there is no sharp dividing line between them as regards the index. Many brittle materials as brittle, depending on the conditions of testing.

4. Find all the words with –s endings in the text. Explain their origin.

5. Form the degrees of comparison of the adjectives:

large, permanent, great, slight, short, conventional

6. Translate the sentences into English using the following constructions:

as…as

twice as…as

three times as…as

Этот материал в два раза прочнее, чем тот материал.

Эта балка в три раза длиннее, чем та.

Продолжительность этого процесса такая же, как и того процесса.

Величина этой константы в пять раз больше, чем той константы.

Результат этого эксперимента так же важен, как и того эксперимента.

Объем этой машины в два раза меньше, чем объем той машины.

7. Correct the mistakes. Each word has one mistake. Write the words correctly.

Coper, aluminum, pemanent, posessing, brittl, yielde, speciman, prorperty.

8. State if the following statements correspond to the content of the text:

1. The ability of material to acquire large permanent deformation with the fracture is known as ductility.

2. The measure of ductility is the percentage elongation at rupture.

3. A property opposite to ductility is brittleness.

4. Ductile and brittle materials behave similarly in compression tests.

5. The division of materials into ductile and brittle is conventional for the science.

9. Translate into English:

1. Очень большое влияние на проявление свойств пластичности и хрупкости оказывают скорость нагружения и температура.

2. При быстром нагружении более резко проявляется свойство хрупкости, а при медленном – свойство пластичности.

3. Хрупкое стекло способно при длительном воздействии нагрузки при нормальной температуре получать остаточные деформации.

4. Пластичные же материалы, такие как малоуглеродистая сталь, под воздействием резкой ударной нагрузки проявляют хрупкие свойства.

5. Одной из основных технологических операций, позволяющих изменять в нужном направлении свойства материала, является термообработка.

6. Испытание образцов на растяжение-сжатие дает объективную оценку свойств материала.

7. У пластичных материалов прочностные характеристики на растяжение и сжатие сопоставляют по пределу текучести.

8. В отличие от растяжения, результаты испытания оказываются зависящими от формы поперечного сечения.