Part 1. Learning the vocabulary

 

1. Pronounce the following words correctly:

Amorphous; crystalline; viscous; fluid; polycrystalline; lattice; repulsion; linear; quantum; row; oscillatory.

 

2. Memorise the following words:

solid	- твердое тело
randomly	- случайно, беспорядочно
lattice	- решетка
mutual attraction	- взаимное притяжение
repulsion	- отталкивание
linear	- линейный
quantum	- количество, сумма, доля часть, квант
overall	- полный, общий
oscillatory	- колебательный
distortion	- искажение, искривление
intracrystalline	- внутрикристаллический
tension test	- тест на растяжение
molecular structure	- строение молекулы
amorphous	- аморфный
crystalline	- кристаллический
viscous fluid	- вязкая жидкость
rolling	- прокатка
drawing	- протяжка, волочение
property	- качество, свойство
plastic deformations	- пластическая деформация
zone of general yielding	- зона текучести
strain hardening	- деформационное упрочнение
specimen	- образец
slip bands	- кромка ползучести
axis	- ось
shearing stress	- касательное напряжение
plane	- плоскость
magnitude	- величина, размеры
elastic deformation	- упругая деформация

 

Part 2. Translation practice

Выполните следующие предтекстовые задания:

Прочитайте текст 1.

В каждом предложении найдите подлежащее и сказуемое.

Найдите группы зависимых от них слов (второстепенные члены предложения).

4. Переведите все незнакомые слова. Выпишите термины в словарь и найдите их значение по словарю.

Определите, к какой предметной области относится этот текст.

Сделайте письменный перевод текста. Перечитайте текст и отредактируйте его (уберите повторы слов; избегайте смещения логического ударения, поэтому главную мысль помещайте в конец предложения; переводите цепочки из существительных справа налево, способом смыслового развертывания).

Помните, что особенности грамматики научно-технического текста состоят в следующем:

• В научном тексте при переводе нередко прибегают к замене пассивных конструкций иными средствами выражения, более свойственными русскому языку: предложение «This question was discussed at the conference» можно перевести следующими способами:

Этот вопрос был обсужден на конференции.

Этот вопрос обсуждался на конференции.

Этот вопрос обсуждали на конференции.

Конференция обсудила этот вопрос.

• Для научно-технического текста характерны безличные и неопределенно-личные конструкции (it was decided, it has been found expedient, it is to be noted, it is necessary, it is important, care must be taken).

 

Text 1

Deformation Mechanism

So far when speaking of tension tests, we have been concerned upon the internal processes taking place in the material. At the same time the nature of variation of the force P as a function of 1 admits of a physical interpretation on the basis of the concepts of molecular structures of solids.

Solids are divided into amorphous and crystalline ones. So far as the former are concerned the tension test diagram of such solids is not of a stable nature: it depends to a considerable extent on the duration of applied loads and the materials themselves exhibit in their behavior a analitative similarity to a viscous fluid. Therefore we shall discuss only the mechanism of deformation of metals.

All metals, as employed in mechanical engineering, have a polycrystalline structure, i.e. they are composed of a large number of small irregular crystals randomly arranged within the volume of the metal. In some cases crystals have an insignificant orientation depending on the nature of the process (rolling, drawing). Metal atoms are arranged in a definite order within crystals and form a regular space lattice. The arrangement of the atoms depends on their properties. It also changes with variation of the physical properties. It also changes with variation of the physical conditions of crystallization.

There exist constant forces of interaction between atoms of a crystal lattice. When the distance between two atoms is large forces of mutual attraction come into play, and when the distance is small, forces of repulsion. The presence of these forces and the laws of their variation for different directions and distances determine the system of crystallization peculiar to a given metal. For a free, unloaded crystal the system of these forces is as strictly defined as the arrangement of the atoms themselves.

If external forces are applied to a crystal the atoms in the lattice undergo mutual displacement and the forces of interaction between them change. The relation between the forces of interaction and displacements is of a complex functional nature. Within small displacements however, this relation may be regarded as different relations for a large number of randomly oriented crystals result integrally in a proportional relation between displacements of points in a body and external forces, which finds its expression in Hooke’s law.

Consider now the process of development of plastic deformations, experiments show that plastic deformations are caused by distortions in crystal lattice. In the zone of general yielding and strain hardening occur the surface of the specimen is covered by a system of fine lines, known as slip bands. These lines have preferential directions making an angle close to 45 degrees with the axis of the bar and are practically coincident with the planes of maximum shearing stresses.

As a result of sliding down inclined planes the bar is elongated. The actual picture is more complicated as it is of a three-dimensional character and the shear takes place not only in a single family of parallel planes, but generally in all families of planes making an angle close to 45 degrees with the axis of the bar.

Within a single plastic deformations are caused by the displacements of part of the crystal down a plane by a whole number of elements of the lattice. The minimum plastic deformation corresponds to the displacement by one element. This is a sort of quantum of plastic deformation. As a result of this displacement each proceeding atom takes the place of the successive atom with the result that all atoms are ultimately found to be in the positions characteristic of a given crystal structure, consequently, the crystal retains its properties and only changes the outward configuration.

The forces of interaction between the atoms of a crystal lattice can be found by the methods of solid state physics from the analysis of the crystal structure. If, the magnitude of shearing forces necessary to produce plastic deformations is expressed in terms of the forces of interaction, the stress evaluated is found to be thousands of times greater than the stress observed in tests with crystals.

This process can be illustrated by the simple model. There is a row of vertically places bars on a rigid plane. If their number were large, an appreciable overall force would obviously be required to knock down all the bars simultaneously. It is sufficient, however, to push me extreme bar. Then a wave of collisions will pass through the row and a considerable part of the bars will be floored. A similar situation is observed in crystals. A local overloading of any of the cells usually plays the role of an initial exciter in the lattice. Such an overloading is always possible owing to an irregular shape of the crystal or some of its structural imperfections.

The passage of an atom to a new position is accompanied by dynamic effects. The atom acquires kinetic energy and performs an oscillatory motion about the new equilibrium position. Thus heat is generated: the specimen becomes noticeably heated during plastic deformation.

In metals the development of plastic deformations begins at relatively small loads. Among a large number of randomly arranged crystals there are always some least favorably oriented and having internal defects which make plastic changes possible at relatively small forces within the elastic zone. The number of such crystals is not, however, large and local plastic deformations do not materially affect the general linear relation between force and displacement characteristic of the first stage of loading.

As a result of the application of external forces to the specimen the atoms in the crystals are displaced not only by a whole number of positions but some distortion of the crystal lattice also persists. Consequently elastic deformation as well as plastic is produced. Upon unloading the shape of the distorted lattice is recovered, i.e., the elastic deformation is relieved. The plastic deformation is not recovered.

It is important that the process of relieving elastic deformation follows the same laws of variation of intracrystalline forces as in the initial stage of loading. At considerable tensile forces plastic deformations are accompanied by the destruction of intercrystalline and interatomic bonds and the specimen fracture.

It is essential to not that the picture of development of plastic deformations outlined above retains its qualitative features for a body of any shape regardless of the laws of external force distribution. Hence, the linear relation between displacements are forces is characteristic within certain limits not only of a tensile specimen, but, as a rule, of any complex structure. The same is true of the law of unloading. The straight line of unloading in the test diagram for a structure.

Part 3. Speaking practice

1. Translate the words with -ward, -wards suffixes denoting direction:

Outward, forward, backward, afterward, downward, toward, northward(s), southward(s), rearward(s), homeward(s), sideward(s).