What are the external forces that cause the elastic deformation of materials? Describe those forces that change the form and size of materials.

What are the results of external forces?

What kinds of deformation are the combinations of tension and compression?

What is the result of tension? What happens if the

Elastic limit of material is exceeded under tension?

What do we call fatigue? When does it occur? What are the results of fatigue?

What do we call creep? When does this type of permanent deformation take place? Whataretheresultsofcreep?

Find the following  word combinations in

The text:

1.       отвечать требованиям современной технологии.

Используя лабораторные методы.

Новые способы использования металлов.

Сжатие, растяжение, изгиб, кручение, срез.

Возвращать первоначальный размер и форму.

Внешняя сила.

Постоянная деформация.

Уменьшение объема.

Растягивающие и сжимающие силы.

Превышать предел упругости материала.

Повторяющиеся циклические напряжения.

Разрушение материала.

Развитие и распространение мелких трещин.

Сопротивление материалов ползучести и усталости.

7.7. Translate into English the following sentences:

Упругая деформация — это реакция всех материалов на внешние силы, такие, как растяжение, сжатие, скручивание, изгиб и срез.

Усталость и ползучесть материалов являются результатом внешних сил.

Внешние силы вызывают постоянную деформацию и разрушение материала.

Растягивающие и сжимающие силы работают одновременно, когда мы изгибаем или скручиваем материал.

Растяжение материала выше предела его упругости дает постоянную деформацию или разрушение

TEXT 2

 PROPERTIES OF MATERIALS

Density (specific weight) is the amount of mass in a unit volume. It is measured in kilograms per cubic metre. The density of water is 1000 kg/m3 but most materials have a higher density and sink in water. Aluminium alloys, with typical densities around 2800 kg/m3 are considerably less dense than steels, which have typical densities around 7800 kg/m3. Density is important in any application where the material must not be heavy.

Stiffness (rigidity) is a measure of the resistance to deformation such as stretching or bending. The Young modulus is a measure of the resistance to simple stretching or compression* It is the ratio of the applied force per unit area (stress) to the fractional elastic deformation (strain). Stiffness is important when a rigid structure is to be made.

Strength is the force per unit area (stress) that a material can support without failing. The units are the same as those of stiffness, MM/m2, but in this case the deformation is irreversible. The yield strength is the stress at which a material first deforms plastically. For a metal the yield strength may be less than the fracture strength, which is the stress at which it breaks. Many t 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 needed, such as car body parts. Materials that are not ductile are brittle. Ductile materials can absorb energy by deformation but brittle materials cannot.

Toughness is the resistance of a material to breaking ■ when there is a crack in it. For a material of given toughness, the stress at which it will fail is inversely proportional to the square root of the size of the largest defect present. Toughness is different from strength; the toughest steels, for example, are different from the ones with highest tensile strengths Brittle materials have low toughness: glass can be broken along a chosen line by first 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.

Creep resistance is the resistance to a gradual permanent change of shape, and it becomes especially important at higher temperatures. A successful research has been made in materials for machine parts that operate at high temperatures and under high tensile forces without gradually extending, for example the parts of plane engines.

ДОПОЛНИТЕЛЬНЫЙСЛОВАРЬ;

ability [ a' biliti] способность absorb [ sb' zo: b] поглощать amount [ a' maunt] количество

application [,aepli'keijsn] применение brittle ['britl] хрупкий, ломкий

Car body кузовавтомобиля

constituent [кэп ' stitjuan t] компонент

crack [kraek] трещина creepresistance устойчивость к ползучести definition [,defTniJan] определение density ['densiti] плотность

ductility [dAk'tihti] ковкость, эластичность failure ['feiljs] повреждение, разрушение

gradualf'grasdjual] постепенный

rigid ['ri(%id] –жесткий. To sink  - тонуть.  squareroot[ skwea'rud]- квадратный корень

 stiffness [' stifnis] жесткость strain [ strein]- нагрузка, напряжение, деформация

strength [ strepG] прочность stress [ stres]- давление, напряжение