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MECHANICAL PROPERTIES of MATERIALS

Materials Science and Technology is the study of ma­terials and how they can be fabricated to meet the needs of modern technology. Using the laboratory techniques and knowledge of physics, chemistry, and metallurgy, scientists are finding new ways of using metals, plastics and other materials.

Engineers must know how materials respond to exter­nal forces, such as tension, compression, torsion, bend­ing, and shear. All materials respond to these forces by elastic deformation. That is, the materials return their original size and form when the external force disap­pears. The materials may also have permanent deforma­tion or they may fracture. The results of external forces are creep and fatigue.

Compression is a pressure causing a decrease in vol­ume. When a material is subjected to a bending, shear­ing, or torsion (twisting) force, both tensile and compressive forces are simultaneously at work. When a metal bar is bent, one side of it is stretched and subjected to a tensional force, and the other side is compressed.

Tension is a pulling force; for example, the force in a cable holding a weight. Under tension, a material usu­ally stretches, returning to its original length if the force does not exceed the material's elastic limit. Under larger tensions, the material does not return completely to its original condition, and under greater forces the mate­rial ruptures.

Fatigue is the growth of cracks under stress. It oc­curs when a mechanical part is subjected to a repeated or cyclic stress, such as vibration. Even when the maximum stress never exceeds the elastic limit, failure of the ma­terial can occur even after a short time. No deformation is seen during fatigue, but small localized cracks develop and propagate through the material until the remain­ing cross-sectional area cannot support the maximum stress of the cyclic force. Knowledge of tensile stress, elastic limits, and the resistance of materials to creep and fatigue are of basic importance in engineering.

Creep is a slow, permanent deformation that results from a steady force acting on a material. Materials at high temperatures usually suffer from this deformation. The gradual loosening of bolts and the deformation of components of machines and engines are all the exam­ples of creep. In many cases the slow deformation stops because deformation eliminates the force causing the creep. Creep extended over a long time finally leads to the rupture of the material.

Переведите следующие словосочетания:

1. отвечать требованиям современной технологии (meet the needs of modern technology)

2. используя лабораторные методы (Using the laboratory techniques)

3. новые способы использования металлов (new ways of using metals)

4. сжатие, растяжение, изгиб, кручение, срез (compression, tension, bend­ing, torsion, shear)

5. возвращать первоначальный размер и форму (return original size and form)

6. внешняя сила (external force)

7. постоянная деформация (permanent deforma ­ tion)

8. уменьшение объема (decrease in vol­ume)

9. растягивающие и сжимающие силы (tensile and compressive forces)

10. превышать предел упругости материала (exceed the material's elastic limit)

11. повторяющиеся циклические напряжения (repeated or cyclic stress)

12. разрушение материала (failure of the ma­terial)

13. развитие и распространение мелких трещин (small localized cracks develop and propagate)

14. сопротивление материалов ползучести и устало­сти (resistance of materials to creep and fatigue)

Тема № 8 Электрическая цепь

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https://en.wikipedia.org/wiki/Circuit_diagram

Essay

According to GOST 2.701-2008, a schematic diagram is defined as “a scheme defining the full composition of elements and connections between them and, as a rule, giving a detailed idea of ​​the principles of operation of the product”.

The electrical elements in the diagram are depicted by conventional symbols, the outline and dimensions of which are established in the ESKD and / or IEC standards or based on them. If necessary, apply non-standardized symbols. Usually, they are explained in the free field of the scheme.

All the elements and devices shown in the diagram are assigned conditional alphanumeric reference designations.

Data on the elements and devices shown in the product diagram is recorded in the list of elements. The connection between conventional graphic symbols and the list of elements is carried out through reference designations.

Grammar Exercise

Порядок слов в предложении

Выберите правильный порядок слов в предложении:

1.