Properties of Engineering Materials

Properties of engineering materials are known to affect manufacture and application of them. While using engineering materials we must know their physical characteristics. All engineering materials have definite characteristics which determine their abilities to assume external loads because of which materials change their shape. Metals are known to be subjected to the influence of external forces when they are treated. These forces are called “loads” and may have different characteristics: according to their value they may be small or large; according to the duration and character of their action they may be constant or impact. According to the influence of the load upon the metal causing different changes of its shape, loads are distinguished as compression, tensile, torsional, shearing and bending ones. By testing a metal under a load one can define what mechanical properties it has. In other words, one can determine strength, elasticity, plasticity, hardness and other properties of the metal. In order to have a clear conception of the metal properties it is subjected to tests on special devices and machines. The determination of these properties is made in the laboratory using a specimen of the metal to be tested.

Strength is the property of hard materials to be subjected to the influence of external forces without incurring damage and without changing their shape. The ultimate tensile strength of a material is that unit stress developed in the material by maximum slowly applied load that the material can resist without rupturing in a tensile test. A stress is stated to be a force within a body which resists deformation due to an externally applied load. If this load acts upon a surface of unit area, it is called “a unit force”, and the stress resisting it is called “a unit stress”. An external force acting upon an elastic material, the material is deformed and the deformation is in proportion to the load. This distortion or deformation is called “strain”.

Special machines, called “rupture machines”, are used to test metals for strength. When testing a specimen, the upper clamp remains fixed and the lower one is being slowly lowered, thus causing the extension of the specimen. The load upon the specimen may be easily determined at any moment by means of pointer indications of the dial.

Elasticity is the ability of a material to change its shape under the influence of external loads and return to its original form upon removal of the loads. All materials are elastic but the range of elasticity varies for different materials. Elasticity is evaluated by means of the modulus of elasticity. The modulus of elasticity is considered to be the ratio of the unit stress to the unit deformation within the proportional limit of the material to be tested. A rupture machine may be used to determine the elasticity of metals.

Plasticity is that property of a material when under the influence of loads, specimens of different materials may elongate while their cross-section decreases. Plasticity is the opposite of elasticity. So, plasticity is the ability of material to change its form without breaking under the influence of load and preserve this changed form after removal of the load. For determining the plasticity of metals a rupture machine may be used too.

Hardness is the property to resist deformation under applied load. Hardness is the most important mechanical property of metals.

Language study

1. Make the nouns from the following verbs:

to compress, to develop, to determine, to extend, to remove, to evaluate, to deform, to penetrate, to resist, to indicate, to manufacture, to apply.

2. Make the adjectives from the following verbs:

to differ, to resist, to extend, to define, to consider.

3. Give the synonyms to the following words:

to affect, to define, various, power, application, transforming, to apply, to treat.

4. Give the antonyms to the following words:

indefinite, internal, large, constant, upper, soft.

5. Find the sentences with the Complex Objects and Complex Subjects in the text and translate them into Ukrainian.

6. Read the sentences with the Complex Subject and translate them into Ukrainian

1. The American delegation is believed to come at the end of the year.

2. The lecture was said to be interesting.

3. The members of the committee are reported to have come to an agreement.

4. Our institute is considered to be the best in the town.

5. A computer centre is expected to be installed at our institute.

6. Young engineers are now expected to use high-speed digital computers.

7. Our students seem to know English well.

8. He proved to be a good teacher of the Ukrainian language.

9. We are sure to take part in the research.

10. We are lucky to complete the research in time.