Mechanical properties of metals and alloys

Materials possess a lot of properties, including the following: mechanical properties, chemical properties, electrical properties, thermal properties, optical properties, magnetic properties. The properties of a material determine its usability and, consequently, its engineering application. The mechanical properties are of great importance in industrial applications of metals so they require much attention in their study.

Strength. - The strength of a material is the property of resistance to external loads or stresses without incurring structural damage. The term ultimate strength refers to the unit stress (pounds per square inch) developed in the material by the maximum slowly applied load that the material can resist without rupturing in a tensile test. The tensile test is the one most often applied to metals because it tells so much more about their properties than any other single test. In metallurgy, breaking is often spoken of as failure, or rupture, or fracture; the fracture of a metal is the name given to the surface across which the break has occurred. The strength of metals and alloys depends upon two factors, namely, the strength of the crystals of which the metals are constructed and the strength of adherence between these crystals.

Stress and Strain. - A stress is the 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 a unit stress. Quantitatively, then, stress is a force per unit area; on the European continent it is expressed in kilograms per square millimeter, in the United States, pounds per square inch.

When an external force acts upon an elastic material, the material is deformed and the deformation is in proportion to the load. This deformation is strain, and unit strain is measured in the United States in inches per inch, while in Europe it is measured in centimeters per centimeter. Unit strain, then is a ratio of distances or lengths.

Elasticity. - Any material subjected to an external load is distorted or strained. Elastically stressed materials return to their original dimen­sions when the load is released if the load is not too great. Such distortion or deformation is in proportion to the amount of the load up to a certain point, but when the load is too great the material is permanently deform­ed, and when the load is increased further to a certain point the material breaks. The property of regaining the original dimensions upon removal of the external load is known as elasticity.

(to be continued)

Find gerunds in the text and comment on their use.

6. Complete the phrases from the text:

1 The strength of a material is the property of…

2 A stress is the force within a body which …

3 Strain is …

4 Unit strain is a ratio of …

5 Elasticity is …

7. Answer the questions:

What properties do materials have?

What is a unit stress? Hw is it different from a unit force?

What test is most frequently applied to describe metals? Why?

How is breaking often spoken of in metallurgy? What is the difference between the terms?

How is stress quantitatively expressed in Europe and in the US?

Read the text and choose the best title for it.

1 The limit of elasticity

2 The modulus of elasticity

3 A constant property of steel

Make sure that you know the following words and word combinations:

stiffness – жесткость

hot working – горячая обработка; горячая деформация

cold working - холодная обработка; холодная деформация

 

Text B.

Within the limit of elasticity the ratio of stress to strain is known as the modulus of elasticity (i. e. measure of elasticity). The modulus of elasticity expresses the stiffness of a material. For steel and most metals this is a constant property very little affected by heat-treatment, hot or cold working, or the actual ultimate strength of the metal. Their moduli of elasticity show that, when equal-size bars of steel and aluminium are subjected to the same load, the resulting elastic deformation in the aluminum will be almost three times as great as in the steel bar.

Subsection B

1. Learn the words:

stress-strain curve	кривая напряжение - деформация
to decrease	уменьшать
mild steel	мягкая сталь
normalized steel	нормализованная сталь
specimen	образец
to support	поддерживать
cross-sectional area	площадь поперечного сечения
tensile strength	прочность на разрыв
a piece	деталь
ductility	вязкость
yield point	предел текучести
capacity	способность; возможность; качество
to denote	означать
obviously	очевидно
elongation	удлинение
reduction of area	уменьшение площади поперечного сечения (при обработке изделия)
value	значение; величина
tension test	испытание на растяжение/разрыв
gradually	постепенно
impact test	испытание на удар
malleability	ковкость; пластичность
to permit	разрешать
to roll	прокатывать
to hammer	ковать
a thin sheet	тонкий лист (металла)
lead	свинец
tin	олово
to lack	не хватать
to be drawn	волочить (о проволоке)
brittleness	хрупкость
fatigue failure	усталостное разрушение
tension	напряжение; растяжение
indentation	отпечаток (при испытании на твердость)
to scratch	царапать

2. Guess the meaning of the words and word combinations:

visible, permanent, reverse, elastic limit, opposite, term,, to confuse, synonymously, alternation, to produce, compression, statically; cold-worked steel

3. Identify the part of speech and translate the words:

Repeat, repetition, repeated; alternation, to alternate, alternating; to produce, production, productive, productivity, product, producer.