Fergana polytechnic insitute mechanical engineering faculty department of mechanical engineering and automation

Corrosion of metals. 
Plastic deformation of metals is an extremely important property, because metal 
pressure processing (rolling, hammering, etc.) is based on the metal's plasticity. In 
addition, the plasticity of metals is of great importance for the careful (reliable) 
operation of structures and details made of them. 
the voltage acting on the object reaches the value 

v 
, the object collapses. Plastic 
metals are viscous, brittle metals are brittle. Normal stresses lead to brittle failure and 
tangential stresses lead to viscous failure. 
Plastic deformation breaks the crystal lattice of the metal, changes its shape and 
creates a number of structural defects. Metal grains are deformed and texture is formed. 
Dislocations strongly influence the strength properties of a metal.
Under the influence of plastic deformation, the metal is refined, its strength and 
hardness increase, and its plasticity decreases. Such a phenomenon is called rivet 
(naklen, nagartovka). Plastic deformation causes the metal to increase its internal 
energy and generate internal stresses. 
The metal grains are deformed and a special deformation texture is created. At 
the same time, especially linear defects increase as the degree of deformation increases. 
Discretions have a strong influence on the strength properties of the metal. The figure 
shows the effect of disclacations on the strength of the metal. When the number of 
dislocations is small, the metal deforms well and its strength decreases. 
As the density of dislocations increases above a certain value, the number of 
dislocations increases to such an extent that they begin to interfere with each other as 
a result of movement, and this phenomenon leads to the strengthening of the metal. 
According to the research of SS Steinberg, approximately 90% of the energy 
spent on deformation of metal is released in the form of heat energy, and 10% creates 
internal stresses in the metal. 

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34 
According to the classification of NN Davidenkov, these internal stresses are 
divided into three types: first, second and third type stresses. The first type of stress is 
balanced in macro-sizes, the second type of stress is balanced in micro-size (grain, 
block), the third type of stress is balanced in the size of crystal lattices. 
Plastically deformed metal is in an unstable state, because changes in it increase 
its internal energy. Spontaneous events occur that cause the metal to transition to a 
stable state. A rise in temperature increases these phenomena. New grains begin to 
grow instead of deformed grains. Such a phenomenon is called recrystallization. 
The recrystallization temperature depends on the purity of the metal and is 
determined by the following formula. 
𝜏
𝑟𝑒𝑘
= 𝛼𝜏
𝑠
here 
𝛼
-coefficient, for pure metals 
𝛼
=0.1-0.4; 0.6-0.84 for solid solutions; 

s 
- 
metal liquid temperature. 
The phenomenon of recrystallization also 

consists of the appearance and 
growth of t 
rec crystallization nuclei. 
The properties of the recrystallized metal return to their 
original values: plastic properties increase, strength properties decrease. 
The practical significance of the recrystallization temperature is very great. A 
recrystallization annealing heat treatment is used to remove the nick. Working of metal 
under hot pressure is also determined by this temperature. 
Mechanical properties are determined by the nature of the pressure applied 
during the testing of metals: static, dynamic and repeated-variable pressures. 
All mechanical tests are standardized to obtain comparable results. When 
determining the properties of materials under the influence of various pressures, their 
properties in stretching, compression, twisting, bending, fatigue and other tests are 
determined. 
Regardless of the applied load, the external force produces normal and tangential 
stresses in the specimen. Tangential stresses produce plastic deformation in the sample 
and cause brittle fracture . Normal stresses cause the metal to undergo elastic 
deformation and brittle fracture. 
The 

resulting 

max 
in the sample
is called the loading unit with respect to 

max :

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35 

= 

max 
/ 

max 
the load is unique 

( if 
G
max 
is greater), the more loads are loaded. 
The engineer obtains information about the mechanical properties of materials 
from spravochniks . To use this information wisely, the requirement is to understand 
the content of mechanical tests.