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Thus, we can impact on strength, rigidity and stability by
changing the nature of deformation or varying external, geometric
or physical factors.
Strength of materials is the science of engineering methods of
calculation of structural elements and machine parts for strength,
rigidity and stability. It examines the behavior of deformable solid
bodies in various types of loads.
Strength of materials is an experimental and theoretical science.
It uses the knowledge gained in the study of theoretical mechanics,
solid state physics, mathematics and science of materials. It is a
related science with more exact science – mechanics of deformable
solid body and, in its turn, serves as the basis for the study of many
engineering disciplines (fig.1.1).

1.2 The real object and computational model

Research of the real object begins with the choice of the
computational model. In the strength of materials we schematize:
material, geometry of calculating object, supporting fixing and
loading.

1.2.1 Model of the material

Physical model of the material is based on four hypotheses.
1) The material has a solid structure. This simplification allows
not taking into account the characteristics of atomic-molecular
structure of matter and applies mathematical tools of continuous
functions.
2) The material is homogeneous, i.e. all points have the same
properties. This simplification allows not taking into account the
features of the microstructure of the material (polycrystalline
structure, foreign inclusions, cracks, etc.).
3) The material is isotropic, i.e. has in all directions the same
properties. An individual crystal metal is anisotropic. However,
due to little grainy structure (many crystals are randomly) material
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