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Impact strength a is defined as the work A , spent on
fracture specimen bending the shock referred to the working area
its cross section F

A P h  h 2 
1
a   . (7.29)
F F
The higher the value a , the better the material resists
impact.
The magnitude of the impact strength is significantly
affected by temperature, which decreases a with the decrease,
sometimes very dramatically. Also a significant impact on the
value of toughness with residual stresses which may occur in the
surface layers of the material under mechanical or thermo-
chemical processing, chemical composition of steels (especially
increasing the number of carbon and phosphorus), which should
be kept in mind when designing structures.

7.3 Fluctuations of systems with one degree of freedom

Elastic systems experiencing vibrations are separated by a
number of degrees of freedom. The number of degrees of freedom
is the number of independent coordinates that define the position
of mass. Strictly speaking, the real elastic system is always
infinite number of degrees of freedom. The study of oscillations
of systems with distributed masses can be simplified if we replace
the real system design model, which take into account only the
mass transport applied to the system, and the masses of the
elements of neglect or reduce them also lumped masses. Then the
degree of freedom of the system is determined only by the
coordinates of the center of mass concentrated in some of its
locations.
The possibility of replacing the actual system design model
must be clarified in each case based on the specific terms of this
problem. The final criterion of admissibility or inadmissibility
adopted calculation scheme is its experimental verification.
Depending on the nature of the forces that support
oscillations we distinguish free and forced vibrations. The free

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