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     

t 

1
0
0
 Й    if   , а   .
eqv 1 3

       
3
c
Today in practical calculations the first theory of strength is
rarely used. It has a satisfactory convergence of experimental data
only for some brittle materials, provided that the absolute value of
one of the principal stresses is much greater than the absolute
values of the other principal stresses.
Recall that at the central tensile or compression the calculation
of strength should be done for major normal stresses, however this
does not mean that we use the first theory, it should be understood
that in this case there is a dangerous point linear stress state and
the calculation by any theory of strength will give the same result.
The second theory, or the theory of the largest linear
deformations, is the hypothesis that the strength of the material in
difficult stress state will be provided if the largest relative linear
deformation does not exceed the allowable determined in linear
stress state.
According to this theory the condition of strength, such as for
plastic material has the form

     ,
max
E
if    it is given by the generalized Hooke's law (3.25),
max 1
we obtain
 Й    (     )   . (3.34)

eqv 1 2 3
The second theory has satisfactory strength convergence with
experimental data only under certain stressful conditions for brittle
materials, so in the practice of engineering calculations is hardly
used.
The third theory, or the theory of the largest tangential stresses,
is the hypothesis that the strength of the material in difficult stress
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