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 2 x  dQ
 2 Q 2 Q
 x dQ   , thence   2 .
Q 2g 2g  Q
As part of the technical effort theory assume that
 
x x
 ,
 
where  – static displacement of cross section at the point of
impact;  – the same for any cross section.
x
Finally we get

  2 x dQ   2 x dx
Q l (7.28)
   .
 2 Q  2 l
For example, for the rod, shown in fig. 7.3 we obtain

2 l
 Px  2
   dx  x dx
 EF  1
  l 2  0 3  .
 Pl  l 3
  l
 EF 
Analyzing the expression for the dynamic coefficients of
the different types of impact loading, we see that in order to
reduce stress we should seek to increase susceptibility of the rod,
which is achieved by increasing its length, the use of buffer
cushioning devices, replacing one material with another with a
lower modulus of elasticity. Comparing formulas (7.14) and
(7.27), we see that taking into account the mass of the rod reduces
the calculated stress at impact. This is mainly due to the loss of
kinetic energy of a falling load at inelastic impact.

7.2.6 Strength of materials on impact

Upon impact the large speed of loading makes the
formation and development of plastic deformation of the material

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