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N
  x , (2.7)
o  1 
br   sin 2  
 2 

where  - the angle of the face side of the rod;  - the angle
between the fiber and the axis of the rod; r - the radius of the
cylindrical surface of the rod.
At a low stress angle  value obtained by the formula (2.5) is
close to the truth.
N N
  x  x .
A 2 b r tg

For example, if   12  , then the error does not exceed 2%.

2.4 Longitudinal and cross deformations

Consider a rod of a rectangular cross section (fig.2.6). Under
the influence of tensile forces the rod is deforming. Its length is
increasing, and cross sections are reducing.

Figure 2.6

The value l  l l  is called absolute extension of a rod or
0
absolute longitudinal deformation.

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