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resistance properties of the material, or, as they say, its sensitivity
to stress concentration. Effect of stress concentration on the
fatigue strength into account by using the effective or actual,
stress concentration factor, which is determined experimentally

 
k   1 або k   1 , (6.6)
 
 
 1k  1k
where  ,  – border endurance laboratory sample without
 1  1
hub;  ,  – border endurance issued hub.
 1k  1k
In the absence of experimental data, we can use the theoretical
concentration factor

  max , (6.7)


where  – stresses determined by methods of the theory of
max
elasticity and  – methods of strength of materials (i.e.,
excluding the hub).
Effective concentration ratio k is almost always less than the

theoretical  . Reducing the effect of concentration due to actual

material properties estimated coefficient of sensitivity q :
k  1
q   . (6.8)
  1

The higher limit of the strength of the metal, the greater q (for
0
carbon steel q  0,6 0,8 , for high q 1 ; iron for q  ; i.e.
coarse material q is less than the fine). Knowing the value q ,
you can set the ratio between k і  :
 

k  1  q   . (6.9)
 1
 
Sample size (scale factor). Limit of endurance decreases with
increasing sample size. This is because at larger sizes increases
the likelihood of various internal defects. In addition, the
processing details of the surface layer increases, and this
strengthening is relatively greater for smaller sample.

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