Goodman fatigue equation

The Goodman fatigue equation is used by engineers for fatigue analysis. The equation is used to make correlations of experimental fatigue data of metals and other materials. The Goodman fatigue equation is also used to determine the failure mecahnisms of sucker rods in pumping oil wells world wide, and to help design new sucker rod strings for rod-pumped oil wells.

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From similar triangles the Goodman fatigue equation is :

( 4a) τm /Sus + τa /Ses = 1/n in which the stress components are given by

                                     τm   =   Ks 8 FmC / πd2     where   Fm   =   ( Fhi + Flo ) /2     and 
                                     τa   =   Kh 8 Fa C / πd2     where   Fa   =   ( Fhi - Flo ) /2