The equation of the second portion of the fatigue fracture kinetic diagram for various additional load ratios

The second portion of the fatigue fracture kinetic diagram is described by a reliable equation with additional load ratios R in the case of the crack-tip closure effect and by the Forman equation for the values of load ratio R^* in the case without the crack closure effect. We have obtained the analytical dependence of the effective range of the stress intensity factor ΔK_eff on the nominal range ΔK_R for the first part of the second portion of the fatigue fracture kinetic diagram (ΔK_1-2,R≤ΔK_R≤ΔK_fcl,R) with various load ratios. Institute of Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 2, pp. 75–80, March–April, 2000.