Fatigue lives of 18G2A and 10HNAP steels under variable amplitude and random non-proportional bending with torsion loading

The paper contains the results of fatigue tests of 18G2A and 10HNAP steels under proportional and non-proportional bending with torsion. The circular smooth specimens were tested. The tests were carried out at the fatigue test stands MZGS-200PL and MZGS-200L. It was found that experimental lives under non-proportional loading of the tested steels are greater (even 10 times) than under proportional loadings at the same levels of normal and shear stresses. The best results of experimental and calculation lives consistence for the considered materials was obtained using the criterion of maximum shear stresses in the critical plane and the Palmgren–Miner hypothesis of damage accumulation.