The paper contains a comparison of the results of calculation and experiment for the IOHNAP alloy steel. Specimens made of this steel were subjected to uniaxial constant-amplitude and random loading with both zero and non-zero mean values of loading. For determination of the steel fatigue life, the energy parameter including the mean value of loading was proposed. Under random loading, cycles were counted with the rain flow algorithm, and fatigue damage was accumulated with the Palmgren-Miner hypothesis. For the registered stress histories, elastic-plastic strains were calculated with the kinematic hardening model proposed by Mróz.

The paper contains the tatigue tests results for specimens made of three cast irons under proportional and non-proportional variable amplitude tension with torsion. The experimental data for long fatigue life have been compared with those calculated according to the algorithm with use of the modified criterion of the maximum normal stress in the critical plane. In the considered algorithm the Palmgren-Miner hypothesis of damage cumulation seems to he useless whereas the Serensen-Kcgaycv hypothesis gives satisfactory results. Applying the method of fatigue damage cumulation we obtain the critical plane direction which agrees with the experimental fracture plane very well.