The influence of the mean stress on fatigue life of 10HNAP steel under random loading

This paper contains the results of uniaxial random load fatigue tests with different mean values performed on 10HNAP steel specimens. The experimental fatigue life was compared with the life determined according to different methods of amplitude transformation of the cycles. Cycles were counted with the rain flow algorithm and damage was cumulated with the Palmgren–Miner hypothesis. It has been shown that in the case of “symmetric” stress histories with zero expected values, the mean values of selected cycles do not strongly influence the calculated fatigue life and transformation of the cycle amplitudes; hence, no mean stress correction for cycle mean values different from zero is required. As for the “asymmetric” histories, the algorithm of transformation of the stress history (because of its global expected value different from zero) gives similar results to the algorithm of amplitude transformation of cycles. A suitable choice of the transformation relationship is very important. In the case of 10HNAP steel, stress amplitude transformation according to the Goodman relationship gives good results.