With the purpose of investigating the fatigue life under combined bending and torsional stresses acting at different frequencies, a testing machine was constructed, and tests were carried out on S45C carbon steel specimens. The ratio of the frequency of reversed torsion to that of reversed bending was in the range of 0.19 to 4.9.
In the previous paper, the method to estimate the fatigue life under a monofrequency in-phase combined stress was proposed. In this paper, in order to extend the method to the bifrequency case, the following assumption was made: -if the torsional component of a bifrequency combined stress is changed to a different torsional stress which would induce the same damage as that of the original one after the same number of bending cycles, the resultant combined stress can be considered as same as the monofrequency case, and the preceding method should be applicable.
The experimental results obtained supported this conception, especially in the high-stress region.
