Abstract
It is well known that the mean stress as well as the stress amplitude are often varied under the service loading conditions and the fatigue damage can be accumulated by the stress even below the fatigue limit.
In this study, therefore, the effects of the mean stress on the behavior of cyclic plastic strain and on the fatigue life were investigated in both regions above and below the fatigue limit with the smooth specimens of a 0.38% carbon steel. Cumulative damage below the fatigue limit was examined by the repeated two-step tests composed of a single cycle of high level stress range-pair and a large number of low level stress range-pair, the mean stress of which was changed variously.
Two effects of the mean stress were found; The one was the effect to cause one directional deformation which resulted in the increase of the plastic strain range-pair corresponding to the high level stress. The other was the damaging or strengthening effect, i. e. the tensile mean stress made the fatigue life shorter and the compressive one longer. This effect was found to be relatively marked at the low level of the mean stress. Moreover, it was noticed that, if the mean stress cyclically reversed, even the compressive mean stress might have the same damaging effect as the tensile one.
