Abstract
In the previous paper, the authors described on the effects of the cycle ratios of the primary stresses on the fatigue lives under the cumulative stresses, by gradually changing the cycle ratios on three kinds of primary stress levels (those were: 30% higher, 20% higher and the same height of the fatigue limit of virgin material), and found that there were cycle ratios of primary stresses which make the fatigue lives maximum or minimum. In this paper, the authors have checked the effects of the secondary stresses on the fatigue lives, in detail, by increasing or decreasing the secondary stresses step by step from the primary stress levels under the cycle ratios of primary stresses selected according to the previously reported test which had the most remarkable effects on the fatigue lives (those were: n1/N1≈2/5, 1/2, 3/4). The conclusions were:
(1) In the case of high carbon steel (as S 50 C), the fatigue lives were shortened than those of virgin materials only when the primary stress levels were located far higher than the fatigue limit of virgin materials, and the fatigue lives were, on the contrary, prolonged when the primary stress levels were located in the neighbourhood of the fatigue limit.
(2) In the case of low carbon steels (as S 10 C), the fatigue lives were prolonged whether the secondary stresses were higher or lower than the primary stresses. The fatigue lives, however, were not so prolonged as in the case of high carbon steels (as S 50 C) when the primary stress levels were located in the neighbourhood of the fatigue limit.
