衝撃プログラム荷重下における疲労強度と疲労損傷の累積について

Abstract

To clarify the understressing effect in the two-steps program load condition involving the transitional impact load at the rise time to higher stress level σ1, a series of the rotating bending fatigue tests have been planned and conducted.On this experiment, the maximum stress σmax introduced by the impact loading and the program period m, which is the sum of the period for the primary stress m1 and that for the secondary stress m2, were taken as the experimental variables. On the other hand, the period for the primary stress, m1, was held constant as m1=2sec., and the magnitudes of the primary and secondary stress, σ1 and σ2, were fixed to the values of 13.4kg/mm2 and 11.0kg/mm2 respectively to lie below the fatigue limit of the fundamental S-N curve obtained under the constant load condition.The main results obtained are as follows: It was recongnized that the understressing following the maximum stress acted as the weakening factor as a whole in the range of this experiment, and that the cumulative damage in the meaning of the Miner's rule became larger. In other words, the weakening effect of the understressing gradually decreased when the magnitude of the maximum stress took a higher value especially in the case of the relatively short program period m=4. And then, according to the estimation from the view point of the hysteresis energy calculated with the assumption that the cumulative hysteresis energy needed for failure takes the same value in spite of the difference in load pattern, it was revealed that the weakening effect of the understressing increased in its amount but decreased in its contribution fraction when the program period m became longer.