Abstract
The fatigue life of 0.09%C Al-killed steel under program loading of multiple repeated two step stresses, which were composed of a over-stress and a under-stress, was investigated.
The predicted fatigue life was calculated from the basic fatigue damage of one stress cycle: exp(Aσ+D) and the fatigue damage function: exp(Aσ+D)·exp(-mσpN'), by applying the authors' prediction method for fatigue life and endurance limit of metals under service loads1).
It was found that the predicted fatigue life and endurance limit of the Al-killed steel were in good agreement with the tested values when the adequate values of m and p were applied.
In the previous study1), it was reported that Aσα should be used as the basic fatigue damage for predicting the fatigue life of 0.11%C rimmed steel under the same program loading. The present study showed that exp(Aσ+D) is adequate as the basic fatigue damage in the case of Al-killed steel. Therefore, either Aσα or exp(Aσ+D) must be chosen depending upon the kind of metals in order to predict their fatigue lives.
The crack growth rate was analyzed by the use of stress intensity factor and the ratio of the period of crack growth to the total life was obtained by counting the beach marks on the surface of fractured specimens.
The scattering of fatigue lives in the neighborhood of fatigue limit under program loading was analyzed.
