抄録
On the fatigue strength of steels under multiple repeated stress in two stress levels, one of the authors reported previously some experimental results. But in those cases we treated the specimens without notches. Therefore in this research, the authors made many fatigue tests on the specimens with circumferential notches under two stress levels, and investigated the effects of “primary stress”on the fatigue life of the“secondary stress”.
Specimens made of 0.13%C carbon steel have been tested by Ono's rotating bending fatigue testing machin.
Summary of the results is as follows.
(1) In general, the theory that fatigue fracture occurs at∑n/N=1 does not reproduce the experimental results. But the result of the specimens with notches are more in agreement with ∑n/N=1 than the results of the specimens without notches.
(2) In the cases where the primary stress is relatively small, the value of ∑n/N is larger than 1 in most cases when the secondary stress is larger than the primary stress and the value of ∑n/N is nearly equal to or larger than 1 when the secondary stress is smaller than the primary stress.
(3) When the primary stress is relatively large and the secondary stress is smaller than the primary stress, the value of ∑n/N is nearly equal to 1, but little smaller than 1.
(4) When the results of this experiments about the mile steel specimens with notches are compared with those about the mile steel, medium steel and hard steel specimens without notches, then the results of this experiments seems to have a character just between the cases of mild steel without notches and of medium or hard steel without notches.
