鋼の疲労進行過程の静的ねじり試験法による研究 (第2報)

Abstract

Continued from the 1st report, we studied the fatigue processes for the slightly tension-worked or strain-aged steels with high and low carbon contents, and compared them with the result for the annealed steel. The results obtained are as follows:(1) The fatigue process in case of the repeated stress below fatigue limit.a) For the high carbon steelThe progress of fatigue with the increase of number of stress cycles does not occur in either tension-worked or strain-aged steel. But, when the number of stress cycles increases, the phenomenon of work hardening by the repeated stress may be noticed, though it is slighter than for the annealed steel.b) For the low carbon steelWhen the repeated stress is small, the stage of work hardening by the repeated stress alone progresses with the increase of number of cycles, and the next stage does not occur. But, when the repeated stress is near the fatigue limit in either tension-worked or strain-aged steel, it progresses up to the stage of formation of submicroscopic cracks together with the increase of number of cycles. As the fatigue failure does not occur in the larger number of cycles, it is considered that this process of formation of submicroscopic cracks stops after a certain extent.(2) The fatigue process in case of the repeated stress above fatigue limit.In either tension-worked or strain-aged steel, this process is characterized by the same four stages as mentioned concerning the annealed steel (the 1st report). But the relative duration of these stages differs according to the kind of steel, high or low, tension-worked or strain-aged, or to the degrees of overstress.(3) The cycle ratio at the time of formation of submicroscopic cracks.a) It becomes small with the increase of repeated stress in either tension-worked or strain-aged steel. (This is the same as the result for the annealed steel.)b) It is smaller in the low carbon steel than in the high carbon steel.c) The tension-working makes it smaller, but the strain-aging makes it larger than in the annealed steel.