鋼の疲労進行過程の静的ねじり試験法による研究 (第1報)

Abstract

We studied the fatigue process for the annealed high (0.82% C) and low (0.08% C) carbon steel by the method of static torsional test.The results obtained are as follows:(1) The fatigue process in case of the repeated stress below fatigue limit.In either high or low carbon steel, the progress of fatigue with the increase of number of stress cycles does not occur. But the phenomenon of work hardening by the repeated stress is found slightly.(2) The fatigue process in case of the repeated stress above fatigue limit.In either high or low carbon steel, this process is characterized by the next four stages: stage 1, work hardening by the repeated stress; stage 2, formation of submicroscopic cracks; stage 3, growth of cracks; stage 4, fracture. But the relative duration of these stages differs according to the percentage of overstress or carbon content of steel.(3) The cycle ratio at the time of formation of submicroscopic cracks.It becomes small with the increase of repeated stress and the decrease of carbon content of steel.(4) The comparison with the result of study by the electro-magnetic method (previous reported).These two results coincide closely with each other. Therefore, we could understand the reliability of electro-magnetic method by which we inspect the degree of fatigue progress for steels non-destructively.