鋼の弾性履歴現象と疲労強度

抄録

The authors have previously reported on the mirror extensometer which magnified the longitudinal elongation and the contraction of the specimen under axial fatigue load as much as 2000 times, and on some of the experimental results obtained of two kinds of steel.
In this paper, similar experiments were made on five kinds of carbon steel. The strain occurred on each specimen under completely reversed axial load was measured through the test. The plastic strain, by which we mean half the width of a hysteresis loop on the stress-strain diagram, was obtained from a simple calculation.
There was ovserved a difference between the behaviour of plastic strain of the low carbon steels and that of the high carbon steels. Howevever, the variation of the plastic strain was moderate and converged to some final value. One exception was the case of 0.25% carbon steel. This steel showed a quite different and complicated behaviour of the plastic strain that offered us a subject of more detailed investigation in future. For the other steels, there exists a linear relationship between the plastic strain and the number of stress cycles to failure when plotted on a log-log paper. A similar relationship was found when the hysteresis energy was plotted instead of the plastic strain. Some discussions were also made on the stress-strain curves under fatigue load.