疲労限度以下の応力による2段2重変動応力下の疲労破壊に及ぼす微小切欠きの形状と水素の影響

概要

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It is usually regarded as a common understanding that fatigue failure would not occur if all stresses were kept below fatigue limit diagram. However, it was shown that fatigue failure occurred in some special cases of variable amplitude loading condition even when all stresses were kept below fatigue limit diagram in the case of small-notched specimen. The cause of such a phenomenon was examined using two-step stress pattern for low alloy steel SCM440H. In the case of constant stress amplitude loading, non-propagating crack was formed only at low mean stress region and not formed at high mean stress. However, in the case of two step stress pattern in which the first step stress was chosen as R=-1 and the second step stress was with high mean stress, a non-propagating crack was formed by the first step stress. This crack functioned as a pre-crack for the second step stress with high mean stress. In this study, the effect of notch shape was examined. The effect of absorbed hydrogen was also investigated. Absorption of 0.3ppm hydrogen caused more reduction of fatigue limit.
2008-10-25