OS0506 切欠き底に発生した微小疲労き裂の進展挙動に及ぼす切欠き半径および応力比の影響(OS5-2 き裂進展・計測,OS-5 材料の疲労挙動と損傷評価1)

Abstract

It has been recognized that the threshold stress intensity factor range ΔK_<th> of a short crack is lower than that of a long crack. This behavior is unsafe in mechanical design if only ΔK_<th> of long crack is considered. Therefore many researchers have studied short crack behavior using plane fatigue test specimen. These studies provided quantitative understanding of the short crack behavior in relation to crack closure. However, for a short crack at notch root, the behavior has not been clarified yet. In this study, crack propagation tests using various kinds of notched specimens with a short pre-crack were done to consider the effect of notch root radius and stress ratios on the crack propagation behavior of the short crack at notch root. The crack closure was different depending on the stress ratio as well as notch root radius. This resulted difference in the ΔK_<th> of the short crack. When high stress ratio was applied, since there was no crack closure the ΔK_<th> was relatively low regardless of notch root radius. The effect of notch root radius on the ΔK_<th> of the short crack at notch root was significant when the stress ratio was low. The change in ΔK_<th> with the decrease in notch root radius could be understood by development of crack closure.