溶接継手疲労寿命に及ぼす熱影響部の繰返し負荷下の材料挙動の影響

抄録

Fatigue crack propagation stage is considered to be the dominant in fatigue fracture of welded joints and some solutions regarding stress issue have been developed. In order to ensure reliability of large scale welded structures, multilateral countermeasure for various factors including microstructure in the HAZ (Heat affected zone) which can affect crack initiation should also be considered. However, the effect of HAZ microstructure has not been fully evaluated due to the difficulty and effort required for a systematic experimental procedure. In the present study, elastic-plastic behaviors under static and cyclic loading in HAZ microstructures made by simulated thermal cycle of a welded joint were investigated. By inputting cyclic tensile properties of these microstructures to finite element analysis of welded joint, damage caused by cyclic loading was calculated. Regardless of consideration of HAZ distribution, fatigue crack initiation site was predicted around welded toe of cruciform welded joint due to large degree of stress concentration. On the other hand, it was confirmed that the predicted fatigue crack initiation life the joint with the HAZ strength was longer than that of the joint with homogeneous base metal property. It is suggested that fatigue life of welded joint can be improved by controlling fatigue crack initiation and initial propagation process even in joints which fatigue crack propagation stage is considered to be dominant.