Stress intensity factors for transformed surface flaws and remaining fatigue lives based on flaw-to-surface proximity rules

内部欠陥から表面亀裂に変換する際の応力拡大係数及び変換規則を踏まえた疲労余寿命

長谷川 邦夫*; Strnadel, B.*; Li, Y. ; Lacroix, V.*

Hasegawa, Kunio*; Strnadel, B.*; Li, Y.; Lacroix, V.*

Subsurface flaws are sometimes found as blowholes near free surfaces of structural components. It can be easily expected that the stress intensity factor at the tip of the subsurface flaw increases with decreasing the ligament distance. Fitness-for-service (FFS) codes provide flaw-to-surface proximity rules which are transformation from subsurface to surface flaw. Although the concept of the proximity rules of the FFS codes are the same, the specific criteria for the rules on transforming subsurface flaws to surface flaws are different amongst FFS codes. This study demonstrates the proximity criteria provided by the FFS codes and indicates that the increment of the stress intensity factors before and after the transformation from subsurface to surface flaws. In addition, it is shown that remaining fatigue lives for pipes with flaws are strongly affected by the location at the transformation from subsurface to surface flaws.