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Fatigue crack growth calculations for vessels considering subsurface to surface flaw proximity rules

内部欠陥の表面欠陥への置き換えルールを考慮した圧力容器の疲労き裂進展計算

Lacroix, V.*; 長谷川 邦夫; Li, Y. 

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

日本及び米国の維持規格では、機器の自由表面に接近する内部欠陥を表面欠陥に置き換える接近性ルールがあるが、その根拠は明確ではない。この背景を踏まえて、著者らはこれまでに試験結果に基づいた接近性ルールを提案した。本論文では原子炉圧力容器に内部欠陥を仮定し、従来の規格にある接近性ルールと新たに提案した接近性ルールについて、拡張有限要素法XFEMにより疲労による余寿命を求めた。異なるアスペクト比及び内部欠陥と自由表面までの距離を考慮した計算結果として、異なる接近性ルールによる疲労余寿命に顕著な違いがないことが分かった。

If a subsurface flaw is located near a component surface, the subsurface flaw is transformed to a surface flaw in accordance with a subsurface-to-surface flaw proximity rule. The authors have proposed a new subsurface-to-surface flaw proximity rule based on the experiments data and the interaction of stress intensity factors. In this study, eXtended Finite Element fatigue crack growth calculations were carried out for thick wall component like vessels with subsurface flaws, using the proposed subsurface-to-surface flaw proximity rule and the proximity rule provided in the current ASME Code Section XI. Different flaw aspect ratios and ligament distances from subsurface flaws to inner surface of vessel were taken into account. As the results, the current proximity rule and proposed one provide relatively similar fatigue lives, whatever the aspect ratios of the initial subsurface flaws. However, when the thickness of the component decreases this similarity between both proximity rules appears not to be valid anymore.

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