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Stress intensity factor solutions for subsurface flaws in plates subjected to polynomial stress distributions

平板中内部亀裂の応力拡大係数の解について

Lu, K.; 勝山 仁哉; Li, Y.; 岩松 史則*

Lu, K.; Katsuyama, Jinya; Li, Y.; Iwamatsu, Fuminori*

圧力容器の板厚内部に存在する楕円亀裂の応力拡大係数の解は日本機械学会維持規格に記載されている。しかし、圧力容器内表面近傍の楕円亀裂については、その応力拡大係数の解はまだ提案されていない。本論文では、この内表面近傍の楕円亀裂を対象として、その応力拡大係数の解を提案した。提案解は、亀裂のアスペクト比については0から0.5、欠陥深さ比については0から0.8、板厚方向亀裂位置については0.01と0.1を考慮するとともに、応力分布については板厚方向の4次多項式を考慮できる。本提案解は、維持規格に提案できる成果であるとともに、確率論的破壊力学解析コードの精度向上を実現できるものである。

Stress intensity factor (SIF) solutions for subsurface flaws near the free surface in plates were numerically investigated based on the finite element analyses. The flaws with aspect ratios $$a/l$$ = 0, 0.1, 0.2, 0.3, 0.4 and 0.5, the normalized ratios $$a/d$$ = 0, 0.1, 0.2, 0.4, 0.6 and 0.8 and $$d/t$$ = 0.01 and 0.1 were taken into account, where a is the half flaw depth, l is the flaw length, $$d$$ is the distance from the center of the subsurface flaw to the nearest free surface and t is the wall thickness. Fourth-order polynomial stress distributions in the thickness direction were considered. In addition, probabilistic fracture mechanics analyses were also performed and some example solutions obtained in this work were used to evaluate the conditional probability of failure of a reactor pressure vessel under a pressurized thermal shock event. The results indicated that the numerical SIF solutions calculated in this study are effective in engineering applications.

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