著者

周 世栄 村上 敬宜 福島 良博 ベレッタ ステファノ

出版者

社団法人日本鉄鋼協会

雑誌

鐵と鋼 : 日本鐡鋼協會々誌 (ISSN:00211575)

巻号頁・発行日

vol.87, no.12, pp.748-755, 2001-12

被引用文献数

2

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It is well known that the scatter of fatigue strength of high strength steels is caused by nonmetallic inclusions. The lower bound of the scatter of fatigue strength can be predicted by considering the maximum size of nonmetallic inclusions. Thus, it is of practical importance to estimate the maximum size of nonmetallic inclusions by appropriate inclusion rating methods. Most rational and convenient method to predict the maximum size of inclusions is the one based on the statistics of extremes. Therefore, recently the inclusion rating based on the statistics of extremes has been used by many industries, though the rating methods are mostly two-dimensional (2D) optical methods. It is known that the accuracy of the 2D method is lower than the exact 3D method. In addition, when multiple type inclusions having different chemical composition are contained in a material, the statistics of extremes distribution does not necessarily become a single straight line but become a bilinear line. The objectives of the present study are (1) to clarify the validity of the 2D method and (2) to establish the method to predict the maximum inclusion size when the statistics extremes distribution becomes bilinear. The results obtained show that the 2D method is basically correct as predicted by the computer simulation. When a bilinear distribution is obtained, it is necessary to determine the minimum inspection area S_<crit> for predicting the maximum size of the larger type inclusions, which become the fatigue fracture origins of components.

著者

村上 敬宜 金崎 俊彦 福島 良博 田中 裕之 戸室 仁一 久保山 孝治 松栄 雅樹 伊藤 義雄 安藤 晴彦

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集 A編 (ISSN:03875008)

巻号頁・発行日

vol.75, no.749, pp.93-102, 2009-01-25 (Released:2017-06-09)

参考文献数

6

被引用文献数

4 7

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The fatigue failure analysis of SUS316L flexible hose of the hydrogen station which was demonstrated during EXPO 2005 in Nagoya was carried out. The fatigue fracture surface where hydrogen leakage was detected showed clear striations which revealed a unique evidence of hydrogen effect on the ratio of striation height and spacing. The number of striations observed on the leakage fracture surface was 270. Considering that the number of hydrogen supply to the fuel cell buses was 280, it can be concluded that the fatigue fracture process during the demonstration is completely controlled by microplasticity resulting ductile fracture contrary to the conventional concept expressed with a term of decohesion or hydrogen embrittlement. The striation data were used to make the fatigue crack growth rate equation which was applied to the life prediction and structural integrity assessment for a new hydrogen station. The fatigue crack growth data showed the evidence of a strong frequency effect of fatigue crack growth rate of SUS316L used in the hydrogen environment with 8 minutes hydrogen supply time at the hydrogen station.