Improvement of Omega Method for Creep Life Prediction

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著者

    • MARUYAMA Kouichi
    • Department of Materials Science, Faculty of Engineering, Tohoku University
    • NONAKA Isamu
    • Research Institute, Ishikawajima-Harima Heavy Industries, Co., Ltd.
    • SAWADA Kota
    • Department of Materials Science, Faculty of Engineering, Tohoku University
    • SATO Hiroyuki
    • Department of Materials Science, Faculty of Engineering, Tohoku University
    • KOIKE Jun-ichi
    • Department of Materials Science, Faculty of Engineering, Tohoku University
    • UMAKI Hideo
    • Power Plant Division, Ishikawajima-Harima Heavy Industries, Co., Ltd.

抄録

Omega method has been proposed for predicting rupture life from creep strain ε-time <i>t</i> data. The method is based on a linear relation between logarithm of creep rate ε and strain, namely a creep curve without the primary and secondary creep stages. Such a linear relation, however, seldom holds in real creep data. In this paper, the original equation is modified to the following form:<br><br>ε =ε<sub>0</sub>+<sub>Ω</sub><SUP><U>1</U></SUP> {ln (1+ζ<i>t</i>)-ln (1-η<i>t</i>)}<br><br>where ε<sub>0</sub>, Ω, ζ and η are parameters characterizing a creep curve. The first and second terms in the parentheses describe primary creep and tertiary creep, respectively. The equation is applied to ferritic steels. The four parameters of the equation can uniquely be determined for a creep curve with a curved ln ε-ε relation. The equation can well reproduce creep curves with a prominent primary creep stage. Because of the high reproducibility, the modified equation can predict rupture life with higher accuracy at an earlier stage of creep than the original equation.

収録刊行物

  • ISIJ international  

    ISIJ international 37(4), 419-423, 1997-04-15 

    The Iron and Steel Institute of Japan

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