Improvement of Omega Method for Creep Life Prediction.

  • 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.

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Abstract

Omega method has been proposed for predicting rupture life from creep strain ε-time t 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 =ε0+Ω1 {ln (1+ζt)-ln (1-ηt)}<br><br>where ε0, 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.

Journal

  • ISIJ International

    ISIJ International 37 (4), 419-423, 1997

    The Iron and Steel Institute of Japan

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