IMPROVEMENT OF OMEGA-METHOD FOR CREEP LIFE PREDICTION

Omega method has been proposed for predicting rupture life from creep strain epsilon-time t data. The method is based on a linear relation b etween logarithm of creep rate epsilon and strain, namely a creep curv e without the primary and secondary creep stages. Such a linear relati on, however, seldom holds in real creep data. In this paper, the origi nal equation is modified to the following form: epsilon = epsilon(0)+O mega/1{In(1+zeta t)-In(1-eta t)} where epsilon(0), Omega, zeta and eta are parameters characterizing a creep curve. The first and second ter ms in the parentheses describe primary creep and tertiary creep, respe ctively. The equation is applied to ferritic steels. The four paramete rs of the equation can uniquely be determined for a creep curve with a curved In be relation. The equation can well reproduce creep curves w ith a prominent primary creep stage. Because of the high reproducibili ty, the modified equation can predict rupture life with higher accurac y at an earlier stage of creep than the original equation.