Effect of Nonproportional Loading on Creep-Fatigue Life of SUS304 Steel Subjected to CC-Type Combined Push-Pull Loading and Cyclic Torsion at 973K in Air
Katsuyuki TOKIMASA, Shigeo SAGARA and Daiki FUJINAKA
Abstract:This paper investigates the applicability of the procedure proposed by one of the authors for estimating the nonproportional loading effect on PP test lives to the estimation of the creep-fatigue lives of SUS304 austenitic stainless steel subjected to nonproportionally combined push-pull and cyclic torsion under CC type strain waveform. Fully reversed strain-controlled CC tests were conducted on thin-walled tubular specimens of SUS304 steel at 973 K in air under in-phase and 90 deg out-of-phase straining conditions. The partitioned inelastic strain range versus life equations, ¢Ćcc versus Ncc relationships, obtained from three different proportional loading conditions, such as push-pull, cyclic torsion, and in-phase combined push-pull and cyclic torsion, are found to be correlated with one another by the multiaxiality factor. By using the multiaxiality modified ¢Ćpp versus Npp and ¢Ćcc versus Ncc relationshipsCthe 90deg out-of-phase straining CC test lives were estimated by the proposed procedure, where the strain range partitioning was done by superposing the hysteresis loops of PP tests on those of CC tests. As the results, the estimated lives are found to agree well with the experimental lives in adopting the superposition method rather than the rapid loading method. Key Words:Multiaxial fatigue, Nonproportional loading, Life prediction, Multiaxiality factor, Strain range partitioning method, Equivalent shear strain amplitude, SUS304