Strain rate sensitivity behavior of a structural steel during low-cycle fatigue investigated using indentation

Abstract

In this study, a series of experiments consisting of low-cycle fatigue, constant loading rate indentation, creep indentation experiments, optical microscopy examination, and transmission electron microscopy were performed to investigate the strain rate sensitivity behavior of SS400 structural steel under cyclic loading conditions. 400 indentations were conducted in the displacement control mode at different strain rate indentations varied from 0.02 s−1 to 0.2 s−1 and the effects of strain rate indentation on mechanical properties were investigated on four fatigue failure specimens. An analytical method was used to estimate mechanical properties of the structural steel from the loading/unloading curves. The results indicated that the yield strength and the strain hardening exponent strongly depended on both the strain rate indentation and the strain amplitude. Yield strength and strain hardening exponent tended to increase when the strain amplitude increased. The strain rate sensitivity (SRS) was also determined from the yield strength and the creep indentation data, and the dependency of the strain rate sensitivity on the strain amplitude level was examined. The results showed that the strain rate sensitivity exhibited decrease almost linearly when the strain amplitude increased from 0.4% to 1.0%. The results of the present study were used to assess and understand the strain rate sensitivity behavior of SS400 structural steel during low-cycle fatigue.