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.

在这项研究中，进行了一系列由低循环疲劳，恒定加载速率压痕，蠕变压痕实验，光学显微镜检查和透射电子显微镜组成的实验，以研究SS400结构钢在循环加载条件下的应变速率敏感性行为。在位移控制模式下以不同的应变速率进行了400次压痕，压痕范围从0.02 s ^-1到0.2 s ^-1并在四个疲劳失效试样上研究了应变速率压痕对力学性能的影响。一种分析方法被用来根据加载/卸载曲线来估算结构钢的机械性能。结果表明，屈服强度和应变硬化指数在很大程度上取决于应变速率压痕和应变幅度。应变幅度增加时，屈服强度和应变硬化指数趋于增加。还根据屈服强度和蠕变压痕数据确定了应变率敏感性（SRS），并检查了应变率敏感性对应变幅度水平的依赖性。结果表明，当应变幅度从0.4％增加到1.0％时，应变率灵敏度几乎呈线性下降。