Abstract
For the purpose of clarifying the effect of strain waveform on creep-fatigue property under variable straining, two-step variable straining (high-low and low-high) tests were conducted on Mod. 9Cr-1Mo steel at 600°C in air under PC (fast-slow) and CC (slow-slow) type strain waveforms, and the experimental results were compared with the previously reported results obtained under PP (fast-fast) and CP (slow-fast) type strain waveforms. In both high-low and low-high tests, 1.0% was chosen as the higher strain range, and 0.8% and 0.4% as the lower strain ranges.
The main results obtained in the present study are as follows.
(1) Independent of strain waveform, the high-low and low-high test results could be predicted by the linear damage rule (LDR) when the lower strain range was 0.8%, whereas the deviation of the experimental data from LDR prediction was found when the lower strain range was 0.4%.
(2) Such a deviation of the experimental data from LDR prediction was similar to that in CP type strain waveform, but was much smaller than that in PP type strain waveform.
(3) The previously proposed creep-fatigue life prediction model under variable straining for the PP and CP data can be successfully applied to PC and CC type strain waveforms, suggesting that in Mod. 9Cr-1Mo steel 2(a0)pp=2.5×10-4mm and 2(a0)cp≈2(a0)pc≈2(a0)cc≈10-3mm.
