Characterization of Low Cycle Fatigue Performance of New Ferritic P92 Steel at High Temperature: Effect of Strain Amplitude

Low cycle fatigue (LCF) tests were performed at various strain amplitudes ranging from 0.2 to 0.8% to investigate the effects of strain amplitude on cyclic softening behavior and LCF lifetime of new ferrtic P92 steel. LCF tests were conducted under strain controlled in fully reversed manner with strain rate of 1.0 × 10^-3 s^-1 at high temperature of 650 °C. A novel fatigue life end criterion was adopted in this analysis. The effects of strain amplitude on the cyclic softening behavior, the evolution of plastic strain amplitude, hysteresis loop area, and the fatigue life were discussed. Similar softening curves were achieved except for the strain amplitude of 0.2%. The evolution of hysteresis loop areas at the smaller strain range amplitude (less than 0.4%) is contrary to the larger ones. A modified life prediction model was proposed based on Coffin-Manson model and energy-based model, comparison of predicted lifetime and experimental data shows that the model gives a good estimation. In order to better understand the basic stress-strain behavior, time-independent cyclic plasticity model was used to represent the cyclic mechanical behavior of this steel. Comparison of the simulated and experimental results shows that the proposed model can give a reasonable prediction of stress-strain hysteresis loop for P92 steel at high temperature.