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

Abstract

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 Â 10 À3 s À1 at high temperature of 650 8C. 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.

Experimental and numerical characterization of low cycle fatigue and creep fatigue behaviour of P92 steel welded joint

“…Geometry of the welded groove, complexity of the microstructure, and different crack propagation behaviour are accounted for the difference. This shows the agreement with our previous research of the PM, 31 and this phenomenon also validates our reasoning that the higher cyclic stress in higher strain amplitude was caused by the higher strain hardening behaviour in the first cycle. This phenomenon is in accordance with common sense, because tensile holding not only introduces more inelastic strain but also accelerates the evolution of microstructure.…”

“…Similarly, according to Figure 6, it is not difficult to conclude that the classification is also suitable for the cyclic behaviour of cross-weld specimens. 31 However, detail observation of the cyclic stress in the first cycle reveals that higher strain amplitude has the higher initial cyclic stress. It seems that there is a little difference from PM whose cyclic stress is almost stabilized when strain amplitude is larger than 0.4%.…”

“…It seems that there is a little difference from PM whose cyclic stress is almost stabilized when strain amplitude is larger than 0.4%. 31 However, detail observation of the cyclic stress in the first cycle reveals that higher strain amplitude has the higher initial cyclic stress. Therefore, the higher cyclic stress response is caused by the higher strain hardening, which is induced by the higher stain amplitude.…”

“…The cycle is normalized by the failure cycle (N f ); this is to better understand the different cyclic stress response at different loading conditions. In our previous study, 31 we have come to the conclusion that LCF cyclic softening curve of P92 steel at high temperature could be divided into 3 stages: rapid softening stage, stabilization stage, and damage evolution stage or accelerated stage. In our previous study, 31 we have come to the conclusion that LCF cyclic softening curve of P92 steel at high temperature could be divided into 3 stages: rapid softening stage, stabilization stage, and damage evolution stage or accelerated stage.…”

“…In Figure 6, effect of strain amplitude ( Figure 6A) and effect of holding time and holding direction ( Figure 6B) are presented. In our previous study, 31 we have come to the conclusion that LCF cyclic softening curve of P92 steel at high temperature could be divided into 3 stages: rapid softening stage, stabilization stage, and damage evolution stage or accelerated stage. Similarly, according to Figure 6, it is not difficult to conclude that the classification is also suitable for the cyclic behaviour of cross-weld specimens.…”