Characterization of Low Cycle Fatigue of Ferritic-Martensitic P92 Steel: Effect of Temperature

Isothermal, strain-controlled low cycle fatigue (LCF) tests of P92 steel are conducted in air at different temperatures ranging from 20 to 650 °C and various strain ranges to clarify the influence of temperature on its LCF behavior. A symmetrical triangular wave form and a constant 1.0 × 10^-3 s^-1 strain rate are employed for all the tests. Cyclic softening behavior is expressed in two ways: peak tensile stress in terms of cycle numbers and in terms of accumulated inelastic strain. Based on the definition of "inelastic ratio," correlation between the value of accumulated inelastic strain (Ïμ in,II) at the beginning of the second softening stage and the inelastic ratio can be distinctively divided into three regions. The modified cyclic plasticity model, in which a linear term is added into the isotropic hardening variable, is developed to simulate the stress-strain hysteresis loop and the cyclic softening curve. Additionally, parameters in the modified isotropic hardening variable at different temperatures are correlated to the cyclic softening phenomenon. Performances of the modified model are assessed by comparing predictions with experimental results. Good predictive capability of the modified constitutive model is obtained. Strain controlled low cycle fatigue tests of P92 steel at different temperatures and various strain ranges are conducted to investigate the effect of temperature. The correlation between cyclic stress response and accumulated inelastic strain is achieved and the relationship between inelastic ratio with the accumulated inelastic strain at the beginning of the second softening stage can be divided into three regions.