Study of High-Temperature Low-Cycle Fatigue Behavior and a Unified Viscoplastic-Damage Model for Heat-Resistant Cast Iron

Isothermal low-cycle fatigue (LCF) tests on heat-resistant QTRSi4Mo1 cast iron were carried out at 500 and 760 °C. The results showed that the cast iron exhibited initial cyclic hardening followed by saturation at 500 °C, while gradual cyclic softening occurred at 760 °C due to a more pronounced creep effect. A unified viscoplastic-damage constitutive model incorporating two nonlinear and one linear strain range-dependent drag stress components was developed to model the distinct strain range-dependent deformation behaviors. The piecewise damage evolution law was introduced to reflect the slow linear and rapid nonlinear evolution characteristics during damage development. Furthermore, the parameter identification approach for the unified viscoplastic-damage model was proposed, including the initial estimates combined with the genetic algorithm-based global optimization procedure. The results showed that the proposed viscoplastic-damage model can simulate the cyclic deformation behaviors and predict the LCF failure life of heat-resistant QTRSi4Mo1 cast iron.