High-temperature Cyclic Deformation Behavior and Damage-coupled Unified Viscoplastic Constitutive Model for a Ductile Cast Iron QTRSi4Mo1

Isothermal low cycle fatigue tests for a ductile cast iron QTRSi4Mo1 were carried out at 500°C and 760°C. The results showed that it 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 damage-coupled unified viscoplastic 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 the rapid nonlinear evolution characteristics during the damage development. Furthermore, the parameter identification approach for the unified viscoplastic model was proposed, including the initial estimates combined with the genetic algorithm-based global optimization procedure. The results showed that the proposed damage-coupled viscoplastic model can simulate the cyclic deformation behaviors and predict the LCF failure life of the ductile cast iron QTRSi4Mo1.