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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, for modeling the distinct strain range-dependent deformation behaviors at different temperatures. In the model, a modified damage evolution law was introduced. 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 proposed model can simulate the strain range-dependent cyclic deformation behaviors and predict the LCF failure life of the investigated material.