Thermodynamic consistency-based modelling of creep kinematic hardening and damage behavior

Creep deformation and damage critically affect the safety of high-temperature components in aerospace, nuclear power, and transportation. A rigorous description of deformation and damage under complex creep loading from an energy perspective still requires further development. This study develops a thermodynamically consistent constitutive framework combining kinematic hardening and damage evolution. Long- and short-range back stresses describe history effects and anelasticity, while damage is modelled through creep free energy degradation and stress-dependent driving forces, capturing the transition from hardening to softening. The framework reproduces key features such as variable-load creep, cyclic torsional creep, and the shift from decelerating to accelerating strain rates. Results reveal that early creep is governed by back stress hardening, whereas long-term softening and rupture arise from progressive damage. This unified, thermodynamically based approach provides a practical tool for predicting creep behaviour and lifetime, offering guidance for the design and assessment of high-temperature structural materials.