It has been demonstrated that the loading history takes into account the loading sequence and loading interaction effects. Nonlinear damage models based on fatigue driving stress theory consider the loading sequence but exclude the loading interaction effects. In this study, a novel evolution curve for fatigue driving stress was created by including the loading interaction factor in the equation of driving stress evolution. Through using fatigue driving stress equivalence, the remaining fatigue life under varying amplitude loading was then predicted by an enhanced fatigue driving stress model. Compared with Miner's rule, the K-R model, Zhu's model, and Li's model, this new model gave more accurate and reliable predictions.

In order to accurately predict creep deformation and damage evolution of nickel-based superalloy GH4169, a novel damage constitutive model, which can be called TTC CDM-based model, was proposed based on TTC relations and continuum damage mechanics (CDM). The stress and temperature dependence of constants were all determined in the novel model, which overcame the weakness of the traditional CDM-based model and made the model have the satisfactory abilities of interpolation and extrapolation. Microstructural study has revealed that the creep fracture mode gradually converts from intergranular brittle fracture to transgranular ductile fracture as the stress decreases. And the critical conditions were identified. It was determined that the novel model accurately predicted the minimum creep rate, rupture time, creep deformation and damage evolution process of GH4169. Furthermore, the nonlinear creep damage accumulation effect was also revealed by the novel model, i.e. the total creep life of GH4169 will be reduced if high stress or high temperature condition was applied first, which was consistent with previous experimental results of variable creep load.

Variable creep load is one of the most important failure modes for hot-component of aero-engine. To accurately predict creep damage and remaining life, a novel nonlinear creep damage accumulation model is proposed based on the Wilshire function and isodamage line, which takes the influence of load history into account and uses ultimate tension strength to compensate the temperature effect. Experimental result of tests on four kinds of material were utilized to verify the accuracy of the proposed model and to compare it with existing models. It was determined that the novel model was better at predicting damage accumulation than all others model. Furthermore, the proposed model elucidates the evolutionary process of creep damage, and four cases of damage evolution process are discussed.