Progressive degradation of material mechanical properties in the low cycle fatigue (LCF) and creep-fatigue (CF) interaction at high temperature affects the safe operation of in-service materials. By considering material degradation, the present work aims to establish a method for evaluating LCF and CF damage levels with wide applicability. Material-level data accumulations as well as theoretical foundations of LCF and CF are presented, including interrupted LCF and CF tests, subsequent tensile tests and energy-based damage models. A damage variable representing the degradation of material mechanical properties is then defined based on the tensile plastic strain energy density (TPSED), the physical mechanism of which is reflected in the microstructure evolution and fracture appearance. By taking into consideration the material degradation threshold in the traditional damage summation rule, a new three-dimensional (3D) damage interaction diagram is established, where the additional third axis indicates the material degradation level. Finally, taking GH4169 alloy and P92 steel as examples, this work demonstrates the implemented procedures of damage level evaluation, which has been validated via the experimental data.

在高温下的低周疲劳（LCF）和蠕变疲劳（CF）相互作用中材料力学性能的逐渐退化影响在役材料的安全运行。通过考虑材料降解，本工作旨在建立一种具有广泛适用性的评估 LCF 和 CF 损伤水平的方法。介绍了材料级数据积累以及 LCF 和 CF 的理论基础，包括间断 LCF 和 CF 测试、后续拉伸测试和基于能量的损伤模型。然后基于拉伸塑性应变能密度（TPSED）定义代表材料机械性能退化的损伤变量，其物理机制反映在微观结构演变和断裂外观中。通过考虑传统损伤求和规则中的材料退化阈值，建立了新的三维（3D）损伤相互作用图，其中附加的第三轴表示材料退化水平。最后，以 GH4169 合金和 P92 钢为例，演示了损伤等级评估的实施程序，并通过实验数据进行了验证。