Fatigue and creep-fatigue reliability assessment integrating cumulative damage-damage threshold interference principle

Reliable life design and damage level evaluation are essential to ensure safe operation and healthy maintenance of high-temperature components. It can be more challenging when considering the degradation of material mechanical property during low cycle fatigue (LCF) and creep-fatigue (CF). To tackle this problem, experimental data accumulations and theoretical foundations, including damage summation rules representing mechanical property degradation and CF damage models are introduced. Following the modified damage-damage threshold interference principle, a three-dimensional reliability assessment diagram is constructed for a low-pressure turbine disk as an example, where the additional third axis represents mechanical property degradation. Among them, probabilistic damage threshold distributions are obtained by the Latin Hypercube Sampling and linear fitting as well as probabilistic damage distributions at weakness hotspots are acquired with the help of finite element analysis. Joint failure evaluation is more conservative since it incorporates all the failure possibilities within the weakness region. Finally, a procedure of residual lifetime design and damage level evaluation is proposed for components with various applications within the framework of LCF and CF reliability analysis.