Effect of Cycle Duration and Phasing on Thermomechanical Fatigue of Dog-Bone Specimens Made form Steel

Problem statement: Lifetime of standard dog-bone specimens made form steel as affected by phasing between thermal cycles and strains cycles and by cycle duration in thermomechanical fatigue is assessed under various conditions of loading. Approach: The methodology used was based on finite element post-processing analysis by specialized fatigue software package that takes into account coupling of damage from three primary sources: Fatigue, oxidation and creep. Results: A parametric study has been conducted for various thermomechanical loadings and effects of phasing and cycle duration on lifetime have been evaluated. The associated percentages of damage mechanisms due to fatigue, oxidation and creep have been determined. Conclusion: It has been shown that both phasing and cycle duration have considerable effect on lifetime. In the range of parameters investigated, the in-phase cycles were found to reduce considerably damage in the specimen for low pressures and low temperatures. The results have shown also that there was no way of unique comparison of the various phasing configurations, since there exists always a case of thermomechanical loading for which one phasing configuration yields higher damage than any another configuration.