Mechanical components are frequently subjected to severe cyclic pressure and/or temperature loadings. Therefore, numerical and analytical low cycle fatigue methods become widely used in the field of engineering to estimate the design fatigue lives. The primary aim of this work is to evaluate the accuracy of the most commonly used numerical and analytical low cycle fatigue life methods for specimens made of 316 LN austenitic stainless steel and subjected to fully reversed uniaxial tension-compression loading, in the room temperature condition. It was found that both Maximum shear strain and Brown-Miller criterions result in a very conservative estimation for uniaxially loaded specimens, however, Maximum shear strain criteria provides better results compared to the Brown-Miller criteria. The total strain energy density approach was also used, and both the Masing and non-Masing analysis were adopted in this study. It is found that the Masing model provides conservative fatigue lives, and non-Masing model results in a more realistic fatigue life prediction for 316 LN stainless steel for both low and high strain amplitude. The fatigue design curves obtained from the commonly used analytical low cycle fatigue equations were reexamined for 316 LN SS. The obtained design curves from Langer model and its modified versions are non-conservative for this type of material. Consequently, the authors suggest new optimized parameters to fit the given test data. The obtained curve using the currently suggested parameters is in better agreement with the experimental data for 316 LN SS.

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

When coupling with temperature is incorporated, the problem of fatigue is formulated within the general framework of thermomechanical fatigue. Considering the special case of steel structures, in addition to variations of material and fatigue parameters with temperature, fatigue damage depends on the phasing existing between the concomitant strain and temperature cycles. In this work, the extended finite element method is used to simulate crack growth under thermomechanical fatigue coupling. Assuming large cycle duration for which temperature variations can be considered to be uniform, this approach is applied in the context of linear elastic fracture mechanics for the particular case of the three dimensional Compact-Tension specimen. The objective is to attempt understanding more closely crack growth mechanism under thermomechanical loading. Characterization of fatigue was assessed as function of phasing and strain restraint.

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