A two-scale thermodynamic entropy model for rapid high-cycle fatigue property evaluation of welded joints

This investigation attempts to propose a two-scale thermodynamic entropy model that can quantify the micro-scale fatigue behaviors from the macroscopic level. Both non-damaging anelastic and damaging inelastic microstructural motions that cause entropy generation at different stress amplitude blocks of specimens are considered. On this basis, a thermodynamically based correlation between the macro-stress amplitude and the microstructural motion is constructed following the framework of thermodynamics. Butt joints made of low carbon steel are used as the experimental materials in this work. The fatigue limit of welded joints is estimated in a short time using the developed approach in combination with the correlation coefficient optimization method. Finally, the fracture fatigue entropy (FFE) model, corresponding to the twoscale theory, is developed to achieve fast prediction of fatigue life by considering the threshold value associated with the irreversible inelastic entropy generation in high-cycle fatigue. The results show that the predicted data are in satisfactory agreement with the experimental data.