An improved constitutive model for rapid fatigue properties evaluation based on fatigue damage entropy

A constitutive model, which reflects the non-linear response association between microstructural motion and thermodynamic entropy production, is improved in this study. Two critical stress amplitudes associated with two microstructural movement mechanisms are considered in the improved constitutive model. The determination procedures for the parameters of the presented model are developed. Entropy generation data from three materials computed by two calculation methodologies, collected from the experiment and literature, are used to validate the improved model. Subsequently, a rapid fatigue life estimation method is proposed by using the accumulated entropy corresponding to fatigue damage, i.e. FFE, related to irreversible inelastic microstructural motion. Fatigue tests of welded joints fabricated by Q310NQL2 and Q345NQR2 steels, Q235 steel specimens, as well as experimental data, stainless steel specimens, collected from the literature, are employed to determine the values of the parameters of the developed model. The model is then used to forecast the S–N curve of butt joints with a 50% survival probability, and on this basis, the S–N curve with a certain confidence level is well estimated by the improved statistical method. This enhanced model may offer a fast forecast of the P–S–N curve at a certain confidence level within a limited set of tested data ranges.