Fatigue life prediction in nickel-based superalloys using unified mechanics theory

Under strain-controlled cyclic loading at elevated temperature (650 degrees C), the low-cycle fatigue behavior of an advanced nickel-based superalloy (RR1000) has been studied. In the current study, a unified mechanics theory (UMT)-based model is presented and applied to predict the fatigue life of nickel-based superalloy (RR1000). Entropy is used as a damage metric in the fatigue life prediction of material in the present study. The entropy generation rate under the mechanical loading conditions is calculated by considering plastic deformation as the governing mechanism for dissipation. Using the UMT, damage in nickel-based superalloy (RR1000) is evaluated to predict low-cycle fatigue life. Also, the stress-strain hysteresis loop prediction has been done at any strain amplitude without making use of curve-fitting phenomenological models. The hysteresis loops can be predicted at any given number of cycles for all strain amplitudes using UMT without doing complete fatigue experiments, which in turn reduces the efforts and costs of the cumbersome fatigue experiments.