LCF behavior and life modeling of DZ125 under complicated load condition at high temperature

Based on the author and co-worker's systemically experimental investigation on low cycle fatigue (LCF) of directiona lly solidified (DS) Ni-based superalloy DZ125 at 850 and 980?, LCF behavior analysis and life modeling are carried out here, where the influence of temperature, strain ratio, stress concentration, dwell types and dwell times on fatigue resistance is considered. (1) The steady cyclic stress/strain response is captured based on the transversely isotropic continuum elastic-viscoplasticity model. (2) For the coherent face centered cubic (FCC) structure of DS Ni-based superalloy DZ125, it is physically motivated to consider slip planes as critical plane under fatigue load, the mean stress modified Smith-Watson-Topper (SWTM) parameter Δγ_max(τ_max+τ_m)/2 on the discrete crystallographic slip planes is evaluated. The combination of the theory of critical distance and critical plane method exhibits acceptable predicted LCF life affected by stress concentration. (3) Based on SWTM parameter, Miner's linear cumulative damage theory and Larson-Miller plots, accurate life prediction on smooth LCF with complicated dwell forms is gotten. However, to predict the LCF life affected by dwells and stress concentration, the critical distance concept and the average processed creep stress is introduced, which shows acceptable accuracy of predicted LCF life.