13th International Conference on Fracture June 16–21, 2013, Beijing, China LCF behavior and life modeling of DZ125 under complicated load condition at high temperature Yang Xiaoguang*，Huang Jia，Shi Duoqi，Hu Xiaoan, Dong Chengli School of Energy and Power Engineering, Beihang University, Beijing 100191, China * Corresponding author: yxg@buaa.edu.cn Abstract Based on the author and co-worker’s systemically experimental investigation on low cycle fatigue (LCF) of directionally 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 ∆γmax∙(τmax+τm)/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. Keywords Low cycle fatigue, Dwell times, Stress concentration, Theory of critical distance, Critical plane method 1 Introduction Ni-based DS superalloy is increasingly being applied for turbine blades in high performance aircraft engines for superior creep and fatigue strength at high temperatures [1]. Turbine components work in harsh and vibration environments, such as increased operating temperatures, existed cooling holes on blades and vanes; dwell effects is also introduced by start-up, operation, and shut-down sequences. So life modeling of hot sections components of gas turbines is complicated by the presence of stress concentration, dwell times, elevated temperature. However, much more interest has been still precipitated in developing models to obtain accurate predicted service life for costly inspecting, servicing, and replacing of damaged components [2]. According to the literature survey, critical plane based life models and theory of critical distance are typical methods developed for predicting continuous smooth and notched LCF life of DS superalloy. Critical plane methods are originally developed for multi-axial fatigue; this method could predict not only the fatigue life but also the
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