13th International Conference on Fracture June 16–21, 2013, Beijing, China location and direction of the crack. With well-defined crystallographic slip planes of DS superalloy, the plastic flow takes place along the slip planes and eventually persistent slip bands start to appear, which might act as fatigue crack initiation location. So it is physical based to consider crystallographic slip planes as critical planes. Up to now, lots of critical plane approaches, such as stress based, strain based or energy based models, have been proposed [3]. Arakere and Swanson [4], Naik [5] considered the octahedral and cube slip planes as critical planes, and then correlated damage parameters on these planes with LCF behavior of PW1480/1493 and HCF behavior of PW1484. The results showed that damage parameters on critical plane were partly promising. Moreover, life prediction using the maximum peak stress or strain is often conservative for characterizing the fatigue life affected by stress concentration. The theory of critical distance is proposed by Neuber [6] and Peterson [7], who assumes that fatigue damage cannot be correctly estimated except the entire stress or strain field damaging the fatigue fracture process zone is taken into account, this method has been successfully applied to predict the fatigue life with different load conditions from the LCF to HCF region. However, lots of work still needs to be done on evaluating the accuracy and reliability of more materials systematically. For the FCC structure of DS and single crystal (SC) superalloy, when the notched component is subjected to cyclic load condition, the combination of critical plane and critical distance method is an interesting attempt. Up to now, lots of work following this combined theory has been carried out. Based on the elastic-plastic finite element analysis (FEA), Zhang Li et al [8] obtained the stress/strain condition at notch root, but just the critical plane method and isotropic material is evaluated；Zhufeng Yue et al [9] considered the slip planes as critical planes and assumed the mean stress modified resolved shear stress range as fatigue damage parameter, this method shows good prediction ability of SC superalloy DD3, but critical distance concept was not evaluated. Especially, Leidermark et al [10] carried out notch fatigue investigation on SC superalloy MD2, they found that conservative predicted life will be obtained if only the slip systems based critical plane method was adopted, but obvious improvement could be seen when the critical distance concept is introduced. Meanwhile, when considering the influence of dwell times, not only the individual effects of fatigue and creep damages, but also effect of their interaction should be considered. Continuum damage mechanics (CDM) method [11] is a traditional one for fatigue life prediction affected by dwells. However, a simply and efficient approach is Miner’s linear cumulative damage theory [12], where the creep damage could be determined by the classic Larson-Miller plots [13]. DZ125 is DS superalloy exhibits excellent high temperature thermo-mechanical properties. For the typical load condition of turbine blades, much more interest of our research group on DZ125 has been precipitated on experimental investigation, constitutive modeling and life prediction, which mainly consider the influence of temperature, strain ratio, stress concentration, dwell types and dwell times. Although lots of research of DZ125 has been carried out [14, 15], life modeling of LCF on
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