Abstract: Considering the plastic flow and crack initiation mechanism occurred on the slip systems of ni-base directionally solidified (DS) supealloy, the critical plane method with the combination of “hot point” concept and theory of critical distance(TCD) is conducted on low cycle fatigue (LCF) life prediction of notched DZ125 at 850 ℃. The damage parameter on slip planes is the maximum resolved shear strain range ∆γmax. The obtained results exhibits that the prediction ability of the “Hot point” method is conservative and Kt related. Furthermore, TCD is introduced and the analysis results show that the critical distance is not only related to material, failure cycles and stress ratio, but also related to the degree of stress concentration. Using the sharp notch as standard sample or dealing critical distance with statistics average method, the scatter band of predicted life is more than 10. However, based on the Kt modified critical distance, the scatter band is increased to 2.

Key words: Critical plane method, Low cycle fatigue, Ni-base directionally solidified(DS) superalloy, Slip system, Theory of critical distance