13th International Conference on Fracture June 16–21, 2013, Beijing, China dwell times on fatigue resistance is obvious. ① The cyclic stress response of DZ125 is temperature dependent. At 850℃ it is cyclic hardening, but it seems to be slight cyclic softening at 980℃. ② The fatigue resistance at 850℃ is better than 980℃ in long life region, but worse fatigue strength is obtained at 850℃ in short life regime. ③ Roughly, the introduction of compressive, tensile and balanced strain dwell times can all lead to obvious fatigue life degradation, but the balanced dwell type gets the entirely shortest life, the tensile dwell type with reduced mean stress shows predominant fatigue property at low strain range but bad fatigue resistance at high strain range. ④ The cyclic hardening behavior could be observed with no strain dwell times, but it turns to be cyclic softening behavior with dwell times. Especially the relaxation of cyclic peak stress is also closely associated with dwell times. ⑤ Based on the similar fatigue life between Rε=0 and -1 with no dwell times at both 850 and 980℃, the continuous fatigue with strain ratio equals to -1 is more sensitive to dwell times. Compared with smooth fatigue life at 850℃, obvious life degradation is induced by stress concentration. Furthermore life degradation is happened with added stress dwell times. (2) The critical method is used and damage parameters on critical plane is the modified SWT parameter; Moreover, the failure cycles related critical distance concept is combined for predicting fatigue life affected by stress concentration where a factor of two is obtained. Based on SWTM parameter, Miner’s linear cumulative damage theory and Larson-Miller plots, a factor of three is obtained in spite of the complicated dwell forms on smooth specimens. Furthermore, with added critical distance concept and confirmed creep equivalent stress, the prediction LCF life affected by both dwell times and stress concentration is successfully carried out. 6 References [1] R. Mucke, O.E. Bernhardi, A constitutive model for anisotropic materials based on Neuber's rule. Comput Method Appl M, 192 (2003) 37-38. [2] ZJ. Moore, Life modeling of notched CM247LC DS Nickel-base superalloy. Atlanta: Georgia Institute of Technology, 2008. [3] A. Karolczuk, E. Macha, A review of critical plane orientations in multiaxial fatigue failure criteria of metallic materials. Int J Fracture, 134 (2005) 267-304. [4] N.K. Arakere, G. Swanson, Effect of crystal orientation on fatigue failure of single crystal nickel base turbine blade superalloys. J Eng Gas Turb Power, 124 (2002) 161-76. [5] RA. Naik, DP. Deluca, Critical plane fatigue modeling and characterization of single crystal nickel superalloys. J Eng Gas Turb Power, 126 (2004) 391-400. [6] H. Neuber, Theory of notch stresses: principles for exact calculation of strength with reference to structural form and material. 2rd ed. Berlin: Springer Verlag; 1958. [7] RE. Peterson, Notch sensitivity. In: G. Sines, JL. Waisman, editors. Metal fatigue, New York: McGraw Hill (1959) 293-306. [8] ZHANG Li, CHENG Jin, LI Xinggang. The fatigue life prediction method of notched specimen based on the critical plane. Journal of Astronautics, 28 (2007)
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