13th International Conference on Fracture June 16–21, 2013, Beijing, China —6— 0 1 0 2 0 3 0 4 0 5 0 6 0 0 3 0 0 6 0 0 9 0 0 1 2 0 0 1 5 0 0 N , c y c l e Δ S / S , % Fig.4 Relations of percentage of stress attenuation to cycle N Table.2 Data of crack initiation and initiation life Specimen No. Percentage of stress attenuation ΔS/S，% Crack initiation length a0/mm Crack initiation Life Ni Entire life N Ni/N /% 5 5.33 2.10 808 1003 80.6 6 5.33 2.10 876 1228 77.7 7 5.33 2.10 1044 1372 76.1 average 5.33 2.10 909 1168 78.1 Table 2 indicate that equivalent value of crack initiation of the structural steel 10CrNiMo is close to 2.0mm and initiation life is approximately 900 cycles, which is nearly 80% of the entire life. 6. Conclusions (1)Any equivalent value of crack initiation, corresponding percentage of stress attenuation, can be calculated and crack initiation life be predetermined, according to prediction model for low cycle fatigue crack initiation proposed by damage mechanics theory, combining with some simple tests. (2)Relative error between average of real equivalent crack length and that from prediction model is not more than 5.0%, which manifests that the prediction model is reliable and applicable. (3) When the total strain amplitude is 0.6%, equivalent value of crack initiation of the structural steel 10CrNiMo is close to 2.0mm and initiation life is approximately 900 cycles, which is nearly 80% of the entire life, on the basis of prediction model and related tests, which will be referred to in engineering application and design. References [1] Fuchs H O and Stephens R I. Metal Fatigue in Engineering. New York: John Wiley and Sons,1980, 67. [2] Pearson S. Roy. Air. Estab. Tech. Report 71109,1971.
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