13th International Conference on Fracture June 16–21, 2013, Beijing, China -4- 10 20 30 40 50 60 70 80 -3 -4 -5 Δ Kth C B A Region Ⅲ Region Ⅱ Region Ⅰ HPS 485W B=19.5mm R=0.1 log ΔK( MPa×m1/2) log(da/dN) (mm/cycle) -6 Figure 4. log(da/dN) and log(△K) curve for 19.5mm specimens 3. Test result analysis Ren et al. conducted da/dN test for 24mm, 32mm and 50mm 14MnNb steel under load ratio of R=0.1, 0.2 and 0.5 [8]. The test result of Ren Weixin is shown in Table 3. Neglecting thickness effect, compare da/dN test result of HPS 485W and 14MnNb was conducted. For R=0.1, the tested m is ranging from 2.53 to 3.28 and C is ranging from 2.29×10-12m/cycle to 2.19×10-11m/cycle for HPS 485W, while the tested m is ranging from 2.67 to 3.74 and C is ranging from 5.83×10-10m/cycle to 1.98×10-8m/cycle for 14MnNb. For R=0.5, the tested m is ranging from 2.72 to 4.13 and C is ranging from 2.37×10-13m/cycle to 1.48×10-11m/cycle for HPS 485W, while the tested m is ranging from 3.39 to 4.08 and C is ranging from 3.08×10-10m/cycle to 1.76×10-9m/cycle for 14MnNb. Learn from comparative result, the tested value of m is similar for traditional bridge steel 14MnNb and HPS 485W, which is about 3. However, the tested value of C for HPS 485W is much smaller than 14MnNb. Fatigue crack growth rate is increasing with the increase of C and m, so compared with traditional 14MnNb, HPS 485W has superior fatigue crack resistance. The average value of m in Table 3 is 3.17. Using this average value of m=3.17, the log(da/dN) and log(△K) curves are re-fitted by Paris equation for HPS485W specimens. The re-fitting test result is shown in Table 4. The correlated coefficient in Table 4 means the derivation from average value for all the HPS 485W specimens. Learn from Table 4, firstly, for the same load ratio R, thickness of specimen has obvious affection for fatigue crack propagate rate. Secondly, for specimen with same thickness, with the increase of R, value of C is increasing, which means fatigue crack growth rate is increasing. Table 3. da/dN test result for 14MnNb Regression Parameters Thickness R m C（m/cycle） Correlation coefficient 0.1 3.59~3.74 5.83～8.38×10-10 0.97～0.99 0.2 3.31~3.72 6.55×10-10～ 1.31×10-9 0.97～0.99 23.5mm 0.5 3.81~3.97 3.83～5.39×10-10 0.97～0.99 0.1 2.67~2.91 1.02~1.98×10-8 0.99 0.2 3.45~3.52 1.01~1.62×10-9 0.99 31.5mm 0.5 3.39~3.75 4.81×10-10~1.76×10-9 0.95~0.99 49.5mm 0.1 2.97~3.24 2.87~6.43×10-9 0.99
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