13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- relationship between the tensile speed u t and the strain rate for 0.03mm ρ= and 0.2mm. Here the results for 5 10 , u t = 6 10 mm s and step load u t =∞ are also indicated when the maximum displacement is 1.5mm. It is seen that the strain rate is proportional to the tensile speed when 5000 u t mm s ≤ . However, the strain rate becomes constant when 5 10 u t mm s ≥ . 5. Dynamic stress and strain rate distributions of the minimum section Figure 9(a) and Fig.10(a) show the dynamic stress distributions at the minimum section when the maximum dynamic stress appears. From Fig. 9(a), it is seen that the maximum dynamic stress ( ) max t σ at the notch root when 0.03mm ρ= is 14.48 times than that of the nominal stress ( ) nom t σ at the minimum section at each time for Case 1 –Case 5. On the other hand, from Fig. 10(a), it is seen that the maximum dynamic stress ( ) max t σ at the notch root when 0.2mm ρ= is 6.43 times than that of the nominal stress ( ) nom t σ at the minimum section at each time for Case 1 –Case 5. The stress concentration factor coincides with the static stress concentration factor obtained by Noda–Takase [12]. Figure 9(a) and Fig.10(a) show the strain rate distributions at the minimum section when the maximum strain rate appears. From Figure 9 (b), it is seen that the maximum strain rate ( ) max t ε at notch root when 0.03mm ρ= is 22.87 times than that of the nominal strain rate ( ) nom t ε at the minimum section for Case 1 –Case 5. From Fig. 10 (b), it is seen that the maximum strain rate ( ) max t ε at the notch root when 0.2mm ρ= is 8.72 times than that of the nominal strain rate ( ) nom t ε at the minimum section for Case 1 –Case 5. Figure 8. Maximum strain rate and converged strain rate vs. tensile speed 10 100 1000 10 4 10 5 10 6 100 1000 10 4 10 5 10 6 10 7 ・・・∞ Strain rate ε at the notch root A [s -1 ] Tensile speed u/t [mm/s] ε const when ρ=0.2 ε const when ρ=0.03 ε max when ρ=0.2 ε max when ρ=0.03 A
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