13th International Conference on Fracture June 16–21, 2013, Beijing, China -7- fitting our results with experiments and MD modeling. At the same time, the fracture model gives correct slopes of the curve ( ) sp / d dt σ ε in the both regimes of nucleation, and these slopes are not regulated by the model parameters. For unequivocal selecting of the parameters a simultaneous comparison with experimental data at the moderate strain rates (heterogeneous nucleation) and with results of MD simulations at very high strain rates (homogeneous nucleation) is optimal. Figure 2. The strain dependence of stresses at two constant strain rates in the monocrystalline copper (a). Strain dependences of the average micro-cracks radius (1), the critical radius (2) and the concentration of micro-cracks (3) at the constant strain rate и 107 s-1 (b). Figure 3. The strain rate dependences of the dynamic strength of copper (a) and aluminum (b). For copper (a): experimental data for monocrystals 1 – [2] and 3 – [20]; experimental data for polycrystals 2 – [2], 4 – [21], 9 – [22], 10 – [4], 11 – [23]; markers 5 for monocrystal and 6 for polycrystal are the results of MD [7]; lines are predictions of the model for monocrystals 7 and polycrystals 8. For aluminum (b): experimental data, 1 - monocrystal [1], 2 - polycrystal of 99.9% purity [24], 3 – alloy AlMg6 [25], 4 - commercially pure aluminum AD1 [26], 8 – polycristals [3], 10 – [22], 11 – [4]; results of MD for monocrystals (5) - [10] and 9 - [9]; lines are predictions of the model for monocrystals 6 and polycrystals 7.
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