Analytic representations of dislocation velocity

As shown in Fig. 21 for Ta and Fig. 22 for Mo, the activation enthalpy for a/2 111 screw dislocation motion below the Peierls stress in the thermally activated regime is accurately represented by the following well-known analytic form  

Values of the parameters AHq(P), tp, p, and q are listed in Table 4 for the 10 cases for which full activation enthalpy curves for Ta, Mo, and V have been calculated. 

(15) is used in both the lattice-based and ParaDiS DD codes although with different treatments of the internal parameters tiHaiP), zp, p, and q. In the lattice-based code, the parameters in Table 4 have been used directly, except for tp in Ta, which has been scaled by a factor of 0.5 to account for the apparent overestimate of the Peierls stress relative to experiment noted in Fig. 18. In ParaDiS, however, additional modeling has been introduced to smooth the pressure dependence of the internal parameters. First, p and q are assumed to be universal constants, which have been fixed in our ParaDiS simulations at p — 0.50 and q — 1.23. In addition, AHo(P) and Tp are assumed to obey the high-pressure scahng laws 

In the lattice-based DD code, the screw dislocation velocity below the Peierls stress in the thermally activated regime is calculated as 

Dislocations and Plasticity in bcc Transition Metals at High Pressure 

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