Dislocation drag coefficient

Since the dislocation drag coefficient B represents the transfer of momentum per unit area, we assume that B/m remains constant as the velocity increases and hence... 

Dislocation motion in the clear region between obstacles is determined by the viscous drag coefficient B [2]. The relationship between the applied shear stress and dislocation velocity is... 

Intrinsic resistance to dislocation motion can be measured in either of two ways direct measurements of individual dislocation velocities (Vreeland and Jassby, 1973) or by measurements of internal friction (Granato, 1968). In both cases, for pure simple metals there is little or no static barrier to motion. As a result of viscosity there is dynamic resistance, but the viscous drag coefficient is very small (10" to 10" Poise). This is only 0.1 to 1 percent of the viscosity of water (at STP) and about 1 percent of the viscosity of liquid metals at their... 

Drag force, Bv, where B is the drag coefficient and v is the dislocation velocity. Peierls stress Fpeierb. 

For a given material, this input takes the form of an activation enthalpy versus shear stress curve and phonon-drag coefficients calculated for each pressure under consideration. Here full activation enthalpy curves have been calculated at selected pressures in Ta, Mo, and V, and phonon drag has been studied as a function of pressure and temperature in the case of Ta. These results have been fitted and modeled in suitable analytic forms to interface smoothly with the DD simulation codes. Detailed DD simulations have then been carried out in Ta and Mo as a function of pressure, temperature, and strain rate. Our DD simulations have been performed in part with the pioneering lattice-based serial code developed for bcc metals [21,22] but even more extensively with the general node-based Parallel Dislocation Simulator (ParaDiS) code recently developed at the Lawrence Livermore National Laboratory [27-30]. 

Dislocation-free crystals, 38 Dislocations, 38, 46 Distribution coefficient, 41, 43 Divorced eutectics, 83 Drag, 135... 

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