Viscosity resisting dislocation motion

The coefficient, p, of the viscosity resisting dislocation motion is the shear stress at the glide plane, x divided by the frequency of momentum transfer, v. The maximum value that x can have is about Coct/47i, and as mentioned above v = 1013/sec for the Al atoms,so p = Coct./47rv = 4x 10 3 Poise.This is comparable to the dislocation viscosity coefficients in other metallic systems. Another view of the viscosity is Andrade s theory in which ... 

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... 

When normal sites in a crystal structure are replaced by impurity atoms, or vacancies, or interstitial atoms, the local electronic structure is disturbed and local electronic states are introduced. Now when a dislocation kink moves into such a site, its energy changes, not by a minute amount but by some significant amount. The resistance to further motion is best described as an increase in the local viscosity coefficient, remembering that plastic deformation is time dependent. A viscosity coefficient, q relates a rate d8/dt with a stress, x ... 

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See also in sourсe #XX -- [ ]

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