Multiple cross glide

Flinn et al. [30] describes an experimental impact technique in which <100)-oriented LiF single crystals ( 8 ppm Mg) are loaded in a controlled manner and the multiplication of screw dislocations is measured. The peak shear stress in this relatively soft material is 0.01 GPa. For shear impulses exceeding approximately 40 dyne s/cm, dislocation multiplication is adequately described by the multiple-cross-glide mechanism [(7.24)] with m = l/bL = (2-4) X 10 m, in reasonable agreement with quasi-static measurement [2]. 

Although this sometimes occurs through the operation of Frank-Read sources it is not generally observed. What does generally occur is similar, but more complex. The process is called multiple-cross-glide, and was proposed by Koehler (1952). Its importance was hrst demonstrated experimentally by Johnston and Gilman (1959). In addition to its existence, they showed that the process produces copious dislocation dipoles which are responsible for deformation-hardening. 

The multiple-cross-glide process does not lead to steady-state dislocation multiplication. It does lead to a proportionality between the dislocation density at N, a given time and the rate of increase of dislocation density, dN/dt, that is, to first order kinetics. Thus, the dislocation density grows exponentialy with time ... 

Cross-gliding of screw dislocations has an important effect on the overall plastic deformations of crystals because it is the primary cause of both multiplication, and strain-hardening as discussed above. 

The other important multiplication, which takes place via cross glide, occurs more readily than that which operates through the classical Frank-Read mechanism. In a dislocation loop, that part of the line which has a screw orientation can move out from its slip plane (compare... 

Cascade principle was also combined with cross-count horizontal scavenging [7] in a vertical vessel divided into separation and precipitation chambers, separated by a permeable grid with concave shelves (Fig. 2c). Particles fed from the top pour onto the upper shelf, glide down and fall of its edge where they are scavenged by the cross-current stream. Part of fines is carried into the precipitation chamber and the rest of the mixture falls onto the next shelf for repeated separation. After multiple separations, coarse fraction exits from the separation chamber and fines leave the precipitation chamber. The finest fraction exits with the stream and is collected in cyclones or filters. 

Usually, creep deformation of ice single crystals is associated to a steady-state creep regime, with a stress exponent equal to 2 when basal glide is activated . In the torsion experiments performed, the steady-state creep was not reached, but one would expect it to be achieved for larger strain when the immobilisation of the basal dislocations in the pile-ups is balanced by the dislocation multiplication induced by the double cross-slip mechanism. 

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