Multiplication of Dislocations

The processes involved in the nucleation and multiplication of dislocations during cold working are very complex, and beyond the scope of this section. 

Figure 3-3. Representation of dislocation movement in a Frank-Read dislocation source under stress a. Multiplication of dislocation pinned at a distance l.

In a constant strain-rate experiment, the rapid multiplication of dislocations following the yield point can produce more mobile dislocations than are necessary to maintain the imposed strain-rate and consequently the stress drops. The deformation will continue at a constant stress provided any decrease in u is compensated by an increase in iom, or vice versa. However, in general, the stress rises with increasing strain. The slope (dajdt) of the stress-strain curve is determined by the competition between two dislocation processes namely, work-hardening and recovery, which we now consider briefly. 

Climb, deformation twinning, and prismatic loops are also important in the multiplication of dislocations (6, 7). 

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