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Dislocations
can interact through their associated stress fields. A Frank-Reed source
generates many dislocations on the same slip plane during a plastic deformation
process, and if the leading dislocation from the source is prevented from
moving due to the presence of a barrier such as a grain boundary the other
dislocations from the source will pile up behind it as shown in the diagram.
The barrier is at O and the dislocations all experience the external resolved
shear stress, t0,
as well as interacting with each other through their own stress fields.
If there are (n - 1) dislocations in the pileup, the leading dislocation
experiences a stress due to the pileup t
= nt0.
In addition, the dislocation pileup interacts with the Frank-Reed source
through a backstress that increases as n increases. This will prevent the
source from forming new dislocation loops as well as preventing the expansion
of existing loops. This is an important mechanism in work hardening. |
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