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A
dislocation is characterized by two parameters, the Burgers vector, b,
that measures the slip displacement associated with the line defect, and
the unit line vector, t,
that points in the local direction of the dislocation line. As illustrated
in the diagram, b,
has both constant magnitude and direction at all points on the dislocation
line. The line vector, t,
always points along the dislocation line in the same direction but changes
its orientation as the dislocation line changes orientation.
The
nature of the distortion associated with the dislocation depends upon the
relative orientation of b
and t.
When the two vectors are parallel, the dislocation is a screw dislocation,
when they are orthogonal the dislocation is an edge dislocation. A mixed
dislocation has an arbitrary angle between these two vectors.
These
vectors also define the slip plane of the dislocation. The slip plane must
contain both b
and t.
An edge dislocation therefore has a unique slip plane, however, a screw
dislocation can slip on any plane that passes through the dislocation line. |
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