Dislocation motion

In this picture do we speak of (microscopic) plastic deformation if the edge dislocation has moved all the way to the right and emerges out of the surface? Or if you apply shear stress and stop when the edge dislocation has moved from A to B is it then plastically deformed aswell?

Screw dislocation

How about with this situation? Is it only plastically deformed when the dislocation line has moved all the way to the left and thus the screw dislocation emerging from the crystal?

Ow and one last small question: 'before and after the movement of a dislocation through some particular region of the crystal, the atomic arrangement is ordered and perfect; it is only during the passage of the extra half plane that the lattice structure is disrupted'

This particular region is that the region B to D, when the dislocation starts at A and moves untill emerges? And if the dislocation motion stops while the edge dislocation is at position B or C then this region isn't ordered and perfect? Because there is a linear defect in it?


1 Answer 1


Plastic deformation is defined as non-recoverable deformation. When a stress is applied to the material, it will first deform elastically. When the yield limit is reached, it will deform plastically which for metals means by dislocation motion. If during dislocation motion the stress is removed, the dislocation does not vanish, and the atoms stay in their new locations. Therefore, the answer to your questions is that any dislocation motion of any distance constitutes plastic deformation.

For your last question, when the dislocation has caused any strain, the lattice is imperfect. So the first two subfigures of the top image are imperfect, while the last is "perfect" in the sense of no lattice strain.


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