Edge dislocations have the direction of the burgers vector perpendicular to the dislocation line, while screw dislocations have the direction of the burgers vector parallel to the dislocation line.
12.
When a dislocation line intersects the surface of a metallic material, the associated strain field locally increases the relative susceptibility of the material to acidic etch pit of regular geometrical format results.
13.
The screw dislocation is more difficult to visualise, but basically comprises a structure in which a helical path is traced around the linear defect ( dislocation line ) by the atomic planes of atoms in the crystal lattice.
14.
The process results in a dislocation loop around A and B in the slip plane which expands under continued shear stress, and also in a new dislocation line between A and B which, under renewed or continued shear, can continue to generate dislocation loops in the manner just described.
15.
This is true in the case of an edge dislocation if the scattering vector of the Bragg reflection used is parallel to the Burgers vector of the dislocation, or at least has a component in the plane perpendicular to the dislocation line, but not if it is parallel to the dislocation line.
16.
This is true in the case of an edge dislocation if the scattering vector of the Bragg reflection used is parallel to the Burgers vector of the dislocation, or at least has a component in the plane perpendicular to the dislocation line, but not if it is parallel to the dislocation line.
17.
If a shear stress \ tau is exerted on the slip plane then a force F = \ tau \ cdot bx, where b is the Burgers vector of the dislocation and x is the distance between the pinning sites A and B, is exerted on the dislocation line as a result of the shear stress.
