Equal numbers of dislocations with positive and negative Burgers vectors are present in each sub-area: the net Burgers vector equals zero.
where L is the correlation length, b is the length of the Burgers vector b, [sigma] equals |sin[psi]| where [psi] is the angle between the line vector l of the dislocation and the vector g, where g is the diffraction vector at which Bragg's law holds exactly for the reflection considered (length g; for cubic material it holds: g = ([h.
i], for the dislocations with Burgers vectors inclined to the diffraction vector and for the dislocations with Burgers vectors perpendicular to the diffraction vector equal 0.
Therefore small, Volterra type loops should form first at "soft" spots throughout the glass, with a constant Burgers vector b(M).
In the region of yield, in order to develop the loop further through the next regions M[prime], additional dislocation loops of Burgers vector [Delta]b = b(M[prime]) - b(M) have to be added to the main loop b(M), where the local Burgers vector b(M[prime]) fitting molecular arrangements in zone M[prime] differ too much from the initial shift b(M).
This whole defect configuration depicts how a Somigliana loop extends in a glass, with its Burgers vector varying continuously as <b> [+ or -] [Delta]b.
0,ij]dV, produced in a volume dV by the movement of a dislocation of Burgers vector b over an area dA of an interface of normal n, is known to depend only on b and n through the general relation (13):