Burger s vector

Burger s vector A measure of the crystal lattice displacement resulting from the passage of a dislocation. 

The Burger s vector is drawn from the finish to the start of the path. 

The second type of line defect, the screw dislocation, occurs when the Burger s vector is parallel to the dislocation line (OC in Figure 1.33). This type of defect is called a screw dislocation because the atomic structure that results is similar to a screw. The Burger s vector for a screw dislocation is constructed in the same fashion as with the edge dislocation. When a line defect has both an edge and screw dislocation... 

Figure 1.33 Representation of defect line (OC), Burger s circuit and Burger s vector in a screw dislocation. From Z. Jastrzebski, The Nature and Properties of Engineering Materials, 2nd ed. Copyright 1976 by John Wiley Sons, Inc. This material is used by permission of John Wiley Sons, Inc.

Dislocation Type Burger s Vector Propagation Direction... 

Screw II to dislocation line L to dislocation line, L to Burger s vector... 

In this expression r is some combination of elastic constants ( 1q11 erg/cm ), b the magnitude of the Burger s vector of the dislocation, a the nearest neighbor distance in the crystal and... 

The Burger s vector value (bj for polymer materials is determined fi om the relationship ... 

Figure6.7 Dislocations can have various widths depending on the atomic bonding. The dislocation displacement is spread over several atoms. The motion of the dislocation involves individual atomic displacements less than the Burger s vector. The shaded atoms indicate the position of the atoms after a small displacement.

Because such a large number of dislocations exist in a crystal, dislocations often intersect, and the interaction between dislocations results in various physical phenomena occiuring in crystals. The energy of a dislocation is proportional to the square of its Burger s vector b. Two dislocations can coalescence spontaneously if the total energy of the coalesced dislocation is smaller than the sum of the energies of the two... 

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