What is positive edge dislocation?

What is positive edge dislocation?

Edge dislocation is considered positive when compressive stresses present above the dislocation line, and is represented by ┴. If the stress state is opposite i.e. compressive stresses exist below the dislocation line, it is considered as negative edge dislocation, and represented by ┬.

What are the features of dislocations in metals?

Dislocations are defined as the irregularities in the structure of metals. These arise from misplacement of bonds of the atoms in a part of the plane of a crystal and are considered to be weak centres. They are instrumental in affecting the breaking stress and plastic and chemical properties of crystals.

In which plane of HCP crystal slip occurs more commonly?

Slip in hexagonal close packed (hcp) metals is much more limited than in bcc and fcc crystal structures. Usually, hcp crystal structures allow slip on the densely packed basal {0001} planes along the <1120> directions.

What is edge dislocation and screw dislocation?

Edge and Screw Dislocations. • In an edge dislocation, localized lattice distortion exists along the. end of an extra half-plane of atoms. • A screw dislocation results from shear distortion.

What is the fundamental difference between edge and screw dislocation?

The difference between edge and screw dislocation is that the edge dislocation occurs when an extra half-plane of atoms exists in the middle of the crystal lattice whereas the screw dislocation occurs when the planes of atoms in the crystal lattice trace a helical path around the dislocation line.

What is the stacking sequence of the BCC structure?

BCC structure has no closed-packed planes and therefore does not have a stacking sequence. Neither does at have stacking faults.

When do dislocations form junctions in slip systems?

Reactions between dislocations gliding in non-coplanar slip systems form junctions, except in the case of annihilations of two attractive dislocations gliding in two slip planes that contain their Burgers vector (the colinear interaction, cf. [8] ).

How does configuration asymmetry and Poisson’s ratio affect BCC metals?

The effects of configuration asymmetry and Poisson’s ratio are more marked in BCC metals than in FCC metals. These two major effects arise from a number of concurring dislocation mechanisms, which are discussed in some detail.

Is it possible to model the mechanical response of BCC slip systems?

In BCC metals, the few available results are restricted to interactions between the a /2<111> {110} slip systems. The modelling of the mechanical response requires, however, the knowledge of all interactions of the a /2<111> {110} and a /2<111> {112} slip systems.