# Materials Science and Engineering/List of Topics/Mechanics of Materials/Dislocation Mechanics

## Dislocation Mechanics

### Dislocations - Geometrical Aspects

A dislocation is a linear or one-dimensional defect around which some of the atoms are misaligned.

#### Edge Dislocation

Edge dislocation is a linear defect that centers around the line that is defined along the end of the extra half-plane of atoms.  This is sometimes termed the dislocation line, which,for the edge dislocation in is perpendicular to the plane of the page. Within the region around the dislocation line there is some localized lattice distortion.The atoms above the dislocation line are squeezed together, and those below are pulled apart; this is reflected in the slight curvature for the vertical planes of atoms as they bend around this extra half-plane

#### Screw Dislocation

Screw dislocation may be thought of as being formed by a shear stress that is applied to produce the distortion. the upper front region of the crystal is shifted one atomic distance to the right relative to the bottom portion. The atomic distortion associated with a screw dislocation is also linear and along a dislocation line. The screw dislocation derives its name from the spiral or helical path or ramp that is traced around the dislocation line by the atomic planes of atoms. Sometimes the symbol is used to designate a screw dislocation.

#### Orowan's Equation

The density of Cu is 8.9g/cm^3 and its atomic weight (or mass) is 63.546. It has the FCC structure. Determine its Orowan’s theoretical strength in the [110] direction if its Young’s modulus E is 200 GPa.