Dislocations, Dislocation Motion, and Slip Systems

What is a dislocation?

• An imperfection in the atom

• An edge defect

• A line imperfection in an otherwise perfect crystal

• A screw defect

This type of force moves dislocations through a crystal:

• compression

• torsion

• tension

• shear

Regions within a crystal where planes of atoms can slide past one another.

• substitutional

• dislocation

• slip plane

• work-hardening

• grain boundary

Regions in crystals where atoms are not perfectly aligned due to the presence of an extra partial plane of atoms.

• screw dislocation

• edge dislocation

• slip plane

• grain boundary

What is this?

• edge dislocation

• screw dislocation

• mixed dislocation

What is this?

• Edge dislocation

• Screw dislocation

• Mixed dislocation

What is this?

• Edge dislocation

• Screw dislocation

• Mixed dislocation

How do you make an edge dislocation move?

• Apply a shear stress perpendicular to the Berger's vector and parallel to the dislocation

• Apply a shear stress parallel to the Berger's vector and the dislocation

• Apply a shear stress parallel to the Berger's vector and perpendicular to the dislocation

• Apply a shear stress perpendicular to the Berger's vector and the dislocation

Why are covalently-bonded materials brittle?

• The bonds are directional which prevents dislocations from moving

• The bonds are easy to break

• They don't have dislocations

If covalently-bonded materials are brittle, why aren't polymers?

• The bonds are easier to break

• They're amorphous which allows the long chains of bonds to disentangle, stretch, and rotate

• The bond directions go the other way