1. Compressive lattice strain
Tensile lattice strain

6. As the two dislocation approach each other they start to interact.
The compressive regions (purple) repel each other
as do the tensile regions (orange).
This increases the material’s strength.

7. I aint movin’ – you have to push really hard.

8. The row of atoms above the dislocations have high compressive lattice strain and those below have high tensile lattice strain. It takes much higher stress levels to cause this “double” dislocation to move. Dislocation “tangling” is an effective strengthening mechanism which results from high dislocation density (lots of dislocations in the material).