Plastic Deformation

· For a crystalline material: b₁ = b₂ = b, i.e. F_r = ± Gb²/2πr
· If the dislocations are of the "same sign" (have parallel Burgers vectors) they repel each other
· Dislocations of opposite sign (anti-parallel Burgers vectors) attract each other
· Dislocations generated by a Frank-Reed source on a single slip plane have the same Burgers vector, and the free dislocation loops repel each other.

From: Hull, "Introduction to Dislocations," Pergamon (1965)

· If the motion of one free loop is stopped, the other dislocations from the source will pile up behind this stopped dislocation (as illustrated) and reduce the plastic deformation. This increases the work hardening rate.