Edge dislocation moving through a crystal lattice under applied shear stress
An edge dislocation is a line defect with Burgers vector b perpendicular to the dislocation line. Under shear stress τ, it glides when τ > τ_Peierls ≈ (2G/1−ν)·exp(−2πw/b), where w is the dislocation width. Dislocation motion requires ~1000× less stress than moving perfect lattice planes, explaining why metals plastically deform far below theoretical shear strength.