How line defects move through crystal lattices, producing permanent deformation
Metals deform plastically via dislocations — line defects in the crystal lattice (here shown as ⊥ symbols). A dislocation moves when shear stress τ exceeds the Peierls-Nabarro barrier. Thermal fluctuations allow thermally-activated motion below the barrier. Taylor hardening: dislocations block each other. Density ρ grows, yield stress ~ √ρ. Burger's vector b defines slip direction. Plastic strain = ρ·b·L (Orowan equation).