Crystal Defects: Dislocation Glide (2D)

Applied Load

Shear stress τ 0 MPa

Pinned — stress below critical resolved shear stress.

Live Readout

τ / τ_crit

Core position

2 / 14

Cumulative slip

0.00 b

State

Pinned

How it works

Real crystals almost never break by snapping every atomic bond across a plane at once — the stress needed for that is far higher than what actually deforms metals. Instead an edge dislocation — a line defect where an extra half-plane of atoms wedges into the lattice — glides sideways one lattice spacing at a time, breaking only the row of bonds right at its core.

The dislocation moves once the resolved shear stress τ exceeds a critical threshold τ_crit (the critical resolved shear stress, CRSS). Below it the defect sits pinned; above it, glide speed grows with the excess stress (τ − τ_crit). Each full pass of the core shifts the upper half of the crystal by one Burgers vector b relative to the lower half.

The bending of the bond network around the core follows the real isotropic-elasticity edge-dislocation displacement field u(x,y) — the same equations used in dislocation theory, with Poisson's ratio ν softening the field's decay away from the core. When the dislocation reaches the free surface it leaves a permanent atomic-height slip step — the microscopic origin of plastic deformation in ductile metals like copper, aluminum and steel.

Lattice atom Dislocation core Slip step