Indentation Size Effect: Nix-Gao Strain Gradient Plasticity

Press a virtual pyramidal indenter into a crystal at nanometre depths and watch hardness rise as the indent shrinks — the Indentation Size Effect. A geometric argument by Nix & Gao (1998) explains it: bending the lattice around a sharp tip demands geometrically necessary dislocations whose density scales as 1/h, and once that density is folded into strain-gradient plasticity it predicts (H/H₀)² = 1 + h*/h. This simulator renders the indenter and a live cloud of GND loops scaled directly from that density, tracks hardness, the H/H₀ ratio, GND density and contact radius as you drag the depth slider, and plots the full H(h) curve so you can see where a given material's h* sits relative to the current depth.