σ = G·(ε_el) ε̇_pl = n·R·sinh(σ/σ₀) R = ν₀·exp(−Δ/T)
STZ theory (Falk-Langer 1998): plasticity in amorphous solids arises from small clusters ("shear transformation zones") that undergo irreversible shear. Stress-driven activation, avalanche-like slip events.