Yield criteria for pressure-sensitive materials: soils, rocks, concrete, and polymers
The Drucker-Prager yield criterion F = α·I₁ + √J₂ − k = 0 generalizes von Mises to pressure-dependent materials. Here I₁ = tr(σ) is the first stress invariant (mean pressure) and J₂ = ½s:s is the second deviatoric invariant. Parameters α and k relate to friction angle φ and cohesion c via Mohr-Coulomb matching. The stress point lies INSIDE the yield surface in the elastic domain; plastic flow occurs on the surface.