Compare yield criteria for 3D stress states including anisotropic materials.

Isotropic criteria: von Mises (smooth cylinder in principal stress space), Tresca (hexagonal prism), Drucker-Prager (cone for pressure-sensitive materials). For anisotropic materials like rolled sheets, Hill's criterion adds directional strength ratios. Yield locus shape affects forming limits and springback. FEA material models must match actual behavior - isotropic hardening vs kinematic hardening affects cyclic loading predictions significantly.