forked from 1b-agent/fieldcraft-upstream
Two more large-strain options on the isotropic constants, decoupled like neo-Hookean with the volume kappa/2 (J - 1)^2: Mooney-Rivlin with C10 = mu/2 - C01 (0 <= C01 <= mu/2) and Yeoh with C10 = mu/2 and the higher terms C20, C30, so the small-strain material is the elastic one everywhere. MaterialModel::Polynomial gives the isochoric stress and tangent from Holzapfel's fictitious quantities (eqs. 6.168, 6.193), consistent by central differences, equal to neo-Hookean with C10 alone; hybrid elements take it. Abaqus writes *HYPERELASTIC, MOONEY-RIVLIN and YEOH; LS-DYNA keeps refusing hyperelastic materials in nonlinear steps by name. Verified in uniaxial and equibiaxial tension and pure shear against the compressible closed form (exact). Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm