forked from 1b-agent/fieldcraft-upstream
Neo-Hookean, Mooney–Rivlin and Yeoh materials in explicit dynamics, in total form from the deformation gradient (objective by construction): the one-point hex8 takes its mean F over the undeformed element and the stress τ/J; tet4 takes the isochoric stress of its own F with the average nodal pressure of the decoupled volumetric energy (Bonet–Burton at finite strain). Each element's frequency bound follows the tangent's largest normal stiffness. Small-displacement steps and thermal strain of hyperelastic elements are refused by name. Verified by uniaxial strain to λ = 1.5 of all three laws on hex8 and tet4 against the material point (to rounding), and the oracle case explicit-neo-hookean-implicit: a quasi-static explicit pull against the implicit nonlinear solver (lateral contraction to 0.09%, stress to 0.03%). Co-Authored-By: Claude Opus 5.5 <[email protected]> Claude-Session: https://claude.ai/code/session_01UhhZMBTviDQxZvwnyP89fo