forked from 1b-agent/fieldcraft-upstream
jyvikoandClaude Opus 5.5
8ca2dddeec
Theory cases for the nonlinear solver, each frozen as a fixture: uniaxial stretch of a neo-Hookean block to twice its length (closed form), the nonlinear patch test on a distorted hex8 mesh, a quarter turn of the same mesh (objectivity: zero stress), the elastica of a hex20 cantilever at P L²/(E I) = 1, 2, 5, 10 against Bisshopp–Drucker (0.2–0.5 %), and the inflation of a thick neo-Hookean tube by a follower pressure against Rivlin's closed form (0.08 % at the bore). A finite-strain Cook's membrane is pending its transcribed reference. docs/fem.md describes the formulation, the material point interface, the follower-pressure choice and what nonlinear steps refuse; the literature, parity and roadmap pages follow. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01NmAttHhUZTokgPeEJia8sm
Uniaxial stretch of a neo-Hookean block
A unit cube of 2 × 2 × 2 hex20 elements, symmetry planes x = 0, y = 0, z = 0, the face x = 1 pulled to x = 2 (λ = 2) in a nonlinear static step; E = 10, ν = 0.3 with the neo-Hookean option (μ = 3.84615, κ = 8.33333). The lateral stretch l = 0.813143719 solves σ_yy = 0 (bisection on the closed form), and σ_xx = 8.060135422. The deformation is homogeneous, so every element reproduces it exactly.