New file src/materials/neo_hookean.jl implementing simplest hyperelasticity:
- NeoHookean struct with shear modulus μ and Lamé parameter λ
- Convenience constructor from E and ν engineering constants
- strain_energy() computes ψ = μ/2·(I₁-3) - μ·ln(J) + λ/2·ln²(J)
- Stress S = 2·∂ψ/∂C via automatic differentiation
- Tangent 𝔻 = 4·∂²ψ/∂C² via automatic differentiation
- Uses Tensors.jl built-in AD (no ForwardDiff dependency)
- Total Lagrangian formulation with 2nd PK stress
- 253 lines with comprehensive theory documentation
Jukka Aho
1a0066dea0