Mooney-Rivlin

struct MooneyRivlin <: ConstitutiveModels.AbstractHyperelasticModel{3, 0}

$\psi = \frac{1}{2}\left[\frac{1}{2}\left(J^2 - 1\right) - \ln J\right] + C_1\left(\bar{I}_1 - 3\right) + C_2\left(\bar{I}_2 - 3\right)$

helmholtz_free_energy(
    _::MooneyRivlin,
    props,
    Δt,
    ∇u,
    θ,
    Z_old,
    Z_new
) -> Any

initialize_props(
    _::MooneyRivlin,
    inputs::Dict{String}
) -> Any

pk1_stress(
    _::MooneyRivlin,
    props,
    Δt,
    ∇u,
    θ,
    Z_old,
    Z_new,
    _::ConstitutiveModels.ForwardDiffAD
) -> Any