Mooney-Rivlin

struct MooneyRivlin <: ConstitutiveModels.AbstractHyperelasticity

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

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

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

pk1_stress(_::MooneyRivlin, props, ∇u, θ) -> Any