Saint Venant-Kirchoff

struct SaintVenantKirchhoff <: ConstitutiveModels.AbstractHyperelasticModel{2, 0}

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

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