neohooke.hh

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// SPDX-FileCopyrightText: 2021-2024 The Ikarus Developers mueller@ibb.uni-stuttgart.de
// SPDX-License-Identifier: LGPL-3.0-or-later
 
#pragma once
 
#include <ikarus/finiteelements/mechanics/materials/interface.hh>
#include <ikarus/utils/tensorutils.hh>
 
namespace Ikarus {
 
template <typename ST>
struct NeoHookeT : public Material<NeoHookeT<ST>>
{
  [[nodiscard]] constexpr std::string nameImpl() const noexcept { return "NeoHooke"; }
 
  explicit NeoHookeT(const LamesFirstParameterAndShearModulus& mpt)
      : lambdaAndmu_{mpt} {}
 
  using ScalarType                    = ST;
  static constexpr int worldDimension = 3;
  using StrainMatrix                  = Eigen::Matrix<ScalarType, worldDimension, worldDimension>;
  using StressMatrix                  = StrainMatrix;
 
  static constexpr auto strainTag          = StrainTags::rightCauchyGreenTensor;
  static constexpr auto stressTag          = StressTags::PK2;
  static constexpr auto tangentModuliTag   = TangentModuliTags::Material;
  static constexpr bool energyAcceptsVoigt = false;
  static constexpr bool stressToVoigt      = false;
  static constexpr bool stressAcceptsVoigt = false;
  static constexpr bool moduliToVoigt      = false;
  static constexpr bool moduliAcceptsVoigt = false;
  static constexpr double derivativeFactor = 2;
 
  template <typename Derived>
  ScalarType storedEnergyImpl(const Eigen::MatrixBase<Derived>& C) const noexcept {
    static_assert(Concepts::EigenMatrixOrVoigtNotation3<Derived>);
    if constexpr (!Concepts::EigenVector<Derived>) {
      const auto traceC  = C.trace();
      const auto logdetF = log(sqrt(C.determinant()));
      return lambdaAndmu_.mu / 2.0 * (traceC - 3 - 2 * logdetF) + lambdaAndmu_.lambda / 2.0 * logdetF * logdetF;
    } else
      static_assert(!Concepts::EigenVector<Derived>,
                    "NeoHooke energy can only be called with a matrix and not a vector in Voigt notation");
  }
 
  template <bool voigt, typename Derived>
  auto stressesImpl(const Eigen::MatrixBase<Derived>& C) const {
    static_assert(Concepts::EigenMatrixOrVoigtNotation3<Derived>);
    if constexpr (!voigt) {
      if constexpr (!Concepts::EigenVector<Derived>) {
        const auto logdetF = log(sqrt(C.determinant()));
        const auto invC    = C.inverse().eval();
        return (lambdaAndmu_.mu * (StrainMatrix::Identity() - invC) + lambdaAndmu_.lambda * logdetF * invC).eval();
      } else
        static_assert(!Concepts::EigenVector<Derived>,
                      "NeoHooke can only be called with a matrix and not a vector in Voigt notation");
    } else
      static_assert(voigt == false, "NeoHooke does not support returning stresses in Voigt notation");
  }
 
  template <bool voigt, typename Derived>
  auto tangentModuliImpl(const Eigen::MatrixBase<Derived>& C) const {
    static_assert(Concepts::EigenMatrixOrVoigtNotation3<Derived>);
    if constexpr (!voigt) {
      const auto invC    = C.inverse().eval();
      const auto logdetF = log(sqrt(C.determinant()));
      const auto CTinv   = tensorView(invC, std::array<Eigen::Index, 2>({3, 3}));
      static_assert(Eigen::TensorFixedSize<ScalarType, Eigen::Sizes<3, 3>>::NumIndices == 2);
      Eigen::TensorFixedSize<ScalarType, Eigen::Sizes<3, 3, 3, 3>> moduli =
          (lambdaAndmu_.lambda * dyadic(CTinv, CTinv) +
           2 * (lambdaAndmu_.mu - lambdaAndmu_.lambda * logdetF) * symTwoSlots(fourthOrderIKJL(invC, invC), {2, 3}))
              .eval();
      return moduli;
    } else
      static_assert(voigt == false, "NeoHooke does not support returning tangent moduli in Voigt notation");
  }
 
  template <typename STO>
  auto rebind() const {
    return NeoHookeT<STO>(lambdaAndmu_);
  }
 
private:
  LamesFirstParameterAndShearModulus lambdaAndmu_;
};
 
using NeoHooke = NeoHookeT<double>;
 
} // namespace Ikarus