LinearIsotropicElasticity.cxx

// Copyright 2023, UChicago Argonne, LLC
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// Software Name: NEML2 -- the New Engineering material Model Library, version 2
// By: Argonne National Laboratory
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#include "neml2/models/solid_mechanics/LinearIsotropicElasticity.h"
#include "neml2/tensors/SSR4.h"
 
namespace neml2
{
register_NEML2_object(LinearIsotropicElasticity);
 
OptionSet
LinearIsotropicElasticity::expected_options()
{
  OptionSet options = Elasticity::expected_options();
  options.doc() += " for linear isotropic material. \\f$ \\boldsymbol{\\sigma} = K \\tr "
                   "\\boldsymbol{\\varepsilon}_e + 2 G \\text{dev} \\boldsymbol{\\varepsilon}_e "
                   "\\f$, where \\f$ K \\f$ and \\f$ G \\f$ are bulk and shear moduli, "
                   "respectively. For convenience, this object only requests Young's modulus and "
                   "Poisson's ratio, and handles the Lame parameter conversion behind the scenes.";
 
  options.set<CrossRef<Scalar>>("youngs_modulus");
  options.set("youngs_modulus").doc() = "Young's modulus";
 
  options.set<CrossRef<Scalar>>("poisson_ratio");
  options.set("poisson_ratio").doc() = "Poisson's ratio";
 
  return options;
}
 
LinearIsotropicElasticity::LinearIsotropicElasticity(const OptionSet & options)
  : Elasticity(options),
    _E(declare_parameter<Scalar>("E", "youngs_modulus")),
    _nu(declare_parameter<Scalar>("nu", "poisson_ratio"))
{
}
 
void
LinearIsotropicElasticity::set_value(bool out, bool dout_din, bool /*d2out_din2*/)
{
  // We need to work with the bulk modulus K and the shear modulus G so that the expression for
  // stiffness and compliance can be unified:
  const auto K = _E / 3 / (1 - 2 * _nu);
  const auto G = _E / 2 / (1 + _nu);
  const auto vf = _compliance ? 1 / (3 * K) : 3 * K;
  const auto df = _compliance ? 1 / (2 * G) : 2 * G;
 
  if (out)
    _to = vf * SR2(_from).vol() + df * SR2(_from).dev();
 
  if (dout_din)
  {
    const auto I = SSR4::identity_vol(options());
    const auto J = SSR4::identity_dev(options());
    _to.d(_from) = vf * I + df * J;
  }
}
} // namespace neml2