AssociativeIsotropicPlasticHardening.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/AssociativeIsotropicPlasticHardening.h"
 
namespace neml2
{
register_NEML2_object(AssociativeIsotropicPlasticHardening);
 
OptionSet
AssociativeIsotropicPlasticHardening::expected_options()
{
  OptionSet options = FlowRule::expected_options();
  options.doc() += " This object calculates the rate of equivalent plastic strain following "
                   "associative flow rule, i.e. \\f$ \\dot{\\varepsilon}_p = - \\dot{\\gamma} "
                   "\\frac{\\partial f}{\\partial k} \\f$, where \\f$ \\dot{\\varepsilon}_p \\f$ "
                   "is the equivalent plastic strain, \\f$ \\dot{\\gamma} \\f$ is the flow rate, "
                   "\\f$ f \\f$ is the yield function, and \\f$ k \\f$ is the isotropic hardening.";
 
  options.set<VariableName>("isotropic_hardening_direction") =
      VariableName("state", "internal", "Nk");
  options.set("isotropic_hardening_direction").doc() =
      "Direction of associative isotropic hardening which can be calculated using Normality.";
 
  options.set<VariableName>("equivalent_plastic_strain_rate") =
      VariableName("state", "internal", "ep_rate");
  options.set("equivalent_plastic_strain_rate").doc() = "Rate of equivalent plastic strain";
 
  return options;
}
 
AssociativeIsotropicPlasticHardening::AssociativeIsotropicPlasticHardening(
    const OptionSet & options)
  : FlowRule(options),
    _Nk(declare_input_variable<Scalar>("isotropic_hardening_direction")),
    _ep_dot(declare_output_variable<Scalar>("equivalent_plastic_strain_rate"))
{
}
 
void
AssociativeIsotropicPlasticHardening::set_value(bool out, bool dout_din, bool d2out_din2)
{
  // For associative flow,
  // ep_dot = - gamma_dot * Nk
  //     Nk = df/dk
 
  if (out)
    _ep_dot = -_gamma_dot * _Nk;
 
  if (dout_din)
  {
    _ep_dot.d(_gamma_dot) = -_Nk;
    _ep_dot.d(_Nk) = -_gamma_dot;
  }
 
  if (d2out_din2)
  {
    // I don't know when this will be useful, but since it's easy...
    auto I = Scalar::identity_map(options());
    _ep_dot.d(_gamma_dot, _Nk) = -I;
    _ep_dot.d(_Nk, _gamma_dot) = -I;
  }
}
} // namespace neml2