AssociativeKinematicPlasticHardening.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/AssociativeKinematicPlasticHardening.h"
#include "neml2/tensors/SSR4.h"
 
namespace neml2
{
register_NEML2_object(AssociativeKinematicPlasticHardening);
 
OptionSet
AssociativeKinematicPlasticHardening::expected_options()
{
  OptionSet options = FlowRule::expected_options();
  options.doc() +=
      " This object calculates the rate of kinematic plastic strain following associative flow "
      "rule, i.e. \\f$ \\dot{\\boldsymbol{K}}_p = - \\dot{\\gamma} \\frac{\\partial f}{\\partial "
      "\\boldsymbol{X}} \\f$, where \\f$ \\dot{\\boldsymbol{K}}_p \\f$ is the kinematic plastic "
      "strain, \\f$ \\dot{\\gamma} \\f$ is the flow rate, \\f$ f \\f$ is the yield function, and "
      "\\f$ \\boldsymbol{X} \\f$ is the kinematic hardening.";
 
  options.set<VariableName>("kinematic_hardening_direction") =
      VariableName("state", "internal", "NX");
  options.set("kinematic_hardening_direction").doc() =
      "Direction of associative kinematic hardening which can be calculated using Normality.";
 
  options.set<VariableName>("kinematic_plastic_strain_rate") =
      VariableName("state", "internal", "Kp_rate");
  options.set("kinematic_plastic_strain_rate").doc() = "Rate of kinematic plastic strain";
 
  return options;
}
 
AssociativeKinematicPlasticHardening::AssociativeKinematicPlasticHardening(
    const OptionSet & options)
  : FlowRule(options),
    _NX(declare_input_variable<SR2>("kinematic_hardening_direction")),
    _Kp_dot(declare_output_variable<SR2>("kinematic_plastic_strain_rate"))
{
}
 
void
AssociativeKinematicPlasticHardening::set_value(bool out, bool dout_din, bool d2out_din2)
{
  // For associative flow,
  // Kp_dot = - gamma_dot * NX
  //     NX = df/dX
 
  if (out)
    _Kp_dot = -_gamma_dot * _NX;
 
  if (dout_din || d2out_din2)
  {
    auto I = SR2::identity_map(options());
 
    if (dout_din)
    {
      _Kp_dot.d(_gamma_dot) = -_NX;
      _Kp_dot.d(_NX) = -_gamma_dot * I;
    }
 
    if (d2out_din2)
    {
      // I don't know when this will be useful, but since it's easy...
      _Kp_dot.d(_gamma_dot, _NX) = -I;
      _Kp_dot.d(_NX, _gamma_dot) = -I;
    }
  }
}
} // namespace neml2