AssociativePlasticFlow.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/AssociativePlasticFlow.h"
#include "neml2/tensors/SSR4.h"
 
namespace neml2
{
register_NEML2_object(AssociativePlasticFlow);
 
OptionSet
AssociativePlasticFlow::expected_options()
{
  OptionSet options = FlowRule::expected_options();
  options.doc() +=
      " This object calculates the rate of plastic strain following associative flow rule, i.e. "
      "\\f$ \\dot{\\boldsymbol{\\varepsilon}}_p = - \\dot{\\gamma} \\frac{\\partial f}{\\partial "
      "\\boldsymbol{M}} \\f$, where \\f$ \\dot{\\boldsymbol{\\varepsilon}}_p \\f$ is the plastic "
      "strain, \\f$ \\dot{\\gamma} \\f$ is the flow rate, \\f$ f \\f$ is the yield function, and "
      "\\f$ \\boldsymbol{M} \\f$ is the Mandel stress.";
 
  options.set<VariableName>("flow_direction") = VariableName("state", "internal", "NM");
  options.set("flow_direction").doc() = "Flow direction which can be calculated using Normality";
 
  options.set<VariableName>("plastic_strain_rate") = VariableName("state", "internal", "Ep_rate");
  options.set("plastic_strain_rate").doc() = "Rate of plastic strain";
 
  return options;
}
 
AssociativePlasticFlow::AssociativePlasticFlow(const OptionSet & options)
  : FlowRule(options),
    _NM(declare_input_variable<SR2>("flow_direction")),
    _Ep_dot(declare_output_variable<SR2>("plastic_strain_rate"))
{
}
 
void
AssociativePlasticFlow::set_value(bool out, bool dout_din, bool d2out_din2)
{
  // For associative flow,
  // Ep_dot = gamma_dot * NM
  //     NM = df/dM
 
  if (out)
    _Ep_dot = _gamma_dot * _NM;
 
  if (dout_din || d2out_din2)
  {
    auto I = SR2::identity_map(options());
 
    if (dout_din)
    {
      _Ep_dot.d(_gamma_dot) = _NM;
      _Ep_dot.d(_NM) = _gamma_dot * I;
    }
 
    if (d2out_din2)
    {
      // I don't know when this will be useful, but since it's easy...
      _Ep_dot.d(_gamma_dot, _NM) = I;
      _Ep_dot.d(_NM, _gamma_dot) = I;
    }
  }
}
} // namespace neml2