PerzynaPlasticFlowRate.cxx

// Copyright 2023, UChicago Argonne, LLC
// All Rights Reserved
// Software Name: NEML2 -- the New Engineering material Model Library, version 2
// By: Argonne National Laboratory
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#include "neml2/models/solid_mechanics/PerzynaPlasticFlowRate.h"
 
namespace neml2
{
register_NEML2_object(PerzynaPlasticFlowRate);
 
OptionSet
PerzynaPlasticFlowRate::expected_options()
{
  OptionSet options = PlasticFlowRate::expected_options();
  options.doc() =
      "Perzyna's viscous approximation of the consistent yield envelope (with a power "
      "law), i.e. \\f$ \\dot{\\gamma} = \\left( \\frac{\\left< f \\right>}{\\eta} \\right)^n \\f$, "
      "where \\f$ f \\f$ is the yield function, \\f$ \\eta \\f$ is the reference stress, and \\f$ "
      "n \\f$ is the power-law exponent.";
 
  options.set<CrossRef<Scalar>>("reference_stress");
  options.set("reference_stress").doc() = "Reference stress";
 
  options.set<CrossRef<Scalar>>("exponent");
  options.set("exponent").doc() = "Power-law exponent";
 
  return options;
}
 
PerzynaPlasticFlowRate::PerzynaPlasticFlowRate(const OptionSet & options)
  : PlasticFlowRate(options),
    _eta(declare_parameter<Scalar>("eta", "reference_stress")),
    _n(declare_parameter<Scalar>("n", "exponent"))
{
}
 
void
PerzynaPlasticFlowRate::set_value(bool out, bool dout_din, bool d2out_din2)
{
  // Compute the Perzyna approximation of the yield surface
  auto Hf = math::heaviside(Scalar(_f));
  auto f_abs = math::abs(Scalar(_f));
  auto gamma_dot_m = math::pow(f_abs / _eta, _n);
  auto gamma_dot = gamma_dot_m * Hf;
 
  if (out)
    _gamma_dot = gamma_dot;
 
  if (dout_din || d2out_din2)
  {
    auto dgamma_dot_df = _n / f_abs * gamma_dot;
 
    if (dout_din)
      _gamma_dot.d(_f) = dgamma_dot_df;
 
    if (d2out_din2)
      _gamma_dot.d(_f, _f) = (1 - 1 / f_abs) * dgamma_dot_df;
  }
}
} // namespace neml2