[mgis.fenics] Error in the implementation of the phase-field behaviour

[thelfer]

Hi @bleyerj,

Looks like there is something wrong in the implementation of the phase-field behaviour as the History function is taken at the beginning of the time step and not the end as it should.

@Integrator {
  // remove useless warnings, as we always compute the tangent operator
  static_cast<void>(computeTangentOperator_);
  ∂q∕∂Δg = Gc*l₀* tmatrix<N, N, real>::Id();
  ∂Y∕∂Δd = Gc/l₀+2*H;
  q = Gc*l₀*(g+Δg);
  Y = ∂Y∕∂Δd ⋅ (d+Δd)-2*H;
}

shall be:

@Integrator {
  // remove useless warnings, as we always compute the tangent operator
  static_cast<void>(computeTangentOperator_);
  const auto H_tdt = H+dH;
  ∂q∕∂Δg = Gc*l₀* tmatrix<N, N, real>::Id();
  ∂Y∕∂Δd = Gc/l₀+2*H_tdt;
  q = Gc*l₀*(g+Δg);
  Y = ∂Y∕∂Δd ⋅ (d+Δd)-2*H_tdt;
}