void
FiniteStrainRatePlasticMaterial::computeQpStress()
{
RankTwoTensor dp,sig;
//Obtain previous plastic rate of deformation tensor
dp=_plastic_strain_old[_qp];
//Solve J2 plastic constitutive equations based on current strain increment
//Returns current stress and plastic rate of deformation tensor
returnMap(_stress_old[_qp], _strain_increment[_qp], _elasticity_tensor[_qp], dp, sig);
_stress[_qp] = sig;
//Rotate the stress to the current configuration
_stress[_qp] = _rotation_increment[_qp] * _stress[_qp] * _rotation_increment[_qp].transpose();
//Updates current plastic rate of deformation tensor
_plastic_strain[_qp] = dp;
//Evaluate and update current equivalent plastic strain
_eqv_plastic_strain[_qp] = std::pow(2.0/3.0,0.5) * dp.L2norm();
//Calculate elastic strain increment
RankTwoTensor delta_ee = _strain_increment[_qp]-(_plastic_strain[_qp]-_plastic_strain_old[_qp]);
//Update elastic strain tensor in intermediate configuration
_elastic_strain[_qp] = _elastic_strain_old[_qp] + delta_ee;
//Rotate elastic strain tensor to the current configuration
_elastic_strain[_qp] = _rotation_increment[_qp] * _elastic_strain[_qp] * _rotation_increment[_qp].transpose();
//Rotate to plastic rate of deformation tensor the current configuration
_plastic_strain[_qp] = _rotation_increment[_qp] * _plastic_strain[_qp] * _rotation_increment[_qp].transpose();
//Update strain in intermediate configuration
_total_strain[_qp] = _total_strain_old[_qp] + _strain_increment[_qp];
//Rotate strain to current configuration
_total_strain[_qp] = _rotation_increment[_qp] * _total_strain[_qp] * _rotation_increment[_qp].transpose();
}
void
FiniteStrainPlasticMaterial::computeQpStress()
{
// perform the return-mapping algorithm
returnMap(_stress_old[_qp],
_eqv_plastic_strain_old[_qp],
_plastic_strain_old[_qp],
_strain_increment[_qp],
_elasticity_tensor[_qp],
_stress[_qp],
_eqv_plastic_strain[_qp],
_plastic_strain[_qp]);
// Rotate the stress tensor to the current configuration
_stress[_qp] = _rotation_increment[_qp] * _stress[_qp] * _rotation_increment[_qp].transpose();
// Rotate plastic strain tensor to the current configuration
_plastic_strain[_qp] =
_rotation_increment[_qp] * _plastic_strain[_qp] * _rotation_increment[_qp].transpose();
_Jacobian_mult[_qp] = _elasticity_tensor[_qp];
}
void
FiniteStrainPlasticBase::computeQpStress()
{
if (_fspb_debug == 3)
{
checkJacobian();
mooseError("Jacobian has been checked. Exiting with no error");
}
preReturnMap();
/**
* the idea in the following is to potentially subdivide the
* strain increment into smaller portions
* First one subdivision is tried, and if that fails then
* 2 are tried, then 4, etc. This is in the hope that the
* time-step for the entire mesh need not be cut if there
* are only a few "bad" quadpoints where the return-map
* is difficult
*/
bool return_successful = false;
// number of subdivisions of the strain increment currently being tried
unsigned int num_subdivisions = 1;
while (num_subdivisions <= _max_subdivisions && !return_successful)
{
// prepare the variables for this set of strain increments
RankTwoTensor dep = _strain_increment[_qp]/num_subdivisions;
RankTwoTensor stress_previous = _stress_old[_qp];
RankTwoTensor plastic_strain_previous = _plastic_strain_old[_qp];
std::vector<Real> intnl_previous;
intnl_previous.resize(_intnl_old[_qp].size());
for (unsigned int a = 0; a < _intnl_old[_qp].size(); ++a)
intnl_previous[a] = _intnl_old[_qp][a];
// now do the work: apply the "dep" over num_subdivisions "substeps"
for (unsigned substep = 0 ; substep < num_subdivisions ; ++substep)
{
return_successful = returnMap(stress_previous, plastic_strain_previous, _intnl_old[_qp], dep, _elasticity_tensor[_qp], _stress[_qp], _plastic_strain[_qp], _intnl[_qp], _f[_qp], _iter[_qp]);
if (return_successful)
{
// record the updated variables in readiness for the next substep
stress_previous = _stress[_qp];
plastic_strain_previous = _plastic_strain[_qp];
for (unsigned int a = 0; a < _intnl_old[_qp].size(); ++a)
intnl_previous[a] = _intnl[_qp][a];
}
else
break; // oh dear, we need to increase the number of subdivisions
}
if (!return_successful)
num_subdivisions *= 2;
}
if (!return_successful)
{
_console << "After making " << num_subdivisions << " subdivisions of the strain increment with L2norm " << _strain_increment[_qp].L2norm() << " the returnMap algorithm failed\n";
_fspb_debug_stress = _stress_old[_qp];
_fspb_debug_pm.assign(numberOfYieldFunctions(), 1); // this is chosen arbitrarily - please change if a more suitable value occurs to you!
_fspb_debug_intnl.resize(numberOfInternalParameters());
for (unsigned a = 0 ; a < numberOfInternalParameters() ; ++a)
_fspb_debug_intnl[a] = _intnl_old[_qp][a];
checkDerivatives();
checkJacobian();
mooseError("Exiting\n");
}
postReturnMap();
//Update measures of strain
_elastic_strain[_qp] = _elastic_strain_old[_qp] + _strain_increment[_qp] - (_plastic_strain[_qp] - _plastic_strain_old[_qp]);
_total_strain[_qp] = _total_strain_old[_qp] + _strain_increment[_qp];
//Rotate the tensors to the current configuration
_stress[_qp] = _rotation_increment[_qp]*_stress[_qp]*_rotation_increment[_qp].transpose();
_elastic_strain[_qp] = _rotation_increment[_qp] * _elastic_strain[_qp] * _rotation_increment[_qp].transpose();
_total_strain[_qp] = _rotation_increment[_qp] * _total_strain[_qp] * _rotation_increment[_qp].transpose();
_plastic_strain[_qp] = _rotation_increment[_qp] * _plastic_strain[_qp] * _rotation_increment[_qp].transpose();
}
