void
IDGMaterial :: giveInternalLengthDerivative(FloatMatrix &answer, MatResponseMode mode, GaussPoint *gp, TimeStep *tStep)
{
MaterialMode mMode = gp->giveMaterialMode();
if ( mMode == _PlaneStress ) {
answer.resize(5, 5);
answer.zero();
if ( mode == TangentStiffness ) {
IDGMaterialStatus *status = static_cast< IDGMaterialStatus * >( this->giveStatus(gp) );
FloatArray stress = status->giveTempStressVector();
stress.resize(3);
StressVector fullStress(stress, _PlaneStress);
FloatArray sigPrinc;
FloatMatrix nPrinc;
// get principal trial stresses (ordered) and principal stress directions
fullStress.computePrincipalValDir(sigPrinc, nPrinc);
if ( sigPrinc.at(1) > 0 ) {
if ( sigPrinc.at(2) > 0 && sigPrinc.at(1) != sigPrinc.at(2) ) {
double gamma = beta + ( 1 - beta ) * sigPrinc.at(2) * sigPrinc.at(2) / ( sigPrinc.at(1) * sigPrinc.at(1) );
double dL2dS1 = 4. * gamma * cl * cl * ( beta - 1. ) * sigPrinc.at(2) * sigPrinc.at(2) / ( sigPrinc.at(1) * sigPrinc.at(1) * sigPrinc.at(1) );
double dL2dS2 = 4. * gamma * cl * cl * ( 1. - beta ) * sigPrinc.at(2) / ( sigPrinc.at(1) * sigPrinc.at(1) );
double dLdN = ( gamma * gamma - 1. ) * cl * cl / ( sigPrinc.at(2) - sigPrinc.at(1) );
answer.at(1, 1) = nPrinc.at(1, 1);
answer.at(1, 2) = nPrinc.at(1, 2);
answer.at(2, 1) = nPrinc.at(2, 1);
answer.at(2, 2) = nPrinc.at(2, 2);
answer.at(3, 3) = dL2dS1;
answer.at(4, 4) = dL2dS2;
answer.at(5, 5) = dLdN;
}
}
}
} else {
OOFEM_ERROR("Unknown material mode.");
}
}
void
IDGMaterial :: giveInternalLength(FloatMatrix &answer, MatResponseMode rMode, GaussPoint *gp, TimeStep *tStep)
{
if ( averType == 0 ) {
answer.resize(1, 1);
answer.at(1, 1) = cl;
} else if ( averType == 1 ) {
answer.resize(1, 1);
FloatArray gpCoords;
if ( gp->giveElement()->computeGlobalCoordinates( gpCoords, gp->giveNaturalCoordinates() ) == 0 ) {
OOFEM_ERROR("computeGlobalCoordinates of GP failed");
}
this->giveDistanceBasedCharacteristicLength(gpCoords);
answer.at(1, 1) = cl;
} else if ( averType == 2 ) {
MaterialMode mMode = gp->giveMaterialMode();
if ( mMode == _PlaneStress ) {
answer.resize(2, 2);
answer.zero();
IDGMaterialStatus *status = static_cast< IDGMaterialStatus * >( this->giveStatus(gp) );
FloatArray stress = status->giveTempStressVector();
StressVector fullStress(stress, _PlaneStress);
FloatArray sigPrinc;
FloatMatrix nPrinc;
// get principal stresses (ordered) and principal stress directions
fullStress.computePrincipalValDir(sigPrinc, nPrinc);
if ( nPrinc.giveNumberOfRows() == 0 ) {
nPrinc.resize(2, 2);
nPrinc.at(1, 1) = 1;
nPrinc.at(2, 2) = 1;
}
// principal internal lengths
double l1 = cl0;
double l2 = cl0;
double gamma;
if ( sigPrinc.at(1) > 0 ) {
if ( sigPrinc.at(2) > 0 ) {
gamma = beta + ( 1 - beta ) * sigPrinc.at(2) * sigPrinc.at(2) / ( sigPrinc.at(1) * sigPrinc.at(1) );
} else {
gamma = beta;
}
} else {
gamma = 1;
}
l2 = l2 * gamma;
// compose the internal Length matrix in global coordinates
// the first subscript refers to coordinate
// the second subscript refers to eigenvalue
double n11 = nPrinc.at(1, 1);
double n12 = nPrinc.at(1, 2);
double n21 = nPrinc.at(2, 1);
double n22 = nPrinc.at(2, 2);
answer.at(1, 1) = l1 * l1 * n11 * n11 + l2 * l2 * n12 * n12;
answer.at(1, 2) = l1 * l1 * n11 * n21 + l2 * l2 * n12 * n22;
answer.at(2, 1) = l1 * l1 * n11 * n21 + l2 * l2 * n12 * n22;
answer.at(2, 2) = l1 * l1 * n21 * n21 + l2 * l2 * n22 * n22;
} else {
OOFEM_ERROR("Unknown material mode.");
}
}
}
// returns the stress vector in 3d stress space
// computed from the previous plastic strain and current total strain
void
MisesMat :: performPlasticityReturn(GaussPoint *gp, const FloatArray &totalStrain)
{
double kappa, yieldValue, dKappa;
FloatArray reducedStress;
FloatArray strain, plStrain;
MaterialMode mode = gp->giveMaterialMode();
MisesMatStatus *status = static_cast< MisesMatStatus * >( this->giveStatus(gp) );
StressVector fullStress(mode);
this->initTempStatus(gp);
this->initGpForNewStep(gp);
// get the initial plastic strain and initial kappa from the status
status->givePlasticStrain(plStrain);
kappa = status->giveCumulativePlasticStrain();
// === radial return algorithm ===
if ( mode == _1dMat ) {
LinearElasticMaterial *lmat = this->giveLinearElasticMaterial();
double E = lmat->give('E', gp);
/*trial stress*/
fullStress.at(1) = E * ( totalStrain.at(1) - plStrain.at(1) );
double sigmaY = sig0 + H * kappa;
double trialS = fullStress.at(1);
trialS = fabs(trialS);
/*yield function*/
yieldValue = trialS - sigmaY;
// === radial return algorithm ===
if ( yieldValue > 0 ) {
dKappa = yieldValue / ( H + E );
kappa += dKappa;
fullStress.at(1) = fullStress.at(1) - dKappa *E *signum( fullStress.at(1) );
plStrain.at(1) = plStrain.at(1) + dKappa *signum( fullStress.at(1) );
}
} else if ( ( mode == _PlaneStrain ) || ( mode == _3dMat ) ) {
// elastic predictor
StrainVector elStrain(totalStrain, mode);
elStrain.subtract(plStrain);
StrainVector elStrainDev(mode);
double elStrainVol;
elStrain.computeDeviatoricVolumetricSplit(elStrainDev, elStrainVol);
StressVector trialStressDev(mode);
elStrainDev.applyDeviatoricElasticStiffness(trialStressDev, G);
/**************************************************************/
double trialStressVol;
trialStressVol = 3 * K * elStrainVol;
/**************************************************************/
// store the deviatoric and trial stress (reused by algorithmic stiffness)
status->letTrialStressDevBe(trialStressDev);
status->setTrialStressVol(trialStressVol);
// check the yield condition at the trial state
double trialS = trialStressDev.computeStressNorm();
double sigmaY = sig0 + H * kappa;
yieldValue = sqrt(3. / 2.) * trialS - sigmaY;
if ( yieldValue > 0. ) {
// increment of cumulative plastic strain
dKappa = yieldValue / ( H + 3. * G );
kappa += dKappa;
StrainVector dPlStrain(mode);
// the following line is equivalent to multiplication by scaling matrix P
trialStressDev.applyDeviatoricElasticCompliance(dPlStrain, 0.5);
// increment of plastic strain
dPlStrain.times(sqrt(3. / 2.) * dKappa / trialS);
plStrain.add(dPlStrain);
// scaling of deviatoric trial stress
trialStressDev.times(1. - sqrt(6.) * G * dKappa / trialS);
}
// assemble the stress from the elastically computed volumetric part
// and scaled deviatoric part
double stressVol = 3. * K * elStrainVol;
trialStressDev.computeDeviatoricVolumetricSum(fullStress, stressVol);
}
// store the effective stress in status
status->letTempEffectiveStressBe(fullStress);
// store the plastic strain and cumulative plastic strain
status->letTempPlasticStrainBe(plStrain);
status->setTempCumulativePlasticStrain(kappa);
}
