//Jacobian for stress update algorithm
void
FiniteStrainPlasticMaterial::getJac(RankTwoTensor sig, RankFourTensor E_ijkl, Real flow_incr, RankFourTensor* dresid_dsig)
{
RankTwoTensor sig_dev, flow_tensor, flow_dirn;
RankTwoTensor dfi_dft,dfi_dsig;
RankFourTensor dft_dsig,dfd_dft,dfd_dsig;
Real sig_eqv/*,val*/;
Real f1,f2,f3;
RankFourTensor temp;
sig_dev=getSigDev(sig);
sig_eqv=getSigEqv(sig);
getFlowTensor(sig,&flow_tensor);
flow_dirn=flow_tensor;
f1=3.0/(2.0*sig_eqv);
f2=f1/3.0;
f3=9.0/(4.0*pow(sig_eqv,3.0));
for (int i=0;i<3;i++)
for (int j=0;j<3;j++)
for (int k=0;k<3;k++)
for (int l=0;l<3;l++)
dft_dsig(i,j,k,l)=f1*deltaFunc(i,k)*deltaFunc(j,l)-f2*deltaFunc(i,j)*deltaFunc(k,l)-f3*sig_dev(i,j)*sig_dev(k,l);
dfd_dsig=dft_dsig;
*dresid_dsig=E_ijkl.invSymm()+dfd_dsig*flow_incr;
}
// Jacobian for stress update algorithm
void
FiniteStrainPlasticMaterial::getJac(const RankTwoTensor & sig,
const RankFourTensor & E_ijkl,
Real flow_incr,
RankFourTensor & dresid_dsig)
{
RankTwoTensor sig_dev, df_dsig, flow_dirn;
RankTwoTensor dfi_dft, dfi_dsig;
RankFourTensor dft_dsig, dfd_dft, dfd_dsig;
Real sig_eqv;
Real f1, f2, f3;
RankFourTensor temp;
sig_dev = sig.deviatoric();
sig_eqv = getSigEqv(sig);
df_dsig = dyieldFunction_dstress(sig);
flow_dirn = flowPotential(sig);
f1 = 3.0 / (2.0 * sig_eqv);
f2 = f1 / 3.0;
f3 = 9.0 / (4.0 * Utility::pow<3>(sig_eqv));
dft_dsig = f1 * _deltaMixed - f2 * _deltaOuter - f3 * sig_dev.outerProduct(sig_dev);
dfd_dsig = dft_dsig;
dresid_dsig = E_ijkl.invSymm() + dfd_dsig * flow_incr;
}
//Jacobian for stress update algorithm
void
FiniteStrainRatePlasticMaterial::getJac(const RankTwoTensor & sig, const RankFourTensor & E_ijkl, Real flow_incr, Real yield_stress, RankFourTensor & dresid_dsig)
{
unsigned i, j, k ,l;
RankTwoTensor sig_dev, flow_tensor, flow_dirn,fij;
RankTwoTensor dfi_dft;
RankFourTensor dft_dsig, dfd_dft, dfd_dsig, dfi_dsig;
Real sig_eqv;
Real f1, f2, f3;
Real dfi_dseqv;
sig_dev = sig.deviatoric();
sig_eqv = getSigEqv(sig);
getFlowTensor(sig, yield_stress, flow_tensor);
flow_dirn = flow_tensor;
dfi_dseqv = _ref_pe_rate * _dt * _exponent * std::pow(macaulayBracket(sig_eqv / yield_stress - 1.0), _exponent - 1.0) / yield_stress;
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dfi_dsig(i,j,k,l) = flow_dirn(i,j) * flow_dirn(k,l) * dfi_dseqv; //d_flow_increment/d_sig
f1 = 0.0;
f2 = 0.0;
f3 = 0.0;
if (sig_eqv > 1e-8)
{
f1 = 3.0 / (2.0 * sig_eqv);
f2 = f1 / 3.0;
f3 = 9.0 / (4.0 * std::pow(sig_eqv, 3.0));
}
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dft_dsig(i,j,k,l) = f1 * deltaFunc(i,k) * deltaFunc(j,l) - f2 * deltaFunc(i,j) * deltaFunc(k,l) - f3 * sig_dev(i,j) * sig_dev(k,l); //d_flow_dirn/d_sig - 2nd part
dfd_dsig = dft_dsig; //d_flow_dirn/d_sig
dresid_dsig = E_ijkl.invSymm() + dfd_dsig * flow_incr + dfi_dsig; //Jacobian
}
//Jacobian for stress update algorithm
void
FiniteStrainRatePlasticMaterial::getJac(const RankTwoTensor & sig, const RankFourTensor & E_ijkl, Real flow_incr, Real yield_stress, RankFourTensor & dresid_dsig)
{
RankTwoTensor sig_dev, flow_tensor, flow_dirn,fij;
RankTwoTensor dfi_dft;
RankFourTensor dfd_dft, dfd_dsig, dfi_dsig;
Real sig_eqv;
Real f1, f2, f3;
Real dfi_dseqv;
sig_dev = sig.deviatoric();
sig_eqv = getSigEqv(sig);
getFlowTensor(sig, yield_stress, flow_tensor);
flow_dirn = flow_tensor;
dfi_dseqv = _ref_pe_rate * _dt * _exponent * std::pow(macaulayBracket(sig_eqv / yield_stress - 1.0), _exponent - 1.0) / yield_stress;
dfi_dsig = flow_dirn.outerProduct(flow_dirn) * dfi_dseqv; //d_flow_increment/d_sig
f1 = 0.0;
f2 = 0.0;
f3 = 0.0;
if (sig_eqv > 1e-8)
{
f1 = 3.0 / (2.0 * sig_eqv);
f2 = f1 / 3.0;
f3 = 9.0 / (4.0 * std::pow(sig_eqv, 3.0));
}
dfd_dsig = f1 * _deltaMixed - f2 * _deltaOuter - f3 * sig_dev.outerProduct(sig_dev); //d_flow_dirn/d_sig - 2nd part
//Jacobian
dresid_dsig = E_ijkl.invSymm() + dfd_dsig * flow_incr + dfi_dsig;
}
void
RedbackMechMaterialCC::getJac(const RankTwoTensor & sig,
const RankFourTensor & E_ijkl,
Real flow_incr,
Real sig_eqv,
Real pressure,
Real p_yield_stress,
Real q_yield_stress,
Real pc,
RankFourTensor & dresid_dsig)
{
unsigned i, j, k, l;
RankTwoTensor sig_dev, flow_dirn_vol, flow_dirn_dev, fij, flow_dirn, flow_tensor;
RankTwoTensor dfi_dft;
RankFourTensor dfd_dsig, dfi_dsig;
Real f1, f2;
Real dfi_dseqv_dev, dfi_dseqv_vol, dfi_dseqv;
pc *= -1;
sig_dev = sig.deviatoric();
dfi_dseqv = getDerivativeFlowIncrement(sig, pressure, sig_eqv, pc, q_yield_stress, p_yield_stress);
getFlowTensor(sig, sig_eqv, pressure, pc, flow_dirn);
/* The following calculates the tensorial derivative (Jacobian) of the residual with respect to stress, dr_dsig
* It consists of two terms: The first is
* dr_dsig = (dfi_dseqv_dev*flow_dirn_dev(k,l)) * flow_dirn_dev(i,j)
* which is the tensorial product of the flow increment tensor times the flow direction tensor
*
* The second is the product of the flow increment tensor times the derivative of the flow direction tensor
* with respect to the stress tensor. See also REDBACK's documentation
* */
// This loop calculates the first term
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dfi_dsig(i, j, k, l) = flow_dirn(i, j) * flow_dirn(k, l) * dfi_dseqv;
// Real flow_tensor_norm = flow_dirn.L2norm();
// This loop calculates the second term. Read REDBACK's documentation
// (same as J2 plasticity case)
f1 = 0.0;
f2 = 0.0;
if (sig_eqv > 1e-8)
{
f1 = 3.0 / (_slope_yield_surface * _slope_yield_surface);
f2 = 2.0 / 9.0 - 1.0 / (_slope_yield_surface * _slope_yield_surface);
}
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dfd_dsig(i, j, k, l) =
f1 * deltaFunc(i, k) * deltaFunc(j, l) -
f2 * deltaFunc(i, j) * deltaFunc(k, l); // d_flow_dirn/d_sig - 2nd part (J2 plasticity)
// dfd_dsig = dft_dsig1/flow_tensor_norm - 3.0 * dft_dsig2 /
// (2*sig_eqv*flow_tensor_norm*flow_tensor_norm*flow_tensor_norm); //d_flow_dirn/d_sig
// TODO: check if the previous two lines (i.e normalizing the flow vector) should be activated or not. Currently we
// are using the non-unitary flow vector
dresid_dsig = E_ijkl.invSymm() + dfd_dsig * flow_incr + dfi_dsig; // Jacobian
}
/**
* Implements the return-map algorithm via a Newton-Raphson process.
* This idea is fully explained in Simo and Hughes "Computational
* Inelasticity" Springer 1997, for instance, as well as many other
* books on plasticity.
* The basic idea is as follows.
* Given: sig_old - the stress at the start of the "time step"
* plastic_strain_old - the plastic strain at the start of the "time step"
* eqvpstrain_old - equivalent plastic strain at the start of the "time step"
* (In general we would be given some number of internal
* parameters that the yield function depends upon.)
* delta_d - the prescribed strain increment for this "time step"
* we want to determine the following parameters at the end of this "time step":
* sig - the stress
* plastic_strain - the plastic strain
* eqvpstrain - the equivalent plastic strain (again, in general, we would
* have an arbitrary number of internal parameters).
*
* To determine these parameters, introduce
* the "yield function", f
* the "consistency parameter", flow_incr
* the "flow potential", flow_dirn_ij
* the "internal potential", internalPotential (in general there are as many internalPotential
* functions as there are internal parameters).
* All three of f, flow_dirn_ij, and internalPotential, are functions of
* sig and eqvpstrain.
* To find sig, plastic_strain and eqvpstrain, we need to solve the following
* resid_ij = 0
* f = 0
* rep = 0
* This is done by using Newton-Raphson.
* There are 8 equations here: six from resid_ij=0 (more generally there are nine
* but in this case resid is symmetric); one from f=0; one from rep=0 (more generally, for N
* internal parameters there are N of these equations).
*
* resid_ij = flow_incr*flow_dirn_ij - (plastic_strain - plastic_strain_old)_ij
* = flow_incr*flow_dirn_ij - (E^{-1}(trial_stress - sig))_ij
* Here trial_stress = E*(strain - plastic_strain_old)
* sig = E*(strain - plastic_strain)
* Note: flow_dirn_ij is evaluated at sig and eqvpstrain (not the old values).
*
* f is the yield function, evaluated at sig and eqvpstrain
*
* rep = -flow_incr*internalPotential - (eqvpstrain - eqvpstrain_old)
* Here internalPotential are evaluated at sig and eqvpstrain (not the old values).
*
* The Newton-Raphson procedure has sig, flow_incr, and eqvpstrain as its
* variables. Therefore we need the derivatives of resid_ij, f, and rep
* with respect to these parameters
*
* In this associative J2 with isotropic hardening, things are a little more specialised.
* (1) f = sqrt(3*s_ij*s_ij/2) - K(eqvpstrain) (this is called "isotropic hardening")
* (2) associativity means that flow_dirn_ij = df/d(sig_ij) = s_ij*sqrt(3/2/(s_ij*s_ij)), and
* this means that flow_dirn_ij*flow_dirn_ij = 3/2, so when resid_ij=0, we get
* (plastic_strain_dot)_ij*(plastic_strain_dot)_ij = (3/2)*flow_incr^2, where
* plastic_strain_dot = plastic_strain - plastic_strain_old
* (3) The definition of equivalent plastic strain is through
* eqvpstrain_dot = sqrt(2*plastic_strain_dot_ij*plastic_strain_dot_ij/3), so
* using (2), we obtain eqvpstrain_dot = flow_incr, and this yields
* internalPotential = -1 in the "rep" equation.
*/
void
FiniteStrainPlasticMaterial::returnMap(const RankTwoTensor & sig_old,
const Real eqvpstrain_old,
const RankTwoTensor & plastic_strain_old,
const RankTwoTensor & delta_d,
const RankFourTensor & E_ijkl,
RankTwoTensor & sig,
Real & eqvpstrain,
RankTwoTensor & plastic_strain)
{
// the yield function, must be non-positive
// Newton-Raphson sets this to zero if trial stress enters inadmissible region
Real f;
// the consistency parameter, must be non-negative
// change in plastic strain in this timestep = flow_incr*flow_potential
Real flow_incr = 0.0;
// direction of flow defined by the potential
RankTwoTensor flow_dirn;
// Newton-Raphson sets this zero
// resid_ij = flow_incr*flow_dirn_ij - (plastic_strain - plastic_strain_old)
RankTwoTensor resid;
// Newton-Raphson sets this zero
// rep = -flow_incr*internalPotential - (eqvpstrain - eqvpstrain_old)
Real rep;
// change in the stress (sig) in a Newton-Raphson iteration
RankTwoTensor ddsig;
// change in the consistency parameter in a Newton-Raphson iteration
Real dflow_incr = 0.0;
// change in equivalent plastic strain in one Newton-Raphson iteration
Real deqvpstrain = 0.0;
// convenience variable that holds the change in plastic strain incurred during the return
// delta_dp = plastic_strain - plastic_strain_old
// delta_dp = E^{-1}*(trial_stress - sig), where trial_stress = E*(strain - plastic_strain_old)
RankTwoTensor delta_dp;
// d(yieldFunction)/d(stress)
RankTwoTensor df_dsig;
// d(resid_ij)/d(sigma_kl)
RankFourTensor dr_dsig;
// dr_dsig_inv_ijkl*dr_dsig_klmn = 0.5*(de_ij de_jn + de_ij + de_jm), where de_ij = 1 if i=j, but
// zero otherwise
RankFourTensor dr_dsig_inv;
// d(yieldFunction)/d(eqvpstrain)
Real fq;
// yield stress at the start of this "time step" (ie, evaluated with
// eqvpstrain_old). It is held fixed during the Newton-Raphson return,
// even if eqvpstrain != eqvpstrain_old.
Real yield_stress;
// measures of whether the Newton-Raphson process has converged
Real err1, err2, err3;
// number of Newton-Raphson iterations performed
unsigned int iter = 0;
// maximum number of Newton-Raphson iterations allowed
unsigned int maxiter = 100;
// plastic loading occurs if yieldFunction > toly
Real toly = 1.0e-8;
// Assume this strain increment does not induce any plasticity
// This is the elastic-predictor
sig = sig_old + E_ijkl * delta_d; // the trial stress
eqvpstrain = eqvpstrain_old;
plastic_strain = plastic_strain_old;
yield_stress = getYieldStress(eqvpstrain); // yield stress at this equivalent plastic strain
if (yieldFunction(sig, yield_stress) > toly)
{
// the sig just calculated is inadmissable. We must return to the yield surface.
// This is done iteratively, using a Newton-Raphson process.
delta_dp.zero();
sig = sig_old + E_ijkl * delta_d; // this is the elastic predictor
flow_dirn = flowPotential(sig);
resid = flow_dirn * flow_incr - delta_dp; // Residual 1 - refer Hughes Simo
f = yieldFunction(sig, yield_stress);
rep = -eqvpstrain + eqvpstrain_old - flow_incr * internalPotential(); // Residual 3 rep=0
err1 = resid.L2norm();
err2 = std::abs(f);
err3 = std::abs(rep);
while ((err1 > _rtol || err2 > _ftol || err3 > _eptol) &&
iter < maxiter) // Stress update iteration (hardness fixed)
{
iter++;
df_dsig = dyieldFunction_dstress(sig);
getJac(sig, E_ijkl, flow_incr, dr_dsig); // gets dr_dsig = d(resid_ij)/d(sig_kl)
fq = dyieldFunction_dinternal(eqvpstrain); // d(f)/d(eqvpstrain)
/**
* The linear system is
* ( dr_dsig flow_dirn 0 )( ddsig ) ( - resid )
* ( df_dsig 0 fq )( dflow_incr ) = ( - f )
* ( 0 1 -1 )( deqvpstrain ) ( - rep )
* The zeroes are: d(resid_ij)/d(eqvpstrain) = flow_dirn*d(df/d(sig_ij))/d(eqvpstrain) = 0
* and df/d(flow_dirn) = 0 (this is always true, even for general hardening and
* non-associative)
* and d(rep)/d(sig_ij) = -flow_incr*d(internalPotential)/d(sig_ij) = 0
*/
dr_dsig_inv = dr_dsig.invSymm();
/**
* Because of the zeroes and ones, the linear system is not impossible to
* solve by hand.
* NOTE: andy believes there was originally a sign-error in the next line. The
* next line is unchanged, however andy's definition of fq is negative of
* the original definition of fq. andy can't see any difference in any tests!
*/
dflow_incr = (f - df_dsig.doubleContraction(dr_dsig_inv * resid) + fq * rep) /
(df_dsig.doubleContraction(dr_dsig_inv * flow_dirn) - fq);
ddsig =
dr_dsig_inv *
(-resid -
flow_dirn * dflow_incr); // from solving the top row of linear system, given dflow_incr
deqvpstrain =
rep + dflow_incr; // from solving the bottom row of linear system, given dflow_incr
// update the variables
flow_incr += dflow_incr;
delta_dp -= E_ijkl.invSymm() * ddsig;
sig += ddsig;
eqvpstrain += deqvpstrain;
// evaluate the RHS equations ready for next Newton-Raphson iteration
flow_dirn = flowPotential(sig);
resid = flow_dirn * flow_incr - delta_dp;
f = yieldFunction(sig, yield_stress);
rep = -eqvpstrain + eqvpstrain_old - flow_incr * internalPotential();
err1 = resid.L2norm();
err2 = std::abs(f);
err3 = std::abs(rep);
}
if (iter >= maxiter)
mooseError("Constitutive failure");
plastic_strain += delta_dp;
}
}
/*
*Solves for incremental plastic rate of deformation tensor and stress in unrotated frame.
*Input: Strain incrment, 4th order elasticity tensor, stress tensor in previous incrmenent and
*plastic rate of deformation tensor gradient.
*/
void
FiniteStrainPlasticMaterial::solveStressResid(RankTwoTensor sig_old,RankTwoTensor delta_d,RankFourTensor E_ijkl, RankTwoTensor *dp, RankTwoTensor *sig)
{
RankTwoTensor sig_new,delta_dp,dpn;
RankTwoTensor flow_tensor, flow_dirn;
RankTwoTensor resid,ddsig;
RankFourTensor dr_dsig,dr_dsig_inv;
Real /*sig_eqv,*/flow_incr,f,dflow_incr;
Real err1,err2,err3;
unsigned int plastic_flag;
unsigned int iter,maxiter=100;
Real eqvpstrain,eqvpstrain_old,deqvpstrain,fq,rep;
Real yield_stress;
sig_new=sig_old+E_ijkl*delta_d;
eqvpstrain_old=eqvpstrain=_eqv_plastic_strain_old[_qp];
yield_stress=getYieldStress(eqvpstrain);
plastic_flag=isPlastic(sig_new,yield_stress);//Check of plasticity for elastic predictor
if (plastic_flag==1)
{
iter=0;
dflow_incr=0.0;
flow_incr=0.0;
delta_dp.zero();
deqvpstrain=0.0;
sig_new=sig_old+E_ijkl*delta_d;
getFlowTensor(sig_new,&flow_tensor);
flow_dirn=flow_tensor;
resid=flow_dirn*flow_incr-delta_dp;//Residual 1 - refer Hughes Simo
f=getSigEqv(sig_new)-yield_stress;//Residual 2 - f=0
rep=-eqvpstrain+eqvpstrain_old+flow_incr;//Residual 3 rep=0
err1=resid.L2norm();
err2=fabs(f);
err3=fabs(rep);
while ((err1 > _rtol || err2 > _ftol || err3 > _eptol) && iter < maxiter )//Stress update iteration (hardness fixed)
{
iter++;
getJac(sig_new,E_ijkl,flow_incr,&dr_dsig);//Jacobian
dr_dsig_inv=dr_dsig.invSymm();
fq=getdYieldStressdPlasticStrain(eqvpstrain);
dflow_incr=(f-flow_tensor.doubleContraction(dr_dsig_inv*resid)+fq*rep)/(flow_tensor.doubleContraction(dr_dsig_inv*flow_dirn)-fq);
ddsig=dr_dsig_inv*(-resid-flow_dirn*dflow_incr);
flow_incr+=dflow_incr;
delta_dp-=E_ijkl.invSymm()*ddsig;
sig_new+=ddsig;
deqvpstrain=rep+dflow_incr;
eqvpstrain+=deqvpstrain;
getFlowTensor(sig_new,&flow_tensor);
flow_dirn=flow_tensor;
resid=flow_dirn*flow_incr-delta_dp;
f=getSigEqv(sig_new)-yield_stress;
rep=-eqvpstrain+eqvpstrain_old+flow_incr;
err1=resid.L2norm();
err2=fabs(f);
err3=fabs(rep);
}
if (iter>=maxiter)
{
_stress[_qp](2,2)=1e6;
printf("Constitutive Error: Too many iterations %f %f %f \n",err1,err2, err3);//Convergence failure
return;
}
dpn=*dp+delta_dp;
}
*dp=dpn;//Plastic strain in unrotated configuration
*sig=sig_new;
_eqv_plastic_strain[_qp]=eqvpstrain;
}
void
RedbackMechMaterialCC::getJac(const RankTwoTensor & sig,
const RankFourTensor & E_ijkl,
Real flow_incr,
Real sig_eqv,
Real pressure,
Real p_yield_stress,
Real q_yield_stress,
Real yield_stress,
RankFourTensor & dresid_dsig)
{
unsigned i, j, k, l;
RankTwoTensor sig_dev, flow_dirn_vol, flow_dirn_dev, fij, flow_dirn, flow_tensor;
RankTwoTensor dfi_dft;
RankFourTensor dfd_dsig, dfi_dsig;
Real f1, f2, f3;
Real dfi_dp, dfi_dseqv;
Real pc = -yield_stress;
sig_dev = sig.deviatoric();
getDerivativeFlowIncrement(dfi_dp, dfi_dseqv, sig, pressure, sig_eqv, pc, q_yield_stress, p_yield_stress);
getFlowTensor(sig, sig_eqv, pressure, q_yield_stress, p_yield_stress, yield_stress, flow_dirn);
/* The following calculates the tensorial derivative (Jacobian) of the
*residual with respect to stress, dr_dsig
* It consists of two terms: The first is
* dr_dsig = (dfi_dseqv_dev*flow_dirn_dev(k,l)) * flow_dirn_dev(i,j)
* which is the tensorial product of the flow increment tensor times the flow
*direction tensor
*
* The second is the product of the flow increment tensor times the derivative
*of the flow direction tensor
* with respect to the stress tensor. See also REDBACK's documentation
* */
f1 = 0.0;
f2 = 0.0;
f3 = 0.0;
if (sig_eqv > 1e-10)
{
f1 = 3.0 / (_slope_yield_surface * _slope_yield_surface);
f2 = 2.0 / 9.0 - 1.0 / (_slope_yield_surface * _slope_yield_surface);
f3 = 3.0 / (2.0 * sig_eqv);
}
// This loop calculates the first term
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dfi_dsig(i, j, k, l) = flow_dirn(i, j) * (f3 * sig_dev(k, l) * dfi_dseqv + dfi_dp * deltaFunc(k, l) / 3.0);
// This loop calculates the second term.
for (i = 0; i < 3; ++i)
for (j = 0; j < 3; ++j)
for (k = 0; k < 3; ++k)
for (l = 0; l < 3; ++l)
dfd_dsig(i, j, k, l) = f1 * deltaFunc(i, k) * deltaFunc(j, l) + f2 * deltaFunc(i, j) * deltaFunc(k, l);
dresid_dsig = E_ijkl.invSymm() + dfd_dsig * flow_incr + dfi_dsig; // Jacobian
}
/*
*Solves for incremental plastic rate of deformation tensor and stress in unrotated frame.
*Input: Strain incrment, 4th order elasticity tensor, stress tensor in previous incrmenent and
*plastic rate of deformation tensor.
*/
void
FiniteStrainRatePlasticMaterial::returnMap(const RankTwoTensor & sig_old, const RankTwoTensor & delta_d, const RankFourTensor & E_ijkl, RankTwoTensor & dp, RankTwoTensor & sig)
{
RankTwoTensor sig_new, delta_dp, dpn;
RankTwoTensor flow_tensor, flow_dirn;
RankTwoTensor resid,ddsig;
RankFourTensor dr_dsig, dr_dsig_inv;
Real flow_incr, flow_incr_tmp;
Real err1, err3, tol1, tol3;
unsigned int iterisohard, iter, maxiterisohard = 20, maxiter = 50;
Real eqvpstrain;
Real yield_stress, yield_stress_prev;
tol1 = 1e-10;
tol3 = 1e-6;
iterisohard = 0;
eqvpstrain = std::pow(2.0/3.0,0.5) * dp.L2norm();
yield_stress = getYieldStress(eqvpstrain);
err3 = 1.1 * tol3;
while (err3 > tol3 && iterisohard < maxiterisohard) //Hardness update iteration
{
iterisohard++;
iter = 0;
delta_dp.zero();
sig_new = sig_old + E_ijkl * delta_d;
flow_incr=_ref_pe_rate*_dt * std::pow(macaulayBracket(getSigEqv(sig_new) / yield_stress - 1.0), _exponent);
getFlowTensor(sig_new, yield_stress, flow_tensor);
flow_dirn = flow_tensor;
resid = flow_dirn * flow_incr - delta_dp;
err1 = resid.L2norm();
while (err1 > tol1 && iter < maxiter) //Stress update iteration (hardness fixed)
{
iter++;
getJac(sig_new, E_ijkl, flow_incr, yield_stress, dr_dsig); //Jacobian
dr_dsig_inv = dr_dsig.invSymm();
ddsig = -dr_dsig_inv * resid;
sig_new += ddsig; //Update stress
delta_dp -= E_ijkl.invSymm() * ddsig; //Update plastic rate of deformation tensor
flow_incr_tmp = _ref_pe_rate * _dt * std::pow(macaulayBracket(getSigEqv(sig_new) / yield_stress - 1.0), _exponent);
if (flow_incr_tmp < 0.0) //negative flow increment not allowed
mooseError("Constitutive Error-Negative flow increment: Reduce time increment.");
flow_incr = flow_incr_tmp;
getFlowTensor(sig_new, yield_stress, flow_tensor);
flow_dirn = flow_tensor;
resid = flow_dirn * flow_incr - delta_dp; //Residual
err1=resid.L2norm();
}
if (iter>=maxiter)//Convergence failure
mooseError("Constitutive Error-Too many iterations: Reduce time increment.\n"); //Convergence failure
dpn = dp + delta_dp;
eqvpstrain = std::pow(2.0/3.0, 0.5) * dpn.L2norm();
yield_stress_prev = yield_stress;
yield_stress = getYieldStress(eqvpstrain);
err3 = std::abs(yield_stress-yield_stress_prev);
}
if (iterisohard>=maxiterisohard)
mooseError("Constitutive Error-Too many iterations in Hardness Update:Reduce time increment.\n"); //Convergence failure
dp = dpn; //Plastic rate of deformation tensor in unrotated configuration
sig = sig_new;
}
bool
FiniteStrainPlasticBase::returnMap(const RankTwoTensor & stress_old, const RankTwoTensor & plastic_strain_old, const std::vector<Real> & intnl_old, const RankTwoTensor & delta_d, const RankFourTensor & E_ijkl, RankTwoTensor & stress, RankTwoTensor & plastic_strain, std::vector<Real> & intnl, std::vector<Real> & f, unsigned int & iter)
{
// Assume this strain increment does not induce any plasticity
// This is the elastic-predictor
stress = stress_old + E_ijkl * delta_d; // the trial stress
plastic_strain = plastic_strain_old;
for (unsigned i = 0; i < intnl_old.size() ; ++i)
intnl[i] = intnl_old[i];
iter = 0;
yieldFunction(stress, intnl, f);
Real nr_res2 = 0;
for (unsigned i = 0 ; i < f.size() ; ++i)
nr_res2 += 0.5*std::pow( std::max(f[i], 0.0)/_f_tol[i], 2);
if (nr_res2 < 0.5)
// a purely elastic increment.
// All output variables have been calculated
return true;
// So, from here on we know that the trial stress
// is inadmissible, and we have to return from that
// value to the yield surface. There are three
// types of constraints we have to satisfy, listed
// below, and calculated in calculateConstraints(...)
// Plastic strain constraint, L2 norm must be zero (up to a tolerance)
RankTwoTensor epp;
// Yield function constraint passed to this function as
// std::vector<Real> & f
// Each yield function must be <= 0 (up to tolerance)
// Internal constraint(s), must be zero (up to a tolerance)
std::vector<Real> ic;
// During the Newton-Raphson procedure, we'll be
// changing the following parameters in order to
// (attempt to) satisfy the constraints.
RankTwoTensor dstress; // change in stress
std::vector<Real> dpm; // change in plasticity multipliers ("consistency parameters")
std::vector<Real> dintnl; // change in internal parameters
// The following are used in the Newton-Raphson
// Inverse of E_ijkl (assuming symmetric)
RankFourTensor E_inv = E_ijkl.invSymm();
// convenience variable that holds the change in plastic strain incurred during the return
// delta_dp = plastic_strain - plastic_strain_old
// delta_dp = E^{-1}*(trial_stress - stress), where trial_stress = E*(strain - plastic_strain_old)
RankTwoTensor delta_dp;
// The "consistency parameters" (plastic multipliers)
// Change in plastic strain in this timestep = pm*flowPotential
// Each pm must be non-negative
std::vector<Real> pm;
pm.assign(numberOfYieldFunctions(), 0.0);
// whether line-searching was successful
bool ls_success = true;
// The Newton-Raphson loops
while (nr_res2 > 0.5 && iter < _max_iter && ls_success)
{
iter++;
// calculate dstress, dpm and dintnl for one full Newton-Raphson step
nrStep(stress, intnl_old, intnl, pm, E_inv, delta_dp, dstress, dpm, dintnl);
// perform a line search
// The line-search will exit with updated values
ls_success = lineSearch(nr_res2, stress, intnl_old, intnl, pm, E_inv, delta_dp, dstress, dpm, dintnl, f, epp, ic);
}
if (iter >= _max_iter || !ls_success)
{
stress = stress_old;
for (unsigned i = 0; i < intnl_old.size() ; ++i)
intnl[i] = intnl_old[i];
return false;
}
else
{
plastic_strain += delta_dp;
return true;
}
}
