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Implemented Associative viscoplastic flow rule with MCC model #15

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Merged
larsblatny merged 6 commits into from
Feb 27, 2026
Merged

Implemented Associative viscoplastic flow rule with MCC model #15

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ab91220
Implemented Associative viscoplastic flow rule with MCC model
atpellet Oct 9, 2025
e07b8fc
Merge branch 'master' into Associative_Viscoplasticity
atpellet Nov 12, 2025
19ae5aa
Modified flow rule to resemble a Duvaut-Lion. Also proposed solution …
atpellet Nov 12, 2025
4962660
MCCVisc2: reformulated DL-type and removed need for returning delta_g…
larsblatny Feb 18, 2026
eaa3b14
removed changes from helper function
larsblatny Feb 18, 2026
4373c6e
added boolean option use_duvaut_lion_formulation, merged MCCVisc and …
larsblatny Feb 26, 2026
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191 changes: 113 additions & 78 deletions src/simulation/plasticity.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -33,7 +33,7 @@ void Simulation::plasticity(unsigned int p, unsigned int & plastic_count, TM & F
// If hardening law:
// q_yield = f(q_max, hardening variable) ....

T delta_gamma = hencky_deviatoric_norm - q_yield / e_mu_prefac; // this is eps_pl_dev_instant
T delta_gamma = hencky_deviatoric_norm - q_yield / e_mu_prefac; // this is eps_pl_dev_inst

if (delta_gamma > 0){ // project to yield surface
plastic_count++;
Expand Down Expand Up @@ -281,7 +281,12 @@ void Simulation::plasticity(unsigned int p, unsigned int & plastic_count, TM & F
T delta_gamma;

if (perzyna_exp == 1){
delta_gamma = (q_trial-q_yield) / (f_mu_prefac + q_yield*perzyna_visc/dt);
if (use_duvaut_lions_formulation){
delta_gamma = (q_trial-q_yield) / (f_mu_prefac*(1+perzyna_visc/dt));
}
else{
delta_gamma = (q_trial-q_yield) / (f_mu_prefac + q_yield*perzyna_visc/dt);
}
if (delta_gamma < 0){
debug("DPVisc: FATAL negative delta_gamma = ", delta_gamma);
exit = 1;
Expand All @@ -298,16 +303,30 @@ void Simulation::plasticity(unsigned int p, unsigned int & plastic_count, TM & F
exit = 1;
}

T tm = perzyna_visc * delta_gamma + dt;
T tmp = dt / tm;
T tmp1 = std::pow(tmp, perzyna_exp);
T residual;
T residual_diff;
if (use_duvaut_lions_formulation){

residual = q_trial - q_yield - f_mu_prefac * ( std::pow(perzyna_visc/dt*delta_gamma, perzyna_exp) + delta_gamma );
if (std::abs(residual) < 1e-2) {
break;
}
residual_diff = -f_mu_prefac * ( std::pow(perzyna_visc/dt, perzyna_exp) * perzyna_exp * std::pow(delta_gamma, perzyna_exp-1) + 1 );

T residual = (q_trial - f_mu_prefac * delta_gamma) * tmp1 - q_yield;
if (std::abs(residual) < 1e-2) {
break;
}
else{

T residual_diff = -f_mu_prefac * tmp1 + (q_trial - f_mu_prefac * delta_gamma) * perzyna_exp * std::pow(tmp, perzyna_exp - 1) * (-perzyna_visc * dt) / (tm * tm);
T tm = perzyna_visc * delta_gamma + dt;
T tmp = dt / tm;
T tmp1 = std::pow(tmp, perzyna_exp);

residual = (q_trial - f_mu_prefac * delta_gamma) * tmp1 - q_yield;
if (std::abs(residual) < 1e-2) {
break;
}
residual_diff = -f_mu_prefac * tmp1 + (q_trial - f_mu_prefac * delta_gamma) * perzyna_exp * std::pow(tmp, perzyna_exp - 1) * (-perzyna_visc * dt) / (tm * tm);

}

if (std::abs(residual_diff) < 1e-14){ // otherwise division by zero
debug("DPVisc: FATAL residual_diff too small in abs value = ", residual_diff);
Expand Down Expand Up @@ -493,10 +512,9 @@ void Simulation::plasticity(unsigned int p, unsigned int & plastic_count, TM & F
T p_trial = p_stress;
T q_trial = q_stress;

if (plastic_model == PlasticModel::MCCVisc){
if (use_mibf)
particles.muI[p] = M;
}
if (use_mibf)
particles.muI[p] = M;


bool perform_rma;
T p_c;
Expand Down Expand Up @@ -526,98 +544,115 @@ void Simulation::plasticity(unsigned int p, unsigned int & plastic_count, TM & F
exit = 1;
}


if (perform_rma) { // returns true if it performs a return mapping
plastic_count++;

T ep = p_stress / (K*dim);
T eps_pl_vol_inst = hencky_trace + dim * ep;
particles.eps_pl_vol[p] += eps_pl_vol_inst;
T b = 1; // must be equal to one unless using duvaut lion formulation

T delta_gamma;
////////////////////////////////////////////////////////////////
if (plastic_model == PlasticModel::MCCVisc){

T q_yield = q_stress;

if (perzyna_exp == 1){
delta_gamma = (q_trial-q_yield) / (f_mu_prefac + q_yield*perzyna_visc/dt);
if (delta_gamma < 0){
if (delta_gamma > -1e-14){
delta_gamma = 0;
}
else{
debug("MCCVisc: FATAL negative delta_gamma = ", delta_gamma);
exit = 1;
}
if (use_duvaut_lions_formulation){
b = 1.0 / (1.0 + perzyna_visc / dt); // b defined such that "stress = (1-b) * strain_trial + b * stress_yield"
if (perzyna_exp != 1){
debug("MCCVisc: FATAL viscous exponent must be 1 when use_duvaut_lions_formulation = true");
exit = 1;
}
}
else{ // persyna_exp is not one
else{ // perzyna
T delta_gamma;
T q_yield = q_stress;

if (perzyna_exp == 1){
delta_gamma = (q_trial-q_yield) / (f_mu_prefac + q_yield*perzyna_visc/dt);
if (delta_gamma < 0){
if (delta_gamma > -1e-14){
delta_gamma = 0;
}
else{
debug("MCCVisc: FATAL negative delta_gamma = ", delta_gamma);
exit = 1;
}
}
}
else{ // perzyna_exp is not one

delta_gamma = 0.01 * (q_trial - q_yield) / f_mu_prefac; // initial guess
delta_gamma = 0.01 * (q_trial - q_yield) / f_mu_prefac; // initial guess

int max_iter = 60;
for (int iter = 0; iter < max_iter; iter++) {
if (iter == max_iter - 1){ // did not break loop
debug("MCCVisc: FATAL did not exit loop at iter = ", iter);
exit = 1;
}
int max_iter = 60;
for (int iter = 0; iter < max_iter; iter++) {
if (iter == max_iter - 1){ // did not break loop
debug("MCCVisc: FATAL did not exit loop at iter = ", iter);
exit = 1;
}

T tm = perzyna_visc * delta_gamma + dt;
T tmp = dt / tm;
T tmp1 = std::pow(tmp, perzyna_exp);
T tm = perzyna_visc * delta_gamma + dt;
T tmp = dt / tm;
T tmp1 = std::pow(tmp, perzyna_exp);

T residual = (q_trial - f_mu_prefac * delta_gamma) * tmp1 - q_yield;
if (std::abs(residual) < 1e-2) {
break;
}
T residual = (q_trial - f_mu_prefac * delta_gamma) * tmp1 - q_yield;
if (std::abs(residual) < 1e-2) {
break;
}

T residual_diff = -f_mu_prefac * tmp1 + (q_trial - f_mu_prefac * delta_gamma) * perzyna_exp * std::pow(tmp, perzyna_exp - 1) * (-perzyna_visc * dt) / (tm * tm);
T residual_diff = -f_mu_prefac * tmp1 + (q_trial - f_mu_prefac * delta_gamma) * perzyna_exp * std::pow(tmp, perzyna_exp - 1) * (-perzyna_visc * dt) / (tm * tm);

if (std::abs(residual_diff) < 1e-14){ // otherwise division by zero
debug("MCCVisc: FATAL residual_diff too small in abs value = ", residual_diff);
exit = 1;
}
if (std::abs(residual_diff) < 1e-14){ // otherwise division by zero
debug("MCCVisc: FATAL residual_diff too small in abs value = ", residual_diff);
exit = 1;
}

delta_gamma -= residual / residual_diff;
delta_gamma -= residual / residual_diff;

if (delta_gamma < 0) // not possible and can also lead to division by zero
delta_gamma = 1e-10;
if (delta_gamma < 0) // not possible and can also lead to division by zero
delta_gamma = 1e-10;

} // end N-R iterations
} // end N-R iterations

} // end if perzyna_exp == 1
} // end if perzyna_exp == 1

q_stress = std::max(q_yield, q_trial - f_mu_prefac * delta_gamma); // delta_gamma = dt * gamma_dot_S
q_stress = std::max(q_yield, q_trial - f_mu_prefac * delta_gamma); // delta_gamma = dt * gamma_dot_S

if (use_mibf){
if (hardening_law == HardeningLaw::ExpoImpl){
p_c = std::max(T(0), p0 * std::exp(-xi*particles.eps_pl_vol[p]));
}
else if (hardening_law == HardeningLaw::SinhImpl){
p_c = std::max(T(0), K * std::sinh(-xi*particles.eps_pl_vol[p] + std::asinh(p0/K)));
}
} // end if use_duvaut_lions_formulation

} // end if MCCVisc
////////////////////////////////////////////////////////////////

T eps_pl_vol_inst = - b * (p_trial - p_stress) / K;
T eps_pl_dev_inst = b * (q_trial - q_stress) / e_mu_prefac;

particles.eps_pl_vol[p] += eps_pl_vol_inst;
particles.eps_pl_dev[p] += eps_pl_dev_inst;

if ( (p_stress < -beta * p_c + stress_tolerance) || (p_stress > p_c - stress_tolerance) ){
particles.muI[p] = M;
particles.delta_gamma[p] = d_prefac * eps_pl_dev_inst / dt;

T h_vol = - p_trial / K - eps_pl_vol_inst;
T h_dev = q_trial / e_mu_prefac - eps_pl_dev_inst;
hencky = h_dev * hencky_deviatoric + (h_vol/dim) * TV::Ones();
particles.F[p] = svd.matrixU() * hencky.array().exp().matrix().asDiagonal() * svd.matrixV().transpose();

if (use_mibf){
if (hardening_law == HardeningLaw::ExpoImpl){
p_c = std::max(T(0), p0 * std::exp(-xi*particles.eps_pl_vol[p]));
}
else if (hardening_law == HardeningLaw::SinhImpl){
p_c = std::max(T(0), K * std::sinh(-xi*particles.eps_pl_vol[p] + std::asinh(p0/K)));
}

if ( (p_stress < -beta * p_c + stress_tolerance) || (p_stress > p_c - stress_tolerance) ){
particles.muI[p] = M;
}
else{
if (use_duvaut_lions_formulation){
particles.muI[p] = ( (e_mu_prefac*h_dev-q_trial*(1-b))/b ) / std::sqrt((p_stress + beta * p_c) * (p_c - p_stress));
}
else{
particles.muI[p] = q_stress / std::sqrt((p_stress + beta * p_c) * (p_c - p_stress));
}
}
} // end if use_mibf

} // end if MCCVisc
////////////////////////////////////////////////////////////////


delta_gamma = (q_trial - q_stress) / f_mu_prefac;
particles.eps_pl_dev[p] += (1.0/d_prefac) * delta_gamma;
particles.delta_gamma[p] = delta_gamma / dt;

hencky = q_stress / e_mu_prefac * hencky_deviatoric - ep*TV::Ones();
particles.F[p] = svd.matrixU() * hencky.array().exp().matrix().asDiagonal() * svd.matrixV().transpose();
} // if perform_rma
} // end MCC / MCCVisc
} // end if perform_rma
} // end MCC or MCCVisc

} // end plastic_model type

Expand Down
1 change: 1 addition & 0 deletions src/simulation/simulation.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -93,6 +93,7 @@ class Simulation{
// Perzyna
T perzyna_exp = 1;
T perzyna_visc = 0;
bool use_duvaut_lions_formulation = false;

// MCC
T beta = 0;
Expand Down