1. Varchanis, S; Makrigiorgos, G; Moschopoulos, P; Dimakopoulos, Y; Tsamopoulos, J

Modeling the rheology of thixotropic elasto-visco-plastic materials Journal Article

In: Journal of Rheology, 63 (4), pp. 609-639, 2019, ISSN: 01486055, (cited By 1).

Abstract | Links | BibTeX | Tags: elasto-visco-plastic, EVP, materials, rheology, SAOS

@article{Varchanis2019609,

title = {Modeling the rheology of thixotropic elasto-visco-plastic materials},

author = {S Varchanis and G Makrigiorgos and P Moschopoulos and Y Dimakopoulos and J Tsamopoulos},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-85066807729&doi=10.1122%2f1.5049136&partnerID=40&md5=2852b6137d879bf29a4d75dab0888ded},

doi = {10.1122/1.5049136},

issn = {01486055},

year = {2019},

date = {2019-01-01},

journal = {Journal of Rheology},

volume = {63},

number = {4},

pages = {609-639},

abstract = {To describe the macroscopic rheological behavior of thixotropic elasto-visco-plastic (TEVP) materials, phenomena that take place in their microstructure must be accounted for. To this end, we couple the tensorial constitutive model by Saramito for EVP materials with thixotropy, extending the ideas of isotropic hardening, and with kinematic hardening (KH), to account for back stresses. We use a scalar variable that describes the level of structure at any instance and a modified Armstrong-Frederick KH equation, thus providing rules governing the dynamics of the apparent yield stress. The material viscosity, yield stress, and back stress modulus feature a nonlinear dependence on the structural parameter, enabling the model to make accurate predictions with a single structural parameter. To avoid unphysical stress evolution in both shear and extensional flows, we propose a modified back stress constitutive equation that keeps the components of the stress tensor bounded. The predictions of the new model are compared to experimental data and predictions of previously proposed TEVP models in simple rheometric flows, including steady and step-shear tests, flow reversal, intermittent step tests, small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear. In most cases, the proposed model reproduces more accurately these experimental data than the other models, highlighting its predictive capabilities. Moreover, SAOS illustrates that introducing viscoplasticity via the Saramito model necessarily reduces G″ to zero in the linear strain regime. This calls for model adjustments in the solid state. Finally, we examined the proposed model in uniaxial elongation and concluded that it is important to include this flow in the rheological characterization and modeling of such systems. © 2019 The Society of Rheology.},

note = {cited By 1},

keywords = {elasto-visco-plastic, EVP, materials, rheology, SAOS},

pubstate = {published},

tppubtype = {article}

}

To describe the macroscopic rheological behavior of thixotropic elasto-visco-plastic (TEVP) materials, phenomena that take place in their microstructure must be accounted for. To this end, we couple the tensorial constitutive model by Saramito for EVP materials with thixotropy, extending the ideas of isotropic hardening, and with kinematic hardening (KH), to account for back stresses. We use a scalar variable that describes the level of structure at any instance and a modified Armstrong-Frederick KH equation, thus providing rules governing the dynamics of the apparent yield stress. The material viscosity, yield stress, and back stress modulus feature a nonlinear dependence on the structural parameter, enabling the model to make accurate predictions with a single structural parameter. To avoid unphysical stress evolution in both shear and extensional flows, we propose a modified back stress constitutive equation that keeps the components of the stress tensor bounded. The predictions of the new model are compared to experimental data and predictions of previously proposed TEVP models in simple rheometric flows, including steady and step-shear tests, flow reversal, intermittent step tests, small amplitude oscillatory shear (SAOS) and large amplitude oscillatory shear. In most cases, the proposed model reproduces more accurately these experimental data than the other models, highlighting its predictive capabilities. Moreover, SAOS illustrates that introducing viscoplasticity via the Saramito model necessarily reduces G″ to zero in the linear strain regime. This calls for model adjustments in the solid state. Finally, we examined the proposed model in uniaxial elongation and concluded that it is important to include this flow in the rheological characterization and modeling of such systems. © 2019 The Society of Rheology.2. Fraggedakis, D; Dimakopoulos, Y; Tsamopoulos, J

Yielding the yield stress analysis: A thorough comparison of recently proposed elasto-visco-plastic (EVP) fluid models Journal Article

In: Journal of Non-Newtonian Fluid Mechanics, 238 , pp. 170-188, 2016, ISSN: 03770257, (cited By 12).

Abstract | Links | BibTeX | Tags: elasto-visco-plastic, EVP, falling sphere, LAOS, Viscometric

@article{Fraggedakis2016170,

title = {Yielding the yield stress analysis: A thorough comparison of recently proposed elasto-visco-plastic (EVP) fluid models},

author = {D Fraggedakis and Y Dimakopoulos and J Tsamopoulos},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84999836120&doi=10.1016%2fj.jnnfm.2016.11.007&partnerID=40&md5=bc94ab444300e53cd26ce592cbced071},

doi = {10.1016/j.jnnfm.2016.11.007},

issn = {03770257},

year = {2016},

date = {2016-01-01},

journal = {Journal of Non-Newtonian Fluid Mechanics},

volume = {238},

pages = {170-188},

abstract = {We examine and compare five constitutive models, which have been recently proposed to describe the behavior of elasto-visco-plastic fluids. The comparison is performed in simple rheometric flows, i.e. simple-shear, uniaxial elongation and large amplitude oscillatory tests and in the complex flow generated by a falling spherical particle. The first set of three models do not explicitly include shear-thinning. These are the ones proposed by Saramito (2007), Park and Liu (2010) and Belblidia et al. (2011). The first one has been derived under a thermodynamic framework, while the other two have been based on viscosity regularization methods. When spatial and temporal inhomogeneity are not present in the flow field, the models generally produce acceptable predictions, except for: (a) the BWW in predicting the primary normal stress under small shear rate and under small strain in the LAOStrain test, (b) all models in predicting different parts of the spectra of G′ and G″, although the predictions of the SRM can be corrected when kinematic hardening is accounted for and (c) the P&L model in LAOStress because of nonexistence or multiplicity of solutions. In the complex flow, the predictions of each model are compared with the experimental data of Holenberg et al. (2012) under non shear-thinning conditions and the predictions of the SRM model are clearly superior. The second set of models have been proposed by Saramito (2009) to explicitly account for shear thinning either by extending the Herschel–Bulkley model to include elastic effects, SRM-HB, or by introducing a PTT-type term in the constitutive model, SRM-PTT. Both these models provide acceptable results in the rheometric tests. In the falling sphere test, their predictions are compared with the experimental results by Putz et al. (2008) for the settling of a particle under conditions that the Carbopol solution exhibits shear-thinning. Here the SRM-HB is found to be superior. © 2016},

note = {cited By 12},

keywords = {elasto-visco-plastic, EVP, falling sphere, LAOS, Viscometric},

pubstate = {published},

tppubtype = {article}

}

We examine and compare five constitutive models, which have been recently proposed to describe the behavior of elasto-visco-plastic fluids. The comparison is performed in simple rheometric flows, i.e. simple-shear, uniaxial elongation and large amplitude oscillatory tests and in the complex flow generated by a falling spherical particle. The first set of three models do not explicitly include shear-thinning. These are the ones proposed by Saramito (2007), Park and Liu (2010) and Belblidia et al. (2011). The first one has been derived under a thermodynamic framework, while the other two have been based on viscosity regularization methods. When spatial and temporal inhomogeneity are not present in the flow field, the models generally produce acceptable predictions, except for: (a) the BWW in predicting the primary normal stress under small shear rate and under small strain in the LAOStrain test, (b) all models in predicting different parts of the spectra of G′ and G″, although the predictions of the SRM can be corrected when kinematic hardening is accounted for and (c) the P&L model in LAOStress because of nonexistence or multiplicity of solutions. In the complex flow, the predictions of each model are compared with the experimental data of Holenberg et al. (2012) under non shear-thinning conditions and the predictions of the SRM model are clearly superior. The second set of models have been proposed by Saramito (2009) to explicitly account for shear thinning either by extending the Herschel–Bulkley model to include elastic effects, SRM-HB, or by introducing a PTT-type term in the constitutive model, SRM-PTT. Both these models provide acceptable results in the rheometric tests. In the falling sphere test, their predictions are compared with the experimental results by Putz et al. (2008) for the settling of a particle under conditions that the Carbopol solution exhibits shear-thinning. Here the SRM-HB is found to be superior. © 20163. Fraggedakis, D; Dimakopoulos, Y; Tsamopoulos, J

Yielding the yield stress analysis: A thorough comparison of recently proposed elasto-visco-plastic (EVP) fluid models Journal Article

In: Journal of Non-Newtonian Fluid Mechanics, 236 , pp. 104-122, 2016, ISSN: 03770257, (cited By 17).

Abstract | Links | BibTeX | Tags: elasto-visco-plastic, EVP, falling sphere, LAOS, Viscometric

@article{Fraggedakis2016104,

title = {Yielding the yield stress analysis: A thorough comparison of recently proposed elasto-visco-plastic (EVP) fluid models},

author = {D Fraggedakis and Y Dimakopoulos and J Tsamopoulos},

url = {https://www.scopus.com/inward/record.uri?eid=2-s2.0-84986893199&doi=10.1016%2fj.jnnfm.2016.09.001&partnerID=40&md5=e42bb4e2b966ac1f1eb985155ad207ce},

doi = {10.1016/j.jnnfm.2016.09.001},

issn = {03770257},

year = {2016},

date = {2016-01-01},

journal = {Journal of Non-Newtonian Fluid Mechanics},

volume = {236},

pages = {104-122},

abstract = {We examine and compare five constitutive models, which have been recently proposed to describe the behavior of elasto-visco-plastic fluids. The comparison is performed in simple rheometric flows, i.e. simple-shear, uniaxial elongation and large amplitude oscillatory tests and in the complex flow generated by a falling spherical particle. The first set of three models do not explicitly include shear-thinning. These are the ones proposed by Saramito [21], Park & Liu [27] and Belblidia et al. [28]. The first one has been derived under a thermodynamic framework, while the other two have been based on viscosity regularization methods. When spatial and temporal inhomogeneity are not present in the flow field, the models generally produce acceptable predictions, except for: (a) the BWW in predicting the primary normal stress under small shear rate and under small strain in the LAOStrain test, (b) all models in predicting different parts of the spectra of G′ and G″, although the predictions of the SRM can be corrected when kinematic hardening is accounted for and (c) the P&L model in LAOStress because of nonexistence or multiplicity of solutions. In the complex flow, the predictions of each model are compared with the experimental data of Holenberg et al. [34] under non shear-thinning conditions and the predictions of the SRM model are clearly superior. The second set of models have been proposed by Saramito [22] to explicitly account for shear thinning either by extending the Herschel–Bulkley model to include elastic effects, SRM-HB, or by introducing a PTT-type term in the constitutive model, SRM-PTT. Both these models provide acceptable results in the rheometric tests. In the falling sphere test, their predictions are compared with the experimental results by Putz et al. [15] for the settling of a particle under conditions that the Carbopol solution exhibits shear-thinning. Here the SRM-HB is found to be superior. © 2016 Elsevier B.V.},

note = {cited By 17},

keywords = {elasto-visco-plastic, EVP, falling sphere, LAOS, Viscometric},

pubstate = {published},

tppubtype = {article}

}

We examine and compare five constitutive models, which have been recently proposed to describe the behavior of elasto-visco-plastic fluids. The comparison is performed in simple rheometric flows, i.e. simple-shear, uniaxial elongation and large amplitude oscillatory tests and in the complex flow generated by a falling spherical particle. The first set of three models do not explicitly include shear-thinning. These are the ones proposed by Saramito [21], Park & Liu [27] and Belblidia et al. [28]. The first one has been derived under a thermodynamic framework, while the other two have been based on viscosity regularization methods. When spatial and temporal inhomogeneity are not present in the flow field, the models generally produce acceptable predictions, except for: (a) the BWW in predicting the primary normal stress under small shear rate and under small strain in the LAOStrain test, (b) all models in predicting different parts of the spectra of G′ and G″, although the predictions of the SRM can be corrected when kinematic hardening is accounted for and (c) the P&L model in LAOStress because of nonexistence or multiplicity of solutions. In the complex flow, the predictions of each model are compared with the experimental data of Holenberg et al. [34] under non shear-thinning conditions and the predictions of the SRM model are clearly superior. The second set of models have been proposed by Saramito [22] to explicitly account for shear thinning either by extending the Herschel–Bulkley model to include elastic effects, SRM-HB, or by introducing a PTT-type term in the constitutive model, SRM-PTT. Both these models provide acceptable results in the rheometric tests. In the falling sphere test, their predictions are compared with the experimental results by Putz et al. [15] for the settling of a particle under conditions that the Carbopol solution exhibits shear-thinning. Here the SRM-HB is found to be superior. © 2016 Elsevier B.V.