List of Journal Publications
2024
111.
Grazioli, D., Gangi, G., Nicola, L., Simone, A.
Predicting mechanical and electrical failure of nanowire networks in flexible transparent electrodes Journal Article
In: COMPOSITES SCIENCE AND TECHNOLOGY, vol. 245, no. 110304, 2024.
Abstract | BibTeX | Tags: electrodes, nanowires | Links:
@article{D.2024,
title = {Predicting mechanical and electrical failure of nanowire networks in flexible transparent electrodes},
author = {D. Grazioli and G. Gangi and L. Nicola and A. Simone},
doi = {https://doi.org/10.1016/j.compscitech.2023.110304},
year = {2024},
date = {2024-01-05},
urldate = {2024-01-05},
journal = {COMPOSITES SCIENCE AND TECHNOLOGY},
volume = {245},
number = {110304},
abstract = {Flexible transparent electrodes employing metal nanowires (NWs) find extensive use in various applications such as optoelectronic devices, solar cells, light-emitting diodes, and transparent heaters. NW networks in flexible transparent electrodes can withstand mechanical deformations and conduct electricity but are susceptible to localized damage caused by mechanical stress and current density concentration. This localized damage ultimately results in electrode failure. Our study aims to track locally induced damage from both mechanical and electrical sources and assess their collective influence on electrode performance until failure occurs. To this end, we create two-dimensional digital samples that represent the NW networks, transform them into beam networks and equivalent resistor networks, and perform finite element simulations of the mechanical and electrical network responses while varying the NW content.
Our simulations reveal crack-like patterns in the distribution of damaged elements at network failure that depend on the process inducing the damage. While our results suggest that the impact of electrically induced damage on overall network stability is more significant than that of mechanically induced damage, the latter must not be ignored.},
keywords = {electrodes, nanowires},
pubstate = {published},
tppubtype = {article}
}
Flexible transparent electrodes employing metal nanowires (NWs) find extensive use in various applications such as optoelectronic devices, solar cells, light-emitting diodes, and transparent heaters. NW networks in flexible transparent electrodes can withstand mechanical deformations and conduct electricity but are susceptible to localized damage caused by mechanical stress and current density concentration. This localized damage ultimately results in electrode failure. Our study aims to track locally induced damage from both mechanical and electrical sources and assess their collective influence on electrode performance until failure occurs. To this end, we create two-dimensional digital samples that represent the NW networks, transform them into beam networks and equivalent resistor networks, and perform finite element simulations of the mechanical and electrical network responses while varying the NW content.
Our simulations reveal crack-like patterns in the distribution of damaged elements at network failure that depend on the process inducing the damage. While our results suggest that the impact of electrically induced damage on overall network stability is more significant than that of mechanically induced damage, the latter must not be ignored.
Our simulations reveal crack-like patterns in the distribution of damaged elements at network failure that depend on the process inducing the damage. While our results suggest that the impact of electrically induced damage on overall network stability is more significant than that of mechanically induced damage, the latter must not be ignored.
2023
110.
Grazioli, D., Dadduzio, Alberto C, Roso, Martina, Simone, A.
Quantitative electrical homogeneity assessment of nanowire transparent electrodes Journal Article
In: NANOSCALE, vol. 15, no. 14, pp. 6770–6784, 2023.
Abstract | BibTeX | Tags: electrodes, nanowires | Links:
@article{Grazioli2023,
title = {Quantitative electrical homogeneity assessment of nanowire transparent electrodes},
author = {D. Grazioli and Alberto C Dadduzio and Martina Roso and A. Simone},
doi = {10.1039/d2nr06564a},
year = {2023},
date = {2023-01-01},
journal = {NANOSCALE},
volume = {15},
number = {14},
pages = {6770–6784},
publisher = {ROYAL SOC CHEMISTRY},
abstract = {The homogeneous distribution of electric current (electrical homogeneity) is not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, thus masking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance R-w and R-j, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation. The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes. Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio R-w/R-j. We observe that a significant reduction of contact resistance is not necessary to ensure a high degree of homogeneity. The ideal condition of negligible junction resistance (R-w >> R-j) leads to the best-case scenario, a situation which is closely approached if R-w approximate to R-j (15% difference at the most in terms of homogeneity index).},
keywords = {electrodes, nanowires},
pubstate = {published},
tppubtype = {article}
}
The homogeneous distribution of electric current (electrical homogeneity) is not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, thus masking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance R-w and R-j, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation. The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes. Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio R-w/R-j. We observe that a significant reduction of contact resistance is not necessary to ensure a high degree of homogeneity. The ideal condition of negligible junction resistance (R-w >> R-j) leads to the best-case scenario, a situation which is closely approached if R-w approximate to R-j (15% difference at the most in terms of homogeneity index).
109.
Rafols, F Perez, Dokkum, JS Van, Nicola, L
On the interplay between roughness and viscoelasticity in adhesive hysteresis Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 170, 2023.
Abstract | BibTeX | Tags: Adhesion and adhesives, Adhesive hysteresis, contact mechanics, Viscoelastic material | Links:
@article{PerezRafols2023,
title = {On the interplay between roughness and viscoelasticity in adhesive hysteresis},
author = {F Perez Rafols and JS Van Dokkum and L Nicola},
doi = {10.1016/j.jmps.2022.105079},
year = {2023},
date = {2023-01-01},
urldate = {2023-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {170},
publisher = {PERGAMON-ELSEVIER SCIENCE LTD},
abstract = {Viscoelasticity and roughness are among the possible causes of the adhesive hysteresis displayed by soft contacts. Viscoelasticity causes an increased effective work of adhesion due to stiffening of the contact, while roughness is responsible for elastic instabilities. Herein, we explore the interplay between viscoelasticity and roughness by simulating in two dimensions the retraction of a rigid cylinder, with wavy surface profile, from a viscoelastic half-space. The wave amplitude and length are varied to induce instabilities in the load-to-area response, while the retraction velocity is increased to promote viscoelasticity. Results show that, in the regime where viscoelasticity is confined to the edges of the wavy contact, the contributions of viscoelasticity and waviness to adhesive hysteresis are nearly independent and additive. At low retraction rates, the instabilities in the load-area curve typical of rough elastic contacts are suppressed by viscoelasticity: the contact stiffens to promote a stable decrease of the contact area with load. This occurs with a minimal change in work of adhesion. However, when the instantaneous limit is met at high retraction rates, mechanical instabilities appear.},
keywords = {Adhesion and adhesives, Adhesive hysteresis, contact mechanics, Viscoelastic material},
pubstate = {published},
tppubtype = {article}
}
Viscoelasticity and roughness are among the possible causes of the adhesive hysteresis displayed by soft contacts. Viscoelasticity causes an increased effective work of adhesion due to stiffening of the contact, while roughness is responsible for elastic instabilities. Herein, we explore the interplay between viscoelasticity and roughness by simulating in two dimensions the retraction of a rigid cylinder, with wavy surface profile, from a viscoelastic half-space. The wave amplitude and length are varied to induce instabilities in the load-to-area response, while the retraction velocity is increased to promote viscoelasticity. Results show that, in the regime where viscoelasticity is confined to the edges of the wavy contact, the contributions of viscoelasticity and waviness to adhesive hysteresis are nearly independent and additive. At low retraction rates, the instabilities in the load-area curve typical of rough elastic contacts are suppressed by viscoelasticity: the contact stiffens to promote a stable decrease of the contact area with load. This occurs with a minimal change in work of adhesion. However, when the instantaneous limit is met at high retraction rates, mechanical instabilities appear.
108.
Civiero, R, Rafols, F Perez, Nicola, L
Modeling contact deformation of bare and coated rough metal bodies Journal Article
In: MECHANICS OF MATERIALS, vol. 179, 2023.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Self-affine surfaces, Strain hardening | Links:
@article{Civiero2023,
title = {Modeling contact deformation of bare and coated rough metal bodies},
author = {R Civiero and F Perez Rafols and L Nicola},
doi = {10.1016/j.mechmat.2023.104583},
year = {2023},
date = {2023-01-01},
journal = {MECHANICS OF MATERIALS},
volume = {179},
publisher = {ELSEVIER},
abstract = {The effect of the presence of a passivation layer on a metal rough surface during contact loading is investigated by means of dislocation dynamics simulations. The metal body is modeled as an FCC single crystal with a self-affine rough surface that is either bare, or covered by a thin coating, impenetrable to dislocations. This analysis permits to isolate the effect of surface roughening driven by dislocation motion: when the surface is bare the dislocations can glide out, leaving crystallographic steps at the surface that modify the local roughness; when the surface is passivated, dislocations are stopped by the interface.},
keywords = {contact mechanics, dislocation dynamics, Self-affine surfaces, Strain hardening},
pubstate = {published},
tppubtype = {article}
}
The effect of the presence of a passivation layer on a metal rough surface during contact loading is investigated by means of dislocation dynamics simulations. The metal body is modeled as an FCC single crystal with a self-affine rough surface that is either bare, or covered by a thin coating, impenetrable to dislocations. This analysis permits to isolate the effect of surface roughening driven by dislocation motion: when the surface is bare the dislocations can glide out, leaving crystallographic steps at the surface that modify the local roughness; when the surface is passivated, dislocations are stopped by the interface.
2022
107.
Goudarzi, M., Grazioli, D., Simone, A.
An efficient computational approach for three-dimensional modeling and simulation of fibrous battery electrodes Journal Article
In: INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, vol. 123, no. 7, pp. 1513–1546, 2022.
Abstract | BibTeX | Tags: embedded fiber model, fibrous electrode, Finite element method, lithium-ion battery electrodes modeling and simulation, nanowire and structural batteries | Links:
@article{Goudarzi2022,
title = {An efficient computational approach for three-dimensional modeling and simulation of fibrous battery electrodes},
author = {M. Goudarzi and D. Grazioli and A. Simone},
doi = {10.1002/nme.6881},
year = {2022},
date = {2022-01-01},
journal = {INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING},
volume = {123},
number = {7},
pages = {1513–1546},
publisher = {John Wiley and Sons Ltd},
abstract = {Fibrous electrodes are a promising alternative to conventional particle-based lithium-ion battery electrodes. In this contribution, we propose an efficient computational approach for the modeling and simulation of electrochemical phenomena taking place in fibrous electrodes during battery charge/discharge processes. Since each fiber is explicitly modeled by means of a dimensionally reduced embedded fiber model, the framework enables simulations in a three-dimensional setting with relatively modest discretization and computational requirements compared to simulations with fully resolved fiber discretizations. The approach is applied to electrodes with high volume fractions of high aspect ratio fibers. Various local and global quantities are analyzed and results are compared to those obtained with the standard finite element method and the pseudo-2D model.},
keywords = {embedded fiber model, fibrous electrode, Finite element method, lithium-ion battery electrodes modeling and simulation, nanowire and structural batteries},
pubstate = {published},
tppubtype = {article}
}
Fibrous electrodes are a promising alternative to conventional particle-based lithium-ion battery electrodes. In this contribution, we propose an efficient computational approach for the modeling and simulation of electrochemical phenomena taking place in fibrous electrodes during battery charge/discharge processes. Since each fiber is explicitly modeled by means of a dimensionally reduced embedded fiber model, the framework enables simulations in a three-dimensional setting with relatively modest discretization and computational requirements compared to simulations with fully resolved fiber discretizations. The approach is applied to electrodes with high volume fractions of high aspect ratio fibers. Various local and global quantities are analyzed and results are compared to those obtained with the standard finite element method and the pseudo-2D model.
106.
Liu, Dy, Boom, Sj, Simone, A., Aragon, Am
An interface-enriched generalized finite element formulation for locking-free coupling of non-conforming discretizations and contact Journal Article
In: COMPUTATIONAL MECHANICS, vol. 70, no. 3, pp. 477–499, 2022.
Abstract | BibTeX | Tags: Contact, Enriched FEM, IGFEM, Lagrange multipliers, Multiple-point constraints, Non-conforming meshes | Links:
@article{Liu2022,
title = {An interface-enriched generalized finite element formulation for locking-free coupling of non-conforming discretizations and contact},
author = {Dy Liu and Sj Boom and A. Simone and Am Aragon},
doi = {10.1007/s00466-022-02159-w},
year = {2022},
date = {2022-01-01},
journal = {COMPUTATIONAL MECHANICS},
volume = {70},
number = {3},
pages = {477–499},
publisher = {SPRINGER},
abstract = {We propose an enriched finite element formulation to address the computational modeling of contact problems and the coupling of non-conforming discretizations in the small deformation setting. The displacement field is augmented by enriched terms that are associated with generalized degrees of freedom collocated along non-conforming interfaces or contact surfaces. The enrichment strategy effectively produces an enriched node-to-node discretization that can be used with any constraint enforcement criterion; this is demonstrated with both multi-point constraints and Lagrange multipliers, the latter in a generalized Newton implementation where both primal and Lagrange multiplier fields are updated simultaneously. We show that the node-to-node enrichment ensures continuity of the displacement field-without locking-in mesh coupling problems, and that tractions are transferred accurately at contact interfaces without the need for stabilization. We also show the formulation is stable with respect to the condition number of the stiffness matrix by using a simple Jacobi-like diagonal preconditioner.},
keywords = {Contact, Enriched FEM, IGFEM, Lagrange multipliers, Multiple-point constraints, Non-conforming meshes},
pubstate = {published},
tppubtype = {article}
}
We propose an enriched finite element formulation to address the computational modeling of contact problems and the coupling of non-conforming discretizations in the small deformation setting. The displacement field is augmented by enriched terms that are associated with generalized degrees of freedom collocated along non-conforming interfaces or contact surfaces. The enrichment strategy effectively produces an enriched node-to-node discretization that can be used with any constraint enforcement criterion; this is demonstrated with both multi-point constraints and Lagrange multipliers, the latter in a generalized Newton implementation where both primal and Lagrange multiplier fields are updated simultaneously. We show that the node-to-node enrichment ensures continuity of the displacement field-without locking-in mesh coupling problems, and that tractions are transferred accurately at contact interfaces without the need for stabilization. We also show the formulation is stable with respect to the condition number of the stiffness matrix by using a simple Jacobi-like diagonal preconditioner.
105.
Perez-Rafols, F., Nicola, L.
Incipient sliding of adhesive contacts Journal Article
In: FRICTION, vol. 10, no. 6, pp. 963–976, 2022.
Abstract | BibTeX | Tags: Adhesion, incipient sliding, traction-separation laws | Links:
@article{PerezRafols2022,
title = {Incipient sliding of adhesive contacts},
author = {F. Perez-Rafols and L. Nicola},
doi = {10.1007/s40544-021-0546-9},
year = {2022},
date = {2022-01-01},
journal = {FRICTION},
volume = {10},
number = {6},
pages = {963–976},
publisher = {Tsinghua University},
abstract = {A model is proposed herein to investigate the incipient sliding of contacts in the presence of both friction and adhesion, where the interfacial response is modeled based on traction-separation laws. A Maugis-like parameter is defined to characterize the response in the tangential direction. Subsequently, the model is used to investigate the contact between a smooth cylinder and a flat body, where adhesion-friction interactions are strong. A range of behaviors are observed when a tangential displacement is imposed: When the parameter is low, the contact pressure exhibits a relatively constant profile; when it is high, a pressure spike is observed at the edge of the contact. This difference is caused by a significant interface compliance in the former case, which limits the amount of slip. The results for the mid-range values of the Maugis-like parameter can qualitatively replicate various experiments performed using polydimethylsiloxane (PDMS) balls.},
keywords = {Adhesion, incipient sliding, traction-separation laws},
pubstate = {published},
tppubtype = {article}
}
A model is proposed herein to investigate the incipient sliding of contacts in the presence of both friction and adhesion, where the interfacial response is modeled based on traction-separation laws. A Maugis-like parameter is defined to characterize the response in the tangential direction. Subsequently, the model is used to investigate the contact between a smooth cylinder and a flat body, where adhesion-friction interactions are strong. A range of behaviors are observed when a tangential displacement is imposed: When the parameter is low, the contact pressure exhibits a relatively constant profile; when it is high, a pressure spike is observed at the edge of the contact. This difference is caused by a significant interface compliance in the former case, which limits the amount of slip. The results for the mid-range values of the Maugis-like parameter can qualitatively replicate various experiments performed using polydimethylsiloxane (PDMS) balls.
104.
Irani, N., Murugesan, Y., Ayas, C., Nicola, L.
Effect of dislocation core fields on discrete dislocation plasticity Journal Article
In: MECHANICS OF MATERIALS, vol. 165, 2022.
Abstract | BibTeX | Tags: Dislocation climb, Dislocation core, dislocation dynamics, Plasticity | Links:
@article{Irani2022,
title = {Effect of dislocation core fields on discrete dislocation plasticity},
author = {N. Irani and Y. Murugesan and C. Ayas and L. Nicola},
doi = {10.1016/j.mechmat.2021.104137},
year = {2022},
date = {2022-01-01},
journal = {MECHANICS OF MATERIALS},
volume = {165},
publisher = {Elsevier B.V.},
abstract = {Discrete dislocation plasticity is a modeling technique that treats plasticity as the collective motion of dislocations. The dislocations are described through their elastic Volterra fields, outside of a cylindrical core region, with a few Burgers vectors of diameter. The contribution of the core fields to the dislocation dynamics is neglected, because it is assumed that their range is too short to be of influence. The aim of this work is to assess the validity of this assumption. In recent ab-initio studies it has been demonstrated that the dislocation core fields are significant up to a distance of ten Burgers vector from the dislocation line. This is a longer range influence than expected and can give rise to changes in the evolving dislocation structure and in the overall response of a plastically deforming body. It is indeed experimentally observed that dislocations pile up against strong interfaces, and that the spacing between dislocations at the front of these pile-ups can be less than ten Burgers vectors. In this work, 2-D discrete dislocation plasticity simulations are performed to investigate the effect of core fields on edge dislocation interactions. The results of the simulations, which include core fields for the first time, show indeed that dislocations that are very closely spaced experience additional glide or climb due to core fields. The effect is however negligible when compared to glide and climb due to Volterra fields or due to the external load.},
keywords = {Dislocation climb, Dislocation core, dislocation dynamics, Plasticity},
pubstate = {published},
tppubtype = {article}
}
Discrete dislocation plasticity is a modeling technique that treats plasticity as the collective motion of dislocations. The dislocations are described through their elastic Volterra fields, outside of a cylindrical core region, with a few Burgers vectors of diameter. The contribution of the core fields to the dislocation dynamics is neglected, because it is assumed that their range is too short to be of influence. The aim of this work is to assess the validity of this assumption. In recent ab-initio studies it has been demonstrated that the dislocation core fields are significant up to a distance of ten Burgers vector from the dislocation line. This is a longer range influence than expected and can give rise to changes in the evolving dislocation structure and in the overall response of a plastically deforming body. It is indeed experimentally observed that dislocations pile up against strong interfaces, and that the spacing between dislocations at the front of these pile-ups can be less than ten Burgers vectors. In this work, 2-D discrete dislocation plasticity simulations are performed to investigate the effect of core fields on edge dislocation interactions. The results of the simulations, which include core fields for the first time, show indeed that dislocations that are very closely spaced experience additional glide or climb due to core fields. The effect is however negligible when compared to glide and climb due to Volterra fields or due to the external load.
103.
Aramfard, Mohammad, RAFOLS, Francisco PEREZ, Nicola, L.
A 2D dual-scale method to address contact problems Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 171, 2022.
Abstract | BibTeX | Tags: contact mechanics, friction, Indentation, Multiscale modeling | Links:
@article{Aramfard2022,
title = {A 2D dual-scale method to address contact problems},
author = {Mohammad Aramfard and Francisco PEREZ RAFOLS and L. Nicola},
doi = {10.1016/j.triboint.2022.107509},
year = {2022},
date = {2022-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {171},
publisher = {ELSEVIER SCI LTD},
abstract = {A seamless 2D dual-scale computational scheme is developed to study contact problems. The model consists of an atomistic domain close to the contact, coupled with an elastic continuum domain away from the contact. The atomistic formulation provides a description of the contact interaction through interatomic potentials and permits to capture atomic wear and defect formation in the contact region. The fields in the continuum domain are calculated by an efficient FFT-based Green's function method. The novel scheme is validated against full atomistic simulations and applied to study the effect of adhesion on the scratching of a rough copper surface by a rigid smooth spherical tip.},
keywords = {contact mechanics, friction, Indentation, Multiscale modeling},
pubstate = {published},
tppubtype = {article}
}
A seamless 2D dual-scale computational scheme is developed to study contact problems. The model consists of an atomistic domain close to the contact, coupled with an elastic continuum domain away from the contact. The atomistic formulation provides a description of the contact interaction through interatomic potentials and permits to capture atomic wear and defect formation in the contact region. The fields in the continuum domain are calculated by an efficient FFT-based Green's function method. The novel scheme is validated against full atomistic simulations and applied to study the effect of adhesion on the scratching of a rough copper surface by a rigid smooth spherical tip.
102.
Bian, J, Nicola, L
Oscillation of a graphene flake on an undulated substrate with amplitude gradient Journal Article
In: COMPUTATIONAL MATERIALS SCIENCE, vol. 211, 2022.
Abstract | BibTeX | Tags: Graphene flake, Oscillator, Undulation gradient | Links:
@article{Bian2022,
title = {Oscillation of a graphene flake on an undulated substrate with amplitude gradient},
author = {J Bian and L Nicola},
doi = {10.1016/j.commatsci.2022.111522},
year = {2022},
date = {2022-01-01},
journal = {COMPUTATIONAL MATERIALS SCIENCE},
volume = {211},
publisher = {ELSEVIER},
abstract = {The oscillation of a graphene flake on a substrate with undulated surface is investigated by classical molecular dynamics simulation. The gradient in amplitude of the undulation is found to provide the driving force for the motion of the graphene flake, which slides on top of a graphene layer that well conforms to the substrate. The oscillatory motion of the flake can be well described by the equation of motion of a damped oscillator, with damping factor corresponding to the friction coefficient between the flake and the graphene layer on which it glides. When the amplitude gradient increases, the oscillation frequency increases as well. The shape of the graphene flake is found to have a strong influence on friction, as some geometries promote in-plane rotation. The results in the present study point to an alternative approach to transport or manipulation of nanosized objects.},
keywords = {Graphene flake, Oscillator, Undulation gradient},
pubstate = {published},
tppubtype = {article}
}
The oscillation of a graphene flake on a substrate with undulated surface is investigated by classical molecular dynamics simulation. The gradient in amplitude of the undulation is found to provide the driving force for the motion of the graphene flake, which slides on top of a graphene layer that well conforms to the substrate. The oscillatory motion of the flake can be well described by the equation of motion of a damped oscillator, with damping factor corresponding to the friction coefficient between the flake and the graphene layer on which it glides. When the amplitude gradient increases, the oscillation frequency increases as well. The shape of the graphene flake is found to have a strong influence on friction, as some geometries promote in-plane rotation. The results in the present study point to an alternative approach to transport or manipulation of nanosized objects.
101.
Bian, Jianjun, Nicola, L.
Lubrication of rough copper with few-layer graphene Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 173, 2022.
Abstract | BibTeX | Tags: friction, Graphene, Interlocking, Rough surface | Links:
@article{Bian2022a,
title = {Lubrication of rough copper with few-layer graphene},
author = {Jianjun Bian and L. Nicola},
doi = {10.1016/j.triboint.2022.107621},
year = {2022},
date = {2022-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {173},
publisher = {ELSEVIER SCI LTD},
abstract = {It has been demonstrated through experiments and simulations that friction decreases significantly when graphene is used as a solid lubricant on various materials. However, the effect of increasing the number of graphene layers on lubrication is controversial. Some studies predict an increase of friction with the number of layers that can be imputed to increased contact area, others a decrease in friction attributed to increased flexural rigidity of the layers. Herein, atomistic simulations are performed to investigate the atomic mechanisms by which few-layers graphene lubricate rough copper surfaces when probed by a smooth tip. The results of the simulations show that increasing the number of graphene layers drastically reduces friction, while the deformation mechanism is found to change from atomic wear to recoverable flattening of surface steps, as the amount of interlocking between the surfaces is reduced.},
keywords = {friction, Graphene, Interlocking, Rough surface},
pubstate = {published},
tppubtype = {article}
}
It has been demonstrated through experiments and simulations that friction decreases significantly when graphene is used as a solid lubricant on various materials. However, the effect of increasing the number of graphene layers on lubrication is controversial. Some studies predict an increase of friction with the number of layers that can be imputed to increased contact area, others a decrease in friction attributed to increased flexural rigidity of the layers. Herein, atomistic simulations are performed to investigate the atomic mechanisms by which few-layers graphene lubricate rough copper surfaces when probed by a smooth tip. The results of the simulations show that increasing the number of graphene layers drastically reduces friction, while the deformation mechanism is found to change from atomic wear to recoverable flattening of surface steps, as the amount of interlocking between the surfaces is reduced.
100.
Müser, Martin H, Nicola, L.
Modeling the surface topography dependence of friction, adhesion, and contact compliance Journal Article
In: MRS BULLETIN, vol. 47, no. 12, pp. 1221–1228, 2022.
Abstract | BibTeX | Tags: Adhesion, Contact, friction | Links:
@article{Mueser2022,
title = {Modeling the surface topography dependence of friction, adhesion, and contact compliance},
author = {Martin H Müser and L. Nicola},
doi = {10.1557/s43577-022-00468-2},
year = {2022},
date = {2022-01-01},
journal = {MRS BULLETIN},
volume = {47},
number = {12},
pages = {1221–1228},
publisher = {SPRINGER HEIDELBERG},
abstract = {The small-scale topography of surfaces critically affects the contact area of solids and thus the forces acting between them. Although this has long been known, only recent advances made it possible to reliably model interfacial forces and related quantities for surfaces with multiscale roughness. This article sketches both recent and traditional approaches to their mechanics, while addressing the relevance of nonlinearity and nonlocality arising in soft- and hard-matter contacts.},
keywords = {Adhesion, Contact, friction},
pubstate = {published},
tppubtype = {article}
}
The small-scale topography of surfaces critically affects the contact area of solids and thus the forces acting between them. Although this has long been known, only recent advances made it possible to reliably model interfacial forces and related quantities for surfaces with multiscale roughness. This article sketches both recent and traditional approaches to their mechanics, while addressing the relevance of nonlinearity and nonlocality arising in soft- and hard-matter contacts.
2021
99.
Alves, P. D., Simone, A., Duarte, C. A.
A generalized finite element method for three-dimensional fractures in fiber-reinforced composites Journal Article
In: MECCANICA, vol. 56, no. 6, pp. 1441–1473, 2021.
Abstract | BibTeX | Tags: Embedded reinforcement method with bond Slip (ERS), Fiber reinforced composites (FRC), Finite element method (FEM), Generalized finite element method (GFEM) | Links:
@article{Alves2021,
title = {A generalized finite element method for three-dimensional fractures in fiber-reinforced composites},
author = {P. D. Alves and A. Simone and C. A. Duarte},
doi = {10.1007/s11012-020-01211-4},
year = {2021},
date = {2021-01-01},
journal = {MECCANICA},
volume = {56},
number = {6},
pages = {1441–1473},
publisher = {Springer Science and Business Media B.V.},
abstract = {This paper presents a methodology for the analysis of three-dimensional static fractures in fiber-reinforced materials. Fibers are discretely modeled using a modification of the embedded reinforcement method with bond Slip (mERS) that allows its combination with a generalized finite element method (GFEM) for three-dimensional fractures. Since the GFEM mesh does not need to fit fracture surfaces or fibers, the GFEM–mERS can handle fibers bridging across crack faces at arbitrary angles. The method is verified against three-dimensional FEM solutions using conformal discretizations for crack surfaces and fiber boundaries. The comparison of the method against experimental data and convergence studies of the h- and p-version of the method is also presented.},
keywords = {Embedded reinforcement method with bond Slip (ERS), Fiber reinforced composites (FRC), Finite element method (FEM), Generalized finite element method (GFEM)},
pubstate = {published},
tppubtype = {article}
}
This paper presents a methodology for the analysis of three-dimensional static fractures in fiber-reinforced materials. Fibers are discretely modeled using a modification of the embedded reinforcement method with bond Slip (mERS) that allows its combination with a generalized finite element method (GFEM) for three-dimensional fractures. Since the GFEM mesh does not need to fit fracture surfaces or fibers, the GFEM–mERS can handle fibers bridging across crack faces at arbitrary angles. The method is verified against three-dimensional FEM solutions using conformal discretizations for crack surfaces and fiber boundaries. The comparison of the method against experimental data and convergence studies of the h- and p-version of the method is also presented.
98.
Goudarzi, M., Corso, F. Dal, Bigoni, D., Simone, A.
Dispersion of rigid line inclusions as stiffeners and shear band instability triggers Journal Article
In: INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES, vol. 210-211, pp. 255–272, 2021.
Abstract | BibTeX | Tags: Embedded reinforcement model, Finite element method, Material instability, Rigid line inclusions, Shear band formation | Links:
@article{Goudarzi2021,
title = {Dispersion of rigid line inclusions as stiffeners and shear band instability triggers},
author = {M. Goudarzi and F. Dal Corso and D. Bigoni and A. Simone},
doi = {10.1016/j.ijsolstr.2020.11.006},
year = {2021},
date = {2021-01-01},
journal = {INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES},
volume = {210-211},
pages = {255–272},
publisher = {Elsevier Ltd},
abstract = {A dispersion of stiff and thin (‘rigid line’) inclusions (RLIs) in a matrix material may result beneficial for stiffening in the elastic range, but might be detrimental to strength, as material instabilities may be triggered by inclusions when the matrix is brought to a viscoplastic-damaging state. This dual role of RLIs is investigated by means of the embedded reinforcement model. Validated against available analytical predictions, this numerical model is employed to assess the roles of RLIs’ orientation, interaction, volume fraction, and distribution, considering up to 1500 inclusions. When the matrix material deforms inelastically, RLIs produce stress concentrations that promote the nucleation of shear bands. These are characterized at collapse for many distributions of RLIs, showing that their effects range from almost negligible to a disrupting alteration of the dominant failure mechanism. In the latter case, it is shown that the dominant shear bands can be fragmented by RLIs into a mosaic of tiny localization bands. These results offer new insights into energy dissipation mechanisms of reinforced materials, as they are promoted or inhibited by the interactions of rigid line inclusions.},
keywords = {Embedded reinforcement model, Finite element method, Material instability, Rigid line inclusions, Shear band formation},
pubstate = {published},
tppubtype = {article}
}
A dispersion of stiff and thin (‘rigid line’) inclusions (RLIs) in a matrix material may result beneficial for stiffening in the elastic range, but might be detrimental to strength, as material instabilities may be triggered by inclusions when the matrix is brought to a viscoplastic-damaging state. This dual role of RLIs is investigated by means of the embedded reinforcement model. Validated against available analytical predictions, this numerical model is employed to assess the roles of RLIs’ orientation, interaction, volume fraction, and distribution, considering up to 1500 inclusions. When the matrix material deforms inelastically, RLIs produce stress concentrations that promote the nucleation of shear bands. These are characterized at collapse for many distributions of RLIs, showing that their effects range from almost negligible to a disrupting alteration of the dominant failure mechanism. In the latter case, it is shown that the dominant shear bands can be fragmented by RLIs into a mosaic of tiny localization bands. These results offer new insights into energy dissipation mechanisms of reinforced materials, as they are promoted or inhibited by the interactions of rigid line inclusions.
97.
Zhuo, M., Grazioli, D., Simone, A.
Tensorial effective transport properties of Li-ion battery separators elucidated by computational multiscale modeling Journal Article
In: ELECTROCHIMICA ACTA, vol. 393, 2021.
Abstract | BibTeX | Tags: Computational homogenization, Concentration-dependent transport property, Ionic transport in lithium ion battery separators, Multiscale battery component modeling, Time-evolving microstructure | Links:
@article{Zhuo2021,
title = {Tensorial effective transport properties of Li-ion battery separators elucidated by computational multiscale modeling},
author = {M. Zhuo and D. Grazioli and A. Simone},
doi = {10.1016/j.electacta.2021.139045},
year = {2021},
date = {2021-01-01},
journal = {ELECTROCHIMICA ACTA},
volume = {393},
publisher = {Elsevier Ltd},
abstract = {Existing battery modeling works have limitations in addressing the dependence of transport properties on local field variations and characterizing the response of anisotropic media. These limitations are tackled by means of a nested finite element (FE2) multiscale framework in which microscale simulations are employed to comprehensively characterize an anisotropic medium (macroscale). The approach is applied to the numerical simulation of transport processes in lithium ion battery separators. From the microscale solution, homogenized fluxes and their dependence on the downscaled macroscale variables are upscaled, thereby replacing otherwise assumed macroscale constitutive laws. The tensorial nature of macroscale effective transport properties stems from the numerical treatment. The proposed approach is verified against full-scale simulations. Several numerical examples are used to demonstrate the perils associated with accepted procedures, leading in some cases to severe discrepancies in the prediction of field quantities (from differences in the potential drop across the separator of about 27% for a fixed microstructure to more than 100% in the case of an evolving microstructure). Despite the use of simplified assumptions (e.g., synthetic microstructures), the numerical results demonstrate the importance of a tensorial description of transport properties in the modeling of battery processes.},
keywords = {Computational homogenization, Concentration-dependent transport property, Ionic transport in lithium ion battery separators, Multiscale battery component modeling, Time-evolving microstructure},
pubstate = {published},
tppubtype = {article}
}
Existing battery modeling works have limitations in addressing the dependence of transport properties on local field variations and characterizing the response of anisotropic media. These limitations are tackled by means of a nested finite element (FE2) multiscale framework in which microscale simulations are employed to comprehensively characterize an anisotropic medium (macroscale). The approach is applied to the numerical simulation of transport processes in lithium ion battery separators. From the microscale solution, homogenized fluxes and their dependence on the downscaled macroscale variables are upscaled, thereby replacing otherwise assumed macroscale constitutive laws. The tensorial nature of macroscale effective transport properties stems from the numerical treatment. The proposed approach is verified against full-scale simulations. Several numerical examples are used to demonstrate the perils associated with accepted procedures, leading in some cases to severe discrepancies in the prediction of field quantities (from differences in the potential drop across the separator of about 27% for a fixed microstructure to more than 100% in the case of an evolving microstructure). Despite the use of simplified assumptions (e.g., synthetic microstructures), the numerical results demonstrate the importance of a tensorial description of transport properties in the modeling of battery processes.
96.
Ponson, L., Shabir, Z., Abdulmajid, M., Giessen, E. Van Der, Simone, A.
Unified scenario for the morphology of crack paths in two-dimensional disordered solids Journal Article
In: PHYSICAL REVIEW. E, vol. 104, no. 5, 2021.
Abstract | BibTeX | Tags: cracks, generalized finite element method, Hurst exponent, roughness | Links:
@article{Ponson2021,
title = {Unified scenario for the morphology of crack paths in two-dimensional disordered solids},
author = {L. Ponson and Z. Shabir and M. Abdulmajid and E. Van Der Giessen and A. Simone},
doi = {10.1103/PhysRevE.104.055003},
year = {2021},
date = {2021-01-01},
journal = {PHYSICAL REVIEW. E},
volume = {104},
number = {5},
publisher = {American Physical Society},
abstract = {A combined experimental and numerical investigation of the roughness of intergranular cracks in two-dimensional disordered solids is presented. We focus on brittle materials for which the characteristic length scale of damage is much smaller than the grain size. Surprisingly, brittle cracks do not follow a persistent path with a roughness exponent ζ≈0.6-0.7 as reported for a large range of materials. Instead, we show that they exhibit monoaffine scaling properties characterized by a roughness exponent ζ=0.50±0.05, which we explain theoretically from linear elastic fracture mechanics. Our findings support the description of the roughening process in two-dimensional brittle disordered solids by a random walk. Furthermore, they shed light on the failure mechanism at the origin of the persistent behavior with ζ≈0.6-0.7 observed for fractures in other materials, suggesting a unified scenario for the geometry of crack paths in two-dimensional disordered solids.},
keywords = {cracks, generalized finite element method, Hurst exponent, roughness},
pubstate = {published},
tppubtype = {article}
}
A combined experimental and numerical investigation of the roughness of intergranular cracks in two-dimensional disordered solids is presented. We focus on brittle materials for which the characteristic length scale of damage is much smaller than the grain size. Surprisingly, brittle cracks do not follow a persistent path with a roughness exponent ζ≈0.6-0.7 as reported for a large range of materials. Instead, we show that they exhibit monoaffine scaling properties characterized by a roughness exponent ζ=0.50±0.05, which we explain theoretically from linear elastic fracture mechanics. Our findings support the description of the roughening process in two-dimensional brittle disordered solids by a random walk. Furthermore, they shed light on the failure mechanism at the origin of the persistent behavior with ζ≈0.6-0.7 observed for fractures in other materials, suggesting a unified scenario for the geometry of crack paths in two-dimensional disordered solids.
95.
Bian, J., Nicola, L.
On the lubrication of rough copper surfaces with graphene Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 156, 2021.
Abstract | BibTeX | Tags: friction, Graphene, Lubrication, Rough surface | Links:
@article{Bian2021,
title = {On the lubrication of rough copper surfaces with graphene},
author = {J. Bian and L. Nicola},
doi = {10.1016/j.triboint.2020.106837},
year = {2021},
date = {2021-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {156},
publisher = {Elsevier Ltd},
abstract = {Graphene is well known as a solid lubricant for nanoscale devices and is generally used to decrease friction between flat surfaces. In this work, we investigate its performance as a lubricant for rough surfaces. To this end, the problem of a silicon tip sliding on a rough copper single crystal, bare or covered by a graphene layer, is addressed through molecular dynamics simulations. To simplify the analysis, the copper crystal is taken to be quasi-three dimensional, so that the roughness profile is constant along the short periodic dimension. Results show markedly different deformation mechanisms in copper, depending on whether the rough surface is bare, covered with a stretched graphene layer, or with a wrinkled graphene layer. The wrinkled layer appears to be the best solution to reduce friction.},
keywords = {friction, Graphene, Lubrication, Rough surface},
pubstate = {published},
tppubtype = {article}
}
Graphene is well known as a solid lubricant for nanoscale devices and is generally used to decrease friction between flat surfaces. In this work, we investigate its performance as a lubricant for rough surfaces. To this end, the problem of a silicon tip sliding on a rough copper single crystal, bare or covered by a graphene layer, is addressed through molecular dynamics simulations. To simplify the analysis, the copper crystal is taken to be quasi-three dimensional, so that the roughness profile is constant along the short periodic dimension. Results show markedly different deformation mechanisms in copper, depending on whether the rough surface is bare, covered with a stretched graphene layer, or with a wrinkled graphene layer. The wrinkled layer appears to be the best solution to reduce friction.
94.
Murugesan, Y., Venugopalan, S. P., Nicola, L.
On sub-surface stress caused by contact roughness in compressible elastic solids Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 159, 2021.
Abstract | BibTeX | Tags: Compressibility, Contact, Rough surfaces, Simulation | Links:
@article{Murugesan2021,
title = {On sub-surface stress caused by contact roughness in compressible elastic solids},
author = {Y. Murugesan and S. P. Venugopalan and L. Nicola},
doi = {10.1016/j.triboint.2021.106867},
year = {2021},
date = {2021-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {159},
publisher = {Elsevier Ltd},
abstract = {Contact between elastic bodies with self-affine rough surfaces is mostly studied with a focus on determining surface fields, despite body fields are of great importance to establish, for instance, when and where elasticity breaks down. This work aims at analyzing the effect of contact roughness on the body fields of compressible frictionless solids modeled using Green's function molecular dynamics. Although area-load curves are insensitive to changes in the Hurst exponent as long as they are correctly normalized and are clearly not affected by compressibility, the Von-Mises stress is found to depend on both Hurst exponent and Poisson's ratio.},
keywords = {Compressibility, Contact, Rough surfaces, Simulation},
pubstate = {published},
tppubtype = {article}
}
Contact between elastic bodies with self-affine rough surfaces is mostly studied with a focus on determining surface fields, despite body fields are of great importance to establish, for instance, when and where elasticity breaks down. This work aims at analyzing the effect of contact roughness on the body fields of compressible frictionless solids modeled using Green's function molecular dynamics. Although area-load curves are insensitive to changes in the Hurst exponent as long as they are correctly normalized and are clearly not affected by compressibility, the Von-Mises stress is found to depend on both Hurst exponent and Poisson's ratio.
93.
Dokkum, J. S. Van, Perez-Rafols, F., Dorogin, L., Nicola, L.
On the retraction of an adhesive cylindrical indenter from a viscoelastic substrate Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 164, 2021.
Abstract | BibTeX | Tags: Adhesion contact, Boundary Element Method, Indentation, Line contact | Links:
@article{VanDokkum2021,
title = {On the retraction of an adhesive cylindrical indenter from a viscoelastic substrate},
author = {J. S. Van Dokkum and F. Perez-Rafols and L. Dorogin and L. Nicola},
doi = {10.1016/j.triboint.2021.107234},
year = {2021},
date = {2021-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {164},
publisher = {Elsevier Ltd},
abstract = {The retraction of a cylindrical rigid indenter from a viscoelastic substrate is studied by means of an efficient Green's function method. Hysteresis is observed in the load to area relationship in accordance with experimental results. Although our model relaxes many assumptions posed by LEFM-based analytical theories, the results fall between the limits, at high and low retraction velocities, predicted by the theories. Approaching the high velocity instantaneous limit requires, however, very high velocities or Maugis parameter. The work of adhesion is found to change during retraction. A non-dimensional parameter is proposed to estimate the effect of viscoelasticity in adhesive hysteresis.},
keywords = {Adhesion contact, Boundary Element Method, Indentation, Line contact},
pubstate = {published},
tppubtype = {article}
}
The retraction of a cylindrical rigid indenter from a viscoelastic substrate is studied by means of an efficient Green's function method. Hysteresis is observed in the load to area relationship in accordance with experimental results. Although our model relaxes many assumptions posed by LEFM-based analytical theories, the results fall between the limits, at high and low retraction velocities, predicted by the theories. Approaching the high velocity instantaneous limit requires, however, very high velocities or Maugis parameter. The work of adhesion is found to change during retraction. A non-dimensional parameter is proposed to estimate the effect of viscoelasticity in adhesive hysteresis.
92.
Gandin, A., Murugesan, Y., Torresan, V., Ulliana, L., Citron, A., Contessotto, P., Battilana, G., Panciera, T., Ventre, M., Netti, A. P., Nicola, L., Piccolo, S., Brusatin, G.
Simple yet effective methods to probe hydrogel stiffness for mechanobiology Journal Article
In: SCIENTIFIC REPORTS, vol. 11, no. 1, 2021.
Abstract | BibTeX | Tags: | Links:
@article{Gandin2021,
title = {Simple yet effective methods to probe hydrogel stiffness for mechanobiology},
author = {A. Gandin and Y. Murugesan and V. Torresan and L. Ulliana and A. Citron and P. Contessotto and G. Battilana and T. Panciera and M. Ventre and A. P. Netti and L. Nicola and S. Piccolo and G. Brusatin},
doi = {10.1038/s41598-021-01036-5},
year = {2021},
date = {2021-01-01},
journal = {SCIENTIFIC REPORTS},
volume = {11},
number = {1},
publisher = {Nature Research},
abstract = {In spite of tremendous advances made in the comprehension of mechanotransduction, implementation of mechanobiology assays remains challenging for the broad community of cell biologists. Hydrogel substrates with tunable stiffness are essential tool in mechanobiology, allowing to investigate the effects of mechanical signals on cell behavior. A bottleneck that slows down the popularization of hydrogel formulations for mechanobiology is the assessment of their stiffness, typically requiring expensive and sophisticated methodologies in the domain of material science. Here we overcome such barriers offering the reader protocols to set-up and interpret two straightforward, low cost and high-throughput tools to measure hydrogel stiffness: static macroindentation and micropipette aspiration. We advanced on how to build up these tools and on the underlying theoretical modeling. Specifically, we validated our tools by comparing them with leading techniques used for measuring hydrogel stiffness (atomic force microscopy, uniaxial compression and rheometric analysis) with consistent results on PAA hydrogels or their modification. In so doing, we also took advantage of YAP/TAZ nuclear localization as biologically validated and sensitive readers of mechanosensing, all in all presenting a suite of biologically and theoretically proven protocols to be implemented in most biological laboratories to approach mechanobiology.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
In spite of tremendous advances made in the comprehension of mechanotransduction, implementation of mechanobiology assays remains challenging for the broad community of cell biologists. Hydrogel substrates with tunable stiffness are essential tool in mechanobiology, allowing to investigate the effects of mechanical signals on cell behavior. A bottleneck that slows down the popularization of hydrogel formulations for mechanobiology is the assessment of their stiffness, typically requiring expensive and sophisticated methodologies in the domain of material science. Here we overcome such barriers offering the reader protocols to set-up and interpret two straightforward, low cost and high-throughput tools to measure hydrogel stiffness: static macroindentation and micropipette aspiration. We advanced on how to build up these tools and on the underlying theoretical modeling. Specifically, we validated our tools by comparing them with leading techniques used for measuring hydrogel stiffness (atomic force microscopy, uniaxial compression and rheometric analysis) with consistent results on PAA hydrogels or their modification. In so doing, we also took advantage of YAP/TAZ nuclear localization as biologically validated and sensitive readers of mechanosensing, all in all presenting a suite of biologically and theoretically proven protocols to be implemented in most biological laboratories to approach mechanobiology.
2020
91.
Aragon, A. M., Simone, A.
Discussion on “A linear complete extended finite element method for dynamic fracture simulation with non-nodal enrichments” [Finite Elem. Anal. Des. 152 (2018)] by I. Asareh, T.-Y. Kim, and J.-H. Song Journal Article
In: FINITE ELEMENTS IN ANALYSIS AND DESIGN, vol. 168, 2020.
Abstract | BibTeX | Tags: DE-FEM, IGFEM, NXFEM, strong discontinuities, Weak discontinuities, XFEM | Links:
@article{Aragon2020,
title = {Discussion on “A linear complete extended finite element method for dynamic fracture simulation with non-nodal enrichments” [Finite Elem. Anal. Des. 152 (2018)] by I. Asareh, T.-Y. Kim, and J.-H. Song},
author = {A. M. Aragon and A. Simone},
doi = {10.1016/j.finel.2019.103340},
year = {2020},
date = {2020-01-01},
journal = {FINITE ELEMENTS IN ANALYSIS AND DESIGN},
volume = {168},
publisher = {Elsevier B.V.},
abstract = {The subject paper purportedly proposes a novel enriched finite element method for modeling problems with strong discontinuities such as those encountered in fracture mechanics. The purpose of this document is to demonstrate that the method in the subject paper (Non-nodal eXtended Finite Element Method, NXFEM) is conceptually identical to the Discontinuity-Enriched Finite Element Method (DE-FEM) [Int. J. Numer. Meth. Eng. 2017; 112:1589–1613] proposed by Aragón and Simone.},
keywords = {DE-FEM, IGFEM, NXFEM, strong discontinuities, Weak discontinuities, XFEM},
pubstate = {published},
tppubtype = {article}
}
The subject paper purportedly proposes a novel enriched finite element method for modeling problems with strong discontinuities such as those encountered in fracture mechanics. The purpose of this document is to demonstrate that the method in the subject paper (Non-nodal eXtended Finite Element Method, NXFEM) is conceptually identical to the Discontinuity-Enriched Finite Element Method (DE-FEM) [Int. J. Numer. Meth. Eng. 2017; 112:1589–1613] proposed by Aragón and Simone.
90.
Zhuo, M., Grazioli, D., Simone, A.
Active material utilization and capacity of fiber-based battery electrodes Journal Article
In: ELECTROCHIMICA ACTA, vol. 333, 2020.
Abstract | BibTeX | Tags: Active material utilization, Fiber orientation effect, Fiber-based composite electrode, Optimal active-conductive material ratio, Resistor network model | Links:
@article{Zhuo2020,
title = {Active material utilization and capacity of fiber-based battery electrodes},
author = {M. Zhuo and D. Grazioli and A. Simone},
doi = {10.1016/j.electacta.2019.134929},
year = {2020},
date = {2020-01-01},
journal = {ELECTROCHIMICA ACTA},
volume = {333},
publisher = {Elsevier Ltd},
abstract = {This study presents a three-dimensional computational model to evaluate effective conductivity and capacity of fiber-based battery electrodes. We employ electrodes composed of conductive and active material nanofibers dispersed in an electrolyte matrix. The effective conductivity is calculated by means of an equivalent resistor network model, while capacity evaluation is based on the identification of active material fibers that are accessible to electrons (i.e., those connected with the electronically conductive network). When a constraint is applied to the total fiber content, an optimal active-conductive material ratio is determined that maximizes the active material utilization and the electrode capacity. We also study fiber orientation effects on the electrode electrochemical properties. It is found that fiber orientation has a strong impact on the percolation threshold, and this impact also reflects on the active material utilization: the more the fiber orientation deviates from the ideal isotropic distribution, the lower the utilization of active material fibers. This is of special interest for practical applications where geometrical constraints on fiber orientation arise, as in the case of electrospun fibers deposited on a substrate. The results of this study are therefore meant to give an insight into how a fibrous electrode architecture performs and suggest effective design solutions.},
keywords = {Active material utilization, Fiber orientation effect, Fiber-based composite electrode, Optimal active-conductive material ratio, Resistor network model},
pubstate = {published},
tppubtype = {article}
}
This study presents a three-dimensional computational model to evaluate effective conductivity and capacity of fiber-based battery electrodes. We employ electrodes composed of conductive and active material nanofibers dispersed in an electrolyte matrix. The effective conductivity is calculated by means of an equivalent resistor network model, while capacity evaluation is based on the identification of active material fibers that are accessible to electrons (i.e., those connected with the electronically conductive network). When a constraint is applied to the total fiber content, an optimal active-conductive material ratio is determined that maximizes the active material utilization and the electrode capacity. We also study fiber orientation effects on the electrode electrochemical properties. It is found that fiber orientation has a strong impact on the percolation threshold, and this impact also reflects on the active material utilization: the more the fiber orientation deviates from the ideal isotropic distribution, the lower the utilization of active material fibers. This is of special interest for practical applications where geometrical constraints on fiber orientation arise, as in the case of electrospun fibers deposited on a substrate. The results of this study are therefore meant to give an insight into how a fibrous electrode architecture performs and suggest effective design solutions.
89.
Salehani, M. Khajeh, Dokkum, J. S., Irani, N., Nicola, L.
On the load-area relation in rough adhesive contacts Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 144, 2020.
Abstract | BibTeX | Tags: Adhesion, Cohesive-zone model, Contact area and load, Self-affine roughness | Links:
@article{KhajehSalehani2020,
title = {On the load-area relation in rough adhesive contacts},
author = {M. Khajeh Salehani and J. S. Dokkum and N. Irani and L. Nicola},
doi = {10.1016/j.triboint.2019.106099},
year = {2020},
date = {2020-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {144},
publisher = {Elsevier Ltd},
abstract = {It is well established that, at small loads, a linear relation exists between contact area and reduced pressure for elastic bodies with non-adhesive rough surfaces. In the case of adhesive contacts, however, there is not yet a general consensus on whether or not linearity still holds. In this work evidence is provided, through numerical simulations, that the relation is non-linear. The simulations here presented can accurately describe contact between self-affine adhesive rough surfaces, since they rely on Green's function molecular dynamics to describe elastic deformation and on coupled phenomenological traction-separation laws for the interfacial interactions. The analysis is performed for two-dimensional compressible and incompressible bodies under plane strain conditions. Interfaces with various roughness parameters and work of adhesion are considered.},
keywords = {Adhesion, Cohesive-zone model, Contact area and load, Self-affine roughness},
pubstate = {published},
tppubtype = {article}
}
It is well established that, at small loads, a linear relation exists between contact area and reduced pressure for elastic bodies with non-adhesive rough surfaces. In the case of adhesive contacts, however, there is not yet a general consensus on whether or not linearity still holds. In this work evidence is provided, through numerical simulations, that the relation is non-linear. The simulations here presented can accurately describe contact between self-affine adhesive rough surfaces, since they rely on Green's function molecular dynamics to describe elastic deformation and on coupled phenomenological traction-separation laws for the interfacial interactions. The analysis is performed for two-dimensional compressible and incompressible bodies under plane strain conditions. Interfaces with various roughness parameters and work of adhesion are considered.
2019
88.
Grazioli, D., Verners, Osvalds, Zadin, Vahur, Brandell, Daniel, Simone, A.
Electrochemical-mechanical modeling of solid polymer electrolytes: Impact of mechanical stresses on Li-ion battery performance Journal Article
In: ELECTROCHIMICA ACTA, vol. 296, pp. 1122–1141, 2019.
Abstract | BibTeX | Tags: Battery performance, Electrochemical-mechanical coupling, Mechanical properties, Partial molar volume, Solid polymer electrolytes | Links:
@article{Grazioli2019,
title = {Electrochemical-mechanical modeling of solid polymer electrolytes: Impact of mechanical stresses on Li-ion battery performance},
author = {D. Grazioli and Osvalds Verners and Vahur Zadin and Daniel Brandell and A. Simone},
doi = {10.1016/j.electacta.2018.07.234},
year = {2019},
date = {2019-01-01},
journal = {ELECTROCHIMICA ACTA},
volume = {296},
pages = {1122–1141},
publisher = {Elsevier Ltd},
abstract = {We analyze the effects of mechanical stresses arising in a solid polymer electrolyte (SPE) on the electrochemical performance of the electrolyte component of a lithium ion battery. The SPE is modeled with a coupled ionic conduction-deformation model that allows to investigate the effect of mechanical stresses induced by the redistribution of ions. The analytical solution is determined for a uniform planar cell operating under galvanostatic conditions with and without externally induced deformations. The roles of the polymer stiffness, internally-induced stresses, and thickness of the SPE layer are investigated. The results show that the predictions of the coupled model can strongly deviate from those obtained with an electrochemical model-up to +38% in terms of electrostatic potential difference across the electrolyte layer-depending on the combination of material properties and geometrical features. The predicted stress level in the SPE is considerable as it exceeds the threshold experimentally detected for irreversible deformation or fracture to occur in cells not subjected to external loading. We show that stresses induced by external solicitations can reduce the concentration gradient of ions across the electrolyte thickness and prevent salt depletion at the electrode-electrolyte interface.},
keywords = {Battery performance, Electrochemical-mechanical coupling, Mechanical properties, Partial molar volume, Solid polymer electrolytes},
pubstate = {published},
tppubtype = {article}
}
We analyze the effects of mechanical stresses arising in a solid polymer electrolyte (SPE) on the electrochemical performance of the electrolyte component of a lithium ion battery. The SPE is modeled with a coupled ionic conduction-deformation model that allows to investigate the effect of mechanical stresses induced by the redistribution of ions. The analytical solution is determined for a uniform planar cell operating under galvanostatic conditions with and without externally induced deformations. The roles of the polymer stiffness, internally-induced stresses, and thickness of the SPE layer are investigated. The results show that the predictions of the coupled model can strongly deviate from those obtained with an electrochemical model-up to +38% in terms of electrostatic potential difference across the electrolyte layer-depending on the combination of material properties and geometrical features. The predicted stress level in the SPE is considerable as it exceeds the threshold experimentally detected for irreversible deformation or fracture to occur in cells not subjected to external loading. We show that stresses induced by external solicitations can reduce the concentration gradient of ions across the electrolyte thickness and prevent salt depletion at the electrode-electrolyte interface.
87.
Grazioli, D., Zadin, Vahur, Brandell, Daniel, Simone, A.
Electrochemical-mechanical modeling of solid polymer electrolytes: Stress development and non-uniform electric current density in trench geometry microbatteries Journal Article
In: ELECTROCHIMICA ACTA, vol. 296, pp. 1142–1162, 2019.
Abstract | BibTeX | Tags: Battery performance, Electrochemical-mechanical coupling, Non-uniform electric current density, Solid polymer electrolytes, Trench geometry microbattery | Links:
@article{Grazioli2019a,
title = {Electrochemical-mechanical modeling of solid polymer electrolytes: Stress development and non-uniform electric current density in trench geometry microbatteries},
author = {D. Grazioli and Vahur Zadin and Daniel Brandell and A. Simone},
doi = {10.1016/j.electacta.2018.07.146},
year = {2019},
date = {2019-01-01},
journal = {ELECTROCHIMICA ACTA},
volume = {296},
pages = {1142–1162},
publisher = {Elsevier Ltd},
abstract = {We study the effect of mechanical stresses arising in solid polymer electrolytes (SPEs) on the electrochemical performance of lithium-ion (Li-ion) solid-state batteries. Time-dependent finite element analyses of interdigitated plate cells during a discharge process are performed with a constitutive model that couples ionic conduction within the SPE with its deformation field. Due to the coupled nature of the processes taking place in the SPE, the non-uniform ionic concentration profiles that develop during the discharge process induce stresses and deformations within the SPE; at the same time the mechanical loads applied to the cell affect the charge conduction path. Results of a parametric study show that stresses induced by ionic redistribution favor ionic transport and enhance cell conductivity-up to a 15% increase compared to the solution obtained with a purely electrochemical model. We observe that, when the contribution of the mechanical stresses is included in the simulations, the localization of the electric current density at the top of the electrode plates is more pronounced compared to the purely electrochemical model. This suggests that electrode utilization, a limiting factor for the design of three-dimensional battery architectures, depends on the stress field that develops in the SPE. The stress level is indeed significant, and mechanical failure of the polymer might occur during service.},
keywords = {Battery performance, Electrochemical-mechanical coupling, Non-uniform electric current density, Solid polymer electrolytes, Trench geometry microbattery},
pubstate = {published},
tppubtype = {article}
}
We study the effect of mechanical stresses arising in solid polymer electrolytes (SPEs) on the electrochemical performance of lithium-ion (Li-ion) solid-state batteries. Time-dependent finite element analyses of interdigitated plate cells during a discharge process are performed with a constitutive model that couples ionic conduction within the SPE with its deformation field. Due to the coupled nature of the processes taking place in the SPE, the non-uniform ionic concentration profiles that develop during the discharge process induce stresses and deformations within the SPE; at the same time the mechanical loads applied to the cell affect the charge conduction path. Results of a parametric study show that stresses induced by ionic redistribution favor ionic transport and enhance cell conductivity-up to a 15% increase compared to the solution obtained with a purely electrochemical model. We observe that, when the contribution of the mechanical stresses is included in the simulations, the localization of the electric current density at the top of the electrode plates is more pronounced compared to the purely electrochemical model. This suggests that electrode utilization, a limiting factor for the design of three-dimensional battery architectures, depends on the stress field that develops in the SPE. The stress level is indeed significant, and mechanical failure of the polymer might occur during service.
