List of Journal Publications
2023
11.
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
10.
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.
2019
9.
Venugopalan, S. P., Nicola, L.
Indentation of a plastically deforming metal crystal with a self-affine rigid surface: A dislocation dynamics study Journal Article
In: ACTA MATERIALIA, vol. 165, pp. 709–721, 2019.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Plasticity, Self-affine surfaces | Links:
@article{Venugopalan2019,
title = {Indentation of a plastically deforming metal crystal with a self-affine rigid surface: A dislocation dynamics study},
author = {S. P. Venugopalan and L. Nicola},
doi = {10.1016/j.actamat.2018.10.020},
year = {2019},
date = {2019-01-01},
journal = {ACTA MATERIALIA},
volume = {165},
pages = {709–721},
publisher = {Acta Materialia Inc},
abstract = {Although indentation of elastic bodies by self-affine rough indenters has been studied extensively, little attention has so far been devoted to plasticity. This is mostly because modeling plasticity as well as contact with a self-affine rough surface is computationally quite challenging. Here, we succeed in achieving this goal by using Green's function dislocation dynamics, which allows to describe the self-affine rough surface using wavelengths spanning from 5 nm to 100 micron. The aim of this work is to gain understanding in how plastic deformation affects the contact area, contact pressure and hardness, gap profile and subsurface stresses, while the roughness of the indenter is changed. Plastic deformation is found to be more pronounced for indenters with larger root-mean-square height and/or Hurst exponent, and to be size dependent. The latter means that it is not possible to scale observables, as typically done in elastic contact problems. Also, at a given indentation depth (interference) the contact area is smaller than for the corresponding elastic contact problem, but gap closure is more pronounced. Contact hardness is found to be much larger than what reported by classical plasticity studies. Primarily, this is caused by limited dislocation availability, for which the stiffness of the deforming crystal is in between that of a linear elastic and an elastic-perfectly plastic material. When calculating hardness and nominal contact pressure, including very small wavelength in the description of the surface is not necessary, because below a given wavelength the subsurface stresses become invariant to a further decrease in true contact area. This is true for both elastic and plastic materials. Considering small wavelengths is instead required to capture accurately roughening and contact stress distribution.},
keywords = {contact mechanics, dislocation dynamics, Plasticity, Self-affine surfaces},
pubstate = {published},
tppubtype = {article}
}
Although indentation of elastic bodies by self-affine rough indenters has been studied extensively, little attention has so far been devoted to plasticity. This is mostly because modeling plasticity as well as contact with a self-affine rough surface is computationally quite challenging. Here, we succeed in achieving this goal by using Green's function dislocation dynamics, which allows to describe the self-affine rough surface using wavelengths spanning from 5 nm to 100 micron. The aim of this work is to gain understanding in how plastic deformation affects the contact area, contact pressure and hardness, gap profile and subsurface stresses, while the roughness of the indenter is changed. Plastic deformation is found to be more pronounced for indenters with larger root-mean-square height and/or Hurst exponent, and to be size dependent. The latter means that it is not possible to scale observables, as typically done in elastic contact problems. Also, at a given indentation depth (interference) the contact area is smaller than for the corresponding elastic contact problem, but gap closure is more pronounced. Contact hardness is found to be much larger than what reported by classical plasticity studies. Primarily, this is caused by limited dislocation availability, for which the stiffness of the deforming crystal is in between that of a linear elastic and an elastic-perfectly plastic material. When calculating hardness and nominal contact pressure, including very small wavelength in the description of the surface is not necessary, because below a given wavelength the subsurface stresses become invariant to a further decrease in true contact area. This is true for both elastic and plastic materials. Considering small wavelengths is instead required to capture accurately roughening and contact stress distribution.
8.
Venugopalan, S. P., Irani, N., Nicola, L.
Plastic contact of self-affine surfaces: Persson's theory versus discrete dislocation plasticity Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 132, 2019.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Persson's theory, Plasticity, Self-affine surfaces | Links:
@article{Venugopalan2019a,
title = {Plastic contact of self-affine surfaces: Persson's theory versus discrete dislocation plasticity},
author = {S. P. Venugopalan and N. Irani and L. Nicola},
doi = {10.1016/j.jmps.2019.07.019},
year = {2019},
date = {2019-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {132},
publisher = {Elsevier Ltd},
abstract = {Persson's theory allows for a fast and effective estimate of contact area and contact stress distributions when a flat and a self-affine rough surface are pressed into contact. For elastic bodies, the results of the theory have been shown to be in very good agreement with rather costly simulations. The theory has also been extended to plastic bodies. In this work, the results of Persson's theory for plastic bodies are compared with those of discrete dislocation plasticity. The area-load curves obtained by theory and simulations are found to be in good agreement when the rough surface has a very small root-mean-square (rms) height. For larger rms heights, which are more realistic for metal surfaces, the agreement is no longer good unless in the theory, instead of a size-independent material strength, one uses a rms height- and resolution-dependent yield strength. A modification of this type, i.e., the use of a yield strength dependent on size, does however not lead to agreement between the probability distributions of the contact stress, which is much broader in the simulations than in the theory. The most likely reason for this discrepancy is that the theory, apart from neglecting plasticity size dependence, only applies to elastic-perfectly plastic bodies and therefore, neglects strain hardening.},
keywords = {contact mechanics, dislocation dynamics, Persson's theory, Plasticity, Self-affine surfaces},
pubstate = {published},
tppubtype = {article}
}
Persson's theory allows for a fast and effective estimate of contact area and contact stress distributions when a flat and a self-affine rough surface are pressed into contact. For elastic bodies, the results of the theory have been shown to be in very good agreement with rather costly simulations. The theory has also been extended to plastic bodies. In this work, the results of Persson's theory for plastic bodies are compared with those of discrete dislocation plasticity. The area-load curves obtained by theory and simulations are found to be in good agreement when the rough surface has a very small root-mean-square (rms) height. For larger rms heights, which are more realistic for metal surfaces, the agreement is no longer good unless in the theory, instead of a size-independent material strength, one uses a rms height- and resolution-dependent yield strength. A modification of this type, i.e., the use of a yield strength dependent on size, does however not lead to agreement between the probability distributions of the contact stress, which is much broader in the simulations than in the theory. The most likely reason for this discrepancy is that the theory, apart from neglecting plasticity size dependence, only applies to elastic-perfectly plastic bodies and therefore, neglects strain hardening.
2017
7.
Venugopalan, Syam P., Müser, Martin H., Nicola, L.
Green's function molecular dynamics meets discrete dislocation plasticity Journal Article
In: MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, vol. 25, no. 6, 2017.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Green's functions | Links:
@article{Venugopalan2017,
title = {Green's function molecular dynamics meets discrete dislocation plasticity},
author = {Syam P. Venugopalan and Martin H. Müser and L. Nicola},
doi = {10.1088/1361-651X/aa7e0e},
year = {2017},
date = {2017-01-01},
journal = {MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING},
volume = {25},
number = {6},
publisher = {Institute of Physics Publishing},
abstract = {Metals deform plastically at the asperity level when brought in contact with a counter body even when the nominal contact pressure is small. Modeling the plasticity of solids with rough surfaces is challenging due to the multi-scale nature of surface roughness and the length-scale dependence of plasticity. While discrete-dislocation plasticity (DDP) simulations capture size-dependent plasticity by keeping track of the motion of individual dislocations, only simple two-dimensional surface geometries have so far been studied with DDP. The main computational bottleneck in contact problems modeled by DDP is the calculation of the dislocation image fields. We address this issue by combining two-dimensional DDP with Green's function molecular dynamics. The resulting method allows for an efficient boundary-value-method based treatment of elasticity in the presence of dislocations. We demonstrate that our method captures plasticity quantitatively from single to many dislocations and that it scales more favorably with system size than conventional methods. We also derive the relevant Green's functions for elastic slabs of finite width allowing arbitrary boundary conditions on top and bottom surface to be simulated.},
keywords = {contact mechanics, dislocation dynamics, Green's functions},
pubstate = {published},
tppubtype = {article}
}
Metals deform plastically at the asperity level when brought in contact with a counter body even when the nominal contact pressure is small. Modeling the plasticity of solids with rough surfaces is challenging due to the multi-scale nature of surface roughness and the length-scale dependence of plasticity. While discrete-dislocation plasticity (DDP) simulations capture size-dependent plasticity by keeping track of the motion of individual dislocations, only simple two-dimensional surface geometries have so far been studied with DDP. The main computational bottleneck in contact problems modeled by DDP is the calculation of the dislocation image fields. We address this issue by combining two-dimensional DDP with Green's function molecular dynamics. The resulting method allows for an efficient boundary-value-method based treatment of elasticity in the presence of dislocations. We demonstrate that our method captures plasticity quantitatively from single to many dislocations and that it scales more favorably with system size than conventional methods. We also derive the relevant Green's functions for elastic slabs of finite width allowing arbitrary boundary conditions on top and bottom surface to be simulated.
2016
6.
Sun, Fengwei, Giessen, Erik Van Der, Nicola, L.
Dry frictional contact of metal asperities: A dislocation dynamics analysis Journal Article
In: ACTA MATERIALIA, vol. 109, pp. 162–169, 2016.
Abstract | BibTeX | Tags: dislocation dynamics, friction, Rough surface, Size effect | Links:
@article{Sun2016,
title = {Dry frictional contact of metal asperities: A dislocation dynamics analysis},
author = {Fengwei Sun and Erik Van Der Giessen and L. Nicola},
doi = {10.1016/j.actamat.2016.02.033},
year = {2016},
date = {2016-01-01},
journal = {ACTA MATERIALIA},
volume = {109},
pages = {162–169},
publisher = {Elsevier Ltd},
abstract = {Discrete dislocation plasticity simulations are performed to investigate the static frictional behavior of a metal asperity on a large single crystal, in contact with a rigid platen. The focus of this study is on understanding the relative importance of contact slip opposed to plasticity in a single asperity at the micrometer size scale, where plasticity is size dependent. Slip of a contact point is taken to occur when the shear traction exceeds the normal traction at that point times a microscopic friction coefficient. Plasticity initiates through the nucleation of dislocations from Frank-Read sources in the metal and is modeled as the collective motion of edge dislocations. Results show that plasticity can delay or even suppress full slip of the contact. This generally happens when the friction coefficient is large. However, if the flattening depth is sufficiently large to induce nucleation of a large dislocation density, slip is suppressed even when the friction coefficient is very small. This study also shows that when self-similar asperities of different size are flattened to the same depth and subsequently loaded tangentially, their frictional behavior appears size independent. However, when they are submitted to the same contact pressure, smaller asperities slip while larger asperities deform plastically.},
keywords = {dislocation dynamics, friction, Rough surface, Size effect},
pubstate = {published},
tppubtype = {article}
}
Discrete dislocation plasticity simulations are performed to investigate the static frictional behavior of a metal asperity on a large single crystal, in contact with a rigid platen. The focus of this study is on understanding the relative importance of contact slip opposed to plasticity in a single asperity at the micrometer size scale, where plasticity is size dependent. Slip of a contact point is taken to occur when the shear traction exceeds the normal traction at that point times a microscopic friction coefficient. Plasticity initiates through the nucleation of dislocations from Frank-Read sources in the metal and is modeled as the collective motion of edge dislocations. Results show that plasticity can delay or even suppress full slip of the contact. This generally happens when the friction coefficient is large. However, if the flattening depth is sufficiently large to induce nucleation of a large dislocation density, slip is suppressed even when the friction coefficient is very small. This study also shows that when self-similar asperities of different size are flattened to the same depth and subsequently loaded tangentially, their frictional behavior appears size independent. However, when they are submitted to the same contact pressure, smaller asperities slip while larger asperities deform plastically.
2015
5.
Sun, Fengwei, Giessen, Erik Van Der, Nicola, L.
Interaction between neighboring asperities during flattening: A discrete dislocation plasticity analysis Journal Article
In: MECHANICS OF MATERIALS, vol. 90, pp. 157–165, 2015.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Rough surface, Size effect | Links:
@article{Sun2015,
title = {Interaction between neighboring asperities during flattening: A discrete dislocation plasticity analysis},
author = {Fengwei Sun and Erik Van Der Giessen and L. Nicola},
doi = {10.1016/j.mechmat.2015.04.012},
year = {2015},
date = {2015-01-01},
journal = {MECHANICS OF MATERIALS},
volume = {90},
pages = {157–165},
publisher = {Elsevier},
abstract = {Discrete dislocation plasticity simulations are performed to investigate the role of interaction between neighboring asperities on the contact pressure induced by a rigid platen on a rough surface. The rough surface is modeled as an array of equispaced asperities with a sinusoidal profile. The spacing between asperities is varied and the contact pressure necessary to flatten the surface to a given strain is computed. Plasticity in the asperities and in the crystal below is described by the collective glide of dislocations of edge character. Results show that the mean contact pressure necessary to flatten closely spaced asperities is larger than that required to flatten widely separated asperities. A small dependence on asperity density is already observed for a purely elastic material, but it is enhanced for small asperities, in the presence of dislocation plasticity. Plastic strain gradients, dislocation limited plasticity and interaction between neighboring plastic zones all contribute to what we will call the asperity density effect. Since dislocation limited plasticity plays a dominant role, the asperity density effect will mainly be relevant for surfaces having small asperity roughness.},
keywords = {contact mechanics, dislocation dynamics, Rough surface, Size effect},
pubstate = {published},
tppubtype = {article}
}
Discrete dislocation plasticity simulations are performed to investigate the role of interaction between neighboring asperities on the contact pressure induced by a rigid platen on a rough surface. The rough surface is modeled as an array of equispaced asperities with a sinusoidal profile. The spacing between asperities is varied and the contact pressure necessary to flatten the surface to a given strain is computed. Plasticity in the asperities and in the crystal below is described by the collective glide of dislocations of edge character. Results show that the mean contact pressure necessary to flatten closely spaced asperities is larger than that required to flatten widely separated asperities. A small dependence on asperity density is already observed for a purely elastic material, but it is enhanced for small asperities, in the presence of dislocation plasticity. Plastic strain gradients, dislocation limited plasticity and interaction between neighboring plastic zones all contribute to what we will call the asperity density effect. Since dislocation limited plasticity plays a dominant role, the asperity density effect will mainly be relevant for surfaces having small asperity roughness.
4.
Song, H., Dikken, R. J., Nicola, L., Giessen, E. Van Der
Plastic ploughing of a sinusoidal asperity on a rough surface Journal Article
In: JOURNAL OF APPLIED MECHANICS, vol. 82, no. 7, 2015.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, friction | Links:
@article{Song2015,
title = {Plastic ploughing of a sinusoidal asperity on a rough surface},
author = {H. Song and R. J. Dikken and L. Nicola and E. Van Der Giessen},
doi = {10.1115/1.4030318},
year = {2015},
date = {2015-01-01},
journal = {JOURNAL OF APPLIED MECHANICS},
volume = {82},
number = {7},
publisher = {American Society of Mechanical Engineers (ASME)},
abstract = {Part of the friction between two rough surfaces is due to the interlocking between asperities on opposite surfaces. In order for the surfaces to slide relative to each other, these interlocking asperities have to deform plastically. Here, we study the unit process of plastic ploughing of a single micrometer-scale asperity by means of two-dimensional dislocation dynamics simulations. Plastic deformation is described through the generation, motion, and annihilation of edge dislocations inside the asperity as well as in the subsurface. We find that the force required to plough an asperity at different ploughing depths follows a Gaussian distribution. For self-similar asperities, the friction stress is found to increase with the inverse of size. Comparison of the friction stress is made with other two contact models to show that interlocking asperities that are larger than ∼2 μm are easier to shear off plastically than asperities with a flat contact.},
keywords = {contact mechanics, dislocation dynamics, friction},
pubstate = {published},
tppubtype = {article}
}
Part of the friction between two rough surfaces is due to the interlocking between asperities on opposite surfaces. In order for the surfaces to slide relative to each other, these interlocking asperities have to deform plastically. Here, we study the unit process of plastic ploughing of a single micrometer-scale asperity by means of two-dimensional dislocation dynamics simulations. Plastic deformation is described through the generation, motion, and annihilation of edge dislocations inside the asperity as well as in the subsurface. We find that the force required to plough an asperity at different ploughing depths follows a Gaussian distribution. For self-similar asperities, the friction stress is found to increase with the inverse of size. Comparison of the friction stress is made with other two contact models to show that interlocking asperities that are larger than ∼2 μm are easier to shear off plastically than asperities with a flat contact.
2012
3.
Sun, Fengwei, der Giessen, Erik Van, Nicola, L.
Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study Journal Article
In: WEAR, vol. 296, no. 1-2, pp. 672–680, 2012.
Abstract | BibTeX | Tags: contact mechanics, dislocation dynamics, Rough surface, Size effect, Surface topography | Links:
@article{Sun2012,
title = {Plastic flattening of a sinusoidal metal surface: A discrete dislocation plasticity study},
author = {Fengwei Sun and Erik Van der Giessen and L. Nicola},
doi = {10.1016/j.wear.2012.08.007},
year = {2012},
date = {2012-01-01},
journal = {WEAR},
volume = {296},
number = {1-2},
pages = {672–680},
publisher = {Elsevier Ltd},
abstract = {The plastic flattening of a sinusoidal metal surface is studied by performing plane strain dislocation dynamics simulations. Plasticity arises from the collective motion of discrete dislocations of edge character. Their dynamics is incorporated through constitutive rules for nucleation, glide, pinning and annihilation. By analyzing surfaces with constant amplitude we found that the mean contact pressure is inversely proportional to the wavelength. For small wavelengths, due to interaction between plastic zones of neighboring contacts, the mean contact pressure can reach values that are about 1/10 of the theoretical strength of the material, thus significantly higher than what is predicted by simulations that do not account for size dependent plasticity. Surfaces with the same amplitude to period ratio have a size dependent response, such that if we interpret each period of the sinusoidal wave as the asperity of a rough surface, smaller asperities are harder to be flattened than large ones. The difference between the limiting situations of sticking and frictionless contacts is found to be negligible.},
keywords = {contact mechanics, dislocation dynamics, Rough surface, Size effect, Surface topography},
pubstate = {published},
tppubtype = {article}
}
The plastic flattening of a sinusoidal metal surface is studied by performing plane strain dislocation dynamics simulations. Plasticity arises from the collective motion of discrete dislocations of edge character. Their dynamics is incorporated through constitutive rules for nucleation, glide, pinning and annihilation. By analyzing surfaces with constant amplitude we found that the mean contact pressure is inversely proportional to the wavelength. For small wavelengths, due to interaction between plastic zones of neighboring contacts, the mean contact pressure can reach values that are about 1/10 of the theoretical strength of the material, thus significantly higher than what is predicted by simulations that do not account for size dependent plasticity. Surfaces with the same amplitude to period ratio have a size dependent response, such that if we interpret each period of the sinusoidal wave as the asperity of a rough surface, smaller asperities are harder to be flattened than large ones. The difference between the limiting situations of sticking and frictionless contacts is found to be negligible.
2010
2.
Zhang, Yun-He, Nicola, L.
Effect of template shape on metal nanoimprinting: A dislocation dynamics study Journal Article
In: JOURNAL OF ZHEJIANG UNIVERSITY. SCIENCE A, vol. 11, no. 10, pp. 722–726, 2010.
Abstract | BibTeX | Tags: dislocation dynamics, Nanoimprinting, Simulations | Links:
@article{Zhang2010,
title = {Effect of template shape on metal nanoimprinting: A dislocation dynamics study},
author = {Yun-He Zhang and L. Nicola},
doi = {10.1631/jzus.A1000175},
year = {2010},
date = {2010-01-01},
journal = {JOURNAL OF ZHEJIANG UNIVERSITY. SCIENCE A},
volume = {11},
number = {10},
pages = {722–726},
publisher = {ZHEJIANG UNIV},
abstract = {Dislocation dynamics simulations are performed to investigate the effect of template shape on the nanoimprinting of metal layers. To this end, metal thin films are imprinted by a rigid template made of an array of equispaced indenters of various shapes, i.e., rectangular, wedge, and circular. The geometry of the indenters is chosen such that the contact area is approximately the same at the final imprinting depth. Results show that, for all template shapes, the final patterns strongly depend on the dislocation activity, and that each imprint differs from the neighboring ones. Large material pile ups appear between the imprints, such that polishing of the metal layer is suggested for application of the patterns in electronics. Rectangular indenters require the lowest imprinting force and achieve the deepest retained imprints.},
keywords = {dislocation dynamics, Nanoimprinting, Simulations},
pubstate = {published},
tppubtype = {article}
}
Dislocation dynamics simulations are performed to investigate the effect of template shape on the nanoimprinting of metal layers. To this end, metal thin films are imprinted by a rigid template made of an array of equispaced indenters of various shapes, i.e., rectangular, wedge, and circular. The geometry of the indenters is chosen such that the contact area is approximately the same at the final imprinting depth. Results show that, for all template shapes, the final patterns strongly depend on the dislocation activity, and that each imprint differs from the neighboring ones. Large material pile ups appear between the imprints, such that polishing of the metal layer is suggested for application of the patterns in electronics. Rectangular indenters require the lowest imprinting force and achieve the deepest retained imprints.
2005
1.
Nicola, L., der Giessen, Erik Van, Needleman, Alan
Size effects in polycrystalline thin films analyzed by discrete dislocation plasticity Journal Article
In: THIN SOLID FILMS, vol. 479, no. 1-2, pp. 329–338, 2005.
Abstract | BibTeX | Tags: dislocation dynamics, Grain boundary, Interface, Stress | Links:
@article{Nicola2005a,
title = {Size effects in polycrystalline thin films analyzed by discrete dislocation plasticity},
author = {L. Nicola and Erik Van der Giessen and Alan Needleman},
doi = {10.1016/j.tsf.2004.12.012},
year = {2005},
date = {2005-01-01},
journal = {THIN SOLID FILMS},
volume = {479},
number = {1-2},
pages = {329–338},
abstract = {Stress development and relaxation in polycrystalline thin films perfectly bonded to a stiff substrate is analyzed numerically. The calculations are carried out within a two-dimensional plane strain framework. The film-substrate system is subject to a prescribed temperature decrease, with the coefficient of thermal expansion of the metal film larger than that of the substrate. Plastic deformation arises solely from the glide of edge dislocations. The dislocations nucleate from pre-existing Frank-Read sources, with the grain boundaries and film-substrate interface acting solely as impenetrable barriers to dislocation glide. At each stage of loading, a boundary value problem is solved to enforce the boundary conditions and the stress field and the dislocation Structure are obtained. The results of the simulations show both film-thickness and a am size dependent strengthening of polycrystalline films. Limited plasticity occurs in films with a sufficiently small grain-size, mainly due to a reduced nucleation rate in the constrained grain geometry.},
keywords = {dislocation dynamics, Grain boundary, Interface, Stress},
pubstate = {published},
tppubtype = {article}
}
Stress development and relaxation in polycrystalline thin films perfectly bonded to a stiff substrate is analyzed numerically. The calculations are carried out within a two-dimensional plane strain framework. The film-substrate system is subject to a prescribed temperature decrease, with the coefficient of thermal expansion of the metal film larger than that of the substrate. Plastic deformation arises solely from the glide of edge dislocations. The dislocations nucleate from pre-existing Frank-Read sources, with the grain boundaries and film-substrate interface acting solely as impenetrable barriers to dislocation glide. At each stage of loading, a boundary value problem is solved to enforce the boundary conditions and the stress field and the dislocation Structure are obtained. The results of the simulations show both film-thickness and a am size dependent strengthening of polycrystalline films. Limited plasticity occurs in films with a sufficiently small grain-size, mainly due to a reduced nucleation rate in the constrained grain geometry.
