List of Journal Publications
2017
10.
Siang, Kelvin Ng Wei, Nicola, L.
Static friction of sinusoidal surfaces: a discrete dislocation plasticity analysis Journal Article
In: PHILOSOPHICAL MAGAZINE, vol. 97, no. 29, pp. 2597–2614, 2017.
Abstract | BibTeX | Tags: Contact, discrete dislocation plasticity, friction, Size effect | Links:
@article{NgWeiSiang2017,
title = {Static friction of sinusoidal surfaces: a discrete dislocation plasticity analysis},
author = {Kelvin Ng Wei Siang and L. Nicola},
doi = {10.1080/14786435.2017.1344785},
year = {2017},
date = {2017-01-01},
journal = {PHILOSOPHICAL MAGAZINE},
volume = {97},
number = {29},
pages = {2597–2614},
publisher = {Taylor and Francis Ltd.},
abstract = {Discrete dislocation plasticity simulations are carried out to investigate the static frictional response of sinusoidal asperities with (sub)-microscale wavelength. The surfaces are first flattened and then sheared by a perfectly adhesive platen. Both bodies are explicitly modelled, and the external loading is applied on the top surface of the platen. Plastic deformation by dislocation glide is the only dissipation mechanism active. The tangential force obtained at the contact when displacing the platen horizontally first increases with applied displacement, then reaches a constant value. This constant is here taken to be the friction force. In agreement with several experiments and continuum simulation studies, the friction coefficient is found to decrease with the applied normal load. However, at odds with continuum simulations, the friction force is also found to decrease with the normal load. The decrease is caused by an increased availability of dislocations to initiate and sustain plastic flow during shearing. Again in contrast to continuum studies, the friction coefficient is found to vary stochastically across the contact surface, and to reach locally values up to several times the average friction coefficient. Moreover, the friction force and the friction coefficient are found to be size-dependent.},
keywords = {Contact, discrete dislocation plasticity, friction, Size effect},
pubstate = {published},
tppubtype = {article}
}
Discrete dislocation plasticity simulations are carried out to investigate the static frictional response of sinusoidal asperities with (sub)-microscale wavelength. The surfaces are first flattened and then sheared by a perfectly adhesive platen. Both bodies are explicitly modelled, and the external loading is applied on the top surface of the platen. Plastic deformation by dislocation glide is the only dissipation mechanism active. The tangential force obtained at the contact when displacing the platen horizontally first increases with applied displacement, then reaches a constant value. This constant is here taken to be the friction force. In agreement with several experiments and continuum simulation studies, the friction coefficient is found to decrease with the applied normal load. However, at odds with continuum simulations, the friction force is also found to decrease with the normal load. The decrease is caused by an increased availability of dislocations to initiate and sustain plastic flow during shearing. Again in contrast to continuum studies, the friction coefficient is found to vary stochastically across the contact surface, and to reach locally values up to several times the average friction coefficient. Moreover, the friction force and the friction coefficient are found to be size-dependent.
2016
9.
Siang, Kelvin Ng Wei, Nicola, L.
Discrete dislocation plasticity analysis of contact between deformable bodies of simple geometry Journal Article
In: MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING, vol. 24, no. 4, 2016.
Abstract | BibTeX | Tags: Contact, discrete dislocation plasticity, Size effect | Links:
@article{NgWeiSiang2016,
title = {Discrete dislocation plasticity analysis of contact between deformable bodies of simple geometry},
author = {Kelvin Ng Wei Siang and L. Nicola},
doi = {10.1088/0965-0393/24/4/045008},
year = {2016},
date = {2016-01-01},
journal = {MODELLING AND SIMULATION IN MATERIALS SCIENCE AND ENGINEERING},
volume = {24},
number = {4},
publisher = {Institute of Physics Publishing},
abstract = {A contact mechanical model is presented where both metal bodies can deform by discrete dislocation plasticity. The model intends to improve on previous dislocation dynamics models of contact, where only a plastically deformable body was considered, flattened by a rigid platen. The effect of the rigid platen was mimicked through boundary conditions acting on the deformable body. While the formulation is general, the simulations presented here are only performed for contact between a plastically deforming body with sinusoidal surface and a flat body that is either elastic or rigid. Results show that the contact conditions, i.e. frictionless and full stick, affect the morphology of the contact as well as the contact pressure distribution. This is because dislocations can glide through the frictionless contact and fragment it, but do not penetrate a sticking contact. Average quantities like mean apparent contact pressure and total plastic slip are, instead, independent of contact conditions and of the details of the contact area. A size dependence is observed in relation to the onset of plastic deformation, where surfaces with smaller wavelength and amplitude require a larger contact pressure to yield than self similar surfaces with larger wavelength. The size dependence is very pronounced when the flat body is rigid, but fades when the compliance of the flat body is large.},
keywords = {Contact, discrete dislocation plasticity, Size effect},
pubstate = {published},
tppubtype = {article}
}
A contact mechanical model is presented where both metal bodies can deform by discrete dislocation plasticity. The model intends to improve on previous dislocation dynamics models of contact, where only a plastically deformable body was considered, flattened by a rigid platen. The effect of the rigid platen was mimicked through boundary conditions acting on the deformable body. While the formulation is general, the simulations presented here are only performed for contact between a plastically deforming body with sinusoidal surface and a flat body that is either elastic or rigid. Results show that the contact conditions, i.e. frictionless and full stick, affect the morphology of the contact as well as the contact pressure distribution. This is because dislocations can glide through the frictionless contact and fragment it, but do not penetrate a sticking contact. Average quantities like mean apparent contact pressure and total plastic slip are, instead, independent of contact conditions and of the details of the contact area. A size dependence is observed in relation to the onset of plastic deformation, where surfaces with smaller wavelength and amplitude require a larger contact pressure to yield than self similar surfaces with larger wavelength. The size dependence is very pronounced when the flat body is rigid, but fades when the compliance of the flat body is large.
2015
8.
Dikken, Robbert Jan, Giessen, Erik Van Der, Nicola, L.
Plastic shear response of a single asperity: A discrete dislocation plasticity analysis Journal Article
In: PHILOSOPHICAL MAGAZINE, vol. 95, no. 34, pp. 3845–3858, 2015.
Abstract | BibTeX | Tags: Contact, discrete dislocation plasticity, friction, single asperity | Links:
@article{Dikken2015,
title = {Plastic shear response of a single asperity: A discrete dislocation plasticity analysis},
author = {Robbert Jan Dikken and Erik Van Der Giessen and L. Nicola},
doi = {10.1080/14786435.2015.1102982},
year = {2015},
date = {2015-01-01},
journal = {PHILOSOPHICAL MAGAZINE},
volume = {95},
number = {34},
pages = {3845–3858},
publisher = {Taylor and Francis Ltd.},
abstract = {We investigate the plastic shear response during static friction of an asperity protruding from a large FCC single crystal. The asperity is in perfectly adhesive contact with a rigid platen and is sheared by tangentially moving the platen. Using discrete dislocation plasticity simulations, we elucidate the plastic shear behaviour of single asperities of various size and shape, in search for the length scale that controls the plastic behaviour. Since plasticity can occur also in the crystal, identification of the length scale that controls a possible size-dependent plastic behaviour is far from being trivial. It is found that scaling down the dimensions of an asperity results in a higher contact shear strength. The contact area is dominant in controlling the plastic shear response, because it determines the size of the zone, in and below the asperity, where dislocation nucleation can occur. For a specific contact area, there is still a dependence on asperity volume and shape, but this is weaker than the dependence on contact area alone.},
keywords = {Contact, discrete dislocation plasticity, friction, single asperity},
pubstate = {published},
tppubtype = {article}
}
We investigate the plastic shear response during static friction of an asperity protruding from a large FCC single crystal. The asperity is in perfectly adhesive contact with a rigid platen and is sheared by tangentially moving the platen. Using discrete dislocation plasticity simulations, we elucidate the plastic shear behaviour of single asperities of various size and shape, in search for the length scale that controls the plastic behaviour. Since plasticity can occur also in the crystal, identification of the length scale that controls a possible size-dependent plastic behaviour is far from being trivial. It is found that scaling down the dimensions of an asperity results in a higher contact shear strength. The contact area is dominant in controlling the plastic shear response, because it determines the size of the zone, in and below the asperity, where dislocation nucleation can occur. For a specific contact area, there is still a dependence on asperity volume and shape, but this is weaker than the dependence on contact area alone.
7.
Sun, Fengwei, Giessen, Erik Van Der, Nicola, L.
Effect of plastic flattening on the shearing response of metal asperities: A dislocation dynamics analysis Journal Article
In: JOURNAL OF APPLIED MECHANICS, vol. 82, no. 7, 2015.
Abstract | BibTeX | Tags: contact mechanics, discrete dislocation plasticity | Links:
@article{Sun2015a,
title = {Effect of plastic flattening on the shearing response of metal asperities: A dislocation dynamics analysis},
author = {Fengwei Sun and Erik Van Der Giessen and L. Nicola},
doi = {10.1115/1.4030321},
year = {2015},
date = {2015-01-01},
journal = {JOURNAL OF APPLIED MECHANICS},
volume = {82},
number = {7},
publisher = {American Society of Mechanical Engineers (ASME)},
abstract = {Discrete dislocation (DD) plasticity simulations are carried out to investigate the effect of flattening and shearing of surface asperities. The asperities are chosen to have a rectangular shape to keep the contact area constant. Plasticity is simulated by nucleation, motion, and annihilation of edge dislocations. The results show that plastic flattening of large asperities facilitates subsequent plastic shearing, since it provides dislocations available to glide at lower shear stress than the nucleation strength. The effect of plastic flattening disappears for small asperities, which are harder to be sheared than the large ones, independently of preloading. An effect of asperity spacing is observed with closely spaced asperities being easier to plastically shear than isolated asperities. This effect fades when asperities are very protruding, and therefore plasticity is confined inside the asperities.},
keywords = {contact mechanics, discrete dislocation plasticity},
pubstate = {published},
tppubtype = {article}
}
Discrete dislocation (DD) plasticity simulations are carried out to investigate the effect of flattening and shearing of surface asperities. The asperities are chosen to have a rectangular shape to keep the contact area constant. Plasticity is simulated by nucleation, motion, and annihilation of edge dislocations. The results show that plastic flattening of large asperities facilitates subsequent plastic shearing, since it provides dislocations available to glide at lower shear stress than the nucleation strength. The effect of plastic flattening disappears for small asperities, which are harder to be sheared than the large ones, independently of preloading. An effect of asperity spacing is observed with closely spaced asperities being easier to plastically shear than isolated asperities. This effect fades when asperities are very protruding, and therefore plasticity is confined inside the asperities.
2014
6.
Zhang, Yunhe, Gao, Yanfei, Nicola, L.
Lattice rotation caused by wedge indentation of a single crystal: Dislocation dynamics compared to crystal plasticity simulations Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 68, no. 1, pp. 267–279, 2014.
Abstract | BibTeX | Tags: discrete dislocation plasticity, Dislocation sources and obstacles, Indentation size effects, Lattice rotation fields | Links:
@article{Zhang2014a,
title = {Lattice rotation caused by wedge indentation of a single crystal: Dislocation dynamics compared to crystal plasticity simulations},
author = {Yunhe Zhang and Yanfei Gao and L. Nicola},
doi = {10.1016/j.jmps.2014.04.006},
year = {2014},
date = {2014-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {68},
number = {1},
pages = {267–279},
publisher = {Elsevier Ltd},
abstract = {A number of recent experimental efforts such as electron back scattering technique and three-dimensional X-ray structural microscopy have revealed the intriguing formation of sectors of lattice rotation fields under indentation. In the case of wedge indentation, the in-plane rotation changes sign from one sector to another. Although the lattice rotation fields can be used to compute the geometrically necessary dislocation (GND) densities, it remains unclear how these sectors can be related to the hardness and therefore to the indentation size effects, i.e., the increase of indentation hardness with the decrease of indentation depth. Crystal plasticity simulations in this work reproduce the experimental findings at large indentation depth. On the contrary, discrete dislocation plasticity can only capture the sectors found experimentally when there is a high obstacle density and large obstacle strength. Obstacle density and strength, however, have little effect on the hardness. In other words, there is no one-to-one correspondence between the lattice rotation patterns and the indentation size effects. The presence of obstacles favors the dislocation arrangements that lead to the experimentally found rotation sectors. Using the similarity solutions of indentation fields and the solution of localized deformation fields near a stationary crack, a simple model is developed that explains the dislocation pattern evolution, its relationship to the lattice misorientations, and more importantly its dependence on obstacles.},
keywords = {discrete dislocation plasticity, Dislocation sources and obstacles, Indentation size effects, Lattice rotation fields},
pubstate = {published},
tppubtype = {article}
}
A number of recent experimental efforts such as electron back scattering technique and three-dimensional X-ray structural microscopy have revealed the intriguing formation of sectors of lattice rotation fields under indentation. In the case of wedge indentation, the in-plane rotation changes sign from one sector to another. Although the lattice rotation fields can be used to compute the geometrically necessary dislocation (GND) densities, it remains unclear how these sectors can be related to the hardness and therefore to the indentation size effects, i.e., the increase of indentation hardness with the decrease of indentation depth. Crystal plasticity simulations in this work reproduce the experimental findings at large indentation depth. On the contrary, discrete dislocation plasticity can only capture the sectors found experimentally when there is a high obstacle density and large obstacle strength. Obstacle density and strength, however, have little effect on the hardness. In other words, there is no one-to-one correspondence between the lattice rotation patterns and the indentation size effects. The presence of obstacles favors the dislocation arrangements that lead to the experimentally found rotation sectors. Using the similarity solutions of indentation fields and the solution of localized deformation fields near a stationary crack, a simple model is developed that explains the dislocation pattern evolution, its relationship to the lattice misorientations, and more importantly its dependence on obstacles.
2010
5.
Shishvan, Siamak Soleymani, Nicola, L., Giessen, Erik Van Der
Bauschinger effect in unpassivated freestanding thin films Journal Article
In: JOURNAL OF APPLIED PHYSICS, vol. 107, no. 9, 2010.
Abstract | BibTeX | Tags: Bauschinger effect, discrete dislocation plasticity, polycrystals | Links:
@article{Shishvan2010,
title = {Bauschinger effect in unpassivated freestanding thin films},
author = {Siamak Soleymani Shishvan and L. Nicola and Erik Van Der Giessen},
doi = {10.1063/1.3407505},
year = {2010},
date = {2010-01-01},
journal = {JOURNAL OF APPLIED PHYSICS},
volume = {107},
number = {9},
publisher = {AMER INST PHYSICS},
abstract = {Two-dimensional (2D) discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect (BE) in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.},
keywords = {Bauschinger effect, discrete dislocation plasticity, polycrystals},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional (2D) discrete dislocation plasticity simulations are carried out to investigate the Bauschinger effect (BE) in freestanding thin films. The BE in plastic flow of polycrystalline materials is generally understood to be caused by inhomogeneous deformation during loading, leading to residual stress upon unloading. This inhomogeneity can be caused by dislocation pile-ups, variations in texture, grain orientations, and grain size. To study the BE, columnar-grained films as well as films with multiple grains across the thickness are considered. The film is modeled in a 2D framework by a unit cell consisting of an array of grains with different orientation. In order to capture the interaction among grains, we motivate and explore the use of an affine deformation assumption on the grain level to mimic the three-dimensional geometry in this framework. It is shown that the dispersion of grain size in a film together with the size-dependence of yield strength leads to significant BEs in bare films. Quantitative comparison of simulations with experimental data is provided.
2007
4.
Nicola, L., Bower, A. F., Kim, K. -S., Needleman, A., der Giessen, E. Van
Surface versus bulk nucleation of dislocations during contact Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 55, no. 6, pp. 1120–1144, 2007.
Abstract | BibTeX | Tags: contact mechanics, discrete dislocation plasticity, Indentation, Residual stress, Size effect | Links:
@article{Nicola2007,
title = {Surface versus bulk nucleation of dislocations during contact},
author = {L. Nicola and A. F. Bower and K. -S. Kim and A. Needleman and E. Van der Giessen},
doi = {10.1016/j.jmps.2006.12.005},
year = {2007},
date = {2007-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {55},
number = {6},
pages = {1120–1144},
abstract = {The indentation of single crystals by a periodic array of flat rigid contacts is analyzed using discrete dislocation plasticity. Plane strain analyses are carried out with the dislocations all of edge character and modeled as line singularities in a linear elastic solid. The limiting cases of frictionless and perfectly sticking contacts are considered. The effects of contact size, dislocation source density, and dislocation obstacle density and strength on the evolution of the mean indentation pressure are explored, but the main focus is on contrasting the response of crystals having dislocation sources on the surface with that of crystals having dislocation sources in the bulk. When there are only bulk sources, the mean contact pressure for sufficiently large contacts is independent of the friction condition, whereas for sufficiently small contact sizes, there is a significant dependence on the friction condition. When there are only surface dislocation sources the mean contact pressure increases much more rapidly with indentation depth than when bulk sources are present and the mean contact pressure is very sensitive to the strength of the obstacles to dislocation glide. Also, on unloading a layer of tensile residual stress develops when surface dislocation sources dominate.},
keywords = {contact mechanics, discrete dislocation plasticity, Indentation, Residual stress, Size effect},
pubstate = {published},
tppubtype = {article}
}
The indentation of single crystals by a periodic array of flat rigid contacts is analyzed using discrete dislocation plasticity. Plane strain analyses are carried out with the dislocations all of edge character and modeled as line singularities in a linear elastic solid. The limiting cases of frictionless and perfectly sticking contacts are considered. The effects of contact size, dislocation source density, and dislocation obstacle density and strength on the evolution of the mean indentation pressure are explored, but the main focus is on contrasting the response of crystals having dislocation sources on the surface with that of crystals having dislocation sources in the bulk. When there are only bulk sources, the mean contact pressure for sufficiently large contacts is independent of the friction condition, whereas for sufficiently small contact sizes, there is a significant dependence on the friction condition. When there are only surface dislocation sources the mean contact pressure increases much more rapidly with indentation depth than when bulk sources are present and the mean contact pressure is very sensitive to the strength of the obstacles to dislocation glide. Also, on unloading a layer of tensile residual stress develops when surface dislocation sources dominate.
2005
3.
Nicola, L., der Giessen, E. Van, Needleman, A.
Two hardening mechanisms in single crystal thin films studied by discrete dislocation plasticity Journal Article
In: PHILOSOPHICAL MAGAZINE, vol. 85, no. 14, pp. 1507–1518, 2005.
Abstract | BibTeX | Tags: discrete dislocation plasticity, hardening, Thin films | Links:
@article{Nicola2005b,
title = {Two hardening mechanisms in single crystal thin films studied by discrete dislocation plasticity},
author = {L. Nicola and E. Van der Giessen and A. Needleman},
doi = {10.1080/14786430500036611},
year = {2005},
date = {2005-01-01},
journal = {PHILOSOPHICAL MAGAZINE},
volume = {85},
number = {14},
pages = {1507–1518},
abstract = {Two-dimensional discrete dislocation plasticity simulations of the evolution of thermal stress in single crystal thin films on a rigid substrate are used to study size effects. The relation between the residual stress and the dislocation structure in the films after cooling is analyzed using dislocation dynamics. A boundary layer characterized by a high stress gradient and a high dislocation density is found close to the impenetrable film-substrate interface. There is a material-dependent threshold film thickness above which the dislocation density together with the boundary layer thickness and stress state are independent of film thickness. In such films the stress outside the boundary layer is on average very low, so that the film-thickness-independent boundary layer is responsible for the size effect. A larger size effect is found for films thinner than the threshold thickness. The origin of this size effect stems from nucleation activity being hindered by the geometrical constraint of the small film thickness, so that by decreasing film thickness, the dislocation density decreases while the stress in the film increases. The size dependence is only described by a Hall–Petch type relation for films thicker than the threshold value.},
keywords = {discrete dislocation plasticity, hardening, Thin films},
pubstate = {published},
tppubtype = {article}
}
Two-dimensional discrete dislocation plasticity simulations of the evolution of thermal stress in single crystal thin films on a rigid substrate are used to study size effects. The relation between the residual stress and the dislocation structure in the films after cooling is analyzed using dislocation dynamics. A boundary layer characterized by a high stress gradient and a high dislocation density is found close to the impenetrable film-substrate interface. There is a material-dependent threshold film thickness above which the dislocation density together with the boundary layer thickness and stress state are independent of film thickness. In such films the stress outside the boundary layer is on average very low, so that the film-thickness-independent boundary layer is responsible for the size effect. A larger size effect is found for films thinner than the threshold thickness. The origin of this size effect stems from nucleation activity being hindered by the geometrical constraint of the small film thickness, so that by decreasing film thickness, the dislocation density decreases while the stress in the film increases. The size dependence is only described by a Hall–Petch type relation for films thicker than the threshold value.
2004
2.
Nicola, L., der Giessen, Erik Van, Needleman, Alan
Relaxation of thermal stress by dislocation motion in passivated metal interconnects Journal Article
In: JOURNAL OF MATERIALS RESEARCH, vol. 19, no. 4, pp. 1216–1226, 2004.
Abstract | BibTeX | Tags: discrete dislocation plasticity, metal interconnects, Thin films | Links:
@article{Nicola2004,
title = {Relaxation of thermal stress by dislocation motion in passivated metal interconnects},
author = {L. Nicola and Erik Van der Giessen and Alan Needleman},
doi = {10.1557/JMR.2004.0158},
year = {2004},
date = {2004-01-01},
journal = {JOURNAL OF MATERIALS RESEARCH},
volume = {19},
number = {4},
pages = {1216–1226},
publisher = {Materials Research Society},
abstract = {The development and relaxation of stress in metal interconnects strained by their surroundings (substrate and passivation layers) is predicted by a discrete dislocation analysis. The model is based on a two-dimensional plane strain formulation, with deformation fully constrained in the line direction. Plastic deformation occurs by glide of edge dislocations on three slip systems in the single-crystal line. The substrate and passivation layers are treated as elastic materials and therefore impenetrable for the dislocations. Results of the simulations show the dependence of the stress evolution and of the effectiveness of plastic relaxation on the geometry of the line. The dependence of stress development on line aspect ratio, line size, slip plane orientation, pitch length, and passivation layer thickness are explored.},
keywords = {discrete dislocation plasticity, metal interconnects, Thin films},
pubstate = {published},
tppubtype = {article}
}
The development and relaxation of stress in metal interconnects strained by their surroundings (substrate and passivation layers) is predicted by a discrete dislocation analysis. The model is based on a two-dimensional plane strain formulation, with deformation fully constrained in the line direction. Plastic deformation occurs by glide of edge dislocations on three slip systems in the single-crystal line. The substrate and passivation layers are treated as elastic materials and therefore impenetrable for the dislocations. Results of the simulations show the dependence of the stress evolution and of the effectiveness of plastic relaxation on the geometry of the line. The dependence of stress development on line aspect ratio, line size, slip plane orientation, pitch length, and passivation layer thickness are explored.
2003
1.
Nicola, L., der, Giessen Van, Needleman, E.
Discrete dislocation analysis of size effects in thin films Journal Article
In: JOURNAL OF APPLIED PHYSICS, vol. 93, no. 10, pp. 5920–5928, 2003.
Abstract | BibTeX | Tags: discrete dislocation plasticity, size effects, Thin films | Links:
@article{Nicola2003,
title = {Discrete dislocation analysis of size effects in thin films},
author = {L. Nicola and Giessen Van der and E. Needleman},
doi = {10.1063/1.1566471},
year = {2003},
date = {2003-01-01},
journal = {JOURNAL OF APPLIED PHYSICS},
volume = {93},
number = {10},
pages = {5920–5928},
abstract = {A discrete dislocation plasticity analysis of plastic deformation in metal thin films caused by thermal stress is carried out. The calculations use a two-dimensional plane-strain formulation with only edge dislocations. Single crystal films with a specified set of slip systems are considered. The film-substrate system is subjected to a prescribed temperature history and a boundary value problem is formulated and solved for the evolution of the stress field and for the evolution of the dislocations structure in the film. A hard boundary layer forms at the interface between the film and the substrate, which does not scale with the film thickness and thus gives rise to a size effect. It is found that a reduction in the rate of dislocation nucleation can occur abruptly, which gives rise to a two-stage hardening behavior.},
keywords = {discrete dislocation plasticity, size effects, Thin films},
pubstate = {published},
tppubtype = {article}
}
A discrete dislocation plasticity analysis of plastic deformation in metal thin films caused by thermal stress is carried out. The calculations use a two-dimensional plane-strain formulation with only edge dislocations. Single crystal films with a specified set of slip systems are considered. The film-substrate system is subjected to a prescribed temperature history and a boundary value problem is formulated and solved for the evolution of the stress field and for the evolution of the dislocations structure in the film. A hard boundary layer forms at the interface between the film and the substrate, which does not scale with the film thickness and thus gives rise to a size effect. It is found that a reduction in the rate of dislocation nucleation can occur abruptly, which gives rise to a two-stage hardening behavior.
