List of Journal Publications
2023
3.
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.
2019
2.
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.
1.
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.
