List of Journal Publications
2019
3.
Salehani, M. Khajeh, Irani, N., Nicola, L.
Modeling adhesive contacts under mixed-mode loading Journal Article
In: JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS, vol. 130, pp. 320–329, 2019.
Abstract | BibTeX | Tags: Adhesive contacts, Contact area, Green's function molecular dynamics, Onset of sliding, Reattachment | Links:
@article{KhajehSalehani2019,
title = {Modeling adhesive contacts under mixed-mode loading},
author = {M. Khajeh Salehani and N. Irani and L. Nicola},
doi = {10.1016/j.jmps.2019.06.010},
year = {2019},
date = {2019-01-01},
journal = {JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS},
volume = {130},
pages = {320–329},
publisher = {Elsevier Ltd},
abstract = {Experiments show that when an adhesive contact is subjected to a tangential load the contact area reduces, symmetrically or asymmetrically, depending on whether the contact is under tension or compression. What happens after the onset of sliding is more difficult to be assessed because conducting experiments is rather complicated, especially under tensile loading. Here, we provide through numerical simulations, a complete picture of how the contact area and tractions of an adhesive circular smooth punch evolve under mixed-mode loading, before and after sliding. First, the Green’s function molecular dynamics method is extended to include the description of the interfacial interactions between contacting bodies by means of traction–separation constitutive laws that enforce coupling between tension (or compression) and shear. Next, simulations are performed to model sliding of a circular smooth punch against a flat rigid substrate, under tension and compression. In line with the experimental observations, the reduction in the contact area during shear loading is found to be symmetric under tension and asymmetric under compression. In addition, under tensile loading, full detachment is observed at the onset of sliding with a non-zero value of the tangential force. After the onset of sliding and the occurrence of slip instability, the contact area abruptly increases (reattachment), under both tension and compression. For interfaces with high friction, the reattachment occurs only partially. However, a full reattachment is attainable when friction is low.},
keywords = {Adhesive contacts, Contact area, Green's function molecular dynamics, Onset of sliding, Reattachment},
pubstate = {published},
tppubtype = {article}
}
Experiments show that when an adhesive contact is subjected to a tangential load the contact area reduces, symmetrically or asymmetrically, depending on whether the contact is under tension or compression. What happens after the onset of sliding is more difficult to be assessed because conducting experiments is rather complicated, especially under tensile loading. Here, we provide through numerical simulations, a complete picture of how the contact area and tractions of an adhesive circular smooth punch evolve under mixed-mode loading, before and after sliding. First, the Green’s function molecular dynamics method is extended to include the description of the interfacial interactions between contacting bodies by means of traction–separation constitutive laws that enforce coupling between tension (or compression) and shear. Next, simulations are performed to model sliding of a circular smooth punch against a flat rigid substrate, under tension and compression. In line with the experimental observations, the reduction in the contact area during shear loading is found to be symmetric under tension and asymmetric under compression. In addition, under tensile loading, full detachment is observed at the onset of sliding with a non-zero value of the tangential force. After the onset of sliding and the occurrence of slip instability, the contact area abruptly increases (reattachment), under both tension and compression. For interfaces with high friction, the reattachment occurs only partially. However, a full reattachment is attainable when friction is low.
2018
2.
Dokkum, J. S., Salehani, M. Khajeh, Irani, N., Nicola, L.
On the Proportionality Between Area and Load in Line Contacts Journal Article
In: TRIBOLOGY LETTERS, vol. 66, no. 3, 2018.
Abstract | BibTeX | Tags: Contact area, Greenwood and Williamson, Random rough surface, Reduced pressure, Root-mean-square gradient | Links:
@article{Dokkum2018,
title = {On the Proportionality Between Area and Load in Line Contacts},
author = {J. S. Dokkum and M. Khajeh Salehani and N. Irani and L. Nicola},
doi = {10.1007/s11249-018-1061-7},
year = {2018},
date = {2018-01-01},
journal = {TRIBOLOGY LETTERS},
volume = {66},
number = {3},
publisher = {Springer New York LLC},
abstract = {The relative contact area of rough surface contacts is known to increase linearly with reduced pressure, with proportionality factor . In its common definition, the reduced pressure contains the root-mean-square gradient (RMSG) of the surface. Although easy to measure, the RMSG of the entire surface does not coincide, at small loads, with the RMSG over the actual contact area , which gives a better description of the contact between rough surfaces. It was recently shown that, for Hertzian contacts, linearity between area and load is indeed obtained only if the RMSG is determined over the actual contact area. Similar to surface contacts, in line contacts, numerical data are often studied using theories that predict linearity by design. In this work, we revisit line contact problems and examine whether or not the assumption of linearity for line contacts holds true. We demonstrate, using Green's function molecular dynamics simulations, that for line contacts is not a constant: It depends on both the reduced pressure and the Hurst exponent. However, linearity holds when the RMSG is measured over the actual contact area. In that case, we could compare for line and surface contacts and found that their ratio is approximately 0.9. Finally, by analytically deriving the proportionality factor using in the original model of Greenwood and Williamson, a value is obtained that is surprisingly in good agreement with our numerical results for rough surface contacts.},
keywords = {Contact area, Greenwood and Williamson, Random rough surface, Reduced pressure, Root-mean-square gradient},
pubstate = {published},
tppubtype = {article}
}
The relative contact area of rough surface contacts is known to increase linearly with reduced pressure, with proportionality factor . In its common definition, the reduced pressure contains the root-mean-square gradient (RMSG) of the surface. Although easy to measure, the RMSG of the entire surface does not coincide, at small loads, with the RMSG over the actual contact area , which gives a better description of the contact between rough surfaces. It was recently shown that, for Hertzian contacts, linearity between area and load is indeed obtained only if the RMSG is determined over the actual contact area. Similar to surface contacts, in line contacts, numerical data are often studied using theories that predict linearity by design. In this work, we revisit line contact problems and examine whether or not the assumption of linearity for line contacts holds true. We demonstrate, using Green's function molecular dynamics simulations, that for line contacts is not a constant: It depends on both the reduced pressure and the Hurst exponent. However, linearity holds when the RMSG is measured over the actual contact area. In that case, we could compare for line and surface contacts and found that their ratio is approximately 0.9. Finally, by analytically deriving the proportionality factor using in the original model of Greenwood and Williamson, a value is obtained that is surprisingly in good agreement with our numerical results for rough surface contacts.
1.
Salehani, M. Khajeh, Irani, N., Müser, M. H., Nicola, L.
Modelling coupled normal and tangential tractions in adhesive contacts Journal Article
In: TRIBOLOGY INTERNATIONAL, vol. 124, pp. 93–101, 2018.
Abstract | BibTeX | Tags: Adhesion and friction, Contact area, Pull-off load | Links:
@article{KhajehSalehani2018,
title = {Modelling coupled normal and tangential tractions in adhesive contacts},
author = {M. Khajeh Salehani and N. Irani and M. H. Müser and L. Nicola},
doi = {10.1016/j.triboint.2018.03.022},
year = {2018},
date = {2018-01-01},
journal = {TRIBOLOGY INTERNATIONAL},
volume = {124},
pages = {93–101},
publisher = {Elsevier Ltd},
abstract = {This paper presents a nanoscale-inspired continuum model to capture the coupling of adhesion and friction in contact-mechanics problems. The method relies on Green's function molecular dynamics to calculate the elastic body fields and on a phenomenological mixed-mode coupled cohesive-zone model to describe the interplay between normal and tangential tractions, i.e. adhesion and friction. While the presented formulation is applicable to linearly elastic solids with generic surface roughness, the focus of our analysis is on the indentation of an array of circular rigid punches into a flat, deformable solid. Our results show that the coupling between adhesion and friction leads to an increase in the contact size and a decrease in the pull-off load.},
keywords = {Adhesion and friction, Contact area, Pull-off load},
pubstate = {published},
tppubtype = {article}
}
This paper presents a nanoscale-inspired continuum model to capture the coupling of adhesion and friction in contact-mechanics problems. The method relies on Green's function molecular dynamics to calculate the elastic body fields and on a phenomenological mixed-mode coupled cohesive-zone model to describe the interplay between normal and tangential tractions, i.e. adhesion and friction. While the presented formulation is applicable to linearly elastic solids with generic surface roughness, the focus of our analysis is on the indentation of an array of circular rigid punches into a flat, deformable solid. Our results show that the coupling between adhesion and friction leads to an increase in the contact size and a decrease in the pull-off load.
