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A comment on a hybrid asperity-Persson friction rubber theory by A Emami, S Khaleghian and S Taheri. Friction 9(6): 1707--1725 (2021)
dear collegues, I may be interested to share your views on an "asperity theory" modified Persson's rubber friction contact mechanics theory which I find not clearly motivated and seems to lead to erroneous conclusions ---- but I am also unable to reproduce the results claimed by the authors. The preprint is here, and the original paper attached: https://www.researchgate.net/publication/359392510
A comment on Asperity-based modification on theory of contact mechanics and rubber friction for self-affine fractal surfaces by A Emami, S Khaleghian and S Taheri. Friction 9(6): 1707--1725 (2021). Prof. M.Ciavarella
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 Emami2021_Article_Asperity-basedModificationOnTh.pdf | 2.58 MB |
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update: the authors have found an error in their paper
PS: there is an update. The authors of Emami's paper have contacted me and finally found there was a very bad typo in the paper in FRICTION, and after correction (see my updated preprint), the situation is better.
In fact, there is a deviation also in Persson's theory fudge factor which hasn't been studied properly.
Reading Dapp et al (2014), there is evidence that Persson's fudge factor doesn't work well at low pressures.
So, although I don't think the Emami paper gives a final answer to the problem, their theory being a little confused, they raise a good point.
Dapp, W. B., Prodanov, N., & Müser, M. H. (2014). Systematic analysis of Persson’s contact mechanics theory of randomly rough elastic surfaces. Journal of Physics: Condensed Matter, 26(35), 355002.
The results are shown in figure 15 (varying ζ for p0 = const) and figure 16 (for ζ = 64, varying p0, and therefore ar). They reveal that using (8) indeed significantly improves agreement between theory and numerical measurements compared with the original theory where S ≡ 1. Nevertheless, the total elastic energy is still overestimated by ≈ 10% even with the more complicated functional form. At low pressures, even the correction factor is insufficient to get theory and measurement to agree.