Contact and Deformation of Randomly Rough Surfaces with Varying Root-Mean-Square Gradient

Lattice Boltzmann direct numerical simulation of turbulent open-channel flows over randomly distributed hemispheres at $Re_{\unicode[STIX]{x1D70F}}=600$ is carried out to reveal the influence of roughness parameters related to a probability density function of rough-surface elevation on turbulence by analysing the spatial and Reynolds- (double-) averaged Navier–Stokes equation. This study specifically concentrates on the influence of the root-mean-square roughness and the skewness, and profiles of turbulence statistics are compared by introducing an effective wall-normal distance defined as a wall-normal integrated plane porosity. The effective distance can completely collapse the total shear stress outside the roughness sublayer, and thus the similarity of the streamwise mean velocity is clearer by introducing the effective distance. In order to examine the influence of the root-mean-square roughness and the skewness on dynamical effects that contribute to an increase in the skin friction coefficient, the triple-integrated double-averaged Navier–Stokes equation is analysed. The main contributors to the skin friction coefficient are found to be turbulence and drag force. The turbulence contribution increases with the root-mean-square roughness and/or the skewness. The drag force contribution, on the other hand, increases in particular with the root-mean-square roughness whereas an increase in the skewness does not increase the drag force contribution because it does not necessarily increase the surface area of the roughness elements. The contribution of the mean velocity dispersion induced by spatial inhomogeneity of the rough surfaces substantially increases with the root-mean-square roughness. A linear correlation is confirmed between the root-mean-square roughness and the equivalent roughness while the equivalent roughness monotonically increases with the skewness. A new correlation function based on the root-mean-square roughness and the skewness is developed with the available experimental and direct numerical simulation data, and it is confirmed that the developed correlation reasonably predicts the equivalent roughness of various types of real rough surfaces.

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On the Nature of O-Rings in Contact With Rough Surfaces

Journal of Tribology ◽

10.1115/1.3261705 ◽

1988 ◽

Vol 110 (4) ◽

pp. 632-637 ◽

Cited By ~ 5

Author(s):

W. E. Warren ◽

J. G. Curro ◽

D. E. Amos

Keyword(s):

Theoretical Analysis ◽

Root Mean Square ◽

Contact Pressure ◽

Contact Force ◽

Rough Surfaces ◽

Fundamental Importance ◽

Elastic Behavior ◽

Surface Irregularity ◽

Mean Square ◽

Irregular Surfaces

This work provides a theoretical analysis of the elastic behavior of an O-ring compressed between two rigid plates with irregular surfaces. Relations between deflection, contact force and contact pressure are obtained. The contact pressure, which is of fundamental importance in establishing criteria for effective sealing, is dependent upon both the amplitude and wavelength of the surface irregularity. This analysis suggests that surfaces in contact with O-ring seals should be characterized by the root mean square slope Δq in addition to the usual Ra which depends on amplitude only.

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Deterministic normal contact of rough surfaces with adhesion using a surface integral method

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2020.0281 ◽

2020 ◽

Vol 476 (2242) ◽

pp. 20200281 ◽

Cited By ~ 1

Author(s):

Ali Ghanbarzadeh ◽

Mostafa Faraji ◽

Anne Neville

Keyword(s):

Surface Roughness ◽

Root Mean Square ◽

Fundamental Problem ◽

Rough Surfaces ◽

Adhesive Contact ◽

Mean Square ◽

Surface Integral ◽

Normal Contact ◽

Surface Integration ◽

Effect Of Surface

The fundamental problem of adhesion in the presence of surface roughness and its effect on the prediction of friction has been a hot topic for decades in numerous areas of science and engineering, attracting even more attention in recent years in areas such as geotechnics and tectonics, nanotechnology, high-value manufacturing and biomechanics. In this paper a new model for deterministic calculation of the contact mechanics for rough surfaces in the presence of adhesion is presented. The contact solver is an in-house boundary element method that incorporates fast Fourier transform for numerical efficiency. The adhesive contact model considers full Lennard-Jones potentials and surface integration at the asperity level and is validated against models in the literature. Finally, the effect of surface roughness on the adhesion between surfaces was studied, and it was shown that the root mean square gradient of surface roughness can change the adhesive pressures irrespective of the root mean square surface roughness. We have tested two adhesion parameters based on Johnson's modified criteria and Ciavarella's model. We showed that Civarella's model introduces the most reasonable criteria suggesting that the RMS roughness and large wavelength of surfaces roughness are the important parameters of adhesion between rough surfaces.

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A New Adaptive-Surface Elastic-Plastic Contact Model of Rough Surfaces: Parameter Correlations

Materials Science Forum ◽

10.4028/www.scientific.net/msf.532-533.961 ◽

2006 ◽

Vol 532-533 ◽

pp. 961-964

Author(s):

Min Song

Keyword(s):

Rough Surface ◽

Root Mean Square ◽

Rough Surfaces ◽

Computing Time ◽

Contact Model ◽

Asperity Contact ◽

Mean Square ◽

Elastic Plastic ◽

Surface Profiles

Based on an presented adaptive-surface elastic-plastic asperity contact model which can greatly decrease contact computing time and keep the precision loss less than 5%, a series of 2-D rough surface profiles with different roughness and correlative length are numerically generated to investigate how to select the threshold used in this model for different adaptive rough surfaces. The results show that well acceptable precision of the elastic-plastic contact calculation would be derived when the ratio of threshold to root mean square curvature, δ 1.0 10 6mm2 − < × .

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On Pastewka and Robbins' Criterion for Macroscopic Adhesion of Rough Surfaces

Journal of Tribology ◽

10.1115/1.4034530 ◽

2016 ◽

Vol 139 (3) ◽

Cited By ~ 12

Author(s):

M. Ciavarella

Keyword(s):

Rough Surface ◽

Root Mean Square ◽

Rough Surfaces ◽

Mean Square ◽

Asperity Model ◽

Factor Α ◽

Rms Amplitude ◽

Simplified Form

Pastewka and Robbins (2014, “Contact Between Rough Surfaces and a Criterion for Macroscopic Adhesion,” Proc. Natl. Acad. Sci., 111(9), pp. 3298–3303) recently have proposed a criterion to distinguish when two surfaces will stick together or not and suggested that it shows quantitative and qualitative large conflicts with asperity theories. However, a comparison with asperity theories is not really attempted, except in pull-off data which show finite pull-off values in cases where both their own criterion and an asperity based one seem to suggest nonstickiness, and the results are in these respects inconclusive. Here, we find that their criterion corresponds very closely to an asperity model one (provided we use their very simplified form of the Derjaguin–Muller–Toporov (DMT) adhesion regime which introduces a dependence on the range of attractive forces) when bandwidth α is small, but otherwise involves a root-mean-square (RMS) amplitude of roughness reduced by a factor α. Therefore, it implies that the stickiness of any rough surface is the same as that of the surface where practically all the wavelength components of roughness are removed except the very fine ones.

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