Contact mechanics: contact area and interfacial separation from small contact to full contact

Abstract

We present a molecular dynamics study of the contact between a rigid solid with a randomly rough surface and an elastic block with a flat surface. The numerical calculations mainly focus on the contact area and the interfacial separation from small contact (low load) to full contact (high load). For small load the contact area varies linearly with the load and the interfacial separation depends logarithmically on the load. For high load the contact area approaches the nominal contact area (i.e., complete contact), and the interfacial separation approaches zero. The numerical results have been compared with analytical theory and experimental results. They are in good agreement with each other. The present findings may be very important for soft solids, e.g., rubber, or for very smooth surfaces, where complete contact can be reached at moderate high loads without plastic deformation of the solids.

Leak rate of seals: Comparison of theory with experiment

“…The main problem is the influence of surface roughness on the contact mechanics at the seal-substrate interface. Most surfaces of engineering interest have surface roughness on a wide range of length scales [3], e.g, from cm to nm, which will influence the leak rate and friction of seals, and accounting for the whole range of surface roughness is impossible using standard numerical methods, such as the Finite Element Method.In this paper we present experimental results for the leak-rate of rubber seals, and compare the results to a novel theory [3,4,5], which is based on percolation theory and a recently developed contact mechanics theory [6,7,8,9,10,11,12], which accurately takes into account the elastic coupling between the contact regions in the nominal rubber-substrate contact area. Earlier contact mechanics models, such as the GreenwoodWilliamson[13] model or the model of Bush et al [14], neglect this elastic coupling, which results in highly incorrect results [15,16], in particular for the relations between the squeezing pressure and the interfacial separation [17].…”

“…The (apparent) relative contact area A(ζ)/A 0 at the magnification ζ can be obtained using the contact mechanics formalism developed elsewhere [6,8,9,10,11], where the system is studied at different magnifications ζ. We have [6,7] A(ζ)…”

MD/FE Multiscale Modeling of Contact

“…MD simulations are used to investigate nanoscale mechanisms at the origin of adhesive and friction forces [7,[14][15][16][26][27][28][29][30][31][32][33][34]. Besides the refined mechanical description achieved by MD models, severe limitations should be noted.…”

On the dependence of the leak rate of seals on the skewness of the surface height probability distribution

“…The critical constriction will have the lateral size λ c = L/ζ c and the surface separation at this point is denoted by u c . We can calculate u c using a recently developed contact mechanics theory [12] (see below). As we continue to increase the magnification we will find more percolating channels between the surfaces, but these will have more narrow constrictions than the first channel which appears at ζ = ζ c , and as a first approximation one may neglect the contribution to the leak-rate from these channels [6].…”

“…The (apparent) relative contact area A(ζ)/A 0 and the interfacial separation u 1 (ζ) at the magnification ζ can be obtained using the contact mechanics formalism devel- oped elsewhere [12][13][14][15][16][17][18][19]. We define u 1 (ζ) to be the (average) height separating the surfaces which appear to come into contact when the magnification decreases from ζ to ζ − ∆ζ, where ∆ζ is a small (infinitesimal) change in the magnification.…”