Superlubricity and frictional anisotropy

Hirano, Motohisa; Shinjo, Kazumasa

doi:10.1016/0043-1648(93)90207-3

Cited by 124 publications

(79 citation statements)

References 17 publications

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“…Surfaces rarely share a common period, and the force per area preventing lateral motion averages to zero as the contact size grows [23,24]. In our simulations, k Ia T depends strongly on d ′ /d, σ ′ /σ, l min , and the orientations of the solids, and the total lateral stiffness is generally too small to distinguish on the scale of Fig.…”

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confidence: 89%

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Stiffness of Contacts between Rough Surfaces

2011

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The effect of self-affine roughness on solid contact is examined with molecular dynamics and continuum calculations. The contact area and normal and lateral stiffnesses rise linearly with the applied load, and the load rises exponentially with decreasing separation between surfaces. Results for a wide range of roughnesses, system sizes and Poisson ratios can be collapsed using Persson's contact theory for continuous elastic media. The atomic scale response at the interface between solids has little affect on the area or normal stiffness, but can greatly reduce the lateral stiffness. The scaling of this effect with system size and roughness is discussed. PACS numbers: 46.55.+d, 62.20.Qp, 81.40.Pq The presence of roughness on a wide range of length scales has profound effects on contact and friction between experimental surfaces. Under a broad range of conditions [1][2][3][4][5][6], the area of intimate contact between rough surfaces A c is orders of magnitude smaller than the apparent surface area A 0 . As discussed below, this provides the most common explanation for Amontons' laws that friction is proportional to load and independent of A 0 . Because A c is small, the interfacial region is very compliant. In a range of applications the interfacial compliance can significantly reduce the stiffness of macroscopic joints formed by holding two components together under pressure [1,7].In this paper, we examine the effect of surface roughness on the normal and lateral stiffness of contacts between elastic solids using molecular dynamics (MD) and continuum calculations. The results provide a numerical test of recent continuum theories [8,9] and their applicability to real solids. The contact area and normal stiffness approach continuum predictions rapidly as system size increases. Continuum theory also captures the internal deformations in the solid under tangential load, but the total lateral stiffness may be greatly reduced by atomic scale displacements between contacting atoms on the opposing surfaces. This makes it a sensitive probe of the forces underlying friction and may help to explain unexpectedly small experimental results [10].The topography of many surfaces can be described as a self-affine fractal [2,11]. Over a wide range of lengths, the root mean squared (rms) change in height dh over a lateral distance ℓ scales as a power law: dh ∼ ℓ H , where the roughness or Hurst exponent H is typically between 0.5 and 0.9. Greenwood and Williamson (GW) considered the peaks of rough landscapes as independent asperities and found that A c rose linearly with normal load F N for nonadhesive surfaces [2]. This explains Amontons's laws if there is a constant shear stress at the interface. A linear scaling of area with load is also obtained from Persson's scaling theory, which includes elastic coupling between contacts approximately [12,13].Dimensional analysis implies that the linear relation between load and area must have the form( 1) where a modulus like the contact modulus E ′ is the only dimensional quantity char...

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confidence: 89%

“…Surface atoms form a square lattice that is rotated by 45 • relative to that of the rigid surface. This rotation and the choice of d/d ′ prevent commensurate locking of the surfaces [23,24]. Substrate atoms separated by r interact with a Lennard-Jones (LJ) potential:…”

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confidence: 99%

Stiffness of Contacts between Rough Surfaces

2011

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“…For angles in between commensurate situations, the flake is approximately incommensurate and the potential barriers to sliding are averaged out. In this situation, an almost frictionless sliding was observed 9,11,12 , a phenomenon often referred to as superlubricity [13][14][15][16] . Recently, extremely high speed superlubricity has been observed for micron sized graphene flakes 17 .…”

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confidence: 99%

Superlubric to stick-slip sliding of incommensurate graphene flakes on graphite

et al. 2013

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We calculate the friction of fully mobile graphene flakes sliding on graphite. For incommensurately stacked flakes, we find a sudden and reversible increase in friction with load, in agreement with experimental observations. The transition from smooth sliding to stick-slip and the corresponding increase in friction is neither due to rotations to commensurate contact nor to dislocations but to a pinning caused by vertical distortions of edge atoms also when they are saturated by Hydrogen. This behavior should apply to all layered materials with strong in-plane bonding.

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“…Consequently, the friction resistance and wear damage get to lowering [11]. Another work indicates that the magnetic field may boost the orientation of liquid crystal molecules into friction surface, so that the lubricity of liquid crystal compound was increased [12]. Further, MHD deals with the motion of highly conducting fluids in the presence of magnetic field.…”

Section: Introductionmentioning

confidence: 99%

Hydromagnetic Squeeze Films between Porous Rectangular Plates with Couplestress Fluids

2012

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The theoretical investigation made in this paper is to study the effect of transverse magnetic field on the performance characteristics of porous squeeze film lubrication between two rectangular plates with couplestress fluids. A most general modified Reynolds equation is derived using Stokes constitutive equations for couplestress fluids. The fluid in the film region and in the porous region has been modeled as a couplestress fluid. The analysis takes into account velocity slip at the porous interface using Beavers-Joseph criterion. A closed-form expression for pressure, load carrying capacity and squeeze film time are obtained. The results are presented for different operating parameters. It is observed that effect of couplestresses on the MHD squeeze film lubrication between porous rectangular plates is to increase the load carrying capacity significantly and to delay the time of approach as compared to the corresponding non-magnetic case and Newtonian case.

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Superlubricity and frictional anisotropy

Cited by 124 publications

References 17 publications

Stiffness of Contacts between Rough Surfaces

Stiffness of Contacts between Rough Surfaces

Superlubric to stick-slip sliding of incommensurate graphene flakes on graphite

Hydromagnetic Squeeze Films between Porous Rectangular Plates with Couplestress Fluids

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