Optimal Energy Dissipation in Sliding Friction Simulations

Abstract

Non-equilibrium molecular dynamics simulations, of crucial importance in sliding friction, are hampered by arbitrariness and uncertainties in the removal of the frictionally generated Joule heat. Building upon general pre-existing formulation, we implement a fully microscopic dissipation approach which, based on a parameter-free, non-Markovian, stochastic dynamics, absorbs Joule heat equivalently to a semi-infinite solid and harmonic substrate. As a test case, we investigate the stick-slip friction of a slider over a two-dimensional Lennard-Jones solid, comparing our virtually exact frictional results with approximate ones from commonly adopted dissipation schemes. Remarkably, the exact results can be closely reproduced by a standard Langevin dissipation scheme, once its parameters are determined according to a general and self-standing variational procedure

Connection between sliding friction and phonon lifetimes: Thermostat-induced thermolubricity effects in molecular dynamics simulations

“…For both the harmonic and anharmonic substrate, at the highest sliding speed v = 0.01 considered (which remains well below the speed of sound), the curve of F fr versus γ reveals a maximum. The existence of the friction maximum agrees with previous studies [1,3,7], and is attributed to phonon backreflections, which are maximally suppressed at the friction maximum. However, still considering the highest sliding speed, the data also reveal that the substrate temperature, T sub , varies with γ, reaching, in fact, a minimum at the friction maximum (with the value of T sub then being close to T lan of the thermostat).…”

Generalized Langevin equation: An efficient approach to nonequilibrium molecular dynamics of open systems

“…Of particular interest in many applications is understanding the thermal conductivity of materials (i.e., molecular junctions [1,2], nanotubes [3][4][5][6][7], nanorods [8], nanowires [9], semiconductors [10]) and the heat transport within nanodevices [11][12][13]. Other applications in which the nonequilibrium properties of materials are of interest include (a) the bulk energy dissipation in crystals due to an excited point defect [14] or crack propagation [15]; (b) interfacial chemical reactions between adsorbed molecules and the surface that generate excess energy which is dissipated into the surface [16,17]; (c) surfaces interacting with energetic lasers [18], atomic/ionic [19,20] or molecular beams [21] when substantial energy is released along the particles trajectory into the surface; (d) in tribology, where two surfaces shear upon each other with bonds between them forming and breaking that results in consuming and releasing a considerable amount of energy [22][23][24]; and (e) molecules which are driven by a heat gradient [25].…”

Mechanics of rough contacts in elastic and viscoelastic thin layers

“…Indeed, the almost totality of the boundary element methodologies formulated in the real space and presented in literature ( [54], [33], [27], [47]) relies on the half-space assumption, which consists in assuming that the thickness of the solids in contact is much larger than the contact area. In principle, boundary elements techniques derived in the Fourier space can tackle contact problems with surfaces characterised by layers of finite thickness ( [68], [66], [67]); however, systematic investigations of the effects related to the thin layer mechanics are not common in literature. Furthermore, studies performed adopting finite element methodologies ( [56], [24], [25]), molecular dynamics simulations ( [62], [61], [63]) and hybrid techniques ( [64], [65]), which intrinsically consider the bulk of the contact solids in their formulation, usually do not pay attention to the finite size effects and employs models with thickness values that are believed, on heuristic basis, to be large enough to avoid any influence given by the thickness.…”