Molecular dynamics simulations of mixed lubrication with smooth particle post-processing

Abstract

A post-processing method for molecular dynamics (MD) simulations of friction based on the smooth particle approach is proposed, allowing--among other features--the introduction and evaluation of a solid-solid contact area arising due to direct asperity interaction. In order to illustrate the feasibility of this scheme, a large number of MD calculations of lubricated nanotribological systems with various asperity geometries and carefully selected numbers of lubricant molecules were carried out and analysed. In this manner, it is shown that the friction force as a function of load agrees very well with a three-parameter friction law which, in addition to the adhesion- and the load-controlled terms, contains a load-independent offset.

Advances in nonequilibrium molecular dynamics simulations of lubricants and additives

“…The resulting load versus friction behaviour was then analysed to study these parameters affected the friction coefficient and the extrapolated friction force at zero load (Derjaguin offset). A smooth-particle-based evaluation method [240] was used to visualize the sliding interface between the two OFM layers. This allowed the definition and calculation of a dimensionless normalized sliding resistance area, which was then related to the Derjaguin offset.…”

Definition and detection of contact in atomistic simulations

“…Solhjoo and Vakis [16] defined the contact distance as being slightly larger than the first neighbor distance based on crystallographic packing factors. Eder et al [17] suggested that, in the case of an amorphous structure, a statistical value could be used for the definition of the contact distance, namely the radial distribution function.…”

“…Furthermore, in a system with amorphous structure, the peaks are by definition not related to any specific crystal structure, demonstrating the randomness of the atoms' positions in the system. For an amorphous system, Eder et al [17] suggested that a value slightly smaller than the first minimum in the g(r) plots can be assigned as the contact distance. In yet another approach to detect atoms at contact based on the potential energy of each atom, Solhjoo and Vakis [18] showed that surface atoms have higher potential energies than atoms in the bulk.…”

“…Detection of these transferred atoms is crucial, because failure to do so results in a higher number of contacting atoms; therefore, the estimated contact area could be unreasonably higher than the actual one. In order to solve this problem, Eder et al [17] suggested that these atoms could be identified from their mean velocities in the sliding direction over a span of time. In another method, Spijker et al [15] stored the atoms of the contacting parts into clusters by a depth-first search algorithm: whenever a cluster was found to be disconnected from other clusters in the original part, the atoms of that cluster were considered as the transferred ones.…”

A molecular dynamics simulation of boundary lubrication: The effect of n-alkanes chain length and normal load

“…However, there is a limited number of works on boundary lubrication by MD simulation that take the asperity contact with lubricant into account. Eder et al [16] proposed a smooth particle approach to define and calculate the asperity contact area and lubricant cavity volume. The influence of different shaped asperities and normal load on the contact area and friction force was discussed.…”