Multiscale Friction Simulation of Dry Polymer Contacts: Reaching Experimental Length Scales by Coupling Molecular Dynamics and Contact Mechanics

Abstract

This work elucidates friction in Poly-Ether-Ether-Ketone (PEEK) sliding contacts through multiscale simulations. At the nanoscale, non-reactive classical molecular dynamics (MD) simulations of dry and water-lubricated amorphous PEEK-PEEK interfaces are performed. During a short running-in phase, we observe structural transformations at the sliding interface that result in flattening of the initial nanotopographies accompanied by strong polymer chain alignment in the shearing direction. Our MD simulations reveal a linear pressure-dependence of the shear stress τMD (P,σH2o) [MPa]=0.18P + 50.5 - 1.25σH2o, where σH2o [nm-2] is the surface number density of adsorbed water molecules. This constitutive law is of central importance for our multiscale approach, since it forms a link between MD and elastoplastic contact mechanics calculations. An integration of τMD (P,σH2o) over the real area of contact yields a macroscopic friction coefficient μmacro (σH2o) that allows for a meaningful comparison with friction coefficients μexp≈0.5-0.7 which are in good agreement with the calculated dry friction coefficients μmacro(σH2o=0).For milder experimental loads, our multiscale model suggests that the lower friction states with μexp≈0.2 originate in the presence of physisorbed molecules (e.g. water), which significantly reduce interfacial adhesion.

A review of advances in tribology in 2020–2021

“…80(a)). A linear pressure-shear stress dependence was revealed, and this dependence was summarized as a nanoscale friction law, which bridged between molecular [941,943,948,949]. Reproduced with permission from Ref.…”

“…The wear mechanism of PTFE under water lubrication also changed from mixed lubrication to elastohydrodynamic lubrication. Savio et al [941] elucidated friction in poly-ether-ether-ketone (PEEK) sliding contact by the classical molecular dynamics simulations of dry and water-lubricated amorphous PEEK-PEEK interfaces at the nanoscale (Fig. 80(a)).…”

“…Reproduced with permission from Ref. [941], © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature, 2021; Reproduced with permission from Ref. [943], © American Chemical Society, 2022; Reproduced with permission from Ref.…”

“…Fig 80. Atomistic or coarse-grained molecular dynamics simulations of tribology of polymeric materials[941,943,948,949]. Reproduced with permission from Ref [941],.…”

“…Atomistic or coarse-grained molecular dynamics simulations of tribology of polymeric materials[941,943,948,949]. Reproduced with permission from Ref [941],. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature, 2021; Reproduced with permission from Ref [943],.…”