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Multiscale friction simulation of dry polymer contacts: Reaching experimental length scales by coupling molecular dynamics and contact mechanics

: Savio, D.; Hamann, J.; Romero, P.A.; Klingshirn, C.; Bactavatchalou, R.; Dienwiebel, M.; Moseler, M.


Tribology letters 69 (2021), No.2, Art. 70, 16 pp.
ISSN: 1023-8883
ISSN: 1573-2711
Journal Article
Fraunhofer IWM ()
contact mechanics; Molecular dynamics; Multiscale Simulation; PEEK; polymer friction; tribometer

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. The MD simulations also reveal a linear pressure - shear stress dependence and large adhesive friction in dry conditions. This dependence, summarized in a nanoscale friction law, is of central importance for our multiscale approach, since it forms a link between MD and elastoplastic contact mechanics calculations. An integration of the nanoscale friction law over the real area of contact yields a macroscopic friction coefficient that allows for a meaningful comparison with measurements from macroscopic tribometer experiments. Severe normal loading conditions result in significant wear and high experimental friction coefficients µ≈0.5-0.7, which are in good agreement with the calculated values from the multiscale approach in dry conditions. For milder experimental loads, our multiscale model suggests that lower friction states with µ≈0.2 originate in the presence of physisorbed molecules (e.g., water), which significantly reduce interfacial adhesion.