Tribophyiscal scaling effects in friction and wear of polymers on small‐ and large‐scale tests

Abstract

AbstractCoefficients of friction and wear rates for polyacetal and polytetrafluoroethylene are measured on small‐scale cylinder‐on‐plate tests and large‐scale flat‐on‐flat tests. Three models for extrapolation between small‐ and large‐scale test results, which are based on experimental parameters, are presented: (i) one single mechanical parameter (normal load), (ii) the contact‐pressure–sliding‐velocity model (temperature limit), and (iii) a macroscopic geometry model. The last model is most extensively evaluated and considers thermal effects, sample geometry and contact conditions. After correction for the thermal sliding regime and viscoelastic deformation, the coefficients of friction can be extrapolated while the wear rates are more sensitive to the contact situation. High‐temperature tests on small scale are not representative for high‐load tests on large scale. Besides mechanical effects such as stress concentrations and debris mobility, variations in polymer structure under sliding (formation of rigid amorphous phase) and chemical interactions (wear debris polymerisation) also change with testing scale. The latter effects are explicitly illustrated from spectroscopic measurements on the worn surfaces. Copyright © 2008 John Wiley & Sons, Ltd.