Semi-analytical calculation model for friction of polymers on the example of POM ∣ PE-UHMW and steel ∣ PE-UHMW

Abstract In this paper, a semi-analytical calculation model for the coefficient of friction (COF) of single spherical protrusions is presented. It allows the prediction of the deformative friction part ( μ def ) and adhesive friction part ( μ adh ) of the friction pairings steel ∣ polyethylene with ultra-high molecular weight (PE-UHMW) and polyoxymethylene (POM) ∣ PE-UHMW. The experimental studies included unlubricated friction tests, which served to determine the total COF ( μ tot ), as well as tests being lubricated with silicone oil, from which μ def is obtained. Based on the verification tests, it could be shown that both states of lubrication result in the same deformation and that the relationship between the rear angle ( ω ) and μ def postulated in the calculation model is valid. Therefore, friction tests with segmented spheres were carried out, which allow a specific variation of the ω . It can be concluded that for both pairings the μ def is generally of minor significance (approx. 1/3 μ tot ) and the influence of the μ adh predominates (approx. 2/3 μ tot ) the friction process. Furthermore the μ tot decreases with increasing contact pressure especially in the low pressure range and depends on the form of motion (continuous and discontinuous).