Contact Area and Shear Stress in Repeated Single-Asperity Sliding of Steel on Polymer
A model for the contact area of a single asperity sliding in a groove after repeated cycles is presented. Based only on the asperity geometry and on data from friction experiments, the model predicts the area of the asymmetric elliptical contact of the asperity sliding in its own groove. It thus allows to determine the shear stress of the steel–polymer couple in the relevant geometry without need for further microscopy of indenter or groove. The model was validated by experiments with an indenter manufactured from slide bearing steel and polyether-ether ketone (PEEK) as substrate. In experiments of 1000 repeated cycles, the contact area was found to vary with varying load and sliding velocity, while the shear stress was 20.5 MPa at a normal pressure of 50–70 MPa, independent of velocity when friction heating is still negligible. Model and experimental confirmation advance single-asperity friction experiments into an efficient method to extract shear stress and contact area for an understanding of sliding friction in metal-polymer contacts.
KeywordsAsperity scratching Contact area Shearing PEEK
The authors acknowledge financial support of the German Research Foundation (Deutsche Forschungsgemeinschaft) on the projects BE 4238/7-2 and SCHL 280/22-2, Evonik Industries AG, Germany, for the donation of the experimental materials, and thank Eduard Arzt for the continuous support of this project. The authors are also grateful to Karl-Peter Schmitt of INM for his help in tribological tests.
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