Correlation between Scratching and Macroscopic Sliding Properties of Polymer/Metal-Pairs based on Mechanism Analysis

• Applicants: Professor Dr. Roland Bennewitz; Professor Dr.-Ing. Alois K. Schlarb
• Subject Area: Plastics Engineering
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 250158768

Friction and wear of sliding contacts between polymers and metals depend critically on the roughness of the metal counterbody. The interaction of roughness asperities with the polymer surface contributes to friction and leads to ploughing, material transformation, and transfer film formation. The underlying mechanisms are investigated in single-asperity scratching experiments. Our project explores the connection between the mechanisms revealed by microscopic scratching experiments and the results of macroscopic standard tests in tribology. In the first phase of the project, we have established quantitative links between the different length and velocity scales by means of multi-pass scratching, using single micro-asperities crafted from the steel counter body of macroscopic tests. Further successful strategies for linking microscopic phenomena and macroscopic tests included novel high-resolution pin-on-flat experiments and measurements across the glass transition temperature. In the continuation of the project, we propose to extend the approach with three key aspects. We will reveal the influence of internal friction in the polymeric materials, i.e. of the thermo-mechanical bulk properties, on friction and wear. We will clarify the transfer film mechanisms of different polymers at the single asperity level in correlation to the lubricating function of transfer films on rough and smooth areas of the steel surface. Finally, we will address the frictional energy input and temperature in general in relation to the viscoelasticity of worn polymer surfaces and the resulting wear performance. Our project builds on the complementary expertise in the Nanotribology Group of the INM - Leibniz Institute for New Materials, Saarbrücken, and the Chair of Composite Engineering at the University of Kaiserslautern. The successful project will not only contribute to the understanding of key mechanisms in polymer-steel tribology and thus to a rational design of new polymeric tribomaterials, but also establish novel methods in multi-scale tribology which can be applied beyond these systems.

• DFG Programme: Research Grants