Mechanismenbasierte Aufklärung von Zusammenhängen zwischen Kratzversuchen und makroskopischen Gleitexperimenten bei Kunststoff/Metall-Paarungen
Zusammenfassung der Projektergebnisse
In this project, the analysis of friction and wear mechanisms was the basis for a successful correlation of experimental results for sliding polymer/steel contacts, recorded in classical macroscopic tests and in single-asperity scratching tests. Two mechanisms were identified as particularly important for such correlation, the formation of transfer films and the evolution of frictional characteristics when the temperature was increased across the glass transition. In order to obtain data for the correlation across length scales, we implemented a number of novel testing strategies dedicated to the goal of the project. On the microscopic side, we realized single-asperity scratching experiments with thousands of cycles in order to work with a transfer film formation which was similar to macroscopic tests. Realistic transfer films were also supported by manufacturing the micro-scale asperities for scratching experiments from the steel which served as counterbody in macroscopic experiments. On the macroscopic side, we implemented inductive heating for reliable temperature control in block-on-disc tribological tests. We also transferred the block-on-disc configuration into a high-resolution tribometer to bridge the gap in velocities between length scales. Finally, we developed and verified a model to determine the real area of contact between a hard asperity and the corresponding groove in a soft material created in previous sliding cycles. The analysis of experimental results with this model helped us to identify situations in which shearing is a dominant mechanism and to calculate the shear stress in those contacts. A key result of our project is an extended confirmation of the view that friction and wear in polymer/steel couples are controlled by the sliding of steel roughness asperities in matching grooves in the polymer. Not only did we find quantitative agreement in friction coefficient between macroscopic tests and adequate scratching experiments, we also found that the transition from the initial creation of grooves by asperity plowing to the steady-state shearing of asperities against the walls of the grooves proceeds in similar manner in both experiments. Most important, we observed that the development of transfer films nucleates around asperities and that a similar formation of transfer film in both experiments leads to the same microstructure of film patches. The thermal properties of the polymer were of importance for the correlation of results from different experiments in two respects: On the one hand, we showed that the similarity of friction coefficient across length scales is higher for polymers with higher thermal stability. This observation can be understood considering the frictional heating in macroscopic experiments, which does not occur in scratching experiments. On the other hand, we demonstrated that friction increases at all length scales when crossing the glass transition to higher temperatures. However, for temperatures above the glass transition, friction characteristics may differ due to different development of transfer films. Our research strategy of implementing similar contact geometries in different tribological tests became particularly fruitful when comparing the results as function of the product pv of pressure and velocity. Except for the scratching depth of single asperities, which should not be compared to the wear height loss, all results exhibit good overlap at between the different pv regimes. We hope that the results of the project will guide the further development of polymeric tribomaterials and encourage novel testing strategies which are based on the analysis of mechanisms, in particular in tribofilm formation.
Projektbezogene Publikationen (Auswahl)
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Micro friction and wear properties of PEEK PA66 and POM. Global Conference on Polymer and Composite Materials (PCM 2016), May 20-23, 2016, Hangzhou, China
Pei, Xianqiang; Bennewitz, Roland
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Micro-scratching as a method of tribological studies on polymers. Nanobrücken 2016: a nanomechanical testing workshop & Hysitron user meeting, March 2-4, 2016, Saarbrücken, Germany
Pei, Xian-Qiang; Bennewitz, Roland; Lin, Leyu; Schlarb, Alois K.
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Multiple scratch studies on PEEK using different steel indenters. Nanobrücken: a nanomechanical testing workshop and Hysitron user meeting, March 2-4, 2016, Saarbrücken, Germany
Choi, H.; Pei, Xianqiang; Bennewitz, Roland
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Novel Experiments Reveal Scratching and Transfer Film Mechanisms in the Sliding of the PEEK/Steel Tribosystem. Tribol. Lett. 2016, 63: 40
Pei, X.-Q.; Lin, L.Y.; Schlarb, A.K.; Bennewitz, R.
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Energieeffizienz durch ungeschmierte Kunststoff/Metall-Tribosysteme, Werkstoffwoche, September 29, 2017, Dresden
Schlarb, A.K.
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Single asperity experiments in understanding macroscopoic polymer tribology. WTC- the 6th World Tribology Congress, September 17-22, 2017, Beijing, China
Pei, Xian-Qiang; Bennewitz, Roland
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Friction and wear of PEEK in continuous sliding and unidirectional scratch tests. Tribol. Int. 2018, 122: 108-113
Lin, L.Y.; Pei, X.-Q.; Bennewitz, R.; Schlarb, A.K.
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The role of singleasperity experiments in tribology. 8th Nanobrücken workshop, Universität Erlangen, February 20-22, 2018, Erlangen, Germany
Bennewitz, R.; Rittgen, K.; Caron, A.; Pei, X.; Lin, L.Y.; Schlarb, A.K.
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Contact area and shear stress in repeated single-asperity sliding of steel on polymer. Tribol. Lett. 2019; 67: 30
Pei, X.-Q.; Lin, L.Y.; Schlarb, A.K.; Bennewitz, R.
