Ice friction plays a central role in vehicle and a human motion during winter, in sport engineering or in geological processes. Although various in their area, all of these topics require similar understanding, namely understanding of how the ice surface behaves when it gets into contact with an external body. The aim of the work undertaken in the frame of this thesis was to propose a methodology chain which can help to investigate the frictional and contact mechanical processes especially active during rubber – ice interaction; and to use this chain in broadening our understanding in the physics of tire-ice contact. Specifically, during the doctoral work reported here laboratory scale rubber-ice friction tests were carried out and studied in details using various microscopy and surface topography techniques under the most severe conditions, on medium warm and on warm ice. The result of the study using different microscopy techniques allowed to confirm the presence of several frictional mechanisms. Their relevance was found to be dependent not only on the ice surface but also on the slider material. Significantly different mechanisms were activated for soft and for hard rubber compounds. For soft compounds, the governing frictional mechanisms were the removal of surface frost via cutting and/or frictional heating, scratching of the softening ice by hard filler particles and shearing of a quasi-liquid layer by capillary drag. For stiffer compounds, the contact proved to be more localized, resulting in high local pressures, causing plastic deformation and larger scale local melting. Additional multiscale surface analysis was also performed by White Light Interferometry, which is based on topography measurement. It showed the early appearance in all tests of circular liquid like features on ice. They were interpreted as quasi liquid droplets, indicating the generic importance of thermally activated processes with their presence. Modification of the rubber surface roughness using different silica types also proved to impact the tribological performance, mostly by modifying the extent of ice scratching. Further explanation of the contact processes was gained from quantitative analysis of the Real Area of Contact. Micro-Computed Tomography (micro-CT), coupled with specific image analysis algorithms was introduced for first time in rubber contact mechanical analysis. It allowed to directly visualize and quantify the contact state on micro scale without disturbing the tribo system. Different contact pairs were investigated, allowing to compare the rubber-ice contact to the better understood rubber-dry rough surface contact. The results highlighted the importance of the rubber roughness and surface quality. The better understanding of the governing tribological processes of the rubber – ice interaction helps to open new research directions and thus to improve the rubber compounds and tire tread patterns.
|Julkaisun otsikon käännös||Micro contact analysis of rubber-ice interaction during frictional processes|
|Tila||Julkaistu - 2017|
|OKM-julkaisutyyppi||G5 Tohtorinväitöskirja (artikkeli)|