Defence of dissertation in the field of engineering design and production, vehicle engineering, András Kriston, M.Sc. (Eng.)

What affects rubber frictional performance on ice?

The public examination of the doctoral dissertation of András Kriston, M.Sc. (Eng.)., will be held on 30 June 2017 at 12.00 at the Aalto University School of Engineering. The title of the dissertation is Micro contact analysis of rubber-ice interaction during frictional processes. The field of the dissertation is engineering design and production, vehicle engineering, rubber/ice friction.

The good frictional performance of rubber on ice heavily influences vehicles’ mobility at winter conditions. In this dissertation, a methodology chain was developed using various microscopical imaging techniques in order the reveal the main frictional mechanisms when tire tread rubber slides on ice. The studies presented in this thesis help to broaden our understanding in the physics of tire-ice contact.

By analyzing the ice surface at its post-sliding state, different kind of contact marks can be observed depending on simulated traffic conditions (i.e. ice surface contamination), rubber hardness and rubber surface roughness. The results showed that it is not possible to single out one specific frictional mechanism due to the complexity of the tribosystem. The friction can be low when the rubber compound is harder, or the ice surface temperature is higher resulting local melting spots, leading to more hydrodynamic friction. Contrary, when the rubber compound is soft enough, or the ice surface temperature is colder, the likelihood of melting is low thus other mechanisms like deforming ice surface asperities and ploughing by hard fillers in rubber are more dominant. Interestingly, it was observed that pre-melted ice layer always lubricates the contact surface.

To overcome on the difficulties of observing three-dimensional micro contact state when rubber is squeezed against different type of road surfaces, a new, micro-computed-tomography based method was proposed. As a result, it was seen that the contact area on ice-like flat road surface is governed by the deformation of the rubber surface asperities, while on a rough road surface the contact is driven by the bulk deformation of the rubber. The nature of the contact state influences the frictional mechanisms of rubber on road surfaces. The large variety of observed frictional and contact mechanisms indicates that all modern tire compound development needs to fulfil multiplicity of requirements. Optimizing dynamic stiffness of the rubber, a good control over the rubber surface roughness and improving the molecular level interactions, like adhesion, can improve the performance of tires on icy surfaces.

Opponent: Dr. Lasse Makkonen, VTT Technical Research Centre of Finland, Finland

Supervisor: Professor Kari Tammi, Aalto University, Finland

Advisors: Dr. Tibor Fülöp, Goodyear S.A., Luxembourg; Ari Tuononen, D.Sc.,Aalto University, Finland

Electronic dissertation: https://aaltodoc.aalto.fi/handle/123456789/26855

Contact information: András Kriston, andras.kriston@aalto.fi