CHARACTERIZATION OF MICROTEXTURE RELATED TO WET ROAD/TIRE FRICTION

Abstract

This paper deals with the determination of roughness parameters which could be used to study the influence of microtexture on wet road/tire friction. Two types of surface were studied: laboratory-made GRAP specimens, which surface is composed of similar size coarse aggregates, and road specimens taken from test sites. Friction and surface geometry were measured after polishing. GRAP specimens were polished in laboratory using a projection method. Road surfaces were polished by traffic. Friction was measured by means of SRT pendulum. Microtexture was measured by a non-contact method using auto focus laser sensor and also by a contact method using stylus sensor. Relevance of roughness parameters was evaluated from their correlation with friction. Research was focused on shape parameters. Criteria were defined to select surface peaks, which are likely to touch the tire rubber, and valleys. Fair correlations were found with two parameters: one characterizing surface relief, defined from the curve connecting profile peaks, and one related to peak contact pressure, defined from the curve connecting profile peaks and valleys. The influence of the number of indenters on friction was found to be significant also. A predictive equation was derived empirically, which gives reasonable friction values compared with measured values. Suitability of measurement techniques to FRAP and road specimens is discussed. The influence of profile type on results was also dealt with. Finally, comparisons between results obtained from this study and those from previous works were made.