Analysis of factors influencing the friction coefficients of shoe sole materials

The slip resistance of pedestrian surfaces is usually characterized by friction coefficients measured with samples of shoe sole materials. The factors that influence the results of friction measurements were investigated for two elastomer materials and leather using the portable tribometer Floor Slide Control 2000, which was operated under varying conditions in a climate chamber on two reference surfaces. The friction behaviour observed was in accordance with viscoelastic material properties and depended on the softness of the shoe sole materials. Temperature and mechanical abrasion of the sole materials during the measurements were the factors with the greatest systematic effects on the dynamic coefficients of friction. In some cases, the coefficients of friction also depended on the direction in which a test material was slid along the same track, indicating an influence of local floor surface variations. For dry leather, the influence of relative air humidity on the measured friction coefficients strongly depended on the floor surface. Due to varying systematic influences, the standard deviations of the friction coefficients in series of 20 repetitive measurements (repeatability standard deviation) differed for the individual material combinations. Linear regression analysis of the data revealed that pure random contributions to the repeatability standard deviation were similar and around 0.005 for all investigated materials.