Shoe-Floor Frictional Properties for Varying Sliding Speed, Pressure and Contaminant

Abstract

Injuries resulting from slips and falls are a major health concern. Current devices to measure slip resistance of shoe-floor-contaminant interfaces attempt to mimic biomechanical conditions (shoe angle, sliding speed, and normal force); however, the results are variable, depending upon the measurement methods used. Thus, an understanding of shoe-floor surface interaction from a theoretical view could provide insights into coefficient of friction (COF) of the shoe-floor interface and improve testing procedures. The purpose of this work was to provide basic measurement towards an understanding of the fundamental characteristics of shoe-floor friction. In experiment #1, the effects of nominal pressure and sliding speed on COF are examined for dry conditions using two common shoe materials. In experiment #2, effects of sliding speed on COF when a contaminant is present are examined for the same shoe materials. All experiments were conducted on a tribometer where a patch of shoe material was loaded on a rotating disc of floor material. The two shoe materials were polyurethane and polyvinyl chloride. Three load levels corresponding to nominal pressures of 4.3, 22.1 and 57.6 kPa on the polyurethane and 3.8, 19.6 and 51.2 kPa on the polyvinyl chloride and three speed levels of 16, 78 and 156 mm/sec were examined in experiment #1. In experiment #2 six levels of speed were adjusted at 16, 39, 78, 117, 156 and 195 mm/sec. COF were measured using the tribometer with a computerized data acquisition system. Nominal pressure was determined from the apparent contact area and the applied load. Three trials were recorded and averaged for each condition. In experiment #1, the COF was found to be smaller at lower speeds and nominal pressures but was independent of pressure and speed at moderate and higher speeds and pressures. At low nominal pressures, few asperities may have been in contact between the shoe and floor material, which may have caused the lower COF. In experiment #2, COF decreased with increasing sliding speed. The shape of this curve was similar to the Stribeck curve. Therefore, it was determined that as sliding speed increased, fluid thickness increased, which decreased the interaction of asperities between the shoe and floor surfaces.