The Effects of Floor Roughness on Shoe-Floor Friction Adhesion and Hysteresis

Slip and fall accidents are a major source of occupational accidents. The coefficient of friction (CoF) that is required for gait is approximately 0.2. Floor roughness has been demonstrated to affect the available CoF. Building on this knowledge, this research aims to investigate the effect of changing floor roughness on two components of friction: adhesion and hysteresis. The experiments were carried out using a custom developed pin-on-disk type tribometer. Two common types of rubber shoe material, with Shore A hardness 50 and 95, were slid over ceramic tiles that were prepared to different roughness levels. The tiles were abraded using aluminum oxide media (commonly called “sand blasting”). Three levels of roughness were achieved, measured using the average peak height (Rz) with a stylus profilometer: 16.6 μm, 24.3 μm, and 34.6 μm. The experiments were conducted at 0.01 m sec-1 at a contact pressure of 266.1 kPa under ambient conditions to specifically examine the role of adhesion and hysteresis in the absence of hydrodynamic effects. The coefficient of friction was recorded without lubricant (dry) and lubricated with: 2% detergent solution, canola oil, and SAE 75W140 gear oil. Hysteresis was measured with SAE 75W140 because the high lubricity of the gear oil minimizes adhesion. Adhesion in dry and wet conditions was measured by subtracting the hysteresis from the coefficient of friction. Hysteresis was found to increase from 0.101 to 0.358 for the hard rubber and from 0.269 to 0.611 for the soft rubber when floor roughness was increased from 16.6 μm and 34.6 μm. Higher roughness was also associated with a decrease in dry adhesion from 0.651 to 0.277 for the hard rubber and from 0.435 to 0.041 for the soft rubber. Wet adhesion decreased from 0.285 to 0.049 for soft rubber on detergent. Canola oil, for both hard and soft, and detergent combined with hard rubber did not make a significant difference in the adhesion available. Hysteresis, which is a more robust form of friction in the presence of fluids, was found to be positively correlated with floor roughness while adhesion was negatively correlated with roughness. This indicates that increased floor friction is associated with better floor slip-resistance in the presence of fluids. Abrasively blasting floor tiles to increase the roughness of the floor surface, may lead to improved boundary lubrication friction, particularly when accompanied by soft shoe materials.