In the material designing process of footwear outer-soles, a grip property of rubber is of crucial importance under water or oil lubricated condition. In general, contact states between rubber and floors under lubricated conditions are influenced by various factors, i. e. viscosity of a lubricant, sliding velocity, normal force, surface roughness and wettability between the two substrates. It has been said that lubrication conditions can be distinguished based on Stribeck curves, which are described by the relationship between Sommerfeld numbers and dynamic friction coefficients. Wettability under the static condition is estimated by the spreading coefficient, which is used to evaluate the energy balance of interface free energies at a triple line. The purpose of this study is to investigate influences of surface free energies, viscosities, sliding velocities and surface roughnesses on dynamic friction coefficients of rubber under lubricated conditions. The influences of spreading coefficients on the behaviors of Stribeck curves and the relationship between dewetting velocities and dynamic friction coefficients are also discussed.
