Friction Coefficient of Rough Indoor Flooring Materials

Abstract

The present study investigates the effect of the surface roughness of polymeric indoors floorings on the static friction of bare foot as well as foot wearing cotton and polymeric socks under dry, water, water + 5.0 vol. % soap, oil and water + 5.0 vol. % oil lubricated sliding conditions. Polymeric floor sheets of different roughness ranging from 0.05 and 11.0 µm were tested. The tested material is commonly used in entrance areas or corridors and in the sport halls. Cotton and polymeric socks as well as bare foot were frictionally tested. The results were compared to the friction caused by shoes as simulated by rubber test specimens of vee shape treads were prepared in the form of square sheets of 100 ´ 100 mm, 10.0 mm thickness. Experiments were carried out using a test rig designed and manufactured to measure the friction coefficient between the foot and the tested polymeric flooring materials. The experimental results showed that, at dry sliding, friction coefficient of rubber decreased with increasing surface roughness, while for bare foot and polymeric socks, friction coefficient decreased down to minimum then increased with increasing the surface roughness. Besides, friction coefficient decreased with increasing applied load. Minimum friction was observed at surface roughness ranging between 6-9 µm. In water lubricated sliding, friction coefficient of rubber increased up to maximum then decreased with increasing surface roughness. Maximum friction values were observed at surface roughness values ranging from 1.5 to 2.0 ?m Ra. Cotton socks showed the highest friction coefficient followed by rubber, bare foot then polymeric socks at 11 µm Ra. Friction coefficient drastically decreased with increasing surface roughness at water and detergent lubricated sliding. For the tested flooring materials lubricated by oil, friction coefficient of rubber increased up to maximum values then decreased with increasing the surface roughness of the flooring materials. The maximum friction values were noticed at 4.0 µm Ra. Bare foot displayed drastic reduction in friction coefficient, while cotton socks showed the highest values. When water was diluted by 5.0 wt. % oil, rubber smooth flooring surface displayed values of friction coefficient close to that observed for hydrodynamic lubrication where the two sliding surfaces are separated by the fluid film. As the roughness increased the fluid film was broken and friction increased. Cotton socks showed the highest friction compared to bare foot and polymeric socks.