TRIBOLOGICAL CONCEPTS INVOLVED IN SLIPPING ACCIDENT ANALYSIS

According to tribology science, the friction force produced at the sli ding interface between a rubber piece and an inflexible surface presen ts three main components: the first is due to molecular adhesion betwe en the two bodies, it occurs at the regions of real contact; the secon d is a hysteresis component resulting from the periodic excitation of the bulk of the rubber by surface roughness; the third is due to effec ts of product shape. The shape of the elastomer product and the condit ions in which the friction occurs (lubricant, roughness of the inflexi ble surface, etc.) determine the appearance of each one of these compo nents and its importance. Experimentations made by the French national research and safety Institute (INRS) revealed adhesion and hysteresis components in the lubricated friction of an elastomer over a represen tative sample of industrial floor surfaces. Measurements have been mad e by means of a portable friction tester (PFT) assessing sliding resis tance of floor coverings. The sliding movement takes place between a b raked test wheel and the floor covering. The effect of product shape i s insignificant as the wheel is covered with smooth elastomer. The fri ction force produced at the sliding interface between the elastomer an d the floor covering has been evaluated on smooth and rough floors, an d under different lubrication conditions (flooded with water, large, m edium and small quantities of mineral oil). Several test wheels, with different and sometimes used rubber coverings, have been employed. The friction force is altered when the elastomer composition or the state of the elastomer that is covering the test wheel changes. The differe nces pointed out depend also on floor covering roughness and lubricati on. The importance of either the adhesion or hysteresis components of the friction force in accordance with the composition and the state of the elastomer that is covering the test wheel, the lubricant amount, and the floor covering roughness enable the interpretation of these di fferences. Some experimental results are explained from the squeeze lu bricant film process. This experimental study permits a better underst anding of phenomena produced at the sliding interface between a rubber sole and a floor covering when a pedestrian slips. It also plays a gr eat part in bringing the portable friction tester into operation in or der to carry out a measurement campaign of slipping resistance of indu strial floors.