Tribological concepts involved in slipping accident analysis.

According to tribology science, the friction force produced at the sliding interface between a rubber piece and an inflexible surface presents three main components: the first is due to molecular adhesion between the two bodies, it occurs at the regions of real contact; the second is a hysteresis component resulting from the periodic excitation of the bulk of the rubber by surface roughness; the third is due to effects of product shape. The shape of the elastomer product and the conditions in which the friction occurs (lubricant, roughness of the inflexible surface, etc.) determine the appearance of each one of these components 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 representative sample of industrial floor surfaces. Measurements have been made by means of a portable friction tester (PFT) assessing sliding resistance of floor coverings. The sliding movement takes place between a braked test wheel and the floor covering. The effect of product shape is insignificant as the wheel is covered with smooth elastomer. The friction force produced at the sliding interface between the elastomer and the floor covering has been evaluated on smooth and rough floors, and under different lubrication conditions (flooded with water, large, medium 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 differences pointed out depend also on floor covering roughness and lubrication. 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 differences. Some experimental results are explained from the squeeze lubricant film process. This experimental study permits a better understanding of phenomena produced at the sliding interface between a rubber sole and a floor covering when a pedestrian slips. It also plays a great part in bringing the portable friction tester into operation in order to carry out a measurement campaign of slipping resistance of industrial floors.