Slipperiness of footwear and mechanisms of walking friction on icy surfaces

Abstract

The coefficient of kinetic friction of 49 types of footwear was determined using a prototype apparatus simulating actual foot slippage on dry and wet smooth ice at surface temperatures of − 10° C and 0° C, respectively. The effects of soling material type, hardness, and tread design on the frictional properties were assessed in particular. In addition the effect of strewing sand on ice was studied. The fundamental mechanisms of the friction of polymers on ice are discussed briefly in the paper. The properties of ice had the greatest influence on the coefficient of kinetic friction, and hence, slip resistance. Of the assessed footwear, over 90% was classified as very slippery on wet ice, and 60% as slippery on dry ice. Five footwear types were slip-resistant on dry ice but only one on wet ice. None were slip-resistant on both wet and dry ice. Soft heel and sole materials (Shore A < 60) of thermoplastic rubber with a cleated area as large as possible are recommended for winter footwear on dry ice. For wet ice, however, new developments are needed, e.g. very hard (Shore A > 85) soling materials with sharp cleats in combination with a softer base material. Strewing sand on ice improved the slip resistance to a safer level, particularly on wet ice.