Influence of Vertically Treaded Outsoles on Interfacial Fluid Pressure, Mass Flow Rate, and Shoe–Floor Traction during Slips

Abstract

Accidental injuries due to slips and falls are considered serious threats to public safety. Sufficient friction at the footwear and flooring interface is essential to reduce slip-related risks. The presence of slippery fluidic contaminants, such as water, further reduces friction and increases the risks of slip-related accidents drastically. While the effect of floorings and contaminants on footwear traction has been measured extensively across a variety of footwear designs, only a few studies have explored the science of the outsole design and its role in providing sufficient traction. In this work, the tread design of a commonly encountered outsole pattern, i.e., with vertically oriented tread channels, was parametrically altered across its width and gap. Based on the impressions of an original footwear design, nine outsoles were fabricated. The induced fluid pressures, mass flow rates, and traction were quantified by using a computational fluid dynamics (CFD) framework and through slip testing experiments. Outsoles that had wide treads with small gaps decreased the overall slipping risk on dry floorings. As compared to the tread area, tread gaps were found to be a dominating parameter in providing adequate shoe–floor traction in wet slipping conditions. The methods, including the outcomes presented in this work, are anticipated to advance the understanding of the science behind footwear friction and help footwear manufacturers optimize outsole designs to reduce slip and fall risks.