Effect of the Stepped Parallel Groove Number and Surface Roughness on Friction Enhancement of Rubber Blocks in Glycerol Solutions

In work environments where walking surfaces may be contaminated by liquid, safety footwear must provide high slip resistance. One method to enhance friction on wet or contaminated interfaces is to regulate fluid pressure through surface texturing of the footwear outsole. However, the optimal texture geometry and distribution for achieving high friction, as well as the effect of rubber surface roughness on texture performance, remain unclear. The objective of this study was to examine the effect of the number of stepped parallel grooves and the surface roughness of rubber blocks on their friction in glycerol solutions. A stepped parallel groove texture, designed to generate negative fluid pressure, was machined onto rubber blocks with varying surface roughness. Friction tests were then conducted in a glycerol solution. The results showed that the stepped parallel groove texture generated negative fluid pressure and affected both static and kinetic friction forces. The static friction force increased continuously with the number of stepped parallel grooves. By contrast, the kinetic friction force exhibited different trends depending on the surface roughness of the rubber. For rough-surface specimens, the kinetic friction force increased with the number of grooves up to three, beyond which it plateaued. For smooth-surface specimens, it gradually decreased as the number of grooves increased. These results suggest that machining an optimal number of stepped parallel grooves can enhance friction characteristics in liquid environments. This effect is particularly pronounced for rough-surface rubber, offering a practical strategy for improving slip resistance in liquid-contaminated workplaces.