Dynamic mechanical analysis as a predictor for slip resistance and traction in footwear

Adequate friction between footwear and surface is essential to reduce the risk of slipping (Chang et al., 2001) and maximise athletic performance (Luo & Stefanyshyn, 2011). Footwear outsole materials are constructed of viscoelastic elastomers (e.g. rubber or thermoplastic polyurethane (TPU)). The mechanical properties of outsoles are frequently measured with simple tools, e.g. durometer for hardness and profilometer for surface roughness (Iraqi et al., 2020).

However, viscoelastic elastomers have complicated material characteristics, and are highly dependent of temperature and load frequency. These material characteristics have previously been investigated with dynamic mechanical analyses (DMA) in relation to friction between rubber and surface in tire-road friction scenarios (Lorenz et al., 2015).

The outcome measures are G′´ (energy loss in internal motion), G′ (elastic response), and tan(δ) (G′′/G′). Tan(δ) is a measure of the material’s ability to lose energy by internal friction. However, DMA as a tool for optimising footwear traction has received very little or no attention in footwear science.

It is believed that the friction properties of outsoles are affected by sliding speed, which may change the elastic response and loss factor.