Biofidelic mechanical ageing of ethylene vinyl acetate running footwear midsole foam

Abstract

Simple manipulation of force-time input is a potential strategy to increase the biofidelity of running footwear mechanical ageing. The purpose of this study was to compare a Dwell protocol, which incorporated a recovery period characteristic of the float phase of running, to traditional sinusoidal ageing. A second aim was to use the protocol to compare the mechanical ageing performance of foam, a halved commercial running shoe, and a cylindrical plug cut from a running shoe to quantify effects due to testing geometry and to estimate the contribution of midsole foam to shoe energy management. Dwell was more biofidelic and less aggressive than Sine because (1) net displacement and energy absorption were greater than Sine and (2) net displacement and energy absorption decreased at a slower rate than Sine. Using a 60 mm diameter cylindrical plug to estimate the performance of a halved shoe with 100 mm contact area led to 20% overestimation of energy absorption. Comparing the performance of a slab of foam and a cylindrical plug cut out from a shoe, the midsole was estimated to manage 90% of the energy. Differences between sample types were also related to stiffness, yield behavior, and resulting hysteresis curve shapes, which revealed that the outsole improved sample deformation and durability. Overall, results supported that Dwell improved the biofidelity of mechanical ageing, testing geometry is an important consideration in experimental design, and most of the energy was managed by the midsole.

Effect of mechanically aged minimalist and traditional footwear on female running biomechanics

“…Similarly, input parameters were expected to affect the level of material degradation because degradation by cyclic fatigue has been shown to be quite sensitive to selected input parameters. 22,42 Degradation has been shown to proceed more rapidly due to several factors related to running kinematics and kinetics, including (1) decreasing the recovery time between impacts 42 or (2) increasing the number of cycles, peak force, engineering stress, or loading rate. 42,43 However, understanding the origin and degree of footwear degradation was improved by also quantifying the subject-driven input parameters (i.e.…”

“…22,42 Degradation has been shown to proceed more rapidly due to several factors related to running kinematics and kinetics, including (1) decreasing the recovery time between impacts 42 or (2) increasing the number of cycles, peak force, engineering stress, or loading rate. 42,43 However, understanding the origin and degree of footwear degradation was improved by also quantifying the subject-driven input parameters (i.e. specific variables directly related to kinematics and kinetics), which helped explain why degradation generally occurred more rapidly for the MS shoe and forefoot region, compared to TS and heel, respectively.…”

Resources for sports engineering education

“…Allen et al [105] highlight the potential for auxetic foam to be applied to snow sport safety devices, and this paper could assist with teaching material fundamentals, such as stress, strain and Poisson's ratio. Recent work by Lippa et al [106,107] demonstrates how to mechanically age running shoes and assess degradation.…”

Effect of Rest Periods on Mechanical Ageing of Running Shoes

“…Mechanical ageing is a technique used to impose and measure shoe degradation by repeatedly compressing the midsole in a test machine to mimic running [4,[10][11][12][13][14][15][16]. The midsole is compressed many times, and the energy absorbed within a loading cycle is compared at set intervals related to running distances.…”

“…Recent work on mechanical ageing of shoes has used a dwell plus sine rather than the traditional continuous sine waveform [11][12][13][14] to factor in the time between foot strikes or 'float phase' of running. The short dwell periods (~0.5 s) allow the foam midsole to slightly recover and give less pronounced degradation that is more in line with natural ageing.…”