Meeting Abstract
Legged, terrestrial animals use a variety of foot shapes for moving across diverse terrain. Granular substrates such as sand, snow and cobbles display complex behavior that can range from solid to fluid in a step. The effects of foot morphology on the dynamics of interaction between feet and granular substrates remain poorly understood. The goal of this study was to characterize the effect of toe spacing on foot-ground interactions. To this end, we measured the force response to the intrusion of two parallel square rods into dry poppy seeds while varying rod gap spacing. This interaction was also numerically simulated using the discrete element method (LIGGGHTS®), and the total force on the two intruders was calculated. We hypothesized that total force would decrease as the gap between the two rods increased, with the greatest force produced at a zero gap. Our results show, however, that a peak in the total force occurs at a gap of ~3 particle diameters, which was 20 % greater than the force at large separation (>11 particle diameters), beyond which total produced force plateaued. We propose that this peak in force is the result of particle jamming between the two intruders. To quantify the degree of particle jamming, interparticle forces at different gaps were calculated. As expected, the total number of strong forces—identified as force chains—in the particle domains indicated greater particle jamming at gaps surrounding the peak force. These findings indicate that gap size between toes can significantly affect total force response to granular intrusion, and particle jamming can play a determining role in identifying the optimal gap spacing between toes to maximize force response.
