Dynamic interactions of a driven pendulum with photoelastic granular media

Interactions between a speed-driven pendulum and an array of photoelastic particles are studied to further the current understanding of granular media response during legged locomotion. A two-dimensional experiment is set up and used to study the motions of granular particles and force chains inside the media. A pendulum with a drive at the pivot is used to swing the pendulum through the granular media. For four different pendulum actuation speeds, high speed videos are recorded in order to capture granular media response during the interactions with the pendulum. Image processing algorithms are employed to track positions and calculate velocities of the granular particles. For all studied drive speeds, the maximum particle speed in the vertical direction is found to be the same, whereas in the horizontal direction, the maximum particle speeds are found to be higher with higher rotor speeds. In addition, the photoelastic property of the particles allows the authors to observe force distribution inside the media, and the evolutions of force chains in two dimensions. For a selected drive speed, snapshots of the force chains inside the granular media during the interactions with the pendulum are presented. Through this study, the authors have introduced dynamical use of photoelastic particles to unravel soil dynamics during legged locomotion. This approach can be used to obtain insights into particle dynamics and force chains inside the media and form a picture of the collective soil behavior during interactions with locomotion mechanisms.