Bio-inspired-Rotational-Penetration-and-Self-burrowing-Robot

Seed awns (Erodium and Pelargonium) bury themselves into ground for germination usinghygroscopic coiling and uncoilingmovements. Similarly,wormlizards (Amphisbaenia) create tunnels for habitation by oscillating their heads along the long axis of the trunks. Inspired by these burrowing strategies, this research aims to understand these mechanisms from a soil mechanics perspective, investigate the factors influencing penetration resistance, and develop a self-burrowing technology for subterranean explorations. The rotational movements of seed awns, specifically their coiling and uncoiling movements, were initially examined using the Discrete Element Method (DEM) under shallow and dry conditions. The findings suggest that rotation reduces penetration resistance by decreasing penetrator-particle contact number and the force exerted, and by shifting the contact force away from vertical direction. The effects of rotation were illustrated through the force chain network, displacement field, and particle trajectories, supporting the "force chain breakage" hypothesis and challenging the assumptions of previous analytical models. The factors reducing penetration resistance were subsequently examined, both numerically and experimentally. The experimental results link the reduction of horizontal penetration resistance to embedment depth and penetrator geometry. Notably, both numerical and experimental results confirm that the reduction of penetration resistance is determined by the relative slip velocity, not by the absolute values. The reduction initially spikes sharply with the relative slip velocity, then increases at a slower rate, leveling off at higher relative slip velocities. Additional findings revealed a minimal impact of relative density, particle shape, and inertial number on penetration resistance reduction. Conversely, interface friction angle appeared to increase the reduction, while penetrator roundness and confining pressure decreased it. The investigation also extended to the effect of rotational modes on the reduction of penetration resistance. Reductions between cone-continuous rotation (CCR) and cone-oscillatory rotation (COR) cases were i comparable. However, whole-body-continuous rotation (WCR) yielded a higher reduction under the same relative slip velocities. Interestingly, the amplitude of oscillation movement demonstrated a negligible effect on the reduction. Lastly, a self-burrowing soft robot was constructed based on these insights. Preliminary findings indicate that the robot can move horizontally, leveraging a combination of extensioncontraction and rotational movements.