Collaborative Research: Elasto-Granular Interactions Between Morphing Skins and Soils

This award will support research at the intersection of geotechnical engineering and structural mechanics, with an eye toward the realization of flexible burrowing probes for applications including site investigation and underground excavation. Flexible probes and robots typically comprise a linear actuator and a compliant skin – a shell-like structure that is carefully patterned to achieve desired and usually extreme morphing behaviors. As the actuator elongates or shortens, the skin interacts with the surrounding soil, endowing the probe with the capacity of moving through the burrow following bioinspired forms. To overcome limitations imposed by current skin designs, this research introduces the idea of multi-modal skins, that can radially expand while generating pop-up features that induce the anisotropic friction necessary for motion within the burrow. To avoid extensive trial and error in the skin design, this project aims at providing an understanding of the “elasto-granular” interactions between elementary features of such morphing skins (e.g., the pop-up plates that yield anisotropic friction) and granular media. This understanding is leveraged to realize a burrowing probe that will be subjected to extensive tests to evaluate the burrowing performance of the skin and its capacity to interact with the surrounding soil in meaningful ways. The ideas within this project will promote the utilization of flexible geotechnical systems, that leverage structural flexibility to achieve innovative functionalities. Moreover, the knowledge on elasto-granular interactions created in this project can be exported to other fields, such as agriculture and biomedical engineering. Our outreach and educational activities, revolving around the theme of “flexible civil engineering systems”, will give students opportunities to see civil engineering systems under a new light and to understand that flexible structures, like those found in nature, are extremely useful in a variety of civil engineering applications. The primary objective of this research is to provide an understanding of the microscopic and macroscopic interactions between “architected” shape-morphing shells and granular media and to leverage this knowledge to guide the realization of probes for underground burrowing and exploration. To reach this objective, our work aims at exploring the interface between the nonlinear mechanics of flexible structures and the mechanics of granular media and soils. This research will use a holistic approach based on: i) theoretical studies on the skins’ morphing capacity using structural mechanics and kinematic theories; ii) stress predictions using the finite element method; iii) studies on microscopic elasto-granular interactions via discrete element modeling and X-ray CT scan-assisted direct shear experiments; and v) macroscopic validation of skin behavior via visualization tank experiments and discrete-element simulations on the burrowing of a probe equipped with such skin. This project will lay the foundation for the rational application of architected shells as morphing skins for burrowing probes. This project is jointly funded by the Engineering for Civil, Mechanical and Manufacturing Innovation (CMMI) Division and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.