Functional nonlinearities enable compliance-switching in elastogranular structures
Embargo Date
2028-05-29
OA Version
Citation
Abstract
Mechanical metamaterials are engineered structures that exhibit mechanical properties that differ from their constituent parts. They often consist of repeating unit cells of a structural component, such as beams, plates, and shells, that introduce geometric nonlinearities (e.g. buckling, large rotations) which can be leveraged to create a structure with unique attributes (e.g. negative Poisson’s ratio; chirality). The combination of elastic components (shells and rods) and granular components (spheres and rocks) allows for the creation of a new set of metamaterials, where the relative – and often tunable – stiffness of each component dictates the resultant physical behavior. These elastogranular materials combine the geometric nonlinearities of mechanical metamaterials with a jamming-like phase transition to allow for new, functional behaviors. In this dissertation, experiments and scaling analyses are used to create and investigate elastogranular shells and knit columns for their tunable behavior. The elastogranular shells showcase compliance-switching, functionalization of defects, and shape-locking behavior while elastogranular knit columns exhibit load-bearing capability, tunable stiffness, and shear resistance. We begin by introducing a multilayered elastogranular shell composed of two elastic inner and outer shells sandwiching and fully encapsulating a monolayer of spherical grains. By changing the differential internal pressure applied to the shell, as well as the granular packing fraction of the enclosed grains, we are able to achieve tunable compliance-switching in the small deflection regime. We derive a scaling relation for the dimensionless force using parameters unique to elastogranular shells that build upon the classical theory of thin shells. Next, we take the same elastogranular shell platform and introduce vacancy defects in the granular arrangement. We explore the impact of these defects on critical buckling load in the large displacement regime. A range of indentation and defect locations are swept to better understand their interaction and effect on critical buckling behavior. Finally, we present elastogranular knit columns as a mechanical metamaterial for structural applications. We examine the effect of various parameters on knit column stiffness and resistance to shear. Then we model the behavior of the knit column to extract stiffness behavior. In this thesis we introduce an approach to analyzing adaptable structures whose tunable properties allow them to be utilized in multifunctional applications.
Description
2026