Compliance-Shifting Structures using Elastogranular Shells

Shells and grains separately exhibit complex nonlinear behavior when confined - shells buckle and snap, while grains transition from fluid-like to solid-like. When coupled, elastogranular structures have the ability to display a remarkable variety of mechanical behaviors. Here we create an elastogranular shell where spherical grains are sandwiched between two thin, elastic layers. By evacuating the air enclosed by the two layers, we can tune the stiffness of the elastogranular shell and alter its critical buckling load. Introducing controlled defects in the arrangement of the grains allows us to more finely tune critical buckling parameters, as the shell must balance the combined effects of defect size and resultant granular packing density. Defects in the surface of jammed grains have a counterintuitive effect on the shell’s buckling load, as they can stiffen the shell away from the defect. Using our elastogranular shell model, we better understand the associated mechanics in order to utilize buckling behavior in potential applications for creating compliance-switching structures in soft robotics.