Buckling-induced encapsulation of structured elastic shells under pressure

Abstract

We introduce a class of continuum shell structures, the Buckliball, which undergoes a structural transformation induced by buckling under pressure loading. The geometry of the Buckliball comprises a spherical shell patterned with a regular array of circular voids. In order for the pattern transformation to be induced by buckling, the possible number and arrangement of these voids are found to be restricted to five specific configurations. Below a critical internal pressure, the narrow ligaments between the voids buckle, leading to a cooperative buckling cascade of the skeleton of the ball. This ligament buckling leads to closure of the voids and a reduction of the total volume of the shell by up to 54%, while remaining spherical, thereby opening the possibility of encapsulation. We use a combination of precision desktop-scale experiments, finite element simulations, and scaling analyses to explore the underlying mechanics of these foldable structures, finding excellent qualitative and quantitative agreement. Given that this folding mechanism is induced by a mechanical instability, our Buckliball opens the possibility for reversible encapsulation, over a wide range of length scales.

Buckling Pneumatic Linear Actuators Inspired by Muscle

“…[12][13][14] An emerging opportunity in the engineering of soft machines is to harness these instabilities to achieve new functionalities. [15][16][17] For example, buckling has proven useful in the design of stretchable soft electronics, [18,19] tunable materials, [20][21][22][23] and fluidic actuators. [24] We have previously demonstrated that reversible buckling of elastomeric beams can be used to make a torsional soft actuator.…”

Elastomeric Tiles for the Fabrication of Inflatable Structures

“…We derived the designs of the structures that we fabricated and tested empirically, but they are conceptually related to shape-changing solids. [18][19][20]23] Future demonstrations will apply the design rules established in these related structures to optimize and expand the varieties of motions achievable by soft structures. Further, the advantages this approach offers to the fabrication of topologically complex (in terms of mechanical and physical properties) structures will provide routes to new shape-changing structures with additional functionalities (e.g., electrical conductivity) that were previously inaccessible.…”

“…[18][19][20][21][22][23] This control is achieved by designing structures with mechanical instabilities that buckle in a predictable way when subjected to mechanical deformation (e.g., compression). [18][19][20]23] Following this approach it is possible to produce structures that undergo large (>50%), isotropic volume changes, and that have negative…”

“…[19,20] Shape-changing solids offer functionality that is useful to a range of applications including encapsulation, impact absorption, filtration, and rapid construction (i.e., foldable/deployable structures). [19] We have developed a new class of soft actuators-PDMS structures containing embedded pneumatic networks (pneu-nets)-that operate by the pressurization and inflation of these pneunets. [4] By designing systems that incorporate multiple, independently addressable pneu-nets, we have created soft machines and robots that are inexpensive, light weight, and simple to fabricate, design, and operate.…”

Self-Folding Textiles through Manipulation of Knit Stitch Architecture

“…Structures have also been created through the use of three-dimensional (3D) printing technology, where engineered mechanical instabilities produce folding behaviors as the object is compressed [8]. Using origami-like patterns and the self-folding behavior of knits, textiles exhibiting auxetic behavior have been developed [9][10][11][12][13].…”