’Buckliball’ opens new avenue in design of foldable engineering structures

Inspired by a toy, the 'buckliball' - a collapsible structure fabricated from a single piece of material - represents a new class of 3-D, origami-like structures. Motivated by the desire to determine the simplest 3-D structure that could take advantage of mechanical instability to collapse reversibly, a group of engineers at MIT and Harvard University were stymied - until one of them happened across a collapsible, spherical toy that resembled the structures they'd been exploring, but with a complex layout of 26 solid moving elements and 48 rotating hinges. The toy inspired the engineers to create the "buckliball," a hollow, spherical object made of soft rubber containing no moving parts, but fashioned with 24 carefully spaced dimples. When the air is sucked out of a buckliball with a syringe, the thin ligaments forming columns between lateral dimples collapse. This is the engineering equivalent of applying equal load on all beams in a structure simultaneously to induce buckling, a phenomenon first studied by mathematician Leonhard Euler in 1757. When the buckliball's thin ligaments buckle, the thicker ligaments forming rows between dimples undergo a series of movements the researchers refer to as a "cooperative buckling cascade." Some of the thick ligaments rotate clockwise, others counterclockwise - but all move simultaneously and harmoniously, turning the original circular dimples into vertical and horizontal ellipses in alternating patterns before closing them entirely. As a result, the buckliball morphs into a rhombicuboctahedron about half the size (46 percent) of the original sphere.