The Buckliball: Pressure Induced Pattern Transformation of a Structured Elastic Shell

We report an experimental and computational study of a patterned elastic shell which, under pressure loading, undergoes a transformation in its structural configuration. The geometry of the ball comprises of an elastomeric spherical shell patterned with a regular array of circular holes. These voids are covered with a thin membrane, thereby making the ball air tight. Upon reduction of the internal pressure, the thin membranes first invert their curvatures inward. Consequently, beyond the critical pressure, the thin ligaments between the holes buckle leading to a cooperative buckling cascade of the skeleton of the ball. During this process, the initially circular holes evolve into an elliptical shape, and eventually become fully closed. This pattern transformation is induced by mechanical instability that opens the possibility for reversible encapsulation, over a wide range of length scales.