S1E3

Abstract:

Owning to the shape-morphing capacities of Kirigami, this paper cutting ancient art have inspired a variety of engineering advancements, especially in soft robotics and flexible electronics. Distinct from shape-shifting of an origami sheet which is mainly governed by folding pattern geometries, shape-morphing of a kirigami patterned sheet is governed by both pattern geometry and applied loading conditions through stretching, bending, and twisting. Through experiments, theoretical formulation, and finite element simulation, I will demonstrate how to exploit the simplest form of kirigami, linear parallel cut pattern, for tunnable architected materials and soft robotic gripper.

Abstract:

Kirigami, has recently enabled the design of stretchable mechanical metamaterials that can be easily realized by embedding arrays of periodic cuts into an elastic sheet. While in flat kirigami sheets, the ligaments buckle simultaneously as Euler columns, leading to a continuous phase transition; in this talk, I will demonstrate that kirigami shells can also support discontinuous phase transitions. Specifically, in cylindrical kirigami shells, the snapping-induced curvature inversion of the initially bent ligaments results in a pop-up process that first localizes near an imperfection and then, as the deformation is increased, progressively spreads through the structure. We find that the width of the transition zone as well as the stress at which propagation of the instability is triggered can be controlled by carefully selecting the geometry of the cuts and the curvature of the shell.

Moreover, we also exploit kirigami principles to design inflatables that can mimic target shapes upon pressurization. Our system comprises a kirigami sheet embedded into an unstructured elastomeric membrane. We show that the inflated shape can be controlled by tuning the geometric parameters of the kirigami pattern. Then, by applying a simple optimization algorithm, we identify the best parameters that enable the kirigami inflatables to transform into a family of target shapes at a given pressure. Furthermore, thanks to the tessellated nature of the kirigami, we show that we can selectively manipulate the parameters of the single units to allow the reproduction of features at different scales and ultimately enable a more accurate mimicking of the target.

Abstract:

The integration of soft materials—biological tissues, hydrogels, ionogels, and elastomers—is a rapidly developing fundamental technology of our time. Whereas hard materials have been adhered using adhesives of hard polymers since antiquity, these hard polymers are in general unsuited to adhere soft materials, because the hard polymers constrain the deformation of the soft materials. This paper describes a design principle to use hard polymers to adhere soft materials, such that adhesion remains tough after the adhered soft materials are subject to many cycles of large stretch in the plane of their interface. The two soft materials have stretchable polymer networks, but need not have functional groups for adhesion. We adhere the two soft materials by forming, in situ at their interface, islands of a hard polymer. The adhesion is tough if the islands themselves are strong, and the polymers of the islands are in topological entanglement with the polymer networks of the two soft materials. The adhesion is stretchable if the islands are smaller than the flaw sensitivity length. We demonstrate several methods of forming the hard polymer islands, and study the mechanics and chemistry of adhesion. The design principle will enable many hard polymers to form tough and stretchable adhesion between soft materials.