Liu, M., Domino, L., de Dinechin, I. D., Taffetani, M., & Vella, D.* (2023). Snap-induced morphing: From a single bistable shell to the origin of shape bifurcation in interacting shells. J Mech. Phys. Solids, 170, 105116.

Abstract: The bistability of embedded elements provides a natural route through which to introduce reprogrammability to elastic meta-materials. One example of this is the soft morphable sheet, in which bistable elements that can be snapped up or down, are embedded within a soft sheet. The state of the sheet can then be programmed by snapping particular elements up or down, resulting in different global shapes. However, attempts to leverage this programmability have been limited by the tendency for the deformations induced by multiple elastic elements to cause large global shape bifurcations. We study the root cause of this bifurcation in the soft morphable sheet by developing a detailed understanding of the behaviour of a single bistable element attached to a flat ‘skirt’ region. We study the geometrical limitations on the bistability of this single element, and show that the structure of its deformation can be understood using a boundary layer analysis. Moreover, by studying the compressive strains that a single bistable element induces in the surrounding skirt we show that the shape bifurcation in the soft morphable sheet can be delayed by an appropriate design of the lattice on which bistable elements are placed.

Mao, J. J.*, Wang, S., Tan, W.*, & Liu, M.* (2022). Modular multistable metamaterials with reprogrammable mechanical properties. Engineering Structures, 272, 114976.

Abstract: Owing to extensive potential applications in various engineering areas, the multistable metamaterials with remarkable mechanical properties have gained increasing interest from both academia and industry recently. However, the functionality of existing multistable metamaterials is hard to adjust once fabricated. To overcome the limitation, in this paper, we propose an idea of modular multistable metamaterial (MMM) with reprogrammable mechanical properties, which is assembled by unit cells with tunable snap-through behaviours. The unit cell is made by a dismountable bar and a fixed frame containing two bistable curved beams. By inserting the bar with different length into the frame, we can change the shape of curved beams and therefore tune the snap-through behaviour of the unit cell, which lies the foundation of its tunable multistabilities. We evaluate these tunabilities of geometry and mechanical properties of single unit cell by employing theoretical analyses and validate them by numerical simulations. The obtained quantitative results provide us the design guide for assembling of the MMM. We fabricate a certain number of components by 3D printing and assemble them as a unidirectional MMM to examine its reprogrammable macroscopic mechanical behaviours. We firstly investigate the tunable load–displacement responses experimentally and numerically; and then explore the tunable bandgaps through numerical simulations. Finally, we demonstrate the broader possibilities of assembly to form bi- and tri-directional, as well as gradient MMMs. The results presented in this paper have great significance for the design of modular metamaterials and expanding their application prospects in engineering structures.