Shape-changing shell-like structures

Abstract

Plants such as Dionaea muscipula (Venus Flytrap) can change the shape of their shell-like leaves by actively altering the cell pressures. These leaves are hydraulic actuators that do not require any complex controls and that possess an energy efficiency that is unmatched by natural or artificial muscles (Huber et al 1997 Proc. R. Soc. A 453 2185-205). We extend our previous work (Pagitz et al 2012 Bioinspir. Biomim. 7 016007) on pressure-actuated cellular structures by introducing a concept for shape-changing shell-like structures that can significantly alter their Gaussian curvature. The potential of this concept is demonstrated by a hemispherical shell that can reversibly change the sign of its Gaussian curvature. Furthermore, it is shown that a snap-through behaviour, similar to the one known from Dionaea muscipula, can be achieved by lowering the pressure in a single layer of cells.

Fast nastic motion of plants and bioinspired structures

“…Inspired by the hydraulic movements of D. muscipula and M. pudica, Pagitz et al developed a model for morphing structures driven by pressure-actuated cellular structures [99]. The researchers further refined this model by introducing a shell-like structure that can, through its characteristic "snap-through" morphology, change the sign of its Gaussian curvature [100]. These shape changing structures, driven by multi-layer cellular pressure actuation, have potential applications in aerospace engineering, automobile engineering, architectural design, etc.…”

Experimental study on bistable behaviour of anti-symmetric laminated cylindrical shells in thermal environments

“…As a novel composite structure, not only does it have the advantages of light weight, superior mechanical properties and higher utilization ratio in space, but also is able to stay in two different stable shapes without the need for an ongoing actuation force [1]. This makes bistable composite structures promising candidates as morphing structures in various fields, such as morphing skins [2], wind turbine blades [3], unmanned air vehicle (UAV) wings [4] and vibration energy harvesting [5], etc. There are two kinds of bistable structures in general: [0/90] n unsymmetric cross-ply laminate [6] and [+a/Àa] n anti-symmetric laminated cylindrical shell (ALCS) [7].…”

Geometrically controlled snapping transitions in shells with curved creases

“…For example, Venus flytraps (Dionaea muscipula) use this mechanism to generate a snapping motion to close their leaves (11), hummingbirds (Aves: Trochilidae) twist and rotate their curved beaks to catch insect prey (14), and engineered microlenses use a combination of bending and stretching energy to rapidly switch from convex to concave shapes to tune their optical properties (12). Despite the ability to engineer bistability and snapping transitions in a variety of systems by using prestress or material anisotropy (18)(19)(20)(21)(22)(23)(24), a general geometric design rule for creating a snap between stable states of arbitrary surfaces does not exist. This stands in stark contrast to the well-known rules and consequences for folding of a flat sheet, as shown in origami design (25)(26)(27).…”