Real-time reversible tunable elasticity in cellular solids via electromagnetic actuation

The ability for reversible, real-time control of elastic moduli in solids can find significant application in advanced mechanical components, protective structures, and biomedical devices. Here, we propose a novel concept for controlling the linear and nonlinear elastic properties of cellular structures via electromagnetically triggered mechanisms in the cellular solid. Three structural systems with orthotropic material properties were proposed and studied numerically, experimentally, and analytically. Using the proposed concept, the elastic modulus can be controlled over two to four orders of magnitude. The Poisson ratio of the isotropic structure can be varied from 0 to 0.5 continuously. The adjustments over nonlinear elastic (i.e., buckling) behavior of the structure are achieved by activation of supplementary cell walls in the lattice through electromagnetic actuation. Magnetic actuation will hamper the first symmetrical buckling pattern of the structure and force the structure to buckle according to a higher buckling pattern with smaller sinusoidal wavelength in the cell walls. The uniaxial buckling strength of the structure was tuned over two orders of magnitude

SpiderWeb honeycombs

A new class of hierarchical fractal-like honeycombs inspired by the topology of the “spiderweb” were introduced and their small and large deformations were investigated analytically, numerically, and experimentally. Small deformation elasticity results show that the isotropic in-plane elastic moduli (Young’s modulus and Poisson’s ratio) of the structures can be controlled over several orders of magnitude by tuning dimension ratios in the hierarchical pattern of spiderweb, and the response can vary from bending to stretching dominated. In large deformations, spiderweb hierarchy postpones the onset of instability compared to stretching dominated triangular honeycomb (which is indeed a special case of the proposed spiderweb honeycomb) and exhibits hardening behavior due to geometrical nonlinearity. Furthermore, simple geometrical arguments were obtained for large deformation effective Poisson’s ratio of first-order spiderweb honeycombs, which show good agreement with numerical and experimental results. Spiderweb honeycombs exhibit auxetic behavior depending on the nondimensional geometrical ratio of spiderweb

Lattice Materials With Reversible Foldability

The authors introduce a new class of lattice materials, where a controlled simultaneous folding of the lattice walls results in a significant size reduction while preserving the overall shape of the original lattice. This reversible folding scheme results in 67 and 50% reduction in size at each level for lattices with triangular and square grid topologies, respectively, while the design enables multiple levels of folding to achieve a desired final size. The authors study the elastic properties and the phononic band structure of the lattice at different stages of folding, using analytical and finite element methods. The proposed concept provides new opportunities for the development of multifunctional deployable structures through significant changes in the size and properties of lattice materials by folding

Origami-Based Cellular Metamaterial With Auxetic, Bistable, And Self-Locking Properties

We present a novel cellular metamaterial constructed from Origami building blocks based on Miura-ori fold. The proposed cellular metamaterial exhibits unusual properties some of which stemming from the inherent properties of its Origami building blocks, and others manifesting due to its unique geometrical construction and architecture. These properties include foldability with two fully-folded configurations, auxeticity (i.e., negative Poisson\u27s ratio), bistability, and self-locking of Origami building blocks to construct load-bearing cellular metamaterials. The kinematics and force response of the cellular metamaterial during folding were studied to investigate the underlying mechanisms resulting in its unique properties using analytical modeling and experiments

Honeycomb phononic crystals with self-similar hierarchy

We highlight the effect of structural hierarchy and deformation on band structure and wave-propagation behavior of two-dimensional phononic crystals. Our results show that the topological hierarchical architecture and instability-induced pattern transformations of the structure under compression can be effectively used to tune the band gaps and directionality of phononic crystals. The work provides insights into the role of structural organization and hierarchy in regulating the dynamic behavior of phononic crystals, and opportunities for developing tunable phononic devices.Engineering and Applied Science

Hierarchical honeycomb auxetic metamaterials

Most conventional materials expand in transverse directions when they are compressed uniaxially resulting in the familiar positive Poisson’s ratio. Here we develop a new class of two dimensional (2D) metamaterials with negative Poisson’s ratio that contract in transverse directions under uniaxial compressive loads leading to auxeticity. This is achieved through mechanical instabilities (i.e., buckling) introduced by structural hierarchy and retained over a wide range of applied compression. This unusual behavior is demonstrated experimentally and analyzed computationally. The work provides new insights into the role of structural organization and hierarchy in designing 2D auxetic metamaterials, and new opportunities for developing energy absorbing materials, tunable membrane filters, and acoustic dampeners