Three-dimensional mechanical metamaterials with a twist

Abstract

Rationally designed artificial materials enable mechanical properties that are inaccessible with ordinary materials. Pushing on an ordinary linearly elastic bar can cause it to be deformed in many ways. However, a twist, the counterpart of optical activity in the static case, is strictly zero. The unavailability of this degree of freedom hinders applications in terms of mode conversion and the realization of advanced mechanical designs using coordinate transformations. Here, we aim at realizing microstructured three-dimensional elastic chiral mechanical metamaterials that overcome this limitation. On overall millimeter-sized samples, we measure twists per axial strain exceeding 2°/%. Scaling up the number of unit cells for fixed sample dimensions, the twist is robust due to metamaterial stiffening, indicating a characteristic length scale and bringing the aforementioned applications into reach.

New Twists of 3D Chiral Metamaterials

“…Motifs of 3D periodic chiral mechanical metamaterials. [25] Other work has successfully demonstrated this mapping, [19] but not in a unique manner. [18] b) A metamaterial based on this chiral unit cell has been realized and characterized experimentally in ref.…”

“…Metamaterials with bistable or buckling unit cells also show such scale-dependent behavior. [19]. [10,26] Other recent work on artificial chiral architectures in 3D has pointed at the importance of chirality in shearing auxetics (see Figure 1d), in that mechanically rigid and compliant structures can be created by combining elements with different handedness.…”

“…It allows for "programming" the effective properties of the metamaterial over a relatively wide range. [19] d) Chiral shearing auxetic. [20] Adv.…”

“…Static Regime: While the theory of Eringen chiral micropolar continuum mechanics (and Cosserat mechanics) has been worked out many years ago, [16] detailed blueprints for experiments on corresponding chiral 3D metamaterials have only been published quite recently. [18][19][20][21][22][23] Figure 1 shows a selection of schemes of corresponding metamaterial unit cells.…”

Encoding Smart Microjoints for Microcrawlers with Enhanced Locomotion

“…Using direct laser writing (DLW), we demonstrate that the bilayer‐based microbeam made of pH‐response smart materials can trigger a size‐dependent layer‐by‐layer sequential swelling effect that induces nonmonotonic bending deformations during the swelling process. This inspired us to fabricate 4D‐printed microcrawlers with controllable microjoint structures capable of spontaneous deformations in response to ambient pH stimulation.…”