Combinatorial design of textured mechanical metamaterials

Abstract

The structural complexity of metamaterials is limitless, but, in practice, most designs comprise periodic architectures that lead to materials with spatially homogeneous features. More advanced applications in soft robotics, prosthetics and wearable technology involve spatially textured mechanical functionality, which requires aperiodic architectures. However, a naive implementation of such structural complexity invariably leads to geometrical frustration (whereby local constraints cannot be satisfied everywhere), which prevents coherent operation and impedes functionality. Here we introduce a combinatorial strategy for the design of aperiodic, yet frustration-free, mechanical metamaterials that exhibit spatially textured functionalities. We implement this strategy using cubic building blocks-voxels-that deform anisotropically, a local stacking rule that allows cooperative shape changes by guaranteeing that deformed building blocks fit together as in a three-dimensional jigsaw puzzle, and three-dimensional printing. These aperiodic metamaterials exhibit long-range holographic order, whereby the two-dimensional pixelated surface texture dictates the three-dimensional interior voxel arrangement. They also act as programmable shape-shifters, morphing into spatially complex, but predictable and designable, shapes when uniaxially compressed. Finally, their mechanical response to compression by a textured surface reveals their ability to perform sensing and pattern analysis. Combinatorial design thus opens up a new avenue towards mechanical metamaterials with unusual order and machine-like functionalities.

Exploiting Microstructural Instabilities in Solids and Structures: From Metamaterials to Structural Transitions

“…15(b)), and in aperiodic architectures, it typically prevents a coherent and predictable response. However, a combinatorial strategy was introduced recently to design aperiodic and frustration-free mechanical metamaterials that exhibit spatially textured functionalities [201].…”

Action-at-a-distance metamaterials: Distributed local actuation through far-field global forces

“…Designer materials, where rationally designed geometry at the small-scale gives rise to unusual material properties at the macro-scale, are often called metamaterials. Depending on the type of the targeted property, such designer materials may be called mechanical metamaterials, [1][2][3][4][5][6] optical metamaterials, 7-10 acoustic metamaterials, [11][12][13][14][15] or meta-biomaterials. [16][17][18] The unusual properties together with other design features could then be used to create advanced functionalities such as shape-morphing 19,20 and tunable/(re)-programmable mechanical behavior.…”

Snap-buckling in asymmetrically constrained elastic strips

“…Recently, new mechanical systems with emergent functionalities, so-called mechanical metamaterials, have been inspired by topological insulators, in which only the surface boundaries can behave as conductors [69]. Small mechanically asymmetric building blocks are combined, and it is now possible to create materials with unusual order and machine-like functionalities (e.g., using 3D printers) [70,71]. Several of the properties that we report in this study, such as the switch between compressive and tensile loading, the discontinuous force change upon snap-buckling, and hysteretic behavior, are all uniquely determined and predicted by the externally controllable strain ǫ y .…”