Using 3D printers, researchers have created a metamaterial from cubic building blocks that responds to compression forces by a rotation. Usually, this can only be achieved by transmission using a crankshaft, for example. If a force is exerted from above onto a material, the latter deforms in various ways. It may be bulged, compressed, or bent; however, according to the rules of mechanics, it will not rotate.

The researchers designed a filigree cubic structure that reacts to loading by a rotation around its axis. Using computer simulation, a design was developed with the new mechanical property. Calculations revealed that the desired behavior is shown by a complex chiral structure, i.e. a structure that cannot be mapped to its mirror image, similar to the left and the right hand.

The filigree cubes consist of bars and rings that are connected to each other in a certain pattern. The arms that connect the ring structures with the corners of the cube move vertically downwards under load. This movement leads to a rotation of the rings. These rotation movements, in turn, transmit forces to the corners of the horizontal planes of the cube such that the complete structure starts to twist around its axis.

Towers of the cubic structures of variable sizes, strengths, and pieces were produced using a 3D microprinting method. The edge length of the cubes ranged from 100 to 500 μm. The researchers built towers of 4 to 500 cubes, and 2 mm height. To check their theory, the team also built towers of achiral cubes, i.e. cubes that can be mapped to their mirror image.

Forces from above are transmitted to the vertical ring structures via bars. The rotation of the rings exerts forces onto the corners of the horizontal planes of the cube. (T. Frenzel/KIT)
Towers of up to 500 chiral cubic structures rotated around their axis under load. Achiral structures do not exhibit this behavior. (T. Frenzel/KIT)

Towers assembled from chiral blocks started to rotate around their axis under the impact of force. A rotation was measured by up to two degrees per percent of deformation. The towers made of achiral cubic structures did not exhibit this rotation. The stiffness of the towers increased with the number of cubes, although the dimensions of the individual components decreased proportionally.

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