Automatic design of chiral mechanical metamaterials

Automatic design of mechanical metamaterials is key to achieving efficiencies in terms of a desired functionality that can far exceed the rationally designed man-made solutions. Here, we introduce a discrete element model capable of describing the mechanical response of three-dimensional trussed structures under a predetermined external perturbation and coupling it to an optimization algorithm in order to produce chiral mechanical metamaterials, twisting under compression and thus converting linear motion into rotation. By comparing the machine-designed structures with pre-existing human-designed solutions, we show that the former can achieve a much higher efficiency in terms of rotating angle per unit compressive strain. We confirm our results by finite element calculations and by experiments on 3D printed structures. The presented method paves the way to the discovery of novel functional mechanisms that can act over a broad size range, from micro- to macroscales, giving rise to a countless number of possible solutions for functional mechanical metamaterials.