Mechanical metamaterials with programmable compression-twist coupling

The rational design of mechanical metamaterials has the potential to grant them with properties unattainable by bulk materials. This paper describes twisting mechanical metamaterials (TMMs), a new class of programmable matter whose rationally designed architecture endows them with compression-twist coupling, a property absent in conventional materials. Upon compression, the cellular architecture of TMMs efficiently transforms longitudinal strain into unidirectional or bidirectional twisting—free from mechanical frustrations and independent of the flexible material chosen to fabricate the TMM. TMMs can be rapidly designed using an automated generative algorithm, which enables the tailoring of their twisting properties (up to 3.24° twist per % strain) and Poisson's ratio (−0.6 to +1.22) using only two design parameters. The scalable architecture of TMMs does not suffer from size effects which impair their twist per unit strain. Bidirectional TMMs autonomously switch their direction of rotation during uniform displacement-controlled compressive loading, conferring them with non-interchangeable compression-twist coupling. The capability of TMMs to controllably convert translation to rotation blurs the boundary between materials and machines, expanding the range of mechanical properties currently accessible to 3D printed materials and paving the way toward the creation of future programmable matter. (paper)