General assembly rules for metamaterials with scalable twist effects

Abstract

Metamaterials with twist effects can exhibit remarkable rotational deformation under tension or compression, a behavior that is uncommonly observed in conventional materials. Despite its promise in achieving complex engineering functionalities, the twist effect is unscalable and will quickly diminish as the number of unit cells increases, which is the major restriction for practical applications. In this study, we use screw theory to rigorously analyze the relationship between microscale geometries and twist effects, unraveling the mechanism underlying the loss of scalability. We further propose a general assembly rule for metamaterial crystals to achieve scalable effects. A simplified analytical model is developed to characterize the scalability of the twist. Through simulation, analytical models, and physical experiments, we demonstrate the flexibility and superiority of the proposed assembly rules in enabling scalable twist effects for various unit-cell designs, different strain levels, and even twists around multiple axes. This constitutes an important step towards scaling up the twist effects for real applications.