Variable Stiffness Metastructures Through Reversible Lamination

Temporal control of structural stiffness can enable on-demand customized mechanical performance, with potential applications ranging from robotic grippers to morphing space structures. A key requirement for these applications is the ability to operate in many stiffness regimes, so as to adapt to a wide spectrum of loading conditions. Existing methods address this challenge by constructing lattices consisting of variable stiffness components leveraging electromagnets or bi-stable structures. However, these implementations do not consider the weight or energy efficiency of the structure, both critical constraints in aerospace applications. Additionally, the lack of computationally efficient predictive models prevents operation in real-time. In this work, we demonstrate a novel variable stiffness metastructure concept composed of hinges where steel sheets are reversibly laminated with dry adhesives via electrostatic actuation. The hinges are lightweight, maintain all stiffness regimes passively, and offer simple boundary conditions for integration into lattices. These hinges are combined into an anti-tetrachiral lattice, transforming binary stiffness modulation of individual elements in bending into high-resolution stiffness control of the entire structure in compression. Using an analytic and semi-empirical homogenization approach, we develop and validate an efficient modeling technique with a 100x improvement in computational time over full-fidelity finite element simulations. We demonstrate precise stiffness control with 256 achievable stiffness states in a lattice with only 12 variable stiffness hinges.