Thermally activated tunable auxeticity in periodic lattice structures

摘要

Auxetic lattice structures, characterized by a negative Poisson’s ratio, are advantageous in a variety of fields such as sports, architecture, soft robotics, and bio-medical devices. The auxeticity stems from the topology and the geometry of the struts. Currently, many well-known auxetic unit cells available in literature are employed to enhance performance. In this work, we propose a design concept for smart structures that transition from non-auxetic to auxetic through thermal excitation. We consider two infinitely periodic lattices - a square lattice and a triangular lattice - comprising bi-layer struts with different thermo-mechanical properties. Thermal excitation leads to the bending of the struts, thereby changing the conformation of the lattice and inducing an auxetic response. By employing moderate rotations theory, we develop tools that enable one to determine the thermally-induced deformations. Next, using finite element (FE) simulations, we investigate the dependence of the Poisson’s ratio and the response of the lattice on the geometry, the layer properties, and the applied thermal excitation. We show that temperature can be used to control the Poisson’s ratio over a wide range, which depends on the lattice topology. Specifically, periodic square lattices can achieve Poisson’s ratios between 0 to − 0 . 8 , and triangular lattices can switch between auxetic and non-auxetic behavior. The findings from this work can be used to design lattices with different topologies that exhibit a wide range of Poisson’s ratios and responses, which include transitions from auxetic to non-auxetic. • Design concept for thermally activated periodic lattices that transition from non-auxetic to auxetic. • Simulations showing a wide range of Poisson’s ratios that can be achieved using thermal excitation in periodic lattices. • Analytical equations that enable inverse design of the response of lattice structures via temperature. • Findings can be used to thermally induce a wide range of behaviors in lattice structures.