We analyse the anisotropic thermal expansion properties of a two-dimensional structurally rigid construct made from rods of different materials connected together through hinges to form triangular units. In particular, we show that this system may be made to exhibit negative thermal expansion coefficients along certain directions or thermal expansion coefficients that are even more positive than any of the component materials. The end product is a multifunctional system with tunable thermal properties that can be tailor-made for particular practical applications.

The highly symmetric hexachiral honeycomb with an isotropic Poisson’s ratio of −1 is one of the earliest and most well-known examples of auxetic mechanical metamaterials and has been proposed for numerous applications ranging from satellite antennas to stents. In this work, we propose a novel, less symmetric generic form of the hexachiral honeycomb that is made up of three sets of unequally sized ligaments rather than six identical ones and has the potential to exhibit a wide range of negative Poisson’s ratios. Using finite element analysis, we investigated the deformation behaviour of these generic hexachiral systems and derived an analytical model which may be used to predict the Poisson’s ratio of these systems. The results obtained indicate that the hexachiral topology is extremely versatile with respect to its potential to exhibit diverse mechanical properties and it is hoped that this added tunability will enhance the functionality and applicability of this class of auxetic mechanical metamaterials.