Three-dimensional auxetic materials with controllable thermal expansion

Thermal expansion and stress of solid materials can significantly affect structural safety and instrument accuracy in many engineering fields. An alternative way to overcome these drawbacks is to use materials with controllable coefficients of thermal expansion (CTEs). This work presents a new three-dimensional (3D) material with controllable CTEs that is composed of chiral honeycomb layers connected by a set of inclined struts. Although each single chiral layer has positive CTEs, by carefully designing geometric parameters and material constituents, the negative thermal expansion (NTE) can be established. Analytical solutions of the equivalent CTEs are proposed using the classical beam theory, which were verified by finite element simulations. The results show that the proposed material can achieve a large range of CTEs (from positive to negative), and has negative Poisson's ratios in the chiral honeycomb planes. In addition, isotropic negative and zero thermal expansion can be obtained with appropriate design parameters.