A novel 3D structure with tunable Poisson's ratio and tailorable coefficient of thermal expansion based on a tri-material triangle unit

Auxetic materials and negative thermal expansion materials show great application potential in many important fields. In this paper, a novel three-dimensional truss structure with a tunable Poisson's ratio and tailorable coefficient of thermal expansion was developed. Since the deformation of each rod was dominated by axial tension or compression, the structure showed high stiffness. Equations regarding equivalent elasticity parameters and coefficients of thermal expansion of the structure were obtained by displacement and unit force methods. A numerical simulation verification was performed by ANSYS 16.0 software. The verification results indicated that the formulas have high precision and wide application scope. Through parametric analysis, we obtained the conditions for achieving a negative Poisson's ratio and negative thermal expansion coefficient. We also concluded that this material could realize a three-dimensional negative Poisson's ratio and bidirectional negative thermal expansion simultaneously by choosing reasonable geometric parameters and material combinations.