An Auxetic Material With Negative Coefficient of Thermal Expansion and High Stiffness

Thermal stress has a negative effect on structural safety in many engineering fields, so it is particularly important to eliminate this negative effect as much as possible. This problem can be solved by designing the microstructure of the materials to make the coefficient of thermal expansion (CTE) close to 0, while negative thermal expansion (NTE) materials can become an important part of zero thermal expansion materials. Negative Poisson's ratio (NPR) materials have been favored by researchers because of their bright application prospects in many fields such as medical treatment and engineering. The research of lightweight mechanical metamaterials with both NTE and NPR effects is of great significance for the development of smart sensors with mechanical and temperature sensitivities, and the realization of multi-functional integration of structure. Inspired by the structure of natrolite, a material which can adjust the CTE and Poisson's ratio (PR) in a large range at the same time is designed in this paper. The analytical formulas of the equivalent CTE, PR and Young's modulus are derived and verified by finite element simulation. Meanwhile, the concept of stiffness index is introduced and analyzed by theoretical and finite element methods. Furthermore, the shear modulus of the material is analyzed by finite element method. The results show that the analytical formulas are valid for the material and the material can not only realize NTE and NPR effects at the same time, but also exhibits high stiffness in the principal axis and other directions. In addition, 3D material extended by the proposed 2D material is proposed and verified by finite element method whose parameter analysis have also been carried out, which can achieve NTE and NPR effects in three directions.