A Novel Re-Entrant-Type Metamaterial with Tunable Negative Poisson's Ratios and Coefficients of Thermal Expansion

Introducing bi-material double-triangular elements into a standard re-entrant structure, a novel metamaterial is proposed in this work. The effect of geometrical parameters on negative Poisson's ratio (NPR) and coefficient of thermal expansion (CTE) is studied theoretically and verified by finite element (FE) method. Results show that the proposed structure provides tunable Poisson's ratios in wide ranges (from negative to positive) by adopting base materials with different elastic moduli. The horizontal Poisson's ratio of the structure increases with the increment of the re-entrant angle, and decreases with the decrement of the elastic modulus ratio (i.e., the ratio of the elastic modulus of MAT-1 and MAT-2); while the vertical Poisson's ratio decreases with the increment of the re-entrant angle, but is independent on the elastic modulus ratio. Moreover, comparing with various reported re-entrant structures, the proposed design enhances elastic modulus significantly owing to the introduced bi-material triangles. The structure also exhibits tailorable CTEs. The CTE of the structure decreases with the increment of the CTE ratios and the re-entrant angle.