A hybrid design for bending and stretching dominated metamaterial with tailorable thermal expansion

In this work, a novel metamaterial with an enhanced programmable CTE range is proposed by combing the bi-material bending-dominated chiral unit cell and stretching-dominated triangle unit cell. In the design process, the three sides of the original triangle unit cell are replaced using bi-material anti-chiral unit cells with positive CTE or negative CTE. The materials with high CTE (Nylon) and low CTE (PVE) are selected to realize thermal deformation. Four models with a chiral block size of 80 × 80 mm², namely NTE#1, NTE#2, NTE#3, and NTE#4, are designed, analyzed, and discussed. To examine the tailorable CTE range and zero CTE, the parameter analyses are comprehensively carried out using the verified finite element models. The results demonstrate a more than threefold enhancement in the CTE range of the initial triangle metamaterial, accompanied by substantial improvements in its design smoothness, continuity, and flexibility. The combination design extended the tailorable CTE range to −710 ∼ 818 ppm/°C when the temperature increases from 30 °C to 60 °C. In addition, the curve of zero CTE with different parameter combinations is obtained. The aim of this work is to construct a new metamaterial with enhanced thermal–mechanical stability to balance the interface thermal deformation of composites in engineering devices, e.g., aerospace and precision instruments. Based on these findings, the structural stiffness and temperature range are still limited and worth studying further.