3D printing of chiral carbon fiber reinforced polylactic acid composites with negative Poisson's ratios

Auextic materials possessing negative Poisson's ratios have gained great research interest by virtue of its various exotic mechanical properties while most of these metamaterials rely on the hollow cellular configuration, largely undermining the overall mechanical performance. It therefore restricts their application in load-bearing engineering fields. In order to solve this issue, we first designed a new class of chiral structures by integrating various polynomial curves. Based on the state-of-the-art 3D printing technique, these auxetic geometries were then fabricated into high-performance composites with chopped carbon fiber (CF) as the reinforcement. Guided by experimental characterization and finite element analysis, the influences of the polynomial orders (n) and the incorporation of CF on the mechanical properties were systematically studied. Results showed that the auxetic behaviour can be tailored by varying the n value inside the polynomial equation. Moreover, the tensile modulus, strength and energy absorption at break of printed chiral samples were all enhanced with the addition of CF, especially for the large improvement of modulus and absorbed energy by 2-fold. Hence, these novel chiral composites present great potential in the development of high performance mechanical metamaterials.