3D-printed short carbon fibre reinforced perforated structures with negative Poisson's ratios: Mechanisms and design

This study investigates the compressive responses and mechanisms of perforated structures made of pure nylon polymer (NP) and short carbon fibre reinforced nylon polymer (SCF/NP) with negative Poisson's ratio (NPR), and proposes an improved lightweight auxetic structure. A theoretical analysis is performed for predicting the Poisson's ratios of perforated auxetic structures, and validated experimentally. A comparison between conventional and auxetic perforated structures under compression shows that the SCF/NP specimens have higher stiffness than the NP structures and the auxetic structure can reach a NPR of about −1. The effects of perforation geometry and material type on the mechanical properties are investigated. Results depict a decrease in nominal stress with an increase in the perforation gap, but the perforation gap increase leads to enhancement of relative density, effective strain and average Poisson's ratio. Further, SCF/NP structures have advantages over NP structures due to their higher effective strain, effective specific energy absorption (SEA) and relative Young's modulus. Subsequently, an improved auxetic structure is designed, and a comparative study between the designed structure and two common auxetic structures (with the same relative density of 0.32) shows that the designed auxetic structures have the highest SEA and relative Young's modulus with the strongest auxetic effect (smallest average Poisson's ratio).