Metallic 2D and 3D re-entrant honeycomb auxetics produced by WAAM

This study addresses the main challenges in manufacturing large-scale metallic auxetic structures, characterised by a negative Poisson’s ratio, focusing on achieving suitable geometry control, surface finish, and structural integrity using Wire Arc Additive Manufacturing (WAAM). Specifically, the research employs the Cold Metal Transfer (CMT) process to fabricate 2D and 3D carbon steel auxetic cells. The primary objective is to address the challenges associated with the production of these structures. A comprehensive experimental and numerical analysis was conducted to investigate the influence of various factors, such as internal defects or geometric irregularities, such as pores and surface waviness, on the mechanical behaviour of the 2D and 3D auxetic cells under tensile and compressive loads, respectively. The compression tests revealed that despite minor defects and geometric imperfections, the manufactured cells consistently exhibit a negative Poisson’s ratio. This suggests that the WAAM-produced auxetic structures are viable and capable of maintaining their unique mechanical properties. Furthermore, the study emphasises the significance of parameters such as orientation and the number of auxetic cells in governing the overall auxetic behaviour of the components.