Toward enhanced mechanical rigidity: additive manufacturing of auxetic tubes with PU core and comparative analysis of unique structural behaviors

The pursuit of enhancing manufacturing and production processes has given rise to Additive Manufacturing, a methodology characterized by the production of polymeric, metallic, or composite components with high precision, commonly referred to as three-dimensional printing technology (3D printing). Currently gaining momentum across various sectors, 3D printing is favored for its streamlined production using CAD models in software, finding applications in health, structural and numerical optimization, industrial and construction, automotive, aerospace, and other fields. Furthermore, in the realm of advanced materials, research aims to discover unique structures with noteworthy properties. Auxetic structures, notable for their negative Poisson's ratio, present a characteristic that diverges from conventional materials, showcasing volumetric expansion under tensile forces, in contrast to the contraction experienced by conventional materials. This study endeavors to fabricate auxetic tubes filled with a PU core using Additive Manufacturing and subject them to compression tests. The mechanical test responses will be analyzed and compared with existing literature to assess the enhancement in mechanical rigidity without a significant increase in structural weight. Results indicate that the re-entrant structure yielded the best outcomes, with an energy absorption ratio of 1.08 J/g and an incremental ratio of 23.59, correlating the percentage increase in energy absorption with the percentage increase in mass. Additionally, unexpected behaviors were observed in certain structures: the anti-trichiral structure exhibited a Zero Poisson Ratio (ZPR) behavior, and the dragonfly structure, while inconclusive, leaned toward a ZPR behavior due to the foam diminishing the auxetic effect of the structure.