Design and Mechanical Properties of a 3D Orthogonal U‐Shaped Accordion Zero Poisson's Ratio Metamaterial

This paper presents a 3D orthogonal U‐shaped accordion zero‐Poisson's‐ratio metamaterial (3D‐OUA) for a honeycomb structure with dimensional stability, tunable mechanics, and high impact absorption. The design merges a re‐entrant auxetic unit with accordion‐bellows folding. By altering the transverse bars in the re‐entrant zone and replacing the sharp corners with cosine‐curved rods, the structure exhibits a clear zero‐Poisson's‐ratio effect in the elastic regime and alleviates local stress concentrations. A finite element model (FEM) in Ansys Material Designer computes equivalent Young's modulus, shear modulus, and Poisson's ratio in the linear elastic regime, validated by quasi‐static compression tests. The effects of four key adjustable geometric parameters, namely the cosine‐rod amplitude A , cosine‐rod half‐period h , rod width t , and extrusion depth b , on the equivalent properties are explored. A 3D‐OUA array‐filled crash box is assessed under frontal low‐speed impact, oblique impact, and varying velocities, and compared with hexagonal nested and cross‐shaped fillings. Under the 10° oblique impact, the total energy absorption of 3D‐OUA is approximately 4.14% higher than that of cross‐shaped. Results show near‐zero Poisson's ratio, tunable properties, and improved crashworthiness with enhanced energy absorption and lower peak crushing force.