Development, 3D printing, and mechanics of novel auxetic unit cell monostructures

Complex structures with unique mechanics are pivotal to advancing additive manufacturing, enabling applications where traditional methods are impractical. This study presents a novel 3D auxetic S-shaped monostructure designed for scalability, tunability, and printability using vat photopolymerization. Unit cell geometries were fabricated and experimentally evaluated under quasi-static loading conditions, with full-field analyses providing insights into their structural performance. Benchmarking against common auxetic structures (re-entrant and star topologies) highlighted the superior capabilities of the proposed design. The S-shaped monostructures exhibited geometric insensitivity in their force-displacement responses, with a stiffness of similar to 180 N/m, withstanding large displacements of 11 mm without fracture or self-contact and supporting forces up to 1.8 N (i.e., 95 times their weight) before fully recovering upon unloading. Computational and experimental results demonstrated robust spatial auxeticity, persisting up to 85 % of axial global displacement due to geometry-driven rigid body motion, independent of base material properties. The S-shaped structures achieved superior auxetic performance (nu(maxti) approximate to -0.43) compared to re-entrant (nu(maxti) approximate to -0.30) and star (nu(maxti) approximate to - 0.05) counterparts, with a monotonic and reversible auxetic response throughout loading. Strain contour analyses from digital image correlation validated the reduced stress concentrations and rigid body-dominated mechanism. The exceptional auxeticity and mechanical resilience of the S-shaped monostructures suggest promising applications in advanced designs, including 3D stackable configurations for impact mitigation applications.