Beyond Poisson’s Ratio: Material–Process Performance of Additively Manufactured Auxetic Lattices

Auxetic lattices are usually tailored through geometry, whereas the effect of the constituent material and manufacturing route at fixed architecture has received little replicated experimental attention. One re-entrant lattice design was produced in nine material/process variants and tested in quasi-static tension (10 specimens per variant, N = 90): polylactic acid (PLA), impact-modified PLA, glycol-modified polyethylene terephthalate (PETG), acrylonitrile butadiene styrene (ABS), acrylonitrile styrene acrylate (ASA), UltraT and Flex 3D by fused deposition modeling (FDM), and polyamide 12 (PA12) by FDM and by selective laser sintering (SLS). Maximum force Fmax, crosshead displacement at peak load u(Fmax), archived structural stiffness k and mechanical work W14 up to 14 mm displacement depended strongly on the variant (p < 0.001; Kruskal–Wallis ε2 = 0.908–0.942). PLA reached the highest mean Fmax (68.48 ± 2.40 N), whereas PETG accumulated the highest mean W14 (622.80 ± 28.03 N mm), 7.9% more than PLA (95% simultaneous confidence interval 1.2–14.5%), despite a 4.3% lower Fmax. SLS PA12 exceeded FDM PA12 by 11.0% in Fmax and by 21.9% in W14. The W14 ranking refers to the 14 mm limit, and k is interpreted as an archived descriptor. Previously processed optical measurements gave effective Poisson’s ratios of −1.043 to −1.052 for eight variants; these values are reported descriptively, and a linear finite-element model illustrates the auxetic mechanism. Force, displacement at peak load and mechanical work should therefore complement Poisson’s ratio in material selection for auxetic lattices.