Effect of Chiral Arm Angle on the Stiffness, Auxeticity and Energy Absorption of Polyamide-12 Tetra-Chiral Lattices Under Quasi-Static Compression: A Numerical Baseline Study.

Chiral auxetic lattices convert axial loading into node rotation, producing negative Poisson's ratios and high energy absorption. This purely numerical study establishes a quasi-static baseline for additively manufacturable polyamide-12 (PA12) tetra-chiral lattices in which the chiral arm angle (0-90°) is treated as a design variable; no experiments were performed, and the model is verified rather than validated. Geometrically non-linear elastoplastic finite element analyses with a data-sheet-derived bilinear PA12 card and frictional self-contact were carried to 20% nominal strain and supported by mesh convergence, seeded-imperfection and friction sensitivity studies, a full-field lateral-strain measure and a refined sweep at 5° resolution. The arm angle switches the response between a stretch-dominated non-auxetic regime (0°, 50-90°) and a rotation-dominated auxetic regime (15-45°) whose lateral kinematics are not sensitive to mesh density, friction and seeded imperfections. The 15° lattice maximizes stiffness and peak force but is an isolated spike in the refined sweep, exhibits a collapse-mode bifurcation whose branch is selected by the discretization, and reaches the PA12 ductility limit after 3.5 mm of stroke. The 30° architecture sustains 9.4 mm before fracture onset and delivers the highest damage-bounded specific energy absorption of the auxetic window (820 J/kg on the baseline mesh), emerging as the design optimum.