Effects of Node Fillet Radius on Compressive Properties and Energy Absorption of FDM-Fabricated PETG Auxetic Honeycombs.

Node fillet radius has a pronounced effect on the compressive performance of fused deposition modeling (FDM)-printed polymer honeycombs, yet quantitative design guidelines for PETG auxetic structures remain scarce. The effects of gradient node fillet radii (R0-R7 mm) on the load-bearing capacity, deformation mechanisms and energy absorption of PETG auxetic honeycombs were investigated by quasi-static compression tests. Results reveal a dual competing mechanism: stress homogenization improves crushing stability, whereas nodal cross-section weakening reduces structural stiffness. Among the six configurations, R5 (35.7% radius-to-cell ratio) achieved the best balanced performance, with a peak strength of 0.35 MPa and specific energy absorption of 335.25 J/kg, and crushed progressively without catastrophic load drops. At R3 mm, nodal weakening raised the working stress and caused premature brittle fracture; at R7 mm, excessive filleting lowered peak strength to 0.30 MPa, slightly below the unfilleted control. Although unfilleted R0 showed the highest total energy absorption, specific energy absorption (342.62 J/kg) and efficiency (46.97%), its right-angle nodes induced disordered brittle collapse that compromises service safety. The resulting Pareto trade-off shows that moderate filleting best balances strength and energy absorption, providing parameter guidance for the topology optimization of 3D-printed polymer lightweight protective components.