Compressive Deformation, Damage Evolution, and Energy Absorption of 3D-Printed PLA and Short-Carbon-Fiber-Reinforced PLA Auxetic Metamaterials.

Auxetic mechanical metamaterials convert axial compression into lateral contraction, providing deformation modes that are attractive for lightweight energy absorbers. Here, fused deposition modeling was used to fabricate polylactic acid (PLA) and 10 wt% short-carbon-fiber-reinforced PLA (CF/PLA) auxetic metamaterials with arrow, re-entrant hexagonal, star-shaped, and chiral rotating topologies. Thermal analysis, tensile testing, and three-point bending first established the effect of carbon-fiber addition on the printable matrix. Quasi-static compression experiments were then combined with finite-element simulations using pressure-dependent plasticity and ductile damage to resolve topology-dependent collapse and energy partition. Adding 10 wt% short carbon fibers increased the tensile modulus from 2.33 to 3.72 GPa and raised the plateau stresses of the auxetic structures by about 50%. The star-shaped CF/PLA metamaterial showed the highest specific energy absorption (approximately 4.7 J/g), whereas the chiral rotating topology showed the largest relative improvement, exceeding 130%. Fiber reinforcement improved stiffness and load transfer but promoted stress localization at hinges, re-entrant corners, and ligament junctions. These findings elucidate the material-topology trade-off between stiffness enhancement and localized embrittlement, offering practical guidelines for designing crashworthy 3D-printed composite metamaterials.