Effect of geometrical grading on the low-velocity impact behavior of sandwich structures with 3D-printed auxetic core materials

Cellular core sandwich panels, traditionally utilizing honeycomb geometry, are widely recognized for their lightweight design and effective energy absorption. Auxetic geometries, characterized by a negative Poisson’s ratio, have emerged as promising alternatives, offering enhanced mechanical properties and energy absorption. This study experimentally examines the influence of geometrical grading on the low-velocity impact response of sandwich panels with auxetic core materials, with potential applications in protecting civil infrastructure against impact loads. The sandwich panels were constructed by bonding aluminum face sheets to 3D-printed cellular cores made from polylactic acid (PLA). Seven cellular core designs were evaluated, including one conventional honeycomb structure, two auxetic configurations (trichiral and hexachiral), and four graded auxetic geometries, all fabricated using fused deposition modeling. Results showed that the graded geometries exhibited improved damage distribution, lower permanent deformation depths, and higher crushing force efficiency and specific energy absorption compared to honeycomb and non-graded auxetic geometries. Notably, the graded geometry transitioning from hexachiral to trichiral units absorbed 98.9% and 99.8% of the impact energy at 25 J and 50 J, respectively. The graded designs with denser core geometry near the impact surface demonstrated superior crashworthiness. These findings underscore the potential of graded auxetic geometries in applications demanding high energy absorption and impact resistance, such as the protection of critical infrastructure against dynamic loading scenarios. The study suggests that incorporating graded auxetic structures in cellular core designs can provide considerable performance enhancements over traditional configurations, particularly in terms of impact mitigation and structural resilience.