In-Plane Impact Response of Re-Entrant Auxetic Honeycombs with Spatially Graded Material Strength

Re-entrant auxetic honeycombs have attracted considerable interest as lightweight energy-absorbing structures because of their distinctive deformation mechanisms and favorable crushing characteristics. This study investigates the dynamic in-plane crushing response of isotropic and functionally graded re-entrant honeycombs, emphasizing material-property grading rather than conventional geometric grading. Cellular geometry, relative density, and structural mass were maintained identically, while grading was introduced exclusively through continuous variation in parent-material yield strength along the crushing direction. A rate-independent elastic–perfectly plastic model was employed at impact velocities of 50, 75, and 100 m/s, and the numerical response was assessed against an established analytical prediction of dynamic crushing resistance. The results show that strength grading influences collapse localization, force transmission, and progressive cellular compaction. Compared with the isotropic configuration, the graded structures exhibit reduced maximum crushing forces while maintaining or improving mean crushing resistance, energy absorption, specific energy absorption, and crush force efficiency. The effects depend on impact velocity and reflect interactions among structural inertia, collapse progression, and spatially distributed plastic resistance. A relatively compliant impact-side region facilitates controlled deformation initiation, while progressively stronger regions sustain resistance during subsequent collapse. Overall, strength grading improves the balance between peak-load reduction and energy absorption without changing cellular architecture or structural mass.