Repeated impact response and energy absorption of geometrically graded chiral sandwich panels

Engineering structures are often exposed to repeated impacts, necessitating materials with high damage tolerance. This study investigated the repeated low-velocity impact response of sandwich panels with auxetic cores, with a specific focus on the effect of geometrical grading. Aluminum face sheets were bonded to 3D-printed polylactic acid (PLA) cores, including honeycomb (HC), uniform auxetic (trichiral (3C) and hexachiral (6C)), and a graded chiral (GC) design. Experimental results demonstrated the superior performance of the GC core, which experienced eight successive 25 J impacts while maintaining structural integrity. The GC design absorbed up to 91.2% of the incident energy and improved crushing force efficiency (CFE) by 62% compared to baseline geometries. These enhancements were attributed to the geometrically gradual density transition that promoted uniform stress distribution and extensive plastic deformation. The findings confirmed that geometrically graded chiral panels offer exceptional resistance to repeated impacts, highlighting their potential for lightweight, damage-tolerant applications in automotive and aerospace engineering.