Damage Characteristics of Grid Sandwich Structure Enhanced by Filled Foam and FMLs Face Sheet Under Low‐Velocity Impact

ABSTRACT This study aims to investigate the low‐velocity impact performance and failure mechanisms of a sandwich structure with fiber metal laminates as face sheets and fiber‐reinforced grid as core skeleton, while analyzing the influence mechanism of foam‐filled core on structural impact behavior. Based on grid geometry, a combined experimental–numerical approach (based on grid geometry), low‐velocity impact analyses were performed at three characteristic locations (center, rib, intersection) under 20 J, 40 J, and 60 J, exploring structural responses and performance. Comparing dynamic responses and fracture morphologies across energies/locations revealed the structure's energy absorption, load transfer, and damage patterns. Additionally, a 3D numerical model for the low‐velocity impact process was established via the VUMAT user subroutine, incorporating progressive damage behaviors of aluminum alloy, CFRP layers, and PMI foam. Failure mechanisms were evaluated using simulated final failure modes and damage evolution. Findings show that under the same impact energy, both primary load‐bearing components and damage modes depend significantly on impact location. Foam filling enhances impact resistance by constraining grid local buckling via densification, thus reconstructing load transfer paths.