Effect of design parameters of auxetic structure core on quasi-static and low-velocity impact response of glass fiber reinforced polymer composite sandwich structures

This study explores the effect of auxetic unit cell geometry and wall thickness on the energy absorption performance of sandwich composites under quasi-static and low-velocity impact (LVI) loading. Four auxetic geometries reentrant, arrowhead, starshaped, and kiteshaped were 3D-printed using ABS material and first evaluated through quasi-static compression tests with three wall thicknesses (0.44, 0.62, and 0.80 mm). Results showed that thinner-walled specimens exhibited higher initial peak forces but more brittle collapse, while thicker-walled designs provided smoother force responses. The arrowhead geometry with 0.44 mm wall thickness exhibited the highest peak crushing force (6.413 kN) while 0.44 mm starshaped geometry showed the maximum specific energy absorption (SEA) value of 6.226 J/g. Based on these results, representative auxetic cores were embedded into GFRP/epoxy sandwich panels and tested under 100 J LVI using a drop-weight setup. Among the tested configurations, the reentrant core exhibited the highest peak contact force (16.96 kN), while the arrowhead core achieved the highest absorbed energy (87.30 J) and SEA (1.89 J/g), indicating a more progressive deformation. The kiteshaped core provided the longest impact duration and smoothest deceleration profile, suggesting superior energy distribution. Finite element simulations in LS-DYNA correlated well with quasi-static compression experimental results, capturing the deformation mechanisms and validating the structural response. The findings highlight the critical role of unit cell topology and wall thickness in tailoring the impact performance of auxetic core sandwich structures for lightweight and energy-absorbing applications.