Progressive crushing and energy absorption behavior of CFRP/316L multi-layer staggered cross-lattice-core sandwich structures under quasi-static compression

Lightweight energy-absorbing sandwich structures require a balance among energy absorption, structural mass, peak load, and crushing stability. This study proposes a multi-layer staggered cross-lattice-core sandwich structure and directly compares an all-316L stainless steel configuration (M1) with a T300 CFRP face-sheet/316L core configuration (M2) under an identical core architecture. Quasi-static compression experiments and finite element simulations were conducted to examine the effects of core topology and face-sheet material, followed by a parametric investigation of core-wall thickness, core-height distribution, and CFRP ply angle. The staggered multi-layer architecture facilitated progressive layer-by-layer crushing and maintained a more continuous load-transfer path through the thickness. Among the tested configurations, M1-N6 achieved the highest total energy absorption, whereas M2-N5 exhibited the highest specific energy absorption of 9.13 J/g, 33.48% higher than that of M1-N5, highlighting the trade-off between absolute energy absorption and mass-specific efficiency. The finite element model reproduced the principal deformation modes and force-displacement responses observed experimentally and was subsequently used to evaluate the parametric trends. Among the investigated discrete cases, core-height distribution produced the largest variation in energy-absorption performance. Increasing the upper-core wall thickness enhanced energy absorption but also increased peak crushing force, whereas CFRP ply angle had a comparatively smaller influence on the overall response. These results indicate that the global crushing response is governed mainly by the progressive deformation and geometric distribution of the metallic core, while the CFRP face sheets primarily improve mass efficiency and provide boundary constraint. The findings provide a physically grounded basis for balancing total energy absorption, lightweight efficiency, and peak-load control in CFRP/metal multilayer sandwich structures.