Mechanical Properties and Energy Absorption Characteristics of Ring Lattice Sandwich Structures Under Compressive Load

To enhance critical infrastructure protection against low-cost UAV impacts, this study proposes a novel ring lattice sandwich structure (RLSS) fabricated via an economical interlocking-assembly-brazing method. Its quasi-static compressive behavior is systematically investigated through experiments, numerical simulations, and theoretical analysis. Theoretical models for relative density and initial yield stress are validated against experiments, with errors of 7.1% and 6.6%, respectively. Quasi-static tests show that the one-layer RLSS exhibits a specific energy absorption (SEA) of 8.67 J/g, while the two-layer structure drops to 5.66 J/g due to inter-layer torsional instability. SHPB impact tests at strain rates of 750–1369 s−1 demonstrate a pronounced strain-rate effect, with dynamic increase factors ranging from 1.14 to 1.43. Numerical simulations accurately reproduce the experimental deformation modes and reveal that multi-layer (2–5 layers) RLSSs reduce SEA by 46.9% compared with the one-layer simulated value of 9.43 J/g. Adding a 0.3-mm inner panel in simulations restores the crushing mode and raises the SEA of the two-layer structure to 7.19 J/g, surpassing the non-panel counterpart (6.03 J/g). Hybrid core configurations provide additional advantages: Mode I (ring–pyramid with inner panel) enhances total energy absorption with a limited ring-layer count, while Mode II (alternating layers) achieves minimal plateau stress fluctuation (PSF = 0.09). These findings confirm that the proposed RLSS, especially when optimized with thin inner panels or hybrid designs, offers great potential as protective cladding against impact and blast threats.