Concentric honeycomb composite sandwich structures with tunable connection and gradient configurations

With the development of the aerospace industry, sandwich structures are increasingly applied to aircraft fuselages to enhance crashworthiness. Inspired by the arrangement of turtle shells, a concentric honeycomb (double-concentric and triple-concentric) composite sandwich structure is proposed. The concentric honeycombs are connected via transverse and longitudinal connections, and the gradient arrangement strategy is applied to spatial layout. Experimental samples are fabricated using 3D printing technology, and three-point bending tests are conducted. The bending failure process and modes are fully revealed by high-speed cameras. 3D imaging technology is used for damage mechanism analysis and micro-morphology characterization. The results show that compared with traditional honeycombs, the connected configuration honeycombs have higher peak load (+107.7 %), average load (+64.8 %), specific energy absorption (+32.3 %), and load-bearing stability (close to 1). The regulation of transverse connections can achieve low mass and high performance, while gradient configurations show significant differences in specific stiffness, with the maximum difference reaching 46.8 %. This demonstrates the unique force chain synergy and mechanical responses generated by different connection configurations. The methods for achieving force chain transmission modes and deformation regulation mechanisms to meet engineering needs are revealed.