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[Display omitted] • S-shaped reinforced cores are designed by flattening hexagonal honeycomb cores. • S-shaped reinforced structures can effectively change the deformation mode of cores. • The peak load of S-shaped reinforced core can be 86.12% greater than plain core. • Theoretical prediction model of S-shaped reinforced honeycomb cores is proposed. • The design capabilities of cores are expanded because of S-shaped structure. Honeycomb structures serve as the core of sandwich structures in various industries, such as aerospace and rail transit. In this study, a novel design was introduced where hexagonal honeycomb cores were flattened in specific areas to form S-shaped reinforced cores. Compression tests were conducted on S-shaped reinforced honeycomb cores with different rotational structures – left-hand, right-hand, and mixed rotation. The deformation process of these cores was thoroughly investigated. Additionally, a theoretical prediction model was proposed to determine the Young's modulus and peak load of S-shaped reinforced honeycomb cores. The experimental data was compared with the theoretical model to validate its accuracy. Moreover, the study examined the effects of changing the relative density and cell wall angle of S-shaped reinforced honeycomb cores on the peak and specific peak loads. The results demonstrated that the use of S-shaped reinforced structures successfully altered the deformation mode of the honeycomb cores. In particular, the peak loads of S-LL and S-LR specimens were 29.14% and 86.12% higher than that of plain honeycomb, respectively. In summary, increasing the relative density of S-shaped reinforced honeycomb cores proved to enhance the peak load and specific peak load, thereby augmenting the design capabilities of these cores. [ABSTRACT FROM AUTHOR]

In the present study, honeycomb cores with periodic tight zones were proposed for carbon-fiber and aluminum-honeycomb sandwich panels by flattening hexagon-shaped cells of honeycomb walls. In-plane compression tests were performed for sandwich panels with three types of local-tight honeycomb cores to evaluate the effects of the local-tight configurations on mechanical properties and failure modes. Experimental results indicated that the mechanical properties of sandwich specimens were effectively increased by using the proposed local-tight honeycomb cores. In particular, the specific energy absorption of sandwich specimens with a local-orthogonal-tight core was increased by 400.46%. In addition, Digital Image Correlation (DIC) technique was employed to further investigate the compressive behaviors of the sandwich specimens with and without local-orthogonal-tight honeycomb cores. The experimental measurements and detailed DIC observations indicated that the local-orthogonal-tight honeycomb core sandwich structures, which provided improved load transferring paths and reduced mismatch between the high-stiffness face sheets and low-stiffness core, exhibited progressive crushing failure modes. [ABSTRACT FROM AUTHOR]