Research on the failure mechanism and enhanced energy-absorbing capacity for a novel concave octagonal NPR honeycomb structure

The increasing demand for lightweight and safe rail transit structures has highlighted negative Poisson's ratio (NPR) honeycombs as promising energy-absorbing architectures due to their superior failure mechanism and crashworthiness. This study introduces a novel graded concave octagonal NPR honeycomb (G-ICOH), evolved from the conventional inner concave hexagonal honeycomb (ICHH), to enhance deformation stability and energy dissipation efficiency. Specimens were fabricated from AlSi10Mg using selective laser melting followed by T6 heat treatment with residual stresses markedly reduced, confirming reliable material properties. Quasi-static compression tests and finite element simulations revealed that G-ICOH develops a distinct "X-shaped" deformation mode accompanied by a strong NPR effect. Compared to ICHH, G-ICOH demonstrates a ~ 50% reduction in initial peak stress and a smoother plateau stress response, leading to more stable energy dissipation and up to a 7.58% improvement in specific energy absorption. A parametric analysis showed that the foundation thickness-to-beam arm ratio significantly affects plateau stress and energy absorption, while the influence of the intermediate beam gradient and concave angle is comparatively minor. These results provide explicit guidelines for parameter optimization. The proposed G-ICOH structure combines NPR effect with enhanced crashworthiness, offering practical potential for buffer devices, impact protection systems, and lightweight energy-absorbing components in rail transit and broader transportation engineering applications.