Quasi cross-scale effect on composite auxetic honeycomb sandwich structures subjected to dynamic loadings

Composite auxetic sandwich with efficient deformation reinforcement and specific energy absorption emerge as promising candidates for protective applications. This study presents a comprehensive experimental and numerical investigation into the negative Poisson's ratio (NPR) effects manifested in hexagonal honeycomb core sandwich composites under varying loading patterns and intensity levels. A quasi cross-scale analytical framework is established through comparative analysis of dynamic responses across sandwich geometries, effectively bridging structural dimensional characteristics with loading pattern influences. The results demonstrates that the deformation mechanism associated with NPR effect changes significantly with the loading pattern from quasi-static to dynamic planar compressions and then to local impact, which is insensitive to the structural scale under the identical load pattern. The enhanced NPR effect renders dynamic strength increases notably with the increasing structural scale, and the enhance effect is rate-independent for the same configuration. Different from the overall structural reinforcement under planar compressions, the majority of cells remain largely unaffected until the cells in front of the impact site are fully collapsed, indicating the enhanced impact resistance caused by NPR effect is significantly limited by the response velocity of cells. Under the impact, the material properties rather than NPR effects dominate energy absorption performance, with increased impact angles substantially reducing structural deflection and failure. The results of this study deepen the understanding of auxetic honeycomb sandwich structures and may provide new strategies and inspiration for the optimized design of advanced protective structures.