Experimental and numerical study on the out-of-plane behaviour of auxetic and hybrid auxetic structures

Abstract Auxetic Metamaterials having a negative Poisson’s ratio are gaining attention among researchers due to their excellent energy absorption characteristics.Most of the research on auxetic materials is focused on in-plane behaviour,while out-of-plane loads also influence auxetic materials in practical applications. The current study investigates the out-of-plane behaviour of the auxetic and hybrid auxetic structure. The stress concentration regions of the re-entrant structure are reduced by rounding the corners and varying the strut area uniformly. Recently, a hybrid auxetic structure has been proposed,combining theconventional hexagonal honeycomb and the re-entrant honeycomb to enhance the mechanical properties.All samples are fabricated by Fused filament fabrication method using ABS raw material. Samples were subjected to quasi-static uniaxial compression test in out-of-plane loading direction and a numerical model was developed. The stress-strain plots, energy absorption ability and deformation modes were discussed. The study revealed that the gradient material distribution influenced the improvement in the specific energy absorption of the structures. Further, the specific energy absorption of the hybrid structure (HASr 21 J/g) is improved by 61% than the re-entrant auxetic structure (AS 13 J/g) with nearly the same relative density. This helps in using these structures in potential applications requiring the energy absorption during impact loads.