Improved mechanical characteristics of new auxetic structures based on stretch-dominated-mechanism deformation under compressive and tensile loadings

The aim of this paper is to develop two novel in-plane auxetic structures with remarkable stiffness and negative Poisson's ratio (NPR) appropriate for compression and tensile load-bearing structures. The combination of re-entrant and arrow-head (RAH) unit-cells as well as star and arrow-head (SAH) unit-cells are hybridized and configured as new auxetic structures. The conceptual design is based on the stretch-dominated-mechanism (SDM) deformation of the proposed structures. To investigate the mechanical behavior of the designed structures under compressive and tensile loading, the samples are manufactured by 3D fused deposition modeling printing method and subjected to mechanical testing. The results show that the designed structures present tunable NPRs and approximately equal stiffnesses for both compressive and tensile loadings. In addition, an analytical analysis is carried out to determine the elastic constants of the structures, and a finite element (FE) simulation is conducted to verify the results with experimental and theoretical models. Good agreements are found for the elastic constants calculated from the experimental, theoretical, and FE methods. Meanwhile, the effects of the geometry parameters on the mechanical properties of the designed structures are also investigated, and the stiffness, stiffness to relative density ratio, and NPR are compared with those of existing studies. The comparison results suggest that our developed structures can be considered as strong candidates for the next generation of SDM auxetic structures with high stiffness capability and noticeable NPR values.