Bilinear elastic characteristic of enhanced auxetic honeycombs

Auxetic materials exhibit many superior properties but drawback in low stiffness owe to the substantial porosity. Some narrow-ribs enhanced auxetic honeycombs have been designed for improving the in-plane stiffness. For these narrow-ribs enhanced auxetic structures, local buckling likely appears as the reinforcing walls are designed in low thickness for superior auxeticy. In this paper, a novel narrow-ribs enhanced auxetic honeycomb is designed by embedding rhombus into each cell of the normal re-entrant hexagonal honeycomb (NRHH). Analytical model is built to investigate the elastic behaviors of the new proposed honeycomb under uniaxial compression, in which the incremental method is firstly introduced for post-local-buckling analysis. Numerical simulations are carried out to verify the analytical results. It is interesting that bilinear elastic characteristic is found for the stress-strain and transverse strain-longitudinal strain curves of the new proposed honeycomb on account of the local buckling. Parameters studies are performed and the new proposed honeycomb is proved to exhibit superior mechanical properties compared to other narrow-ribs enhanced honeycombs. Significantly, the incremental method brought forward in the present paper for the local buckling analysis can be popularized to other honeycombs enhanced with narrow-ribs. Thus, the bilinear elastic characteristic is a general feature for these honeycombs.