Enhancement of the in‐plane stiffness of the hexagonal re‐entrant auxetic honeycomb cores

In the present work, two new designs of honeycomb structures were presented based on the basic re‐entrant structure namely, splined‐reentrant and stiffened‐reentrant honeycombs. The new structures were designed in order to enhance the in‐plane stiffness and maintaining the auxetic behavior of the structure. In this study, finite elements modeling and experimental work were carried out to evaluate the in‐plane properties of the new designs. The effect of the geometrical parameters such as rib length and rib thickness of the unit cell of the new designs on the in‐plane properties was investigated. Finite elements results showed that the in‐plane stiffness of the new designs was improved significantly compared to the basic re‐entrant structure. Also, the stiffened‐reentrant structure showed better enhancement of the stiffness than the splined‐reentrant structure. For example the modulus of elasticity of the stiffened‐reentrant structure exceeds 16× that of the basic re‐entrant structure in x‐direction and was over two times in the y‐direction with lower values of the negative Poisson's ratio. Compression tests were carried on honeycomb samples made of steel using laser cutting technique with different geometrical parameters. Test results for the three designs were compared with the finite element results and they were in a good agreement.