Quasi-static crushing behavior of novel re-entrant circular auxetic honeycombs

Honeycombs with re-entrant (RE) unit cells were found to have negative Poisson's ratios (NPRs) and enhanced energy absorption capabilities than regular hexagon honeycombs. For further improved energy absorption capacity, a novel re-entrant circular (REC) honeycomb configuration is proposed in this work by replacing the sloped cell wall of the regular re-entrant honeycomb with double circular arc cell walls, which can dissipate extra energy due to more formed plastic angles during the crushing process. The in-plane quasi-static crushing response of the REC honeycomb with large deformation was investigated theoretically and numerically. The numerical modeling methods in LS-DYNA software were validated by using the quasi-static crush test data of 3D-printed REC honeycomb specimens. Experiment and numerical simulations both revealed that quasi-static load can result in an X mode deformation of the REC honeycomb. Based on the simulated deformation profiles of the representative unit, theoretical models were derived to predict the REC honeycomb's crushing strength, i.e. plateau stress. Good agreements were found between the theoretical and the numerical results within a relative error about 9%. Parametric analyses further showed that the unit cell configuration has a great effect on the crushing strength of the REC honeycomb. The REC honeycomb presents a varied Poisson's ratio with the global strain of the honeycomb; smaller radius to height ratio and length to height ratio were found to yield more pronounced NPR effect. Moreover, compared with the regular RE honeycomb, the specific energy absorption of the REC honeycomb is much higher due to the introduction of the double circular arc cell walls.