Study on in-plane mechanical properties of the novel thickness gradient honeycomb structures

As a lightweight protective structure, auxetic honeycombs have a broad application in engineering. In this study, gradient characteristics was introduced into a novel enhanced auxetic honeycomb (NEH). Positive, negative, symmetric positive and symmetric negative gradient NEH (P-NEH, N-NEH, SP-NEH and SN-NEH) were constructed by varying the wall thicknesses, and the relative densities were deduced. The dynamic responses of NEH and reentrant honeycomb (RH) were compared by numerical methods, and it was found that NEH has superior mechanical properties. Subsequently, the in-plane impact dynamics of the NEH were disclosed, and the distortion modes, dynamic response curves, platform stresses, Poisson's ratio distributions, and energy-absorbing effects were examined for various gradient distributions and impact velocities. It was found that the gradient distribution and impact velocity significantly affected the impact resistance of gradient NEHs. The platform stress increased with increasing velocity, and there was a significant difference between the platform stresses of the gradient NEHs at the same impact velocity. Among these, the N-NEH exhibits the highest plateau stress, suggesting that it can effectively enhance the energy absorption capability. When impacted at low speed, the specific energy absorption (SEA) of then N-NEH was 148.2% and 108.1% higher than that of the P-NEH and SN-NEH, respectively. At medium-velocity impact, the SEA of the N-NEH was 124.6%, 28.9%, and 112.9% higher than that of the others, respectively. At high-speed impact, the gradient honeycomb is more susceptible to speed influence, and the N-NEH shows extremely outstanding impact resistance.