Mechanical response and stability of a novel crossed star honeycomb under inclined loading

A novel crossed star-shaped honeycomb (CSSH) is obtained by replacing the horizontal and vertical walls of a classical star-shaped honeycomb (SSH) with crossed inclined walls. Two reinforced crossed star-shaped honeycombs (RCSSH) were further constructed by tailoring the cross-connecting ligaments. In this paper, to reveal the mechanical properties of these honeycombs under inclined loads, tilted specimens of the SSH and the three kinds of CSSHs were fabricated based on the additive manufacturing technique, and quasi-static compression experiments were conducted on them. The experimental results show that all four honeycombs exhibit a significant negative Poisson's ratio phenomenon under inclined loading. Notably, the RCSSH-1 exhibits optimal deformation stability and the strongest energy absorption, with a specific energy absorption (SEA) 165.6 % higher than that of classical SSH. Afterward, to explore the deformation mode, compressive strength, and energy absorption of SSH and three kinds of CSSH under inclined dynamic load, the corresponding numerical models were established, and the numerical methods were validated using experimental data. Then, the relationship between the wall thickness and crashworthiness of the honeycomb with the best energy absorption effect in CSSH was analyzed based on numerical simulations. The results show that both the oblique angle and the wall thickness have a large effect on the compressive strength and energy absorption of the honeycomb. The energy absorption capacity of a honeycomb does not necessarily deteriorate at smaller oblique angles for low-velocity impacts. While at larger oblique angles, all four honeycombs showed unstable deformation, which drastically reduced their mechanical properties; at medium-velocity impact, the compressive strength and energy absorption capacity of the remaining three honeycombs, excluding RCSSH-2, fluctuated less with the increase of the oblique angle; at high-velocity impact, the compressive strengths of the four honeycombs showed a tendency to increase with the increase of the oblique angle, but there was not much difference in their SEA.