Enhancing energy absorption of star-shaped honeycombs by utilizing negative Poisson's ratio effect under high-velocity impact

Abstract

Star-shaped honeycomb (SSH) with negative Poisson's ratio (NPR) effect shows great promise in impact protective engineering. However, it is still unknown whether the NPR effect of SSH can enhance the impact resistance at high impact velocities, particularly regarding the stress evolution. In this paper, we demonstrate that the SSH with NPR can significantly improve the specific energy absorption (SEA) under low impact velocity compared to that with positive Poisson's ratio due to the global in-plane contraction resulting from NPR. However, with increasing the impact velocity, the NPR effects of SSH decrease quickly and even turns to positive Poisson's ratio due to the appearance of localized deformation. These results show that the SSH cannot fully exhibit the energy absorption capacity through global deformation. We then analyze the influence of wall angle and thickness on the NPR and SEA of SSH. The results show that the NPR effect can be maintained successfully at high impact velocities by decreasing the wall angle, resulting in the significant increase in SEA compared to that with larger wall angle. Although the increase of wall thickness leads to the increase of SEA, it has slight influence on the NPR effects. This paper demonstrates the NPR effects on the dynamic behavior of SSH based on the analysis of stress evolution, and suggests the strategy for designing efficient energy-absorbing auxetic honeycomb structure.