## 1 Introduction
[17] carried out experimental and numerical studies on the impact behavior of aluminum re-entrant honeycombs filled by concrete foam and polyurethane (PUR) foam, respectively. Enhanced energy absorption capacity was identified. In addition to re-entrant auvetic honeycombs, [PERSON] et al. [26] carried out a theoretical and numerical study on the in-plane impact behavior of chiral honeycomb. The theoretical solution of yield stress at quasi-static loading was analyzed. Chiral honeycomb showed inapparent peak stress under both low-speed and high-speed impact when compared to conventional hexagonal honeycomb, although the conventional honeycomb exhibited better performance in plastic energy absorption. [PERSON] et al. [27] experimentally and numerically investigated the in-plane local impact resistance of foam-filled chiral composite structures. The participation of foam could further enhance the energy absorption capacity of the chiral structure. [PERSON] et al. [28] first produced a new type of cementitious auxetic structure via 3D-printing technologies. High specific energy absorption and 2.5% reversible deformation were observed. In the last decade, there has been growing interest in the study of 2D auxetic structures. To the authors' knowledge, however, the application of 2D auxetic structures in practical engineering for impact protection is currently lacking. Regarding the mechanical properties of 3D auxetic structures, relatively few studies have explored the dynamic compressive behavior. [PERSON] et al. [29] performed a numerical study on the blast resistance of a sandwich composite structure with a 3D re-entrant honeycomb core. Maximum 70% and 30% reductions in velocity and displacement at the back were, in fact, obtained when compared with an equivalent monolithic panel. [PERSON] et al. [30] experimentally and numerically investigated the dynamic performance of a 3D re-entrant honeycomb, considering the effects of structural geometric parameters and impact velocity. Enhanced energy absorption capacity compared to its 2D structure was confirmed beyond a certain strain. [PERSON] et al. [31] proposed a fabrication process for re-entrant foam. Afterwards, the crashworthiness evaluation of an auxetic foam-filled tube under quasi-static axial loading was investigated through experimental tests and numerical simulations. The superiority of the re-entrant foam-filled square tube was confirmed in terms of all defined crashworthiness parameters when compared to empty and conventional foam-filled square tubes. Although several types of 3D chiral structures [32; 33; 34; 35; 36] have been proposed, the investigations have generally limited on the quasi-static mechanical properties in elastic deformation or dynamic response at low strain rate. Since the above studies on 3D auxetic structures are among the first on this topic, most of them are limited in elastic scope, and the main research objectives are 3D re-entrant structures. With the development of 3D printing, nowadays, 3D auxetic structures can be fabricated easily. Thus, the mechanical properties of various 3D auxetic structures deserve consideration. To the best of the authors' knowledge, there has been no study on the failure behavior and energy absorption of 3D hexagonal chiral structures under compressive loadings. Consequently, there are insufficient data to develop a comprehensive understanding of the effects of various parameters on compressive behavior for the development of design methods in practical engineering. To address the limitations mentioned above, following the authors' prior study on the 2D chiral auxetic structure, this study aims to investigate the compressive response of the novel 3D chiral auxetic structure with the aid of ABAQUS/Explicit. The novel 3D chiral auxetic is designed by orthogonally assembling two 2D chiral auxetics but replacing the circular nodes-based conventional chiral auxetics (ACs) with hexagonal nodes-based chiral auxetics (AHs). Firstly, the FE models were validated against the literature experimental data.