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• A cost-effective fabrication method is proposed. • More pronounced NPR effects can be attained by implemented misplaced design. • The comparative method of specific plateau stress is proposed. • The optimized MRHC structure possesses an excellent energy absorption performance. Two-stage plateau stress structures have emerged as a novel research focus in the field of impact protection and energy absorption. The proposal of structures exhibiting a two-stage plateau stress region is increasingly prevalent. However, the majority of currently available two-stage plateau stress structures are predominantly fabricated using 3D printing technology, which can incur substantial costs. Additionally, the majority of currently proposed two-stage plateau stress structures exhibit diminished plateau stress values and possess limited capabilities for energy absorption. The objective of this study is to develop an economically viable metamaterial that exhibits dual high-level plateau stresses and demonstrates exceptional energy absorption capabilities in two in-plane directions. Based on the concept of misplaced design and traditional reinforced honeycomb structures (RHC), a novel metamaterial named misplaced reinforced-honeycomb (MRHC) has been developed. Aluminum alloy component and stainless stee component are fabricated. After the implementation of the misplaced design, the MRHC structure exhibits a pronounced enhancement in negative Poisson's ratio effect. The influence of misplaced design on the mechanical performance of the MRHC structure, as well as the impact of horizontal cell wall length (l 3) and rotation angles (α and β), has been investigated. The multi-objective optimization has been employed to determine the optimal rotation angles α and β. The optimized MRHC structure was compared to the previously proposed two-stage plateau stress structures, revealing its superior energy absorption capabilities in both the in-plane X and Y directions. The proposed MRHC structure exhibits promising potential for future applications in impact buffering and collision protection fields. [Display omitted] [ABSTRACT FROM AUTHOR]

• Three novel lattices by inserting honeycomb struts into the traditional 3D auxetic structure were proposed. • The tensile and compressive mechanical behaviours of hybrid lattices were studied and compared. • 3D hybrid lattices are more effective in tension-dominated applications. Lattice structures have the potential for application in tensile conditions. However, limited studies have addressed tensile behaviours of such structures and compared them with their compressive behaviours. In this paper, re-entrant structure as the foundation was selected to develop new 3D hybrid auxetic honeycomb lattice structures, each characterized by a unique unit cell configuration that features interconnected centre auxetic honeycomb, differentiating it from 2D hybrid auxetic honeycomb structures. A series of uniaxial quasi-static tensile and compressive tests, followed by simulations were conducted on these structures to investigate and compare their energy absorption characteristics. The results show that there were significant differences between these structures in terms of their mechanical behaviours under tension and compression. Especially, the smallest value of energy absorption under tensile load was 86% higher than the largest value under compressive load. The stiffnesses of these lattice structures under tensile loading were about 84–122 times of those of the identical corresponding structures when they were compressed. Meanwhile, the progressive stretching, buckling and collapse mechanisms observed in these structures exhibited excellent stiffnesses and energy absorptions under tensile and compressive load compared to traditional 3D auxetic as the basic structure. The outer frame structure of lattice structures had a direct influence on Poisson's ratio. The work indicates that the stiffness and energy absorption of the traditional 3D auxetic structure can be enhanced by embedding auxetic and honeycomb umbrella shaped elements. [Display omitted] [ABSTRACT FROM AUTHOR]

• A novel EARE is designed by introducing an elliptical annular into RE cell. • EARE produces extra vertical support without hindering lateral deformation. • EARE concurrently enhances auxetic performance, stiffness, and SEA. • Adjusting geometric parameters rationalizes designing mechanical properties. Auxetic structures have sparked a lot of interest due to their excellent mechanical characteristics and unusual negative Poisson's ratio influence. However, the large porosity property results in low stiffness, which limits their application scope. Current approaches to augment stiffness often result in diminished auxetic performance. Therefore, it is challenging to simultaneously enhance the auxetic, stiffness and energy absorption capacity of auxetic structures. To address this issue, this paper proposes a novel elliptical annular re-entrant honeycomb (EARE) by introducing an elliptical annular structure into a conventional re-entrant honeycomb (RE) cell, which can provide extra longitudinal support without hindering lateral deformation. The plateau stress, Poisson's ratio and energy absorption properties of the EARE are investigated by quasi-static compressive tests and finite element modeling. The results show that the EARE honeycomb has two plateau stages due to the supporting effect of the elliptical annular structure. Compared with the conventional RE honeycomb with the same wall thickness, the EARE honeycomb not only exhibits a stronger auxetic effect embodied in the Poisson's ratio reduced by 5.19%, but also has a higher average plateau stress and a higher specific energy absorption of 171.63% and 28.03%, respectively, which significantly improves the stiffness and energy absorption performance. The parameterized analysis reveals that by appropriately adjusting the geometric parameters, the stiffness, energy absorption, and auxetic effect of the EARE honeycomb can be enhanced. The research findings address the conflict between auxetic performance and honeycomb stiffness, providing new insights into the optimization of honeycomb structure design. [Display omitted] [ABSTRACT FROM AUTHOR]