Improved mixed gradient design method to enhance compression stiffness and energy absorption of auxetic structures

Abstract

The auxetic structure with multi-plateau stress stages exhibited excellent designability while improving mechanical properties. In this study, a mixed gradient design method was proposed to simultaneously enhance the energy absorption capacity and compression stiffness of auxetic structures. According to the different types of cell-walls, star-triangle honeycombs (STH) with uniform thickness were designed, and in-plane crushing tests were carried out to reveal the deformation and energy absorption characteristics. The reliable finite element models were constructed to systematically reveal the deformation sequence and load-bearing characteristics of different types of cell-walls at different deformation stages. Subsequently, different cell-wall thickness ratios (δ) were constructed according to the load-bearing characteristics of different types of cell-walls. Comparative analysis revealed that the thickness ratio ${\delta }_{\text{2}}={\text{t}}_{\text{2}}/\left({\text{t}}_{\text{1}}={\text{t}}_{\text{3}}\right)$ could simultaneously improve the specific energy absorption (SEA) and compression stiffness (E) of STH. Based on the ${\delta }_{\text{2}}$ and keeping the re-entrant cell-wall thickness constant, improved single gradient and mixed gradient thickness design methods were proposed. Finally, the improved single gradient design exhibited a significant enhancement effect on the E of STH. Compared with the traditional thickness gradient (STH-UTG), the SEA and E of STH with mixed thickness gradient were improved by about 52.37 % and 193.34 %, respectively. Consequently, the mixed gradient design methods provide innovative insights for enhancing the mechanical properties of auxetic structures.