Multi-gradient coupling design for auxetic structures with multi-plateau stress to improve energy absorption capacity

Auxetic structures with multi-plateau stress exhibit loading enhancement, independent deformation and tunable properties. In this study, a novel multi-gradient coupled design method was proposed to enhance the energy absorption capacity of auxetic structures. The star-triangular honeycomb (STH-X) in x -direction was taken as the research object, and the in-plane crushing test was carried out to reveal the deformation behavior and mechanical properties of STH-X with different thickness distributions. The deformation sequence and load-bearing mechanisms of different types of cell walls were investigated, and a theoretical model for the plateau stress of STH-X-D was developed. Subsequently, gradient designs were implemented on different types of cell-walls to obtain a periodic thickness gradient STH-X honeycomb (STH-X-PTG), whose specific energy absorption (SEA) was increased by 58.7 % compared with STH-X with uniform thickness (STH-X-U). Combining traditional gradient, periodic thickness gradient and structural parameter gradient, a multi-gradient coupling design was carried out for STH-X (STH-X-MGCD). Under the in-plane crushing load, the deformation mode of STH-X-MGCD was similar to that of STH-X-U, but the SEA increased by about 85.04 %. Finally, the variables of the multi-gradient coupling design were simplified, and multi-objective optimization design method was employed to optimize the structural parameters of STH-X-MGCD. The optimization result STH-X-OB was improved by 27.22 % and 104.53 % compared with the original structure and STH-X-U, respectively. Compared with the classic auxetic structures (star-shaped, re-entrant structures) and auxetic structures with multi-plateau stress (re-entrant star-shaped, elliptical annular re-entrant structures), the STH-X-MGCD demonstrates excellent energy absorption capacity. Thus, the novel multi-gradient coupling design method provides a new concept for improving the mechanical properties of auxetic structures with multi-plateau stress. • A periodic structural gradient designed with different types of cell-wall thickness gradients within cells of STH-X was proposed. • A multi-gradient coupling design method was proposed for STH-X to improve the comprehensive mechanical properties. • Multi-objective optimization design was conducive to obtaining the optimal multi-gradient coupling design scheme.