Deformation and energy absorption characteristics of graded auxetic metamaterials featuring peanut-shaped perforations under in-plane compression

Abstract

The auxetic metamaterials perforated by peanut-shaped holes have been paid much attention recently due to the advantages in alleviating stress concentration, tuning negative Poisson’s ratio (NPR) and stiffness, and reducing material usage. However, few studies pay attention to their graded designs, which have exhibited promising applications in natural biomaterials. In this study, the innovative design of graded auxetic metamaterials featuring peanut-shaped perforations is explored, emphasizing their potential in customizing deformation and energy absorption. By exploring four distinct graded types, including unidirectional gradient (UG), inward gradient (IG), outward gradient (OG) and alternate gradient (AG) and three gradient-controlling ways, including porosity (K), shape coefficient (M), and porosity and shape coefficient changing simultaneously (KM), 12 unique graded structures are developed. The graded specimens under quasi-static compression exhibit distinct deformation behaviors. Subsequently, the graded structures are thoroughly explored by the validated finite element model and the deformation mode, dynamic Poisson’s ratio and energy absorption capacity are comprehensively investigated. Compared to the uniform structure, the distribution and quantity of NPR bands strongly depend on the perforation’s size and the gradient types. Furthermore, UG-KM can significantly amplify the NPR effect, achieving a maximum enhancement of 14.32%. In contrast, AG-K can considerably diminish the NPR effect, with a maximum reduction of 19.37%. Additionally, type OG exhibit superior energy absorption characteristics, with mean stress and specific energy absorption increasing by up to 28.89% and 46.73%, respectively. The findings provide an effective strategy for designing the auxetic metamaterials with tunable deformation and energy absorption characteristics.