Comparative investigation of enhanced compressive mechanical properties of the three auxetic composites

Abstract Filling specific materials into auxetic frameworks exhibit significant potential for enhancing mechanical properties, without change of material’s size and configuration. However, the underlying reinforcement mechanisms need comprehensive exploration and comparison for various auxetic frameworks. In this study, three typical auxetic composites with identical auxetic porosity are designed, including the filled reentrant structure (FR), the filled peanut-shaped-hole-based structure (FP), and the filled elliptical-hole-based structure (FEH). Silicone rubber is used as the filling material. By combining compressive testing and finite element analysis, the compressive behavior of these three auxetic composites is systematically evaluated, revealing substantial improvements in stiffness, strength and energy absorption (EA). It is found that all composites exhibit enhanced mechanical properties, which surpass the combined effects of the individual material phases, thanks to the interaction between the auxetic framework and the soft filler material. More importantly, the FP performs best compared to the FR and FEH. Specifically, at 0.3 compressive strain, the Young’s modulus of the FP is 1.5 and 2.5 times that of the FR and FEH, respectively. The first peak stress of the FP increases by approximately 72% and 121%, compared to the FEH and FR, respectively. Furthermore, the FP exhibits the longest auxetic behavior, the best EA capacity and the highest buckling resistance during compression. Finally, the effects of the main geometrical parameters of the FP on its mechanical properties are investigated. Specifically, at 70% auxetic porosity, the stiffness and EA can respectively increase by 0.43 and 1.28 times, compared to 20% auxetic porosity. These findings facilitate the design and application of the auxetic composites, especially FP, in future developments.