Gradient-stiffness star-shaped auxetic metamaterial for high-energy absorption

Abstract

Conventional uniform auxetic structures typically exhibit single deformation modes and insufficient load-carrying stability, which significantly limit their application in critical energy absorption scenarios. A novel star-shaped metamaterial engineered with a gradient stiffness design was developed in this study to overcome these drawbacks. An analytical constitutive model was established and validated through finite element analysis and compression experiments, showing excellent agreement. Uniquely, this study established a sinusoidal model using a densification approach. By applying the gradient stiffness principle to regulate the deformation process, the design establishes a fail-safe barrier distinct from the sudden buckling often observed in conventional metamaterials. This mechanism ensures structural integrity under extreme deformation, thereby providing reliable overload protection for engineering applications, such as shock absorbers for Martian landers and anticollision hulls. Furthermore, dynamic impact tests verified the superior energy dissipation of the structure compared to traditional cushioning materials. Under quasi-static compression, the peak load-bearing capacity reaches 13.5–21.0 kPa across the studied parameter space, and the maximum strain energy attains 3.98 J at a displacement of 20 mm. Consequently, the proposed metamaterial exhibits higher compressive strength and energy absorption than uniform structures, providing a predictable and robust solution for advanced protective systems.