High stable auxetic metamaterials developed through feature-control topology optimization and additive manufacturing

Auxetic metamaterials with stable deformation modes are essential in engineering applications to achieve desired functionalities, as otherwise they may incur irreversible damage, e.g., structural interference and collision damage. However, only a few works have proposed special architectures relying on inspiration and experience, meaning that their design and fabrication remain challenging due to the lack of a systematic method. Here, we propose a novel feature-control metamaterial topology optimization framework aimed at efficiently exploring auxetic metamaterials with high stability and manufacturability. By integrating the local volume fraction function and skeleton-based length scale function, the method effectively controls material distribution and minimum geometric size, preventing excessively slender features and unmanufacturable configurations. Specimens were fabricated using additive manufacturing, and experimental testing validated the mechanical properties, closely aligning with finite element analysis predictions. Results show that simply increasing the volume fraction in topology optimization to raise the relative density of auxetic metamaterials does not directly enhance stability. Instead, the novel designs effectively prevent instability by incorporating denser structures and localized internal ribs, which improve stiffness and overall load-bearing capacity, as confirmed by extensive simulations and experiments. This approach enhances the design efficiency of stable metamaterials and facilitates the development of advanced configurations, expanding the application of auxetic materials in protective engineering, aerospace, and civil engineering.