Design of lightweight auxetic metastructures with tunable mechanical properties

Abstract Lightweight mechanical metastructures are widely used in the automotive industry and related transportation equipment due to their high specific strength, high specific stiffness, and designability. This study presents an auxetic cylindrical metastructure designed as a lightweight mechanical system with tunable stiffness and strength, offering promising applications in the automotive industry for energy absorption and structural components. The structure employs polylactic acid as the matrix material owing to its favorable printability and mechanical properties. Multiple samples with varying geometric parameters are fabricated via fused deposition modeling to validate the corresponding finite element models. Axial and lateral compression tests reveal distinct deformation mechanisms. Under axial loading, the metastructure exhibits significant necking behavior accompanied by auxetic expansion, with parameter T 3 critically influencing axial stiffness and strength through control of local buckling patterns. During lateral compression, pronounced bending deformation emerges, forming high elastic strain regions near connecting nodes and enabling adjustable lateral deformation. Parameters T 2 and T 3 primarily govern lateral nominal stiffness and strength by affecting deformation mode transitions. Multi-objective optimization using NSGA-II demonstrates a trade-off between the volume fraction and mechanical performance. The optimized design achieves significant mechanical property improvement, as numerically confirmed. This auxetic metastructure provides a novel approach for programmable lightweight system design, with potential applications spanning automotive industry, aerospace, biomedical, and impact-absorption engineering fields.