Semi-auxetic cellular laminate: A novel lightweight stiff material

In this study, the concept of semi-auxetic cellular laminate is introduced, analyzed, and experimentally validated toward designing lightweight and stiff cellular structures. Cellular solids such as honeycombs and foams are widely used in various engineering fields due to their superior mechanical properties. However, their performance in weight-critical applications is constrained by the inherent trade-off between stiffness and density where increasing stiffness results in denser and heavier structures. Herein, a new design strategy is proposed to mitigate this trade-off by stacking cellular layers with contrasting Poisson’s ratios (PRs), i.e., reentrant honeycombs with negative and hexagonal honeycombs with positive PR, to create a semi-auxetic cellular laminate that is stiffer than its individual layers, while maintaining a density between those of the layers. The concept is investigated through development of a numerical modeling framework and proven through 3D printing and testing of a semi-auxetic laminate with optimized geometry. The numerical framework integrated finite element (FE) analysis and surrogate-based multi-objective optimization to characterize and optimize the proposed design. Optimization results revealed that the upper bound of the response space exhibited exceptionally high stiffness-to-weight performance, comparable to those of natural cellular materials. Key insights for further enhancements in the future and potential applications are discussed. • Introducing semi-auxetic cellular laminates combining auxetic and non-auxetic layers. • Stiffness enhancement through stacking cellular layers with contrasting Poisson’s ratios. • Application of a multi-objective optimization framework to design cellular laminates. • Proof-of-concept and validation through testing 3D-printed optimized designs. • Modulus efficiency reaching 85% of solid material at only 13% of weight.