Theoretical Design of Metamaterials with Unique Mechanical Properties

The design of mechanical materials with tailored properties has been subject of significant interest in recent years, driven by advancements in three-dimensional manufacturing processes and optimization techniques. Lattice structures, known for their high strength-to-weight ratio, energy absorption capabilities, and structural stability, play an indispensable role in aerospace, automotive, biomedical, and energy systems. However, achieving systematic design of optimal lattice structures with multiple desired mechanical properties remains a challenging task. Conventional design methods relying on trial and error, or intuition can be time-consuming, costly, and may not guarantee optimal performance. Recent advancements in manufacturing, finite element analysis (FEA), and optimization techniques have expanded the design possibilities for metamaterials, including isotropic and auxetic structures, known for applications like energy absorption due to their unique deformation mechanism and consistent behavior under varying loads. However, achieving simultaneous control of multiple properties, such as optimal isotropic and auxetic characteristics, remains challenging. In this work, Timon Meier et al. from the Laser Thermal Laboratory, Department of Mechanical Engineering, University of California, Berkeley, addressed this challenge by employing a fully automated multi-objective design optimization approach using a genetic algorithm optimization framework. In the study, they introduced a systematic design method that combines modeling, FEA, genetic algorithms, and optimization to create lattice structures with customized mechanical properties. Through strategically arranging eight distinctly neither isotropic nor auxetic unit cell states, the stiffness tensor in a 5 × 5 × 5 cubic symmetric lattice structure was controlled. This design choice results in a large counterintuitive combinatorial design space, providing flexibility in achieving desired mechanical properties. The application of Multiphoton lithography fabrication (MPL) and experimental characterization of the optimized metamaterial highlights a practical real-world use and confirms the close correlation between theoretical and experimental data. The comprehensive methodology integrates automated design, FEA, and optimization with MPL fabrication, and experimental characterization to validate the optimal structure, offering engineers and researchers with a valuable tool for creating lattice structures with customized mechanical properties.