High Strength-to-Weight Ratio Mechanical Metamaterials Targeting Top Left Quadrant of Ashby Charts

Mechanical metamaterials (MMs) with much higher strength-to-weight ratios are becoming revolutionary materials in many engineering fields because of their unique mechanical properties and light weight. This review provides the advancements in lattice, functionally graded, hierarchical, and hybrid structures. The development of tunable and chiral MMs has enabled the design of adaptable, multifunctional materials with applications in body armor, shock absorbtion, and noise-vibration attenuation. Additionally, multiphase and hybrid metamaterials have demonstrated the importance of utilizing novel MM designs, such as kirigami, to achieve tunable Poisson’s ratios and material properties for specific applications. Researchers have also investigated materials inspired by nature for their potential to enhance sustainability, energy absorption, and durability, revealing intriguing applications in biomedical and advanced materials. From the findings of more than 20 recent studies, we present a thorough overview of significant obstacles in scalability, manufacturing constraints, and practical applications. Notwithstanding considerable advancements, the enduring trade-off between attaining high strength and minimal weight continues to be a main challenge for researchers. For future studies, techniques like machine learning (ML) will become important tools for speeding up the design of MMs, and hybrid manufacturing techniques that integrate additive manufacturing (AM) with traditional processes can enhance the production of MMs.