Damage-tolerant mechanical metamaterials designed by fail-safe topology optimization

Mechanical metamaterials are celebrated for their remarkable properties and advances in additive manufacturing, yet their damage tolerance in aerospace and other demanding environments remains underexplored despite their lightweight and high-strength design. This work proposes a novel approach to design damage-tolerant metamaterials using fail-safe topology optimization to ensure their mechanical performance remains resilient to local damages. The design strategy focuses on minimizing metamaterial's weight while preserving its load-bearing capacity post-damage, with the effective bulk modulus used as a measure. To enhance performance under varying, complex, or uncertain loads, an isotropy constraint is incorporated into the design. The proposed method involves a trade-off where the metamaterial's enhanced damage tolerance is achieved by slightly reducing the load-bearing capacity of the intact structure. By tuning structural redundancy, the method facilitates the development of lightweight, mechanically robust structures. Numerical simulations and experimental tests on three-point bending beam structures made from periodically ordered damage-tolerant meta- materials show that the proposed design maintains load-bearing capacity after damage while enhancing safety and reliability by preserving structural integrity and load transfer paths.