Advances in mechanics of hierarchical composite materials

Stronger, tougher, and lighter materials are always among the relentless pursuits of material scientists and engineers. The hierarchical design inspired by nature has been considered as one of the most promising strategies to improve the mechanical properties and functionalities of synthetic materials beyond their present limitations. Therefore, this paper provides a featured review on mechanical studies of hierarchical composite materials, including natural biological materials as well as man-made materials, to shed light on the progress and perspectives of this research field. This review first discusses several typical hierarchical designs observed in nature, followed by four principle mechanisms extracted as the main contributions to the superior mechanical properties. Then, the applications of these principle mechanisms are demonstrated in three typical synthetic material systems, namely, fiber-reinforced composites, network materials, and mechanical metamaterials. Furthermore, the remaining challenges and future perspectives for the design and optimization of hierarchical composites are proposed.