Active mechanical metamaterials are emerging materials receiving tremendous attention in the past decades. Additive manufacturing (AM, or 3D printing) techniques empower the rational design and fabrication of complex, multiscale architectures that enable unprecedented mechanical properties and functionality of metamaterials. Moreover, the use of smart or stimuli-responsive materials for AM of active mechanical metamaterials offers new capabilities to program the mechanical, acoustic, or other functional properties. Herein, we present an overview of recent advances in AM of active mechanical metamaterials. The primary AM techniques used for mechanical metamaterial fabrication are discussed first. Several mechanical metamaterial structures and designs enabled by AM are summarized. Active mechanical metamaterial designs utilizing different stimuli, such as solvents, heat, and magnetic field, are introduced. Additionally, some functional applications of active material systems to create transforming mechanical metamaterials are included. Finally, the outlook and challenges for future research in this field are provided.

Recent advances in additive manufacturing of active mechanical metamaterials

Parameter optimization of bidirectional re-entrant auxetic honeycomb metamaterial based on genetic algorithm

Novel 2D star-shaped honeycombs with enhanced effective Young’s modulus and negative Poisson’s ratio

Additive-manufactured hierarchical multi-circular lattice structures for energy absorption application

Honeycombs derived from the combination of multiple kinds of structures have better energy absorption compared with a single structure. A novel bidirectional re-entrant honeycomb (BRH) is designed by combining four hexagonal honeycombs with the quadrangular-shaped honeycomb (QSH). The correctness and accuracy of two plateau stress theory are verified by the simulations. The effect of geometric parameters on the plateau stress and negative Poisson ′ s ratio (NPR) behavior is studied. The results show that two plateau stress facilitate energy absorption at the low-velocity, and the plateau stress of the BRH is also improved at the medium- and the high-velocity. In addition, the collapsed modes of various velocities and relative density are summarized. These results indicate the BRH has better impact resistance and the energy absorption capacity, and the special energy absorption is adjusted significantly by geometric parameters. Moreover, the NPR effect is more obvious at the low-velocity particularly. Thus, the design method of honeycomb metamaterials can improve the design efficiency for obtaining high performance structures with energy absorption capacity.

Liang Wang

Papers

Novel 2D star-shaped honeycombs with enhanced effective Young’s modulus and negative Poisson’s ratio

3D compression–torsion cubic mechanical metamaterial with double inclined rods

In-plane crushing response of a novel bidirectional re-entrant honeycomb with two plateau stress regions

Compression spin bio-inspired arm: A conceptual model based on compression–torsion cubic mechanical metamaterials with variable cross-section

Three-dimensional enhanced star-shaped honeycombs with negative thermal expansion