Mechanical Metamaterials

A design paradigm to create robust robotic metamaterials using versatile gear clusters is demonstrated. It enables intriguing programmability of elastic properties and shape while preserving stability for intelligent machines.

In natural materials, defects determine many properties. In spin-analogue mechanical metamaterials, deterministically inserted topological defects enable the design of complex deformation and stress distributions.

Efficient strategies to optimize metamaterial design for specific applications are urgently needed despite the rapid progress in this area. Here the authors propose a computational method combining an optimization algorithm with discrete element simulations for the automatic design of mechanical metamaterial actuators.

Origami is a promising source of inspiration in designing foldable structures and reconfigurable metamaterials. Here, building on exact folding kinematic conditions, an algorithmic design of rigidly-foldable origami structures is presented, allowing the engineering of metamaterials with arbitrary complex crease patterns.

Chiral mechanical metamaterials enable unusual effects, such as coupling between strain and twist. Here, manufactured microstructured samples with >10⁵ chiral unit cells exhibit large characteristic lengths, in agreement with analytical and numerical modelling and micropolar continuum elasticity.

Shape-shifting structures are important building blocks in the design of reconfigurable materials and devices with advanced functionalities. Here, versatile metamaterials with 3D-to-3D shape-shifting behavior upon thermal activation are fabricated by adapting a 3D printer to print on curved surfaces.

Long-range interactions have often been considered as a nuisance or correction to the desired features of metamaterials. Here, nonlocal interactions in 2D acoustic metamaterials are instead exploited as a tool to engineer peculiar wave dispersions, such as multiple roton-like minima, leading to negative and triple refraction.

Computing approaches based on mechanical mechanisms are discussed, with a view towards a framework in which adaptable materials and structures act as a distributed information processing network.

A reprogrammable mechanical metamaterial constructed of bistable unit cells that can be switched independently and reversibly between two stable states with distinct mechanical properties using magnetic actuation is demonstrated.

This work presents a mechanical metamaterial with 1D array of bistable arches where nonreciprocity and reversibility can be independently programmed. The effects of asymmetry both at the structural and element level on propagation of transition waves are examined.

Kirigami, a traditional paper cutting art, offers a promising strategy for 2D-to-3D shape morphing through cut-guided deformation. Here, authors report a simple strategy of cut boundary curvature-guided 3D shape morphing and its applications in non-destructive grippers and dynamically conformable heaters.

While origami-inspired metamaterials can spatially fold, they usually collapse along the deployment direction limiting applicability. Here authors introduce a cellular structure that can be reprogrammed in-situ to not only deploy and rigidly flat-fold but also lock and offer rigidity across all directions.

Mechanical logic, while slower than its electronic counterpart, has the potential to be integrated into mechanical devices and a robustness in extreme environments. In this manuscript, Mei et al demonstrate reprogrammable mechanical logic which can perform combinatorial and sequential logic.

4D metamaterials offer the additional functionality of being responsive to external stimuli. Here, a metamaterial-based soft robot is composed of bilayer plates that can rotate and translate in response to thermal stimuli, allowing controlled motion.

A structured fabric constructed of linked hollow polyhedral particles (resembling chain mail) can be simply and reversibly tuned between flexible and rigid states; when it is compressed, its linked particles become jammed.

Microscale architecting enables metamaterials to achieve mechanical properties not accessible to bulk materials. Here the authors show that established design protocols for the fracture of materials need to be revised to predict the failure of these materials.

Nanoarchitected materials have predominantly been studied in the quasi-static regime. Here, the supersonic microparticle impact regime for three-dimensional nanomaterials is uncovered, showcasing extreme energy dissipation and a predictive framework for damage.

Explanation is still lacking for the exotic nonlinear, nonuniform deformation of mechanism-based materials. Here the authors present an analytical framework for a canonical mechanism that can not only predict, but also precisely control deformation in these materials.

Mechanical metamaterials with alternating Poisson’s ratios are desirable for shape-morphing applications. Here the authors achieve this by utilizing self-contacting hard stops and flexible elements of different stiffnesses to achieve time-ordered sequential deformation.