Rationally designed artificial materials enable mechanical properties that are inaccessible with ordinary materials. Pushing on an ordinary linearly elastic bar can cause it to be deformed in many ways. However, a twist, the counterpart of optical activity in the static case, is strictly zero. The unavailability of this degree of freedom hinders applications in terms of mode conversion and the realization of advanced mechanical designs using coordinate transformations. Here, we aim at realizing microstructured three-dimensional elastic chiral mechanical metamaterials that overcome this limitation. On overall millimeter-sized samples, we measure twists per axial strain exceeding 2°/%. Scaling up the number of unit cells for fixed sample dimensions, the twist is robust due to metamaterial stiffening, indicating a characteristic length scale and bringing the aforementioned applications into reach.

http://science.sciencemag.org/content/sci/358/6366/1072.full.pdf

Three-dimensional mechanical metamaterials with a twist

Mechanical Metamaterials and Their Engineering Applications

Mechanical design and multifunctional applications of chiral mechanical metamaterials: A review

Honeycombs are ultra-light materials with outstanding mechanical properties, which mainly originate from their unit cell configurations rather than the properties of matrix materials. Honeycombs are triggering in numerous promising applications in the fields of architecture, automotive, railway vehicle, marine, aerospace, satellite, packaging and medical implants, etc. Here we provide an in-depth overview of some important advances in basic structural design to obtain novel honeycombs with various improved mechanical properties. Firstly, the review introduces the classical honeycomb configurations. Then, a clear classification of advanced designs is established and discussed according to the design scale. The designs on the macro scale are divided into hierarchical, graded and disordered, while the designs on the meso scale are grouped as hybrid, curved ligament and reinforced strut. Moreover, the effects of different designs on the mechanical properties of honeycomb are discussed quantitatively. Finally, we summarize the important potential designs to improve the mechanical properties of honeycombs and the challenges in further research.

Advanced honeycomb designs for improving mechanical properties: A review

Auxetic nail: Design and experimental study

A novel three-dimensional mechanical metamaterial with compression-torsion properties

A novel chiral three-dimensional material with negative Poisson’s ratio and the equivalent elastic parameters

A novel metamaterial with tension-torsion coupling effect

By strengthening the pore with material different from that of matrix, a new type of negative thermal expansion materials with the re-entrant hexagonal honeycomb is designed in this paper. The equivalent Young's modulus, Poisson's ratio and the coefficient of thermal expansion (CTE) are studied by using Timoshenko beam theory and the analytical formulas of these equivalent parameters are derived. The results of analytical formulas and numerical simulation indicate that the CTE of the material can be controlled from positive to negative by changing the geometry features and material properties of the structure. Meanwhile, the negative Poisson's ratio effect of the original re-entrant honeycomb can be preserved. Moreover, this method for designing new metamaterials has also been generalized to three-dimensional materials.

https://iopscience.iop.org/article/10.1088/1361-665X/aacf73/pdf

Bin-Bin Zheng

Papers

A novel three-dimensional mechanical metamaterial with compression-torsion properties

A novel chiral three-dimensional material with negative Poisson’s ratio and the equivalent elastic parameters

A novel metamaterial with tension-torsion coupling effect

A novel re-entrant honeycomb of negative thermal expansion

An auxetic honeycomb structure with series-connected parallograms