Abstract
Three-dimensional (3D) chiral mechanical metamaterials enable behaviors not accessible in ordinary materials. In particular, a coupling between displacements and rotations can occur, which is symmetry-forbidden without chirality. In this work, we solve three open challenges of chiral metamaterials. First, we provide a simple analytical model, which we use to rationalize the design of the chiral characteristic length. Second, using rapid multi-photon multi-focus 3D laser microprinting, we manufacture samples with more than 105 micrometer-sized 3D chiral unit cells. This number surpasses previous work by more than two orders of magnitude. Third, using analytical and numerical modeling, we realize chiral characteristic lengths of the order of ten unit cells, changing the sample-size dependence qualitatively and quantitatively. In the small-sample limit, the twist per axial strain is initially proportional to the sample side length, reaching a maximum at the characteristic length. In the thermodynamic limit, the twist per axial strain is proportional to the square of the characteristic length. We show that chiral micropolar continuum elasticity can reproduce this behavior.
Highlights
Three-dimensional (3D) chiral mechanical metamaterials enable behaviors not accessible in ordinary materials
Our 2017 experiments on pronounced push-to-twist conversion effects in chiral architectures came as somewhat of a surprise2. In these experiments2, we demonstrated large static twist effects in 3D cubic chiral metamaterials composed of moderately large total numbers of cubic unit cells of ≤500
The results presented in refs. 6,7, both show that the behavior of twist versus N can be tailored by the coupling strength between chiral unit cells
Summary
Three-dimensional (3D) chiral mechanical metamaterials enable behaviors not accessible in ordinary materials. Using rapid multi-photon multifocus 3D laser microprinting, we manufacture samples with more than 105 micrometer-sized 3D chiral unit cells This number surpasses previous work by more than two orders of magnitude. Using analytical and numerical modeling, we realize chiral characteristic lengths of the order of ten unit cells, changing the sample-size dependence qualitatively and quantitatively. Cauchy elasticity tensor describes the generally rich connection between strains and stresses, whereas it completely neglects chiral twist effects. Usual strain-related effects do not depend on N On this background, our 2017 experiments on pronounced push-to-twist conversion effects in chiral architectures came as somewhat of a surprise In these experiments, we demonstrated large static twist effects in 3D cubic chiral metamaterials composed of moderately large total numbers of cubic unit cells of ≤500.
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