scholarly journals Large characteristic lengths in 3D chiral elastic metamaterials

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Tobias Frenzel ◽  
Vincent Hahn ◽  
Patrick Ziemke ◽  
Jonathan Ludwig Günter Schneider ◽  
Yi Chen ◽  
...  
Keyword(s):  
Size Dependence ◽  
Characteristic Length ◽  
Axial Strain ◽  
Three Dimensional ◽  
Small Sample ◽  
Micropolar Continuum ◽  
Chiral Metamaterials ◽  
Mechanical Metamaterials ◽  
Unit Cells ◽  
Elastic Metamaterials

AbstractThree-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.

scholarly journals Divergent Design of Mechanical Metamaterials Clan Deducted from Arc-serpentine Curve

2021 ◽  
Author(s):  
Shengli Mi ◽  
Hongyi Yao ◽  
Xiaoyu Zhao ◽  
Wei Sun
Keyword(s):  
Thick Plate ◽  
Three Dimensional ◽  
Spatial Arrangement ◽  
Design Strategies ◽  
Shape Morphing ◽  
Mechanical Metamaterials ◽  
Unit Cells ◽  
Combinatorial Principles ◽  
Composite Curve ◽  
Typical Design

Abstract The exotic properties of mechanical metamaterials are determined by their unit-cells' structure and spatial arrangement, in analogy with the atoms of conventional materials. Companioned with the mechanism of structural or cellular materials1–5, the ancient wisdom of origami6–11 and kirigami12–16 and the involvement of multiphysics interaction2,17,18 enrich the programable mechanical behaviors of metamaterials, including shape-morphing8,12,14,16,19, compliance4,5,8,17,20, texture2,18,21, and topology11,18,22−25. However, typical design strategies are mainly convergent, which transfers various structures into one family of metamaterials that are relatively incompatible with the others and do not fully bring combinatorial principles3,10,26 into play. Here, we report a divergent strategy that designs a clan of mechanical metamaterials with diverse properties derived from a symmetric curve consisting of serpentines and arcs. We derived this composite curve into planar and cubic unit-cells and modularized them by attaching magnetics. Moreover, stacking each of them yields two- and three-dimensional auxetic metamaterials, respectively. Assembling with both modules, we achieved three thick plate-like metamaterials separately with flexibility, in-plane buckling, and foldability. Furthermore, we demonstrated that the hybrid of paradox properties is possible by combining two of the above assembles. We anticipate that this divergent strategy paves the path of building a hierarchical library of diverse combinable mechanical metamaterials and making conventional convergent strategies more efficient to various requests. Main

scholarly journals Non-Auxetic Mechanical Metamaterials

Materials ◽  
2019 ◽  
Vol 12 (4) ◽  
pp. 635 ◽  
Author(s):  
Christa de Jonge ◽  
Helena Kolken ◽  
Amir Zadpoor
Keyword(s):  
Mechanical Properties ◽  
Yield Stress ◽  
Fatigue Behavior ◽  
Analytical Data ◽  
Three Dimensional ◽  
Mechanical Metamaterials ◽  
Macro Scale ◽  
Unit Cells ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

The concept of “mechanical metamaterials” has become increasingly popular, since their macro-scale characteristics can be designed to exhibit unusual combinations of mechanical properties on the micro-scale. The advances in additive manufacturing (AM, three-dimensional printing) techniques have boosted the fabrication of these mechanical metamaterials by facilitating a precise control over their micro-architecture. Although mechanical metamaterials with negative Poisson’s ratios (i.e., auxetic metamaterials) have received much attention before and have been reviewed multiple times, no comparable review exists for architected materials with positive Poisson’s ratios. Therefore, this review will focus on the topology-property relationships of non-auxetic mechanical metamaterials in general and five topological designs in particular. These include the designs based on the diamond, cube, truncated cube, rhombic dodecahedron, and the truncated cuboctahedron unit cells. We reviewed the mechanical properties and fatigue behavior of these architected materials, while considering the effects of other factors such as those of the AM process. In addition, we systematically analyzed the experimental, computational, and analytical data and solutions available in the literature for the titanium alloy Ti-6Al-4V. Compression dominated lattices, such as the (truncated) cube, showed the highest mechanical properties. All of the proposed unit cells showed a normalized fatigue strength below that of solid titanium (i.e., 40% of the yield stress), in the range of 12–36% of their yield stress. The unit cells discussed in this review could potentially be applied in bone-mimicking porous structures.

scholarly journals Optical and Infrared Helical Metamaterials

Nanophotonics ◽  
2016 ◽  
Vol 5 (4) ◽  
pp. 510-523 ◽  
Author(s):  
Johannes Kaschke ◽  
Martin Wegener
Keyword(s):  
Electron Beam Lithography ◽  
Three Dimensional ◽  
Far Field ◽  
Optical Performance ◽  
Chiral Metamaterials ◽  
The Past ◽  
Optical Effects ◽  
Unit Cells ◽  
Novel Applications ◽  
Microfabrication Techniques

AbstractBy tailoring metamaterials with chiral unit cells, giant optical activity and strong circular dichroism have been achieved successfully over the past decade. Metamaterials based on arrays of metal helices have revolutionized the field of chiral metamaterials, because of their capability of exhibiting these pronounced chiro-optical effects over previously unmatched bandwidths. More recently, a large number of new metamaterial designs based on metal helices have been introduced with either optimized optical performance or other chiro-optical properties for novel applications.The fabrication of helical metamaterials is, however, challenging and even more so with growing complexity of the metamaterial designs. As conventional two-dimensional nanofabrication methods, for example, electron-beam lithography, are not well suited for helical metamaterials, the development of novel three-dimensional fabrication approaches has been triggered.Here, we will discuss the theory for helical metamaterials and the principle of operation. We also review advancements in helical metamaterial design and their limitations and influence on optical performance. Furthermore, we will compare novel nano- and microfabrication techniques that have successfully yielded metallic helical metamaterials. Finally, we also discuss recently presented applications of helical metamaterials extending beyond the use of far-field circular polarizers.

scholarly journals Harnessing the anisotropic multistability of stacked-origami mechanical metamaterials for effective modulus programming

2018 ◽  
Vol 29 (14) ◽  
pp. 2933-2945 ◽  
Author(s):  
Sattam Sengupta ◽  
Suyi Li
Keyword(s):  
Adaptive Systems ◽  
Three Dimensional ◽  
Unit Cell ◽  
Effective Modulus ◽  
Stable States ◽  
Mechanical Metamaterials ◽  
Principal Axes ◽  
Unit Cells ◽  
Multiple Unit ◽  
Parametric Analyses

This study examines a three-dimensional, anisotropic multistability of a mechanical meta material based on a stacked Miura-ori architecture, and investigates how such a unique stability property can impart stiffness and effective modulus programming functions. The unit cell of this metamaterial can be bistable due to the nonlinear relationship between rigid-folding and crease material bending. Such bistability possesses an unorthodox property: the arrangement of elastically stable and unstable equilibria are different along different principal axes of the unit cell, so that along certain axes the unit cell exhibits two force–deformation relationships concurrently within the same range of deformation. Therefore, one can achieve a notable stiffness adaptation via switching between the two stable states. As multiple unit cells are assembled into a metamaterial, the stiffness adaptation can be aggregated into an on-demand modulus programming capability. That is, via strategically switching different unit cells between stable states, one can control the overall effective modulus. This research examines the underlying principles of anisotropic multistability, experimentally validates the feasibility of stiffness adaptation, and conducts parametric analyses to reveal the correlations between the effective modulus programming and Miura-ori designs. The results can advance many adaptive systems such as morphing structures and soft robotics.

Intertwined microlattices greatly enhance the performance of mechanical metamaterials

2019 ◽  
Vol 24 (8) ◽  
pp. 2636-2648 ◽  
Author(s):  
Zacharias Vangelatos ◽  
Vasileia Melissinaki ◽  
Maria Farsari ◽  
Kyriakos Komvopoulos ◽  
Costas Grigoropoulos
Keyword(s):  
Strain Hardening ◽  
Bulk Material ◽  
Three Dimensional ◽  
Structural Complexity ◽  
Structural Principle ◽  
Mechanical Metamaterials ◽  
Unit Cells ◽  
Octet Truss ◽  
Enhanced Strain ◽  
Improved Performance

Mechanical metamaterials demonstrate augmented properties derived from their engineered structure. Advances in three-dimensional (3D) printing technologies have enabled the fabrication of complex metamaterial structures even at the microscale, contributing to the development of light-weight materials with superior mechanical properties. However, understanding of metamaterial strain hardening that is intrinsic to both the structure and arrangement of novel unit cells is sparse and fairly empirical. The main objective of this study was to introduce a new design approach for 3D mechanical metamaterials with enhanced strain hardening and energy absorption, fabricated at the microscale by multiphoton lithography, which is the only fabrication technique that can produce micrometer length scales and high structural complexity. This was accomplished by intertwining simple polyhedra to create more complex geometries in 3D space, using penetration twins as a point of reference, a mechanism of crystal in-growth wherein distinct crystals appear to penetrate each other. This structural principle was used to intertwine the lattice members of the structure and tailor their buckling behavior. The present design is inspired by the first stellation of the rhombic dodecahedron. With this concept, plastic deformation can be controlled through localized buckling of select lattice members. Finite element simulations and nanoindentation experiments demonstrate remarkably improved performance with respect to both strain hardening and energy dissipation of the structure compared to both the bulk material and one of the most thoroughly studied ultralight, ultrastiff mechanical metamaterials, the octet truss.

scholarly journals Planar Mechanical Metamaterials with Embedded Permanent Magnets

Materials ◽  
2020 ◽  
Vol 13 (6) ◽  
pp. 1313 ◽  
Author(s):  
Viacheslav Slesarenko
Keyword(s):  
Mechanical Characteristics ◽  
Design Space ◽  
Permanent Magnets ◽  
Three Dimensional ◽  
Three Dimensional Printing ◽  
Numerical Studies ◽  
Mechanical Metamaterials ◽  
Unit Cells ◽  
Post Buckling ◽  
Dimensional Printing

The design space of mechanical metamaterials can be drastically enriched by the employment of non-mechanical interactions between unit cells. Here, the mechanical behavior of planar metamaterials consisting of rotating squares is controlled through the periodic embedment of modified elementary cells with attractive and repulsive configurations of the magnets. The proposed design of mechanical metamaterials produced by three-dimensional printing enables the efficient and quick reprogramming of their mechanical properties through the insertion of the magnets into various locations within the metamaterial. Experimental and numerical studies reveal that under equibiaxial compression various mechanical characteristics, such as buckling strain and post-buckling stiffness, can be finely tuned through the rational placement of the magnets. Moreover, this strategy is shown to be efficient in introducing bistability into the metamaterial with an initially single equilibrium state.

scholarly journals Stiffer, Stronger and Centrosymmetrical Class of Pentamodal Mechanical Metamaterials

Materials ◽  
2019 ◽  
Vol 12 (21) ◽  
pp. 3470 ◽  
Author(s):  
Yan Huang ◽  
Xiaozhe Zhang ◽  
Muamer Kadic ◽  
Gongying Liang
Keyword(s):  
Finite Element Method ◽  
Size Dependence ◽  
Load Factor ◽  
The Finite Element Method ◽  
New Class ◽  
Scalability Analysis ◽  
Mechanical Metamaterials ◽  
Unit Cells ◽  
Anisotropic Structures ◽  
Infinite Case

Pentamode metamaterials have been used as a crucial element to achieve elastical unfeelability cloaking devices. They are seen as potentially fragile and not simple for integration in anisotropic structures due to a non-centrosymmetric crystalline structure. Here, we introduce a new class of pentamode metamaterial with centrosymmetry, which shows better performances regarding stiffness, toughness, stability and size dependence. The phonon band structure is calculated based on the finite element method, and the pentamodal properties are evaluated by analyzing the single band gap and the ratio of bulk and shear modulus. The Poisson’s ratio becomes isotropic and close to 0.5 in the limit of small double-cone connections. Stability and scalability analysis results show that the critical load factor of this structure is obviously higher than the classical pentamode structure under the same static elastic properties, and the Young’s modulus gradually converges to a stable value (the infinite case) with an increasing number of unit cells.

Vacancies for controlling the behavior of microstructured three-dimensional mechanical metamaterials

2018 ◽  
Vol 24 (2) ◽  
pp. 511-524 ◽  
Author(s):  
Z Vangelatos ◽  
K Komvopoulos ◽  
CP Grigoropoulos
Keyword(s):  
Strain Energy ◽  
Three Dimensional ◽  
Crystal Lattices ◽  
Mechanical Metamaterials ◽  
Buckling Behavior ◽  
Unit Cells ◽  
Octet Truss ◽  
Topological States ◽  
Energy Dissipated

Mechanical metamaterials are designed to exhibit enhanced properties not found in natural materials or to bolster the properties of existing materials. The theoretical foundations for tuning the mechanical properties have been established, including topological states, controllable buckling behavior, and quasi-two-dimensional mechanical metamaterials with structures containing vacancies. However, the fabrication and experimental procedures to study these structures at the microscale have not been developed yet and the three-dimensional (3D) architectures examined to date are fairly limited. In this study, 3D mechanical metamaterial structures with select unit cells designed to have vacancies were fabricated by multi-photon lithography, having as the principal objective to control (localize) failure and increase the strain energy capacity of the structure. The metamaterial structure from which all the current designs originate is the octet-truss structure, one of the most widely studied 3D metamaterials. The design of the structures was inspired by the role of vacancies in crystal lattices. Vacancies were introduced in the metamaterial structures to allow localized buckling of lattice members to occur in specific unit cells. The significant increase of the strain energy dissipated in these metamaterials is demonstrated by nanoindentation experiments and finite element results. Vacancy effects on the dynamic response of metamaterial structures are also examined in the light of modal analysis simulations. The findings of this study illustrate the importance of strategically placing vacancies in the microlattices of metamaterial structures to control the overall mechanical behavior and greatly increase strain energy dissipation.

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

scholarly journals Hierarchical mechanical metamaterials built with scalable tristable elements for ternary logic operation and amplitude modulation

2021 ◽  
Vol 7 (9) ◽  
pp. eabf1966
Author(s):  
Hang Zhang ◽  
Jun Wu ◽  
Daining Fang ◽  
Yihui Zhang
Keyword(s):  
Structural Diversity ◽  
Cell Number ◽  
Structural Elements ◽  
Ternary Logic ◽  
Stable States ◽  
One Dimensional ◽  
Logic Operation ◽  
Artificial Materials ◽  
Mechanical Metamaterials ◽  
Unit Cells

Multistable mechanical metamaterials are artificial materials whose microarchitectures offer more than two different stable configurations. Existing multistable mechanical metamaterials mainly rely on origami/kirigami-inspired designs, snap-through instability, and microstructured soft mechanisms, with mostly bistable fundamental unit cells. Scalable, tristable structural elements that can be built up to form mechanical metamaterials with an extremely large number of programmable stable configurations remains illusive. Here, we harness the elastic tensile/compressive asymmetry of kirigami microstructures to design a class of scalable X-shaped tristable structures. Using these structure as building block elements, hierarchical mechanical metamaterials with one-dimensional (1D) cylindrical geometries, 2D square lattices, and 3D cubic/octahedral lattices are designed and demonstrated, with capabilities of torsional multistability or independent controlled multidirectional multistability. The number of stable states increases exponentially with the cell number of mechanical metamaterials. The versatile multistability and structural diversity allow demonstrative applications in mechanical ternary logic operators and amplitude modulators with unusual functionalities.

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