scholarly journals Tunable Negative Poisson’s Ratio in Van der Waals Superlattice

Research ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Xiaowen Li ◽  
Xiaobin Qiang ◽  
Zhenhao Gong ◽  
Yubo Zhang ◽  
Penglai Gong ◽  
...  
Keyword(s):  
Poisson’S Ratio ◽  
Electronic Band Structure ◽  
Hexagonal Boron Nitride ◽  
Van Der Waals ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Electronic Band ◽  
Mechanical Metamaterials ◽  
Wide Range ◽  
Negative Poisson's Ratio

Negative Poisson’s ratio (NPR) materials are functional and mechanical metamaterials that shrink (expand) longitudinally after being compressed (stretched) laterally. By using first-principles calculations, we found that Poisson’s ratio can be tuned from near zero to negative by different stacking modes in van der Waals (vdW) graphene/hexagonal boron nitride (G/h-BN) superlattice. We attribute the NPR effect to the interaction of pz orbitals between the interfacial layers. Furthermore, a parameter calculated by analyzing the electronic band structure, namely, distance-dependent hopping integral, is used to describe the intensity of this interaction. We believe that this mechanism is not only applicable to G/h-BN superlattice but can also explain and predict the NPR effect in other vdW layered superlattices. Therefore, the NPR phenomenon, which was relatively rare in 3D and 2D materials, can be realized in the vdW superlattices by different stacking orders. The combinations of tunable NPRs with the excellent electrical/optical properties of 2D vdW superlattices will pave a novel avenue to a wide range of multifunctional applications.

scholarly journals Analytical relationships for re-entrant honeycombs

2020 ◽  
Author(s):  
Reza Hedayati ◽  
Naeim Ghavidelnia
Keyword(s):  
Yield Stress ◽  
Analytical Solutions ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Fe Method ◽  
Wide Range ◽  
Unit Cells ◽  
Negative Poisson's Ratio ◽  
Internal Angle

Mechanical metamaterials have emerged in the last few years as a new type of artificial material which show properties not usually found in nature. Such unprecedented properties include negative stiffness, negative Poisson’s ratio, negative compressibility and fluid-like behaviors. Unlike normal materials, materials with negative Poisson’s ratio (NPR), also known as auxetics, shrink laterally when a compressive load is applied to them. The 2D re-entrant honeycombs are the most prevalent auxetic structures and many studies have been dedicated to study their stiffness, large deformation behavior, and shear properties. Analytical solutions provide inexpensive and quick means to predict the behavior of 2D re-entrant structures. There have been several studies in the literature dedicated to deriving analytical relationships for hexagonal honeycomb structures where the internal angle θ is positive (i.e. when the structure has positive Poisson’s ratio). It is usually assumed that such solutions also work for corresponding re-entrant unit cells. The goal of this study was to find out whether or not the analytical relationships obtained in the literature for θ>0 are also applicable to 2D-reentrant structures (i.e. when θ<0). Therefore, this study focused on unit cells with a wide range of internal angles from very negative to very positive values. For this aim, new analytical relationships were obtained for hexagonal honeycombs with possible negativity in the internal angle θ in mind. Numerical analyses based on finite element (FE) method were also implemented to validate and evaluate the analytical solutions. The results showed that, as compared to analytical formulas presented in the literature, the analytical solutions derived in this work give the most accurate results for elastic modulus, Poisson’s ratio, and yield stress. Moreover, some of the formulas for yield stress available in the literature fail to be valid for negative ranges of internal angle (i.e. for auxetics). However, the yield stress results of the current study demonstrated good overlapping with numerical results in both the negative and positive domains of θ.

Qualitative Analysis and Design of Mechanical Metamaterials

2017 ◽  
Author(s):  
Sreekalyan Patiballa ◽  
Girish Krishnan
Keyword(s):  
Qualitative Analysis ◽  
Poisson’S Ratio ◽  
Compliant Mechanisms ◽  
Flow Behavior ◽  
Load Flow ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Analysis And Design ◽  
Mechanical Metamaterials ◽  
Negative Poisson's Ratio

This paper presents a new mechanics-based framework for the qualitative analysis and conceptual design of mechanical meta-materials. The methodology is inspired by recent advances in the insightful synthesis of compliant mechanisms by visualizing a kinetostatic field of forces that flow through the mechanism geometry. The framework relates load flow behavior in the microstructure geometry to the global behavior of the materials, such as auxetic (negative poisson’s ratio), high bulk modulus, and high shear modulus. This understanding is used to synthesize and demonstrate novel planar microstructures that exhibit negative poisson’s ratio behavior. Furthermore, the paper identifies three unique classes of qualitative design problems for planar mechanical microstructures that can be potentially solved using this framework.

Development of uni-stretch woven fabrics with zero and negative Poisson’s ratio

2017 ◽  
Vol 88 (18) ◽  
pp. 2076-2092 ◽  
Author(s):  
Adeel Zulifqar ◽  
Tao Hua ◽  
Hong Hu
Keyword(s):  
Poisson’S Ratio ◽  
Tensile Tests ◽  
Research Area ◽  
Woven Fabrics ◽  
Poisson's Ratio ◽  
Negative Poisson’S Ratio ◽  
Wide Range ◽  
Differential Shrinkage ◽  
Weaving Technology ◽  
Negative Poisson's Ratio

Fabrics with zero or negative Poisson’s ratio are referred as auxetic fabrics, which have the unusual property of lateral expansion or zero expansion upon stretch. The use of conventional materials and machinery to produce auxetic fabrics has gained the interest of researchers in recent years. However, this approach is limited to knitted fabrics only. The development of auxetic fabric using conventional yarns and weaving technology is a research area that is still unaddressed. This paper reports a study on the development of a novel class of stretchable auxetic woven fabrics by using conventional yarns and weaving machinery. The phenomenon of differential shrinkage was successfully employed to realize auxetic geometries capable of inducing auxetic behavior in woven fabrics, and a series of auxetic woven fabrics were fabricated with elastic and non-elastic yarns and a dobby machine. The uni-axial tensile tests showed that auxetic woven fabrics developed exhibited zero or negative Poisson’s ratio over a wide range of longitudinal strain.

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