A realistic generic model for anti-tetrachiral systems (original) (raw)
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Tuning the Mechanical Properties of the Anti-Tetrachiral System Using Nonuniform Ligament Thickness
Physica Status Solidi (b), 2020
The mechanical properties of the anti-tetrachiral structure having the thickness of the ligament changing symmetrically around the center are investigated using analytical and numerical methods. For the purpose of deriving a theoretical model, the Euler–Bernoulli beam theory is used to determine the relation among the acting moment, the angle of rotation of the nodes, and the bending energy stored. Analysis of the results indicates that a change in geometry has a minor effect on Poisson’s ratio, if any at all; however, it can result in relatively large changes in Young’s modulus. Hence, it is shown that the mechanical properties can be altered selectively by adjusting the geometric features of chiral structures. The indications of the analytical model are validated using numerical methods for different values of the geometric parameters and are found to be in good agreement. In the process, it is shown that there are regions of the parameter space where the mechanical properties of the anti-tetrachiral are insensitive to variations in certain geometric dimensions.
Advanced Engineering Materials, 2014
Chiral systems may exhibit auxetic behavior, i.e. they may have a negative Poisson's ratio. This particular property has led to their being studied extensively by several authors. A Finite Elements Study is presented here, investigating the mode of connection between the nodes and ligaments in the anti-tetrachiral structure. The results show that the amount of gluing material used to attach the ligaments to the node will not affect the Poisson's ratio, but may have a large influence on the observed stiffness of the structure (Young's modulus). It is also shown that the stiffness of the glue will have a large effect on the mode of deformation of the chiral system. This change in mechanism was found to effect the stiffness of the structure but not its Poisson's ratios.
CHIRAL HONEYCOMB MESO-STRUCTURES FOR SHEAR FLEXURE
2011
Chiral honeycombs are auxetic cellular structures that exhibits negative Poison's ratio. Chiral honeycombs are structures arranged in an array of cylinders connected by ligaments. Four different configurations of these geometries with 4-and 6-ligaments attached are investigated for its use in shear layer of non-pneumatic wheel. The objective of the study is to find an ideal geometry for the shear layer while meeting its requirements of shear properties (about 6.5 MPa effective shear modulus and 0.15 maximum effective shear strain) with polycarbonate as base material. Finite Element (FE) based numerical tests are carried out and optimum chiral mesostructures are found for the target shear properties. Parametric studies on geometries are conducted to find the effect of geometries on the target properties. The effect of cell wall thickness is studied and the optimum thickness is suggested to meet the target requirements. Effect of direction of shear loading has been studied on each different configuration in order to minimize the effect of direction of loading.
On the properties of auxetic meta-tetrachiral structures
Physica Status Solidi B-basic Solid State Physics, 2008
Auxetics are systems which get fatter when stretched and thinner when compressed i.e. they exhibit a negative Poisson's ratio. Here, we present an analysis of a novel class of structures (referred to as ‘meta-chiral') which belong to the class of auxetics constructed using chiral building blocks. We show through analytical modelling that some of these systems can exhibit negative Poisson's ratios, the extent of which will depend, amongst other things, on the geometry of the system. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Dynamic Response of Chiral Truss-core Assemblies
Journal of Intelligent Material Systems and Structures, 2006
Periodic cellular configurations with negative Poisson's ratio have attracted the attention of several researchers because of their superior dynamic characteristics. Among the geometries with a negative Poisson's ratio, the chiral topology features localized deformed configurations when excited at one of its natural frequencies. This is of particular importance as resonance can be exploited to minimize the power required for the appearance of localized deformations, thus giving practicality to the concept. The particular nature of these deformed configurations and the authority provided by the chiral geometry suggest the application of the proposed structural configuration for the design of innovative lifting devices, such as helicopter rotor blades or airplane wings. The dynamic characteristics of chiral structures are here investigated through a numerical model and experimental investigations. The numerical formulation uses dynamic shape functions to accurately describe the behavior of the considered structural assembly over a wide frequency range. The model is used to predict frequency response functions, and to investigate the occurrence of localized deformations. Experimental tests are also performed to demonstrate the accuracy of the model and to illustrate the peculiarities of the behavior of the considered chiral structures.
Advances in Materials Science and Engineering, 2016
The present study investigates the influence of topology and morphology on the effective stiffness of chiral cellular materials in the transverse plane by means of a homogenization method. For this purpose, finite element models of representative volume elements for regular hexagonal and hexagonal-chiral configurations are used and simulations are conducted to quantify how cell topology—that is, chirality inside the cell—and cell wall slenderness affect the effective stiffness. Closed form solutions for regular hexagonal square and triangular RVEs provided in the literature are then taken as a basis for model validation. The results indicate that there are drastic differences between regular hexagonal and hexagonal-chiral configurations, which can be explained in terms of deformation mechanism transformations between bending and stretching. The investigations also reveal the positive impact of cell wall slenderness on stiffness due to volumetric increase in the cell wall material re...
Planar isotropic structures with negative Poisson’s ratio
International Journal of Solids and Structures, 2012
A new design principle is suggested for constructing auxetic structures-the structures that exhibit negative Poisson's ratio (NPR) at macroscopic level. We propose 2D assemblies of identical units made of a flexible frame with a sufficiently rigid reinforcing core at the centre. The core increases the frame resistance to the tangential movement thus ensuring high shear stiffness, whereas the normal stiffness is low being controlled by the local bending response of the frame. The structures considered have hexagonal symmetry, which delivers macroscopically isotropic elastic properties in the plane perpendicular to the axis of the symmetry. We determine the macroscopic Poisson's ratio as a ratio of corresponding relative displacements computed using the direct microstructural approach. It is demonstrated that the proposed design can produce a macroscopically isotropic system with NPR close to the lower bound of À1. We also developed a 2D elastic Cosserat continuum model, which represents the microstructure as a regular assembly of rigid particles connected by elastic springs. The comparison of values of NPRs computed using both structural models and the continuum approach shows that the continuum model gives a healthy balance between the simplicity and accuracy and can be used as a simple tool for design of auxetics.
IJERT-Modeling and Analysis of Structures withNegative Poisson’s Ratio
International Journal of Engineering Research and Technology (IJERT), 2020
https://www.ijert.org/modeling-and-analysis-of-structures-with-negative-poissons-ratio https://www.ijert.org/research/modeling-and-analysis-of-structures-with-negative-poissons-ratio-IJERTV9IS030469.pdf Auxetic structures are the structures with negative poisons ratio and display the peculiar behaviour of lateral expansion when they are stretched which is different from conventional structures. They get equal and opposing densification when compressed. Light weight, high strength, impact damping capabilities, and stiffness offers potential applications in the field of aerospace, automobile crash box, implantable devices, military protection equipment, suspension mount, intelligent actuators. The present work is focused on analysing the directional Auxeticity of tetra chiral Materials through design and analysis. The practical predictions about the global elastic properties of auxetic structures, such as re-entrant hexagonal cell, re-entrant star, re-entrant triangular and lozenge square structures are obtained with parametric 3D NX.11.0 and Ansys 19.2. A fused deposition Modelling in technique is used build prototypes of Auxetic structure. The analysis of the structures clearly established the auxetic behaviour of all the considered model's lateral expansion.