scholarly journals An Isotropic Auxetic Structural Network With Limited Shear Stiffness

2011 ◽  
Author(s):  
Alessandro Spadoni
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Poisson’S Ratio ◽  
Shear Stiffness ◽  
Element Model ◽  
Mirror Image ◽  
Poisson's Ratio ◽  
Structural Components ◽  
Sandwich Construction ◽  
Structural Network

The chiral lattice is a unique structural network not symmetric to its mirror image, and with a negative Poisson’s ratio. Previous investigations have considered this structural network for the design of superior structural components with sandwich construction, but these were limited by the in-plane Poisson’s ratio predicted to be exactly −1. This paper presents estimates of the mechanical properties of the chiral lattice obtained from a multi-cell finite-element model. It is shown that the chiral lattice has a shear stiffness bound by that of the triangular lattice and it is very compliant to direct stresses. The minimum in-plane poisson’s ratio is estimated to be ≈ −0.94.

scholarly journals Idealized 3D Auxetic Mechanical Metamaterial: An Analytical, Numerical, and Experimental Study

Materials ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 993
Author(s):  
Naeim Ghavidelnia ◽  
Mahdi Bodaghi ◽  
Reza Hedayati
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Poisson’S Ratio ◽  
Element Model ◽  
Industrial Applications ◽  
Poisson's Ratio ◽  
Geometrical Parameters ◽  
Mechanical Metamaterials ◽  
Strength And Stiffness ◽  
The One

Mechanical metamaterials are man-made rationally-designed structures that present unprecedented mechanical properties not found in nature. One of the most well-known mechanical metamaterials is auxetics, which demonstrates negative Poisson’s ratio (NPR) behavior that is very beneficial in several industrial applications. In this study, a specific type of auxetic metamaterial structure namely idealized 3D re-entrant structure is studied analytically, numerically, and experimentally. The noted structure is constructed of three types of struts—one loaded purely axially and two loaded simultaneously flexurally and axially, which are inclined and are spatially defined by angles θ and φ. Analytical relationships for elastic modulus, yield stress, and Poisson’s ratio of the 3D re-entrant unit cell are derived based on two well-known beam theories namely Euler–Bernoulli and Timoshenko. Moreover, two finite element approaches one based on beam elements and one based on volumetric elements are implemented. Furthermore, several specimens are additively manufactured (3D printed) and tested under compression. The analytical results had good agreement with the experimental results on the one hand and the volumetric finite element model results on the other hand. Moreover, the effect of various geometrical parameters on the mechanical properties of the structure was studied, and the results demonstrated that angle θ (related to tension-dominated struts) has the highest influence on the sign of Poisson’s ratio and its extent, while angle φ (related to compression-dominated struts) has the lowest influence on the Poisson’s ratio. Nevertheless, the compression-dominated struts (defined by angle φ) provide strength and stiffness for the structure. The results also demonstrated that the structure could have zero Poisson’s ratio for a specific range of θ and φ angles. Finally, a lightened 3D re-entrant structure is introduced, and its results are compared to those of the idealized 3D re-entrant structure.

Young's Modulus and Poisson's Ratio Estimation Based on PSO Constriction Factor Method Parameters Evaluation

2019 ◽  
Vol 9 (2) ◽  
pp. 33-46
Author(s):  
George Lucas Dias ◽  
Ricardo Rodrigues Magalhães ◽  
Danton Diego Ferreira ◽  
Bruno Henrique Groenner Barbosa
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Young’S Modulus ◽  
Cantilever Beam ◽  
Poisson’S Ratio ◽  
Inverse Analysis ◽  
Young's Modulus ◽  
Poisson's Ratio ◽  
Factor Method ◽  
Constriction Factor

The knowledge of materials' mechanical properties in design during product development phases is necessary to identify components and assembly problems. These are problems such as mechanical stresses and deformations which normally cause plastic deformation, early fatigue or even fracture. This article is aimed to use particle swarm optimization (PSO) and finite element inverse analysis to determine Young's Modulus and Poisson's ratio from a cantilever beam, manufactured in ASTM A36 steel, subjected to a load of 19.6 N applied to its free end. The cantilever beam was modeled and simulated using a commercial FEA software. Constriction Factor Method (PSO variation) was used and its parameters were analyzed in order to improve errors. PSO results indicated Young's Modulus and Poisson's ratio errors of around 1.9% and 0.4%, respectively, when compared to the original material properties. Improvement in the data convergence and a reduction in the number of PSO iterations was observed. This shows the potentiality of using PSO along with Finite Element Inverse Analysis for mechanical properties evaluation.

FINITE ELEMENT ANALYSIS OF MECHANICAL DEFORMATION OF CHONDROCYTE TO 2D SUBSTRATE AND 3D SCAFFOLD

2015 ◽  
Vol 15 (05) ◽  
pp. 1550077 ◽  
Author(s):  
JINJU CHEN ◽  
D. L. BADER ◽  
D. A. LEE ◽  
M. M. KNIGHT
Keyword(s):  
Mechanical Properties ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Poisson’S Ratio ◽  
Glass Plate ◽  
Mechanical Deformation ◽  
Poisson's Ratio ◽  
3D Scaffold ◽  
Element Analysis ◽  
Cell Functions

The mechanical properties of cells are important in regulation of many aspects of cell functions. The cell may respond differently to a 2D plate and a 3D scaffold. In this study, the finite element analysis (FEA) was adopted to investigate mechanical deformation of chondrocyte on a 2D glass plate and chondrocyte seeded in a 3D scaffold. The elastic properties of the cell differ in these two different compression tests. This is because that the cell sensed different environment (2D plate and 3D construct) which can alter its structure and mechanical properties. It reveals how the apparent Poisson's ratio of a cell changes with the applied strain depends on its mechanical environment (e.g., the elastic moduli and Poisson's ratios of the scaffold and extracellular matrix) which regulates cell mechanics. In addition, the elastic modulus of the nucleus also plays a significant role in the determination of the Poisson's ratio of the cell for the cells seeded scaffold. It also reveals the intrinsic Poisson's ratio of the cell cannot be obtained by extrapolating the measured apparent Poisson's ratio to zero strain, particularly when scaffold's Poisson's ratio is quite different from the cell.

scholarly journals Modelling of Nanoindentation of TiAlN and TiN Thin Film Coatings for Automotive Bearing

2019 ◽  
Vol 8 (3) ◽  
pp. 7194-7199
Keyword(s):  
Mechanical Properties ◽  
Finite Element Method ◽  
Finite Element ◽  
Yield Strength ◽  
Young’S Modulus ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Poisson's Ratio ◽  
The Finite Element Method ◽  
Element Method

Bearings are critical components for the transmission of motion in machines. Automotive components, especially bearings, will wear out over a certain period of time because they are constantly subjected to high levels of stress and friction. Studies have proven that coatings can extend the lifespan of bearings. Hence, it is necessary to conduct studies on coatings for bearings, particularly the mechanical and wear properties of the coating material. This detailed study focused on the mechanical properties of single-coatings of TiN and TiAIN using the finite element method (FEM). The mechanical properties that can be obtained from nano-indentation experiments are confined to just the Young’s modulus and hardness. Therefore, nanoindentation simulations were conducted together with the finite element method to obtain more comprehensive mechanical properties such as the yield strength and Poisson’s ratio. In addition, various coating materials could be examined by means of these nanoindentation simulations, as well the effects of those parameters that could not be controlled experimentally, such as the geometry of the indenter and the bonding between the coating and the substrate. The simulations were carried out using the ANSYS Mechanical APDL software. The mechanical properties such as the Young’s modulus, yield strength, Poisson’s ratio and tangent modulus were 370 GPa, 19 GPa, 0.21 and 10 GPa, respectively for the TiAlN coating and 460 GPa, 14 GPa, 0.25 and 8 GPa, respectively for the TiN coating. The difference between the mechanical properties obtained from the simulations and experiments was less than 5 %.

Prediction of Elastic Constants of Carbon Fabric/Polyurethane Composites

2016 ◽  
Vol 258 ◽  
pp. 233-236 ◽  
Author(s):  
Shun Fa Hwang ◽  
Hsuan Ting Liu
Keyword(s):  
Finite Element ◽  
Finite Element Model ◽  
Young’S Modulus ◽  
Elastic Constants ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Element Model ◽  
Curing Temperature ◽  
Poisson's Ratio ◽  
Fiber Fabric

The purpose of this work is to study a new composite material consisting of polyurethane (PU) resin and carbon fiber fabric. This PU resin is superior in impact, viscosity, low curing temperature, and short curing time. If this resin is combined with fiber fabric by vacuum assisted resin transfer method, the fabrication time will be short. Since it is a braided composite, it’s important to have a model to predict the elastic constants for different braid angels. To predict the elastic constants including Young’s modulus, shear modulus, and Poisson’s ratio, a finite element model is established. In this model a braided layer is treated as two uni-directional layers. Then, the elastic constants of this composite with different braid angels are estimated. After that, the composites with different braid angels are fabricated and tested to obtain the elastic constants, and the comparison with the finite element results is made. The results indicate that the agreement is very good for the Young’s modulus. For the Poisson’s ratio, the difference between the prediction and the measurement is reasonable. From the comparison, it can be concluded that the finite element model is good. Then, this model is used to predict all in-plane elastic constants for arbitrary braid angles.

A Finite Element Simulation Study on the Properties of a Multi-Material Based Auxetic Metamaterial

2019 ◽  
Author(s):  
Yutai Su ◽  
Xin Wu ◽  
Jing Shi ◽  
Jin Wang
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Young’S Modulus ◽  
Poisson’S Ratio ◽  
Young's Modulus ◽  
Large Strain ◽  
Poisson's Ratio ◽  
Material Structure ◽  
Geometry Design ◽  
Trade Offs

Abstract Auxetic metamaterials have unique structural designs exhibiting zero or negative Poisson’ ratios during stretch/compression processes, which enable many critical applications such as sensing technology, wearable devices, and weight reduction parts. However, it is difficult to achieve ideal performance of various structural designs through geometry manipulation due to the beam/wall buckling under large strain. One way to minimize the occurrence of buckling is by introducing the high elasticity on the joints, but trade-offs exist among different mechanical behaviors. To this end, this study proposes to use a multi-material combining with the structure optimization to design an auxetic structure. The basic re-entrant structure is employed due to its simplicity, and finite element method (FEM) is adopted to demonstrate the effectiveness of this newly proposed strategy regarding the auxetic behaviors. For this multi-material structure, a different Young’s modulus is designed to apply on the additional arch structure. A series of simulations, which consider the influence of the mechanical properties, are conducted to investigate the change of auxetic behaviors such as stress distribution, Poisson’s ratio, and equivalent Young’s modulus against the applied material properties. The results indicate that the mechanical properties are strongly affected by the geometry design and the applied materials properties. Meanwhile, the buckling effect of the beam/wall could be eliminated if the hinge strength is small enough. The trade-off between equivalent mechanical properties and Poisson’s ratio could also be tuned through this newly material-based design.

scholarly journals The Selection and Optimization of the Reconfigurable Shaped Reflector Structure Material

2018 ◽  
Vol 175 ◽  
pp. 01024
Author(s):  
Hang Zhao ◽  
Houfei Fang ◽  
Matthew J. Santer ◽  
Lan Lan ◽  
Yangqing Hou ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Poisson’S Ratio ◽  
Poisson's Ratio ◽  
Finite Element Models ◽  
Main Structure ◽  
Surface Accuracy ◽  
Lattice Materials ◽  
Simulation Results ◽  
Changing Rate

The method of applying deformable 2-D lattice materials in design of the main structure of a reconfigurable shaped reflector is proposed in this paper. Hex-chiral NPR (Negative Poisson's Ratio) lattice, re-entrant NPR lattice and star ZPR (Zero Poisson's Ratio) lattice are investigated in forming the main structure of a reflector, according to the mechanical properties requirement. Finite element models of reflectors built by these three types of lattice materials are developed. An example of a reflector with reconfigurable shape, which is transformed from a standard paraboloid, is given. The curvature change of the deformed shape is calculated. Then, the region with the largest curvature changing rate is found and the configuration of such area is regenerated. Finally, the surface accuracy of the region with the largest curvature changing rate is evaluated for reflectors built by the three compared lattice materials. The simulation results show that the highest surface accuracy is obtained when applying the hex-chiral lattice to the design of the reconfigurable shaped reflector.

scholarly journals Applicability of a Three-Layer Model for the Dynamic Analysis of Ballasted Railway Tracks

Vibration ◽  
2021 ◽  
Vol 4 (1) ◽  
pp. 151-174
Author(s):  
André F. S. Rodrigues ◽  
Zuzana Dimitrovová
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Dynamic Analysis ◽  
Shear Stiffness ◽  
Shear Resistance ◽  
Railway Track ◽  
Fe Model ◽  
Inertial Effects ◽  
Layer Model ◽  
3D Finite Element

In this paper, the three-layer model of ballasted railway track with discrete supports is analyzed to access its applicability. The model is referred as the discrete support model and abbreviated by DSM. For calibration, a 3D finite element (FE) model is created and validated by experiments. Formulas available in the literature are analyzed and new formulas for identifying parameters of the DSM are derived and validated over the range of typical track properties. These formulas are determined by fitting the results of the DSM to the 3D FE model using metaheuristic optimization. In addition, the range of applicability of the DSM is established. The new formulas are presented as a simple computational engineering tool, allowing one to calculate all the data needed for the DSM by adopting the geometrical and basic mechanical properties of the track. It is demonstrated that the currently available formulas have to be adapted to include inertial effects of the dynamically activated part of the foundation and that the contribution of the shear stiffness, being determined by ballast and foundation properties, is essential. Based on this conclusion, all similar models that neglect the shear resistance of the model and inertial properties of the foundation are unable to reproduce the deflection shape of the rail in a general way.

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