Mechanical properties of graphene oxide: A molecular dynamics study

In this paper, the mechanical properties of graphene oxide are obtained using the molecular dynamics analysis, including the ultimate stress, Young modulus, shear modulus and elastic constants, and the results are compared with those of pristine graphene. It is observed that the increase of oxide agents (–O) and (–OH) leads to the increase of C–C bond length at each hexagonal lattice and as a result, alter the mechanical properties of the graphene sheet. It is shown that the elasticity modulus and ultimate tensile strength of graphene oxides (–O) and (–OH) decrease significantly causing the failure behavior of graphene sheet changes from the brittle to ductile. The results of shear loading tests illustrate that the increase of oxide agents (–O/–OH) results in the decrease of ultimate shear stress and shear module of the graphene sheet. It is shown that the increase of oxide agents in the graphene sheet leads to decrease of the elastic constants, in which the reduction of elastic properties in the armchair direction is more significant than the zigzag direction. Moreover, the graphene sheet with oxide agents (–O) and (–O/–OH) presents an anisotropic behavior.     

聚酰胺非晶相弹性性质预测

聚合物基复合材料宏观有效力学性质的确定需要复合材料中各个组分的基本力学性质。采用基于拓扑的关联指数法对11种典型聚酰胺非结晶相的体积模量、泊松比、杨氏模量、剪切模量等弹性性能进行了预测。结果表明,当温度从1K逐步增加到(Tg-20)K时,体积模量、杨氏模量和剪切模量随温度的增加呈指数规律减小;而泊松比则呈线性增加。当温度在玻璃化温度Tg附近(Tg-20)相似文献   

Finite element analysis of elastic property bounds of a composite with randomly distributed particles

The bounds of the elastic properties of an E-glass particle reinforced BISGMA/TEGDMA composite were predicted by a random unit cell model. Two means of tensile loading were used: iso-displacement loading and iso-stress loading. The iso-displacement loading predicts the upper bound of Young’s modulus, while iso-stress loading predicts the practical lower bound of Young’s modulus. The results showed that Young’s modulus increases, while Poisson’s ratio decreases with increasing filler content for both loading conditions. For comparative purposes, the upper and practical lower bounds were also calculated by Hashin’s method, a periodic three-dimensional single-particle, and two-particle unit cells. Analytical solutions using the Mori–Tanaka model and experiments were also conducted for verification purpose. The results showed that the random unit cell predicts better overall bounds for elastic properties.     

Young’s modulus and Poisson’s ratio of concrete at high temperatures: Experimental investigations

When exposed to fire, Young’s modulus of concrete degrades. Thus, exact knowledge of temperature-dependent reduction is important to determine the fire-resistance of concrete or composite members. Nevertheless, existing material properties for the Young’s and shear modulus of concrete are linked with some incertitudes.In addition, normative regulations lack information on the temperature-dependent Poisson’s ratio. In an attempt to overcome some of the existing uncertainties, experimental work was conducted to investigate elastic material properties of fire-exposed concrete. For this purpose, the Impulse Excitation Technique was used as an innovative testing technique. Based on experimental results, the authors propose new elastic material formulations for fire-exposed concrete.     

Prediction of Young’s modulus and Poisson ratio for foamed metals using octahedron model

Abstract

The present paper deals with the mathematical–physical expression of Young’s modulus and Poisson ratio of foamed metals. As it is known that, Young’s modulus and Poisson ratio are two basic mechanical parameters of engineering materials. Foamed metal is a class of excellent engineering materials with dual attributes of structural and functional characteristics; therefore, these two parameters are investigated for these materials, and the relevant mathematical–physical expressions are derived from the ‘octahedron model’ of porous materials in the present paper. The results show that the apparent Young’s modulus displays a quite complicated mathematical relationship to porosity of the porous body, and the apparent Poisson ratio is just a characteristic of the material constant almost not relative to porosity of the foamed metal.     

Brazilian disk test and digital image correlation: a methodology for the mechanical characterization of brittle materials

In this paper, an optimized and reliable approach for the evaluation of the mechanical properties of brittle materials is proposed and applied to the characterization of geopolymer mortars. In particular, the Young’s modulus, the Poisson’s ratio and the tensile strength are obtained by means of a Brazilian disk test combined with the digital image correlation (DIC) technique. The mechanical elastic properties are evaluated by a special routine, based on an over-deterministic method and the least square regression, that allows to fit the displacement fields experienced by the samples during the experiment. Error sources, like center of the disk location and rigid-body motion components, were analyzed and estimated automatically with the proposed procedure in order to perform an accurate evaluation of the elastic constants. The strain field measured by DIC and the computed elastic properties were then used to perform a local stresses analysis. This latter was exploited to investigate the failure mechanisms and to evaluate the tensile strength of the investigated material and the obtained data were compared with those predicted by the ASTM and ISMR standards. Three different loading platens (flat, rod and curved) were adopted for the Brazilian test in order to evaluate their effect on the elastic properties calculation, on the failure mechanisms and tensile strength evaluation. Results reveal that the curve platens are the most suitable for the tensile strength calculation, whereas the elastic properties did not show any influence from the loading configuration. Furthermore, the proposed procedure, of easy implementation, allows to accurately calculate Young’s modulus, Poisson’s ratio and the tensile strength of brittle materials in a single experiment.     

Comparison of different identification techniques for measurement of quasi-zero Poisson’s ratio of fabric-reinforced laminates

The resonalyser method is a material identification technique which is based on the measurement of resonance frequencies of freely suspended rectangular test plates, combined with numerical simulations. By adjusting the ratio of the width to the length of the test plate, the resonance frequencies can be made very sensitive for small variations of Poisson’s ratio. This study examines a fabric-reinforced composite material with a very small value of Poisson’s ratio. The material on which the experiments are performed is a carbon fabric-reinforced polyphenylene sulphide. The accurateness of the determined values of the in-plane elastic properties of the test plates is validated with static tensile tests. First, the four orthotropic elastic properties, Young’s moduli E₁₁ and E₂₂, the in-plane shear modulus G₁₂ and Poisson’s ratio ν₁₂, are identified using the resonalyser technique. Next, the obtained values for Young’s moduli and Poisson’s ratio are validated with static uni-axial tests.It can be concluded that the results derived from both measurement methods corresponded very well.     

A first-principles study on the structural, elastic, electronic, and optical properties of CdRh2O4

The structural, elastic, electronic, and optical properties of CdRh₂O₄ with cubic $ (Fd\overline{ 3} m) $ and orthorhombic (Pnma) structures have been investigated using a pseudopotential plane wave (PP-PW) method within the local density approximation (LDA). The calculated lattice parameters agree reasonably with the experimental values. The single-crystal elastic stiffness constants C _ij s of the cubic and orthorhombic phases are investigated using the stress–strain method. In addition, the polycrystalline elastic properties including bulk modulus, shear modulus, Young’s modulus, bulk modulus–shear modulus ratio, Poisson’s ratio, and elastic anisotropy ratio are determined based on Voigt–Reuss–Hill approach. The use of the hybrid functional sX-LDA leads to considerably improved electronic properties compared to standard LDA approach. On the other hand, the dielectric function, refraction index, reflectivity, conductivity function, and energy-loss spectra were obtained and analyzed on the basis of electronic band structures and density of states.     

The Elastic Constants and Anisotropy of Superconducting MgCNi3 and CdCNi3 Under Different Pressure

The second-order elastic constants (SOECs) and third-order elastic constants (TOECs) of MgCNi₃ and CdCNi₃ are presented by using first-principles methods combined with homogeneous deformation theory. The Voigt–Reuss–Hill (VRH) approximation are used to calculate the bulk modulus B, shear modulus G, averaged Young’s modulus E and Poisson’s ratio ν for polycrystals and these effective modulus are consistent with the experiments. The SOECs under different pressure of MgCNi₃ and CdCNi₃ are also obtained based on the TOECs. Furthermore, the Zener anisotropy factor, Chung–Buessem anisotropy index, and the universal anisotropy index are used to describe the anisotropy of MgCNi₃ and CdCNi₃. The anisotropy of Young’s modulus of single-crystal under different pressure is also presented.     

Mechanical property evaluation of single-walled carbon nanotubes by finite element modeling

Computational simulation for predicting mechanical properties of carbon nanotubes (CNTs) has been adopted as a powerful tool relative to the experimental difficulty. Based on molecular mechanics, an improved 3D finite element (FE) model for armchair, zigzag and chiral single-walled carbon nanotubes (SWNTs) has been developed. The bending stiffness of the graphene layer has been considered. The potentials associated with the atomic interactions within a SWNT were evaluated by the strain energies of beam elements which serve as structural substitutions of covalent bonds. The out-of-plane deformation of the bonds was distinguished from the in-plane deformation by considering an elliptical cross-section for the beam elements. The elastic stiffness of graphene has been studied and the rolling energy per atom has been calculated through the analysis of rolling a graphene sheet into a SWNT to validate the proposed FE model. The effects of diameters and helicity on Young’s modulus and the shear modulus of SWNTs were investigated. The simulation results from this work are comparable to both experimental tests and theoretical studies from the literatures.     

Temperature dependence of the elastic moduli of multiferroic PbFe2/3W1/3O3 ceramics

Elastic properties of multiferroic PbFe_2/3W_1/3O₃ (PFW) ceramics have been studied in a temperature range of 4.2–400 K, which contains the regions of existence of the ferroelectric relaxor and antiferromagnetic phases. The longitudinal, shear, and bulk elasticity moduli, Young’s modulus, and Poisson’s ratio of PFW ceramics have been determined for the first time. Regions of temperature stability of the elastic properties extending over several dozen degrees have been found.     

Theoretical Investigations of the Electronic,Elastic, Thermodynamics Properties and the Superconducting Transition Temperature of MNiBN (M = La,Ca)

The structural, electronic, elastic, and thermodynamic properties and the superconducting transition temperature of MNiBN (M = La, Ca) compounds are investigated by using the first principles within the generalized gradient approximation (GGA). The calculated lattice constants are found in an agreement with the available experimental data, and the deviations are underestimated by less than 2 %. The calculated elastic constants indicate that both of the MNiBN (M = La, Ca) compounds are mechanically stable. The shear modulus, Young’s modulus, Poisson’s ratio σ, and the ratio B/G are also calculated. Finally, the Debye temperature (?? _D) and the superconducting transition temperature are obtained.     

FP-LAPW Calculation of Elastic, Thermal Properties and Chemical Bonding of Heavy REN (RE = Tb–Lu)

The full-potential linearised augmented plane wave (FP-LAPW) method has been used to study the elastic, thermal and bonding properties of heavy rare earth nitrides REN (RE = Tb–Lu). In the present work, band structure and density of states of TbN–LuN are studied. We have calculated the Young’s modulus E, shear modulus G, bulk modulus B, Poisson’s ratio υ, shear anisotropy factor A, and Lame’s coefficients μ & λ for all these compounds. Thermal property such as Debye temperature and average sound velocity have been estimated for all these compounds and their relation to elastic properties is discussed. To understand the bonding nature of these compounds, the electronic charge density has been calculated for all these compounds and the relation of this bonding with the mechanical properties has been studied. From the calculated ratio of bulk to shear modulus B/G, these compounds are found to be brittle in nature. The value of Poisson’s ratio suggests that these compounds are ionic and this is in agreement with the charge density plots which show the ionic bonding nature of these compounds. The G values show that these compounds are easier to shear on the plane [110] rather than on plane [100] for all the compounds except YbN.     

Structural,elastic, and lattice dynamical properties of Germanium diiodide (GeI2)

To investigate the structural, elastic, and lattice dynamical properties of the germanium diiodide, we have performed the first-principles calculations by using the local density approximation method based on density-functional theory. Some basic physical parameters such as lattice constant, bulk modulus and its first derivatives, elastic constants, shear modulus, Young’s modulus, and Poisson’s ratio are calculated. The phonon dispersion curves, electronic band-structures, and total and partial density of states have also been calculated for ground state C6 phase of GeI₂. Our results show that this structure has got 1.72 eV direct band gap. Our secondary results on the temperature-dependent behavior of thermodynamical properties such as entropy, heat capacity, internal energy, and free energy are also presented for the same compounds. The obtained results are in good agreement with the available experimental and other theoretical data.     

Structural and lattice dynamical properties of Zintl NaIn and NaTl compounds

The first-principles calculations based on the density-functional theory have been performed using both the generalized–gradient approximation (GGA) and the local-density approximation (LDA) to investigate many physical properties of NaIn and NaTl compounds. Specifically, the structural (lattice constant, bulk modulus, pressure derivative of bulk modulus, phase transition pressure (P_t)), mechanical (second-order elastic constants (C_ij), Young’s modulus, isotropic shear modulus, Zener anisotropy factor, Poisson’s ratio, sound velocities), thermo dynamical (cohesive energy, formation enthalpy, Debye temperature), and the vibrational properties (phonon dispersion curves and one-phonon density of states) are calculated and compared with the available experimental and other theoretical data. Also, we have presented the temperature variations of various thermo dynamical properties such as free energy, internal energy, entropy and heat capacity for the same compounds.     

Multi Modal Dynamic Linear Viscoelastic Back Analysis for Asphalt Mixes

In this paper, an investigation was performed to determine the accuracy of a simplified viscoelastic back analysis to interpret dynamic loading tests on asphalt mixes (AM). First, quasi-static cyclic tension–compression lab tests were performed on different AM to fit the 3 dimensional 2S2P1D linear viscoelastic (LVE) model. Considering these tests on very different types of AM, a LVE material with “averaged” viscoelastic properties was obtained. Then, these “averaged” viscoelastic properties were considered to perform finite elements method numerical simulations of dynamic loading tests on a cylinder. The simulations were performed at ten different temperatures from \(-\,40\) to 50 \({^\circ }\)C. The longitudinal, flexural and torsional modes of vibration are studied. The complex Young’s modulus and complex Poisson’s ratio were first obtained using the viscoelastic 2S2P1D model at the first resonance frequency for the three studied modes of vibration. Then, a combined viscoelastic back analysis, which has the advantage of simplicity, was used to determine the elastic equivalent properties and the phase angle of the material. The results obtained directly with the 2S2P1D model and the results from the combined viscoelastic back analysis results regarding both the Young’s modulus and the Poisson’s ratio are discussed in the paper.     

Influence of linear work hardening on the elastic–plastic behavior of a functionally graded thick-walled tube

For the problem of a functionally graded thick-walled tube subjected to internal pressure, we have already presented the elasticity solution based on the Voigt method in Xin et al. (Int J Mech Sci 89:344–349, 2014). This paper discusses the elastic–plastic problem of the functionally graded thick-walled tube subjected to internal pressure and gives the solution in terms of volume fractions of the constituents. We assume that the tube consists of two linear work hardening elastic–plastic constituents and the volume fraction of one phase is a power function varied in the radical direction. The Lamé constants and yield stress of the constituents of the FGM tube are given rather than Young’s modulus and yield stress with different unknown parameters of the whole material in the existing papers. As the internal pressure increases, the deformations of one phase and two phases from elastic to plastic are analyzed. The present method is valid for materials with different Poisson’s ratios rather than constant Poisson’s ratios usually used in the existing references to obtain the effective Young’s modulus. More importantly, the influences of linear work hardening on plastic behavior are considered in this work.     

The structural and mechanical properties of CdN compound: A first principles study

First principles calculations are performed to investigate the structural, elastic, and mechanical properties of CdN for various structures: NaCI, CsCl, ZnS, wurtzite, WC, CdTe, NiAs, and CuS. The local density and generalized gradient approximations are used for modeling exchange–correlation effects. Our calculations indicate that CuS (B18) structure is energetically the most stable among the considered structures. The some basic physical properties such as lattice parameters, bulk modulus, and second-order elastic constants are calculated. We have also predicted the shear modulus, Young’s modulus, Poison’s ratio, Debye temperature, and sound velocities. Our structural and some other results are consistent with the available theoretical data.     

Effects of Structural Parameters on the Poisson's Ratio and Compressive Modulus of 2D Pentamode Structures Fabricated by Selective Laser Melting

Metamaterials have been receiving an increasing amount of interest in recent years. As a type of metamaterial, pentamode materials (PMs) approximate the elastic properties of liquids. In this study, a finite-element analysis was conducted to predict the mechanical properties of PM structures by altering the thin wall thicknesses and layer numbers to obtain an outstanding load-bearing capacity. It was found that as the thin wall thickness increased from 0.15 to 0.45 mm, the compressive modulus of the PM structures increased and the Poisson’s ratio decreased. As the layer number increased, the Poisson’s ratio of the PM structures increased rapidly and reaches a stable value ranging from 0.50 to 0.55. Simulation results of the stress distribution in the PM structures confirmed that stress concentrations exist at the junctions of the thin walls and weights. For validation, Ti–6Al–4V specimens were fabricated by selective laser melting (SLM), and the mechanical properties of these specimens (i.e., Poisson’s ratio and elastic modulus) were experimentally studied. Good consistency was achieved between the numerical and experimental results. This work is beneficial for the design and development of PM structures with simultaneous load-bearing capacity and pentamodal properties.     

Modelling of the collision of two viscoelastic spherical shells

In the present paper, the collision of two viscoelastic spherical shells is investigated using the wave theory of impact. The model developed here suggests that after the moment of impact quasi-longitudinal and quasi-transverse shock waves are generated, which then propagate along the spherical shells. The solution behind the wave fronts is constructed with the help of the theory of discontinuities. Since the local bearing of the materials of the colliding viscoelastic shells is taken into account, the solution in the contact domain is found via the modified Hertz contact theory involving the operator representation of viscoelastic analogs of Young’s modulus and Poisson’s ratio. The collision of two elastic spherical shells is considered first, and then using Volterra correspondence principle, according to which the elastic constants in the governing equations should be replaced by the corresponding viscoelastic operators, the solution obtained for elastic shells is extended over the case of viscoelastic shells.