Anisotropic Thermal and Mechanical Characteristics of Graphene: A Molecular Dynamics Study (original) (raw)
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The molecular mechanics study on mechanical properties of graphene and graphite
Applied Physics A, 2014
The elastic and fracture properties of both twodimensional graphene and three-dimensional graphite were calculated based on molecular mechanics method, including the atomic bonding (stretching and bending) and nonbonding (van der Waal) energies. Since graphene and graphite are periodically arranged atomic structures, the representative unit cell could be chosen to illustrate their deformations under uniform loadings. The carbon bond length and angle changes of the graphene/graphite as well as the interlayer distance variations of the graphite under various loading conditions could be realized numerically under the geometry constraints and minimum energy assumption. It was found that the mechanical properties of graphene/graphite demonstrated distinct directional dependences at small and large deformations. In elastic region, graphene was in-plane isotropic, while graphite was transversely isotropic with the symmetry axis along out-ofplane direction. Meanwhile, the in-plane deformation of the representative unit cell was not uniform along armchair direction due to the discrete and non-uniform distributions of the atoms. The fracture of graphene/graphite could be predicted based on critical bond length criteria. It was noticed that the fracture behavior were directional dependent, and the fracture strain under simple tension was lower while loading on zigzag edge of graphene/graphite, which was consistent with molecular dynamics simulation results.
Anisotropic mechanical properties of graphene sheets from molecular dynamics
Physica B: Condensed Matter, 2010
Anisotropic mechanical properties are observed for a sheet of graphene along different load directions. The anisotropic mechanical properties are attributed to the hexagonal structure of the unit cells of the graphene. Under the same tensile loads, the edge bonds bear larger load in the longitudinal mode (LM) than in the transverse mode (TM), which causes fracture sooner in LM than in TM. The Young's modulus and the third order elastic modulus for the LM are slightly larger than that for the TM. Simulation also demonstrates that, for both LM and TM, the loading and unloading stress-strain response curves overlap as long as the graphene is unloaded before the fracture point. This confirms that graphene sustains complete elastic and reversible deformation in the elongation process.
Molecular Dynamics Simulation of Fracture of Graphene
13th International Conference on Fracture (2013)
"A molecular dynamics (MD) simulation to assess the effect of crack length on the ultimate tensile strength of infinitely large armchair and zigzag graphene sheets is presented. The strength of graphene is inversely proportional to the square-root of crack length as in continuum fracture theories. Further comparison of the strength given by MD simulations with Griffith’s energy balance criterion demonstrates a reasonable agreement. Armchair and zigzag graphene sheets with 2.5 nm long crack exhibit around 55% of the strength of pristine sheets. Investigation of the influence of temperature on the strength of graphene indicates that sheets at higher temperatures fail at lower strengths, due to high kinetic energy of atoms. We also observe out-of-plane deformations of the crack tip at equilibrium configuration of both types of sheets due to compressive forces acting on the crack surface. This deformation propagates with applied strain in the direction normal to the crack and eventually generates ripples in the entire sheet."
Mechanical simulation of a single sheet of graphene: a study on the aplications of nanomaterials
2016
Graphene is a bidimensional carbon allotrope with a hexagonal molecular lattice, in which its mechanical, electrical and optical properties have motivated an intense level of research of the scientific community in the last decade. This dissertation’s main objectives are the development of a consistent finite element model for the both linear and non linear simulation of graphene’s mechanical behaviour. Two interatomic potentials were used in the linear simulations of the model to assess their influence on the elastic properties. Non linear simulations were performed to obtain graphene’s mechanical strength. The finite element model results are compared with results collected from previous works on the fields of molecular dynamics and other atomistic computational methods. The present study shows that finite element models are able to predict well the mechanical properties of graphene.
Mechanical properties of double-layered graphene sheets
Computational Materials Science, 2013
In this paper, the molecular structural mechanics method is employed to calculate the mechanical properties of a double-layered carbon graphene sheet more accurately. For this purpose, covalent bonds are modeled using nonlinear beam elements and van der Waals interactions are replaced by nonlinear truss elements. Morse potential and Lennard-Jones potential equations are used to simulate the covalent bonds and van der Waals interactions, respectively. For each atom, van der Waals forces are considered with respect to all the other atoms located in its cutoff radius. In addition to in-plane mechanical properties of single and double-layered graphene sheets some out-of-plane properties like the thickness-wise stiffness and shear modulus are studied. The results indicate that Young's modulus of a double-layered carbon graphene sheet decreases linearly with strain while Poisson's ratio is independent from it. Also it is noted that the thickness-wise stiffness significantly increases while the distance between the two layers declines however the shear modulus is independent from shear strain.
Temperature-dependent elastic properties of single layer graphene sheets
Materials & Design, 2010
Elastic properties of single layer graphene sheets (SLGSs) with different values of aspect ratio are presented by using molecular dynamics simulation. SLGSs subjected to uniaxial tension, shear load and transverse uniform pressure are simulated under temperature varying from 300K to 700K. Based on the classical plate theory, an individual orthotropic plate model is adopted for SLGSs. By direct measuring the
Computational Materials Science, 2016
The modified Nosé-Hoover (NH) thermostat incorporated with molecular dynamics calculation is applied to evaluate the mechanical properties of multi-layered graphene structures at atmospheric pressure, including Young's modulus, shear modulus, Poisson's ratio, specific heats, linear coefficient of thermal expansion (CTE) and thermal conductivity. The thermostat method takes into account the contribution of phonons by virtue of the vibrational energy of the lattice and the zero-point energy, thereby providing a better prediction of the low temperature thermodynamic properties. The focuses of this study are placed on exploring their temperature, size, chirality and layer number dependences. The validity of the calculations is further demonstrated by comparing the calculated results with those derived from the existing thermostats, namely, the standard NH, Nosé-Hoover chain (NHC), ''massive" NHC and velocity-rescaling thermostats, and also with the literature experimental and theoretical data. It was found that the calculated mechanical properties of the graphene sheets agree well with the published experimental and theoretical results. The results also show that their Young's modulus, shear modulus, linear CTE and Poisson's ratio tend to decrease with the increase of temperature, size and layer number, where the linear CTE would eventually converge to that of the bulk graphite. Besides, the heat capacity and thermal conductivity at low temperatures show the high temperature dependences, i.e., the third and k (k = 2-3) power of temperature, which are more consistent with that obtained from Debye model.
Evaluation of Thickness Influence on the Mechanical Properties of Graphene Sheet using Fem
IAEME PUBLICATION, 2015
A computational simulation, FE software ansys has been adopted to evaluate the mechanical properties of defect free and defected graphene sheets. The finite element models are developed using FE software Ansys. Individual graphene sheet is simulated as a frame-like structure and the primary bonds between two nearest-neighboring atoms are treated as beam members. The beam properties for input into a finite element model are calculated via the concept of energy equivalence between molecular mechanics and structural mechanics. The developed models are capable of predicting Young’s moduli, Poisson’s ratio of Graphene sheets under cantilever loading conditions. The response of finite element models showed that the mechanical properties of graphene sheets Young’s moduli are precarious to the graphene thickness. Young’s modulus and Poisson’s ratio of graphene sheet with different width and height of defect free, vacancy defect and stone wales defect is determined and the results are verified with existed literature for defect free condition.
Molecular dynamics simulations of thermal expansion properties of single layer graphene sheets
Molecular Simulation, 2017
The area coefficients of thermal expansion (CTEs) of perfect single layer graphene sheet (SLGS) and SLGS with vacancy defects of different distributions were calculated in this work through molecular dynamics (MD) simulations. The effects of some parameters such as temperature, SLGS size, sample area size, vacancy fraction and vacancy distribution on CTE were investigated extensively. Numerical results clearly revealed that for both perfect and defective SLGSs, the area CTEs are negative and nonlinear with the temperature variation within a wide temperature range. Moreover, the area CTEs tend to be more insensitive to the temperature when temperature is higher than 600 K. The area CTE of a perfect SLGS converges only when the SLGS size and the ratio of the sample size to the SLGS size is above a critical value. When the SLGS size or the sample size is small, the area CTE shows distinct size-dependence. In addition, a set of empirical formulations is proposed for evaluating the area CTEs of perfect SLGSs within a wide temperature range. For the SLGS with vacancy defects, the area CTE decreases with the increase of vacancy fraction within the temperature range considered. Furthermore, compared with a decentralised distribution of vacancy defects, a concentrated distribution leads to a smaller value of area CTE of SLGS, especially for the case of high vacancy fraction.
Crack Propagation Morphologies of Single-Layered Graphene under Various Low Temperatures
2017
The fracture behavior of single layer graphene sheet (SLGS) has been a subject of intensive research in recent years. Understanding the fracture mechanism of graphene under low temperature conditions is crucial for engineering applications of graphene. In this paper, a molecular dynamics (MD) simulation is employed to assess the effect of temperature on fracture properties of SLGS. The evolution of atomically cleaving of graphene is also discussed. A finite area of SLGS is subject to uniaxial tensile load in zigzag direction under various environmental temperatures between 1K and 77K. The effects of temperature on fracture properties as well as cracked morphology of SLGS are investigated. While our simulated results of fracture strength of SLGS agree with reported datum, simulated cracks are nucleated spontaneously instead of artificially inserted. The findings presented herein would help understand the morphology of a single layer pristine graphene sheet subjected to crack propagat...