Avinash Parashar

Effect of Point and Line Defects on Mechanical and Thermal Properties of Graphene: A Review

New materials with distinctive properties are arising and attracting the scientific community at regular intervals. Stiffness and strength are the important factors in determining stability and lifetime of any technological devices, but defects which are inevitable at the time of production can alter the structural properties of any engineering materials. Developing graphene with specific structural properties depends upon controlling these defects, either by removing or deliberately engineering atomic structure to gain or tailoring specific properties. In this article, a comprehensive review of defective graphene sheets with respect to its mechanical and thermal properties are presented and examined.

Representative volume element to estimate buckling behavior of graphene/polymer nanocomposite.

The aim of the research article is to develop a representative volume element using finite elements to study the buckling stability of graphene/polymer nanocomposites. Research work exploring the full potential of graphene as filler for nanocomposites is limited in part due to the complex processes associated with the mixing of graphene in polymer. To overcome some of these issues, a multiscale modeling technique has been proposed in this numerical work. Graphene was herein modeled in the atomistic scale, whereas the polymer deformation was analyzed as a continuum. Separate representative volume element models were developed for investigating buckling in neat polymer and graphene/polymer nanocomposites. Significant improvements in buckling strength were observed under applied compressive loading when compared with the buckling stability of neat polymer.

Optimised cut-off function for Tersoff-like potentials for a BN nanosheet: a molecular dynamics study.

In this article, molecular dynamics based simulations were carried out to study the tensile behaviour of boron nitride nanosheets (BNNSs). Four different sets of Tersoff potential parameters were used in the simulations for estimating the interatomic interactions between boron and nitrogen atoms. Modifications were incorporated in the Tersoff cut-off function to improve the accuracy of results with respect to fracture stress, fracture strain and Youngs modulus. In this study, the original cut-off function was optimised in such a way that small and large cut-off distances were made equal, and hence a single cut-off distance was used with all sets of Tersoff potential parameters. The single value of cut-off distance for the Tersoff potential was chosen after analysing the potential energy and bond forces experienced by boron and nitrogen atoms subjected to bond stretching. The simulations performed with the optimised cut-off function help in identifying the Tersoff potential parameters that reproduce the experimentally evaluated mechanical behaviour of BNNSs.

Tersoff potential with improved accuracy for simulating graphene in molecular dynamics environment

Graphene is an elementary unit for various carbon based nanostructures. The recent technological developments have made it possible to manufacture hybrid and sandwich structures with graphene. In order to model these nanostructures in atomistic scale, a compatible interatomic potential is required to successfully model these nanostructures. In this article, an interatomic potential with modified cut-off function for Tersoff potential was proposed to avoid overestimation and also to predict the realistic mechanical behavior of single sheet of graphene. In order to validate the modified form of cut-off function for Tersoff potential, simulations were performed with different set of temperatures and strain rates, and results were made to compare with available experimental data and molecular dynamics simulation results obtained with the help of other empirical interatomic potentials.

Study of Mode I Fracture of Graphene Sheets Using Atomistic Based Finite Element Modeling and Virtual Crack Closure Technique

In this letter a finite element based atomistic model is proposed. This model was employed to study the mode I fracture characteristics of graphene monolayers. The proposed model was found to be less numerically intensive with fewer degrees of freedom in comparison to other numerical techniques, such as Monte Carlo and molecular dynamics modeling. An approach based on the virtual crack closure technique was employed to develop the atomistic formulation for estimating strain energy release rates for graphene sheets under opening mode.

Multiscale model to investigate the effect of graphene on the fracture characteristics of graphene/polymer nanocomposites.

In this theoretical research work, the fracture characteristics of graphene-modified polymer nanocomposites were studied. A three-dimensional representative volume element-based multiscale model was developed in a finite element environment. Graphene sheets were modeled in an atomistic state, whereas the polymer matrix was modeled as a continuum. Van der Waals interactions between the matrix and graphene sheets were simulated employing truss elements. Fracture characteristics of graphene/polymer nanocomposites were investigated in conjunction with the virtual crack closure technique. The results demonstrate that fracture characteristics in terms of the strain energy release rate were affected for a crack lying in a polymer reinforced with graphene. A shielding effect from the crack driving forces is considered to be the reason for enhanced fracture resistance in graphene-modified polymer nanocomposites.

Molecular dynamics study on the mechanical response and failure behaviour of graphene: performance enhancement via 5–7–7–5 defects

A one atom-thick sheet of carbon exhibits outstanding elastic moduli and tensile strength in its pristine form but structural defects which are inevitable in graphene due to its production techniques can alter its structural properties. These defects in graphene are introduced either during the production process or deliberately by us to tailor its properties. This article discusses the performance enhancement of graphene by introducing pentagon–heptagon–heptagon–pentagon (5–7–7–5) defects. The effect of geometrical parameters such as the nearest neighbour distance and angular orientation between 5–7–7–5 defects on the mechanical properties and failure morphology of graphene was investigated in the frame of molecular dynamics. The mechanical properties and failure morphology of graphene was predicted to be the function of geometrical parameters between 5–7–7–5 defects. It has been predicted from the current study that the brittle behaviour of graphene can be modified to ductile with well controlled distribution of 5–7–7–5 defects. Also it has been predicted that the mechanical properties of graphene can be altered by proper distribution of 5–7–7–5 defects.

Multiscale Model to Study of Fracture Toughening in Graphene/Polymer Nanocomposite

The aim of this letter is to study the fracture toughening in graphene/polymer nanocomposites. Finite element based multiscale model was developed for the proposed study; where graphene is modeled in atomistic scale, whereas displacement and stresses in polymer is modeled in continuum phase. 3D virtual crack closure technique in conjunction with the proposed multiscale model was employed to study the fracturetoughening in graphene/polymer nanocomposites.

Atomistic modeling of graphene/hexagonal boron nitride polymer nanocomposites: a review

Due to their exceptional properties, graphene and hexagonal boron nitride (h‐BN) nanofillers are emerging as potential candidates for reinforcing the polymer‐based nanocomposites. Graphene and h‐BN have comparable mechanical and thermal properties, whereas due to high band gap in h‐BN (~5 eV), have contrasting electrical conductivities. Atomistic modeling techniques are viable alternatives to the costly and time‐consuming experimental techniques, and are accurate enough to predict the mechanical properties, fracture toughness, and thermal conductivities of graphene and h‐BN‐based nanocomposites. Success of any atomistic model entirely depends on the type of interatomic potential used in simulations. This review article encompasses different types of interatomic potentials that can be used for the modeling of graphene, h‐BN, and corresponding nanocomposites, and further elaborates on developments and challenges associated with the classical mechanics‐based approach along with synergic effects of these nano reinforcements on host polymer matrix.

Anisotropic compressive response of Stone–Thrower–Wales defects in graphene: A molecular dynamics study

The mechanical properties of graphene sheet can be tailored with the help of topological defects. In this research article, the effects of Stone–Thrower–Wales (STW) defects on the mechanical properties of graphene sheet was investigated with the help of molecular dynamics based simulations. Authors has made an attempt to analyse the stress field developed in and around the vicinity of defect due to bond reorientation and further systematic evaluation has been carried out to study the effect of these stress fields against the applied axial compressive load. The results obtained with the pristine graphene were made to compare with the available open literature and the results were reported to be in good agreement with theoretical and experimental data. It was predicted that graphene with STW defect cannot able to bear compressive strength in zigzag direction, whereas on the other hand it was predicted that graphene sheet containing STW defect can bear higher compressive load in armchair direction, which shows an anisotropic response of STW defects in graphene. From the obtained results it can be observed that orientation of STW defects and the loading direction plays an important role to alter the strength of graphene under axial compression.