Lattice orientation and crack size effect on the mechanical properties of Graphene

The effect of lattice orientation and crack length on the mechanical properties of Graphene are studied based on molecular dynamics simulations. Bond breaking and crack initiation in an initial edge crack model with 13 different crack lengths, in 10 different lattice orientations of Graphene are examined. In all the lattice orientations, three recurrent fracture patterns are reported. The influence of the lattice orientation and crack length on yield stress and yield strain of Graphene is also investigated. The arm-chair fracture pattern is observed to possess the lowest yield properties. A sudden decrease in yield stress and yield strain can be noticed for crack sizes <10 nm. However, for larger crack sizes, a linear decrease in yield stress is observed, whereas a constant yield strain of ≈≈0.05 is noticed. Therefore, the yield strain of ≈≈0.05 can be considered as a critical strain value below which Graphene does not show failure. This information can be utilized as a lower bound for the design of nano-devices for various strain sensor applications. Furthermore, the yield data will be useful while developing the Graphene coating on Silicon surface in order to enhance the mechanical and electrical characteristics of solar cells and to arrest the growth of micro-cracks in Silicon cells

Growth of zinc oxide nanorod structures: pressure controlled hydrothermal process and growth mechanism

Zinc oxide (ZnO) nanorods of various morphologies are grown on zinc substrate by pressure-assisted hydrothermal process and the growth mechanism is investigated with the help of molecular dynamics (MD) simulation results. Hydrothermally reacted ZnO2 nanostructure bottom-up formation from Zn substrate is a useful process employed here. A systematic study on the role of process control parameters such as pressure and temperature on nanorod growth has been carried out. Correlation among the process parameters to form ordered nanostructures is established. The effect of pressure on the diameter and length of the grown ZnO nanorod structures is studied, which is precisely tunable. With a decrease in pressure from 500 to 400 kPa, the nanorod diameter is reduced by 22.2 %, while its length is increased by 24.8 %. At lower vapor pressure, the nanorod tips are sharper, whereas at higher vapor pressure they are flat. These variations along with a detailed analysis of MD simulations helps us hypothesize that pressure plays an important role in governing the diffusion of oxygen atom onto zinc surface and generating wurtzite phase. Simulation results clearly show that ZnO nanorods lift off due to their interaction with the Zn atoms on the substrate and the resulting forces

Crack propagation in graphene

The crack initiation and growth mechanisms in an 2D graphene lattice structure are studied based on molecular dynamics simulations. Crack growth in an initial edge crack model in the arm-chair and the zig-zag lattice configurations of graphene are considered. Influence of the time steps on the post yielding behaviour of graphene is studied. Based on the results, a time step of 0.1 fs is recommended for consistent and accurate simulation of crack propagation. Effect of temperature on the crack propagation in graphene is also studied, considering adiabatic and isothermal conditions. Total energy and stress fields are analyzed. A systematic study of the bond stretching and bond reorientation phenomena is performed, which shows that the crack propagates after significant bond elongation and rotation in graphene. Variation of the crack speed with the change in crack length is estimated. (C) 2015 AIP Publishing LLC

Chemical-free graphene by unzipping carbon nanotubes using cryo-milling

Current paper reports synthesis of chemical free graphene by unzipping of the carbon nanotubes (CNTs) using high strain rate deformation at 150K. A specially designed cryomill operating at 150 K was used for the experiments. The mechanism of unzipping was further explored using molecular dynamics (MD) simulations. Both experimental and simulation results reveal two modes of unzipping through radial and shear loading. (C) 2015 Elsevier Ltd. All rights reserved

Anaplastic large cell lymphoma presenting as liver abscess and portal Vein thrombosis

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