Akbar Bagri

Using molecular dynamics simulations, we have studied the evolution of epoxy and hydroxyl functional groups on graphene oxide (GO) during high temperature thermal reduction. We find that the reduced GO sheets are characterized by a large number of stable hole-like defects formed by breaking of CC bonds in the basal plane. These defects are always decorated by the carbonyl (C= O) groups and are formed due to the strain in the basal plane created by epoxy and hydroxyl functional groups that are located close to each other. With ...

Purpose: The subject of this paper is to study the thermoelastic behavior of thick functionally graded hollow sphere under thermal and mechanical loads. The mechanical and thermal properties of FG sphere are assumed to be functions of radial position. Design/methodology/approach: In present study, two methods are used to estimate the effective mechanical properties of FG sphere. One of the simplest methods in estimation of the effective mechanical and thermal properties of a mixture of two constituent materials is the Rule of Mixture (R-M) scheme. Another scheme for estimating the mechanical properties is due to the work of Mori-Tanaka. When the mechanical properties of FG sphere are estimated by using the Mori-Tanaka scheme, thermal material properties of FG body may be determined utilizing the R-M or the other methods which will be discussed as follows. Findings: Results for the temperature, radial displacement, radial stress and hoop stress fields through the geometry of the sphe...

This chapter discusses fundamental aspects of the development of statistically equivalent virtual microstructures (SEVMs) and microstructure and property-based statistically equivalent representative volume elements (M-SERVE and P-SERVE) of the Ni-based superalloy at multiple scales. The two specific scales considered for this development are the subgrain scale of intragranular γ − γ′ microstructures and the polycrystalline scale of grain ensembles with annealing twins. A comprehensive suite of computational methods that can translate microstructural data in experimental methods to optimally defined representative volumes for effective micromechanical modeling is the objective of this study. The framework involves a sequence of tasks, viz., serial sectioning, image processing, feature extraction, and statistical characterization, followed by micromechanical analysis and convergence tests for statistical functions. A principal motivation behind this paper is to translate high-fidelit...

This article presents data related to the research article entitled "The effect of coating type on mechanical properties and controlled drug release of PCL/zein coated 45S5 bioactive glass scaffolds for bone tissue engineering" [1]. We provide data on mechanical properties, in vitro bioactivity and drug release of bioactive glass (BG) scaffolds coated by poly (ε-caprolactone) (PCL) and zein used as a controlled release device for tetracycline hydrochloride (TCH). By coating the BG scaffolds with PCL or PCL/zein blend the mechanical properties of the scaffolds were substantially improved, i.e., the compressive strength increased from 0.004±0.001 MPa (uncoated BG scaffolds) to 0.15±0.02 MPa (PCL/zein coated BG scaffolds). A dense bone-like apatite layer formed on the surface of PCL/zein coated scaffolds immersed for 14 days in simulated body fluid (SBF). The data describe control of drug release and in vitro degradation behavior of coating by engineering the concentration of zein. Thus, the developed scaffolds exhibit attractive properties for application in bone tissue engineering research.

ABSTRACT Thermoelasticity theory with two relaxation times is employed to investigate the second sound effect in functionally graded annular disk. The transition in material composition in geometry of the disk is assumed to be in radial direction where a power law form function is considered for the materials distribution. To study the multiphysics of the elastic and thermal fields the coupled form of the equations is considered. The Galerkin finite element method in conjunction with the Laplace transform is used to solve the coupled from equations. The temperature, displacement and stress fields in time domain are obtained using a numerical inversion of the Laplace transform and the material distribution effect on thermal and elastic fields is investigated. Finally, the obtained results are compared with the results of classical thermoelasticity theory.

By use of molecular dynamics simulations, we have studied the evolution of epoxy and hydroxyl functional groups on graphene oxide (GO) during high-temperature thermal reduction. We find that the reduced GO sheets are characterized by a large number of stable holelike defects formed by breaking of C− C bonds in the basal plane.

A one-dimensional generalized thermoelasticity model of a disk based on the Lord–Shulman theory is presented. The dynamic thermoelastic response of the disk under axisymmetric thermal shock loading is studied. The effects of the relaxation time and coupling coefficient are studied. The Laplace transform method is used to transform the coupled governing equations into the space domain, where the Galerkin finite element method is employed to solve the resulting equations in the transformed domain.

In this article a new unified formulation for the generalized coupled thermoelasticity theories is presented. The generalized coupled thermoelasticity theories proposed by Lord–Shulman, Green–Lindsay, and Green–Naghdi are combined into a unified formulation introducing the unified parameters. The formulation is given for the general anisotropic heterogeneous linear thermoelastic materials and then is reduced to the system of equations for the isotropic heterogeneous materials.

A new unified formulation for the generalized theories of the coupled thermoelasticity based on the Lord–Shulman, Green–Lindsay, and Green–Naghdi models is proposed in this paper. The unified form of the governing equations is presented by introducing the unifier parameters. The formulations are derived and given for the anisotropic heterogeneous materials. The unified equations are reduced for the isotropic and homogeneous materials.

This Paper illustrates the behaviour of a functionally graded layer under thermal shock load based on the Lord-Shulman theory. The coupled form of the equations are considered and the material properties of the layer are assumed to vary in a power law form function through the thickness of the layer. The Galerkin finite element method via the Laplace transformation is employed to solve the system of equations in the space domain.

Thermal buckling analysis of rectangular functionally graded plates with initial geometric imperfections is presented in this paper. It is assumed that the non-homogeneous mechanical properties vary linearly through the thickness of the plate. The plate is assumed to be under various types of thermal loadings, such as the uniform temperature rise and nonlinear temperature gradient through the thickness. A double-sine function for the geometric imperfection along the x and y-directions is considered.

In this article, the Green–Lindsay theory of thermoelasticity is employed to study the thermoelastic response of functionally graded hollow spheres. This generalized coupled thermoelasticity theory admits the second sound phenomena and depicts a finite speed for temperature wave propagation. The materials of the hollow sphere are assumed to be graded through its thickness in the radial direction while a symmetric thermal shock load is applied to its boundary.

The generalized coupled thermoelasticity based on the Lord–Shulman (LS) model that admits the second sound effect is considered to study the dynamic thermoelastic response of functionally graded annular disk. The disk material is considered to be graded along the radial direction, where a power law distribution is assumed. The thermal and mechanical waves propagation are investigated applying a sudden thermal exposure to the boundary. The Laplace transform is used to transform the governing equations into the Laplace domain, where the Galerkin finite element method is employed to solve the system of equations in space domain. Finally, the numerical inversion of the Laplace transform is used to obtain the actual physical quantities in the time domain. The time dependent temperature, radial displacement, radial stress, and hoop stress are plotted.

The coupled thermoelastic response of functionally graded annular disk based on the classical theory of thermoelasticity is studied in this paper. The disk is assumed to be under axi-symmetric thermal shock, applied to its inner surface. The disk material is considered to be graded along the radial direction, where a power law distribution is assumed. The method of Laplace transform is used to transform the governing equations into the space domain, where the Galerkin finite element method is employed to solve the resulting equations in the space domain. The inverse Laplace transform into the real time domain is obtained using a numerical inversion method. The time dependent temperature, radial displacement, radial stress, and hoop stress are obtained and plotted. The results are verified with the known data in the literature.

The excellent electrical, optical and mechanical properties of graphene have driven the search to find methods for its large-scale production, but established procedures (such as mechanical exfoliation or chemical vapour deposition) are not ideal for the manufacture of processable graphene sheets. An alternative method is the reduction of graphene oxide, a material that shares the same atomically thin structural framework as graphene, but bears oxygen-containing functional groups. Here we use molecular dynamics simulations to study the atomistic structure of progressively reduced graphene oxide. The chemical changes of oxygen-containing functional groups on the annealing of graphene oxide are elucidated and the simulations reveal the formation of highly stable carbonyl and ether groups that hinder its complete reduction to graphene. The calculations are supported by infrared and X-ray photoelectron spectroscopy measurements. Finally, more effective reduction treatments to improve the reduction of graphene oxide are proposed.