Analysis of Electrical and Thermal Conductivities of Polyethersulfone-Graphite Based Hybrid Nanocomposites

B. T. S. Ramanujam,S. Radhakrishnan,Shripad D. Deshpande 한국고분자학회 2017 Macromolecular Research Vol.25 No.4

Polyethersulfone (PES)-7 wt% graphite- x wt% filler (carbon black (CB), carbon nanofiber (CNF), expanded graphite (ExGr)) hybrid composites are synthesized by solution blending route. The electrical percolation threshold in hybrid composites varies exponentially with the aspect ratio of the second conducting filler. The aspect ratio of the second conducting filler has been found to vary in the order CB < CNF < ExGr. The percolation threshold is identified at 0.05 wt%, 0.4 wt%, 1.3 wt% for ExGr, CNF and CB added PES-7 wt% graphite composites. Through plane thermal conductivity of PES-x wt% graphite-y wt% CB (x=10, 20, 30, 40, 50, 60, y=0, 3, 7) hybrid composites has been found to increase with the addition of CB. Thermal conductivity has been increased to 0.42 W/m-K when 7 wt% CB is added to PES-60 wt% graphite from 0.2 W/m-K. Reduction of interparticular distance with the increased loading of CB facilitates better thermal transport. Aspect ratios of second conducting fillers have been found out from transmission electron microscopy and scanning electron microscopy analysis.

FITTED MESH METHOD FOR SINGULARLY PERTURBED REACTION-CONVECTION-DIFFUSION PROBLEMS WITH BOUNDARY AND INTERIOR LAYERS

Shanthi, V.,Ramanujam, N.,Natesan, S. 한국전산응용수학회 2006 Journal of applied mathematics & informatics Vol.22 No.1

A robust numerical method for a singularly perturbed second-order ordinary differential equation having two parameters with a discontinuous source term is presented in this article. Theoretical bounds are derived for the derivatives of the solution and its smooth and singular components. An appropriate piecewise uniform mesh is constructed, and classical upwind finite difference schemes are used on this mesh to obtain the discrete system of equations. Parameter-uniform error bounds for the numerical approximations are established. Numerical results are provided to illustrate the convergence of the numerical approximations.

Fitted mesh method for singularly perturbed reaction-convection-diffusion problems with boundary and interior layers

V. Shanthi,N. Ramanujam,S. Natesan 한국전산응용수학회 2006 Journal of applied mathematics & informatics Vol.22 No.1-2

A robust numerical method for a singularly perturbed second– order ordinary differential equation having two parameters with a discontinuous source term is presented in this article. Theoretical bounds are derived for the derivatives of the solution and its smooth and singular components. An appropriate piecewise uniform mesh is constructed, and classical upwind finite difference schemes are used on this mesh to obtain the discrete system of equations. Parameter–uniform error bounds for the numerical approximations are established. Numerical results are provided to illustrate the convergence of the numerical approximations.

Analytical model of corrosion-induced cracking of concrete considering the stiffness of reinforcement

Bhargava, Kapilesh,Ghosh, A.K.,Mori, Yasuhiro,Ramanujam, S. Techno-Press 2003 Structural Engineering and Mechanics, An Int'l Jou Vol.16 No.6

The structural deterioration of concrete structures due to reinforcement corrosion is a major worldwide problem. Service life of the age-degraded concrete structures is governed by the protective action provided by the cover concrete against the susceptibility of the reinforcement to the corrosive environment. The corrosion of steel would result in the various corrosion products, which depending on the level of the oxidation may have much greater volume than the original iron that gets consumed by the process of corrosion. This volume expansion would be responsible for exerting the expansive radial pressure at the steel-concrete interface resulting in the development of hoop tensile stresses in the surrounding cover concrete. Once the maximum hoop tensile stress exceeds the tensile strength of the concrete, cracking of cover concrete would take place. The cracking begins at the steel-concrete interface and propagates outwards and eventually resulting in the through cracking of the cover concrete. The cover cracking would indicate the loss of the service life for the corrosion-affected structures. In the present paper, analytical models have been developed considering the residual strength of the cracked concrete and the stiffness provided by the combination of the reinforcement and expansive corrosion products. The problem is modeled as a boundary value problem and the governing equations are expressed in terms of the radial displacement. The analytical solutions are presented considering a simple 2-zone model for the cover concrete viz. cracked or uncracked. A sensitivity analysis has also been carried out to show the influence of the various parameters of the proposed models. The time to cover cracking is found to be function of initial material properties of the cover concrete and reinforcement plus corrosion products combine, type of rust products, rate of corrosion and the residual strength of the cover concrete. The calculated cracking times are correlated against the published experimental and analytical reference data.

Seismic response and failure modes for a water storage structure - A case study

Bhargava, Kapilesh,Ghosh, A.K.,Ramanujam, S. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.1

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

Seismic response and failure modes for a water storage structure − A case study

Kapilesh Bhargava,A. K. Ghosh,S. Ramanujam 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.1

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

Ultimate flexural and shear capacity of concrete beams with corroded reinforcement

Bhargava, Kapilesh,Ghosh, A.K.,Mori, Yasuhiro,Ramanujam, S. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.27 No.3

Assessment of structural behaviour of corrosion affected structures is an important issue, which would help in making certain decisions pertaining to the inspection, repair, strengthening, replacement and demolition of such structures. The paper presents formulations to predict the loss of weight and the loss of cross-sectional area of the reinforcing bar undergoing corrosion based on the earlier study carried out by the present authors (Bhargava et al. 2006). These formulations have further been used to analytically evaluate the ultimate bending moment and ultimate shear force capacity of the corroded concrete beams. Results of the present study indicate that, a considerably good agreement has been observed between the experimental and the analytically predicted values for the weight loss and reduction in radius of the corroded reinforcing bars. A considerably good agreement has also been observed between the experimental and the analytically predicted values of ultimate bending moment and ultimate shear force capacity for the corroded concrete beams.