Faculty Publications
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Item Nano ZnO-activated carbon composite electrodes for supercapacitors(2010) Muthu, M.S.; Bhat, D.K.; Aggarwal, A.; Prahladh Iyer, S.; Sravani, G.A symmetrical (p/p) supercapacitor has been fabricated by making use of nanostructured zinc oxide (ZnO)-activated carbon (AC) composite electrodes for the first time. The composites have been characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD). Electrochemical properties of the prepared nanocomposite electrodes and the supercapacitor have been studied using cyclic voltammetry (CV) and AC impedance spectroscopy in 0.1 M Na2SO4 as electrolyte. The ZnO-AC nanocomposite electrode showed a specific capacitance of 160 F/g for 1:1 composition. The specific capacitance of the electrodes decreased with increase in zinc oxide content. Galvanostatic charge-discharge measurements have been done at various current densities, namely 2, 4, 6 and 7 mA/cm2. It has been found that the cells have excellent electrochemical reversibility and capacitive characteristics in 0.1 M Na2SO4 electrolyte. It has also been observed that the specific capacitance is constant up to 500 cycles at all current densities. © 2010 Elsevier B.V. All rights reserved.Item New manufacturing process of carbon-carbon composites and their mechanical properties(2011) Naik, P.S.; SurendranathanThis paper presents the synthesizing of carbon-carbon (CC) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber volume. The PY used is carbon fiber bundle surrounded by coke and pitch which is enclosed in nylon-6. Three types of samples with fiber weight fractions of 30%, 40% and 50% respectively, are fabricated and tested. In each case, the PY is chopped and filled into a die of required shape and hot pressed at 600°C to get the carbonized composite. To obtain the graphitic structure, the specimen is heat treated at 1800°C followed by soaking for two hours. Further, one cycle pitch impregnation is done by hot isostatic pressing, to eliminate the voids. The characteristics such as hardness, compressive strength and creep, are studied. It is observed that, as the carbon fiber percentage increases the properties also improved, provided sintering is done at fairly higher temperatures. The superiority of the new class of CC composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated. © 2011 CAFET-INNOVA TECHNICAL SOCIETY.Item Effect of fiber weight fraction on mechanical properties of carbon-carbon composites(2012) Naik, P.S.; Orangalu, S.A.; Londhe, N.V.This article presents the synthesis of carbon-carbon (C/C) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber weight fraction. The PY used was carbon fiber bundle surrounded by coke and pitch which was enclosed in nylon-6. Three types of samples with fiber weight fractions of 30, 40, and 50%, respectively, are fabricated and mechanical properties were studied. In each case, the PY was chopped and filled into a die of required shape and hot pressed at 500°C to get the preform composite. To obtain the carbonized and graphitic structure, the specimen was heat treated at 2500°C followed by soaking for 10 to 12 hrs. Further, two cycles pitch impregnation was done by hot isostatic pressing, to eliminate the voids and to increase the density hence to obtain good mechanical properties. The characteristics such as hardness, flexural strength, and impact strengths were studied. It is observed that, as the carbon fiber percentage increases, the properties also get improved, provided sintering is done at fairly higher temperatures such as 2700°C. The superiority of the new class of C/C composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated. Copyright © 2012 Society of Plastics Engineers.Item Microwave synthesized nanostructured TiO 2 -activated carbon composite electrodes for supercapacitor(Elsevier B.V., 2012) Muthu, M.; Bhat, D.K.Electrochemical properties of a supercapacitor based on nanocomposite electrodes of activated carbon with TiO 2 nano particles synthesized by a microwave method have been determined. The TiO 2 /activated carbon nanocomposite electrode with a composition of 1:3 showed a specific capacitance 92 Fg -1 . The specific capacitance of the electrode decreased with increase in titanium dioxide content. The p/p symmetrical supercapacitor fabricated with TiO 2 /activated carbon composite electrodes showed a specific capacitance of 122 Fg -1 . The electrochemical behavior of the neat TiO 2 nanoparticles has also been studied for comparison purpose. The galvanostatic charge-discharge test of the fabricated supercapacitor showed that the device has good coulombic efficiency and cycle life. The specific capacitance of the supercapacitor was stable up to 5000 cycles at current densities of 2, 4, 6 and 7 mA cm -2 . © 2012 Elsevier B.V.Item High power density and improved H2 evolution reaction on MoO3/Activated carbon composite(Elsevier Ltd, 2020) Sangeetha, D.N.; Holla, R.S.; Badekai Ramachandra, B.; Muthu, M.The formation of hexagonal MoO3 (h- MoO3) microrods was favoured at lower pH in the hydrothermal synthesis method. Symmetric and Hybrid supercapacitors were fabricated using h-MoO3/plastic bottle derived activated carbon (PAC) composite in 1 M Na2SO4 aqueous electrolyte. The operating voltage for the aqueous electrolyte was maximized to 1.6 V with this combination. The wide operating voltage led to a maximum specific capacitance of 211 Fg-1, power density of 287 W kg?1 and 79% efficiency even at 5000 charge-discharge cycles for the hybrid supercapacitor combination. The combined effect of PAC micropores along with the 1-D rod-shaped h-MoO3, helped in faster charge-transfer, hence increasing the efficiency of supercapacitors. Further, the composites of defective PAC (PDAC) together with the h-MoO3 when tested for hydrogen evolution reactions (HER), provided lesser onset potential and Tafel slope values of ?0.23 mV and ?93 mVdec?1. There was a change in the structural environment of carbon due to the heteroatom doping and dedoping producing defects in PAC, termed as PDAC. These defects together with the hexagonal microrods of MoO3 provided fast electron transfer towards hydrogen adsorption/desorption hence effectively producing H2. © 2019 Hydrogen Energy Publications LLCItem Influence of oxidation on fracture toughness of carbon-carbon composites for high-temperature applications(Gruppo Italiano Frattura, 2021) Sunil Kumar, B.V.S.; Londe, V.N.; Lokesha, M.; Vasantha Kumar, S.N.; Surendranathan, A.O.Carbon-Carbon Composites (C-CC), used as composites for their remarkable qualities in the space industry and in many other industry sectors. C-CC has proven to be the most efficient material in extreme temperature situations. They are one among the best high-temperature materials with good thermal quality, such as high-temperature stability, outstanding thermal conductivity and low-temperature expansion coefficients. In aircraft, railways, trucks and even race vehicles, C-CC brake disks are in high demand. Compared to the favorable thermal and mechanical qualities of C-CC, their great sensitivity to oxidation in an oxidizing environment at temperatures even around 400°C is a major restriction with these composites. In particular, a study of the C-CC oxidation mechanism helps to create protective measures for these composites. The present experimental study explores the influence of oxidation in static air on the fracture toughness of C-CC. At a temperature of around 400°C to 700°C in an increment of 100°C, an oxidation evaluation of the material is carried out. Results show that there was a significant decrease in the fracture toughness when there was an increase in temperature from 400°C to 700°C. We can observe that C-CC fracture toughness is severely affected by oxidation. The decrease in the fracture toughness value in comparison with room temperature was 6% for 400°C and 45% for 700°C. © 2021.Item Multiscale Numerical Modeling of 2D C/C Composites Considering Pore Size Distribution(American Society of Civil Engineers (ASCE), 2024) Vishnu, O.S.; Pavan, G.S.This study proposes a multiscale numerical modeling procedure to evaluate the elastic properties of two-dimensional (2D) eight-harness satin woven carbon/carbon (C/C) composites. The multiscale modeling technique consists of analysis at the microlevel and mesolevel. In microscale analysis, a 3D representative volume element (RVE) of C/C composite with carbon fiber, pyrolytic carbon, and pores is considered. The microstructure of the C/C composite is analyzed using scanning electron microscope (SEM) images. Statistical characterization of pore distribution inside the C/C composite is performed, and different probability density functions are generated for pores' number, area, and aspect ratio inside the C/C composite. Carbon fibers and pores are inserted in the 3D RVE using the RSA algorithm. The size and shape of the pores inserted in 3D RVE are based on the probability density functions generated. Effective elastic properties of C/C composite at the microscale are computed by finite element analysis (FE) based homogenization and taken as input for the next level of homogenization. The RVE at mesoscale is modeled using the information from SEM images, and FE-based homogenization is performed to compute the effective elastic properties of 8HS woven C/C composite. The effective elastic properties obtained from the numerical study are validated with the results of the uniaxial tensile test performed on 2D C/C composite. The effect of fiber volume fraction, yarn volume fraction, and porosity on elastic properties of 2D 8HS woven C/C composite are also assessed and presented in this study. © 2024 American Society of Civil Engineers.Item Numerical studies on modeling heterogeneity in elastic properties of 8HS woven C/C composites(Taylor and Francis Ltd., 2025) Vishnu, O.S.; Pavan, G.S.; R, S.; Thomas, A.The variation in fiber volume fraction and pores developed at the microscale during the manufacturing process is a source of heterogeneity in the elastic properties of woven Carbon/Carbon (C/C) composites. This study investigates the effect of heterogeneity on the elastic properties of Eight Harness Satin (8HS) woven C/C composites using a two-scale (micro–meso) finite element (FE) homogenization method. At the microscale, variations in fiber volume fraction and porosity are incorporated by generating 25 representative volume elements(RVEs) from the reconstructed CT scan images. The RVEs preserve the shape, size, orientation, and spatial distribution of pores that are present in the microstructure. The carbon fibers are virtually generated inside the 25 micro-RVEs using the random sequential adsorption (RSA) algorithm in accordance with the reconstructed microstructure of actual pores. At the mesoscale, the model incorporates warp and weft yarns embedded in a pyrolytic carbon matrix. Yarn heterogeneity is modeled by subdividing the meso RVE into smaller domains, each assigned elastic properties derived from the microscale RVEs. The degree of heterogeneity was varied using different combinations of the microscale RVEs to assign material properties. This approach effectively incorporates the randomness of the microstructure into the computation of the effective elastic properties of woven composites. The on and off-axis elastic properties of 8HS woven C/C composites are computed, and the results determined from the numerical study are compared with experimental tests conducted on 0° and 45° specimens. This study highlights the importance of fiber volume fraction and pores on material heterogeneity in accurately computing the elastic properties of 8HS woven C/C composites. © 2025 Taylor & Francis Group, LLC.Item Load- and time-dependent three-body abrasive wear in short carbon fiber- and cenosphere-reinforced polymer composites using machine learning approach(Springer Science and Business Media Deutschland GmbH, 2025) Mahesh, V.; Mahesh, V.; Joladarashi, S.; Madhu, N.; Manoj, T.U.; Meghana, D.; Sinchana, K.V.This study investigates the load and time-dependent three-body abrasive wear behavior and surface morphology of polymer composites reinforced with varying proportions of short carbon fiber (Cr) and cenosphere (C) inclusions. Composites with different Cr and C reinforcements—Cr0C0, Cr0C20, Cr20C0, Cr15C5, Cr10C10 and Cr5C15—were subjected to wear tests under loads of 20, 30, and 40 N over exposure times of 5, 10, and 15 min. Mass loss and specific wear rate were evaluated to understand the influence of reinforcement composition and test parameters on wear performance. Surface morphological studies using scanning electron microscopy (SEM) revealed distinct wear mechanisms across composites. The Cr10C10 and Cr15C5 composites demonstrated the lowest specific wear rates of 9.42 × 10–9 and 8.67 × 10–9 m3/Nm, respectively, under a 40 N load at 10 and 15 min, correlating with smoother worn surfaces and fewer micro-cracks. In contrast, the Cr0C20 composite displayed the highest specific wear rate (5.14 × 10–8 m3/Nm) at a 40 N load for 5 min, with SEM images showing more extensive matrix erosion and cenosphere pull-out. The inclusion of cenospheres at higher ratios increased mass loss, especially in high-load conditions, while balanced Cr–C reinforcements (e.g., Cr15C5 and Cr10C10) provided enhanced abrasion resistance and minimized surface damage. These findings underscore the potential for optimizing Cr and C inclusion ratios to develop wear-resistant polymer composites suitable for demanding structural applications. © Iran Polymer and Petrochemical Institute 2025.Item Insights into the influence of microstructure on strength and damage progression in carbon/carbon composites(SAGE Publications Ltd, 2025) Vishnu, O.S.; Pavan, G.S.Microstructural features influence the mechanical properties and damage progression in advanced materials like Carbon/Carbon (C/C) composites. This study proposes a finite element-based framework to analyze the damage mechanism in unidirectional C/C composites incorporating the effects of fiber arrangement, microstructural defects, and fiber-matrix interface. A 3D Representative Volume Element (RVE) is developed, which consists of carbon matrix, randomly distributed carbon fibers, and pores. The pores in the microstructure are modeled as ellipsoids of varying size, shape, and orientation. Separate stress-based failure criteria and fracture energy-based evolution laws are prescribed for fiber, matrix, and fiber-matrix interface. A user-defined material subroutine (UMAT) is developed in the finite element software Abaqus to implement the initiation and progression of damage in the composite constituents. The homogenized stress-strain response is computed under different loading conditions, namely longitudinal, transverse, in-plane shear, and out-of-plane shear loading. The variation of transverse tensile strength with porosity is also examined, highlighting the influence of pore volume fraction on the mechanical performance of the material. The proposed numerical model is validated through comparison with the Chamis analytical model and with numerical and experimental results from the literature. The proposed framework adopts detailed modeling strategies harnessing the power of computation and individual failure criterion-evolution laws for reliable simulation of damage and strength evaluation of composite materials, which are extensively used in advanced aerospace and engineering applications. © The Author(s) 2025