Faculty Publications
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Item Steam as coolant and lubricant in turning of metal matrix composites(2008) Shetty, R.; Pai B, R.B.; Kamath, V.; Rao, S.S.Green cutting has become focus of attention in ecological and environmental protection. Steam is cheap, pollution-free and eco-friendly, and then is a good and economical coolant and lubricant. Steam generator and steam feeding system were developed to generate and feed steam. Comparative experiments were carried out in cutting AA6061-15 vol.% SiC (25 ?m particle size), with cubic boron nitride (CBN) insert KB-90 grade under the conditions of compressed air, oil water emulsion, steam as coolant and lubricant, and dry cutting, respectively. The experimental results show that, with steam as coolant and lubricant, gradual reduction in the cutting force, friction coefficient, surface roughness and cutting temperature values were observed. Further, there was reduction in built up edge formation. It is proved that use of water steam as coolant and lubricant is environmentally friendly. © 2008 Zhejiang University and Springer-Verlag GmbH.Item Temperature dependent structural properties and bending rigidity of pristine and defective hexagonal boron nitride(Institute of Physics Publishing custserv@iop.org, 2015) Thomas, S.; Ajith, K.M.; Chandra, S.; Valsakumar, M.C.Structural and thermodynamical properties of monolayer pristine and defective boron nitride sheets (h-BN) have been investigated in a wide temperature range by carrying out atomistic simulations using a tuned Tersoff-type inter-atomic empirical potential. The temperature dependence of lattice parameter, radial distribution function, specific heat at constant volume, linear thermal expansion coefficient and the height correlation function of the thermally excited ripples on pristine as well as defective h-BN sheet have been investigated. Specific heat shows considerable increase beyond the Dulong-Petit limit at high temperatures, which is interpreted as a signature of strong anharmonicity present in h-BN. Analysis of the height fluctuations, ?h2?, shows that the bending rigidity and variance of height fluctuations are strongly temperature dependent and this is explained using the continuum theory of membranes. A detailed study of the height-height correlation function shows deviation from the prediction of harmonic theory of membranes as a consequence of the strong anharmonicity in h-BN. It is also seen that the variance of the height fluctuations increases with defect concentration. © 2015 IOP Publishing Ltd.Item Directional anisotropy, finite size effect and elastic properties of hexagonal boron nitride(Institute of Physics Publishing helen.craven@iop.org, 2016) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.Classical molecular dynamics simulations have been performed to analyze the elastic and mechanical properties of two-dimensional (2D) hexagonal boron nitride (h-BN) using a Tersoff-type interatomic empirical potential. We present a systematic study of h-BN for various system sizes. Young's modulus and Poisson's ratio are found to be anisotropic for finite sheets whereas they are isotropic for the infinite sheet. Both of them increase with system size in accordance with a power law. It is concluded from the computed values of elastic constants that h-BN sheets, finite or infinite, satisfy Born's criterion for mechanical stability. Due to the the strong in-plane sp2 bonds and the small mass of boron and nitrogen atoms, h-BN possesses high longitudinal and shear velocities. The variation of bending rigidity with system size is calculated using the Foppl-von Karman approach by coupling the in-plane bending and out-of-plane stretching modes of the 2D h-BN. © 2016 IOP Publishing Ltd.Item Microstructural characterization of low temperature plasma-nitrided 316L stainless steel surface with prior severe shot peening(Elsevier Ltd, 2016) Jayalakshmi, M.; Huilgol, P.; Badekai Ramachandra, B.R.; Bhat, K.U.Surface nanocrystallization by severe deformation has proven beneficial as pre-treatment to plasma nitriding. It aids in achieving thicker nitride layers at lower temperatures thus making the process more economical. In austenitic stainless steels, severe deformation leads to formation of strain induced martensite on the surface while plasma nitriding alone forms expanded austenite. However, structural characteristics of surface layer of pre-deformed steel after plasma nitriding is still a matter of debate. In present study, 316L stainless steel was subjected to severe shot peening: followed by plasma nitriding at 400 °C for 4 h. Characteristics of sample surface before and after treatment were analyzed by scanning electron microscopy, X-ray diffractometry and transmission electron microscopy techniques. Results showed that, this duplex treatment leads to formation of about 45 ?m thick nitride layer; without CrN precipitation. This is significantly high compared to reported data considering the temperature and duration of nitriding treatment employed. Selected area electron diffraction pattern from topmost surface confirmed the co-existence of austenite and martensite while subsurface layer was predominantly consisting of lath martensite. This indicates that major phase in the nitrided layer is martensitic in nature and nitrogen supersaturation leads to transformation of small fraction of martensite to expanded austenite. © 2016 Elsevier LtdItem Empirical potential influence and effect of temperature on the mechanical properties of pristine and defective hexagonal boron nitride(Institute of Physics Publishing helen.craven@iop.org, 2017) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.The major objective of this work is to present results of a classical molecular dynamics study to investigate the effect of changing the cut-off distance in the empirical potential on the stress-strain relation and also the temperature dependent Young's modulus of pristine and defective hexagonal boron nitride. As the temperature increases, the computed Young's modulus shows a significant decrease along both the armchair and zigzag directions. The computed Young's modulus shows a trend in keeping with the structural anisotropy of h-BN. The variation of Young's modulus with system size is elucidated. The observed mechanical strength of h-BN is significantly affected by the vacancy and Stone-Wales type defects. The computed room temperature Young's modulus of pristine h-BN is 755 GPa and 769 GPa respectively along the armchair and zigzag directions. The decrease of Young's modulus with increase in temperature has been analyzed and the results show that the system with zigzag edge shows a higher value of Young's modulus in comparison to that with armchair edge. As the temperature increases, the computed stiffness decreases and the system with zigzag edge possesses a higher value of stiffness as compared to the armchair counterpart and this behaviour is consistent with the variation of Young's modulus. The defect analysis shows that presence of vacancy type defects leads to a higher Young's modulus, in the studied range with different percentage of defect concentration, in comparison with Stone-Wales defect. The variations in the peak position of the computed radial distribution function reveals the changes in the structural features of systems with zigzag and armchair edges in the presence of applied stress. © 2017 IOP Publishing Ltd.Item Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-fluctuation method(Academic Press, 2017) Thomas, S.; Ajith, K.M.; Valsakumar, M.C.This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain fluctuation method. The temperature dependence of out-of-plane fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli. © 2017 Elsevier LtdItem Synthesis and photocatalytic properties of graphitic carbon nitride nanofibers using porous anodic alumina templates(Institute of Physics Publishing helen.craven@iop.org, 2017) Suchitra, S.M.; Udayashankar, N.K.In the present study, we describe an effective method for the synthesis of Graphitic carbon nitride (GCN) nanostructures using porous anodic alumina (AAO) membrane as template by simple thermal condensation of cyanamide. Synthesized nanostructure was fully analysed by various techniques to detect its crystalline nature, morphology, luminescent properties followed by the evaluation of its photocatalytic activity in the degradation of Methylene blue dye. Structural analysis of synthesized GCNNF was systematically carried out using x-ray powder diffraction (XRD) and scanning electron microscope (SEM), and. The results confirmed the growth of GCN inside the nanochannels of anodic alumina templates. Luminescent properties of GCNNF were studied using photoluminescence (PL) spectroscopy. PL analysis showed the presence of a strong emission peak in the wavelength range of 350-600 nm in blue region. GCNNF displays higher photocatalytic performance in the photodegradation of methylene blue compare to the bulk GCN. Highlights 1. In the present paper, we report the synthesis of graphitic carbon nitride nanofibers (GCNNF) using porous anodic aluminium oxide membranes as templates through thermal condensation of cyanamide at 500 °C. 2. The synthesis of Graphitic carbon nitride nanofibers using porous andic alumina template is the efficient approach for increasing crystallinity and surface area. 3. The high surface area of graphitic carbon nitride nanofibers has a good impact on novel optical and photocatalytic properties of the bulkGCN. 4. AAO templating of GCN is one of the versatile method to produce tailorable GCN nanostructures with higher surface area and less number of structural defects. 5. Towards photocatalytic degradation of dyes, the tuning of physical properties is very essential thing hence we are succeeded in achieving better catalytic performance of GCN nanostructures by making use of AAO templates. © 2017 IOP Publishing Ltd.Item Influence of porewidening duration on the template assisted growth of graphitic carbon nitride nanostructures(Institute of Physics Publishing helen.craven@iop.org, 2018) Suchitra, S.M.; Udayashankar, N.K.Porous anodic aluminium oxide (AAO) membranes with a highly ordered pore arrangement are typically used as ideal templates for the synthesis of numerous nanostructured materials. Highly ordered templates gained significant attraction due to the fact that they are readily fabricated through self-organised simple anodization process. In this paper, the effect of different pore-widening treatments on the quality of the pores of the AAO templates prepared with different electrolytes were inspected. Results confirmed that, without altering the interpore distance different pore dimensions and diameters of the AAO templates can be easily achieved by chemical pore widening process at room temperature. Also, graphitic carbon nitride nanorods of different dimension have been fabricated from AAO template after porewidening process. These nanostructures are widely used in case of metal free visible light driven photo catalysis, photo degradation of organic pollutants, photo electric conversion and water splitting applications. © 2018 IOP Publishing Ltd.Item Pulsed DC magnetron sputtered titanium nitride thin films for localized heating applications in MEMS devices(Elsevier B.V., 2018) M.a, M.A.; Lakshmi Ganapathi, L.G.; G N V R, V.; Udayashankar, N.K.; Mohan, S.Titanium nitride (TiN) thin films are deposited on Si/SiO2 substratesby using Pulsed DC magnetron sputtering and are characterized for their structural, mechanical and electrical properties for their application as localized heating elements in microsystem devices. The influence of substrate temperature on the properties of TiN films has been investigated. The correlation between the structural orientation with mechanical and electrical properties has been established. The films deposited at a substrate temperature of 300 °C have shown better structural, mechanical and electrical properties. This film has been chosen for the fabrication of microheater and its characterization. A maximum temperature of 250 °C is achieved by applying a power of 2.8 W to the microheater. © 2018 Elsevier B.V.Item A high efficiency on-chip reconfigurable Doherty power amplifier for LTE communication cells(John Wiley and Sons Inc. P.O.Box 18667 Newark NJ 07191-8667, 2018) Kumar, R.; Kanuajia, B.K.; Dwari, S.; Kumar, S.; Song, H.In this paper, a high efficiency on-chip reconfigurable Doherty power amplifier (DPA) with proposed topology is proposed for LTE or 4G communication cells. The proposed DPA consists of input driver topology, hybrid coupler, asymmetric amplifiers, and 1:1 balun filtered network. The proposed input driver circuit provides wide amplified signal operation within range of 2.3GHz to 6GHz with flat gain of 33 dB. The amplified signal is unsteadily divided into two paths toward the carrier and the power amplifier by 900 hybrid couplers and demonstrates 27.6 dB and 28.3 dB of gain along with 83.2% and 84.5% of power added efficiency at average output power of 40 dBm. The high efficiency and almost flatness in gain stability of proposed DPA providing better solution in order to overcome the interference and the broadband issues for LTE communication cells. The balun-filtered network is employed for combined the two outputs of carrier and peak amplifiers that provides more uniform desired band of operation in the frequency responses. The proposed DPA circuit are implemented and optimized by using advanced design RF simulator platform. The fabricated chip is made by using 0.13 ?m GaN HEMT on Si-Nitride monolithic microwave integrated circuit die process. The fabricated chip of DPA provides 85% of PAE with 28 dB gain which are made close agreement with simulation results. The size of chip is 2.8*1.2mm2 which occupies less die area as compared to existing DPAs. © 2018 Wiley Periodicals, Inc.