Journal Articles

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Author: search.filters.author.Hegde, S.

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    Effect of section thickness and modification on thermal analysis parameters of A357 alloy
    (2006) Hegde, S.; Kumar, G.; Prabhu, K.
    Thermal analysis technique relies on the cooling curve obtained when the sample is cooled in a sampling cup. This may not represent the cooling behaviour of the real casting. The microstructure developed during solidification depends not only on the nucleation and modification potential of the melt but also on the thermal gradient imposed during solidification by the mould. The factors affecting the thermal gradient are the mould material and casting section thickness. In the present investigation the effect of modification melt treatment, cooling rate and casting section thickness on the thermal analysis parameters of A357 alloy was studied. It is found that the dimensionless heat flux parameter is high for small section thickness castings. The metal/mould interfacial heat flux is high in a copper mould. Thermal analysis parameters of A357 alloy are found to be affected significantly by the combined action of modification, chilling and section thickness. © 2006 W. S. Maney & Son Ltd.
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    Heat transfer and solidification behaviour of modified A357 alloy
    (2007) Kumar, G.; Hegde, S.; Prabhu, K.N.
    Al-Si alloys are subjected to melt treatment like modification to improve their mechanical properties. Non-destructive technique like thermal analysis is generally used to assess the effectiveness of melt treatment. In the present study, the behaviour of the melt treated Al-7Si-Mg alloy (A357) during solidification with or without chilling was investigated using thermal analysis. Thermal analysis and heat transfer parameters were determined. Thermal analysis parameters were affected significantly by modification and chilling. Modification treatment resulted in the increase of cooling rate, heat evolved, casting/mould interfacial heat flux and eutectic growth velocity. A theoretical model based on undercooling from the equilibrium temperature during eutectic solidification was used to predict growth velocities and eutectic grain size. The eutectic grain sizes estimated using the model and those measured from casting microstructures were found to be in good agreement. © 2006 Elsevier B.V. All rights reserved.
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    Modification of eutectic silicon in Al-Si alloys
    (2008) Hegde, S.; Prabhu, K.N.
    The mechanical properties of Al-Si alloys are strongly related to the size, shape and distribution of eutectic silicon present in the microstructure In order to improve mechanical properties, these alloys are generally subjected to modification melt treatment, which transforms the acicular silicon morphology to fibrous one resulting in a noticeable improvement in elongation and strength. Improper melt treatment procedures, fading and poisoning of modifiers often result in the structure which is far from the desired one. Hence it is essential to assess the effectiveness of melt treatment before pouring. A much investigated reliable thermal analysis technique is generally used for this purpose. The deviation from the standard curve in thermal analysis helps in assessing the level of refinement of the Si structure. In the present review an attempt is made to discuss various aspects of modification, including mechanism, interaction of defects and non-destructive assessment by thermal analysis. © 2008 Springer Science+Business Media, LLC.
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    Effect of modification melt treatment and chilling on eutectic arrest temperature and time during solidification of A357 alloy
    (2011) Prabhu, K.N.; Hegde, S.
    Thermal analysis technique has been recognised as an efficient non-destructive tool to assess the degree of modification in Al-Si alloys. Apart from chemical modification, chilling refines the microstructure. This is particularly significant as majority of Al-Si alloys are cast in metallic moulds. In the present study, the interaction between chilling and modification melt treatment is investigated to assess their effect on thermal analysis parameters using computer aided cooling curve analysis. For modified alloys, the depression of the eutectic arrest temperature was significant at higher cooling rates. The eutectic arrest temperature and time were correlated with the cooling rate using a power law. High cooling regime in thermal analysis plots was attributed to the combined effect of chilling and modification melt treatment on heat transfer. © 2011 Institute of Materials, Minerals and Mining.
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    Heat transfer during solidification of chemically modified Al-Si alloys around a copper chill
    (2011) Prabhu, K.N.; Hegde, S.
    The solidifying metal/chill contour will significantly affect the boundary heat transfer coefficients, and solidification modellers should be aware of the casting conditions for which the heat transfer coefficients are determined. The previous work carried out on solidification of Al-Si alloys in a metallic mould and solidification against bottom/top chills has shown that modification and chilling have synergetic effect resulting in a significant increase in the heat flux transients at the casting/chill interface. In the present work, the heat transfer during solidification of unmodified and chemically modified Al-Si alloys around a cylindrical copper chill was investigated. Heat flux transients were estimated using lumped heat capacitance method. Lower peak heat flux was obtained with chemically modified alloy. This is in contrast to the results reported for alloys solidifying against chills and in metallic moulds. The chill thermal behaviour and heat transfer to the chill material when surrounded by modified and unmodified alloys were explained on the basis of the decrease in the degree of undercooling in the case of modified alloy as compared to unmodified alloy and the change in contact condition and shrinkage characteristics of the alloy due to the addition of chemical modifiers. © 2011 Institute of Materials, Minerals and Mining.
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    Controlled release of nutrients to mammalian cells cultured in shake flasks
    (2012) Hegde, S.; Pant, T.; Pradhan, K.; Badiger, M.; Gadgil, M.
    Though cell culture-based protein production processes are rarely carried out under batch mode of operation, cell line and initial process development operations are usually carried out in batch mode due to simplicity of operation in widely used scale down platforms like shake flasks. Nutrient feeding, if performed, is achieved by bolus addition of concentrated feed solution at different intervals, which leads to large transient increases in nutrient concentrations. One negative consequence is increased waste metabolite production. We have developed a hydrogel-based nutrient delivery system for continuous feeding of nutrients in scale down models like shake flasks without the need for manual feed additions or any additional infrastructure. Continuous delivery also enables maintaining nutrient concentrations at low levels, if desired. The authors demonstrate the use of these systems for continuous feeding of glucose and protein hydrolysate to a suspension Chinese Hamster Ovary (CHO) culture in a shake flask. Glucose feeding achieved using the glucose-loaded hydrogel resulted in a 23% higher integral viable cell density and an 89% lower lactate concentration at the end of the culture when compared with a bolus-feed of glucose. © 2011 American Institute of Chemical Engineers (AIChE).
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    Effect of chemical modification of Al-Si alloys on thermal diffusivity and contact heat transfer at the casting-chill interface
    (2012) Prabhu, K.N.; Jayananda; Hegde, S.
    The heat flow during the unidirectional downward solidification of Al-7Si and Al-12Si alloys was analyzed using thermal analysis technique and inverse modeling. Chills instrumented with thermocouples were brought into contact with a small pool of liquid metal so as to minimize the effect of convection caused by pouring and temperature gradients. Modification melt treatment resulted in an increase in the cooling rate of the solidifying casting near the casting-chill interfacial region. The corresponding interfacial heat flux transients were also found to be higher. The thermal diffusivities of alloys were measured using a laser pulse technique and were found to be higher for modified alloys. However, the increase in the heat flux transients was attributed mainly to the improvement in the casting-chill interfacial thermal contact condition brought about by the decrease in the surface tension of the liquid metal upon the addition of sodium. Copyright © 2012 by ASTM International.
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    Comparison of creep rates of AA 5356 alloy based aluminium silicon carbide composite and AISI 316L stainless steel by indentation creep test method
    (2012) Udaya Prasanna, H.U.; Rajendra Udupa, K.; Hegde, S.
    [No abstract available]
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    A novel approach to investigate effect of magnetic field on dynamic properties of natural rubber based isotropic thick magnetorheological elastomers in shear mode
    (Central South University of Technology f-ysxb@mail.csut.edu.cn, 2015) Hegde, S.; Kiran, K.; Gangadharan, K.V.
    The preparation of natural rubber based isotropic thick magnetorheological elastomers (MRE) was focused on by varying the percentage volume concentration of carbonyl iron powder and developing a test set up to test the dynamic properties. Effect of magnetic field on the damping ratio was studied on the amplification region of the transmissibility curve. The viscoelastic dynamic damping nature of the elastomer was also studied by analyzing the force-displacement hysteresis graphs. The results show that MR effect increases with the increase in magnetic field as well as carbonyl iron powder particle concentration. It is observed that softer matrix material produces more MR effect. A maximum of 125% improvement in the loss factor is observed for the MRE with 25% carbonyl iron volume concentration. FEMM simulation shows that as carbonyl iron particle distribution becomes denser, MR effect is improved. FEMM analysis also reveals that if the distance between the adjacent iron particles are reduced from 20 ?m to 10 ?m, a 40% increase in stored energy is observed. © 2014, Central South University Press and Springer-Verlag Berlin Heidelberg.
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    Scalable and fair forwarding of elephant and mice traffic in software defined networks
    (Elsevier, 2015) Hegde, S.; Koolagudi, S.; Bhattacharya, S.
    A software defined network decouples the control and data planes of the networking devices and places the control plane of all the switches in a central server. These flow based networks do not scale well because of the increased number of switch to controller communications, limited size of flow tables and increased size of flow table entries in the switches. In our work we use labels to convey control information of path and policy in the packet. This makes the core of the network simple and all routing and policy decisions are taken at the edge. The routing algorithm splits the elephant traffic into mice and distributes them across multiple paths, thus ensuring latency sensitive mice traffic is not adversely affected by elephant traffic. We observed that label based forwarding and traffic splitting work well together to enable scalable and fair forwarding. Our approach is topology independent. We present here a few preliminary simulation results obtained by running our routing algorithm on random network topologies. © 2015 Elsevier B.V.