Journal Articles

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    Open die extrusion (ODE) has been done on AISI 1020 steel, commercial purity aluminium and commercial purity titanium, in both direct and inverted modes. It was found that inverted extrusion requires lesser forces than direct extrusion. Limit strains are more for the former than for the later as measured experimentally and as calculated theoretically. Theoretical limit strains are lesser than experimental ones in both the case of rods and tubes. ODE is only for shorter components due to unsupported billet and interference from buckling. It is also only for smaller strains due to interference from upsetting of unsupported billet above the die rather than extrusion through the die. © 2004 Elsevier B.V. All rights reserved.
    (Direct and inverted open die extrusion (ODE) of rods and tubes) Srinivasan, K.; Venugopal, P.
    2004
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    Rheodynamic lubrication of a squeeze film bearing under sinusoidal squeeze motion
    (Springer Science and Business Media, LLC, 2007) Kandasamy, A.; Vishwanath, K.P.
    Lubricants with variable viscosity are assuming importance for their applications in polymer industry, thermal reactors and in biomechanics. With the bearing operations in machines being subjected to high speeds, loads, increasing mechanical shearing forces and continually increasing pressures, there has been an increasing interest to use non-Newtonian fluids characterized by an yield value. The most elementary constitutive equation in common use that describes a material which yields is that of Bingham fluid. In the present work, the problem of a circular squeeze film bearing lubricated with Bingham fluid under the sinusoidal squeeze motion has been analyzed. The shape and extent of the core for the case of sinusoidal squeeze motion has been determined numerically for various values of the Bingham number. Numerical solutions have been obtained for the bearing performances such as pressure distribution and load capacity for different values of Bingham number, Reynolds number and for various amplitudes of squeeze motion. The effects of fluid inertia, non-Newtonian characteristics, and the amplitudes of squeeze motion on the bearing performances have been discussed. Copyright © 2007 SBMAC.
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    Formability limit in containerless (open die) extrusion of commercial purity titanium rods and tubes
    (2008) Srinivasan, K.; Venugopal, P.
    Containerless extrusion requires far less forces compared to conventional direct extrusion of rods and tubes due to the elimination of container wall-billet friction. But the strains that can be imparted are less in the former due to the unsupported billet which gets upset first if the axial stress exceeds yield stress of the billet material. If this stress is equal to yield stress, it corresponds to the limit of the process of pure containerless extrusion. It is found that this limit strain as predicted by theory is far less compared to what is observed experimentally. This discrepancy is explained on the basis of heating that takes place in the deformation zone due to ideal, frictional, and shear work done in carrying out the extrusion process.
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    Inertia effects in circular squeeze film bearing using Herschel-Bulkley lubricants
    (2010) Vishwanath, K.P.; Kandasamy, A.
    Recent engineering trends in lubrication emphasize that in order to analyze the performance of bearings adequately, it is necessary to take into account the combined effects of fluid inertia forces and non-Newtonian characteristics of lubricants. In the present work, the effects of fluid inertia forces in the circular squeeze film bearing lubricated with Herschel-Bulkley fluids with constant squeeze motion have been investigated. Herschel-Bulkley fluids are characterized by an yield value which leads to the formation of a rigid core in the flow region. The shape and extent of the core formation along the radial direction is determined numerically for various values of Herschel-Bulkley number and power-law index. The bearing performances such as pressure distribution and load capacity for different values of Herschel-Bulkley number, Reynolds number, power-law index have been computed. The effects of fluid inertia and non-Newtonian characteristics on the bearing performances have been discussed. © 2009 Elsevier Inc. All rights reserved.
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    Rheodynamic lubrication of an externally pressured thrust bearing using herschel-bulkley fluid with sinusoidal injection
    (Isfahan University of Technology secretary@jafmonline.net, 2012) Jayakaran Amalraj, I.J.; Narasimman, S.; Kandasamy, A.
    Lubricants with variable viscosity are assuming greater importance for its application in polymer industry, thermal reactors and in biomechanics. With the bearing operations in machines being subject to high speeds, loads, increasing mechanical shearing forces and continually increasing pressure, there has been an increasing interest to use non-Newtonian fluids characterized by a yield value. Some of them, which fit into this class, are Bingham, Casson and Herchel-Bulkley models. In the present work, the problem of an externally pressurized thrust bearing lubricated with Herschel-Bulkley fluid under the sinusoidal flow rate has been investigated. Herschel-Bulkley fluids are characterized by a yield value, which leads to the formation of rigid core in the flow region. The shape and extent of the core has been determined numerically for various values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. Numerical solutions have been obtained for the bearing performances such as pressure distribution and load capacity for different values of the Herschel-Bulkley number, power-law index, amplitude of sinusoidal fluid film and time. The effects of sinusoidal injection of the lubricant and the non-Newtonian characteristics on the bearing performances have been discussed.
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    Nano-ZnO particle addition to monolithic magnesium for enhanced tensile and compressive response
    (Elsevier Ltd, 2014) Seetharaman, S.; Nayak, U.; Sabat, R.K.; Suwas, S.; Almajid, A.; Gupta, M.
    In this study, the effects of nanoscale ZnO reinforcement on the room temperature tensile and compressive response of monolithic Mg were studied. Experimental observations indicated strength properties improvement due to nanoscale ZnO addition. A maximum increment in tensile yield strength by ?55% and compressive yield strength by 90% (with reduced tension-compression asymmetry) was achieved when 0.8 vol.% ZnO nanoparticles were added to Mg. While the fracture strain values under tensile loads were found to increase significantly (by ?95%, in case of Mg-0.48ZnO), it remained largely unaffected under compressive loads. The microstructural characteristics studied in order to comprehend the mechanical response showed significant grain refinement due to grain boundary pinning effect of nano-ZnO particles which resulted in strengthening of Mg. Texture analysis using X-ray and EBSD methods indicated weakening of basal fibre texture in Mg/ZnO nanocomposites which contributed towards the reduction in tension-compression yield asymmetry and enhancement in tensile ductility when compared to pure Mg. © 2014 Elsevier B.V. All rights reserved.
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    Evaluation of WEDM performance characteristics of Inconel 706 for turbine disk application
    (Elsevier Ltd, 2015) Sharma, P.; Dupadu, D.; Narendranath, S.
    Inconel 706 is a newly developed superalloy, which offers high mechanical strength alongwith easy fabricability thus making it suitable for turbine disk applications. Although Inconel 706 exhibits a substantial increase in stress rupture and tensile yield strength compared to other superalloys, its conventional machining yields poor surface finish and low dimensional accuracy of the machined components. Hence, wire electrical discharge machining (WEDM) of Inconel 706 has been performed and various performance attributes such as material removal rate (MRR), surface roughness (SR), recast surface, topography, microhardness, microstructural and metallurgical changes of the machined components have been evaluated. The experimental results revealed that servo voltage, pulse on time, and pulse off time greatly influence the MRR and SR. Due to high toughness of Inconel 706, no micro cracks were observed on the machined surface. Micro voids and micro globules are significantly reduced at low pulse on time and high servo voltage. But, there is a propensity of thick recast layer formation at high pulse on time and low servo voltage. EDAX analysis of recast surface exposed the existence of Cu and Zn which have migrated from the brass wire. The subsurface microhardness was changed to 80. ?m due to significant thermal degradation. © 2015 Elsevier Ltd.
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    Quasi-Static and High Strain Rate Compressive Response of Injection-Molded Cenosphere/HDPE Syntactic Foam
    (Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2016) Bharath Kumar, B.R.; Singh, A.K.; Doddamani, M.R.; Luong, D.D.; Gupta, N.
    High strain rate compressive properties of high-density polyethylene (HDPE) matrix syntactic foams containing cenosphere filler are investigated. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10?4 s?1, 10?3 s?1 and 10?2 s?1 strain rates. Further, a split-Hopkinson pressure bar is utilized for characterizing syntactic foams for high strain rate compression. The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10?4 s?1 for HDPE resin and syntactic foams. Theoretical models are used to estimate the effectiveness of cenospheres in reinforcing syntactic foams. © 2016, The Minerals, Metals & Materials Society.
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    Effect of wire diameter on surface integrity of wire electrical discharge machined Inconel 706 for gas turbine application
    (Elsevier Ltd, 2016) Sharma, P.; Dupadu, D.; Narendranath, S.
    Inconel 706 superalloy has established itself in the field of gas turbine industry because of its easy fabricability combined with high mechanical strength. Due to its high stress rupture and tensile yield strength, conventional machining of this superalloy exhibits poor surface and low dimensional accuracy of the machined components. It is well known that most of the gas turbine components include complex shaped profile with high precision and hence, wire electrical discharge machining (WEDM) of Inconel 706 has been performed to achieve the feasibility in manufacturing of complex shaped components for gas turbine application. In the current investigation, the effect of wire diameter on WEDM performance characteristics such as cutting speed, surface roughness, surface topography, recast layer formation, microhardness, microstructural and metallurgical changes have been evaluated. It was investigated that smaller diameter wire is advantageous over the larger diameter wire since it improves productivity as well as surface quality of the machined components under the same settings of control parameters. In addition, smaller diameter wire has shown comparatively lower recast layer thickness, minimum hardness alteration and shorter manufacturing time. The XRD result has confirmed the presence of residual stress within WED machined component. © 2016 The Society of Manufacturing Engineers
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    Effect of simulated heating of plasma coating and ceramic firing on Ti and Ti-6Al-4V
    (Elsevier Editora Ltda, 2019) Kotian, R.; Rao, P.P.; Bangera, M.K.; Madhyastha, P.; Srikant, S.
    The study was performed to understand the impact of heat in plasma coating and ceramic firing of titanium (Ti) and titanium alloy (Ti-6Al-4V) on their mechanical properties, and microstructure. Standard specimens were prepared to measure tensile strength before and after simulated heating cycles using Instron machine of model 4206 at a crosshead speed of 1â»mm/min. Yield strength, ultimate strength, and elongation were recorded. The microstructure was studied using an optical microscope. The mechanical properties, microstructure, and grain size remained the same as that of as-received samples at temperatures of 600 and 700â»°C for both Ti and Ti-6Al-4V. At temperature 800 and 900â»°C decrease in yield strength, and ultimate tensile strength with a change in microstructure was observed. The temperature of plasma coating and ceramic firing that Ti and Ti-6Al-4V metal substrates encounter during the fabrication of coated implants and metal-ceramic restorations do not affect the mechanical properties and microstructure. Above 800â»°C, a significant change in mechanical properties and microstructure is observed. © 2019 The Authors.