Faculty Publications
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Item 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.2004Item Influence of die angle on containerless extrusion of commercially pure titanium tubes(2007) Srinivasan, K.; Venugopal, P.Containerless tube extrusion has been investigated with commerically pure titanium at room temperature and a strain rate of 0.07 s-1 using 20 conical dies of five different strains and four different angles with MoS2 lubricant. Theoretical punch pressures have been calculated using appropriate equations from slab analysis of the process and compared with experimentally determined punch pressures. It is found that there exists an optimum angle at which the punch pressure is the least at a given strain.Item 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.Item Strength deformation behaviour of circular concrete filled steel tubes subjected to pure bending(2009) Chitawadagi, M.V.; Narasimhan, M.C.The strength deformation behaviour of circular steel tubes filled with different grades of concrete under flexure is presented. The effects of steel tube thickness, the cross sectional area of concrete, strength of in-filled concrete and the confinement of concrete on moment capacity and curvature of Concrete Filled steel Tubes (CFTs) are examined. Measured flexural strengths are compared with the values predicted by EC4-1994 and LRFD-AISC-1999 code provisions. A total of ninety nine specimens, all one metre long, were tested with concrete fills of 20, 30 and 40 N/mm2 characteristic strength and with D / t ratio 22.3 to 50.8. Based on the experimental results, an interaction model to predict moment and curvature of the CFT sample is developed. © 2009 Elsevier Ltd. All rights reserved.Item Axial strength of circular concrete-filled steel tube columns - DOE approach(Elsevier Ltd, 2010) Chitawadagi, M.V.; Narasimhan, M.C.; Kulkarni, S.M.This paper presents the effect of changes in diameter of the steel tube (D), wall thickness of the steel tube (t ), strength of in-fill concrete (f cu), and length of the tube (L) on ultimate axial load (P ue) and axial shortening at the ultimate point (?ue ) of circular Concrete Filled steel Tubes (CFT). Taguchi's approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the axial load and the axial shortening at the ultimate point. A total of 243 circular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-2005 and EC4-1994. © 2010 Elsevier Ltd. All rights reserved.Item Axial capacity of rectangular concrete-filled steel tube columns - DOE approach(2010) Chitawadagi, M.V.; Narasimhan, M.C.; Kulkarni, S.M.This paper presents the effect of change in wall thickness of the steel tube (t), strength of in-filled concrete (fcu), cross-sectional area of the steel tube (A) and length of the tube (L) on ultimate axial load and axial shortening at ultimate point of rectangular concrete-filled steel tubes (CFT). Taguchi's approach with an L9 orthogonal array is used to reduce the number of experiments. With the help of initial experiments, linear regression models are developed to predict the ultimate axial load and the axial shortening at ultimate point. A total of 243 rectangular CFT samples are tested to verify the accuracy of these models at three factors with three levels. The experimental results are analyzed using Analysis Of Variance to investigate the most influencing factor on strength and axial shortening of CFT samples. Comparisons are made with predicted column strengths using the existing design codes, AISC-LRFD-1994 and EC4-1994. © 2009 Elsevier Ltd. All rights reserved.Item Effect of Rotational Speeds on the Cast Tube During Vertical Centrifugal Casting Process on Appearance, Microstructure, and Hardness Behavior for Al-2Si Alloy(Springer Boston, 2015) Rao, R.A.; Tattimani, M.S.; Rao, S.S.The flow of molten metal plays a crucial role in determining casting quality. During rotation of the mold, melt flow around its inner circumference determines the final configurations and properties of the cast tube. In this paper, Al-2Si alloy is cast in the vertical mold at the various rotational speeds of the mold. The uniform cylinder tube is formed at a rotational speed of 1000 rpm, while before and beyond this speed, irregular-shaped cast tube is formed. Finally, fine structured grain size with high hardness value is found in uniform cast tube compared with others. © 2014, The Minerals, Metals & Materials Society and ASM International.Item Understanding Melt Flow Behavior for Al-Si Alloys Processed Through Vertical Centrifugal Casting(Taylor and Francis Inc. 325 Chestnut St, Suite 800 Philadelphia PA 19106, 2015) Rao, R.A.; Tattimani, M.S.; Rao, S.S.The objective of this article is to investigate the appearance, microstructure, and hardness of Al-Si alloys Al-12Si and Al-17Si in vertical centrifugal casting process. During rotation of the mold, molten metal flow affects the formation of uniform cylinder. In this study, flow of molten metal for Al-Si alloys at different rotational speeds is focused. It is found that for Al-17Si alloy a uniform cast tube is observed for 1000 rpm, whereas for Al-12Si it is at 1200 rpm; above and below these speeds, irregular cast tubes are formed. Finally, fine structured grain size with high hardness value is found in a uniform cast tube in comparison with others. © 2015 Taylor & Francis Group, LLC.Item Design and experimental characterization of a twin-tube MR damper for a passenger van(Springer Verlag service@springer.de, 2019) Desai, R.M.; Jamadar, M.E.H.; Kumar, H.; Joladarashi, S.; Raja Sekaran, S.C.The smart behavior of magneto-rheological (MR) fluid is used in the present work in designing, experimentally characterizing and analyzing a MR damper for automotive application using the twin-tube damper concept. A commercially available passive damper of a passenger van was tested to find the characteristic damping requirement of the vehicle. With this as reference, a twin-tube MR damper working in valve mode was designed and fabricated. The magnetic flux density induced in the fluid flow gap is maximized using Taguchi analysis and finite element method magnetics (FEMM) software. The FEMM results are validated by verifying with results obtained analytically using electromagnetic circuit theory. The MR damper filled with commercially available MR fluid was experimentally tested in damper testing machine. The results demonstrate that the force developed by the MR damper is indeed increasing with the value of the current supplied. At various frequencies of input oscillation, the energy dissipated by the MR damper in a single cycle increases significantly with current supplied. The novelty of this work is that a twin-tube MR damper working in valve mode was designed as a replacement for the passive damper used in a passenger van. The MR damper thus developed is capable of producing practical levels of damping force at actual operating frequencies and amplitudes of the passive damper in the passenger van. For further analysis, the behavior of the MR damper is modeled by using the Bouc–Wen model for hysteretic systems. A proportional–integral–derivative controller is used to track the desired damping force in time domain to demonstrate the application of the MR damper in a semi-active suspension system. © 2019, The Brazilian Society of Mechanical Sciences and Engineering.Item Experimental and numerical study of laminar separation bubble formation on low Reynolds number airfoil with leading-edge tubercles(Springer, 2020) Sreejith, B.K.; Sathyabhama, A.The present work reports the effect of leading-edge tubercles on aerodynamic performance and flow features of a cambered airfoil E216 at a Reynolds number of 100,000 and at various angles of attack in the pre-stall regime. Amplitude values of 2 mm, 4 mm and 8 mm and wavelength values of 15.5 mm, 31 mm and 62 mm are used for both experimental and simulation studies. The Transition-SST RANS model is used to simulate transition phenomenon (laminar separation bubble) and three-dimensional flow features over the airfoil. Wind tunnel experimental results are used for the performance analysis and the validation of the simulation methodology. The experimental values of Cl and Cd are 1.37 and 0.081, respectively, at a stall angle of 12 ? for the plain airfoil. The experimental results show that the lift generated by tubercled airfoils is higher than that produced by the plain airfoil in the pre-stall region but lower at the stall angle. A maximum benefit of 4.51% in Cl is obtained for the tubercled airfoil with the highest amplitude (8 mm) and wavelength (64 mm) at 6 ? angle of attack. A higher Cd is observed for all the tubercled airfoils than for the plain one. The simulation is mainly carried out to study the flow structure. Simulation results indicate the presence of laminar separation bubbles on the plain airfoil with a straight separation and reattachment line parallel to the trailing edge. The tubercles considerably altered the laminar separation bubble formation and the flow structure. A sinusoidal laminar separation bubble is formed on the tubercled airfoils with reduced bubble length. The laminar separation bubble along the trough is formed ahead of that at peak. Two pairs of counter-rotating vortices are formed on the airfoil surface along the trough at two different chord-wise locations which strongly alter the flow pattern over it. Prandtl’s secondary flow of the first kind is the key reason for the vortex formation. © 2020, The Brazilian Society of Mechanical Sciences and Engineering.