Journal Articles

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    Magnetically induced electrodeposition of Zn-Ni alloy coatings and their corrosion behaviors
    (Elsevier B.V., 2013) Rao, V.R.; Bangera, K.V.; Hegde, A.C.
    The less magnetic features of Zn-Ni alloy compared to Fe-Ni and Fe-Co alloys made it interesting to develop them under the influence of applied magnetic field. In this regard, the effects of a magnetic field (B) applied in a direction parallel and perpendicular to the nominal current, during electrodeposition process of Zn-Ni alloy have been investigated by means of X-ray diffraction and EDX analysis. The modification of crystal orientation by superimposition of a varying magnetic field is studied for alloys of constant nickel content (8 a %.), deposited at optimal current density (j) of 3.0 A dm-2. The effect of magnetic field on crystallographic orientation and hence the corrosion behaviors of the coatings were studied. The preferential orientations (101) and (002) of the zinc phase and (330) ?-Ni 5Zn21 phase are always favored to exist with parallel and perpendicular magnetic field. The preferential (321) ?-Ni 5Zn21 orientation is found to be the characteristic of perpendicular magnetic field. Further, Zn (100) orientation is found to be non-responsive to the effect of parallel magnetic field. The coatings developed using perpendicular magnetic field is more corrosion resistant compare to that for parallel magnetic field. This is attributed to the additional (321) ?-Ni5Zn21 orientations. The changes in the phase structure of the coatings deposited at different magnetic field are attributed to the effect caused by the magnetic convection induced in the electrolytic solution, called MHD effect (magneto-hydrodynamic effect). The chemical composition of the alloy was found to be same in both natural and magnetically induced deposition due to constant Ni content in the bath. The variation in the surface morphology of the coatings was studied by scanning electron microscopy (SEM). The Zn-Ni alloy coating deposited at 0.8 T perpendicular B showed the highest corrosion resistance (with corrosion rate=0.26 × 10-2 mm y-1) compared to the one with no B (corrosion rate = 14.46 × 10-2 mm y-1). The improved corrosion resistance of the coatings was discussed in the light of magnetic field effect on crystallographic orientation. © 2013 Elsevier B.V. All rights reserved.
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    Effect of induced magnetic field on electrocrystallization of Zn-Ni alloy and their corrosion study
    (Springer New York LLC journals@springer-sbm.com, 2014) Rao, V.R.; Hegde, A.C.
    Zn-Ni alloy coatings have been deposited galvanostatically on mild steel under the effect of induced magnetic field (B), using gelatin and glycerol as additives. The effect of field intensity (from 0.05 to 0.4 T) and direction (both parallel and perpendicular) on electrocrystallization process has been studied considering the magnetohydrodynamic effect. The corrosion behaviors of coatings, deposited under different conditions of B, were evaluated by electrochemical AC and DC methods. Under optimal condition of B (perpendicular), Zn-Ni coatings showed about 3 times less corrosion rate (CR) than the one developed under natural convection (B = 0 T), deposited from same bath for same duration. The significant decrease of CR was attributed to unique electrocrystallization process during deposition, favoring increased ?-Ni5Zn21 (321) and decreased ?-Ni 5Zn21 (330) phase. Progressive decrease of CR with increase of B showed that corrosion protection efficacy of the coatings bears close relation with their crystallographic orientations and surface topography, evidenced by XRD study and SEM analysis. The effect of B on thickness, microhardness, surface morphology, phase structure, and the corrosion resistance of coatings was analyzed and results were discussed. © ASM International.
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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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    Magnetoelectrodeposition of Ni-W alloy coatings for enhanced hydrogen evolution reaction
    (Royal Society of Chemistry, 2016) Elias, L.; Cao, P.; Hegde, A.
    The electrocatalytic efficiency of electrodeposited (ED) Ni-W alloy coatings for the hydrogen evolution reaction (HER) has been improved drastically through magnetoelectrodeposition (MED) approach. Ni-W alloy coatings have been developed under different conditions of magnetic field intensity 'B' (applied perpendicular in the range of 0.1-0.4 T), and their electrocatalytic activity for the HER has been tested using cyclic voltammetry (CV) and chronopotentiometry (CP) techniques in 1.0 M KOH solution. A drastic improvement in the electrocatalytic behavior of the MED coating, represented as (Ni-W)B=0.2 T was found as compared to its conventional Ni-W alloy coatings. Improved performance of the MED coatings was explained on the basis of differences in the process of electrocrystallization affected due to the applied magnetic field, supported by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. A magnetic field has been used advantageously for the first time to increase the W content of the alloy. Increased activity of the MED coatings was attributed to the increased W content in the alloy, characterized by the unique (220) reflection, explained by the magnetohydrodynamic (MHD) effect due to Lorentz force. © 2016 The Royal Society of Chemistry.
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    Effect of magnetic field on corrosion protection efficacy of Ni-W alloy coatings
    (Elsevier Ltd, 2017) Elias, L.; Hegde, A.C.
    High corrosion resistant Ni-W alloy coatings were developed using magnetoelectrodeposition (MED) approach for the protection of mild steel substrates. The conditions for the development of more corrosion resistant MED Ni-W alloy coatings were optimized by inducing a magnetic field (B) during deposition, in terms of intensity and direction. The applied magnetic field was used as a tool to alter the crystallinity, composition and thereby the corrosion resistance of the coatings. It was demonstrated that the corrosion resistance of Ni-W alloy coatings can be improved to many folds of its magnitude by MED approach. Significant increase in corrosion resistance exhibited by MED coatings (under both parallel and perpendicular magnetic field, B) is attributed to the increased W content of the alloy affected by an increase in limiting current density (iL). The high corrosion resistance of the MED Ni-W alloy coatings was explained in the light of magnetohydrodynamic (MHD) effect, responsible for the increased W content, brought about by the enhanced mass transport. The inherent limitations of the bath like low iL and induced type of codeposition which impedes the development of W rich alloy coatings has been successfully resolved by MED method. Drastic improvement in corrosion resistance is ascribed to the basic difference in the process of electrocrystallization and phases formed during MED, confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) study. The results are discussed with greater insight into binary alloy deposition and mass transfer process at cathode/electrolyte interface. © 2017 Elsevier B.V.
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    Magnetic-field tuning of whispering gallery mode lasing from ferromagnetic nematic liquid crystal microdroplets
    (OSA - The Optical Society info@osa.org, 2017) Mur, M.; Sofi, J.A.; Kvasi?, I.; Mertelj, A.; Lisjak, D.; Niranjan, V.; Mus?evic?, I.; Dhara, S.
    We report magnetic field tuning of the structure and Whispering Gallery Mode lasing from ferromagnetic nematic liquid crystal micro-droplets. Microlasers were prepared by dispersing a nematic liquid crystal, containing magnetic nanoparticles and fluorescent dye, in a glycerol-lecithin matrix. The droplets exhibit radial director structure, which shows elastic distortion at a very low external magnetic field. The fluorescent dye doped ferromagnetic nematic droplets show Whispering Gallery Mode lasing, which is tunable by the external magnetic field. The tuning of the WGM lasing modes is linear in magnetic field with a wavelength-shift of the order of 1 nm/100 mT. Depending on the lasing geometry, the WGMs are red- or blue-shifted. © 2017 Optical Society of America.
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    Magnetic field and frequency dependent LVE limit characterization of magnetorheological elastomer
    (Springer Verlag service@springer.de, 2017) Poojary, U.R.; Gangadharan, K.V.
    Magnetorheological elastomer (MRE) based semi-active isolators have the potential to replace conventional passive isolators to achieve wide frequency range isolation. The effectiveness of MRE isolator depends on the control strategies developed based on viscoelastic constitutive relations. The theory of linear viscoelasticity is the basis for viscoelastic constitutive relations which can predict the material behavior within a certain strain limit referred as linear viscoelastic (LVE) limit. Beyond the LVE limit, the performance of MRE semi-active isolator exacerbates as the control strategies turns out to be ineffective. In the present study, variation in LVE limit of MRE with the magnetic field and frequency is investigated through forced vibration tests. To exclude the effect of terminal non-linearity on the measurement, the blocked transfer stiffness method described in the ISO 10846-2 is adopted. The results revealed that the LVE limit of MRE is strongly dependant on the magnetic field and exhibited a weak dependency on the operating frequency. Under magnetized state, the transition from linear to non-linear behavior of MRE is at lower strain levels indicating the increased friction energy dissipation at particle–matrix interface. © 2016, The Brazilian Society of Mechanical Sciences and Engineering.
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    Dynamic deformation–dependent magnetic field–induced force transmissibility characteristics of magnetorheological elastomer
    (SAGE Publications Ltd info@sagepub.co.uk, 2017) Poojary, U.R.; Hegde, S.; Gangadharan, K.V.
    The need for broad-band vibration isolation performance of the structures is fulfilled by magnetorheological elastomer–based smart vibration isolation system. The smart isolation capabilities of magnetorheological elastomer isolator vary with the input dynamic deformation levels. In this study, force transmissibility measurement approach is adapted to evaluate the influence of dynamic deformation on the field-induced isolation capabilities of magnetorheological elastomer. The variation in isolation capabilities of magnetorheological elastomer is assessed in terms of isolation effect. Isolation performance of magnetorheological elastomer is enhanced with the increase in the magnetic field. Under increased dynamic deformation levels, the isolation characteristics of magnetorheological elastomer are influenced by the Payne effect. Dominance of the Payne effect under non-magnetized state of magnetorheological elastomer has enhanced the isolation effect at larger strain levels. The influence of strain on isolation characteristics of magnetorheological elastomer is verified from the magnetic force simulation between a pair of dipoles performed in ANSYS (version 14). © 2016, © The Author(s) 2016.
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    Design of magneto-rheological brake for optimum dimension
    (Springer Verlag service@springer.de, 2018) Lijesh, L.; Kumar, D.; Gangadharan, K.V.
    Online control of braking performance of magneto-rheological (MR) brake by bridling the apparent viscosity of MR fluid and by amending magnetic field is considered as an effective and smart option to replace the conventional disc brake. The magnetic field procreated by electromagnet in MR brake is reliant on dimensions and material properties of MR brake (casing, rotor and MR fluid region). Extensive works have been reported on enhancing the magnetic properties of MR fluid to achieve maximum braking performance; however, scarce works are available that reflects that the dimensions of MR brake influence the braking performance. Prior works on MR brakes focus on designing for meticulous outer dimensions of brakes, and thus, their results find little utility to a new designer. Therefore, the objective of the present work is to propose a methodology to determine the dimension of MR brake for a given outer dimensions, which shall provide maximum braking performance. The, braking performance is evaluated by assessing the effective torque and brake density. Magneto-static analysis using ANSYS is employed for determining the magnetic field in the MR region, and thereafter, the braking torque is calculated. From the obtained results, curve fit equations are proposed to estimate the values of (i) MR brake casing thickness, (ii) height of the MR brake to rotor, (iii) thickness of core, and (iv) thickness of MR fluid region, for achieving maximum torque. To validate the proposed methodology, MR brake with two different electromagnets and rotors is developed. The static performance of MR brake is evaluated by measuring the braking torque for different currents using a torque wrench and the dynamic performance of the MR brakes is performed on an MR brake test setup. The dynamic performance is evaluated by measuring viscous torque. Finally, the comparisons of the theoretical and experimental results are performed and the obtained results are presented. © 2018, The Brazilian Society of Mechanical Sciences and Engineering.
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    Integer and fractional order-based viscoelastic constitutive modeling to predict the frequency and magnetic field-induced properties of magnetorheological elastomer
    (American Society of Mechanical Engineers (ASME), 2018) Poojary, U.R.; Gangadharan, K.V.
    Magnetorheological elastomer (MRE)-based semi-active vibration mitigation device demands a mathematical representation of its smart characteristics. To model the material behavior over broadband frequency, the simplicity of the mathematical formulation is very important. Material modeling of MRE involves the theory of viscoelasticity, which describes the properties intermediate between the solid and the liquid. In the present study, viscoelastic property of MRE is modeled by an integer and fractional order derivative approaches. Integer order-based model comprises of six parameters, and the fraction order model is represented by five parameters. The parameters of the model are identified by minimizing the error between the response from the model and the dynamic compression test data. Performance of the model is evaluated with respect to the optimized parameters estimated at different sets of regularly spaced arbitrary input frequencies. A linear and quadratic interpolation function is chosen to generalize the variation of parameters with respect to the magnetic field and frequency. The predicted response from the model revealed that the fractional order model describes the properties of MRE in a simplest form with reduced number of parameters. This model has a greater control over the real and imaginary part of the complex stiffness, which facilitates in choosing a better interpolating function to improve the accuracy. Furthermore, it is confirmed that the realistic assessment on the performance of a model is based on its ability to reproduce the results obtained from optimized parameters. © © 2018 by ASME.