Browsing by Author "Lijesh, L."

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A Pragmatic Optimization of Axial Stack-Radial Passive Magnetic Bearings
(American Society of Mechanical Engineers (ASME) infocentral@asme.org, 2018) Lijesh, L.; Doddamani, M.; Bekinal, S.I.
Passive magnetic bearing's (PMB) adaptability for both lower and higher speed applications demands detailed and critical analysis of design, performance optimization, and manufacturability. Optimization techniques for stacked PMB published in recent past are less accurate with respect to complete optimum solution. In this context, the present work deals with a pragmatic optimization of axially stacked PMBs for the maximum radial load using three-dimensional (3D) equations. Optimization for three different PMB configurations, monolithic, conventional, and rotational magnetized direction (RMD), is presented based on the constraints, constants, and bounds of the dimensions obtained from published literature. Further, to assist the designers, equations to estimate the mean radius and clearance being crucial parameters are provided for the given axial length and outer radius of the stator with the objective of achieving maximum load-carrying capacity. A comparison of the load-carrying capacity of conventional stacked PMB using the proposed equation with the equation provided in literature is compared. Finally, effectiveness of the proposed pragmatic optimization technique is demonstrated by analyzing three examples with reference to available literature. © 2018 by ASME.
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.
Enhancing tribological performance of Ti-6Al-4V by sliding process
(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2018) Kumar, D.; Deepak, K.B.; Muzakkir, S.M.; Wani, M.F.; Lijesh, L.
The exceptional combination of mechanical, physical, and anti-corrosive properties of titanium alloy Ti-6Al-4 V (Ti64) makes it idle material for the applications, e.g., aerospace, automobile, chemical, medical etc. The tribological performance of the Ti64 can be enhanced by developing a protective layer or coating on its surface. A tribo-oxide protective layer on the surface of Ti64 through rubbing process was developed. For this, the tribological behavior of tribo pair, Ti64 pin-alumina disc was studied under dry ambient condition for diverse loading and sliding speed conditions, using pin on disc experimental set-up. The tribological performance was quantified in terms of coefficient of friction and wear rate. The mechanical properties like nano-hardness and elastic modulus of the pins surface were determined. The tribological behavior were extremely transient and depend greatly on what the surface has precisely experienced. Experimental results revealed that deprived tribological properties and higher oxide layer was selected. To enhance the tribological behavior of deprived tribological behavior, the pin with high oxide layer is used.
Multi Response Optimization and Experimental Investigations into the Impact of Wire EDM on the Tribological Properties of Ti–6Al–4V
(Springer India, 2018) Kuriachen, B.; Lijesh, L.; Kuppan, P.
Titanium (Ti) alloy, Ti–6Al–4V (commonly known as Ti64), is employed in numerous applications due to their superior strength to weight ratio, low cost to performance ratio, tensile strength, and corrosion resistance properties. However, due to its poor tribological (friction and wear) properties and difficult-to-machine material, its implementation in the intended applications is limited. Nevertheless, Ti64 can be accurately machined using wire electrical discharge machining (WEDM) and further, this process develops a recast layer on the surface of Ti64, which posses larger percentage of oxygen. Therefore, in the present work, it is hypothesized that, the presence of the recast layer on the surface of Ti64 may enhance its tribological properties. To validate the proposed hypothesis, pins of (1) pure Ti64 and (2) WEDMed Ti64 were slided against EN32 steel disc on a pin on disc experimental setup for load of 50 N, rotational speed of 200 rpm and sliding distance of 500 m. In-situ analysis (scanning electron microscope and energy dispersive spectroscopy) and mechanical properties (nano-hardness and elastic modulus) were performed on the pin’s surface, to identify the change in properties. Obtained results indicated significant increase in the oxide layer formation, consequently enhanced the tribological properties of WEDMed Ti64 compared to pure Ti64. To understand the tribological behavior of WEDMed Ti64 at other rotational speed and load, second set of experiments was performed by varying load (50, 70 and 90 N) and rotational speed of (200, 400 and 600 rpm). It was observed that wear values were not proportional to increase in load and speed. To identify the condition favoring the tribological behavior, multi-response optimization technique was performed and the identified load and speed values for the optimum tribological behavior were estimated. © 2018, The Indian Institute of Metals - IIM.
Parametric studies on bending stiffness and damping ratio of Sandwich structures
(Elsevier B.V., 2018) Rajpal, R.; Lijesh, L.; Gangadharan, K.V.
Sandwich structures are extensively used in aviation industries to reduce the overall weight of the system. Although the mechanical behavior of these structures has been widely studied, the performance of core shape in vibration response has been minimally explored. This study focuses on understanding the various influences of sandwich structures considering the following parameters: (i) nature of core shape, (ii) number of infill shapes, and (iii) orientation of cores, which affect the dynamic behavior of sandwich structures. Nine sandwich structures comprising three different core shapes, hexagon, triangle, and square shapes, in three different orientations, namely 0° 45° and 90° were considered for the present study. These structures in the beginning were put by modal analysis using finite element method (FEM). All the nine structures were printed using the fused deposition method to validate the FEM findings, while the DEWE soft data acquisition system was used to estimate the modal parameters (i) natural frequency and (ii) damping ratio. Natural frequency and damping ratio were estimated using FRF and Nyquist circle plot, respectively. This study demonstrates that although the square core orientated at 0° exhibited superior stiffness in bending loads, the hexagonal core orientated at 0° displayed an admirable combination of both stiffness and damping properties. © 2018 Elsevier B.V.