Browsing by Author "Kumar, G."
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Item Determination of spread activation energy and assessment of wetting behavior of solders on metallic substrates(2010) Prabhu, K.N.; Kumar, G.The effects of substrate material, substrate surface roughness, and operating temperature on the wetting behavior of Sn-37Pb, Sn-3.5Ag, and Sn-9Zn eutectic solders on metallic substrates were investigated. Solder spreading kinetics was successfully represented by the exponential power law (EPL): ?=exp (-K ?n). The EPL parameter K has the significance of accelerating the kinetics of relaxation while the parameter n represents the resistance to spreading process (spread resistance parameter). EPL parameters exhibited a decreasing trend with an increase in surface roughness. Estimated activation energies for solder spreading were found to be in between those reported for inert and highly reactive spreading systems. 2010 American Society of Mechanical Engineers.Item Determination of spread activation energy and assessment of wetting behavior of solders on metallic substrates(American Society of Mechanical Engineers (ASME), 2010) Prabhu, K.N.; Kumar, G.The effects of substrate material, substrate surface roughness, and operating temperature on the wetting behavior of Sn-37Pb, Sn-3.5Ag, and Sn-9Zn eutectic solders on metallic substrates were investigated. Solder spreading kinetics was successfully represented by the exponential power law (EPL): ?=exp (-K ?n). The EPL parameter K has the significance of accelerating the kinetics of relaxation while the parameter n represents the resistance to spreading process (spread resistance parameter). EPL parameters exhibited a decreasing trend with an increase in surface roughness. Estimated activation energies for solder spreading were found to be in between those reported for inert and highly reactive spreading systems. © 2010 American Society of Mechanical Engineers.Item Development, Characterization, Mechanical and Corrosion Behaviour Investigation of Multi-direction Forged Mg–Zn Alloy(Springer International Publishing, 2019) Anne, G.; Ramesh, S.; Kumar, G.; Sahu, S.; Ramesh, M.R.; Shivananda Nayaka, H.; Arya, S.In the present study, homogenized Mg−4%Zn (wt%) alloy was exposed to multi-direction forging (MDF) at 280 °C up to 5 passes successfully. Microstructural evolution, mechanical properties and corrosion behavior of the MDF-processed Mg−4%Zn alloy was investigated using different characterization techniques. Five passes of MDF (cumulative strain, ΣΔε = 3.45) led to the formation of ultrafine grain structure (grain size ~2.3 μm) with high angle grain boundaries (HAGBs) and high dislocation density. Corresponding ultimate tensile strength (UTS) and microhardness were observed to be 228 MPa and 88 Hv. Potentiodynamic polarization test results exhibited higher corrosion resistance (0.38 mm/y) in comparison with that of homogenized condition (1.33 mm/y). © 2019, The Minerals, Metals & Materials Society.Item Development, Characterization, Mechanical and Corrosion Behaviour Investigation of Multi-direction Forged Mg�Zn Alloy(2019) Anne, G.; Ramesh, S.; Kumar, G.; Sahu, S.; Ramesh, M.R.; Shivananda, Nayaka, H.; Arya, S.In the present study, homogenized Mg?4%Zn (wt%) alloy was exposed to multi-direction forging (MDF) at 280 �C up to 5 passes successfully. Microstructural evolution, mechanical properties and corrosion behavior of the MDF-processed Mg?4%Zn alloy was investigated using different characterization techniques. Five passes of MDF (cumulative strain, ??? = 3.45) led to the formation of ultrafine grain structure (grain size ~2.3 ?m) with high angle grain boundaries (HAGBs) and high dislocation density. Corresponding ultimate tensile strength (UTS) and microhardness were observed to be 228 MPa and 88 Hv. Potentiodynamic polarization test results exhibited higher corrosion resistance (0.38 mm/y) in comparison with that of homogenized condition (1.33 mm/y). � 2019, The Minerals, Metals & Materials Society.Item Effect of Equal Channel Angular Pressing on Properties Evaluation of Biodegradable Mg-Zn-Mn Alloy(Springer Science and Business Media Deutschland GmbH, 2021) Ramesh, S.; Kumar, G.; Jagadeesh, C.; Anne, G.; Shivananda Nayaka, H.Equal channel angular pressing (ECAP) was used to process Mg-4Zn-1Mn alloy at 300 °C using route Bc up to 4 pass with a cumulative strain of 3.2. Optical microscope (OM), microstructures results shows homogenized sample grain size was 260 µm, after 4 pass ECAP grain size was decreased to 6 µm. Electron back-scattered diffraction (EBSD) shows the misorientation angle converted from low-angle grain boundaries (LAGB) to high-angle grain boundaries (HAGB). Dislocation density and fine grains were observed from transmission electron microscope (TEM) images. Strength has been increased from 156 to 218 MPa and hardness increased to 68 Hv after 4 pass of ECAP. Fractography analysis revealed that dimple size decreases as ECAP passes increased. XRD analysis shows the peak broadening and intensity variation, because of grain refinement. The corrosion behavior of the homogenized and ECAP-processed samples were investigated by electrochemical tests using simulated body fluids (SBF) at 37 ± 1 °C. The lower corrosion resistance of ECAP-processed Mg-4Zn-1Mn alloy attributed to the strain-induced crystalline defects, subgrain boundaries and high-density dislocations. Enhanced strength and ductility combined with lower corrosion resistance of ECAP-processed Mg-4Zn-1Mn has greater potentials for biomedical implants. © 2021, The Author(s), under exclusive licence to Springer Nature Switzerland AG.Item Effect of section thickness and modification on thermal analysis parameters of A357 alloy(2006) Hegde, S.; Kumar, G.; Prabhu, K.N.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.Item 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.Item Effect of substrate surface roughness on wetting behaviour of vegetable oils(2009) Prabhu, K.N.; Fernades, P.; Kumar, G.Vegetable oils are mainly used in the heat treating industry due to their environmental friendliness. In the present work the effect of surface roughness on spreading of vegetable oils on stainless steel substrates was investigated. Spreading phenomenon was digitally recorded and analyzed. All of the oils under investigation exhibited power law spreading behaviour of the type: A = ktn, where A, t, k and n represent the drop base contact area, spreading time, constant and exponent, respectively. The coconut and sunflower oils exhibited accelerated kinetics owing to their lower viscosity as compared to palm and mineral oils while peanut oil showed intermediate behaviour. Viscous regime was dominant during spreading of mineral and palm oils as compared to that of coconut oil. All the oils took longer period of time on rough surfaces than on smooth surfaces to relax to the same degree of wetting. Oils spreading on rough surfaces had to overcome the additional barrier due to asperities of the rough surface. Contact angle decreased with increase in roughness supporting the Wenzel's proposition. The decrease was significant for increase in roughness from 0.25 ?m to 0.50 ?m for all oils. However, the effect was negligible with further increase in roughness particularly for high viscosity oils. A spread parameter (?) is proposed to account for the variation of contact angle with surface roughness of the substrate and momentum diffusivity of the spreading liquid. The result suggested that low viscosity liquids exhibit improved wetting characteristics during spreading on rough surfaces. A model is proposed to estimate dynamic contact angles on substrates having varying surface roughness. 2008 Elsevier Ltd. All rights reserved.Item Effect of substrate surface roughness on wetting behaviour of vegetable oils(2009) Prabhu, K.N.; Fernades, P.; Kumar, G.Vegetable oils are mainly used in the heat treating industry due to their environmental friendliness. In the present work the effect of surface roughness on spreading of vegetable oils on stainless steel substrates was investigated. Spreading phenomenon was digitally recorded and analyzed. All of the oils under investigation exhibited power law spreading behaviour of the type: A = ktn, where A, t, k and n represent the drop base contact area, spreading time, constant and exponent, respectively. The coconut and sunflower oils exhibited accelerated kinetics owing to their lower viscosity as compared to palm and mineral oils while peanut oil showed intermediate behaviour. Viscous regime was dominant during spreading of mineral and palm oils as compared to that of coconut oil. All the oils took longer period of time on rough surfaces than on smooth surfaces to relax to the same degree of wetting. Oils spreading on rough surfaces had to overcome the additional barrier due to asperities of the rough surface. Contact angle decreased with increase in roughness supporting the Wenzel's proposition. The decrease was significant for increase in roughness from 0.25 ?m to 0.50 ?m for all oils. However, the effect was negligible with further increase in roughness particularly for high viscosity oils. A spread parameter (?) is proposed to account for the variation of contact angle with surface roughness of the substrate and momentum diffusivity of the spreading liquid. The result suggested that low viscosity liquids exhibit improved wetting characteristics during spreading on rough surfaces. A model is proposed to estimate dynamic contact angles on substrates having varying surface roughness. © 2008 Elsevier Ltd. All rights reserved.Item Effect of thermal contact heat transfer on solidification of Pb-Sn and Pb-free solders(2007) Chellaih, T.; Kumar, G.; Prabhu, K.N.The effect of thermal contact heat transfer on the solidification of spherical droplets of four solder alloys, namely, Sn-37Pb, Sn-9Zn, Sn-0.7Cu and Sn-3.5Ag, was studied using SOLIDCAST simulation package. A significant drop in the arrest time was observed for increase in heat transfer coefficient from 1000 to 2000 W/m2 K. Effect of contact conductance and thermal diffusivity of solder alloys on arrest time is quantified by the power relation, ? = m(?{symbol})n where ? and ?{symbol} are defined as arrest time and heat transfer parameters, respectively. Experiments were also carried out to investigate the effect of cooling rate on solidification behaviour of the solder alloys used in simulation. The results indicated the significant effect of mould material on interfacial heat flux and metallurgical microstructure. 2005 Elsevier Ltd. All rights reserved.Item Effect of thermal contact heat transfer on solidification of Pb-Sn and Pb-free solders(Elsevier Ltd, 2007) Chellaih, T.; Kumar, G.; Prabhu, K.N.The effect of thermal contact heat transfer on the solidification of spherical droplets of four solder alloys, namely, Sn-37Pb, Sn-9Zn, Sn-0.7Cu and Sn-3.5Ag, was studied using SOLIDCAST simulation package. A significant drop in the arrest time was observed for increase in heat transfer coefficient from 1000 to 2000 W/m2 K. Effect of contact conductance and thermal diffusivity of solder alloys on arrest time is quantified by the power relation, ? = m(?{symbol})n where ? and ?{symbol} are defined as arrest time and heat transfer parameters, respectively. Experiments were also carried out to investigate the effect of cooling rate on solidification behaviour of the solder alloys used in simulation. The results indicated the significant effect of mould material on interfacial heat flux and metallurgical microstructure. © 2005 Elsevier Ltd. All rights reserved.Item 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.Item 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.Item Influence of Ball Burnishing Process on Equal Channel Angular Pressed Mg-Zn-Si Alloy on the Evolution of Microstructure and Corrosion Properties(Springer Science and Business Media B.V., 2021) Ramesh, S.; Anne, G.; Kumar, G.; Jagadeesh, C.; Shivananda Nayaka, H.In the present study, Mg-4Zn-1Si alloy was subjected to equal channel angular pressing (ECAP) up to 4 passes at 300 °C, followed by ball burnishing using 0.3 mm depth of press, 300 mm/min feed and 1 pass successfully. The effect of ECAP and ECAP + ball burnishing process on microstructure, mechanical properties (tensile and hardness) and corrosion behavior was systematically investigated. After 4 pass ECAP, initial coarse grains (210 ?m) were refined and average grain size is 6 ?m and after ball burnishing, the grain size is found to be 3.3 ?m. Microstructure evolution is discussed using optical images, scanning electron microscope images and transmission electron microscope images. For ECAP samples, maximum strength and hardness was recorded at 3 pass. Both strength and hardness decreased for 4 pass ECAP processed samples, even though grain size decreased, this is because of texture modification in the material. ECAP 4 pass + ball burnished samples exhibited 48.5% enhancement of microhardness as compared to 4 pass ECAP samples. Corrosion resistance of the samples decreased with increase in the number of ECAP passes, this is due to strain-induced grain refinement with more crystalline defects in samples. Combined process of ECAP and ball burnishing effectively reduces the Icorr and this consequently reduces corrosion rate of the Mg–4Zn-1Si alloy. © 2020, Springer Nature B.V.Item Review of non-reactive and reactive wetting of liquids on surfaces(2007) Kumar, G.; Prabhu, K.N.Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems. © 2007 Elsevier B.V. All rights reserved.Item Review of non-reactive and reactive wetting of liquids on surfaces(2007) Kumar, G.; Prabhu, K.N.Wettability is a tendency for a liquid to spread on a solid substrate and is generally measured in terms of the angle (contact angle) between the tangent drawn at the triple point between the three phases (solid, liquid and vapour) and the substrate surface. A liquid spreading on a substrate with no reaction/absorption of the liquid by substrate material is known as non-reactive or inert wetting whereas the wetting process influenced by reaction between the spreading liquid and substrate material is known as reactive wetting. Young's equation gives the equilibrium contact angle in terms of interfacial tensions existing at the three-phase interface. The derivation of Young's equation is made under the assumptions of spreading of non-reactive liquid on an ideal (physically and chemically inert, smooth, homogeneous and rigid) solid, a condition that is rarely met in practical situations. Nevertheless Young's equation is the most fundamental starting point for understanding of the complex field of wetting. Reliable and reproducible measurements of contact angle from the experiments are important in order to analyze the wetting behaviour. Various methods have been developed over the years to evaluate wettability of a solid by a liquid. Among these, sessile drop and wetting balance techniques are versatile, popular and provide reliable data. Wetting is affected by large number of factors including liquid properties, substrate properties and system conditions. The effect of these factors on wettability is discussed. Thermodynamic treatment of wetting in inert systems is simple and based on free energy minimization where as that in reactive systems is quite complex. Surface energetics has to be considered while determining the driving force for spreading. Similar is the case of spreading kinetics. Inert systems follow definite flow pattern and in most cases a single function is sufficient to describe the whole kinetics. Theoretical models successfully describe the spreading in inert systems. However, it is difficult to determine the exact mechanism that controls the kinetics since reactive wetting is affected by a number of factors like interfacial reactions, diffusion of constituents, dissolution of the substrate, etc. The quantification of the effect of these interrelated factors on wettability would be useful to build a predictive model of wetting kinetics for reactive systems. © 2007 Elsevier B.V. All rights reserved.Item Structural Analysis of Non-prismatic Column Using Finite Element Approach(Springer, 2024) Kumar, G.; Kaliveeran, V.Offshore pipelines are subjected to various types of loading, depending upon the sub-sea conditions during their design life. Buckling is a major structural instability problem in the offshore pipelines operating at high pressure and high temperature, along with other causes. Various kinds of non-prismatic sections are generally used in special areas of the pipeline system. The present research work focuses on estimating the structural response (bucking strength, in particular) of the non-prismatic offshore pipelines. Eigenvalue buckling analysis using the Finite Element (FE) method was conducted to find the buckling strength and mode shape of the pipeline model. The non-prismatic pipeline was modeled as 1-D and 3-D FE models; the 1-D model was analyzed using the MATLAB program, and the complete 3-D model was analyzed using the ANSYS workbench. Both the 1-D and 3-D numerical analysis results were compared and verified experimentally. The results of the analysis and their convergence pattern were also discussed. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.Item Subsidence Analysis for Old Abandoned Board and Pillar Coal Mines Using ANSYS and Monte Carlo Simulation(Pleiades Publishing, 2024) Akhil, A.; Pal, S.K.; Tripathi, A.K.; Kumar, G.Abstract: This research paper will cover the possible causes which can lead to subsidence above old abandoned board and pillar coal mines at a shallow depth. The research includes the calculation and analysis of the factor of safety for pillars using ANSYS and Monte Carlo Simulations for ascertaining subsidence. An old abandoned coal mine of South Eastern Coalfields Ltd. (SECL, a subsidiary of Coal India Limited) was considered for the study of coal pillar fatigue and eventual crushing of pillars over a long duration of time, simulation analysis of stress and strength of coal pillars over a long period, change in behavior of factor of safety as the dimension of the pillars changes. © Pleiades Publishing, Ltd. 2024.Item Subsidence Analysis for Old Abandoned Board and Pillar Coal Mines Using ANSYS and Monte Carlo Simulation(Pleiades Publishing, 2023) Akhil, A.; Pal, S.K.; Tripathi, A.K.; Kumar, G.Abstract: Mine Subsidence is a phenomenon of lateral or vertical ground movement caused by a failure initiated at the mine level of man-made underground mines and an abandoned mine is a site where mining activities occurred but acceptable mine closure and reclamation did not take place or was incomplete. Subsidence is one of the major problems which is faced over an old abandoned mine. Presently there are limited means or methods which can predict subsidence over an old abandoned coal mine at a shallow depth efficiently and the precautionary methods that should be taken in these situations. This research paper will cover the possible causes which can lead to subsidence above an old abandoned board and pillar coal mines at a shallow depth. The research includes the calculation of the factor of safety for pillars and analysis of FoS using ANSYS and Monte Carlo Simulations for ascertaining subsidence. An old abandoned coal mine of South Eastern Coalfields Ltd. (SECL, a subsidiary of Coal India Limited), was considered for the study of coal pillar fatigue and eventual crushing of pillars over a long duration of time, simulation analysis of stress and strength of coal pillars over a long period, change in behavior of factor of safety as the dimension of the pillars changes. © Pleiades Publishing, Ltd. 2024.Item Wetting behavior of solders(2010) Kumar, G.; Prabhu, K.N.Lead bearing solders have been used extensively in the assembly of modern electronic circuits. However, increasing environmental and health concerns about the toxicity of lead has led to the development of lead-free solders. Wetting of solders on surfaces is a complex and important phenomenon that affects the interfacial microstructure and hence the reliability of a solder joint. The solder material reacts with a small amount of the base metal and wets the metal by intermetallic compound (IMC) formation. The degree and rate of wetting are the two important parameters that characterize the wetting phenomenon. Contact angle is a measure of the degree of wetting or wettability of a surface by a liquid. Spreading kinetics in a given system is strongly affected by the experimental conditions. In reactive systems like soldering, wetting and chemical interfacial reactions are interrelated, and hence for successful modeling, it is essential to assess the effect of interfacial reactions on kinetics of wetting. Solder wetting necessarily involves the metallurgical reactions between the filler metal and the base metal. This interaction at the solder/base metal interface results in the formation of IMCs. During soldering an additional driving force besides the imbalance in interfacial energies originates from the interfacial reactions. The formation of IMC has significant influence on contact angle. The presence of IMCs (thin, continuous, and uniform layer) between solders and substrate metals is an essential requirement for good bonding. Optimum thickness of an IMC layer offers better wettability and an excellent solder joint reliability. However, due to their inherent brittle nature and tendency to generate structural defects, a too thick IMC layer at the interface may degrade the joint. In this paper, the factors affecting the wetting behavior of solders and evolution of interfacial microstructure are reviewed and discussed. Copyright � 2010 by ASTM International.