Department of Mechanical Engineering

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IIT Jodhpur

The overall theme of this book is related to the topics of solar energy. This book has been divided into four parts. The first part relates to the general issues of clean and sustainable energy. The second part of this book deals with the topic of power generation using solar energy. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

World University root node

Energy, Environment, and Sustainability

Introduction to New Research Directions in Solar Energy Technologies

A fluid dynamics numerical simulation is carried to study the gust characteristics produced downstream of a pair of sinusoidally pitching two-dimensional thin foils with a certain lateral spacing and placed in a freestream flow. The flow was simulated for Reynolds number (Re) = 1.6 × 105, the airfoil pitching angle = 6.9°, and a range of reduced frequencies (0.54 ≤ k ≤ 1.2). Between the two (undulating) wakes of the two foils, the flow is irrotational and unsteady that can be used to study gust response of, for example, micro-air vehicles (MAVS). The maximum gust velocity that can be generated by this technique is, however, limited to (5–7) % of the mean flow velocity. To enhance the gust intensity, a new method is proposed: introduction of a jet at the trailing edge of each pitching foil. Results show that the addition of the trailing jet enhances the gust intensity by 2–7 times for the Re, jet velocity, and the range of reduced frequencies considered. This technique provides a simple, economical, and controlled way to study gust response of MAVs and aircraft in wind tunnels. © 2021, Indian Academy of Sciences.

Sadhana - Academy Proceedings in Engineering Sciences

Gust enhancement using jet at the trailing edge of a pair of pitching foils

Modelling of the spot weld responses, i.e. shear-tensile strength, coach-peel strength, mean dynamic contact resistance and nugget diameter, was carried out along with the optimization of weld process parameters, i.e. weld current, weld time and electrode force. The experiments for weld fabrication were designed using face-centred central composite design under response surface methodology. Experimental results acquired from the designed experiments were used to generate prediction models of the responses using the artificial neural network approach. Hybrid artificial neural network-genetic algorithm technique was used in order to obtain the optimized welding process parameters. Validation checks were done for the optimized parameters and responses in order to justify the adequacy of the models and optimized value. Failure mode analysis was done to determine the plasticity fraction and to relate this with the mode of failure and microhardness values. The shear-tensile strength, coach-peel strength and nugget diameter increase with the corresponding increase in the amount of heat input during the weld fabrication. The optimum process parameters are 8.98 kA of weld current, 284.92 ms of weld time and 3.04 kN of electrode force leading to the response values as shear-tensile strength of 21.93 kN. © 2021, The Indian Institute of Metals - IIM.

Transactions of the Indian Institute of Metals

Investigations on Mechanical Behaviour and Failure Mechanism of Resistance Spot-Welded DP590 Steel Using Artificial Neural Network

The P22/P91 dissimilar weld increasingly used in supercritical power plan boilers calls for experimental investigations on its properties for enhanced performance in high-temperature service conditions. This study investigates the weld joint between P22/P91 steel using tungsten inert gas process employing a P22 matching filler metal. The fabricated weld has been characterized for mechanical properties of tensile strength and microhardness. The microstructural examination has been carried out in the weld region, transition zones, and base metals. The weld was exposed to a temperature of 700 °C in the environment of molten salt (50% Na2SO4 + 50% NaCl) to quantify the effect of high-temperature corrosion at its sight of application. Furthermore, the welds were also shot-peened and its effect on corrosion properties has been examined. The corroded specimens were examined using X-ray diffraction and scanning electron microscope to analyze the oxide scale produced upon exposure to high temperature in a controlled environment. The P22 base metal was found to oxidize more severely as compared to the weld fusion zone. Shot peening improves the corrosion resistance of weld by 7.56%. The results of this study comprehensively cover multiple aspects of weld integrity as per the service conditions, with its results having significant application in the power plant industry. © IMechE 2021.

Proceedings of the Institution of Mechanical Engineers, Part L: Journal of Materials: Design and Applications

Mechanical, microstructure, and hot corrosion investigations on P22/P91 dissimilar tungsten inert gas weld

The work is aimed at characterizing the properties of slag obtained from CaO-CaF2- TiO2-SiO2 based coatings developed for welding the offshore structures. Extreme vertices methodology was used to formulate coating compositions. Iron ore waste red ochre has been used as source of iron in the coating. The slag has been characterized for thermal stability, density, specific heat, enthalpy of reaction, thermal conductivity behavior, and thermal diffusivity. Welding slag was also structurally analyzed for different phases and bonds. Silicate ion (SiO44−) has been found to influence all the slag properties significantly. Effect of coating constituents has been studied using regression analysis. Mineral constituents and their interactions were found to have influential role on thermo-physical, chemical and structural behavior of slags. © 2020, Springer Nature B.V.

Silicon

Characterization of CaO-CaF2-TiO2-SiO2 Based Welding Slags for Physicochemical and Thermophysical Properties

High-performance pipeline steels are frequently used for storage, transportation and energy development applications. Submerged arc welding finds its application to weld thick pipes. Design and development of appropriate welding fluxes provide good structural integrity properties in severe service environments. The present study aims to investigate the effect of laboratory-developed SAW fluxes on the electrochemical corrosion behavior of SAW weldments in different environments. Electrochemical corrosion behavior of weld specimens in different environments was performed using Linear Sweep Voltammetry. Different mediums such as seawater and sodium thiosulphate solution (10−2Mol/l, pH = 3, and 10−3Mol/l, pH = 5) were taken for the corrosion study. The microstructure of the weld specimen reveals the presence of acicular ferrite structure. F3RA and F19RA weld specimen shows a higher corrosion rate in seawater and sodium thiosulphate medium (pH = 3 or 5). © IMechE 2021.

Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering

Effect of SAW fluxes on electrochemical corrosion &amp; microstructural behavior of API X70 weldments

In the present study, galvanized High Strength Interstitial Free (HIF) steel sheets, and Dual Phase (DP780) steel sheets were used for the investigations. Resistance spot weld joints were fabricated between dissimilar steel sheets. The variation in dynamic resistance (DR) with the change in welding process parameters such as weld current, weld time and electrode force were used for establishing the range of adequate weld nugget formation parameters. Effect of these parameters over tensile strength, nugget diameter and the observed failure mode was studied using one factor at a time (OFAT) approach. Microstructure and hardness of parent metal, fusion & HAZ region has also been studied. © IMechE 2020.

Experimental investigation on resistance spot welding of dissimilar weld joints

This work investigates the microstructure and mechanical properties of 2507 super duplex stainless steel and API X70 high strength low alloy steel weld joint. This joint finds application in offshore hydrocarbon drilling riser and oil–gas pipelines. Coated shielded metal arc welding electrodes have been designed and extruded on 309L filler and their performance compared with a commercial austenitic electrode E309L. Filler 309L solidifies in ferrite-austenite (F-A) mode with a resultant microstructure comprising skeletal ferrites with austenite distributed in the interdendritic region. Results of tensile and impact tests indicate that weld fabricated with laboratory-developed electrodes has higher ductility and impact energy than the commercial electrode. The tensile strength and weld hardness of commercial electrodes are superior. The laboratory-made electrode’s microhardness is lower than the commercial electrodes, making the former less prone to failure. An alternative welding electrode coating composition has been suggested through this work and found to be performing satisfactorily and comparable to the commercially available electrodes. © IMechE 2021.

Experimental investigation on dissimilar weld between super duplex stainless steel 2507 and API X70 pipeline steel

This paper reports on the effect of CaO-CaF2-TiO2-SiO2 based electrode coating constituents and their binary, tertiary interactions on the weld metal chemistry of offshore structure. Coating compositions were prepared based on extreme vertices design methodology and extruded on austenitic 309L filler wire. Red ochre, a mineral waste from iron ore site, has been added to coating compositions in uniform quantity to utilize its iron content. Multi-pass weld beads hence deposited on super duplex 2507 grade steel were examined for chemical composition in terms of phosphorus, sulphur, molybdenum, niobium, and iron. Regression analysis was carried out to develop a relationship between the chemical composition and coating constituents, quantifying the effect of interactions. Obtained responses have also been optimized to find the most suitable coating compositions in the desired range of mineral constituents. The developed electrode coatings have been analyzed for their microstructure using scanning electron microscopy equipped with an energy dispersion spectroscope. The work establishes a relation between the coating minerals and their interactions on the weld chemistry. © 2021 Elsevier Ltd and Techna Group S.r.l.