2. Thesis and Dissertations
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Item Development and characterization of Al-Si based functionally graded material through Directional Solidification(National Institute of Technology Karnataka, Surathkal, 2020) N, Ramesh Babu.; Ramesh, M R.Many structural components encounter service conditions and hence required material performance vary with location within the component. It is well known that abrupt transitions in materials composition and properties within a component often result in sharp local concentrations of stress, whether the stress is internal or applied externally. It is also known that these stress concentrations are greatly reduced if the transition from one material to the other is made gradual. By definition, functionally graded materials (FGM’s) are used to produce components featuring engineered gradual transitions in microstructure and/or composition, the presence of which is motivated by functional performance requirements that vary with location within a part. With functionally graded materials, these requirements are met in a manner that optimizes the overall performance of the component. The research on FGM’s is encouraged by the need for properties that are unavailable in any single material and the need for graded properties to offset adverse effects of discontinuities for layered materials. Directional solidification is the common method for fabricating FGM’s which is mainly a composite material which has high differences of density and low solubility on different phases or different materials of the same alloy. The main thrust in the present work is to fabricate FGM’s for solid valve lifter applications. The first phase of study was to fabricate Al-Si based and Al-Si reinforced with 2wt% graphite FGM’s, to accomplish this a novel directional solidification technique combined with lateral vibrations was developed. In the second phase of study, optimization of process parameters i.e. chill material, chill volume and pouring temperature were carried out using taguchi technique through the experiments performed according to the L27 orthogonal array. The optimization was carried out by investigating the influence of process parameters(chill material, chill volume and pouring temperature) on hardness values across the top and bottom portion of the cast specimen. The castings obtained by both with vibrations and without vibrationswere tested. From the obtained results it was revealed that optimized samples obtained with lateral vibrations exhibited better variation in properties compared to the ones obtained without vibrations In the third phase of study, evaluation of mechanical and tribological characteristics was carried out on the optimized sample of Al-Si based FGM and Al-Si reinforced with 2wt% graphite FGMs to understand the significance of lateral vibrations. The FGM’s have been analyzed for microstructure by the scanning electron microscope (SEM) morphologies which revealed that concentration of Si was more at the top portion. The spatial transition of Si can be attributed to the presence of the chill at the bottom and to the influence of lateral vibrations which has led to variation of properties within the structure, these observations were also supported by the hardness values. Ultimate tensile strength (UTS) results also showed shift in the properties from bottom to top portion of the cast. Wear analysis carried out at the top and the bottom portion of the FGM showed that there is a decrease in wear loss, coefficient of friction and specific wear rate at the top portion compared to the bottom portion. Worn-out surface analysis revealed that graphite addition had imparted the self-lubricating property at the top portion which could serve as anti-friction and anti-wear applications in the automotive sector.Item Development of Sandwich Composites from Natural Materials for Bullet Proofing(National Institute of Technology Karnataka, Surathkal, 2019) Sangamesh; RaviShankar, K. S.; Kulakarni, S. M.Ballistic protective materials have been used in the past are replaced with synthetic polymer composites due to their strength to weight ratio. Nowadays, these synthetic materials are being replaced by natural fiber reinforced composites due to the cost and environmental issues. The present investigation relates to the development of natural sandwich/laminated composite material interlock blocks for bullet arresting. Bullet arresting capacity depends on energy absorption. The energy absorption of the material could be increased by different ways. Among which sandwich form of the composite is one of the effective ways of improving the energy absorption capability of PMCs. This study was undertaken to explore the use of natural materials such as Jute epoxy fly ash composite (JEFC), Jute-epoxy fly ash rubber (JEFRC) sandwich composite for ballistic energy absorption. Prior to FE analysis, mechanical characterization of three varieties of jute composites were carried out namely Tossa jute single woven composite (TSWC), White jute single woven composite (WSWC), White jute double woven composite (WDWC) among all Tossa jute single woven composite (TSWC) revealed better mechanical properties. Hence for further analysis, Tossa jute single woven epoxy fly ash composite nothing but Jute epoxy fly ash composite (JEFC) is only used for ballistic FE simulation and as well as for ballistic impact testing of composite plates, blocks and interlock blocks. Finite Element analysis of these plates was carried out for thicknesses (5, 10, 15 mm). JEFC plates and JEFRC sandwiches with the same thickness (15 mm) were fabricated and tested to measure residual velocity and energy absorbed. Among JEFC and JEFRC, JEFRC showed better ballistic performance hence further analysis is carried out on jute-epoxy-fly ash natural rubber sandwich block composite (JEFRC), at different thicknesses of the target plate (50, 75, 100, 150 mm) and three velocities of the projectile (150, 250, 350 m/s). Ballistic parameters were evaluated using commercial FE software. Further same thickness and same configuration sandwich blocks were produced using compression molding machine; these prepared samples were subjected to ballistic impact test by impacting the projectile. From FE analysis and ballistic test, it is confirmed that at about 75 mm thickness the sandwich blockswere capable of arresting the bullet. Further interlock sandwich blocks were produced and tested for ballistic impact, which arrested the bullet half of its thickness. Hence such sandwich interlock blocks are produced to prototype for arresting bullet up to velocity 350 m/s. Fracture behavior is analyzed using SEM.Item Effect of Pulsed Laser Deposited Ceramic Coatings on Microhardness and Corrosion Behavior of Titanium, Ti6al4v and Inconel(National Institute of Technology Karnataka, Surathkal, 2013) C, Sujaya; Shashikala, H.D.Coatings are used to modify and increase the functionality of a bulk surface or substrate without modifying the bulk properties of the material. The present work aims at obtaining uniform adhesive coatings of alumina and silicon carbide on different substrates viz., titanium, Ti6Al4V and inconel by pulsed laser deposition technique using Q-switched Nd: YAG laser at low temperature. Processing parameters such as laser fluence, substrate target distance, substrate temperature and target density during deposition were standardized to get adhesive films. Coated films were characterized using scanning electron microscopy, energy dispersive X-ray spectroscopy, spectrophotometer, optical microscope, nanoindentation, surface roughness measurements using 3D optical profilometer, adhesion test. Microhardness and corrosion studies were carried on substrates and after coating. Composite microhardness of ceramic coated substrates was measured using Knoop indenter and its film hardness was separated from composite hardness using a mathematical model based on modified area-law of mixture. Then by including indentation size effect the film hardness was compared with values obtained using nanoindentation method. Composite hardness as well as film hardness of the ceramic coating was found to be higher compared to the substrates. Corrosion behavior of substrates after ceramic coating was studied using 3.5% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. The Nyquist and the Bode plots obtained from the electrochemical impedance spectroscopy data are fitted by appropriate equivalent circuits. The pore resistance, the charge transfer resistance, the coating capacitance and the double layer capacitance of the coatings were obtained from the equivalent circuit. Alumina coated substrates showed more corrosion resistance than silicon carbide coated substrates. After the corrosion testing, the surface topography of the uncoated and the coated system were examined under scanning electron microscopy. Experimental results confirmed the possibility of using Nd: YAG laser for ceramic film deposition which improves the microhardness and corrosion resistance of the substrate considerablyItem Development and Characterization of Functionally Graded Al-Si Alloy System and Al-Si/SiCP Composites using Centrifuge Casting(National Institute of Technology Karnataka, Surathkal, 2013) S., Kiran Aithal; Desai, Vijay; Narendranath, S.FGM is a material that shows change in magnitude of property values from one end of a specimen or component to the other end. FGM has an intermediate layer whose structure, composition and morphology vary smoothly from one end of the specimen to the other end. Fabrication of FGM and their components with gradient microstructures and properties are challenging. Most of the investigations which focus on material behavior of FGMs are limited to analytical or numerical studies. One of the major bottlenecks with experimental studies is the preparation of FGMs having large property gradation. This necessitates the development of a suitable technique to produce such FGMs with reproducibility of structure and properties. The present work aims at developing a manufacturing technique for the FGMs in order to meet the wide range of and also suitable mechanical and tribological properties for specific thermal and mechanical engineering applications. Among the processing techniques available the most commonly used is horizontal centrifugal method, but, this method is used to produce mainly hallow cylinders. In this work a centrifuge setup is fabricated and FGMs have been successfully developed to produce solid castings. The major advantage of this machine when compared to the conventional machine is that the pouring is done while the mold is stationary and machine operates about a vertical axis. The principal advantage of this is good mold filling combined with microstructural control, which usually results in improved mechanical properties. In this process, when the melt is subjected to high G forces the lighter particles segregate towards the axis of rotation, while the denser particles move away from the axis of rotation depending on the density difference between melt and the reinforcement. This segregation depends on several process parameters such as mold rotational speed (G Factor), pouring temperature, mold temperature etc. The use of aluminum, its alloys and aluminum based composites in the present day has shown many advantages through its unique combination of physical and mechanical properties. The light weight, strength, formability, corrosion resistance, ofIV aluminum, its alloys give it the potential to meet a wide range of design challenges. Taking into consideration the advantages such as high wear resistance, controlled thermal-expansion coefficient, good corrosion resistance, and improved mechanical properties over a range of temperatures that Al alloys and its composites can provide, in this work manufacturing and characterization Al-Si FG alloys and Al-Si-SiCP FG composites have been taken up. Two Al-Si alloys eutectic (12%Si) and hypereutectic (17%Si) were used for producing FG alloys. Further effect of 3 mold rotational speed 200, 300, 400rpm, 2 pouring temperatures 800oC , 900oC and 2 mold temperatures ambient and preheating the mold at 180oC temperature were studied. Similarly FG composites were also produced using Al-17%Si and Al-12% Si as matrix with SiCP as reinforcement. Three different volume fractions of SiCP were used to produce FG composites. The FG composites were produced using 900oC pouring temperature with preheating the mold at 180oC under 200, 300, 400rpm mold rotational speed. The structure and properties of the FG alloys and Composites are studied to understand the effect of different process parameters. The Al-Si FGM specimens are studied for distribution of Si along the length of the specimen (from bottom to top) using optical microscope. The hardness's is measured along the length of the specimen using Brinell hardness tester. Sliding wear tests at room temperature are conducted at normal loads of 40, 60, and 80N and at 1.466m/s sliding speed for a constant sliding distance 879.6m in order to measure the wear resistance and friction characteristics. Similar tests were carried out for FG composites. Diametral compressive strength were conducted to know the strength of the specimen along the length at bottom, middle and top regions. It is found that the FG alloy and Composites are produced successfully using centrifuge technique. In both alloy and composite the gradation occurs at higher rpm, teeming temperature and mold temperature. The experimental findings of hardness and the wear tests provide adequate proof on the gradation characterization (% volume fraction of primary Si, % volume fraction of SiCP and rim thickness) done using microstructural studies.Item AB Initio Studies of the Ground State Structure and Properties of Boron Carbides and Ruthenium Carbides(National Institute of Technology Karnataka, Surathkal, 2016) G, Harikrishnan; K. M, AjithThis work investigates the ground state structure and properties of Boron Carbides (B12C3 and B13C2 stoichiometries) and Ruthenium Carbides (RuC, Ru2C and Ru3C stoichiometries), each belonging to a class of hard materials. Exhaustive crystal structure search using evolutionary algorithm and density functional theory is performed in each of these stoichiometries. The lowest energy structures emerging from the structure search are further relaxed and their ground properties are computed using DFT. The work in B12C3 stoichiometry provides the first independent confirmation using structure search that B11Cp(CBC) is the ground state structure of this stoichiometry. It is established that mechanically and dynamically stable structures with base-centered monoclinic symmetry can be at thermodynamical equilibrium at temperatures up to 660 K in B12C3, raising the possibility of identifying the monoclinic symmetry in experimental measurements. A demonstration of experimentally identifiable signatures of monoclinic symmetry is provided through the computed cumulative infrared spectrum of some of the systems. The work in B13C2 stoichiometry has conclusively solved the long standing problem of the discrepancy between the DFT calculations and the experimental observations over the semiconducting nature of B13C2. The remarkable success of a newly identified 30-atomcell structure in explaining many of the experimental data on B12C3 and B13C2 provides the first definitive evidence that structures with larger unit cells, are associated with crystals of these stoichiometries even at the ground state. The work in Ruthenium Carbide stoichiometries has gathered into a coherent perspective the widely varying structures proposed from experimental reports of synthesis, computational modeling and crystal structure search and provided conclusive structural candidates to be pursued in experiments. The study of the pressure-induced variation of their stability and properties has set indicators and benchmarks for future experimental investigations. The estimation of hardness of all the systems has underlined their importance in many applications, with nearly superhard values for some of them.