1. Ph.D Theses
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/1/11
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Item 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 Thermo-Elastic Response of Thin Functionally Graded Beams Under Various Heat Loads – Theoretical Studies and Experimental Validation(National Institute of Technology Karnataka, Surathkal, 2017) Vithal, Malik Pravin; Kadoli, RavikiranSuitability of functionally graded materials (FGMs) as structural members in modern industrial applications such as mechanical, aerospace, nuclear engineering and reactors are being explored vehemently. Considering the potential applications in thermal environment, functionally graded material structures may undergo various types of heat loads such as sudden heating or step heating, moving heat load, gradual heating, point heat load and or shock load, periodic and aperiodic thermal loads. The research related to fabrication of FGM structures and their theoretical modeling is very scarce. Researchers are exploring the manufacturing techniques to produce FGM structures with varying percentages of constituent materials. In the view of this fact, present work attempts to study the static deflection, free vibration and response to thermal loads of functionally graded beams numerically and validate them experimentally. The functionally graded SUS316-Al2O3 beams with ceramic content varying from 0 to 40% are prepared by plasma spraying technique while the functionally graded Al-Al2O3 beams with ceramic content varying from 0 to 50% are prepared using powder metallurgy process. A microstructure study is carried out using SEM to understand the distribution of various elements in the plasma sprayed and powder metallurgy process FGM beam samples. Nonlinear finite element analysis accounting the von Kármán strain is used to obtain static deflection and free vibration of a clamped free and clampsimple support functionally graded beam. The results are experimentally validated with the functionally graded SUS316-Al2O3 and Al-Al2O3 beam. The numerical results had an error of 4.05-12.91% for the deflection and 2.02 to 14.31 % for the fundamental frequency in case of SUS316-Al2O3 beam and more than 50% for deflection and fundamental frequency in case of Al-Al2O3 beam with respect to experimental results. The porosity plays an important role and governs the Young’s modulus of the sintered material which directly effects the deflection and free vibration frequency results. The commonly used and accepted theoretical models for Young’s modulus with porosity effect available in the literature were used to obtain the theoretical results. 24-31% reduction in error was observed for pure aluminium beam while the error reduced byiv 13% for Al-Al2O3 FGM beam. ANSYS 3D 20 noded structural solid element is used to study the role of shear deformation of the FGM samples on displacements and natural frequencies. The first mode of vibration obtained from numerical approach and ANSYS 3D element are much closer to experimental results. However, the nonlinear finite element FGM code provide poor results for higher modes compared to ANSYS 3D element. The nonlinear thermo-elastic analysis of thin functionally graded SUS316-Al2O3 beam accounting the von-Kármán strain and temperature dependent material properties under different heat loads and structural boundary conditions is also attempted. A two dimensional Lagrangian rectangular finite element is used to obtain the temperature distribution on the transverse plane of the beam. The significance of geometric nonlinearity is illustrated through numerical exercise. As the thermal load increases, the thermal deflection of FG beam are higher compared to linear analysis. Furthermore, the power law index also has a pronounced role. The numerical results of the static deflection of FG beam, in general, depends on power law index. Apart, the deflection produced by linear and nonlinear approach are considerably different. Thermo-elastic deflection and thermal stresses are evaluated for various structural and thermal boundary conditions. Thermo-elastic oscillations along with deflection are observed in case of beams subjected to step, concentrated line and shock heat load whereas thermoelastic deflection is observed for beams subjected to moving heat load. In case of shock heat load, irrespective of the power law index, the time for maximum temperature rise of the beam material is same, whereas the maximum elastic deflection occurs either after or before the maximum temperature rise depending on the power law index. The thermo-elastic deflection increase continuously irrespective of the power law index for line heat source. When FGM beams are subjected to moving heat source the time for maximum deflection depends on the power law index whereas the time for maximum temperature rise is independent of the power law index. In general, temperature dependency of material properties influence the amplitude of thermal oscillations. High thermal stresses are induced in beams with pin-pin and clamp-pin boundary condition as compared to hinge-hinge beam.v Thermal analysis is carried out on SUS316-Al2O3 and Al-Al2O3 FGM beam with heat source at one end. The temperature distribution is simulated using ANSYS and is validated with the experimental results. The temperature profile from ANSYS simulation results are in good agreement with experiment the with an error of 17% near the heat source while the maximum error 5.65% is observed 50mm away from heat source. Thermal vibration and induced thermal deflection studies have been carried out on the SUS316-Al2O3 FGM beam sample under clamp free boundary condition with heat applied at clamp end using electric heating coil. The response of the 2 FGM beams and pure SUS316 beam are studied at various heat loads varying from 2.925 W to 23.9 W. Theoretical model is validated with experimental results for SUS316-Al2O3 FGM beam sample-1. The experimental results are in close comparison with the theoretical results.