2. Thesis and Dissertations
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Item Investigation on Mechanical Properties of Filament Wound Composites for Pressure Vessel(National Institute of Technology Karnataka, Surathkal, 2021) Biradar, Srikumar.; Joladarashi, Sharnappa.; Kulkarni, S M.Metallic pressure vessels or cylinders used over many decades for processing food and beverages products, transportation of chemicals, storage of hazardous and nonhazardous chemicals for prolonged durations have been carrying limitations throughout their service period. Few limitations such as, the weight of the cylinders, corrosion and erosion effect, risk of sudden failure. The current study is connected to development of an alternative material for existing metallic cylinders to overcome few limitations. In the present study, filament wound GFRP (Glass fiber Reinforced Polymer) is proposed, which is having high strength to weight ratio compared to the existing metallic material. The FE (Finite Element) analysis of cylindrical pressure vessels used for LPG storage is carried out by alternative materials such as LCS (Low Carbon Steel), Aluminium 6061 T6, and GFRP. Based on maximum specific strength, the best alternative material obtained among others is GFRP, and this material is chosen for further studies. The GFRP pressure vessel cylinder is further studied by varying filament winding process parameters such as fiber volume fraction (0.55,0.65,0.75), winding angle (±45°, ±50°, ±55°, ±60°, ±65°, ±70°,±75°) and stacking sequence (SS1, SS2, SS3, SS4, SS5, SS6) using FE analysis tool. A total of 336 FE simulations were carried out, i.e., with PVC (Poly-Vinyl Chloride) liner (168) and without PVC liner (168). The optimization tool MCDM (Multi criteria Decision Making) VIKOR method is used for the selection of best alternative among existing 168 FE simulation compositions (with PVC liner). The liner act as leak-proof material in filament wound composite vessels and hence can be used for storage or processing of different viscous and non-viscous fluids. The optimization of the FE simulation result leads to best attribute, which is selected and fabricated as per its respective fabrication iii process parameters for experimental studies. Similarly, next to five attributes are selected as per available testing laboratory facilities (physical, mechanical and tribological, hygrothermal ageing). The filament wound GFRP cylinders are cut into test coupons for physical, mechanical, and tribological characterization studies. Further hygrothermal ageing of all 6 compositions are studied. In hygrothermal ageing effect is studied using three different fluids such as tap water, sea water, and tap water with oil. The hygrothermal ageing is carried out for a period of 45 days at a constant temperature of 80°C. The aged and unaged samples are subjected to mechanical tests such as hoop tensile strength, tensile, compression, and bending tests. The mechanical test results are compared for a possible reduction in strength of aged filament wound GFRP samples. The obtained results are further examined with fractography study using Scanning Electron Microscope (SEM). The different mechanical testing results (ultimate tensile strength, ultimate compressive strength, ultimate flexural strength, hoop tensile strength) highlights that the filament wound GFRP samples are moderately affected by ageing. In overall, in the case of FE simulations studies, the product with composition of fiber volume fraction, Vf = 0.55, winding angle = ±55° and stacking sequence of (±55°2/90°2/±55°2) is suggested as the best alternative or attribute-based on average Von Mises of 45.64 MPa and hoop stress of 44.82 MPa compared to other compositions. As far as the experimental study of filament wound GFRP test coupons is concerned, retention of important mechanical properties such as tensile, compression, flexural, and hoop tensile strength is the main factor. Hence it is observed from different hygrothermal ageing effect studies that filament wound GFRP material with 1200TEX is least or moderately iv affected by hygrothermal ageing. The product which has the least ageing effect and having the highest strength (hoop tensile, tensile, compression, and flexural strength) retention rate (nearly 90%) is product-P1(055WA55SS1) with compositions of fiber volume fraction, Vf = 0.55, winding angle of ±55º, stacking sequence of SS1 = (±φ°2/90°2/±φ°2). Hence this product P1 can be suggested as an alternative material to existing metallic material for elevated temperature applications (up to 80ºC).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 Influence of Austempering and Quenching and Partitioning (Q&P) Heat Treatment on the Mechanical Properties and Wear Behavior of AISI 9255 Steel(National Institute of Technology Karnataka, Surathkal, 2019) Palaksha, P. A.; Ravi Shankar, K. S.The present investigation deals with the influence of two different heat treatments namely: (i) Austempering and (ii) Quenching & Partitioning (Q&P) on the microstructure, mechanical properties and dry sliding wear behavior of AISI 9255 high silicon steel. The as-received steel was checked for microstructure that comprised of pearlite, pro-eutectoid ferrite and undissolved cemetite, Mechanical properties mainly tensile strength of 800 MPa, % elongation of 14.1 and hardness of 334 HV. Specific wear rate was found to be 4.076 ×10-5 mm3/N-m. Austempering was carried out on the test samples by initial austenitisation at 900 oC for 45 minutes and thereafter quenching to various temperatures from 280 to 400 oC and holding for varying lengths of time from 15 to 180 minutes, which generates bainite microstructure that mainly comprises of bainitic ferrite and retained austenite (RA). Accordingly, variation in the bainitic morphology from acicular (lower bainite) to lath (upper bainite) was observed with the increasing temperature from 280 to 400 oC. However, increase in austempering time for all temperatures revealed a bit densely packed bainite structure. As a result there was a decrease in the RA; the quantity of decrease was further confirmed by x-ray diffraction (XRD) analysis. When compared to the properties of as-received steel, significant improvement in the tensile properties was observed for all austempered specimens; superior combination of tensile strength and % elongation was attained at austempering time of 15 min, i.e. (1852 MPa & 14%) at 280 °C, (1155 MPa & 33.4%) at 360 °C and (1165 MPa & 34%) at 400 °C. Similarly decrease in hardness from 600 to 342 HV was observed with increase in austempering temperature. During tensile loading, there was transformation of blocky RA to strain induced martensite that resulted in excellent strain hardening response from the samples austempered at higher temperatures 360 and 400 oC. Wear test results showed the slight increase in specific wear rate as the austempering time increases from 15 to 180 minutes. The sample austempered at 280 °C for 15 minutes exhibited the least specific wear rate of 2.063×10-5 mm3/N-m implying its superior wear resistance. In another set of heat treatment experiment i.e. quenching and partitioning was carried on the test samples by initial austenitisation at 900 oC for 45 minutes followed by quenching to 190 oC and finally partitioning at various temperatures from 280 to 400 oC and holding for varying lengths of time from 15 to 90 minutes. This heat treatmentgenerate multiphase microstructures mainly consisting of martensite of both lath and plate-type, transitional ε-carbides in tempered martensite matrix, lower bainite and RA for all the conditions. At higher partitioning temperatures i.e. 360 and 400 oC reveals some bainitic ferrite laths along with martensite and RA. Quantitative analysis shows the decrease in RA content with increasing partitioning time at 280 °C while it remains more or less constant for other partitioning temperatures. RA was non quantifiable for the samples which have undergone prolonged partitioning times at higher temperatures. Electron back scattered diffraction (EBSD) phase distribution maps reveals the RA content quite closer to those measured by XRD. Martensite crystals in inverse pole figure (IPF) maps reveal more of plate like morphology along with some twin orientations. Misorientation profiles indicated that at lower partitioning conditions i.e. 280 °C for 15 & 90 minutes reveals more high-angle grain boundary (HAGB), which signifies the presence of lower bainite in the matrix and similarly at high partitioning condition i.e. 400 °C for 30 minutes shows more lowangle grain boundary (LAGB) indicating the presence of upper bainite along with martensite of various morphologies, transition ε-carbides and RA. Compared to the mechanical and wear properties of as-received steel and austempered specimens, the Q&P treated specimens exhibits higher tensile strength and hardness but without much improvement in % elongation for almost all partitioning conditions. An excellent combination of tensile strength and % elongation was attained at partitioning time of 15 minutes i.e. 1859 MPa and 17% at 280 °C, which was also associated with high hardness value of 660 HV. Specific wear rate shows marginal increase with the increasing partitioning time from 15 to 90 minutes for all temperatures from 280 to 400 °C. The least specific wear rate of 1.18×10-5 mm3/N-m was obtained at a partitioning condition of 280 °C for 15 minutes which is much less compared with that of austempered condition, which was in turn influenced by presence fine martensite packets (lath and plate morphologies), lower bainite along with stabilized RA.Item Study on the Material Engineering aspects of Microwave sintered Aluminum– Cenospheres Composites(2016) Ananda Kumar, M. G.; Nayak, Jagannatha; Seetharamu, S.The thesis brings out the findings from the study undertaken on development of Aluminium based Metal Matrix composite through Powder Metallurgy route. The composite has been fabricated reinforced with various volume percentages of Fly ash Cenospheres particulates ranging from 0 to 50 vol %. The densification of the composites has been achieved through a non conventional sintering route known as Microwave sintering which is different from the well known conventional processing routes. The microwave sintering process appears rapid and economical. The Aluminium composites reinforced with Cenospheres and sintering through Microwave sintered composites have been later characterized for physical properties such as Density, Porosity, Hardness and Water Absorption, Chemical characteristics and Morphology of the synthesized composites and that of the raw materials through Scanning Electron Microscopy and Energy Dispersive X-ray Fluorescence methods. The Phase Analysis of the composites has been carried through Powder route X-ray Diffraction. The composites have also been studied for Mechanical properties such as Compression Strength with Finite Element Analysis and Modulus of Rupture. The composites have been studied for Tribological properties such as Wear and Erosion Resistance, Thermal properties such as Co-efficient of Thermal Expansion, Thermal Shock Resistance and Fusion Temperatures. The above test results have been compared with the results of conventionally prepared AMCs. The study on the various properties on the PM based Aluminium Cenospheres composites sintered in Microwave at 6650C have indicated that Apparent Porosity was about 35% compared to conventionally sintered ones which was around 40.7%. The Bulk Density was seen to reduce from 2.2 to 1.75 g/cc and the BHN values were found decreasing from 46 to 24% for the Microwave sintered samples. The conventionally sintered sample showed Bulk Density reducing from of 2.1to 1.75 g/cc and BHN values were found decreasing from 46 to 24. The BHN values were better than the conventional ones by about 26 %. The CTE of the composites decreased from 25.6 to 7.4 x 10-6/0C with increase in cenospheres content from 0 to 50 vol % forx the conventionally sintered composites. For the microwave sintered composites, the CTE of the composites decreased as the cenospheres content from 25.6 to 3.6 x 10- 6/0C which is much lower than the conventionally sintered samples by 51%. The microwave sintered composites showed lesser erosion loss by about 12-15% compared to conventionally sintered samples. The slide wear data shows that conventionally sintered samples has higher slide wear losses compared to conventionally sintered ones by about 86%. The Flexural strength of the conventionally sintered composites was seen decreasing from 52 to 8.8 MPa while Flexural strength of microwave sintered composites were decreasing from 71.9 to 31.5 MPa with increase in cenospheres content from 10 to 50 vol %. MW sintered was better by about 40% in Flexural Strength compared to the conventionally sintered composites. The Compression strength of the composites containing Cenospheres from 10 vol. % to 50 vol. % was found to decrease from 140.3 to 71.7 MPa with the increase in Cenospheres content, for microwave sintered samples. For the conventionally sintered composites the strength reduced from 140.3 to 71.7 MPa. The compressive strength of microwave sintered samples was more by 17.4 % compared to the conventionally sintered samples. Aluminium metal matrix composites can be fabricated through powder metallurgy route sintered in microwave sintering which is found to be adoptive & effective rapid sintering method. It is possible to fabricate Aluminium Cenospheres ‘Syntactic Foams’ through powder metallurgy microwave sintering and the properties for the same match with those materials for applications in automotives.Item Investigations on High Temperature Corrosion and Erosion Behaviour of Plasma Sprayed Co-Based Composite Coatings(National Institute of Technology Karnataka, Surathkal, 2018) H S, Nithin; Desai, Vijay; M R, RameshThe components of the gas turbines such as combustor and transition duct, exit blades, vanes, and disks operate between the temperatures of 600-800ºC. These components also work typically under higher cyclic loads in association with oxidising, corrosive and erosive environment. Providing surface coating through thermal spray process is one of the promising techniques to protect against such surface degradations and maintain the mechanical stability of underlying components. Plasma spray coating process is one of the most versatile and widely used cost-effective technique to deposit metals and ceramic materials on materials used in structural applications and machine parts to improve their oxidation, hot corrosion, and tribological resistance. The MCrAlY are promising coatings (M=Ni, Co and Fe) for the protection of components such as in the hot sections of gas turbines, aero engines, land-based gas turbines and naval diesel engine manufactured out of superalloys, particularly while operating at high temperatures. In the present study, oxides and carbides reinforced CoCrAlY feedstock powders such as CoCrAlY+28%Al2O3+2%YSZ, CoCrAlY+2%CeO2, CoCrAlY+30%WC-Co and CoCrAlY+30%Cr3C2-NiCr are coated on MDN 321 and Superni 76 superalloys by plasma spray technique. The microstructure, composition, phases and mechanical properties of coatings are characterized to evaluate and investigate their potential under hightemperature erosion, corrosion and oxidation conditions. The high-temperature solid particle erosion experiments were carried out using air jet erosion test rig. Two impact angles; 90° and 30° of the jet are investigated and alumina sand is used as erodent at a temperature of 600°C. The thermo cyclic oxidation and hot corrosion behaviour of coated and uncoated alloys are investigated in both static air and molten salt (Na2SO4-60%V2O5) environment at 700°C for 50 cycles. Each cycle consisted of heating at 700°C for 1 hour, followed by 20 minutes of cooling in static air. The thermogravimetric technique is used to approximate the kinetics of oxidation. The corrosion products and eroded surface are analysed using X-ray diffraction (XRD) and Scanning electron microscopy/Energy dispersive X-ray analysis (SEM/EDAX). The characterization studies have revealed that CoCrAlY+WC-Co coating has achived comapratively higher hardness (384 Hv) and fracture toughness (14.3±3.2 MPa m1/2), whereas CoCrAlY+CeO2 coating exhibited the least porosity and higher bond strength (15.6±2.2 MPa). All the coatings have undergone adhesive fracture during bond strength test indicating better cohesive strength between the splats. CoCrAlY+WC-Co coating has shown superior erosion resistance at 600°C temperature among the coatings with a volume loss of 0.9 mm3 and 2.1 mm3 at 90° and 30° impact angle respectively for 5 cycles. This is mainly attributed to its higher hardness and fracture toughness with lower porosity. CoCrAlY+WC-Co coating has experienced both ductile and brittle mode of erosion mechanism with the coating showing features of indentations, ridges, cracks, ploughing marks, lips and minor carbide pull. WC splats resist the erodent impact with minimal deformation thereby providing the shielding effect to Co matrix. The better erosion resistance of CoCrAlY+CeO2 coatings is owing to its least porosity, higher fracture toughness and microstructure refinement by CeO2 reinforcement. The coating has experienced ductile erosion mechanism with the absence of cracks and crates. CoCrAlY+Al2O3+YSZ coating exhibited brittle fracture and hard phase pull out due to repetitive erodent impact. The CoCrAlY+Cr3C2-NiCr coating showed least erosion resistance and has undergone severe brittle fracture at both impact angle and this mainly due to carbide dissolution at elevated temperature. From the XRD studies of eroded surface and observation of crack formation and oxide fragments, it very strongly indicates that all the coatings have undergone oxidation modified erosion. The hot corrosion tests were conducted under molten salt environment and at 700°C. CoCrAlY+Cr3C2-NiCr coating showed at least of 23% higher hot corrosion resistance than other coatings and also the substrates. This coating has shown dense, thin, continuous Cr rich oxide layer on the surface which contributes to its better performance. The presence of dominant Cr2O3 and CoCr2O4 oxide layer having lower solubility for corrosive melts and oxygen. The presence of stable metal oxide reinforcement of α-Al2O3 with surface oxide scale of Cr2O3, CoCr2O4 and CoAl2O4 results in slow-scale growth kinetics duringhot corrosion of CoCrAlY+Al2O3+YSZ coating. In the case of CoCrAlY+WC-Co coating the formation of CoWO4, CoCr2O4 and Cr2O3 as strong phases with stable CoSO4 provides hot corrosion resistance by developing dense non porous well adhered oxide scale. The growth of CeVO4 as a result of acidic fluxing develops stresses on surrounding splats/oxide scale leads to the development of cracks. The infiltration of molten salt through the cracks results in higher corrosion rate and oxide scale delamination. Thus CoCrAlY+CeO2 coating has shown the least hot corrosion resistance. All the coatings have shown the parabolic weight gain kinetics during hot corrosion studies. The MDN 321 and Superni 76 have shown higher corrosion rate with linear weight gain nature. In oxidation condition, CoCrAlY+Al2O3+YSZ coating has exhibited higher oxidation resistance than other coatings and substrates by showing least weight gain. The coatings experienced parabolic weight gain nature indicating all the possibilities of the formation of protective oxide layer. The uncoated alloys showed para-linear weight gain with a change from steady state to linear condition. The coatings under study have been found to be successful in protecting the given substrate alloys tested under laboratory conditions against erosion, hot corrosion and oxidation. In addition to applications in gas turbine, these coatings can be applied to other applications like superheater zone of coal fired boilers, fluidized bed combustors, industrial waste incinerators and internal combustion engines etc.