1. Ph.D Theses
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Item Development and Characterization of Polydimethylsiloxane and Carbon black Composites for Photo Actuation(National Institute of Technology Karnataka, Surathkal, 2020) Hiremath, Shivashankarayya.; Kulkarni, S M.There has been a rapid increase in the number of multidisciplinary research activities in the last two decades. The limits between disciplines are narrowing, as scientists in distinct areas coming up with intriguing concepts that combine expertise in a distinct field. The motive behind this multidisciplinary research arises from nature. Nature inspires us to mimic or generate thoughts for different applications that can enhance or change the requirements of society. The objective of the present research is to develop a photo actuator using composite material for microcantilevers, micro-grippers, micro-robots, photo-switches, micromotors, energy harvesting, and other smart photo devices. The cantilever beam is designed as a single and bilayer structure, actuated by photothermal action. It consists of polydimethylsiloxane and carbon black composites. Thus, there is thermomechanical deformation owing to the difference in the coefficient of thermal expansion as well as the rise in the thermal conductivity of the composite material. The composite beam also induces thermal stress due to differences in the temperature of the beam involved in the adsorption of the light source. The methods engaged in the current investigation of the photo actuator are empirical, numerical (Finite Element) modeling, analytical, and composite material processing and characterization. The empirical model has been used to comprehend and compare the properties of the composite material. Also, material modeling of more significant characterizations is being studied using numerically. The carbon black and polydimethylsiloxane materials have been procured, and the composites have been synthesized using the solution casting technique. Composite properties have been studied by performing various characterization tests for physical, mechanical, thermal, optical, dielectric, and microstructure. Analytical and numerical studies were implemented to investigate the optimum value by varying the thickness and volume percentage of the filler material at different temperatures. The photo actuation test setup was built, and thex composite beam has been tested. Finally, the proposed conceptual model was developed and tested in the laboratory environment. The approach of empirical and numerical (Finite Element) material modeling, composite material characterization, analytical and numerical modeling of actuator models, and proposed prototypes have been discussed. The empirical models were used to estimate the density, elastic modulus, thermal conductivity, coefficient of thermal expansion, and dielectric permittivity of the composite material, and numerical (FE) modeling is also performed for the more influencing parameters of the actuator. The results of material modeling were compared with experimental results. The carbon black particulate-filled polymer composite is developed for the investigation of density, mechanical, thermal, optical, and dielectric characteristics. The inclusion of the filler significantly improves the features of the matrix material. The density of the composite enhanced as the content of the reinforcement is increased from 5 to 25 Vol %. The elastic modulus of the composite is 57% higher than the plain matrix material. The thermal conductivity of the composite was substantially improved both numerically and experimentally. The inclusion of carbon black fillers into the PDMS leads to the reduction of the coefficient of thermal expansion. Also, the same is proved using the numerical method. The dielectric constant of the composite is improved significantly more by varying filler concentration. Analytical and numerical modeling has been carried out using commercially accessible software. Analytical findings on the deflection of the composite beam are validated with numerical modeling. The results are almost similar to each other, with a varying percentage of carbon black content and a change in the thicknesses of the layers. The bilayer composite beam is significantly more deflective than the single-layer beam. Also, by altering the temperature of the layers, the bilayer composite beam indicates considerably more deflection than the single layer. In continuing with this, the single and bilayer composite beams are tested experimentally, and it is a good agreement with numerical results. Finally, the proposed conceptual model of the photo actuator tested successfully. Attempts arexi being made in the present research to use a polymer composite beam for photo actuation and testing for the suggested prototype system. The dissertation is typically composed of empirical, numerical (FE), analytical modeling, and experimental approaches. Also, the characterization of the composite material and the efficiency of the photo actuator have been highlighted. As a result, PDMS and CB composites could be suggested for one of the photo actuator material.Item Experimental Investigations on Friction Stir Welded Joint of Dissimilar Aluminium Alloys(National Institute of Technology Karnataka, Surathkal, 2019) Anilkumar, K. S.; Murigendrappa, S. M.; Kumar, HemanthaFriction stir welding (FSW) is solid-state joining process for producing similar or dissimilar joints of plates. Joining process carried out by means of a non-consumable rotating tool passed along the joining edges of plates, after developing sufficient amount of heat. The joints may prone to have defects such as pin-hole, cracks, tunnel defects, worm-hole defects, sharp boundary defects, etc. lead to influence the mechanical properties and microstructures. Main motivation of the present study is to produce defect-free joints and, improve the mechanical properties and microstructures of the friction stir welded dissimilar aluminium alloys joint. To achieve these, it is necessary to choose the optimum FSW parameters such as tool plunge depth, tool rotational speed, tool traverse speed, tool tilt angle, etc. The present study focuses on selection of an optimum FSW parameters using a bottom-up optimization experimental approach for joining dissimilar aluminium alloys. Further focuses on the combined effect of tool probe offset and the tool traverse speed on the properties of welded joint. Study also focuses on the fabrication of metal matrix nano composite (MMNC) at the weld nugget zone (WNZ) of the FSW dissimilar aluminium alloys joint. The bottom-up experimental approach has been successfully adopted for joining two dissimilar aluminium alloys of AA2024-T351 and AA7075-T651 in butt-joint configuration for optimizing the FSW parameters such as tool plunge depth (TPD), tool rotation speed (TRS) and tool travel speed (TTS). Optimized FSW parameters for taper threaded cylindrical tool are TPD, 6.20 mm, TRS, 650 rpm and TTS, 150 mm/min yields higher tensile properties such as ultimate tensile strength (UTS) of 435 MPa, yield strength (YS) of 290 MPa, percentage elongation (% EL) of 13, and maximum weld joint efficiency ( ) of 92% with defect-free microstructures of weld region. Similarly, for taper triangle tool the TPD, 6.20 mm, TRS, 950 rpm and TTS, 90 mm/min yields a higher UTS, 440 MPa, YS, 350 MPa, % EL, 17.5 and of 93% with enhanced microstructure characteristics at the weld region. The tool probe offset of 1 mm towards AA7075-T651 favours the flow characteristics of AA7075-T651 towards WNZ. In addition, increase in the TTS ranging from 20-120 mm/min has revealed higher tensile properties. Higher UTS of 435 MPa, YS of 375 MPa, % EL of 13.6 and of 92% obtained for tool probe offset of 1 mm towards AA7075-T651 and TTS of 110 mm/min with constant TPD of 6.20, and TRS of 650 rpm. For the fabrication ofMMNC at the WNZ produced with varying % vol. fractions (5, 8 and 13) of SiCNP revealed a higher tensile properties of UTS of 418 MPa, YS of 247 MPa and % EL of 14.5 for 5% vol. fraction SiCNP with FSW second pass. The decrease in the grain size range 2-4 µm observed at the WNZ of the MMNC compared to the WNZ without SiCNP having grain size range 6-8 µm. The novelty of this work lies in the demonstration of friction stir welded joint of dissimilar aluminium alloys.Item Characterization of CNT Reinforced Al Functionally Graded Composite Laminates(National Institute of Technology Karnataka, Surathkal, 2017) Udupa, Gururaja; Rao, Shrikantha S.; Gangadharan, K. V.Functionally graded composite laminate materials(FGCL) are special kind of new generation materials aimed at meeting new requirements of engineering applications. It contains, two or multi-phase particulate composites in which material composition and microstructure are characterized by continuous, smooth variations on macroscopic scale designed to meet desired functional performance. The absence of sharp interfaces in FGCL reduce chances of material property mismatch and thus leading to significant improvement in damage resistance and mechanical durability. Therefore, FGCL’s are of great interest in disciplines as diverse as civil, electrical, mechanical, nuclear and nano engineering applications. However, the extent to which an FGCL can be tailored to meet the required performance –i.e., the design of FGCL strongly depends on the resultant effective properties and more importantly, on how these properties relate to its functional requirements. Hence, predicting mechanical, thermal or other relevant properties for given microstructure and its spatial distribution plays a significant role in the design of FGCL. Objective and scope of the present work includes planning, preparation of CNT reinforced Al Functionally graded composite laminates by mechanical Powder Metallurgy technique and experimental testing for its characteristic properties. FG samples are prepared by varying the content of CNT (0.1,0.2,0.3,0.4 and 0.5 wt.%)in weight percentage and tested. Such prepared FGCL samples are tested for physical and mechanical properties. Before the FGCL samples are prepared, simple composite samples are prepared for same weight fraction of CNT reinforcement to characterize the microstructure and tested for the hardness. These composites are tested as per the ASTM guidelines. Once the results are confirmed, FGCL samples are designed for same weight fraction of reinforcement in layered fashion. The weight fraction is proportionally increased from 0.1 to 0.5wt.% from one end to the other end of the sample. The density, hardness and tensile behavior of FGCL samples are experimentally evaluated. These properties are found to be increasing with addition of CNT reinforcement. The damping ratio of composite and FGCL is estimated from impact hammer test, which demonstrated the significance of FGCL on the damping characteristics compared to a conventional composite material.At present work, more focus on developing high wear resistance, light weight, good damping material with moderate good thermal conductivity material for brake rotor applications. Experimental investigation on FGCL proved good tensile stress properties with 0.5wt.% CNT reinforcement and these results are proven good agreement with characterization of microstructure. Microhardness for the cross-section of FG samples linearly varies with the increment in CNT reinforcement, which results in the variation of microstructure. Reduction in grain size found for 0.1 to 0.5wt.% CNT reinforcement, observed staggered layer of microstructure. The hardness of the developed material become high on the 0.5wt.% CNT reinforced side. Wear properties are investigated with proper Design of Experiments by using Taguchi techniques for three parameters(Load, Abrasive grit size, Weight percent of CNT). It revealed that reinforcement of CNT affected reduction in the friction between the matting surface due to the formation of lubrication layers. Good wear resistance is observed for 0.25 to 0.4 wt.% CNT reinforcement. This result is in good agreement with the observation of SEM images for same weight fraction of CNT reinforcement. ANOVA results proved load, wear surface(Abrasive grit size) are the prominent factors for wear and CNT reinforcements improved the wear resistance in the materials. Finally, the improvement in thermal conductivity has been observed on CNT reinforcement. Furthermore, FGCL’s are associated with particulate composites where the weight fraction of particles varies in one or several directions. One of the advantages of a monotonous variation of weight fraction of constituent phases is the elimination of stress discontinuity that is often encountered in laminated composites and accordingly, avoiding delaminating-related problems. Investigation on developed FGCL samples found good agreement with the continuity in microstructure without step deviation as well as the hardness variation. Good damping behavior and wear resistance ability with improved thermal conductivity features could be a promising proposition for brake rotor materials. Insertion of developed light weight CNT reinforced FGCL between the cast iron plate on brake rotor make a huge impact on weight reduction and cost economics.