2. Thesis and Dissertations
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Item Inverse Estimation of Multi- Parameters Using Bayesian Framework Combined with Evolutionary Algorithms for Heat Transfer Problems(National Institute of Technology Karnataka, Surathkal, 2020) S, Vishweshwara P.; Gnanasekaran, N.; M, Arun.This thesis focuses on the estimation of unknown parameters using various inverse methods for the heat transfer problems. The first class of problem elaborately discusses about the estimation of interfacial heat transfer coefficients during the solidification of casting. To accomplish this, a prevalent one dimensional transient horizontal directional solidification of Sn-5%wtPb alloy with temperature dependent thermophysical properties and latent heat is considered to be the mathematical model/forward model and numerically solved using Explicit Finite Difference Method to obtain temperature distribution from the known boundary and initial conditions. The temperatures from the forward model is validated with the literature and an absolute error of 5% from the actual measurements was observed. In order to mimic the real time experiments, the temperatures are added with σ=0.01Tmax, σ=0.02Tmax and σ=0.03Tmax Gaussian white noise (simulated measurements) and compared with two different objective functions: (i) Least Squares and (ii) Bayesian Framework. Meantime, to expedite the solution of the inverse problem, the numerical model is then replaced with Artificial Neural Network (ANN), which acts as a fast forward model to estimate the unknown constants present in the correlation of interfacial heat transfer coefficient. A total of 473 data sets of inputs and corresponding outputs were used to create a trained artificial neural network which produced temperatures with an accuracy less than 0.1◦C temperature difference from the exact temperature data. Genetic Algorithm (GA) was implemented as an inverse method and it was found that ANN-GA-Bayesian framework was more effective compared to ordinary least squares for noise added data with an overall average error of 2%. Furthermore, an extended study on the advantage of Bayesian framework for the estimation of multi-parameters during Al-4.5wt%Cu alloy solidification is also discussed in detail. The main aim is to retrieve more information with less available simulated measurements. A sensitivity analysis is performed to understand the dependency of the unknown parameters like modeling error, latent heat and heat transfer coefficient parameters on the solution. It showed that the values of constants of the IHTC correlation and latent heat affect the temperature distribution in casting significantly. For iiithe solution of inverse estimation, the use of two different metaheuristic algorithms (i) Genetic Algorithm (GA) and (ii) Particle Swarm Optimization (PSO) is illustrated. A careful examination of the mentioned algorithms is performed to fix the algorithm parameters. The results revealed that PSO combined with Bayesian framework provides a better computational solution compared to GA-Bayesian with an overall absolute error less than 6%. Also, the study on the effect of multiple sensors revealed that using two sensor the average % error for the estimation of a ,b and latent heat was 0.247, 0.3 and 0.45 respectively and suggesting that two sensors were sufficient for the present analysis. The second class of problem is extended to retrieve the unknown heat flux and heat transfer coefficient for a 3-D steady state conjugate fin heat transfer problem. A mild steel fin with dimensions 150x250x6 mm3 is placed centrally on to an aluminium base of dimensions 150x250x8 mm3 and experiments are conducted for different heat flux values of 305, 544, 853 and 1232 W/m2 and corresponding temperature distribution along the vertical fin is recorded. Navier-Stokes equation is solved to obtain the necessary temperature distribution of the fin. Heat flux with the range between 305W/m2 and 3300 W/m2 and its corresponding temperature distribution of the fin is obtained using commercial software. A total of 24 Computational Fluid Dynamics (CFD) simulations are performed to create a neural network model that can surrogate the forward problem in order to expedite the computational process. The estimation of the heat flux and heat transfer coefficient using GA, PSO and PSO- Broyden Fletcher Goldfarb Shanno (BFGS) is carried out for both simulated and experimental data. A detailed comparison study on the effect of algorithm parameters on the solution is demonstrated in order to examine the performance of the algorithms. For simulated temperature measurements, all the mentioned algorithms proved to be effective but PSO-BFGS estimated the heat flux with an absolute % error of 0.86 and heat transfer coefficient with 0.105% for experimental temperatures. The results show that the PSO-BFGS method outperforms GA and PSO and is observed to be a formidable approach in the estimation of the unknown parametersItem Performance Evaluation of Flexible Jute-Natural Rubber Composites for Impact Behaviour(National Institute of Technology Karnataka, Surathkal, 2020) M, Vishwas.; Joladarashi, Sharnappa.; Kulkarni, S M.A composite material is made from two or more constituent materials with significantly different physical or chemical properties which are combined to produce a material with characteristics different from the individual components. ‗Flexible composites‘ is a term coined to identify the composites making use of elastomeric polymers as matrix. These flexible composites exhibit usable range of deformations which are much larger than conventional stiff composites. The ability of flexible composites to undergo larger deformation and still provide high load carrying ability makes them suitable for many engineering applications. Flexible composites are better energy absorbers compared to conventional stiff composites subjected to impact loading. The objectives and scope of the present study includes proposing, developing and characterizing the flexible ‗green‘ composite for impact applications. An extensive literature review was carried out to explore the potential constituent materials for impact applications and accordingly the present study is carried out to explore the possible use of jute and rubber for impact applications. Initially, the feasibility of using natural rubber (NR) as a constituent material in composite is studied using commercially available finite element (FE) package. Further different stacking sequences of the flexible green sandwich composite are optimized and the three stacking sequences are selected for experimental study. These three optimized stacking sequences of the proposed flexible green sandwich composite are prepared using compression moulding technique and are characterized for their physical and mechanical properties. Further, the proposed flexible green composites are studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment. Finally, the impact behaviour of the proposed flexible composites is studied under low velocity impact (LVI) and lower ballistic impact. The mechanical characterization of the proposed flexible composites revealed that the composite with jute/rubber/jute (JRJ) exhibits better tensile and tear strength compared to jute/rubber/rubber/jute (JRRJ) and jute/rubber/jute/rubber/jute (JRJRJ) with JRJ exhibiting 57.7% and 64.47% higher tensile strength compared to JRRJ and JRJRJ respectively. Also, the tear strength of JRJ is found to be 0.4% and 2.38%higher than JRRJ and JRJRJ respectively. The interlaminar shear strength (ILSS) studies shows that short beam strength of JRJRJ is better compared to JRRJ and JRJ with JRJRJ exhibiting nearly 2.1 times and 2.75 times better ILSS compared to JRRJ and JRJ respectively. The proposed flexible green composites are further studied for their abrasive behaviour under two body environments and erosive behaviour under slurry environment, the outcome of which reveals that JRJ provides better results compared to its counterpart JRRJ and JRJRJ. Various factors affecting the wear behaviour of the flexible composites are also studied from which it is clear that abrading distance and sand concentration affects the weight loss of the proposed flexible green composite in case of two body wear and slurry erosion respectively. Flexible ‗green‘ composites of different stacking sequences are further subjected to impact tests at low velocity and lower ballistic velocity at different impact energies. The results of low velocity impact reveals that flexible green composite with JRJ stacking sequence exhibit better energy absorption and the stacking sequences JRJRJ exhibit better resistance to damage with no appreciable variation in specific energy absorption of the composites. The lower ballistic impact study reveals that the flexible composites are better energy absorbers with JRJRJ exhibiting better lower ballistic response compared to JRJ and JRRJ. The ballistic limit of JRJRJ is enhanced by 39.7% and 6% compared to JRJ and JRRJ respectively. The energy absorption at ballistic limit of JRJRJ is more compared to JRJ and JRRJ by 97.7% and 12.7% respectively. The energy absorption of JRRJ is enhanced by 75.5% compared to JRJ. The specific energy absorption (SEA) of JRJRJ is enhanced by 52% and 2.7% compared to JRJ and JRRJ respectively. The proposed flexible green composite can be a potential material for sacrificial structures in order to protect the primary structural components.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 Severe Plastic Deformation of Copper-Titanium Alloys Using Multi Axial Cryo-forging(National Institute of Technology Karnataka, Surathkal, 2020) S, Ramesh.; Nayaka, H Shivananda.Severe plastic deformation (SPD) is a technique where high strains are induced into the material to produce fine-grained structural materials, thereby improving the wear resistance and corrosion resistance. There is an increase in scientific and industrial interest in the development of bulk ultra-fine-grained (UFG) alloys, intended for structural applications. UFG materials offer vastly improved mechanical and physical properties. They also exhibits superplastic properties at elevated temperatures. SPD is done using Equal Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT), Repetitive Corrugation and Straightening (RCS), Accumulative Roll Bonding (ARB) and Multi Axial Forging (MAF). In MAF, materials are forged repeatedly in a closed die along three orthogonal directions, sequentially. It allows processing of relatively ductile material, because it can be performed at cryogenic temperature. Literature review shows that by using MAF technique, grain refinement phenomena can be observed in some ferrous and non-ferrous metals. MAF is one of the simple and most effective methods of SPD to improve material properties. MAF is a process in which the workpiece is subjected to shear deformation and thus, severe plastic strain is induced into the material without any change in the cross-sectional dimension of the sample. Microstructure has major effect on mechanical properties. MAF process leads to ultrafine-grained microstructure in the material which may show superplastic deformation at low temperature and high strain rate. In FCC structured metals, grain refinement also leads to textural changes i.e. high strengthening at cryogenic condition deformation. Copper-Titanium (Cu-Ti) alloy is the nontoxic substitute for Cu-Be and it showed good mechanical and electrical properties and can be used for the production of high strength spring, corrosion-resistant elements, and electrical connections like contact, relay, gears and electrical wires. Hence, in the present study, three alloys of Cu-Ti, namely, Cu-1.5%Ti, Cu-3%Ti and Cu-4.5%Ti, have been processed by MAF. Microstructural evolution in different MAF cycles is studied and it is correlated to the mechanical properties observed. As UFG materials have much higher hardness, they are expected to have higher wear resistance. MAF processed material exhibits higher wear and corrosion resistance, than the asreceived material. Hence MAF processed samples find wider engineering applications.viii Literature review consists of features of various SPD Techniques, advantages, and limitations. MAF process, parameters which influence MAF process, advantages and applications of MAF processed Cu-Ti alloys are discussed in details. Works of different researchers on MAF processed Copper alloys, with respect to, mechanical properties, wear and corrosion behavior are reported. Motivation from literature survey and objectives of the present work are highlighted. Details of the experimentation performed, right from the process adopted for the development of the UFG Cu-Ti to their characterization, are given in chapter three. Microstructural analyses were performed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Tensile tests were performed on both as-received and MAF processed samples. Dry sliding wear testing was performed using Pin on disc testing machine for both unprocessed and MAF processed samples. For the study of corrosion behavior, electrochemical polarization studies were performed and tofel extrapolation technique was used to obtain the corrosion rates. Chapter 4, Chapter 5 and Chapter 6, explain the results and discussion of various experiments carried out on three alloys Cu-1.5%Ti, Cu-3%Ti and Cu-4.5%Ti Microstructural characterization by OM, SEM, TEM, EBSD and XRD analysis has been discussed. Mechanical properties which includes hardness, tensile followed by fractography has been analyzed. Wear test with different loading conditions and sliding distances has been explained. Corrosion studies by electrochemical measurements test method has been highlighted.Item Grain Refinement and Surface Modification Technique by Equal Channel Angular Pressing and Laser Shock Peening on Magnesium Alloy(National Institute of Technology Karnataka, Surathkal, 2020) R, Praveen T.; Nayaka, H Shivananda.Design and development of any part in mechanical design consists of three elemental parameters. Such as, selection of material, geometrical constrains (dimensioning) and loading or boundary conditions. Boundary conditions are the functional requirements of design which need to be satisfied from the geometry of the component by allowing optimal material to execute the function. Hence, selection of materials is the primary building block of any component in mechanical system. Selection of material is very crucial and based on type of loading, environment conditions and reliability to withstand for long duration. Magnesium and its alloys have drawn great interest from the past decade due to its superior strength to weight ratio, bio-compatibility, effective manufacturing process and other positive attributes, but there are some limitation, such as effective strength, low fatigue life, low wear resistance and high corrosion rate. These properties can be altered by grain boundary characteristics, hence reformation of grain boundary to change the grain behaviour is of significant interest. In most of the methods, one principle technique (controlling cooling rate while solidification, alloying, severe plastic deformation) is used to alter the grain size of a material, which affects the grains in whole material or at near surface. Hence, there is a research gap while combining two different techniques to achieve combination of grains for better application. Severe plastic deformation (SPD) is a top down approach to form fine grains from coarse grain, and equal channel angular pressing (ECAP) is one of the simple procedures in SPD to achieve fine grains effectively. Samples during the ECAP process experience severe shear strain followed by deformation of grains, which rupture the coarse grains into new grains with redistributed grain boundaries. Formation of fine grains and grain boundary redistribution by ECAP enhances the strength and other mechanical properties in accordance with Hall-Petch relation. Conversion of coarse grains into fine grains occurs throughout the sample and resultant grain size depends on number of passes and route of the pass. But the original shape of the sample doesn’t get altered after processing. Laser shock peening (LSP) is a surface treatment process, to induce compressive residual stresses at the surface. This technique involves creating permanent deformation at the surface, which causes grain refinementat near surface. Grain refinement of bulk sample is obtained by ECAP process, whereas grain refinement at the surface of already deformed ECAP processed sample, is obtained by laser shock peening process. Present work describes the combined effect of ECAP and LSP on AM80 magnesium alloy. As-received (cast) AM80 (Wt. 8% of Al, Wt. 1 % of Mn, balance Mg) material is homogenized and processed by ECAP upto 4 passes under route BC. The samples were tested for mechanical properties, which showed enhancement of strength and ductility in ECAP processed samples. Microscopic investigation revealed the formation of fine grains, due to applied shear strain. By increasing the number of ECAP passes, more fine grains are reported. 2–pass ECAP processed sample shows heterogeneous grains, where the large grains were surrounded by small grains, and possess maximum tensile strength of 310 MPa compared to 1, 3 and 4-pass samples. Therefore, 2-pass ECAP processed sample is considered for further processing by LSP. LSP is carried out with a power density of 8 GWcm-2 and repeatedly to achieve different percentage of coverages, LSP processed samples are analysed for mechanical properties and microstructural characterization. Microscopic examination revealed the formation of fine grains in the range of few nanometers after peening near the surface. Scanning electron microscope revealed the formation of flower petal like structures, and transmission electron microscope revealed elongated grains in the form of bands, and these bands overlapped as the percentage of coverage increases. There was a slight increase in tensile strength in LSP processed samples, due to strain hardening at surface. Dimples of various sizes were observed on fracture surface of ECAP+LSP processed region. Mg17Al12, Mg2Al3, MnAl6 with Mg phases were identified by X-ray diffraction. Wear studies of LSP processed region showed an increase in wear resistance, and microscopic image of wear surface reveals the wear mechanisms due to oxidation and ploughing of hard particles. Roughness measurement was carried out on ECAP+LSP processed samples and there was significant influence of peening in increasing roughness of the surface. Nano indentation experiments help to understand the hardness behaviour of processed material at nano scale. An increase in surface hardness is observed with LSP processed samples compared to as-cast and ECAP processed samples. Further, there was anincrease in toughness and yield strength in peened region. D-space measurements were done by X-ray diffraction to measure the lattice space before and after peening, and relative strains were converted into stresses and residual stresses were identified. Tensile residual stress profile is identified in as-cast sample due to solidification of molten metal, and homogenized sample showed decrease in tensile residual stress value due to kinetic grain growth. ECAP processed sample shows compressive residual stresses due to strains induced in between the lattice. But ECAP+LSP processed sample shows higher compressive stress at near surface (peened region). Fatigue experiments played crucial role to characterize the material in cyclic loads for reliability. Experiments were conducted at maximum stress of 120 MPa, with a stress ratio of 0.125. ECAP+LSP processed sample with 100 % coverage took 85268 cycles of load compared to homogenized sample (1 cycle of load). Investigation of fractured surface of fatigue samples showed crack initiation and propagation region followed by rupture. ECAP+LSP processed sample with 100 % of coverage shows, significant gap between crack initiation and rupture region. Hence delay in crack initiation and propagation was observed.Item Mechanical and ThermoMechanical Properties of Woven Sisal Fiber Reinforced Biodegradable Composites(National Institute of Technology Karnataka, Surathkal, 2020) M, Nagamadhu.; Kumar, G C Mohan.; Jeyaraj, P.Natural fiber reinforced composites have extensively used in non-structural components, mainly in the automotive industry. The use of short and random fibers in those composites leads to discontinuity. These create a non-uniform stress distribution in the matrix during loading. Due to this non-uniform stress distribution, the composite fails early with a lower strain rate. This limitation can be overcome by using fabric reinforced composites. However, most of the textile properties are influences the performance of the composites. This study mainly focuses on mechanical (tensile and flexural) and dynamic mechanical characterization of fabric reinforced polymer composites. The thesis work is discussed in three phases: matrix, reinforcement, and composites. In the first phase, Polyvinyl Alcohol (PVA) is cross-linked with Glutaraldehyde (GA) for various volume fractions using a conventional vacuum-assisted pressure compression method. The mechanical and dynamic mechanical properties are carried out to optimize the volume fraction and is found at 20%. In the second phase, three types of woven fabrics prepared to study the effect of textile properties and woven patterns. Two plain woven fabrics (Plain 1 and Plain 2) are prepared with different grams per square meter (GSM). Also, another type of weft rib woven is prepared by keeping the same GSM as Plain 2 to analyze the effect of the woven pattern. The mechanical properties of these three fabrics are investigated and found that weft direction of weft rib fabric exhibits better mechanical properties. In the third phase, the composites are prepared using Plain 1, Plain 2 and Weft rib fabrics as reinforcement in 20% GA cross-linked PVA as matrix material and mechanical and dynamic mechanical properties are analyzed. The mechanical and dynamic mechanical properties of Plain 1 based composites exhibit better at room temperature, while based composites exhibit better dynamic mechanical properties at a higher temperature. It is shown that woven pattern of the fabric influenced significantly on composite properties. Similarly, weft direction of the composite exhibits better mechanical properties than warp direction, and it indicates loading direction also influenced.Item Effect of Process Variables on Residual Stress and Microstructure in Laser Additive Manufacturing of γ-TiAl Alloy(National Institute of Technology Karnataka, Surathkal, 2020) Mallikarjuna; Bontha, Srikanth.; Krishna, Prasad.Laser Metal Deposition (LMD) is used to fabricate intricate three-dimensional parts from metal powder by fusing material in a layer-by-layer manner of a digital Computer Aided Drawing (CAD) model. LMD process employed for processing of various materials such as metals, alloys, functionally graded materials, and repairing purpose. The LMD process involved numerous process conditions, mainly laser power, travel speed, and the powder flow rate. Effect on a layerwise variation of melt pool size, thermal cycle, the cooling rate is required to understand for producing a successful sound part. Experimentally determination of the effect of these process conditions on melt pool, thermal cycle, the cooling rate is extremely difficult. A remedy is to achieve a quantitative understanding of the process through computational modeling approaches. In this work, Laser Engineered Net Shaping (LENS), one of the LMD techniques is used to fabricate inherently brittle γ-TiAl alloy thin-wall structures at various processing conditions. These deposits are expected to develop residual stresses due to the rapid heating and cooling cycles involved in the LMD process. Towards this end, a 3-D nonlinear thermomechanical finite element analysis is performed to simulate the process under various process conditions. A commercially available ANSYS software utilized in conducting a sequentially coupled thermomechanical analysis. The melt pool, thermal gradients, and residual stresses are predicted from the developed FE models. Results indicate that laser absorption coefficient (αA) of γ-TiAl is obtained by a laser surface melting study, and an αA value is 0.13. The simulated thin-wall results show that thermal gradients increased with an increase in the number of deposited layers i.e., from the substrate to the last layer. Cooling rates decreased with increase in the number of deposited layers i.e., from the substrate to the last layer. Along the build direction, tensile stresses are generated at the edges and compressive stresses are generated at the centre region of the thin-wall which increase with increase in distance from the substrate. Along the laser travel direction maximum compressive stresses are observed at the centre of the wall and these stresses decreasein magnitude with increase in distance from the centre. Higher laser power input yields higher residual stresses due to high-thermal gradients, and hence, laser power has a significant impact on the development of residual stresses in the thin-walls. Residual stresses in the deposited thin-wall samples are measured using the X-ray diffraction technique. Reasonable agreement observed between the predicted and measured values of residual stresses. The microstructure, phases, and hardness of the LMD γ-TiAl alloy thin-walls are also analyzed. The microstructure analysis shows fine lamellar structure comprised of γ and α2 phases, which are matches with the existing studies. Microhardness in the bottom area is found higher than the middle and top areas of the thin-wall. The hardness values increased marginally (5%) with the increase in travel speed. Further, melt pool dimensions (length, width, and depth) increased with increase in laser power and decreased with increase in travel speed. During deposition of a layer (which consists of six tracks) the maximum temperature in the melt pool is observed in track 1. Maximum tensile residual stresses are observed in track 1 and these are lower than the yield strength of the material. The magnitude of these stresses decreased from track 2 to 6. Trends of residual stress are found to be independent of the scan strategy (Unidirectional and bidirectional) considered in this study. The state and magnitude of residual stress distribution in the thin-walls and plate are attributes to the transient thermal gradients encountered during deposition.Item Effect of Equal Channel Angular Extrusion on Microstructure Mechanical Properties and Corrosion Behavior of Wrought AZ-Magnesium Alloys(National Institute of Technology Karnataka, Surathkal, 2020) Naik, Gajanan M.; S, Narendranath.Wrought magnesium alloys are lightest engineering material and it has quite special properties which lead to particular applications. In specific, their highest strength to weight ratio, good machinability and high damping capability makes magnesium alloys tremendously attractive in aerospace, electronics, marine and automobile industries. Indeed, Magnesium alloys have poor tensile strength, ductility and corrosion resistance properties associated with other engineering materials like aluminium alloys, steels and super alloys etc. Therefore, many researchers worked on equal channel angular pressing of magnesium alloys to improve the mechanical properties and corrosion resistance. In this work, the effect of channel angles on material properties were investigated during equal channel angular pressing of AZ80/91 magnesium alloy using processing route-R at 523K, 598K and 663K processing temperature. Channel angles of 90⁰ and 110⁰, common corner angle of 30⁰ have been considered for the study. It has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behaviour of AZ80/91 magnesium alloys. Specifically, AZ80/91 Mg alloys processed through 90⁰ channel angle i.e die A is considered as optimal die parameter to improve above-said material properties. Investigation showing with reference to as-received AZ80 and AZ91 Mg alloy indicates 11 %, 14 % improvement of UTS and 69 %, 59 % enhancement in ductility after processing through 4P through die A (90º) at 598K respectively. Also, the corrosion rate reduces to 97 % and 99 % after processing the sample with 4P-ECAP die A (90º) at the same processing temperature for AZ80 and AZ91 Mg alloys respectively. This is mainly due to grain refinement and distribution of Mg17Al12 secondary phase during ECAP. Further, this work investigates the effect of annealing and aging treatment on microstructure and corrosion behaviour of as-received and ECAPed AZ80/91 Magnesium alloys. Here, annealing at 523K, 623K, and 723K were accomplished, meanwhile samples were cooled in the furnace after 6 h and 12 h of diffusion annealing treatment. In this study, samples were characterized by using optical microscopy (OM) and scanning electron microscopy (SEM) and electrochemical corrosion behavior of annealed AZ80/91 Mg alloy has beeninvestigated. With this, an attempt has been made to enhance the corrosion resistance of the AZ80/91 Mg alloy by changing its microstructure and re-distribution of secondary phase during annealing and aging treatment. It was found that corrosion rates are minimum at higher annealing temperature and aging time because of uniform distribution of secondary β-phases in Mg matrix, evidently shown in the microstructure of the heat-treated AZ80/91 Mg alloy. As a result, the annealing treatment at 723K for 12 h aging is desirable to enhance the corrosion resistance. Further enhancement of asreceived and ECAPed AZ80/91 Mg alloys were observed after High Velocity Oxy-Fuel (HVOF) coating of 316 stainless steel powder. Our results revealed that 316 stainless steel coating on ECAP-4P AZ80/91 Mg alloys were uniform and compact on substrate with a thickness of 80±5 µm. Furthermore, HVOF-coating process of 4P-ECAP significantly reduce corrosion rate at 3.5wt.% NaCl solution making it promising for industrial applications. The corrosion behaviour and effect of the ECAPed fine-grained magnesium alloy and coarse-grained as-received AZ80/91 Mg alloy was investigated in a 2.5wt.% NaCl, 3.5wt.% NaCl solution and Natural Sea Water (NSW) in order to explore the corrosion performance of ECAPed magnesium alloys in various environments. From, electrochemical corrosion experiments and surface morphology observations evidently shown that grain refinement exhibited improved corrosion resistance of the AZ80/91 alloy in all environments, also which shown a protective passive film on the surface to shield corrosionItem Investigation on dielectric properties of solid silicone rubber particulate composites(National Institute of Technology Karnataka, Surathkal, 2020) Shankar, B S Manohar.; Kulkarni, S M.Dielectric elastomers belong to the class of electroactive polymers that respond to electrical stimulus by undergoing change in shape. These materials also produce electrical signal on being deformed mechanically. The objective of the present study is to investigate the solid silicone rubber composites as candidate materials for use as dielectric elastomers. Solid silicone rubber along with barium titanate as dielectric and ketjenblack as conductive fillers is processed through high temperature compression moulding to obtain dielectric-dielectric, conductive-dielectric and conductivedielectric-dielectric composites. Property-processing relationships are investigated for these composites by studying the influences of various factors such as type and amount of fillers, amount of curing agent, mixing time and curing temperature using Taguchi design of experiments. The properties investigated include physical, mechanical, dielectric and electromechanical. Various dielectric mixing rules have been evaluated for the dielectric filler composites. Dielectric spectroscopy and SEM characterization have also been carried out on these composites in order to study filler-matrix interactions. Results show that the processing parameters along with fillers have influence on physical, mechanical, dielectric and electromechanical properties of the composites. Conductive fillers have a prominent influence on permittivity of the composites as compared to dielectric fillers. However, they are more reinforcing than dielectric fillers. The investigations reveal improved dielectric permittivity and electromechanical sensitivity of 390% and 100% respectively. Piezoresistive and piezo capacitive sensitivities of 3.7E-3 kPa-1 and 3.9E-3 kPa-1 respectively were achieved in the 0-20 kPa range of pressure for the composites. The processing method adopted ensures uniform distribution and wetting of the fillers in the solid silicone rubber matrix as confirmed through SEM characterisation. Thus, solid silicone rubber composites can be used as promising materials for use as dielectric elastomers.Item Investigation on Wire Electro Discharge Machining Characteristics of TiNiCu Shape Memory Alloys(National Institute of Technology Karnataka, Surathkal, 2020) Roy, Abhinaba.; S, Narendranath.Shape memory alloys are well known across academia and industries due to their unique functional capabilities, such as shape memory effect and superelasticity besides other useful properties. They are also known for their toughness, resistance to corrosion, improved fatigue life and damping capabilities. Shape memory effect is exhibited by these group of alloys due to reverse martensitic phase transformation which transforms de-twinned martensites back to twinned martensites. This phase transformation of shape memory alloys occurs without any change in state of the material, which contextually known as diffusionless transformation. Superelasticity, on the other hand is exhibited by these alloys, when the alloy is handled at an operating temperature higher than its austenitic temperature. Ni rich NiTi shape memory alloy for example can be processed to be superelastic at room temperature. These incredible qualities qualify shape memory alloys as potential materials for smart applications such as sensors and actuators. A vast majority of these alloys exhibit shape memory effect due to thermal load and some of them are also influenced by a magnetic field. Thermally induced shape memory alloys have formed wide applicability due to ease of use and economic factor. Among these alloys, TiNi based shape memory alloys are most widely researched and put into applications compared to Cu-based or Fe-based alloys. Phase transformation temperature of TiNi based shape memory alloys lie within a nominal operating temperature range (60⁰C-100⁰C) which makes them more suitable for sensing and actuating applications. However, with addition of a ternary element, phase transformation temperature of these alloys can be tailored to specific needs. Addition of Cu as ternary element in TiNi binary alloy system was found to reduce its phase transformation temperature and narrow transformation hysteresis. Cu addition also facilitates thermal conductivity making it more sensitive to change in thermal flux. Therefore, TiNiCu ternary shape memory alloys could be used for much sensitive applications. Major challenge these alloys impose is poor machinability with conventional machining techniques. High tool wear, poor machined surface quality and additional post-machining processes compromise finish quality, accuracy of the end product and increase the cost involved. This is where non-conventional machining techniques proved as an added advantage to process these functional alloys and soon became a more popular choice over conventional machining techniques. Non-conventional machining process like laser beammachining (LBM), water jet machining (WJM), electrochemical machining (ECM) and electrodischarge machining (EDM) result to better machining characteristics compared to conventional machining techniques. due to non-contact nature of the tool-workpiece interface. However, thick recast layer, oxidation, burr formation are some of machining defects that non-conventional machining techniques exhibit. Wire electrodischarge machining (WEDM) is a variant of traditional electrodischarge machine (EDM) where machining is carried out using an wire electrode. Sparking between wire electrode and workpiece results in removal of workpiece material through local melting. Advantage of WEDM over EDM is that through CNC any desired profile can be cut imposing minimum damage to workpiece material. Sensors and actuators incorporating shape memory effect are generally micro shaped components which undergoes microscopic shape change. Major aim of this study is to investigate WEDM characteristics of various homologous TiNiCu shape memory alloys and to optimize machining responses so as to produce components without compromising accuracy and quality. Six different TiNiCu shape memory alloys were vacuum melted and characterized in terms of microstructure, phases present, phase transformation temperatures and microhardness. Optical microscope with image analyzer, X-ray diffractrometer, differential scanning calorimeter and microhardness tester were used to perform aforementioned characterization. Further, to determine the quality of machining, the following output responses namely material removal rate (MRR), surface roughness (SR), kerf width (KW), recast layer thickness (RLT), machined surface microhardness (MH) and machined surface morphology were studied and reported. Ti50Ni25Cu25 exhibited least thermal hysteresis (~6⁰C) which indicates its suitability as ideal material for sensor and actuator applications. Due to varying thermal conductivity of vacuum melted homologous TiNiCu shape memory alloys, variation in WEDM responses were observed. Thereafter, prediction of WEDM responses was carried out using Artificial Neural Network (ANN) and optimization of WEDM responses was performed using Genetic Algorithm (GA). After a thorough investigation, WEDM process parameters to machine homologous TiNiCu shape memory alloys were reported and discussed in detail.