2. Thesis and Dissertations
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Item Effects of Gas Diffusion Layer Compression on Electromechanical Properties and Polymer Electrolyte Fuel Cell Performance(National Institute Of Technology Karnataka Surathkal, 2023) Shinde, Umesh; Koorata, Poornesh KumarThe Gas diffusion layer (GDL) is an essential functional component of the Polymer electrolyte fuel cells (PEFC) as it enables the efficient transport of reactants and offers mechanical stability. The influence of compressive loads on the performance of GDL has been the subject of extensive research. In this thesis, a numerical method is explored to investigate interface properties in the bipolar plate (BPP)|GDL and GDL|Polymer electrolyte membrane (PEM) under material and geometrical heterogeneities. Observations indicate that the results are sensitive to GDL material models and endplate designs. This implies that endplates designed to improve the electrical contact resistance and contact pressure at the BPP|GDL interface may not necessarily guarantee an improvement in bulk properties due to a localised, nonintuitive relationship between the electrical interface contact resistance (ICR) and bulk properties. The combined influence of non-uniform ICR and inlet relative humidity (RH), on a single flow channel, along with the heterogeneous flow properties of the GDL, is considered for the PEFC performance evaluation. The results indicate that heterogeneous GDL with non-uniform ICR distribution leads to a ~4.4% decrease in current density at 0.3V compared to homogeneous GDL under full humidification. However, the current density increases by ~19% under fully humidified anode and a partially humidified cathode. Furthermore, the GDL heterogeneity caused by the two clamping designs is simulated to predict the transport characteristics and performance of a 25cm2 active area PEFC. Compared to the conventional endplate design, the proposed endplate configuration offers increased cell performance, which may result from the uniform GDL properties. In addition, the experimental cyclic response of commercially available GDLs with/without MPL (microporous layer) is envisioned for mechanical response at various temperatures and hotpress conditions. The GDL with MPL has a substantial strain response with low force resistance, but GDL w/o MPL has a higher stress-to-strain ratio. The significance of pre- and post-hotpress conditions demonstrated that mechanical response increased by more than 120% in post-hotpress conditions. The thesis concludes with a newly developed phenomenological material model to predict cyclic electrical conductivity in GDLs.Item Mechanical Behaviour of 3d Braided Natural Fibre Fabric Reinforced Biodegradable Composites(National Institute of Technology Karnataka, Surathkal, 2022) Kanakannavar, Sateeshkumar; P., JeyarajSynthetic fibre reinforced composites (such as glass, carbon and kevlar) have high specific strength and modulus and popularly used in the applications of automotive, aerospace and wind energy sectors. These composites are non-degradable and their disposal after the end use is a significant problem. Hence the research in the development of more sustainable and renewable natural fibre filled bio-composites is extremely topical. In this study, to fabricate the biodegradable composites flax fibre is used as filler material and polylactic acid (PLA) polymer is used as matrix material. Flax fibre braided yarn is prepared by solid braiding method, followed by this the plain woven fabric is prepared using a handloom machine. Before the preparation of the composite laminates, PLA and natural fibre braided yarn fabric (NFBF) sheets are prepared by solution casting method. Film stacking method and hot press compression molding methods are used to prepare the composites with the different weight fraction of fibre. In this work, influence of NFBF reinforcement in PLA resin on mechanical properties, thermal buckling, water absorption, biodegradability, wear, fracture toughness, mechanical buckling and free vibration characteristics are investigated. Initially, geometrical and tensile properties of the prepared braided yarn and woven fabric are studied. Mechanical properties of the composites are characterised experimentally in the warp and weft directions of the composite surface plies. The NFBF/PLA composites results are compared with the pristine PLA results. It is observed that the mechanical properties of the composites are improved with the reinforcement of NFBF compared to pure PLA. Warp direction loaded composites showed higher mechanical properties compared to weft direction loaded composites. The NFBF/PLA composites are compared with the other natural fibre PLA composites results reported in literature and it is noticed that the NFBF/PLA composites have moderate tensile strength, higher flexural and impact strengths. Thermal properties (flammability, DSC, TGA, HDT and thermal deflection) of the NFBF/PLA composites are determined experimentally. Thermal deflection behaviour of pure PLA and NFBF/PLA composites are carried out on an in house built experimental set up at different temperature loading conditions. Effect of NFBF reinforcement, its weight percentage, loading direction (warp and weft) of the iii composites and nature of temperature load change on deflection behaviour of the PLA and NFBF/PLA composites are studied. Results revealed that, burning rate of the NFBF/PLA composites is reduced compared to pure PLA. Meanwhile, enthalpy (ΔHm), percentage crystallinity (Χc), thermal stability and HDT are enhanced for the NFBF reinforced PLA composites over pure PLA. Thermal deflection of the composites is reduced compared to pristine PLA and it further decreased with the increase in fibre content. Due to higher modulus and strength associated with the NFBF/PLA composites. Similarly, the warp direction loaded composites showed higher reduction in deflection compared to pure PLA and weft direction loaded composites. The reinforcement of NFBF improved the thermal resistance property and this result for the reduction in thermal deflection peak temperature for different heating cases. Reinforcement also enhanced the thermal sustainability of the composites. Influence of environmental conditions on NFBF/PLA composites are analysed by performing water absorption and soil incubation tests. Water absorption, thickness swelling, flexural tests are performed in different loading directions (warp and weft) of the composites. Similarly, biodegradation study is carried out in a compost soil medium at different incubation time periods (0, 15, 30, 60, 90 days). Biodegradation study is analysed based on weight loss measurement, change in FTIR spectra and reduction in tensile strength. Results revealed that water absorption and thickness swelling are increased with the reinforcement of NFBF, the weft direction loaded composite showed higher water absorption and thickness swelling values. Warp direction loaded composites showed maximum flexural strength and modulus. These values are decreased after water absorption. The NFBF reinforcement also enhanced the biodegradability of the NFBF/PLA composites compared to neat PLA. Tensile properties are decreased with the increase in the incubation time. Biodegradability analysis revealed that NFBF reinforcement enhanced the resistance against degradation than other types of reinforcement. It is due to the high fibre aspect ratio associated with short fibre reinforcement that increases the interaction with water molecules, whereas it is low for braided reinforcement. iv Friction co-efficient and wear rate of the composites are analysed using pin-on-disc tribometer under dry contact sliding condition and various operating conditions (velocity and load) for a fixed sliding distance of 3000 m. The reinforcement of NFBF with the PLA reduced the polymer film generation and improved the surface roughness significantly. Wear rate of the composites are decreased drastically compared to pure PLA. Also, fracture toughness study is performed on single-edge- notched-bend (SENB) specimens using three point bending method. It is found that plane-strain fracture toughness (KIC) and strain energy release rate (GIC) values of the PLA composites are higher than pure PLA for NFBF35 reinforcement. KIC values of the NFBF reinforced PLA composites are much high compared to similar natural fibre composites reported in literature. This is attributed to high resistance offered by the interweaving yarns of the braided fabric hence more energy is required to begin crack propagation compared to other typical forms of reinforcement. Influence of mechanical edge load on free vibration frequencies of NFBF/PLA beam is studied experimentally. Initially, the buckling load of the beam is calculated. Then variation of natural frequencies with and without compression loads is analysed. Buckling strength of the PLA beam is enhanced by NFBF reinforcement. Increase in the axial load results in reduction in the frequencies and the effect is very significant for the lowest frequency for the loads around the buckling load. Furthermore, the lowest frequency increase is very significantly for the loads higher than critical load due to the increase in geometric stiffness.Item Mechanical Characterization of 3D Printed Core and Sandwich Composite(National Institute of Technology Karnataka, Surathkal, 2021) S, Bharath H.; Doddamani, Mrityunjay.Fused filament fabrication (FFF) is one of the most widely used additive manufacturing (AM) techniques to fabricate lightweight complex functional parts with zero tooling cost, lower energy, and reduced material consumption. Three-dimensional (3D) printed lightweight hollow particle-filled syntactic foam core, and sandwich composites are developed using the FFF process in the present work. Hollow glass micro balloons (GMBs) are used as filler particles, and high-density polyethylene (HDPE) is used as matrix material. Hollow GMBs have blended with HDPE matrix by 20, 40, and 60 volume % to form GMB/HDPE blends. These blends are extruded using a single screw extruder to develop lightweight feedstock filaments to be used as input in a 3D printer to print syntactic foam core and sandwich composites. The suitable extruder parameters are chosen to ensure a homogeneous mixture of constituent materials and develop syntactic foam filaments with minimum or no GMB particle breakage. Before printing of syntactic foam core and sandwich structures, the melt flow index (MFI), differential scanning calorimetry (DSC), coefficient of thermal expansion (CTE) and rheological properties of GMB/HDPE blends are studied to optimize the 3DP parameters. An increase in GMB content reduces MFI owing to the filler resistance to HDPE flow. MFI decreased by 23.29, 54.79, and 72.97%, increasing GMB by 20, 40, and 60 vol. %, respectively. A decrease in crystallinity (56.68%) for foam filaments is observed with increasing GMB % compared to HDPE. Compared to filaments, the corresponding prints have higher crystallinity and are anticipated to provide higher dimensional stability and reduce warpage-related issues. CTE values qualitatively exhibit warpage and dimensional stability information of 3D printed HDPE and foam samples. The addition of GMB in the HDPE matrix lowers CTE values. At higher printing temperatures, dimensional stability can be achieved by adding GMB into HDPE. This indicates that the warpage can be avoided to a greater extent in printed components with dimensional stability and lower residual thermal stresses. An increase in filler infusion increases the melt viscosity of the polymer and is observed in the entire frequency sweep during the rheological study of GMB/HDPE blends. At a higher frequency, HDPE shows a shear-thinning region. Similar behavior is observed in foams with a marginal increase in complex viscosity. With the increase in filler content and frequency, both storage and loss modulus are increased. All these properties act as a guideline for selecting appropriate process parameters for the printing of quality components. The performance and behavior of extruded foam filaments are influenced by the interaction of the filler−matrix, filler %, and matrix porosity. For filaments to be used in a 3D printer, adequate spooling stiffness and strength are needed. Hence, tests to find the density and morphology of the extruded filament and tensile properties are performed before printing to check the quality, stiffness, and strength necessary for filament feasibility to be used in a commercially available printer. HDPE filament's experimental and theoretical densities are very close, indicating lower void formations because of its hydrophobic nature. An increase in GMB content increases void content in filaments (0.84 - 7.70%) and prints (2.42 - 9.73%). Higher void content in print, as compared to filaments, indicate that matrix porosity is transferred from the filament to prints. Such porosity in prints amid 100% infill is because of air gaps between the raster (residual micro-porosity). These porosities form three-phase (HDPE, GMB, and raster gap) syntactic foams enhancing the damping capabilities. Tensile testing of extruded filaments is carried out to know its feasibility in a 3D printer. Stiffer intact GMB particles increase filament modulus by 8 - 47% in H20, H40, and H60, respectively, compared to neat HDPE. H20 exhibits more than 40% strain with the highest ultimate tensile strength (UTS) of 12.63 MPa among foams. In comparison, H60 exhibits the highest modulus because of a higher number of intact GMB particles. Strength decreases with increasing filler content as with increasing GMB content, HDPE volume decreases, lowering the ductile phase substantially. Pilot investigations are carried out to propose the suitable printing parameters for printing core (H20-H60) and sandwiches (SH20-SH60) by exploiting Nozzle - 1 and Nozzle - 2 available on the commercial FFF-based printers. GMBs presence in the HDPE matrix reduces the co-efficient of thermal expansion leading to lower warpage and samples with dimensionally closer tolerance. Several initial trials in the pilot investigations did not yield high-quality prints. The reasons for such observations and the possible solutions are discussed that result in sound quality core and sandwiches. Tensile testing of 3D printed samples exhibits similar behavior as that of respective filaments. Among foams, H60 displays the highest modulus and is 48.02% higher than the HDPE print. H20 shows up to 30.48% strain. In HDPE, a long necking region is observed due to raster fibrillation leading to the broom-like fibrous ends. A typical brittle fracture is observed in H40 and H60. 3D printed HDPE and foams modulus is better than respective filaments. The flexural testing of HDPE and syntactic foam core and sandwich composites are carried out in a three-point bending configuration. Foams displayed brittle fracture as compared to neat HDPE, which did not fail until 10% strain. GMB inclusion induces brittleness in the compliant HDPE matrix. An intact GMB particle increases the flexural modulus with higher filler loadings. The H60 modulus is 1.37 times higher than HDPE, while strength is observed to be decreased. Lower strength values are due to the poor interface bonding between constituent elements and raster gaps. Similar behavior is observed in flexural testing of syntactic foam-cored sandwich samples. SH20 did not fail until 10% strain and registered the highest strength as compared to other sandwiches. SH40 and SH60 showed a brittle fracture. SH60 showed the highest modulus compared to other sandwich compositions. The flexural strength of syntactic foam cored sandwich samples are higher than their respective cores. The mechanics of composite beam theory is used for theoretical calculations of critical load. The deviation between the experimental and theoretical loads is noted to be in very good agreement, up to half of the maximum load. The failure mode of sandwich structures is analysed, and it is observed that SH40 and SH60 showed indentation failure. None of the samples failed in shear. All the samples except SH20 fractured in an approximately straight line just below the loading point. Compressive responses of 3D printed core and sandwich samples are investigated at a constant crosshead displacement rate of 0.5 mm/min. The data is analysed using in-house developed MATLAB code to estimate yield strength and modulus for all the samples. HDPE exhibits a higher modulus and is 1.06 times higher than H60. The modulus of foam samples increases with GMB content. H60 displayed the highest modulus among foams due to the presence of intact GMBs at higher filler loading. HDPE displayed 1.23 times higher yield strength compared to H60 samples. The Yield strength of syntactic foams decreases with an increase in filler loading because of poor interface bonding between constituent elements and residual micro-porosities. Similar behavior is observed in sandwich samples as well. Among sandwiches, SH20 has higher yield strength, and SH60 has the highest modulus. The buckling and vibration response of 3D printed foams subjected to axial compression is investigated. The buckling load is estimated using Modified Budiansky Criteria (MBC) and Double Tangent Method (DTM) through the load-deflection plots. The first three natural frequencies and their mode shapes are computed as a function of axial compressive load. It is noted that the natural frequency reduces with an increase in axial compressive load. It is also observed that with an increase in GMB %, the natural frequencies and critical buckling load increase. Analytical solutions obtained from the Euler‐Bernoulli‐beam theory are compared with experimental results. Similar behavior is observed for sandwich samples that displayed global buckling mode during the buckling test, wherein the maximum deflection is reported at the mid-section with no signs of skin wrinkling, delamination, and skin micro buckling. The load-deflection data and frequency obtained experimentally are compared with numerical predictions deduced using finite element analysis (FEA), which is noted to match well. The comparative analysis of 3D printed samples is carried out with samples developed using other thermoplastic manufacturing routes through property maps for specified test conditions. The current work successfully demonstrated the development of lightweight feedstock filament intending to widen available material choices for commercially available 3D printers.Item The Effect of Dual Particle Size SIC Reinforcements and Heat Treatment on Microstructure, Mechanical and Tribological Properties of A357 Composites(National Institute of Technology Karnataka, Surathkal, 2021) L, Avinash.; Bontha, Srikanth.The demand for light-weight materials is increasing in the automobile industry due to the increasing cost of fuel. In particular, there is a huge demand for high-strength and wear-resistant materials for engine cylinder applications. Al-Si-Mg series alloys such as A357 alloy would be an ideal choice for such applications owing to their low density, excellent castability, high strength and wear resistance. Enhancing the strength of any material can be achieved by work hardening, heat treatment, or reinforcing with a hard phase. The present work focused on development of A357 composites wherein the A357 alloy was reinforced with dual-size SiC particles. In the current work, two different sizes of SiC particles (coarse (140 ± 10μm)) and (fine (30 ± 5 μm)) were used to reinforce A357 alloy. Stir casting was used to develop A357 composites, with different weight ratios of the two sizes of SiC powders, keeping the total weight fraction at 6%. Three composites were cast in finger moulds; DPS1 (coarse: fine;1:1), DPS2 (coarse: fine;2:1), and DPS3 (coarse: fine; 1:2). The cast A357 alloy as well as the composites were subjected to heat treatment as per T6 temper conditions. The effect of varying solution temperature (500ºC to 540ºC in steps of 20°C for 9h and keeping aging temperature constant at 150 ºC for 6 h) and aging temperature (160°C to 200°C in steps of 20°C for 6h and keeping solution temperature constant at 540 ºC for 9h) were studied for both A357 alloy and the developed composites. Both A357 alloy and dual-size SiC reinforced composites were subjected to microstructural analysis using optical, scanning, and transmission electron microscopy techniques. Hardness and tensile testing were carried on the A357 alloy and its DPS composites before and after heat treatment. Tribological properties namely wear rate was assessed by conducting dry-sliding wear test using a pin-on-disc machine. In the wear test, the effect of varying load on wear rate was studied by keeping sliding velocity and sliding distance constant. Worn surface analysis was carried out using SEM to study the wear mechanisms operating in both untreated and heat-treated alloy and composites. Mechanical testing results showed improved hardness, yield, and tensile strength values for DPS composites when compared with that of A357 alloy. The strengthening of A357 composites is based on the addition of hard phase like SiC particles to the A357 alloy. The strengthening mechanisms that contributed to improvement in properties were effective load transfer, precipitation hardening and dislocation strengthening due to thermal mismatch. Precipitation hardening occurs for the A357 alloy and its composites because of T6 heat treatment. Formation of βʺ phase and Mg2Si precipitates were primarily responsible for strengthening after heat treatment. Wear rate of composites was found to be less than that of A357 alloy. Prohibition of direct contact between the two mating surfaces by presence of dual-size SiC particles was one of the primary reasons for low wear rate in composites. The key conclusions from this work include: Among the three developed composites, hardness, and wear resistance of DPS2 composite before and after heat treatment was found to be significantly higher than the other two composites (DPS1 and DPS3). Also, the tensile and yield strength values of DPS3 composite before and after heat treatment was found to be significantly higher when compared to the other two composites (DPS1 and DPS2). Lastly, the ratio of coarse particles to fine particles has an effect on the mechanical and tribological properties. Presence of more fine particles was found to be good for strength and ductility whereas more coarse particles were found to be good for hardness and wear resistance.Item Welding of Dissimilar A5754-A5083 and A6061- A6082 Aluminium Alloys for Automotive Applications(National Institute of Technology Karnataka, Surathkal, 2021) Rajeshkumar, R.; Banerjee, Kumkum.; Devakumaran, K.In the present study, dissimilar aluminium alloy combinations A6061 T6-A6082 T6 and A5754 H111-A5083 H111 were welded using the cold metal transfer (CMT), tungsten inert gas (TIG) welding and friction stir welding (FSW) processes. Each dissimilar combination was welded by two different fillers, such as ER4043 and ER5356, in CMT and TIG. Since FSW is a solid-state welding process, no filler materials were used. The miniature tensile samples were extracted from the interface regions of the TIG and CMT welded joints and the stir zone (SZ) of the FSWed joint. The TIG and CMT welded alloys' individual interface microstructure has been correlated with mechanical properties. The SZ of FSWed parts is of prime importance because this zone primarily decides the resulting property of the welded joint. Therefore, the microstructural features and mechanical properties of the SZ in the FSWed joints have been investigated in detail. The tensile properties of the overall weld region samples have been determined using macro-tensile testing samples. The dissimilar A6061-T6 and A6082-T6 joints welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) exhibited higher strength in the A6082 interface in comparison to the A6061 interface. When the dissimilar A5754 and A5083 alloys were welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) fillers, the interface region of the A5083 side exhibited higher strength than the interface region of the A5754. In the FSWed joints, the refined grain structure in SZ increased the hardness and strength. The overall joint tensile properties of the dissimilar joints are essential for identifying a suitable welding process to join A6061-A6082 and A5754-A5083 dissimilar alloys. Among the A6061-A6082 dissimilar joints, the CMT joint produced by ER5356 filler and the FSW joint exhibited higher tensile properties than the other joints. The tensile properties of the A6061-A6082 dissimilar CMT joint produced by ER5356 filler and the FSW joint are nearly the same. However, the FSW process does not use any shielding gas, filler materials, and the surface preparation is also not critical for the process. These factors can play a vital role to reduce the cost of welding effectively. Also, the FSW process is environment friendly, due to the absence of fumes and shielding gases. In the case of A5754-A5083 dissimilar joints, the FSW joint shows higher tensile properties than the other joints. Therefore, the FSW process can be recommended as the preferable joining method among all the investigated processes.Item Mechanical Characterization of Arecanut Husk Fibre Composites Panels Under Static and Dynamic Loading Condition(National Institute of Technology Karnataka, Surathkal, 2020) Muralidhar N.; Kaliveeran, Vadivuchezhian.Arecanut husk fibre is an agricultural waste, which does not contribute to the economy of arecanut plantation. The use of arecanut husk fibre as reinforcing material in the preparation of low cost and low density composite panels provides usability to arecanut husk. Low cost and low density composites have wide range of applications in construction industry, marine structures, automobile industry and aerospace industry. The present work focuses on extraction of arecanut husk fibre with alkali treatment process by using 6 % of sodium hydroxide solution, composite panel preparation and determination of mechanical properties of composite panels under static and dynamic loading condition. Different fibre compositions (fine fibre, coarse fibre and coarse fibre sandwiched with glass fibre) of 15 % by weight were used in the present study. The tensile strength of composites made with fine fibres (15.1 MPa) was observed to be more than that of composites made with coarse fibres (10.8 MPa). Further improvement in tensile strength of composite panels made of coarse arecanut husk fibre layer sandwiched with two layers of glass fibre (24.8 MPa) was observed. The flexural strength of fine fibre composites was more when compared to that of the coarse fibre composites. The average flexural strength of composites reinforced with fine fibre, coarse fibre and coarse fibre sandwiched with glass fibre were observed as 85 MPa, 65 MPa and 240 MPa respectively. The coarse fibre composites resulted in higher impact strength when compared to fine fibre composites. Dynamic mechanical analysis, shows trend of storage modulus increased with increase in loading frequency and variation of increment in storage modulus decreased with increase in frequency. At room temperature, the values of storage modulus are 0.478 GPa, 0.573 GPa and 0.607 GPa for loading frequencies of 5 Hz, 10 Hz and 15 Hz respectively. The arecanut composite can retain its storage modulus up to 80 °C. The glass transition temperature of arecanut husk fibre composites is 105 °C.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 Experimental Investigation of 3d Printed Syntactic Foam Composites(National Institute of Technology Karnataka, Surathkal, 2019) Patil, Balu.; Doddamani, MrityunjayPolymer matrix composites can reduce the structural weight and result in improved fuel efficiency and performance in transportation applications. Thermoplastic matrix composites have been used for semi-structural and engineering applications. In addition to the ease of fabrication using a wide range of forming processes, thermoplastic polymers are recyclable, which is the strong driving force for their current and future applications. Rapid production of high quality components is the key to cost reduction in industrial applications. The present work is the first attempt of manufacturing syntactic foams, hollow particle filled lightweight composites using thermoplastic based fused filament fabrication /fused deposition modeling (FFF/FDM) 3D printing process. High Density Polyethylene (HDPE) is used as the matrix material and fly ash cenospheres as the filler. Development of syntactic foams with cenospheres serves dual purpose of beneficial utilization of industrial waste fly ash and reduction in the component cost. Hollow fly ash cenospheres are blended with HDPE to form cenosphere/HDPE blend and is extruded to filament form and finally fed through 3D printer for printing ecofriendly lightweight syntactic foams. Prior to filament development, thermal degradation, melt flow index (MFI) and rheological properties of cenosphere/HDPE blend are studied. MFI decreased by 39.29, 60.54 and 70.51% with increasing cenospheres content of 20, 40 and 60 vol. % respectively. Rheology study of cenosphere/HDPE blend revealed complex viscosities values are maximum at a lower frequency but decreases with an increasing frequency indicating shear thinning behaviour. Both storage and loss modulus showed an increasing trend with filler content and frequency. Single screw extruder parameters are optimized to develop ecofriendly syntactic foam filament with minimum cenosphere fracture and to obtain homogeneous mixing of constituents. The optimized parameters are used for manufacturing syntactic foams filament with 20, 40 and 60 vol.% cenosphere in HDPE matrix. Further, recycling potential of foam filament is also studied. Density of H40 (HDPE with 40 vol.% ofcenospheres) foams increased in up to two extrusion passes (2X) due to cenosphere breakage and porosity consolidation. Tensile properties of developed filaments are carried out to assess its viability into 3D printer. Tensile modulus and yield strength of neat HDPE filaments increased with each extrusion pass. Specific modulus of 3D printed H40-2X and 3X are 1.6 and 2.6 times higher than the respective filaments, however, fracture strain decreases by up to 40%. For first time extruded (1X) filament with addition of cenosphere density reduces due to intact cenosphere and void formation during extrusion, making it a 3 phase foam material. The void content and weight saving potential increases with increase in filler content and their values are higher for 3D prints than respective filament. Higher filler loading increases filament modulus by 7.72-12.79% as compared to HDPE. Among the foam filaments, H20 composition registered the highest ultimate strength (10.30 MPa) and strain at break (26.20%). Differential scanning calorimeter and X-ray diffraction analysis of neat HDPE and foam filaments crystallinity is used to assess the parametric optimization of 3D printing process. It is observed that addition of cenosphere reduced crystallinity of HDPE. HDPE and foam filaments exhibit lower crystallinity as compared to respective printed material. Coefficient of thermal expansion (CTE) of 3D printed HDPE and its foam is studied to understand warping and shrinkage phenomenon occurring during printing. It is observed that filler addition in HDPE matrix reduces CTE remarkably. Warpage of the specimen is reduced with filler content and print quality is further improvised by optimizing printer speed, layer thickness, print temperature and cooling conditions. Tensile tests are carried out on filaments and printed samples. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile modulus of printed foams increases with filler content. 3D printed HDPE and foams modulus is better than respective feedstock material (filament). Tensile properties of 3D printed HDPE and foams are compared with injection molded samples. 3D printed HDPE registered higher tensile modulus and fracture strength compared to injection molding. Flexural test is conducted on 3D printed sample in two configurations (topand bottom face of print subjected to the load). Results obtained from both configurations reveals that second configuration has shown better flexural modulus and strength. Neat HDPE print did not show any fracture below 10% strain. Flexural modulus increases with cenosphere content. Highest modulus is exhibited by H60 which is 1.56 times better than neat HDPE print. Raster gaps in 3D prints lowers flexural modulus and strength as compared to fully dense injection molded sample. Quasi-static and regular strain rate compressive response is investigated on prints. Compressive behaviour of 3D printed foams follow similar trend in quasi-static and regular compressive mode as reported in fully dense injection molded two-phase foams. Modulus of neat HDPE is higher for all strain rates as compared to foams. Yield strength shows an increasing trend with strain rate. Highest specific compressive modulus and yield strength is observed for H60 and H20 respectively at 0.1 s-1 among foams. Further, HDPE matrix syntactic foam prints are characterized for their viscoelastic properties by dynamic mechanical analysis. Tests are conducted over 30-125°C temperatures. Storage and loss modulus increase with increasing volume fraction of cenospheres, with a slight difference between HDPE, H20 and H40 vol.%, at all temperatures. Storage modulus decreased with increasing temperature for neat HDPE and foam prints. Storage and loss modulus decrease with increasing temperature in the range of 30-125°C, while Tan δ increases. Structureproperty correlations of all the investigated properties are presented with the help of exhaustive SEM images to understand underlying mechanisms. Property maps for selected test conditions are presented for comparative analysis between FFF/FDM based 3D printing of eco-friendly lightweight syntactic foam prints and other processing routes used for thermoplastics. This work is an effort towards making wide material choices availability for FFF based 3D printing industries. Finally, the potential for using the optimized parameters of 3D printing is demonstrated by printing several industrial components as a deliverable of of this work.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 Microstructure and Mechanical Properties of Cast Aluminium-Zinc-magnesium Alloys Processed by Equal Channel Angular Pressing(National Institute of Technology Karnataka, Surathkal, 2019) Manjunath, G. K.; G. V, Preetham Kumar; K, Uday BhatEqual channel angular pressing (ECAP) is one of the severe plastic deformation (SPD) techniques used to develop ultrafine-grained (UFG) materials. In this technique, large amount of shear strain is introduced in the material, without any change in the cross sectional dimensions. Al-Zn-Mg alloys are promising light weight high strength materials, wherein precipitation strengthening will be possible. In this investigation ECAP is used to enhance the strengthening in the Al-Zn-Mg alloys. The alloys studied in the present work were prepared by gravity casting method. ECAP processing was carried out in a die having an internal angle between two channels (Φ) of 120º and outer arc curvature (Ψ) of 30º. The processing was attempted at lowest possible temperature in route BC. Techniques, like optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffractometer were used to characterize and analyse the microstructures before and after ECAP processing. To assess the mechanical properties, microhardness measurement and tensile tests were conducted. Fracture mode and fracture surface morphologies of the tensile test samples of the processed and unprocessed materials were studied. Wear properties were evaluated before and after ECAP processing. Wear mechanisms involved in the samples were studied. Microstructural study reveals that, in as-cast condition, alloys were composed of dendritic structure. Also, with increase in the zinc content in the alloy, volume of precipitates was increased. After ECAP processing, considerable decrease in the grain size of the alloys was noted. Also, after ECAP processing, high density dislocation structures with high fraction of high angle grain boundaries were observed. It was also noticed that, ECAP processing leads to enhance the precipitation kinetics of the alloy. In all three alloys, after ECAP processing, fine size spherical shaped precipitates were noticed and these precipitates were uniformly distributed in the alloy. After ECAP processing, significant improvement in the mechanical properties of the alloys was perceived. Microhardness and strength were increased with increase in the zinc content in the alloy. At the same time, elongation to failure of the alloy decreased with increase in the zinc content. Optimum mechanical properties were perceivedwhen the alloys were processed at lowest possible temperature. Compared to as-cast alloys, microhardness increases by 109% for Al-5Zn-2Mg alloy, 67% for Al-10Zn-2Mg alloy and 58% for Al-15Zn-2Mg alloy, processed at 200 °C. Compared to as-cast alloys, ultimate tensile strength (UTS) increases by 122% for Al-5Zn-2Mg alloy, 153% for Al-10Zn-2Mg alloy and 139% for Al-15Zn-2Mg alloy, processed at 200 °C. Brittle fracture mode was observed during tensile test of as-cast and homogenized samples. The fracture mode was changed to shear fracture after ECAP processing. Large sized dendrites were observed in the fracture surfaces of the as-cast condition tensile test samples. While, narrow and shallow dimples were noticed in the fracture surfaces of the ECAP processed samples. ECAP processing leads to considerable improvement in the wear resistance of the alloys. Wear resistance of the alloys increased with increase in the zinc content. Coefficient of friction of the alloy decreased after ECAP processing. Also, coefficient of friction of the alloy decreased with increase in the zinc content. Irrespective of the applied load, abrasive wear mechanism was reported in the as-cast and homogenized condition samples. In the ECAP processed samples, wear mechanism shifts from adhesive to abrasive wear with increase in the applied load. Also, in the ECAP processed samples, at lower load; transfer of iron particles from the disc surface to the sample surface was noticed. Compared to the Al-5Zn-2Mg and Al-10Zn-2Mg alloys better wear properties were observed in Al-15Zn-2Mg alloy.