2. Thesis and Dissertations
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Item Development and Mechanical Characterization of Halloysite Nanotubes Reinforced Polymer Syntactic Nanocomposite Foams for Weight-Sensitive Structural Applications(National Institute Of Technology Karnataka Surathkal, 2023) Bakshi, Mohammed Sohail; Kattimani, SubhaschandraLightweight syntactic foam composites exhibit high specific strength and modulus. Thus, these are popularly used, from electric vehicle construction to space applications. In the present work, syntactic foam composites are fabricated using cenospheres. Cenosphere, a waste by-product of thermal power plants, is chosen as hollow filler in composites for eco-friendly redressal curbing its environmental impact. Also, a halloysite nanotube (HNT) is an abundantly available natural nanofiller that is utilized to uphold the load-bearing and thermal characteristics of reinforced syntactic foam (RSF) composites. The RSF composite fabrication involves the probe sonication of HNTs and homogenizing them with an epoxy matrix. Later the cenospheres are gently mixed in the HNTs/epoxy blend to obtain a uniformly dispersed mixture and is thus solution casted in the aluminum molds. A constant content of 1 vol.% addition of HNTs is maintained to fabricate all the RSF composites with cenospheres content being varied from 20 - 50 vol.%. Furthermore, the cenosphere epoxy syntactic foam (CESF) composites are fabricated without HNTs addition for comparison study. In this work, the influence of HNTs reinforcement in syntactic foam on mechanical, water absorption, viscoelastic, and thermal properties are studied. Furthermore, the impact of post-curing on the mechanical and thermal characteristics is also investigated. The tensile and flexural tests are carried out to evaluate the mechanical performance of CESF and HNTs RSF composites. The enhancement in tensile modulus and flexural modulus was witnessed by up to 42% and 66%, respectively, for the HNTs RSF as compared to CESF composites. The morphology studies prove the existence of hydrogen bonding among the HNTs, cenosphere, and neat epoxy matrix in RSF composite. Field emission-scanning-electron-microscopy (FESEM) affirms the unique crack deflection phenomenon by HNTs, thus elucidating the structure-property correlation. Furthermore, the effect of post-curing on flexural and compressive properties is discussed. The post-cured HNTs RSF containing 40 vol.% cenospheres (NSF40_H) exhibited a compressive modulus of 33.2% higher than room temperature cured neat epoxy due to improved crosslinking. The addition of HNTs in NSF40_H augments the flexural modulus up to 26.9% compared to post-cured neat epoxy. iiiMoreover, the glass transition temperature (Tg) of CESF composites with 40 vol.% cenospheres was increased by 24.3 °C compared to the room temperature cured sample. The positive shift in Tg can be attributed to the beneficial impact of post-curing, as indicated by differential scanning calorimetry study. A water absorption study is carried out to characterize the efficiency of the HNTs RSF composites exposed to the marine environment. The HNTs addition considerably reduces the diffusion coefficient, sorption coefficient, and permeability of the syntactic foam composites. The compressive modulus of wet HNTs RSF composite registered a higher value than the corresponding sample without HNTs. Dynamic mechanical analysis with temperature sweep (30 – 140 °C) reveal that the storage and loss modulus of RSFs is 1 - 36% and 59 - 113% higher than the neat epoxy. Storage modulus increases with an increase in cenospheres content in the epoxy matrix. However, with the incorporation of HNTs, the storage modulus obtained is higher than that of neat epoxy but still lower as compared to CESFs. With the increase in cenospheres content, loss modulus reduces due to increased frictional energy dissipation compared to matrix viscoelasticity. The thermal studies depict that the Tg value ameliorates with HNTs reinforcement. Also, better thermal stability with appreciable char content is reported from gravimetric analysis with HNTs addition. Further, to understand the underlying mechanism of filler interaction with the matrix, structure-property correlations of evaluated properties are presented using exhaustive SEM, FESEM, and TEM images.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 Buckling and Dynamic Characteristics of Cenosphere/Epoxy Syntactic Foam Composites and Sandwiches under Mechanical and Thermal Loads(National Institute of Technology Karnataka, Surathkal, 2019) Waddar, Sunil Shankar.; Pitchaimani, Jeyaraj; Doddamani, MrityunjayPolymer matrix composites provide lower weight structures and result in improved efficiency and performance in many transportation engineering applications. Thermosetting polymers reinforced with suitable hollow particle constituents, higher specific properties can be achieved. Development of syntactic foams with cenospheres serves dual purpose of beneficial utilization of industrial waste fly ash and reduction in the component cost in addition to weight reduction. In the present study, LAPOX L-12 epoxy resin is used as the matrix material and fly ash cenospheres in as received and silane modified conditions are used as filler material. Manual stirring method is employed for developing cenosphere/epoxy syntactic foams with as received and surface treated cenospheres in 20, 40 and 60 volume %. Sandwich composites are also prepared using sisal fiber woven fabric reinforced in epoxy as facings and syntactic foam as core. With increasing cenosphere content, density of untreated and silane treated foams decreases in general. Influence of cenosphere surface treatment and volume fraction of cenospheres in epoxy matrix on buckling and dynamic characteristics are experimentally investigated in this work. Buckling and free vibration behavior of cenosphere/epoxy syntactic foams under mechanical and thermal loadings are investigated experimentally in this work. Buckling load is obtained from the load-deflection curve based on the Double Tangent Method (DTM) and Modified Budiansky Criteria (MBC). Further, the influence of axial compression load on the natural frequencies associated with the first three transverse bending modes is analyzed. Finally, the buckling loads predicted using DTM and MBC are compared with the buckling load calculated based on the vibration correlation technique (VCT). It is observed that the buckling loads predicted through the three different methods are in close agreement. Experimental results revealed that the buckling load and natural frequency of syntactic foams increase with cenosphere volume fraction. It is observed that natural frequencies reduce with increase in axial compression load for all the modes. However, rapid increase in the fundamental frequency is observed when the compressive load is near and beyond the criticalbuckling load. It is observed that silane modified cenosphere embedded in epoxy matrix registered superior performance (rise in critical buckling load and natural frequencies to the tune of 23.75 and 11.46% respectively) as compared to untreated ones. Experimental results are compared with the analytical solutions that are derived based on Euler-Bernoulli hypothesis and results are found to be in good agreement. Finally, property map of buckling load as a function of density is presented by extracting values from the available literature. Experimental investigation on deflection behavior of fly ash cenosphere/epoxy syntactic foam under thermal environment (three different heating conditions) is investigated. Three different heating cases (increase-decrease, decrease and decreaseincrease) are considered. Influence of fly ash cenosphere volume fraction and nature of temperature variation on deflection behavior of syntactic foam beam is discussed elaborately. The temperature rise on the test specimens are measured using K-type thermocouples and lateral deflections are measured using Linear variable differential transducer (LVDT). The data is collected with the help of in-built LabVIEW program to plot temperature deflection curve. Results reveal that the syntactic foam beam experience snap-through buckling under thermal environment and is reflected by two bifurcation points in temperature-deflection plot also. It is observed that the time duration for which the syntactic foam beam stays in the first buckled position increases with increase in cenosphere content. Thermal environment induces compressive stresses in the samples causing such snap-through buckling. However, such phenomenon is not observed when the syntactic foam beams are exposed to mechanical compressive loads. Temperature variation across the beam length strongly influences snap-through buckling in syntactic foams in addition to volume fraction of filler content. An experimental study on buckling and dynamic response of cenosphere reinforced epoxy composite (syntactic foam) core sandwich beam with sisal fabric/epoxy composite facings under compressive load is presented. Influence of cenosphere loading and surface modification on critical buckling load and natural frequencies of the sandwich beam under compressive load is presented. The critical buckling load isobtained from the experimental load-deflection data while natural frequencies are obtained by performing experimental modal analysis. Results reveal that natural frequencies and critical buckling load increase significantly with fly ash cenosphere content. It is also observed that surface modified cenospheres enhance natural frequencies and critical buckling load of the sandwich beam under compressive load. Vibration frequencies reduce with increase in compressive load. Fundamental frequency increases exponentially in post-buckling regime. Experimentally obtained load-deflection curve and natural frequencies are compared with finite element analysis wherein results are found to be in good agreement. Buckling behaviour of sandwich composites made of syntactic foam core and sisal fabric/epoxy composite facings subjected to non-uniform heating is investigated. The critical buckling and snap-initiation temperatures are found from the temperaturedeflection plots. It is observed that, the critical buckling temperature increase with the filler content in the core material and surface treatment show slightly higher buckling temperature. The sandwich beams undergo snap-through buckling at higher temperatures due to developed viscoelastic forces. Due to increase in stiffness of the beam with filler content the deflection of the beam found to be less. The sandwich beams showed higher buckling temperatures than the neat syntactic foam samples.Item Machinability Characteristics in Drilling of Glass Microballoon /Epoxy Syntactic Foam(National Institute of Technology Karnataka, Surathkal, 2019) Ashrith, H. S.; Doddamani, MrityunjayPolymer composites are steadily substituting the conventional materials in aerospace, marine, automobile and many other engineering applications owing to their unique properties such as lightweight feature combined with high specific strength and superior corrosion resistance. Weight reduction of composite materials is of great interest in aerospace, marine and automobile applications to meet the stringent guidelines of fuel consumption and emissions in the coming years. Structural weight reduction without compromising the desired properties can be achieved by using a unique class of composite called syntactic foams, wherein the matrix is filled with hollow particles called microballoons. Even though the composites are produced to near-net shape, drilling is unavoidable during final stage of production process for the assembly of various structural components using fasteners. Many problems arise during drilling of composites due to non-homogeneous and anisotropic nature of the material. Nearly 60% of the composite parts are rejected during aircraft assembly due to drilling induced damages. The focus of the present study is to achive good quality holes in drilling of glass microballoon/epoxy syntactic foams by selecting appropriate process parameters. In the present investigation, epoxy resin (LAPOX L-12) is used as the matrix resin and borosilicate glass microballoon (GMB) is used as hollow filler without any surface treatment. Syntactic foams are fabricated by dispersing 20, 40 and 60 vol.% GMBs in epoxy matrix using manual stirring method. Nine different types of syntactic foams specimens with 20, 40 and 60 vol.% of GMBs are fabricated using three different densities (varying wall thickness) of GMBs (SID-200Z: 200 kg/m3, SID-270Z: 270 kg/m3 and SID-350Z: 350 kg/m3). All the prepared samples are coded as per EYYY-R convention. Epoxy resin is denoted by ‘E’ and ‘YYY’ represents density of GMBs. Neat epoxy specimens are also fabricated under similar processing conditions for comparison. Extensive micrography of fabricated foams confirms the uniform distribution of GMBs in the epoxy matrix without forming the clusters. Experimental density of all the fabricated syntactic foams is lower than neat epoxy resin. Density of foams decreases with decreasing GMB wall thickness and increasing volume fraction of GMBs. Density reduction in the range of 18-53% is noted as compared to neat epoxy indicating significant weight saving potential of the proposed syntactic foams.Experiments are conducted using vertical computer numerical control machine and TiAlN coated tungsten carbide twist drills of varying diameter based on full factorial design (FFD). Cutting speed (v), feed (f), GMB content (R), GMB wall thickness (w) and drill diameter (D) are taken as input parameters, while thrust force, surface roughness, specific cutting coefficient, cylindricity, exit side circularity error and exit side damage factor are considered as responses for evaluating the quality of drilled hole. Three levels for each input process parameters (v: 25, 75 and 125 m/min; f: 0.04, 0.08 and 0.12 mm/rev; R: 20, 40 and 60 vol.%; w: 0.716, 0.925 and 1.080 µm; D: 8, 12 and 16 mm) are selected to consider the nonlinear effects among the parameters. Experiments are repeated for three times and the average values are used for analysis. Mathematical models based on response surface methodology (RSM) are developed using Minitab 14 software for analyzing the influence of the input parameters on the measured responses. Adequacy of the developed mathematical models is confirmed using analysis of variance. Higher R-squared values indicate that the developed mathematical models can be effectively used as a tool in industrial practices to predict the machinability characteristics of GMB reinforced epoxy foams during drilling. Individual and interaction effect of process parameters on the responses are analyzed using RSM based mathematical models. Individual effects are studied by varying one parameter at a time in the mathematical models while keeping all the remaining process parameters at the intermediate levels. Two parameters are varied at the same time while keeping the other parameters at the intermediate level in the mathematical models to study the interaction effect of process parameters on the chosen responses. Thrust force is found to be increasing with increasing feed and drill diameter, while it decreases with increasing GMB content. Thrust force of all the foams is found to be lower as compared to neat epoxy resin. Thrust force is observed to be decreased by 40-55% as compared to neat epoxy due to the incorporation of GMBs. Drill diameter, feed and GMB content have a significant effect on the thrust force while the effect of cutting speed is found to be insignificant. v125f0.04R60D8 is the optimum condition for minimizing thrust force of E200 and E270 foams while performing machining at v25f0.04R60D8 minimizes the thrust force of E350 syntactic foam. Extensive microscopy is conducted on the drilledspecimens to understand crack initiation and propagation mechanisms. Surface roughness of the drilled hole is measured using Mitutoyo surftest with a cut-off length of 0.8 mm. As compared to neat epoxy, the surface roughness of syntactic foams increases by 14-20 times. However, surface roughness in foams decreases with increasing GMB volume fraction. Surface roughness is strongly governed by drill diameter and cutting speed. Minimum surface roughness for E200 and E270 foams is obtained at v25f0.12R60D16, while v25f0.12R60D12 is found to be optimum for E350 foam. Specific cutting coefficient increases with increasing drill diameter and decreasing feed. Increasing GMB content significantly decreases specific cutting coefficient by 40-55% as compared to neat epoxy specimens. v25f0.12R60D8 is the optimum condition for E350 foam, while machining at v125f0.12R60D8 is found to be beneficial for E200 and E270 foams for minimizing specific cutting coefficient. Coordinate measuring machine is used to measure the cylindricity, exit side circularity and maximum diameter of drilled hole for damage estimations. Cylindricity of the foams increases with increasing the cutting speed, feed and drill diameter. Increasing GMB content decreases the cylindricity by 46-69% as compared to neat epoxy. Drill diameter, feed and GMB content have a significant effect on cylindricity of drilled holes. v25f0.04R60D8 is noted to be the optimum conditions for E200 and E270 foams while v75f0.04R60D8 parametric setting is most suitable for thick-walled (E350) foams to minimize cylindricity. Circularity error increases with increasing cutting speed and drill diameter, while it decreases with increasing feed and GMB content. Increasing the microballoon volume fraction decreases the circularity error of foams by 18-67% as compared to neat epoxy. Circularity error of the holes is highly influenced by drill diameter followed by GMB volume fraction and wall thickness. v25f0.12R60D8 is the optimum condition for minimizing the circularity error of all the type of foams. The damage factor is dependent on the thrust force developed during drilling process. Drill diameter, feed and GMB content have a significant effect on damage factor of the drilled holes. Optimum conditions for minimizing damage factor is observed to same as that of thrust force. A reduction in the damage factor by 26-42% is noted in foams with increasing GMB content as compared to neat epoxy. Optimum conditions based on response surfacemethodology for minimizing all the responses are not same and the trade-off among various process parameters necessitates multi-response optimization. In the present work, grey relation analysis (GRA) is used for finding a specific combination of process parameters for minimizing all the response at the same time to obtain a good quality hole in drilling GMB/Epoxy syntactic foams. According to GRA, v125f0.08R60D8 is the optimal condition for producing a quality hole in E200 foams, whereas v25f0.12R60D8 is found to be optimal for E270 and E350 syntactic foams. Higher GMB content is preferred in the foams from drilling operations perspective, which is also beneficial for weight sensitive applications. Influence of GMB wall thickness on the responses is studied by keeping the GMB content at 60 vol.%, as higher filler content significantly improves the hole quality. Response surface plots for varying wall thickness of GMBs are plotted using the developed mathematical models to study the interaction effects among input process parameters. Increasing microballoon wall thickness from w0.716 to w1.080 increases thrust force, specific cutting coefficient and damage factor by 40%. Surface roughness, cylindricity and circularity error of drilled holes are significantly affected by GMB wall thickness and is found to be decreased by 30, 41 and 56% respectively. Combination of higher particle wall thickness and feed with lower cutting speed and drill diameter (v25f0.12w1.080D8) is the optimum condition for producing a sound hole quality as observed from GRA. Hole quality is highly influenced by drill diameter followed by the interaction between cutting speed and GMB wall thickness. Finally, microscopy is conducted to analyze the shape and size of chips produced during drilling. Cutting tools are inspected using a confocal microscope post drilling operation and micrographs show negligible tool wear due to the superior wear resistance of TiAlN coating. Observations and parameters settings explored in this work offers guidelines for the industrial practitioners to produce quality holes in drilling of GMB reinforced epoxy composites.Item Experimental Investigation of Cenosphere Epoxy Syntactic Foam Composites(National Institute of Technology Karnataka, Surathkal, 2018) Shahapurkar, Kiran; Doddamani, Mrityunjay; Mohan Kumar, G. C.Polymer matrix composites provide lower weight structures and result in improved efficiency and performance in transportation applications. Thermosetting polymers when used with suitable hollow reinforcing constituents, higher specific properties can be achieved that cater to variety of applications. Development of syntactic foams with cenospheres serves dual purpose of beneficial utilization of industrial waste fly ash and reduction in the component cost in addition to weight reduction. In the present study, LAPOX L-12 epoxy resin is used as the matrix material and fly ash cenospheres (hollow microspheres) in as received and silane modified conditions are used as filler. Manual stirring method is employed for developing cenosphere/epoxy syntactic foams with as received and surface treated cenospheres in 20, 40 and 60 volume %. With increasing cenosphere content, density of untreated and silane treated foams decreases. Influence of cenosphere surface treatment and volume fraction of cenospheres in epoxy matrix on compression, quasi-static compression, flexural, tensile, dynamic mechanical analysis, wear and erosion properties are investigated in this work. Effect of arctic conditions on the compressive and flexural response of cenosphere/epoxy syntactic foams is dealt to understand the behavior of foams under extreme conditions. Samples are conditioned under arctic environment at a temperature of -60°C. Compression and flexural tests are then conducted at room temperature as well as at in-situ -60°C on the conditioned samples and compared against unconditioned samples tested at room temperature. For the case of unconditioned samples, compressive strength decreased whereas compressive modulus increased with increasing cenosphere volume fraction for both surface modified and as received cenospheres. For the arctic conditioned samples, a reduction in compressive modulus and significant increase in strength is observed for untreated and treated syntactic foams as compared to their unconditioned counterparts. Increase in flexural modulus is noted while a decrease in flexural strength is observed as compared to neat resin at room temperature with increasing filler content for both untreated and treated cenosphere reinforced syntactic foams. For the case of arcticexposed samples, an apparent increase in flexural modulus is observed as compared to room temperature tested cenospheres/epoxy syntactic foams. In addition, an apparent increase in the flexural strength is noted under arctic environment. Room temperature quasi-static compressive response is investigated at different strain rates. The energy absorption of syntactic foams increases with increase in cenosphere content. Compressive modulus of untreated and treated syntactic foams is observed to be higher than that of neat epoxy sample at the same strain rate. Silane treated foams exhibit higher modulus. Yield strength of untreated and treated foams decreases as compared to neat epoxy. Tensile modulus of both untreated and treated syntactic foams increases with increase in cenosphere volume fraction as compared to neat epoxy. Strength values of syntactic foams show decreasing trend as compared to neat epoxy. Treated syntactic foams registered better results as compared to untreated ones. Storage modulus increases with increasing cenosphere content and decreases with increasing temperature. Loss modulus of syntactic register lower values as compared to neat epoxy, while damping is noted to be increasing. Syntactic foams with treated cenospheres reveal higher values of damping for all the volume fractions. Treated syntactic foams render higher stiffness and damping as compared to untreated syntactic foams and neat epoxy at elevated temperatures. Wear rate decreases with increasing cenosphere content at all the tested conditions. Specific wear rate decreases significantly with increasing applied loads. Further, coefficient of friction decreases with higher filler loading and filler surface modifications. Wear debris is analysed further and disc temperature is also reported. Erosion behavior is studied at room temperature for 30 to 90° impact angles and 30 to 60 m/s velocities. Results show a strong dependence of impact angle and velocity on erosion rate of syntactic foams. With increasing cenosphere content erosion rate decreases for all impact angles. Erosion rate decreases with increasing impact angle and with decreasing velocity. Structure-property correlations of all the investigated properties are presented with the help of exhaustive SEM images to understand underlying mechanisms. Finally, the potential of using the evaluated properties are presented in the form of property map. These property maps provide guidelines toindustrial practioners and researchers in selecting appropriate materials based on the envisaged applications.