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 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 Reinforced HDPE Syntactic Foam Composite(National Institute of Technology Karnataka, Surathkal, 2016) B. R., Bharath Kumar; 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 are the strong driving forces 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 an industrial scale Polymer Injection Molding (PIM) 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. Pressure and temperature used in PIM are optimized to minimize cenosphere fracture and obtain complete mixing of cenospheres with HDPE. The optimized parameters are used for manufacturing syntactic foams with 20, 40 and 60 wt.% cenosphere without any surface treatment initially. With increasing cenosphere content, density and tensile strength reduce and modulus increases. A theoretical model based on a differential scheme is used to estimate the properties of cenospheres by conducting parametric studies because of inherent difficulties in direct measurement of cenosphere properties. Further, the influence of cenosphere surface treatment, functionalization of HDPE and blending method on tensile properties are investigated. Cenospheres are treated with silane and HDPE is functionalized with 10% dibutyl maleate. Tensile test specimens are cast with 20, 40 and 60 wt.% of cenospheres using injection molding. Modulus and strength are found to increase with increasing cenosphere content for composites with treated constituents. Highest modulus and strength were observed for 40 and 60 wt.% untreated mechanically mixed and treated brabender mixed cenospheres/HDPE blends, respectively. These values are 37 and 17% higher than those for virgin andfunctionalized HDPE. Theoretical models are used to assess the effect of particle properties and interfacial bonding on modulus and strength of syntactic foams. Brabender mixing method provided highest ultimate tensile and fracture strengths, which is attributed to the effectiveness of brabender in breaking particle clusters and generating the higher particle-matrix surface area compared to that by mechanical mixing method. Theoretical trends show clear benefits of improved particle-matrix interfacial bonding in the strength results. Effect of surface treatment and blending method on flexural properties is dealt next. Flexural test specimens are cast with 20, 40 and 60 wt.% of cenospheres using PIM. The flexural modulus and strength are found to increase with increasing cenosphere content. Particle breakage increases with the cenosphere content and the measured properties show increased dependence on processing method. Untreated constituents blended by mechanical mixing provide the highest benefit in flexural modulus. Modulus of syntactic foams is predicted by two theoretical models. Bardella-Genna model provides close estimates for syntactic foams having 20 and 40 wt.% cenospheres, while predictions are higher for higher cenosphere content, likely due to particle breakage during processing. The uncertainty in the properties of cenospheres due to defects contribute to the variation in the predicted values. Untreated constituents blended by mechanical mixing route as observed in tensile and flexural characterization registered higher tensile modulus and better flexural performance. Thereby, characterization of cenosphere/HDPE syntactic foams synthesized by mechanical mixing route for untreated constituents is dealt in the subsequent investigations. Quasi-static and high strain rate compressive response is investigated later. Thermoplastic matrix syntactic foams have not been studied extensively for high strain rate deformation response despite interest in them for lightweight underwater vehicle structures and consumer products. Quasi-static compression tests are conducted at 10-4, 10-3 and 10-2 s-1 strain rates. Further, a split-Hopkinson pressure bar (SHPB) is utilized for characterizing syntactic foams for high strain rate compression.The compressive strength of syntactic foams is higher than that of HDPE resin at the same strain rate. Yield strength shows an increasing trend with strain rate. The average yield strength values at high strain rates are almost twice the values obtained at 10-4 s-1 for HDPE resin and syntactic foams. Further, HDPE matrix syntactic foams are characterized for their viscoelastic properties by dynamic mechanical analysis. Tests are conducted over 35-130°C temperatures and 1-100 Hz frequency range and combined using the time-temperature superposition principle to generate a set of isothermal master curves. Storage and loss modulus increase with increasing weight fraction of cenospheres, but with little difference between 40 and 60 wt.%, at all temperatures. The sensitivity of storage modulus to weight fraction of cenospheres increases with increasing frequency. Storage and loss modulus decrease with increasing temperature in the range of 35- 130°C, while tan δ increases. The Williams-Landel-Ferry (WLF) constants are a linearly increasing function of cenosphere weight fraction. Structure-property correlations of all the investigated properties are presented with the help of exhaustive SEM images to understand underlying mechanisms. Finally, the potential for using the optimized parameters of injection molding process is demonstrated by casting several industrial components as a deliverable of this work.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.Item Experimental Investigation of Glass Microballoon/Hdpe Syntactic Foam Composite(National Institute of Technology Karnataka, Surathkal, 2018) M. L, Jayavardhana; Doddamani, MrityunjayPolymer matrix composites inherit good specific values and reduced structural weight making them more promising in automobiles and aerospace applications. Thermoplastic polymers are moldable into different shapes, recyclable and reusable leading to wide usage in semi-structural and engineering applications. These materials are widely used in consumer products and industrial components. Reducing weight of thermoplastic components has been always a high priority in transportation, aerospace, consumer products and underwater vehicle structures. Their current and future potential are driven by processing flexibilities using variety of industrial scale manufacturing techniques and material innovations therein like in foams. Foams are lightweight cellular materials that are widely used in applications such as packaging, thermal insulation, sound absorption, underwater vehicle structures and as the core in sandwich structures used in aircraft. Rapid production of such high quality foam components for industrial applications reduces matrix material requirement and the associated cost. The present study is focused on developing an industrial scale compression molding based processing method for glass microballoon/high density polyethylene (GMB/HDPE) syntactic foams and studying their mechanical properties to develop structure-property correlations. Although glass hollow particle filled lightweight syntactic foams with thermoset matrices have been studied in detail, studies on thermoplastic syntactic foams are scarce. Despite continued interest in developing lightweight thermoplastic syntactic foams, they have not been studied extensively with focus on volume fraction and wall thickness variations. Matrix material used in the present investigation is high density polyethylene (HDPE) and the filler is glass microballoon (GMB), both in as received conditions. Syntactic foam (SF) developed by glass microballoons have benefits like low density, good dimensional stability, high stiffness, material saving and reduced component cost without compromising the specific properties. Blending of GMB in HDPE is carried out using a Brabender mixer with processing parameters optimized for minimal filler breakage. The optimized parameters are used for manufacturing HDPE syntactic foam lumps (brabender output) with 20, 40 and 60 volume % glass microballoon. SF lumpsare processed through compression molding route to form SF sheets that are used for mechanical characterization. In total NINE types of syntactic foams are prepared with three different GMB true particle densities (200, 270 and 350 kg/m3) varying by 20, 40 and 60 volume % in HDPE resin. Different density particle resemble varying wall thickness of GMBs. Lower and higher density values represent thin and thick walled GMBs. Neat HDPE samples are also prepared with similar processing condition as that of foams for comparative analysis. Minimum of five replicates are tested and average values are used for analysis. Uniform distribution of GMBs is observed through micrography affirming the good quality of GMB/HDPE syntactic foam sample processed through the adopted compression molding route. Experimental and theoretical densities of developed syntactic foams are computed. Measured density of all the syntactic foams is lower than neat HDPE resin. Weight saving potential of 10-36% is observed by using GMBs in HDPE matrix. For all particles types, GMB failure is observed to be the highest for syntactic foams containing 60 vol. % GMBs. Increasing glass microballoon content increases particle to particle interaction during processing resulting in particle breakage. Additionally, increasing wall thickness makes GMBs stronger resulting in reduced particle fracture. Particle failure forms glass debris that gets embedded in HDPE matrix. Although fractured particles do not provide reduction in density as planned, they still help in replacing more expensive HDPE resin. Tensile test is conducted at a constant strain rate of 5 mm/min strain rate on trimmed GMB/HDPE foam samples as per ASTM D638-14. Tensile modulus is observed to be highest for the thick walled microballoon having highest filler content as compared to neat resin. Increasing filler content and the wall thickness increases modulus, effect of volume fraction being more prominent. Ultimate tensile strength is seen to be decreased by 32-66% with increasing filler content as compared to neat HDPE. The fracture strength of all the GMB/HDPE foams is 1.3-2.9 times lower than that of the neat HDPE. Neverthless, specific modulus is highest for syntactic foam with thick walled microballoon at 60 vol. % filler loading as compared to neat resin and other foams. Specific strength of GMB/HDPE foams is less compared to neat resin. Highervalues of specific tensile modulus affirm the use of these syntactic foams for weight sensitive applications demanding higher modulus in molded components. Further, tensile test is carried out for lower strain rates (1.6×10-5, 1.6×10-4 and1.6×10-3 s-1). Highest tensile modulus is observed in foams with thin walled microballoons at highest filler loading as compared to neat HDPE at 1.6×10-3 s-1 strain rate. The effect of wall thickness on the modulus of syntactic foams with the same GMB volume fraction is greater at lower strain rates compared to higher ones. Tensile modulus is found to be relatively insensitive to GMB wall thickness variations. Ultimate tensile strength decreases with increasing filler content. Compared to neat HDPE, syntactic foams fracture at lower strain. The fracture strength of all the developed syntactic foams is 1.5-3 times lower than that of the neat HDPE. No clear trend is observed for specific tensile strength. GMB/HDPE foams samples are subjected next to flexural test as per ASTM D790-10. Foams exhibited higher flexural modulus as compared to neat HDPE. Flexural modulus increases while strength decreases with increasing filler content. Additionally, increase in wall thickness increases the flexural modulus. Specific flexural modulus and strength of SF with 350 kg/m3 particle density having 60 vol. % GMB and 200 kg/m3 GMB having 60 vol. % are observed to be 147 and 8% higher compared to neat HDPE samples. Flexural properties are sensitive to volume fraction variations as compared to wall thickness variation. Two theoretical approaches, Porfiri-Gupta and Bardella- Genna model are used to estimate tensile and flexural modulus of syntactic foams. Bardella-Genna model predicts values closer with experimental results for all GMB/HDPE foams tested under tensile (except lower strain tests) and flexural conditions. Outcome of existing literature on tensile and flexural studies is compared with the experimental results of the present work is presented in the form of property maps which helps in material selection for the material scientist/design engineer based on the suitable application. Quasi-static compressive behavior of GMB reinforced HDPE syntactic foams are investigated next. Compression molded GMB/HDPE sheets are subjected to 0.001,0.01 and 0.1 s-1 strain rates. Compressive modulus of foams is higher compared to neat HDPE. Increasing strain rates and decreasing filler content increases yield strength for all the foams investigated compared to neat HDPE. Yield strain and energy absorption of GMB/HDPE foams increases with an increasing strain rate and wall thickness. Specific compressive modulus and strength of GMB/HDPE foams are superior and are comparable to neat HDPE. GMB/HDPE foam achieved high stiffness to weight ratio making them suitable for wide variety of applications. Porfiri-Gupta model based on differential scheme predicts a good estimate of compressive modulus for all the type of GMB/HDPE foams. Property maps are exhibited to present comparative studies of quasi-static compression with existing literature. Further, GMB/HDPE foams are characterized for viscoelastic properties by dynamic mechanical analysis. Test is ramped from 35-150°C at a rate of 5°C/min with the deformation occurring at a constant frequency of 1 Hz. With increase in temperature, storage and loss modulus decreases while tanδ increases with increase in filler loading and wall thickness. Storage modulus and loss modulus increases with increasing wall thickness and volume fraction of GMBs. Damping factor (tanδ) shows an increasing trend with increase in GMB content and wall thickness. Damping factor is less sensitive to glass microballoon content as compared to storage and loss modulus. Structure-property correlations of all the investigated properties are presented with the help of exhaustive SEM images to understand underlying mechanisms. Finally the behavior of material is analyzed using the crystallinity measurement. Crystallinity is observed to be highest for the HDPE as compared to GMB/HDPE foams. Inclusion of GMB decreases the crystallinity signifying stiffness rise of the polymer backbone resulting in ductile to brittle behavioral change. Developed GMB/HDPE syntactic foams achieved better physical and mechanical properties as compared to other thermoplastic foams studied in recent past as exhibited by property maps. Consumption of expensive matrix is reduced by dispersing GMBs leading to lower cost of these syntactic foams. GMB/HDPE foams developed in the present work have a weight saving potential of 36% with betterspecific mechanical properties making them candidate material in weight sensitive and buoyant applications.