2. Thesis and Dissertations
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Item Mechanical and Dynamic Behavior of Additively Manufactured Polymer Nanocomposites(National Institute of Technology Karnataka, Surathkal., 2024) Kumar, Sumodh; M.R., Ramesh; Doddamani, MrityunjayRapid production of high quality components without any additional tools is the key to cost reduction in industrial applications. The present work deals with the additive manufacturing of polymer nanocomposite and their graded variants using fused filament fabrication (FFF) technology based 3D printing process. High Density Polyethylene (HDPE) is used as a matrix, and functionalized MWCNTs are used as a filler material in this work. The development of nanocomposite (NC) with lightweight functionalized MWCNTs serves the purpose of reduction in weight with enhanced properties. The functionalized MWCNTs (0.5%, 1%, 3%, and 5% by weight) are blended with the HDPE to develop functionalized MWCNTs/HDPE NCs in the form of pellets, which are further characterized through scanning electron microscopy (SEM), melt flow index (MFI), and thermogravimetric analysis (TGA). Then, these developed NCs are utilized to extrude NC filaments for 3D printing. The extruded NC filaments are characterized for quality and printability, which are further utilized in 3D printing of NC and functionally graded nanocomposite (FGNC) samples. The 3D printed NCs and FGNCs are comprehensively characterized for prints quality through various techniques such as SEM, rheology, XRD, and density, and finally subjected to the tensile, flexural, compression, hardness, impact, mechanical buckling, free vibration, and thermal buckling. Also, the waste NC filament is investigated for its recycling potential. The SEM analysis revealed the uniform distribution of the functionalized MWCNTs in the HDPE in the developed nanocomposites, extruded nanocomposite filaments, and the 3D printed samples, confirming the suitability of the processing parameters used in the blending, extrusion, and 3D printing. It also revealed the seamless and strong layer bonding in the 3D printed NCs and FGNCs. The rheology findings also confirm the uniform distribution of the fillers qualitatively. It is observed that complex viscosity (η*) for the NCs slightly increases as the functionalized MWCNTs content increases up to 0.5%, and then dramatically increases for 5% (almost two orders) at the low frequency by maintaining a steeper graph, confirming the good dispersion of the MWCNTs in the HDPE matrix. The complex viscosity (η*), storage modulus (E'), and loss modulus (E") of the 3D printed NCs and FGNCs increase while the damping factor (𝑇𝑎𝑛𝛿) decreases as the functionalized reinforcement content rises. The MFI of the developed NCs (H0.5-H5) showed a decreasing trend with increase in the MWCNTs content, confirming the inclusion of the fillers in the matrix. The MFI decreases in the 14.52%-51.60% range for the H0.5- H5 NCs compared to the HDPE. The thermal stability of the developed NCs increases with the addition of the filler. The highest thermal degradation temperature is observed for H5 NC (479.07 ºC). The density of the filaments and the specimens decreases with the increase in the MWCNTs content. The highest density reduction of 16.06% and 15.58%, respectively, is observed in the H5 filament and the respective H5 print compared to the pure HDPE. The density of the FGNCs was also found to decrease with layer gradation. The FGNC-2 exhibited the highest weight-saving potential of 12%. 𝑇𝑀𝑒𝑙𝑡 of the filaments and the specimens increases with an increase in the MWCNT content, while 𝑇𝐶𝑟𝑦𝑠𝑡 increases up to 0.5% and 1% for the filaments and the specimens, respectively, then decreases. 𝛼𝐶𝑟𝑦𝑠𝑡 is higher for the filaments and the specimens than the neat HDPE. The XRD results also revealed the higher crystallinity of the NCs than the pure HDPE. A tensile study of the extruded filaments, NC, and FGNC prints revealed that the modulus and strength increase with the addition of the MWCNTs. The highest tensile modulus and strength are observed for the H5 NC filament, which is 105% and 30% higher than the pure HDPE filament. For the printed NC specimens, the modulus increases by 15.89%, 19.41%, 44.87%, and 81.43% in the H0.5, H1, H3, and H5 NC specimens, respectively, compared to the pure HDPE specimens. The highest modulus is registered for the H5 NC specimen (~81.5%). Further, it is noted that the tensile modulus of the printed specimens is higher than the respective filaments. The tensile modulus of the printed H-H5 NC specimens increased by 15.42%, 13.97%, 13.96%, 15.47%, and 2.38% compared to the respective filaments. The highest tensile strength (UTS) is registered for the H5 (16.6 MPa), 12.16% higher than the pure HDPE. It is noted that the H5 NC specimen has the highest modulus and strength among all the NC specimens, 81.43%, and 12.16%, respectively, higher than the HDPE. Further, the FGNCs are also tested for tensile. It is seen that their modulus and strength increase with the layer gradation. The enhancements in the moduli are 55.15% and 90.41% for the FGNC-1 and the FGNC-2 compared to the pure HDPE, respectively. Moreover, the FGNCs exhibited higher moduli than their respective homogeneous NCs, showing the potential to replace the NCs. The FGNCs showed higher strength than the respective homogeneous NCs, 23.75% and 37.12%, respectively, higher strength than the HDPE are noted for the FGNC-1 and FGNC-2. The tensile properties of the NCs are compared with the existing composites, where it is found that the 3D printed NC sample exhibited the highest tensile strength compared to the other fillers reinforced HDPE composites. The printed NCs and FGNCs are also investigated for the flexural responses. It is observed that the flexural modulus and strength of the NC specimens increase with the MWCNTs increase. The highest modulus and strength, 24.71% and 22.23% are noted for the H5 NC print compared to the neat HDPE. It is noticed that the specific strength and modulus of the printed NC specimens increase with the filler loadings. The H5 specimen showed the highest specific modulus and strength, 47.62% and 44.73% higher than the pure HDPE. For the FGNCs, the flexural moduli and strength are also noted to increase with the layer grading. The highest flexural strength and moduli are exhibited by the FGNC-2, which is 28.57% and 26.83% higher than the pure HDPE. The FGNC-2 also exhibited the highest specific strength and modulus, 46.16% and 44.14%, respectively, higher than the pure HDPE. The flexural behavior of the NCs and the FGNCs was also studied numerically, and the experimental findings were found to match well with the FEA results. The compression, hardness, and impact studies are also conducted on the printed NCs and FGNCs, which revealed an increasing trend of compressive modulus and yield strength with the increased MWCNTs content. The highest compressive modulus and yield strength are found for the H5 NC, which are, respectively, 44.89% and 9.28% higher than the pure HDPE. In the FGNCs, the layer gradation also notes a similar increasing trend. The FGNC-1 and FGNC-2 exhibited 35.75% and 61.14% higher modulus than the pure HDPE with the highest of the FGNC-2. The yield strengths of the FGNC-1 and the FGNC-2 are 8.89% and 11.56% higher than the pure HDPE with the maximum FGNC-2. The hardness and the impact strength of the NCs and FGNCs also increase with the filler content. The highest hardness and impact strength are noted for the H5 NC among all the NCs, while in the case of the FGNCs, are for the FGNC-2. The FGNC-2 exhibited the highest hardness and impact strength, respectively 76.80% and 119.99% higher than the pure HDPE. Mechanical, thermal, and dynamic loading causes instability, leading to the failure of the structure. Therefore, the printed NCs and FGNCs are also investigated for mechanical buckling, free vibration, and thermal buckling behavior. Results revealed that the NCs and the FGNCs buckling strength increases with the increased MWCNTs content. The highest critical buckling load (𝑃𝑐𝑟) is noted for the H5 NC among the NCs, which is 79.03% (by DTM) and 79.13% (by MBC method) compared to the HDPE. The 𝑃𝑐𝑟 of the FGNC-1 and the FGNC-2, calculated from DTM and MBC methods, are 54.38% and 91.34% higher than the pure HDPE. It is noted that the H5 NC and FGNC-2 displayed the highest buckling strength among the 3D printed NCs and FGNCs. The 𝑃𝑐𝑟, calculated from DTM, MBC, and VCT methods, exhibited good agreement. The natural frequency of the NCs and the FGNCs increases with the MWCNTs loading while decreases with increasing compressive load. Their damping factor showed a decreasing trend with the filler loading while observed to be increasing with a rise in the compressive load. The experimental and numerical findings are observed to be in very good agreement. The property chart reveals the superior performance of the H5 NC and the FGNC-2 compared to thermosetting composites. Thermal buckling studies of the NCs and the FGNCs under various heating conditions revealed that the critical buckling temperature (𝑇𝑐𝑟) and the deflection due to heating is very sensitive to heating type. The 𝑇𝑐𝑟 is noted as the highest in case-3 and the lowest in case-2. The maximum deflection is observed in case-2, while no significant difference is observed in case-1 and case-3. The 𝑇𝑐𝑟 of the NCs and FGNCs increases, while the deflection decreases due to the addition of the MWCNTs and their gradation. The highest 𝑇𝑐𝑟 is observed for the H5 NC (11.16% higher than the pure HDPE) and FGNC-2 (19.06% higher than the pure HDPE). The lowest deflection is observed for the H5 NC (53.33% lower than the pure HDPE) and the FGNC-2 (73.34% lower than the pure HDPE), indicating enhanced thermal stability. It is seen that the H5 NC exhibited the superior performance among all the NCs, while the FGNC-2 showed the best performance between the FGNC-1 and FGNC-2. Moreover, the FGNCs exhibited the superior performance to all the homogeneously reinforced NCs. In addition to comprehensive studies on the 3D printed NCs and FGNCs, this work also considered the study on the recycling potential of the waste polymers, which is increasing in the environment and causing many hazardous environmental problems. In this study, the waste extruded nanocomposite filaments that get wasted during filament extrusion are collected and examined for recycling potential. The waste filaments of the functionalized MWCNTs/HDPE NCs (H1 composition) are recycled to obtain the useful NC filaments for utilization in 3D printing. These NC filaments are further tested to check their potential for 3D printing. The samples are 3D printed using the recycled filaments, and subjected to density, XRD, and tensile tests to examine their recycling potential. The recycled filaments and the respective prints showed enhanced density, crystallinity, and tensile properties with respect to the extrusion cycle. After third extrusion cycle, no enhancement in the properties is found. The tensile strength and modulus of 1x, 2x, and 3x prints are 63.82%, 67.11%, and 67.76%, and 45.63%, 55.34%, and 97.81%, respectively, higher than the W/UR print. The highest tensile strength and modulus are observed for 3x print, which is 67.76% and 97.81%, respectively, higher than the W/UR print. This study revealed that the H1 NC filament can be recycled (extruded) three times to achieve property enhancement. The H1-3x print exhibited superior tensile strength and modulus among all the recycled prints. Through such an approach, the environmental pollution due to the plastic waste generated by 3D printing industries can be substantially lowered, in addition to expanding the filament material options for the FFF community. A similar route can also be explored for the other NCs (0.5%, 1%, 3%, and 5 wt.%), increasing application areas across various engineering fields such as structural, marine, aerospace, and automobile. The efforts presented in this research exhibited the potential of the 3D printed NCs and the FGNCs to be utilized as integrated and jointless functional components in a wide spectrum of engineering applications such as marine, automobile, aerospace, construction, defense, electronics, and naval in addition to increasing the novel materials options for 3D printing industries.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 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 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 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.