2. Thesis and Dissertations
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/1/10
Browse
4 results
Search Results
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 Response of 3d Printed Functionally Graded Foam(National Institute Of Technology Karnataka Surathkal, 2023) Dileep, Bonthu; Doddamani, MrityunjayIn additive manufacturing, fused filament fabrication (FFF) based three-dimensional printing (3DP) is one of the most popular rapid processing technologies. The key benefit of 3DP is the ability to build integrated, complex, and tailored components. Increasing the wide variety of materials that can be processed using this process helps increase the flexibility toward part generation. This made the current work focus on developing a glass micro balloon (GMB) reinforced high density polyethylene (HDPE) based syntactic foam filament. Reinforcing the hollow fillers helps in developing the filament for weight sensitive applications. Nevertheless, processing these fillers with improper process parameters and random volume fractions results in filler failure and agglomeration defects. Hence, taking the quality measuring parameters like filament ductility, roughness, ease of process-ability, and defects like agglomeration, filler percentage is maintained in the range of 20-60 volume %. Syntactic foam filaments of 20, 40, and 60 volume percentage GMB filler are extruded with proper circularity and uniform diameter. Part quality mainly depends on the selected manufacturing method and its process parameters. Hence, after filament development, this work's primary objective was to optimize 3D printing parameters to develop a defectless part. An outcome of the number of pilot studies helps identify possible defects in 3D printing and overcome strategies. Finally, printing parameters like speed, nozzle temperature, bed temperature, infill percentage, raster angle, layer height, etc., are finalized for processing syntactic foam filaments through an FFF 3D printer. Using these optimized parameters initially plain H, H20, H40, and H60 beams that are 3D printed. Sandwich and functionally graded beams have many advantages compared to plain beams. The current work trail has developed functionally graded foams, and all configurations of foams like SH 20-60, FGF- 1, 2, 3, and FGSF- 1, 2, 3 are successfully 3D printed using the filament replacement method. Extensive scanning electron microscopic analysis was performed to study the interface bonding between the foam layers, filler sustainability, and filler matrix interface. Results showed that the layers of similar and dissimilar compositions are properly fused by forming a seamless bonding. There is no observable filler failure, but an improper filler matrix interface was observed, which creates porosity in a sample. These voids help in enhancing the weight reduction potential. 3D printed samples are subjected to micro- CT scan to observe the porosity distribution. In this experiment, there was no observable porosity in HDPE layers, whereas some porosity was observed in the foams, and it was quite minimal in H20 and comparatively increased in H60. This porosity estimation is essential. So five samples of each composition are experimentally tested for density measurement, and theoretical density was calculated using a rule of mixtures. The theoretical and experimental density difference is represented as the void percentage. Results showed that the density of the foam increased with an increase in filler percentage and void percentage shows a similar trend for filler. Among graded foams and their respective sandwiches, the void percentage varied in the 4-7% range. The present material is aimed at weight-sensitive applications where the weight saving potential (WSP) plays a crucial role. This WSP increased with an increase in the filler, and it is higher for H60, and in graded foams and their respective sandwiches, it is higher for FGF-2 and FGSF-2. The percentage of WSP for FGF and FGSFs varied in the range of 8-14%. These graded foams are developed for weight sensitive structural and naval applications, so the current work response of these 3D printed foams under various loads and loading conditions was explored. These developed foams are most prone to thrust forces, so the behavior of these foams under compressive loading was studied. It is noted that the compressive modulus increases with the filler content. The graded foams' specific properties exhibited superior response compared to neat HDPE. Among functionally graded foams (FGFs) and functionally graded sandwich foams, FGF-2 (H20-H40-H60) and FGSF-2 (H-H20-H40-H60-H) showed the highest modulus and yield strength. FGF and FGSFs exhibited better energy absorption compared to plain foams. FGF and FGSFs exhibited better energy absorption than foams and are 8 to 19 % more than pure HDPE. All functionally graded foams exhibited a sacrificial failure mechanism. Due to the higher compressive forces, hollow GMB failure was observed in the tested sample. The response of FGF and FGSFs toward transverse loading was studied by performing three-point bending experiment. The test was conducted at crosshead displacement velocities of 2.54 and 3.41 mm/min for FGF and FGSFs. Experimental results of the flexural test showed that graded sandwiches exhibited better strength than the graded core alone. Among all the functionally graded foams (FGFs), FGF-2 exhibited a better specific modulus, and the modulus of FGF-2 enhanced by 33.83% compared to pure HDPE. FEA results showed unsymmetrical stress distribution along the thickness of the sample. A comparative study of experimental and numerical results showed a slight deviation. The better specific properties of the developed graded foams help to create their preference for weight-sensitive structural applications. The behavior of the FGF and FGSFs subjected to axial compressive load and their natural frequency under zero and non-zero loading conditions was studied through buckling and free vibration analysis. The buckling load of these 3D printed beams was estimated from experimentally acquired load-deflection data using the double tangent method (DTM), modified Budiansky criteria (MBC), and vibration correlation technique (VCT). Results showed that critical buckling load increased with an increase in hollow GMB percentage. Among all FGFs, FGF-2 exhibited the highest buckling load. Compared to pure HDPE buckling strength of FGF-1, FGF-2, and FGF-3 calculated using DTM and MBC methods are increased by 39, 78.4, 47 %, 44.68, 87.23, and 53.19%, respectively. Mechanical stability of the 3D printed graded cores increased post sandwiching them with HDPE skin. All FGSFs outperformed their respective cores in terms of buckling load. FGSFs exhibited a similar trend in the core sample. There is no observable delamination between the 3D printed layers and the skin and core interface, even after increasing the load beyond the sample critical buckling load. Natural frequency is one of the crucial parameters of the beam and is evaluated by performing a free vibration test. Results showed that at mode-1, the natural frequency of all FGF and FGSF beams decreases with increasing load up to critical buckling load, and a further increase in load increases the natural frequency. The natural frequency of the beam increases with an increase in filler percentage. Corresponding to all modes, among all FGF and FGSFs, FGSF-2 exhibited higher natural frequency. The damping factor of the beam increases with an increase in load up to the critical buckling point; further, an increase in load results in a decrease in the damping factor. In practical applications of 3D printed beams, they are subjected to non-uniform heating conditions. This necessitates the current work to study the response of these 3D printed plain, graded, and their respective sandwiches towards non-uniform heating. This non-uniform heating was created in an experimental setup by varying the heating position of the IR heater. In case 1 sample was heated at one end. In case- 2 sample was heated at the center of the sample, and in case-3, both ends of the sample are subjected to thermal load. Results showed that the thermal stability of the beams enhanced with an increase in GMB percentage. This thermal stability was further enhanced by varying the GMB volume percentage along the thickness direction and sandwiching it with HDPE skin. All 3D printed samples exhibited maximum deflection in case 2 and minimum deflection in case 1. Comparative results concluded that the beams' thermal stability could be enhanced by grading the material property along the thickness direction and sandwiching it.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.