Faculty Publications

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    Tensile behavior of lightweight foam filament
    (Institute of Physics Publishing helen.craven@iop.org, 2019) Kamath, N.; Anawal, R.; Doddamani, M.
    Filaments of high-Density Polyethylene (HDPE) with Glass Microballoons (GMBs) by20, 40 and 60 volume% are developed and studied for tensile characterization. Density of syntactic foam filaments are lower compared to pure HDPE filaments. The syntactic foam filament developed results in weight saving potential of 28% owing to inclusion of hollow GMBs in matrix resin making them suitable for marine applications. Modulus of syntactic foam filaments increases with increasing GMB volume % compared to neat HDPE. Tensile strength of syntactic foams filaments is lower as compared to pure HDPE filament. These developed lightweight filaments can be used for 3D printing of complex geometries. © 2019 IOP Publishing Ltd. All rights reserved.
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    3D printing of syntactic foam cored sandwich composite
    (Elsevier B.V., 2020) Bonthu, D.; Bharath, H.S.; Gururaja, S.; Prabhakar, P.; Doddamani, M.
    In 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. Optimization of feedstock material and associated 3DP process to achieve the required properties for various applications has been an important research field in the recent past. The main objective of this paper is 3DP of syntactic foam cored sandwich composite all at once (skin-core-skin printing in sequence at once). High density polyethylene (HDPE) and glass microballoon (GMB) reinforced (20, 40, and 60 by volume%) HDPE blends are fed into the extruder for manufacturing respective filaments. These HDPE and HDPE/GMB filaments are further sent to the FFF based printer to realize skin and syntactic foam core respectively of the sandwich. The selection of substrate for printing and the crucial issues associated with the printing of core and sandwich composites are analyzed. The present work successfully demonstrates that by optimizing the printing parameters, good quality core and sandwich structures can be printed all at once without any defects. Finally, the suitable printing parameters are used as boundary conditions in finite element (FE) simulation of sandwich for carrying out thermomechanical analysis to analyze the thermal stress distributions in the prints. © 2020
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    Mechanical behaviour of 3D printed lightweight nano-composites
    (Bentham Science Publishers, 2021) Doddamani, M.
    Background: The nanoclay (NC) and Glass Micro Balloons (GMB) based reinforced polymer composites are explored extensively through traditional processing methods. NC shows substantial enhancement in mechanical properties. Polymer composites developed by reinforcing GMB fillers provide a substantial reduction in weight, which is essential in the marine, aerospace, and au-tomotive field. In this study, an attempt is made by developing polymer nanocomposites by reinforcing NC and GMB particles. Objective: The paper deals with 3-dimensional printing (3DP) of lightweight Nanocomposite Foam (NF) developed by mixing nanoclay (NC) and glass micro balloons (GMB) in high-density polyethylene (HDPE). The NF blend is prepared by keeping NC at 5 weight %. Subsequently, GMBs are added by volume (20-60%) to NC/HDPE blend to realize lightweight NFs. Methods: The lightweight feedstock filaments are developed by extruding the blends using a single screw extruder. The extruded NF filaments are used as input in a 3D printer to print NFs. The density of extruded filaments and prints is measured. The printed NFs are subjected to tensile and flexu-ral testing. Results and Conclusion: With an increase in GMB loading, the density of both filaments and prints decreases. Compared to neat HDPE, printed NFs show ~30% weight-reducing potential. The tensile, flexural modulus and strength increases with GMB loading. NFs exhibited superior mechanical performance as compared to HDPE and NC/HDPE. Further, the property map reveals that the 3D-printed NFs show superior tensile, flexural modulus, and strength in comparison with injection and compression-molded foams. © 2021 Bentham Science Publishers.
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    Compressive response of 3D printed graded foams
    (Elsevier B.V., 2021) Dileep, B.; Doddamani, M.
    The syntactic foams are widely used in aeronautics, underwater vehicle structures, and oil drilling applications. These foams are being extensively utilized in naval applications wherein they are subjected to the compressive forces that are depth-dependent. Developing graded foams with better compressive behavior using three-dimensional printing (3DP) permits realizing complex geometrical structures with numerous advantages compared to conventional processing routes. The present work deals with 3DP of syntactic foams and their graded configuration by embedding (20, 40, and 60 vol%) glass microballoons (GMBs) in high density polyethylene (HDPE). It is noted that the modulus increases with the filler content. Specific properties of the graded foams exhibited superior response as compared to neat HDPE. Among functionally graded foams (FGFs), FGF-2 (20–40–60) showed the highest modulus and yield strength. FGFs exhibited better energy absorption among all the tested samples. GMBs are observed to be intact, and a seamless interface is seen in micrographs of 3D printed graded foams, making them candidate materials for lightweight structural applications. © 2021
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    Mechanical response of additively manufactured foam: A machine learning approach
    (Elsevier B.V., 2022) Neelam, R.; Kulkarni, S.A.; Bharath, H.S.; Powar, S.; Doddamani, M.
    This paper uses ensemble and automated machine learning algorithms to predict the mechanical properties (tensile and flexural strength) of a three-dimensionally printed (3DP) foamed structure. The closed cell foams were made from the most commonly used thermoplastic, High-Density Polyethylene (HDPE). The hollow glass microspheres are infused in HDPE at varying volume %. The available data on these foams' mechanical properties are used by the chosen machine learning (ML) algorithms to propose the best suited algorithm for such a three-phased microstructure as these closed cell foams exhibit. Finally, the strength predictions from the models were validated using experimental data. The models were trained with nozzle temperature, bed temperature, and force values as input parameters. The output parameters predicted were the tensile and flexural strength. LightGBM outperforms all other models in terms of performance among ensemble-based models, while H2OAutoML outperforms all other models. All the ML algorithms produced models with greater than 95% accuracy. Finally, memory and time consumption for each model are presented. © 2022 The Authors
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    3D printed functionally graded foams response under transverse load
    (Elsevier B.V., 2023) Bonthu, D.; Mahesh, V.; Powar, S.; Doddamani, M.
    The applications of 3D printing are rapidly increasing in aerospace and naval applications. Nonetheless, 3D printing (3DP) of graded foams exhibiting property variation along the thickness direction is yet to be explored. In the current work, the different volume fractions of hollow glass micro balloon (GMB) reinforced high-density polyethylene (HDPE) composite based graded foams are 3D printed using the fused deposition modelling (FDM) technique. The bonding between successive layers and porosity distribution of these graded configurations are studied using micro-CT scan. Further, the 3D Printed functionally graded foams (FGFs) are tested for flexural response, and results are compared with numerical values. The micro-CT results showed delamination absence between the layers. In neat HDPE layers, porosity is not evident, while minor porosity creeps in the layers having the highest GMB content. Experimental results of the flexural test showed that the graded sandwiches exhibited better strength than the graded core alone. Compared to neat HDPE, the modulus of FGF-2 (H20–H40–H60) increased by 33.83%, implying better mechanical stiffness. Among all the FGFs, FGF-2 exhibited a better specific modulus. A comparative study of experimental and numerical results showed a slight deviation due to neglecting the induced porosity. © 2023 The Authors
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    Dynamic response of 3D printed functionally graded sandwich foams
    (Emerald Publishing, 2023) Bonthu, D.; Bharath, B.; Bekinal, S.I.; Jeyaraj, J.; Doddamani, M.
    Purpose: The purpose of this study was to introduce three-dimensional printing (3DP) of functionally graded sandwich foams (FGSFs). This work was continued by predicting the mechanical buckling and free vibration behavior of 3DP FGSFs using experimental and numerical analyses. Design/methodology/approach: Initially, hollow glass microballoon-reinforced high-density polyethylene-based polymer composite foams were developed, and these materials were extruded into their respective filaments. These filaments are used as feedstock materials in fused filament fabrication based 3DP for the development of FGSFs. Scanning electron microscopy analysis was performed on the freeze-dried samples to observe filler sustainability. Furthermore, the density, critical buckling load (Pcr), natural frequency (fn) and damping factor of FGSFs were evaluated. The critical buckling load (Pcr) of the FGSFs was estimated using the double-tangent method and modified Budiansky criteria. Findings: The density of FGSFs decreased with increasing filler percentage. The mechanical buckling load increased with the filler percentage. The natural frequency corresponding to the first mode of the FGSFs exhibited a decreasing trend with an increasing load in the pre-buckling regime and an increase in post-buckled zone, whereas the damping factor exhibited the opposite trend. Originality/value: The current research work is valuable for the area of 3D printing by developing the functionally graded foam based sandwich beams. Furthermore, it intended to present the buckling behavior of 3D printed FGSFs, variation of frequency and damping factor corresponding to first three modes with increase in load. © 2023, Emerald Publishing Limited.