Faculty Publications
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Item Additive Manufacturing of Syntactic Foams: Part 2: Specimen Printing and Mechanical Property Characterization(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Saltonstall, B.; Patil, B.; Hoffmann, N.; Doddamani, M.; Gupta, N.High-density polyethylene (HDPE) and its fly ash cenosphere-filled syntactic foam filaments have been recently developed. These filaments are used for three-dimensional (3D) printing using a commercial printer. The developed syntactic foam filament (HDPE40) contains 40 wt.% cenospheres in the HDPE matrix. Printing parameters for HDPE and HDPE40 were optimized for use in widely available commercial printers, and specimens were three-dimensionally (3D) printed for tensile testing at strain rate of 10?3 s?1. Process optimization resulted in smooth operation of the 3D printer without nozzle clogging or cenosphere fracture during the printing process. Characterization results revealed that the tensile modulus values of 3D-printed HDPE and HDPE40 specimens were higher than those of injection-molded specimens, while the tensile strength was comparable, but the fracture strain and density were lower. © 2018, The Minerals, Metals & Materials Society.Item Additive Manufacturing of Syntactic Foams: Part 1: Development, Properties, and Recycling Potential of Filaments(Minerals, Metals and Materials Society 184 Thorn Hill Road Warrendale PA 15086, 2018) Singh, A.K.; Patil, B.; Hoffmann, N.; Saltonstall, B.; Doddamani, M.; Gupta, N.This work focuses on developing filaments of high-density polyethylene (HDPE) and their hollow particle-filled syntactic foams for commercial three-dimensional (3D) printers based on fused filament fabrication technology. Hollow fly-ash cenospheres were blended by 40 wt.% in a HDPE matrix to produce syntactic foam (HDPE40) filaments. Further, the recycling potential was studied by pelletizing the filaments again to extrude twice (2×) and three times (3×). The filaments were tensile tested at 10?4 s?1, 10?3 s?1, and 10?2 s?1 strain rates. HDPE40 filaments show an increasing trend in modulus and strength with the strain rate. Higher density and modulus were noticed for 2× filaments compared to 1× filaments because of the crushing of some cenospheres in the extrusion cycle. However, 2× and 3× filament densities are nearly the same, showing potential for recycling them. The filaments show better properties than the same materials processed by conventional injection molding. Micro-CT scans show a uniform dispersion of cenospheres in all filaments. © 2018, The Minerals, Metals & Materials Society.Item Eco-friendly lightweight filament synthesis and mechanical characterization of additively manufactured closed cell foams(Elsevier Ltd, 2019) Patil, B.; Bharath Kumar, B.R.; Bontha, S.; Balla, V.K.; Powar, S.; Hemanth Kumar, V.H.; Suresha, S.N.; Doddamani, M.Environmentally pollutant fly ash cenospheres (hollow microballoons) are utilized with most widely consumed, relatively expensive high density polyethylene (HDPE) for developing lightweight eco-friendly filament for 3D printing of closed cell foams. Cenospheres (20, 40 and 60 by volume %) are blended with HDPE and subsequently extruded in filament to be used for 3D printing. Cenosphere/HDPE blends are studied for melt flow index (MFI) and rheological properties. MFI decreases with cenospheres addition. Complex viscosity, storage and loss modulus increase with filler loading. DSC results on the filament and printed samples reveal increasing crystallization temperature and decreasing crystallinity % with no appreciable change in peak melting temperature. Cooling rate variations exhibit crystallinity differences between the filament and the prints. CTE decreases with increasing cenosphere content resulting in lower thermal stresses and under diffusion of raster leading to non-warped prints. Micrography on freeze fractured filament and prints show cenospheres uniform distribution in HDPE. Intact cenospheres lower the foam density making it lightweight. Tensile tests are carried out on filaments and printed samples while flexural properties are investigated for 3D prints. Cenospheres addition resulted in improved tensile modulus and decreased filament strength. Tensile and flexural modulus of printed foams increases with filler content. Results are also compared with injection molded samples. Printed foams registered comparable tensile strength. Specific tensile modulus is noted to be increased with cenospheres loading implying weight saving potential of 3D printed foams. Property map reveals printed foams advantage over other fillers and HDPE composites synthesized through injection and compression molding. © 2019 Elsevier LtdItem Compressive behavior of fly ash based 3D printed syntactic foam composite(Elsevier B.V., 2019) Patil, B.; Bharath Kumar, B.R.; Doddamani, M.Syntactic foams are widely used in damage tolerance and low-density applications. In present work compressive behavior of 3D printed three-phase syntactic foams under quasi-static strain rates (0.001, 0.01 and 0.1 s?1) are investigated. Extruded filaments of High density polyethylene (HDPE) with environmentally pollutant fly ash cenospheres (0, 20, 40 and 60 vol%) are used for 3D printing. Micrography reveal that syntactic foam filament and 3D printed samples are three phase systems comprising matrix, cenosphere and porosity. Matrix porosity of about 7% makes these foams lightweight and suitable for buoyant applications. The compressive properties are extracted from the stress-strain plots. It is observed that modulus and specific modulus increases with strain rate and cenosphere content. Specific compressive strength increases with strain rate and decrease with cenosphere content. © 2019 Elsevier B.V.Item Mechanical behavior of additively manufactured nanoclay/HDPE nanocomposites(Elsevier Ltd, 2020) Beesetty, P.; Kale, A.; Patil, B.; Doddamani, M.Nanoclay (NC) has blended with relatively inexpensive, widely consumed HDPE (high density polyethylene) for the development of filament to be used in 3D printers. NC/HDPE blends are prepared by varying NC wt. % (0.5, 1, 2, and 5) and are subjected to melt flow index (MFI) measurements. MFI has noted to be decreasing with NC loadings. NC/HDPE nanocomposite blends are further extruded using a single screw extruder. Developed nanocomposites filaments are fed to the fused filament fabrication (FFF) based 3D printer for realizing NC/HDPE nanocomposite prints. The density of printed sample increases with filler content. Filament and printed samples thermal study is carried out using differential scanning calorimeter (DSC). NC addition increases crystallinity and crystallization temperature without significant change in melting peak temperature. Freeze fractured prints reveal the uniform distribution of NC in HDPE. The tensile test is conducted on the filaments and prints. Further printed nanocomposites are subjected to flexural investigations. Tensile modulus and strength of filament increase with NC additions in HDPE matrix. Tensile and flexural properties (modulus and strength) of the nanocomposite prints increases with NC content. Finally, results obtained from the tensile and flexural tests of prints are compared with different HDPE composites available in the literature. © 2020 Elsevier Ltd