Browsing by Author "Hemanth Kumar, V.H."

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    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 Ltd
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    Investigation of aging effect on asphalt binders using thin film and rolling thin film oven test
    (ASTM International, 2019) Hemanth Kumar, V.H.; Suresha, S.N.
    The effect of short-term aging temperature according to Superpave protocol on rheological properties of asphalt binder using thin film oven (TFO) and rolling thin film oven (RTFO) test was investigated. To evaluate these different aging conditions, two types of unmodified binders and a crumb rubber modified binder (CRMB) was used at three different aging temperatures 163°C, 177°C, and 195°C. To simulate the effect of temperature used during the preparation of CRMB in laboratory and ideal mixing temperature corresponding to 170 ± 20 cP, 177°C and 195°C has been incorporated, respectively. The rheological characterizations of these binders were obtained using dynamic shear rheometer for before and after short-term aging. On the basis of rutting parameter, nonrecoverable creep compliances (Jnr) and percent recovery (%R), as well as the RTFO aging process were found to be more effective than the TFO test for all the selected oven temperatures. However, the complex shear modulus |G*| of the base binders were equivalent to modified binders at 195°C. Additionally, on the basis of frequency sweep test and viscosity curve, the effect of short-term aging in a sample was investigated. However, at 195°C, the flow properties were significantly different for unmodified base binder, except for rubberized binders. From this study, based on its characterization, it is possible to use TFO or RTFO tests at a higher temperature to simulate the aging process for rubber modified binder to the actual hot-mix asphalt process. © © 2019 by ASTM International.