Browsing by Author "Krishna, M."

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    Alkali absorption and durability studies on CFRP laminated composites
    (American Institute of Physics Inc. subs@aip.org, 2020) Mohan Kumar, T.S.M.; Krishna, M.; Joladarashi, S.; Kulkarni, S.
    Fiber Reinforced Plastics (FRP) are widely used in marine, aeronautical, automotive, space applications due to their corrosive resistance and low cost to performance. The main aim of this research was to examine the impact of alkali absorption and durability in the Carbon/Epoxy, Carbon/Vinylester, and Carbon/Isopolyester composites immersed in 13.59 pH alkaline solutions for a maximum of 25 days at 27°C (room temperature) and 65°C. Epoxy, vinyl-ester and Isoployester resin are selected as a matrix material and Poly-acrylonitrile-based Carbon fiber of 200 gsm fabrics is chosen as reinforcement and hand lay-up process is used for fabrication in the ratio of 35: 65 respectively and cured at room temperature with applied pressure using hydraulic press for 24 hrs. Solution of alkali was prepared and specimens were subjected to alkali solution. The moisture absorption was calculated on the basis of rate of moisture for every 5days interval and rate of diffusion coefficient (m2/sec) were calculated. Similarly durability studies (UTS, ILSS and FS) are conducted at 27°C and 65°C. Characterization of the fractured area was done using a scanning microscope. The obtained result rate of moisture absorption in case of neat casting and CFRP specimen shows the maximum alkali absorption in Iso-polyester / carbon whereas the minimum absorption was shown in vinyl ester/carbon specimens at RT and at 65°C over a period of 25days. At room temperature and 65°C the diffusion coefficient (D) was found and identified higher value for Iso-polyester/carbon and low for vinyl ester/carbon this is because Iso-polyester are distributed along the main chain, which makes easily available for reaction but in vinylesters the ester functional groups acts as a shield by methyl groups which restrict the easy absorption. Reduce in percentage in mechanical properties is due to Alkali absorption in terms of reduced degradation values in UTS, Flexural Strength and ILSS samples, carbon / epoxy showed supremacy over vinylester / carbon and iso-polyester / carbon. Scanning electron microscopy images show the embrittlement and micro-cracks on surface due to exposure to the alkali environments, matrix bonded to fiber are hardly identified as the temperature increases. © 2020 Author(s).
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    Micro-Architectural support for High Availability of NoC-based MP-SoC
    (Institute of Electrical and Electronics Engineers Inc., 2019) Singh, R.; Ranga, S.V.; Patil, S.; Krishna, M.; Mehta, M.; Anoop, M.N.; Nandy, S.K.; Haldar, C.; Narayan, R.; Neumann, F.; Baufreton, P.
    In this paper, we focus on increasing the availability of Multi-Processor System on Chip (MP-SoC) for executing user applications, even when some components of the system are faulty. A Network-on-Chip (NoC) provides high bandwidth communication substrate for the multitude of components/modules in such MP-SoCs. Health of such MP-SoC, and hence its availability, is largely dependent on the health of the NoC. We consider an NoC comprising a bidirectional toroidal mesh interconnection of routers. We use a distributed built-in-self-test to identify faulty communication links. We use information so obtained to determine healthy subsystems that can be made available for executing user applications. This feature is key for enhancing availability of MP-SoCs. We realize this feature as a micro-architectural enhancement in MP-SoC that incurs an insignificant hardware overhead of less than 2%. Latency incurred for analyzing availability of MP-SoC is also insignificant. We functionally validate our proposal by emulating the system on a FPGA device and demonstrate increase in availability of the MP-SoC. © 2019 IEEE.
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    Microstructure, mechanical and wear properties of the A357 composites reinforced with dual sized SiC particles
    (2019) Lakshmikanthan, A.; Bontha, S.; Krishna, M.; Koppad, P.G.; Ramprabhu, T.
    Current work reports on the development of A357 alloy composite which is reinforced with dual size SiC particles by stir casting route. Influence of different weight fractions (3% coarse+ 3% fine, 4% coarse + 2% fine, and 2% coarse + 4% fine) of dual size SiC particles on mechanical properties and wear resistance of A357 composites is the focus of this work. Hardness and tensile properties were studied for dual size composites and then were compared with A357 alloy. Microstructural study, fractured surface and worn surface investigation were carried out using optical and scanning electron microscopes respectively. Microstructural analysis showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. Compared to A357 alloy, the composites showed improvement in hardness, yield, and tensile strength. In particular, composite with 4 wt. % of fine and 2 wt. % of large SiC particles displayed the highest tensile strength while composite with 4 wt. % of large and 2 wt. % of fine SiC particles exhibited high hardness and wear resistance among A357 alloy and dual particle size composites. The strengthening mechanisms that contributed to improvement in strength values were effective load transfer and dislocation strengthening due to thermal mismatch. 2019 Elsevier B.V.
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    Microstructure, mechanical and wear properties of the A357 composites reinforced with dual sized SiC particles
    (Elsevier Ltd, 2019) Avinash, A.; Bontha, S.; Krishna, M.; Koppad, P.G.; Ramprabhu, T.
    Current work reports on the development of A357 alloy composite which is reinforced with dual size SiC particles by stir casting route. Influence of different weight fractions (3% coarse+ 3% fine, 4% coarse + 2% fine, and 2% coarse + 4% fine) of dual size SiC particles on mechanical properties and wear resistance of A357 composites is the focus of this work. Hardness and tensile properties were studied for dual size composites and then were compared with A357 alloy. Microstructural study, fractured surface and worn surface investigation were carried out using optical and scanning electron microscopes respectively. Microstructural analysis showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. Compared to A357 alloy, the composites showed improvement in hardness, yield, and tensile strength. In particular, composite with 4 wt. % of fine and 2 wt. % of large SiC particles displayed the highest tensile strength while composite with 4 wt. % of large and 2 wt. % of fine SiC particles exhibited high hardness and wear resistance among A357 alloy and dual particle size composites. The strengthening mechanisms that contributed to improvement in strength values were effective load transfer and dislocation strengthening due to thermal mismatch. © 2019 Elsevier B.V.
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    Solid state amorphization of Mg-Zn-Ca system via mechanical alloying and characterization
    (2017) Manne, B.; Bontha, S.; Ramesh, M.R.; Krishna, M.; Balla, V.K.
    Magnesium based bulk metallic glasses have attracted significant attention of researchers due to better mechanical and corrosion properties when compared to their crystalline counterparts especially for biomedical applications. Scaling up the part size and production volumes of such materials through liquid metallurgy route is challenging. In this work amorphous Ca5Mg60+xZn35?x (X = 0, 3 and 7) alloys have been successfully synthesized through solid state amorphization using a high energy planetary ball mill. X-ray diffraction was used to identify the crystalline phases of the powder during reaction. Evolution of amorphous phase was analysed using a parameter involving the ratio of integral area of peaks to the integral area of background (IPB) obtained from XRD patterns. Results showed reaction time increases with decreasing Zn content in Ca5Mg60+xZn35?x (X = 0, 3 and 7) alloy to obtain maximum amorphous structure with a small amount of residual crystalline phase. Prolonged milling of these powders, to eliminate residual crystalline phases, resulted in the nucleation of Mg102.08Zn39.6 phase. The composition dependent characteristic temperatures and thermal stabilities were studied using differential scanning calorimetry. 2016 The Society of Powder Technology Japan
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    Solid state amorphization of Mg-Zn-Ca system via mechanical alloying and characterization
    (Elsevier B.V., 2017) Manne, B.; Bontha, S.; Ramesh, M.R.; Krishna, M.; Balla, V.K.
    Magnesium based bulk metallic glasses have attracted significant attention of researchers due to better mechanical and corrosion properties when compared to their crystalline counterparts especially for biomedical applications. Scaling up the part size and production volumes of such materials through liquid metallurgy route is challenging. In this work amorphous Ca5Mg60+xZn35?x (X = 0, 3 and 7) alloys have been successfully synthesized through solid state amorphization using a high energy planetary ball mill. X-ray diffraction was used to identify the crystalline phases of the powder during reaction. Evolution of amorphous phase was analysed using a parameter involving the ratio of integral area of peaks to the integral area of background (IPB) obtained from XRD patterns. Results showed reaction time increases with decreasing Zn content in Ca5Mg60+xZn35?x (X = 0, 3 and 7) alloy to obtain maximum amorphous structure with a small amount of residual crystalline phase. Prolonged milling of these powders, to eliminate residual crystalline phases, resulted in the nucleation of Mg102.08Zn39.6 phase. The composition dependent characteristic temperatures and thermal stabilities were studied using differential scanning calorimetry. © 2016 The Society of Powder Technology Japan
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    The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites
    (Elsevier Editora Ltda, 2020) Avinash, A.; Prabhu, T.R.; Babu, U.S.; Koppad, P.G.; Gupta, M.; Krishna, M.; Bontha, S.
    In the present work, the effect of aging temperature and particle size ratio of SiC particles on the mechanical and tribological properties of A357 composites reinforced with dual particle size SiC were investigated. The composites were prepared by melt-stirring assisted permanent mold casting technique with different weight fractions (3% coarse +3% fine, 4% coarse +2% fine, and 2% coarse +4% fine) of large and small size SiC particles. These three prepared composites are referred as DPS1, DPS2 and DPS3 composites. The solutionizing temperature was maintained constant at 540 ?C for 9 h while the aging was done at 160 ?C, 180 ?C and 200 ?C (T6 treatment) for 6 h. Optical and scanning electron microscopy studies showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. High-resolution transmission electron microscopy images showed formation of uniformly dispersed needle-like phase and spherical shaped -Mg2Si precipitates under peak aging conditions. Compared to T6 treated A357 alloy, the T6 treated DPS A357 composites showed improved yield strength, tensile strength, hardness and wear resistance. Among the three composites, hardness and wear resistance of T6 treated DPS2 composite was found to be significantly higher when compared to the other two composites (DPS1 and DPS3). Ratio of large particles to small particles also seems to effect the mechanical and tribological properties. Presence of more small particles was found to be good for strength and ductility whereas more large particles were found to be good for hardness and wear resistance. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license