Faculty Publications

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Author: search.filters.author.Ravishankar, K.S.

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    Mechanical Properties and Characterization of Hybrid Composition Reinforced with Natural Fibers
    (Springer, 2024) Dayanand; Bheemanalli, A.; Sangamesh; Gurumurthy, B.M.; Ravishankar, K.S.
    The current work involves fabrication of hybrid composite by using sisal and roselle natural fibers as reinforcing elements or fillers with epoxy resin (LAPOX L12) and Hardener or catalyst (K6) by hand lay-up method with a 35:75 ratio. Enhancement of mechanical properties in polymer hybrid composites is exhibited by the possible intermixture of roselle and sisal fibers [1]. The effect of loose and continuous fiber (CLFR) and woven mat fiber-reinforced (WMFR) hybrid composite laminates were tested to evaluate the mechanical and physical performance exhibited by them. Water absorption test along with thickness swelling test was carried out and the data was recorded for reference. The tensile strength and modulus of WMFR composite (dry) are reduced by 35% and 17%, respectively, and compressive strength and modulus of WMFR composite (dry) are reduced by 17% and 33%, respectively. It was also noticed that Erosion rate of the samples increases as the increase of sand particle size, sand concentration, and erosion rate is high in case CLFR (4.93%) composite. Water absorption is high in CLFR than in WMFR composite. SEM analysis revealed that fiber pull-out, de-bonding, matrix softening, fiber rupture, sliding tracks, debris, and cracks were the reasons for the failure of composites. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
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    Effect of Surathkal Beach Sand on Mechanical Properties of Polymer Composites
    (Springer, 2025) Bajpai, N.K.; Bheemanalli, A.; Rajole, S.; Sondar, P.; Ravishankar, K.S.
    Although beach sand is available in abundance, its usage in the structural applications has been limited. Prior studies betray that the sand taken in a nanoparticle size for the preparation of polymer nanocomposites yields in improved mechanical and physical polymer properties, also addition of nanophase structure to the polymer has been found to be increasing toughness and cyclic fatigue resistance of the epoxy polymer. The present work uses beach sand as the filler for the reinforced epoxy matrix. Sand-epoxy composites, with different particle sizes (150, 300, 420 μm) and varying filler percentages (5, 10 and 15%) were investigated for mechanical properties. Beach sand nano-particles were considered as high-potential filler materials in the present study owing to their molecular size in a reinforcement and polymer nanocomposites made out of them offer the possibility to develop novel materials with unique properties. As a result, the mixture of 10% filler sand with the particle size of 150 μm showed highest tensile and compressive strength and addition of sand particles beyond 10% led to creation of voids, thereby resulting in decreased strength. It is also noticed that, uniform distribution of sand particles within the matrix and interfacial bonding was the main contributing factors for the increased mechanical properties. The FE analysis of sand epoxy composites was also carried out using ABAQUS finite element analysis tool for flexural failure analysis. Simulations were recorded at various instances till failure. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2025.
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    Development of austempered ductile iron for high tensile and fracture toughness by two step austempering process
    (2008) Ravishankar, K.S.; Udupa, K.R.; Prasad Rao, P.P.
    During conventional austempering austempered ductile iron showed a decrease in fracture toughness with increasing austempering temperature, while the tensile toughness increased. Thus high fracture toughness was associated with low tensile toughness. A two step austempering treatment was then adopted where the samples were first au stem p ered at 3000e for sh ort peri 0 ds varyi ng from 10m in utes to 60 minutes, and then subsequently transferred to a second furnace at 4000e for further austempering for 2 hours. It was found that this resulted in fine ferrite grain size, high carbon content of the retained austenite together with increased stability of the austenite. Under such conditions it was possible to achieve an excellent combination of high fracture toughness and high tensile toughness.
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    Effect of reversion heat treatment on the mechanical properties of thermally embrittled UNS S32760 duplex stainless steel
    (Trans Tech Publications Ltd ttp@transtec.ch, 2015) Natesh, M.; Shamanth, V.; Ravishankar, K.S.
    Duplex Stainless Steels contain very high chromium contents (19-30% by weight) and exhibit excellent corrosion resistance and extremely good mechanical properties. Embrittlement of duplex stainless steels due to precipitation of αʹ upon prolonged exposure in the temperature range of 280°C to 500°C has been a serious limiting factor for its long term usage in the nuclear industry, where the operating temperatures of cooling pipes is around 300°C. In this investigation, the effect of reversion heat treatment on the mechanical properties of a thermally embrittled duplex stainless steel has been studied. The specimens were solutionized, aged and then reversion treated for varying periods. The aged specimens showed significant increase in tensile strength and decrease in ductility in comparison to the ones in solutionized condition. The specimens which were reversion treated showed marginal decrease in tensile strength and significant increase in ductility after 5 minutes of holding time. As the holding time increased, the tensile strength rapidly decreased and ductility increased initially up to 30 minutes of reversion, after which there was no significant change in strength and ductility. © (2015) Trans Tech Publications, Switzerland.
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    Effect of Austempering Heat Treatment Parameters on the Microstructure and Dry Sliding Wear Behaviour of AISI 9255 High Silicon Steel
    (Elsevier Ltd, 2017) Acharya, P.A.; Syamkrishna, P.; Ravishankar, K.S.
    The present investigation is focused to evaluate the dry sliding wear behavior of AISI 9255 high silicon steel austempered at different temperatures and durations. Here three batches of cylindrical test specimens were prepared from as-received high silicon steel and were austenitized at 900 °C for 30 minutes, followed by austempering heat treatment in a salt bath maintained at temperatures 300, 350 and 400 oC for durations between 1 to 4 hours. The samples after austempering were cooled to room temperature in open air. The microstructural analysis was done by using optical microscopy, scanning electron microscopy and x-ray diffraction (XRD) and also hardness test was done using micro vickers hardness tester and correlated to the specific wear rate of the austempered steel. Results indicate that specific wear rate decreases with increase in austempering time and increases with increasing temperature. Specific wear rate was found to be lowest at austempering temperature of 300 °C, which exhibits lower ausferritic structure having high hardness. At higher austempering temperature 400 °C, specific wear rate was observed to be high because of upper ausferritic microstructure having lower hardness. Results reveal that the material with high hardness shows high wear resistance i.e., the one austempered at 300 °C showed superior sliding wear resistance than the rest. © 2017 Elsevier Ltd.
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    Effect of Heat Treatment on the High Cycle Fatigue Behaviour of S2205 Duplex Stainless Steels
    (Elsevier Ltd, 2017) Shamanth, V.; Kumar, P.; Ravishankar, K.S.
    This paper deals with the effect of heat treatment on the high cycle fatigue behavior of duplex stainless steels. In this investigation the specimens were annealed, aged, reversion heat treated and re-aged for varying periods. The results obtained showed that the microstructure plays an important role in the change in fatigue lives. The fatigue resistance was high in the aged and re-aged heat treated condition because of the presence of alpha, alpha prime and some molybdenum rich chromium nitride precipitates in their ferrite matrix. While in the annealed and reversion heat treated condition the samples were free from the precipitates and also there was no much difference in the hardness values of austenite and ferrite phases, hence there was a significant change in their fatigue lives when compared to that of the embrittled samples. © 2017 Elsevier Ltd.
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    Influence of Austempering Heat Treatment on Microstructure and Mechanical Properties of Medium Carbon High Silicon Steel
    (Institute of Physics Publishing michael.roberts@iop.org, 2017) Acharya, P.; Ravishankar, K.S.
    In the present investigation, the influence of austempering heat treatment on the microstructure and mechanical properties of medium carbon high silicon steel was evaluated. The test specimens were machined from the as-received steel and were first austenitised at 900 °C for 45 minutes, followed by austempering heat treatment in salt bath at various temperatures 300 °C, 350 °C and 400 °C for a fixed duration of two hours, after that those specimens were air-cooled to room temperature. The characterization studies were carried out using optical microscope, scanning electron microscope (SEM) and x-ray diffractometer (XRD) and then correlated to the hardness and tensile properties. Results indicate that, the specimens austempered at lower temperature i.e. at 300 °C, which offered high hardness, tensile strength and lower ductility (1857 MPa and 13.3 %) due to the presence of acicular bainite i.e. lower bainite and also some martensite in the microstructure. At 350 °C, reduction in the tensile strength and hardness was observed, but comparatively higher ductility, which was favored by the presence of bainite laths i.e. upper bainitic structure along with higher retained austenite content. Finally at 400 °C, reduction in both ductility and tensile strength was observed, which is due to the precipitation of carbides between the banite laths, however good strain hardening response was observed at austempering temperatures of 350 °C and 400 °C. © Published under licence by IOP Publishing Ltd.
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    Synthesis and comparison of mechanical behavior of fly ash-epoxy and silica fumes-epoxy composite
    (Institute of Physics Publishing michael.roberts@iop.org, 2017) Sangamesh, R.; Ravishankar, K.S.; Kulkarni, S.M.
    Present day innovation requires materials with a typical combination of properties that are not possible by conventional metal, alloys, ceramics and polymeric materials. Particulate reinforcements for polymers are selected with the dual objective of improving composite properties and save on the total cost of the system. The point of this study is to utilize and compare the mechanical properties of filler (fly ash and silica fumes) reinforced epoxy composites. The composites of different proportions by percentage of matrix (100%), fillers (5%, 10% and 15%) volume are developed using hand lay-up process are tested for tensile and compression, according to ASTM Standards. From these mechanical properties, the flexural analysis of these composites is simulated. And which are characterized by Scanning electron microscopy for the fracture surface study, which reveals the brittle fracture, this also conforms from the Finite element analysis (FEA). And the overall mechanical properties of the fly ash reinforced polymer composites were found to have better than silica fumes reinforced composites. © Published under licence by IOP Publishing Ltd.
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    Ballistic Impact Study on Jute-Epoxy and Natural Rubber Sandwich Composites
    (Elsevier Ltd, 2018) Sangamesh, R.; Ravishankar, K.S.; Kulkarni, S.M.
    Since ages, human beings have used different methods to protect themselves and their armors from the impact of bullets/projectiles by using structures made up of wood, metals, glass and sand bags etc. These protective structures are heavy and incur cost and inconvenience to transport. Of late, they are replaced by structures of polymers and their composites, because of their light weight and good corrosion resistance. Ballistic impact analysis of composite materials is necessary in order to establish their use in military, aerospace and automotive applications either through experimental studies or using modeling techniques. The aim of the present investigation is to model and analyze the behavior of composites for ballistic impact. Residual velocity, energy absorption and ballistic limit for three different materials Jute-Epoxy (JE), Rubber (Ru), Jute-Epoxy-Rubber sandwich (JRE) for three thicknesses (5, 10, 15mm) and at three velocities (150, 250, 350 m/s) is studied. The study exhibits a significant amount of energy absorption in rubber, almost 10 times as compared to JE plate. Also damage observed was ductile in the case of rubber, while brittle in JE. Sandwich composites (JRE) displayed energy absorption and ballistic limit on par with rubber plates. Thus the applicability of these sandwiches in ballistic impact is established as better energy absorbing protective target structures. © 2017 Elsevier Ltd.
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    Study on ballistic energy absorption capability of glass-epoxy and jute-epoxy-rubber sandwich composites
    (Trans Tech Publications Ltd ttp@transtec.ch, 2018) Rajole, S.; Ravishankar, K.S.; Kulkarni, S.M.
    High velocity impact analysis of natural fiber reinforced composites is essential as the trend is focused towards the development of light weight, environment-friendly, non-corrosive and economical materials. At present, the defence, aerospace and automobile sectors are using synthetic fiber composites which are expensive and non-eco-friendly. In the present study ballistic impact of jute-epoxy (JEC), glass-epoxy (GEC), jute-epoxy-rubber (JERC) sandwich composites are simulated with different thickness (1, 2 and 3 mm) and velocity variations (100, 200 and 300m/s) using Finite Element analysis software. Although different approaches to the analysis of the effect response of composite structures are available, numerical modeling is based on strict constitutive models is often preferred because it can provide valuable detailed information about the spatial and temporal distribution of damage during the impact. The ballistic parameters such as energy absorption, ballistic limit and fracture behaviors are predicted. The composite is made of 8 noded linear brick elements and the bullet/projectile is modeled as a discrete rigid element in which deformation behavior, energy absorption and penetration behaviors obtained are clearly represented. The simulation results predicted match well with the analytical results obtained. Among all the combination of the materials simulated, the sandwiches have better ballistic qualities. Energy absorption of sandwich(JERC) was found 67 percentage higher than GEC and 56 percentage higher than JEC laminate. In future, these materials can be the alternative materials for defence sector for bullet proofing. © 2018 Trans Tech Publications, Switzerland.