Browsing by Author "Ravishankar, K.S."

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A comparison of high temperature corrosion behaviour between uncoated, Ni-Cr-Mo and Ni-Cr-Al-Y coated 316 stainless steel in ZnCl2-KCl environment
(Elsevier B.V., 2025) Pooja, P.; Vijayan, V.; Ravishankar, K.S.; Madav, V.
High-temperature corrosion poses a significant challenge to the longevity and performance of materials in extreme environments. This study investigates the corrosion behavior of coated and uncoated 316 stainless steel (SS) in ZnCl2-KCl eutectic molten salt vapor at 600 °C. Contrary to expectations, the results indicate that uncoated 316 SS exhibits lesser corrosion compared to certain coated samples over prolonged exposure. Comprehensive analysis, including weight change measurements, electrochemical evaluations, and surface morphology examination, reveals the degradation mechanisms and the efficacy of coatings. Amongst the various materials used for study, NiCrMo coated 316SS showed least corrosion rate of 8.34 mpy and 3.2 mpy after 20 h and 100 h respectively. The findings provide insights into optimizing material protection strategies in harsh chloride containing molten salt environments. © 2025
Ballistic Impact Study on Jute-Epoxy and Natural Rubber Sandwich Composites
(2018) Sangamesh; 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.
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. Â© 2017 Elsevier Ltd.
Ballistic performance study of kevlar29 fibre reinforced polyester composite
(2019) Sangamesh, R.; Shivashankar, H.; Ravishankar, K.S.; Kulkarni, S.M.
Ballistic qualities of the material are important for the military defence barrier application for protection of military persons, their vehicles and equipment. In the present investigation ballistic performance of Kevlar29 fibre reinforced polyester composite (KPC) is analysed. A definite parametric study, taking into account various shape of projectiles (Flat-F, Spherical-S and Conical-C) impact on the composite target of different thicknesses (12, 16 and 20 mm). Impact velocity of the projectile considered for analysis 100-400 m / s. Ballistic parameters such as residual velocity, deformation and penetration behaviour are predicted. Conical projectile has more effect on the composite target compared to other projectile. Composite thickness influenced the energy absorption. The thickness increase from 12 mm to 20 mm which leads to increase in the energy absorption by almost 20%. � 2019 Trans Tech Publications, Switzerland.
Ballistic performance study of kevlar29 fibre reinforced polyester composite
(Trans Tech Publications Ltd ttp@transtec.ch, 2019) Sangamesh, R.; Hiremath, H.; Ravishankar, K.S.; Kulkarni, S.M.
Ballistic qualities of the material are important for the military defence barrier application for protection of military persons, their vehicles and equipment. In the present investigation ballistic performance of Kevlar29 fibre reinforced polyester composite (KPC) is analysed. A definite parametric study, taking into account various shape of projectiles (Flat-F, Spherical-S and Conical-C) impact on the composite target of different thicknesses (12, 16 and 20 mm). Impact velocity of the projectile considered for analysis 100-400 m / s. Ballistic parameters such as residual velocity, deformation and penetration behaviour are predicted. Conical projectile has more effect on the composite target compared to other projectile. Composite thickness influenced the energy absorption. The thickness increase from 12 mm to 20 mm which leads to increase in the energy absorption by almost 20%. Â© 2019 Trans Tech Publications, Switzerland.
Development of austempered ductile iron for high tensile and fracture toughness by two step austempering process
(2008) Ravishankar, K.S.; Udupa, K.R.; 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.
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.
Dissolution of alpha-prime precipitates in thermally embrittled S2205-duplex steels during reversion-heat treatment
(Elsevier, 2015) Shamanth, V.; Ravishankar, K.S.
Duplex stainless steels offer an attractive combination of strength, corrosion resistance and cost. In annealed condition duplex steels will be in thermodynamically metastable condition but when they are subjected to intermediate homologous temperature of ~475. °C and below significant embrittlement occurs, which is one of the key material degradation properties that limits its upper service temperature in many applications. Hence the present study is aimed to study the effect of reversion heat treatment and its time on mechanical properties of the thermally embrittled steel. The results showed that 60. min reversion heat treated samples were able to recover the mechanical properties which were very close to annealed properties because when the embrittled samples were reversion heat treated at an elevated temperature of 550. °C which is above the (?. +. ?') miscibility gap, the ferritic phase was homogenized again. In other words, Fe-rich ? and Cr-rich ?' prime precipitates which were formed during ageing become thermodynamically unstable and dissolve inside the ferritic phase. © 2015 The Authors.
Effect of Austempering Heat Treatment Parameters on the Microstructure and Dry Sliding Wear Behaviour of AISI 9255 High Silicon Steel
(2017) Palaksha, 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.
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 Â°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 Â°C, which exhibits lower ausferritic structure having high hardness. At higher austempering temperature 400 Â°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 Â°C showed superior sliding wear resistance than the rest. Â© 2017 Elsevier Ltd.
Effect of Heat Treatment on the High Cycle Fatigue Behaviour of S2205 Duplex Stainless Steels
(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.
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. Â© 2017 Elsevier Ltd.
Effect of machine scatter on the rotating bending fatigue life of materials
(De Gruyter peter.golla@degruyter.com, 2018) Banavasi Shashidhar, S.M.; Ravishankar, K.S.; Naik, P.S.
Rotating bending fatigue test results vary from specimen to specimen even if materials are tested in a standard laboratory set up because rotating bending fatigue life or fatigue strength depends upon various factors due to its dynamic action. One method of testing may be machine scatter (offset and angular misalignment). Angular misalignments are unavoidable in dynamic machines due to continuous operation leading to transverse vibrations in specimens. The magnitude of transverse vibrations was measured manually by dial gauge arrangement. Experiments were carried out until fracture either with smooth running conditions or with the effects of offset and angular misalignment. The enhanced effect of misalignments on fatigue life was done through the histogram normal distribution technique. There was a clear distinction between the appearances of the fracture surfaces between the specimens subjected to smooth running conditions and specimen vibration, which reveals general fatigue fracture phenomena and intergranular fatigue cracks, larger decohesion of graphite nodules and isolated cleavage facets. The manual technique used without any resistance strain gauges, as they were not efficiently sustainable under repetitive loads, helped in understanding the dynamic machine scatter on fatigue life in an economical way where there were lesser concentrations in these areas. © 2018 Walter de Gruyter GmbH, Berlin/Boston 2018.
Effect of reversion heat treatment on the mechanical properties of thermally embrittled UNS S32760 duplex stainless steel
(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 ?? 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.
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 Î±Ê¹ upon prolonged exposure in the temperature range of 280Â°C to 500Â°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 300Â°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. Â© (2015) Trans Tech Publications, Switzerland.
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.
Effect of thermal and surface chemical treatment on the cyclic oxidation behavior of 7039 aluminum alloy used in aerospace armor applications
(Elsevier Ltd, 2020) Fageehi, Y.; Saminathan, S.; Venugopal, G.; Valder, J.; Kumar, H.; Ravishankar, K.S.
7039 Aluminum alloy is subjected to artificial aging (T6 treatment) at temperatures namely 80, 100, 120, 140, 160 Â°C for various time periods up to 100 h. Based on the Brinell Hardness measurements the artificially aged alloys are categorized into three groups namely under aged, peak aged and overaged based. The specimens from the alloy groups are further subjected to cyclic oxidation measurements at temperatures namely 100, 200 and 300 Â°C. The cyclic oxidation measurements in atmospheric air, revealed that the pre temperature history of the artificially aged alloy has an influence on the cyclic oxidation behavior of the 7039 Aluminum alloy as the under aged alloy showed greater tendency for cyclic oxidation. A surface chemical treatment is employed to coat the alloy by CeO2ceramic coating through chemical bath technique. Cyclic oxidation tests, X-RD and SEM analysis of the 7039 Aluminum alloy specimens with and without ceramic coatings are carried out. Interestingly, the ceramic coated 7039 Aluminum alloy showed greater resistance to oxidation when compared to that of artificially aged alloy specimens. Â© 2020 Elsevier Ltd. All rights reserved.
Experimentation on dynamic compressive response of bio-inspired helicoidal structured Basalt/Hemp/polyurethane rubber sandwich composites
(Elsevier Ltd, 2024) Gowda, D.; Mahesh, V.; Mahesh, V.; Ravishankar, K.S.
In this article, to incorporate sustainability, enhance recyclability and achieve a good trade-off between the cost-weight-energy absorption performance, bioinspired helicoidal structured Basalt (B)/Hemp (H)/Polyurethane (PU) rubber hybrid composites are proposed, and their dynamic compressive response is experimentally investigated using a split Hopkinson pressure bar (SHPB) setup. These composites' high strain rate performance subjected to both in-plane and through-plane directions are studied. The strain rates ranging from 4254 to 10,750 s-1 are achieved by varying the striker bar's input pressure. In addition, the performance of the bioinspired helicoidal design is compared against the uniform monolithic and hybridised fibers laminated structures. The experimental results suggest that the dynamic compressive properties of Basalt/Hemp-helicoidal (BH-helicoidal) laminates were on compar with that of B-laminates, achieving an almost 30% weight reduction. The optimised fiber orientation at a helical angle of 120 enhances interlaminar shear strength, mitigating buckling and delamination failures, thereby improving BH-helicoidal laminate's structural integrity and dynamic compressive properties. Further, the through-plane dynamically loaded samples displayed better compressive properties due to increased stiffness than in-plane samples. The PU rubber matrix was thermally softened at higher strain rates, enhancing the flow stress. The strengthening mechanism of the proposed composites was evaluated through Cowper-Symonds, strain rate sensitivity, and thermal activation volume parameter. Macroscopic and microscopic imaging was proposed to understand the damage behaviour of laminates as a function of loading direction. Overall, BH-helicoidal laminate is favoured for ballistic application due to its cost-effectiveness and sustainable design. © 2024 Elsevier Ltd
High temperature corrosion behaviour of stainless steels and Inconel 625 in hydroxide salt
(Elsevier Ltd, 2021) Pooja, M.; Ravishankar, K.S.; Madav, V.
Biomass gasification had proven to be an alternative source of energy to coal gasification. However, it requires high temperatures of about 1000Â°C for biomass drying and reduction. On the other hand, to reduce the oxidation and corrosion of gasifier structural materials it is important to keep the gasifier working temperature as low as possible. One effective way of keeping the reduction temperature low is to use molten salts as catalyst during biomass gasification. However, by virtue, molten salts cause several corrosion issues in ferrous alloys. In this context, the present study investigates the effect of hydroxide molten salt on the corrosion behaviour of stainless steels such as 316 and 310 and Inconel 625. The samples exposed to the salt at 700Â°C for about 48 h was analysed for corrosion using weight loss method. A scanning electron microscopy analysis of the exposed samples revealed the depth of corrosion and change in microstructure due to molten salt attack. Although all the selected materials suffered severe corrosion, among all, Inconel 625 show higher corrosion resistance. Â© 2021 Elsevier Ltd. All rights reserved.
Impact analysis of natural fiber and synthetic fiber reinforced polymer composite
(2018) Sangamesh; Ravishankar, K.S.; Kulkarni, S.M.
Impact analysis of the composite structure is essential for many fields like automotive, aerospace and naval structure which practically difficult to characterize. In the present study impact analysis of carbon-epoxy (CE) and jute-epoxy (JE) laminates were studied for three different thicknesses. The 3D finite element model was adopted to study the impact forces experienced, energy absorption and fracture behavior of the laminated composites. These laminated composites modeled as a 3D deformable solid element and an impactor at a constant velocity were modeled as a discrete rigid element. The energy absorption and fracture behaviors for various material combinations and thickness were studied. The fracture behavior of these composite showed progressive damage with matrix failure at the initial stage followed by complete fiber breakage. � 2018 Author(s).