Faculty Publications
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Item A Review on Mechanical and Microstructure Properties of Reinforced Concrete Exposed to High Temperatures(Springer, 2021) Goudar, S.K.; Santhosh, S.K.; Das, B.B.This paper presents the recent research progress on the response of concrete exposed to fire or high temperatures. The main highlight of this review paper is a compilation of previously reported data regarding the variations in mechanical properties and microstructure properties of concrete when exposed to high temperatures. The concrete structures get deteriorated at the macro- and microscopic levels due to high-temperature exposure. The macro-level damages can be measured with degradation in mechanical properties such as the reduction in compressive strength, weight loss, changes in elastic properties, reduction of bond strength in reinforced concrete, etc. The macro-cracks on the surface of concrete causes spalling which can be observed after exposing the concrete samples to more than 300 ℃. The compressive strength of the concrete reduces slightly till 400 ℃, and when the temperature increased to 600 ℃, there was an exponential reduction in the compressive strength of concrete. Another important parameter is bond strength degradation, which plays a crucial role in durability issues. To understand the deterioration phenomenon and changes in mechanical properties, the changes at the level of the microstructure of concrete need to be understood. Dehydration of products causes deterioration of mechanical properties and weight loss of concrete when exposed to high temperatures. At different temperatures, the microstructure changes and the response of hydration products such as calcium hydroxide (CH), CSH gel, unhydrated cement and capillary water reported by previous researchers are compiled and discussed. © 2021, Springer Nature Singapore Pte Ltd.Item Influence of Impact Angle and Temperature on Solid Particle Erosion Behavior of Titanium-31(Springer Nature, 2024) Behera, N.; Chandramouli, T.V.; Aprameya, C.R.; Ramesh, M.R.The present work shows the effects of impact angles and temperatures on volumetric erosion loss of titanium-31 alloy. An erosion tester was used to perform the erosion tests with temperatures (200, 400, 600, and 800 °C) and impact angles (30°, 60°, and 90°). The alumina particles (Al2O3) are used as an erodent particle with an average particle size of 50 μm. The microhardness, porosity, and surface roughness of titanium-31 alloy are evalu-ated. SEM/EDS and XRD were used to analyze tita-nium-31 alloy eroded samples. The weight loss method and 3D profilometer determined the volumetric erosion loss. The microhardness of titanium-31 alloy is found to be 337 ± 15HV0.3. The Volumetric erosion loss of tita-nium-31 alloy increased with increasing temperatures from 200 to 800 °C, whereas decreased with increasing impact angle from 30° to 90° for all temperatures. The volumetric erosion loss is higher at a 30° impact angle and lower at a 90° impact angle for all temperatures. As a result, titanium-31 alloy shows the ductile erosion mode for all temperatures. The volumetric erosion loss at 30° impact angles is due to micro-cutting and plough-ing, whereas deep crater, groove, and raised lips are for 90° impact angles. The results of volumetric erosion loss obtained by the weight loss method exhibit a good cor-relation with a 3D optical profilometer. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.Item High temperature tribological studies of cold sprayed nickel based alloy on low carbon steels(Elsevier Ltd, 2019) Padmini, B.V.; Mathapati, M.; Niranjan, H.B.; Sampathkumaran, P.; Seetharamu, S.; Ramesh, M.R.; Mohan, N.The boiler steels of grades SAE213 T11 and T22, find extensive applications in heat exchanger tubes, paper and pulp, chemical industries and refineries. Further, these steels are also used in shafts, cylinders, bearings, and in automotive transmission parts and these aspects are less explored. They experience low wear life in specific components, both at room and slightly higher temperature regimes. In order to protect them from these damages, coatings are deployed involving many techniques like HVOF, Plasma spray, Cold spray etc. so that the life of the components get extended. In cold spray coatings, the powders are fed at very high impact velocities of up to 1200 m/s on the substrate and undergo plastic deformation during the impact. There is no oxidation of the powder takes place during the process, as the coating is done at very less temperature and this is one of the lead characteristic of cold spray technique. This particular work mainly focuses on evaluating the tribological behaviour of nickel based super alloy powder on T11 and T22 low alloy steels by cold spray method, using pin on disc machine both at room temperature as well as at 200, 300 and 400 °C. The associated tests such as hardness, porosity, and microstructure have been undertaken to support the wear data. The wear damage assessment has been carried out using scanning electron microscope to arrive at the mechanism and also to give credence to the wear data. © 2019 Elsevier Ltd.Item High-Temperature Sliding Wear Characterization Studies of AISI 316 L(N) by Surface Profilometry(Springer Science and Business Media Deutschland GmbH, 2020) Aruldev, N.; Parthasarathi, N.L.; Rajasekaran, B.; Borah, U.The major construction material in the Prototype Fast Breeder Reactor (PFBR) is AISI-type 316 L(N) austenitic stainless steel due to its good mechanical properties and compatibility with liquid sodium.Sliding wear experiments were carried out at various temperatures up to 550 ℃ at constant load (20 N) and sliding speed (0.8 m/s) using a pin-on-disc test rig as per the ASTM standard G99-05. Analysis of the test results presented that the wear increased considerably with the temperature. The characterization of worn surface topography is done by a complete profilometry study using Talysurf CLI 1000 surface profilometer. The 3D surfaces were captured both by induction mode by diamond stylus as well as non-contact high-resolution confocal point gauge having range of 3000 μm with 0.25 nm resolution was used for surface profiling. The cold-welded surfaces were analysed by the profilometer, and the geometry of the deposit on the wear track was analysed by the profilometer. The roughness parameters were correlated with the amount of wear data obtained from the experiments at various testing temperatures. As the temperature increases during the sliding wear, the material loss is presented with more furrows resulting in enhanced surface roughness values. © 2020, Springer Nature Singapore Pte Ltd.Item Studies on concrete cylinders subjected to elevated temperatures(2010) Babu Narayan, K.S.; Anil Kumar, G.; Chandrakala, C.; Shashikumar, H.M.; Venkataramana, K.; Yaragal, S.C.; Chinnagiri Gowda, H.C.; Reddy, G.R.; Sharma, A.Concrete is a poor conductor of heat, but can suffer considerable damage when exposed to fire. Concrete in structures is likely to be exposed to high temperatures during fire. The relative properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. Unraveling the heating history of concrete is important to forensic research or to determine whether a fire exposed concrete structures and its components are still structurally sound or not. Assessment of fire damage concrete structures usually starts with visual observation of color change, cracking and spalling. On heating, a change in color from normal to pink is often observed and this is useful since it coincides with the onset of significant loss of concrete strength. This work reports the characteristics of concrete at elevated temperatures. Popular normal strength grades (M20, M25, M30, M35, M40 and M45) produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm diameter and 300mm height cylinders) to obtain more meaningful and realistic data. In the preliminary phase 150 mm diameter and 300mm height cylinders were cast, cured and tested by destructive method for gathering data on strength characteristics. Later these test samples were subjected to elevated temperatures ranging from 100°C to 800°C, in steps of 100°C with a retention period of 2 hours. After exposure, weight losses were determined and then again destructive tests were conducted to estimate the residual split tensile strength. Test results indicated that weight and strength significantly reduces with an increase in temperature. © 2010 CAFET-INNOVA TECHNICAL SOCIETY. All rights reserved.Item Strength retention characteristics of concrete cubes subjected to elevated temperatures(2010) Yaragal, S.C.; Clarke, K.S.; Mahesh Babu, K.; Ashokumar, S.; Venkataramana, K.; Babu Narayan, K.S.; Chinnagiri Gowda, H.C.; Reddy, G.R.; Sharma, A.Concrete in structures is likely to be exposed to high temperatures during fire. The relative properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great interest to the designer. Physical changes like cracking, colour change, spalling and chemical changes like decomposition of Ca(OH)2 and the C-S-H gel take place when subjected to elevated temperatures. This work reports the characteristics of concrete at elevated temperatures. Popular normal strength grades (M20, M25, M30, M35, M40 and M45) produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes) to obtain more meaningful and realistic data. In the preliminary phase 150 mm cubes were cast, cured and tested by destructive method for gathering data on strength characteristics. Later these test samples were subjected to elevated temperatures ranging from 100°C to 800°C, in steps of 100°C with a retention period of 2 hours. After exposure, weight losses were determined and then again destructive tests were conducted to estimate the residual compressive strength. Test results indicated that weight and strength significantly reduces with an increase in temperature. © 2010 CAFET-INNOVA TECHNICAL SOCIETY.Item Studies on normal strength concrete cubes subjected to elevated temperatures(2010) Yaragal, S.C.; Babu Narayan, K.S.; Venkataramana, K.; Kulkarni, K.S.; Gowda, H.C.C.; Reddy, G.R.; Sharma, A.Concrete in structures is likely to be exposed to high temperatures during fire. The probability of its exposure to elevated temperatures is high due to natural hazards, accidents and sabotages. Therefore, the performance of concrete during and after exposure to elevated temperature is a subject of great importance and interest to the designer. Popular normal strength grades of concrete produced by Ready Mix Concrete (RMC) India, Mangalore have been used in production of test specimens (150 mm cubes), cured and tested by destructive method for gathering data on strength characteristics. Later, these test samples were subjected to elevated temperatures ranging from 100 C to 800 C, in steps of 100 C with a retention period of 2 hours. After exposure, weight losses and the residual compressive strength retention characteristics are studied. Test results indicated that weight and strength significantly reduces with an increase in temperature. Residual compressive strength prediction equations are proposed for normal strength concretes subjected to elevated temperatures.Item High temperature performance of self-compacting high-volume fly ash concrete mixes(2011) Amrutha; Nayak, G.; Narasimhan, M.C.; Rajeeva, S.V.Quite often, concrete in structures is likely to get exposed to high temperatures, including an incident of fire. The strength-retention properties of concrete after such an exposure are of great importance in terms of the serviceability of buildings. This paper presents an experimental study on the strength retention and impermeability aspects of a set of self compacting, high-volume fly ash concrete mixes under elevated temperatures. Five selfcompacting concrete mixes with a higher 60% level of cement replacement with fly-ash, are designed and the effects of elevated temperatures, in the range of 200-800 C, on the physical, mechanical and durability properties of these mixes are assessed. The assessment is in terms of the weight losses and the reduction in the compressive strengths of concrete cubes and split tensile strengths of concrete cylinders. The durability characteristics are assessed in terms of RCPT test results on these mixes. Performances of these self compacting concrete mixes (SCC) at elevated temperatures are also compared with two normally-vibrated concrete mixes (NCs) of an equivalent M30 strength grade. Test results indicate that weight of the specimens significantly get reduced with an increase in the level of elevated temperature, with sharp variations beyond 600 C. The experimental results also show that large improvements against chloride-ion penetration and better strength-retention at higher temperatures can be realized with self-compacting high-volume fly-ash concrete mixes additionally admixed with GGBFS and silica fume.Item Fabrication and high-temperature structural characterization study of porous anodic alumina membranes(2012) Choudhari, K.S.; Sudheendra, P.; Udayashankar, N.K.Porous anodic alumina (PAA) membranes with highly ordered array of nanopores were prepared by twostep anodization process. Studies on structural and thermal properties and the thermal stability of the prepared PAA membranes were carried out. Investigation using scanning electron microscopy, atomic force microscopy, X-ray diffraction, thermal analysis and infrared spectroscopy was performed on the prepared PAA membranes at room temperature and in the temperature range 600-1,400 °C. The as-prepared PAA membranes revealed the amorphous nature. Polycrystalline PAA membranes were obtained by annealing carried out at different temperatures. Annealing study confirmed that the heat treatment transformed the amorphous PAA membranes to their crystalline phases, namely, ?-alumina at about 870 °C and then to ?-alumina around 1,250 °C. © Springer Science+Business Media, LLC 2011.Item Diluted magnetism in Mn-doped SrZnO2 single crystals(American Institute of Physics Inc., 2013) Rahman, M.R.; Koteswararao, B.; Huang, S.H.; Kim, K.; Chou, F.C.We have investigated the magnetic properties of Mn- and Cu-substituted SrZnO2 single crystals (SrZn1-xMnxO2 and SrZn1-xCuxO2). We observed signatures of weak ferromagnetism as a sharp increase of magnetic susceptibility below 5 K even in the low-percentage (x = 0.01) of Mn-substituted single crystals. Magnetic susceptibility data measured parallel or perpendicular to the ab-plane yield anisotropic behavior with Curie-Weiss temperature of about -320 K and -410 K, respectively, suggesting the presence of strong antiferromagnetic couplings among Mn at high temperatures, similar to the Mn-doped ZnO and Fe-doped BaTiO3. In contrast, the SrZn0.99Cu0.01O 2 crystal shows paramagnetic behavior down to 2 K. © 2013 AIP Publishing LLC.
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