Faculty Publications
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Item Recent trends and laboratory performance studies on FAM mixtures: A state-of-the-art review(Elsevier Ltd, 2018) Suresha, S.N.; Ningappa, A.In recent years, the testing and evaluation of Fine Aggregate Matrix (FAM) mixtures using Dynamic Shear Rheometer (DSR) which has drawn a growing interest because of its simplicity, reproducibility, and flexibility. However, several research studies have employed various sets of test methods for performance evaluation of FAM mixtures that calls for a critical review of the procedures that have been followed to date. This state-of-the-art review article presents the current work regarding material selection, sample fabrication methods and test methods to evaluate viscoelastic, fracture and healing properties of FAM mixtures. © 2018 Elsevier LtdItem An alloy containing 49 at.% aluminium was heat treated at different temperatures within the ? + ? two-phase field to get five different volume fractions of lamellar constituent. Creep studies were carried out on these samples at five different temperatures in the interval between 1023 and 1223 K, by impression creep technique using four levels of stresses at each temperature. For a given temperature and stress, steady state impression velocity decreased with increasing volume fraction of lamellar constituent. Activation energy for steady state creep increased linearly with lamellar content from 185 kJ/mol at 22 vol.% to 362 kJ/mol at 100 vol.%. The stress exponent was found to be around 1.2 in all the cases. The results show that a fully lamellar structure has a superior behaviour where creep is an important factor.(Carl Hanser Verlag, Effect of microstructure on the impression creep of two-phase titanium aluminide) Prasad Rao, P.; Swamy, K.Shivananda1995Item Investigation into creep behaviour of Sn-40%Pb alloy using impression creep method(2009) Udaya Prasanna, H.U.; Udupa, K.R.; Prabhu, K.N.The creep behaviour of Sn-40%Pb hypereutectic alloys cast in the molds made of different materials was investigated using impression creep technique in the temperature range from zero to 32 °C and under the punching stress of 50 MPa. The creep curves.ie, profiles of indentation depth against time are generated and steady state creep rates (SSCRs) are determined. Activation energy was calculated knowing creep rates at different temperature levels. Standard metallographic technique was used to determine the grain size of alloys which were poured into different molds. It was found that SSCR, at all the temperature levels of testing, is a function of grain size of the material. The activation energy being in the range of 10kJ/mol -12 kJ/mol, suggests that the probable creep mechanism is dislocation glide aided by vacancy diffusion. Results of the experiments are discussed.Item New manufacturing process of carbon-carbon composites and their mechanical properties(2011) Naik, P.S.; SurendranathanThis paper presents the synthesizing of carbon-carbon (CC) composites by preformed yarn (PY) method, by varying the percentage of carbon fiber volume. The PY used is carbon fiber bundle surrounded by coke and pitch which is enclosed in nylon-6. Three types of samples with fiber weight fractions of 30%, 40% and 50% respectively, are fabricated and tested. In each case, the PY is chopped and filled into a die of required shape and hot pressed at 600°C to get the carbonized composite. To obtain the graphitic structure, the specimen is heat treated at 1800°C followed by soaking for two hours. Further, one cycle pitch impregnation is done by hot isostatic pressing, to eliminate the voids. The characteristics such as hardness, compressive strength and creep, are studied. It is observed that, as the carbon fiber percentage increases the properties also improved, provided sintering is done at fairly higher temperatures. The superiority of the new class of CC composites made by the proposed PY technique over those obtained by the conventional methods is also demonstrated. © 2011 CAFET-INNOVA TECHNICAL SOCIETY.Item Indentation creep studies to evaluate the mechanical properties of stainless steel welds(Taylor and Francis Ltd. michael.wagreich@univie.ac.at, 2016) Udaya Prasanna, H.U.; Udupa, K.R.Size being limited for preparing standard specimens for mechanical tests, the weld poses problems to researchers and scientists in estimating the strength parameters and workhardening coefficients. The integrity of the weld is difficult to probe into, particularly when the temperature of operation is much higher than the room temperature. The indentation creep test route is successfully tried by the authors to present a detailed commentary on the mechanical properties of a stainless steel weld at different test temperatures using a methodology whereby the creep test results are correlated to the compression test results and correlation equations developed. As the indentation creep tests can be carried out on a small-sized sample, the method enables one to carry out only this test to judge the mechanical properties of the welds. © 2015 Engineers Australia.Item Time-dependent safety performance of reinforced concrete structures(Emerald Group Holdings Ltd., 2020) Worabo Woju, U.W.; Balu, A.S.Purpose: Performance of the structure depends on design, construction, environment, utilization and reliability aspects. Other factors can be controlled by adopting proper design and construction techniques, but the environmental factors are difficult to control. Hence, mostly in practice, the environmental factors are not considered in the analysis and design appropriately; however, their impact on the performance of the structures is significant along with the design life. It is in this light that this paper aims to perform the time-dependent performance analysis of reinforced concrete structures majorly considering environmental factors. Design/methodology/approach: To achieve the intended objective, a simply supported reinforced concrete beam was designed and detailed as per the Euro Code (EC2). The time-dependent design parameters, corrosion parameters, creep and shrinkage were identified through thorough literature review. The common empirical equations were modified to consider the identified parameters, and finally, the time-dependent performance of reinforced concrete beam was performed. Findings: Findings indicate that attention has to be paid to appropriate consideration of the environmental effect on reinforced concrete structures. In that, the time-dependent performance of reinforced concrete beam significantly decreases with time due to corrosion of reinforcement steel, creep and shrinkage. Originality/value: However, the Euro code, Ethiopian code and Indian code threat the exposure condition of reinforced concrete by providing corresponding concrete cover that retards the corrosion initiation time but does not eliminate environmental effects. The results of this study clearly indicate that the capacity of reinforced concrete structure degrades with time due to corrosion and creep, whereas the action on the structure due to shrinkage increases. Therefore, appropriate remedial measures have to be taken to control the defects of structures due to the environmental factors to overcome the early failure of the structure. © 2020, Emerald Publishing Limited.Item Study of Rheological and Creep Recovery Properties of Asphalt Binder Modified with Waste Toner(American Society of Civil Engineers (ASCE), 2020) Showkat, B.; Suresha, S.; Ningappa, N.Large quantities of waste toner (WT) are generated annually either due to the incessant manufacturing process or from copying machines. Disposal of WT is primarily in landfills, which deteriorates the environment. This study attempts to overcome this predicament by utilizing WT for asphalt pavement construction by means of incorporating it in asphalt binder. The effect of WT on rheological properties of asphalt binder was explored in this research. An unmodified asphalt binder AC30 was adopted and modified with three contents of WT (7%, 14%, and 21% by weight). Tests including high-temperature performance grade (PG), temperature sweep, frequency sweep, and multiple stress creep and recovery (MSCR) were performed in this study. Mixing and compaction temperature was observed to marginally increase on introduction of WT. The addition of WT was perceived to cause a bump in high-temperature PG of AC30 binder. Improvement in rutting resistivity of AC30 binder was recorded. However, a degradation of fatigue resistance was observed. Master curves indicated an enhancement in complex shear modulus (|G*|) and reduction in phase angle (?) at low frequencies due to incorporation of WT. However, at higher frequencies, convergence of the curves was observed. MSCR analysis indicated that WT addition enhanced percent recovery (R) and decreased nonrecoverable creep compliance (Jnr). Overall, the addition of WT was observed to cause changes in the rheological behavior of AC30 binder and an improved resistance to rutting at high temperature. © 2020 American Society of Civil Engineers.Item Creep cavitation damage of K-type thermocouples(Elsevier Ltd, 2023) Rakshan Kumar, J.K.; Bhattacharjee, D.; Dsilva, P.; Praveen, R.; Hegde, S.R.This work investigates premature failure of K-Type thermocouples that were used in a chemical processing plant. The work presents a detailed metallurgical failure analysis involving, site visit, visual inspection, metallography, optical microscopy, scanning electron microscopy, and fractography. The analysis reveals that the thermocouple wires endured creep cavitation damage during service and eventually failed by creep-rupture. Interestingly, the influence of creep on the degradation of industrial thermocouples is not detected and reported thus far. By presenting analytical stress calculations using temperature dependent materials properties, the current work reveals that the thermal expansion mismatch between various materials of thermocouple causes high tensile stresses in the thermocouple wires during elevated temperature services. The work concludes that high tensile stresses at elevated temperature operation caused premature creep failure of the K-type thermocouples. © 2022Item Low stress creep response of PTFE sealants applied to PEM fuel cells(John Wiley and Sons Inc, 2024) Kumar, V.; Koorata, P.K.Viscoelastic properties of polytetrafluoroethylene (PTFE) play a crucial role in forecasting its long-term behavior in engineering applications. An attempt is made to explore the viscoelastic properties of PTFE sealants that are utilized in polymer electrolyte membrane fuel cell (PEMFC). It is to be noted that PTFE sealants are vulnerable to creep under constant loading at elevated temperatures. Moreover, the creep of sealants will lead to leakage of reactants from the cell, which affects the performance of PEMFC. PTFE is an excellent choice as a sealant material in low-temperature polymer electrolyte membrane fuel cell (LT-PEMFC), which operates in the temperature range of 60–80°C. PTFE can be prominently used as sealants in high-temperature polymer electrolyte membrane fuel cell (HT-PEMFC), as it possesses no significant change in its physical properties within the temperature range of −150 to 300°C along with the working conditions of HT-PEMFC. In LT-PEMFC, the sealants will typically be subjected to low stresses in the range of 1–5 MPa. In this article, the creep response of PTFE sealant material is extensively studied at various temperatures of 25 (room temperature), 35, 45, 55, and 65°C and at three stress levels of 2, 3, and 4 MPa. The time–temperature superposition principle is utilized to develop master curve at a reference temperature of 25°C, to forecast long-term creep characteristics of PTFE sealants. Moreover, the master curve for creep compliance is developed for 4.5 h. © 2024 Wiley Periodicals LLC.