Faculty Publications
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Item Identification of invalid time-delay-groups using discriminant and Jacobian-determinant in acoustic emission PD source localisation(Institution of Engineering and Technology journals@theiet.org, 2017) Antony, D.; Punekar, G.S.The key problem in locating a source of partial discharge (PD) using the acoustic emission technique is the error in estimating the signal arrival time from the source to the multiple sensors. When the time difference of arrival approach is used for the PD-source-localisation, some of the measured time-delay-groups will have solution for the time-difference equation in the complex-number-field. This is due to the significant error in the arrival time estimation. Such time-delay-groups should be considered to be invalid. In this study, a function is proposed for identifying the invalid time-delay-groups for the fixed set of coordinates of four sensors and the specific velocity of the acoustic signal used. The negative sign of this function value indicates that the solution is in the complex-number-field. An alternative method for identifying the invalid time-delay-groups is by using Newton's method. The multiple sign changes of the Jacobian-determinant in the iterations of Newton's method shows that the solution is in the complex-number-field. The proposed methods have been tested with data from the existing literature, and results have confirmed the efficacy of these methods in the identification of the invalid time-delay-groups. Discarding such groups of time delays improves the accuracy of statistical PD-source-localisation. © 2016, The Institution of Engineering and Technology.Item Effects of transformer-oil temperature on amplitude and peak frequency of partial discharge acoustic signals(Institute of Electrical and Electronics Engineers Inc., 2018) Shanker, T.B.; Nagamani, H.N.; Antony, D.; Punekar, G.S.The behavior of partial discharge (PD) acoustic emission (AE) signals in the transformer oil for a temperature range of 30-75 °C is studied via laboratory experiments. The AE signals are analyzed using the fast Fourier transform (FFT) to obtain the peak frequency and the AE amplitude. A peculiar behavior of reduction in the peak frequency and the AE amplitude observed above 65 °C is reported. An attempt is made to explain the reduction in the AE amplitude after a certain temperature by correlating it with the properties of the transformer oil such as the viscosity and the breakdown voltage. This AE signal analysis is perhaps an important advancement in the PD diagnosis and the PD spectrum analysis at different temperatures in the transformer oil. © 1986-2012 IEEE.Item Influence of compression toughness on acoustic emissions of cementitious materials(ICE Publishing subscriptions@icepublishing.com, 2019) Vidya Sagar, R.; Shetty, S.; Bhat, A.This paper reports on the variation of acoustic emission (AE) characteristics with the compression toughness of cementitious materials. The purpose of the study was to understand the relation between compression toughness and AE released during the fracture process in cementitious materials. There is limited knowledge about the 'relation between the compression toughness of cementitious materials and the corresponding AE released'. Specimens of different cementitious mixture compositions were tested as per the ASTM C 39 standard in the laboratory under unconfined uniaxial compression, and simultaneously the released AEs were recorded. Specimens consisted of concrete with 20 mm aggregates, concrete with 12 mm aggregates and mortar. AE monitoring system consisting with resonant type differential AE sensors were used to record the AE parameters. A detailed analysis revealed that an inverse relation may exist between the AE energy (S) and compression toughness (T ac) of the cementitious materials. The properties of cementitious materials that influence the relationship between AE energy and compression toughness and the behaviour of AE signals were studied. © 2019 ICE Publishing: All rights reserved.Item Role of longitudinal reinforcement on the behavior of under reinforced concrete beams subjected to fatigue loading(Elsevier Ltd, 2019) Prashanth, M.H.; Singh, P.; Chandra Kishen, J.M.C.In this work, the role of steel reinforcement in under reinforced concrete beams when subjected to flexural fatigue loading is studied using the acoustic emission (AE) technique. Three-point bend notched beams of three different sizes and with varying reinforcement ratios are subjected to step-wise increasing variable amplitude fatigue loading. The crack mouth opening displacement (CMOD) and AE parameters are analyzed to study the evolution of damage, load carrying and failure mechanisms in under reinforced concrete beams. It is concluded that the presence of reinforcement substantially increases the fatigue life. Further, the CMOD could be used as a criterion for failure in reinforced concrete beams under fatigue loading. © 2019 Elsevier LtdItem Fault diagnosis of single-point cutting tool using vibration signal by rotation forest algorithm(Springer Nature, 2019) Aralikatti, S.S.; Ravikumar, K.N.; Kumar, H.In various machining operations, the tool condition monitoring (TCM) is highly necessary to avoid uncertain downtime in production. TCM provides continuously the condition of cutting tool by noticing various parameters such as temperature, acoustic emission and vibration. One of the best ways to monitor the condition of cutting tools for unmanned machining is by observing tool vibration signature. In the present work, vibration signals are acquired from the cutting tool. One healthy state and three faulty conditions of tools are considered for the study. The faulty tools considered in the current study are worn flank, broken tool and extended overhang. The vibration signals of these faulty tool conditions are used to train the machine learning algorithm. Statistical features are extracted from the vibration signal to feed as input to the J48 decision tree. The classifier algorithm used in the current study is rotation forest algorithm. The algorithm uses only significant features which are selected from a decision tree. The algorithm is validated with test dataset to recognize the faulty or healthy state of the tool. It was found that the algorithm could classify the tool condition with 95.00% classification accuracy. © 2019, Springer Nature Switzerland AG.Item Statistical analysis of acoustic emissions generated during unconfined uniaxial compression of cementitious materials(Elsevier Ltd, 2019) Vidya Sagar, R.; Singh, M.; Deepak, S.; Desai, P.R.The article reports a study on the ‘goodness of fit’ of Weibull and Normal (Gaussian) distributions on the compressive strength and the corresponding Acoustic Emissions (AE) of cementitious materials. An attempt has been made to understand the variation of the parameters of the Weibull distribution and the Gaussian distribution carried out on the uniaxial compressive strength data and the corresponding recorded AE parameters. The statistical analysis of ‘Damage Parameter’ based on the peak amplitude of AE signals was also carried out. It was observed that the Weibull distribution was a better fit than Gaussian distribution for compressive strength and damage parameter. But in the case of AE parameters, Gaussian distribution was a better fit. The results obtained from this statistical study may be an addition to the existing knowledge on the statistical approach of AE associated with cementitious materials. A statistical approach may be suitable in predicting the data values without conducting further experiments. The results may be useful to understand the variation of physical properties such as homogeneity and ductility with the variation of compressive strength of cementitious materials and its corresponding AE parameters. © 2019Item An Investigation on the Influence of Thermal Damage on the Physical, Mechanical and Acoustic Behavior of Indian Gondwana Shale(Springer, 2020) Srinivasan, V.; Tripathy, A.; Gupta, T.; Singh, T.N.In the present study, the effect of thermal treatment on the physical, mechanical and fracturing behavior of Gondwana shale samples from India was investigated. Acoustic Emission signals were used to identify the changes brought in by temperature variations on the crack damage zones and failure attributes in shale. The results suggested that mechanical parameters such as uniaxial compressive strength, tensile strength (?t), elastic modulus, mode-I fracture toughness (KIC), cohesion, and brittleness index (B1) exhibited a strong negative correlation with thermal damage (Dt). But, the internal angle of friction and brittleness index (B2) showed a reasonable positive relation with thermal treatment. The deformation of the shale was dominated by its clay mineral enrichment, the characteristics of which changed with heating. The intensity of fracturing as observed from acoustic signals was chiefly controlled by the orientation of bedding planes and the degree of thermal treatment. The initiation and propagation of macro-crack were found to be greatly influenced by the degree of thermal damage. Under compression, thermally damaged samples showed similar deformation pattern, while under Brazilian tensile load, the deformation path became inconsistent with increasing temperatures. It was observed that thermal damage in tested shale decreased the layer compaction, which eased the fracturing intensity, thereby reducing the overall strength of the samples. The present investigation concludes that even a slight change of the thermal conditions can substantially alter shale fracturing behavior and failure attributes posing serious safety concerns of deep geo-engineering structures. © 2020, Springer-Verlag GmbH Austria, part of Springer Nature.Item Characterisation of hydrogen assisted cracking in modified 9Cr-1Mo steel welds using acoustic emission non destructive technique(Taylor and Francis Ltd., 2021) Haneef, T.K.; Chakraborty, G.; Rejeesh, R.; Mukhopadhyay, C.K.; Albert, S.K.This study aims a systematic experimental investigation using acoustic emission (AE) non-destructive technique for online monitoring of hydrogen assisted cracking (HAC) in modified 9Cr-1Mo steel (P91 steel) welds during Gap-Bead on Plate (G-BOP) and implant tests. Welds made without preheating, with different preheating and combined pre and post heating were tested using G-BOP test. AE results of G-BOP tests have shown that time duration in which HAC active varies with temperature of preheating and combined pre and post heating. Reduction of AE activity in welds made with pre and post heating compared to those only made with preheating revealed a beneficial effect of the former in reducing HAC. In the case of implant tests, crack initiation and propagation are identified for different applied loads from the AE analysis. An attempt has been made to compare HAC during G-BOP tests and implant tests using AE frequency analysis. The dominant frequency of AE signals characteristic of HAC has been identified. This study shows the potential of using AE frequency analysis for online monitoring of hydrogen assisted cracking (HAC) in welds. © 2021 Informa UK Limited, trading as Taylor & Francis Group.Item Influence of Fiber Content on Acoustic Emission Characteristics Related to Steel Fiber-Reinforced Concrete Subjected to Unconfined Uniaxial Compression(American Society of Civil Engineers (ASCE), 2021) Vidya Sagar, R.; Ghosh, S.; Kalloli, P.J.; Singh, M.This article reports the experimental study of the influence of the fiber volume content in steel fiber-reinforced concrete (SFRC) on the acoustic emission (AE) characteristics. Plain concrete and SFRC specimens with various steel fiber contents were tested under unconfined uniaxial compression in the laboratory. Both AE testing and ultrasonic pulse velocity (UPV) methods were used to study the fracture process in the specimens. During the fracture process, the generated AE and axial compressive strain were recorded. The differences in AE characteristics of plain concrete and SFRC specimens were discussed. An absence of a considerable amount of AE for a certain period was observed (silent period of AE) near the peak load for SFRC specimens. The AE-based b-value suddenly decreased near the peak load during the fracture process in plain concrete. However, in the case of SFRC specimens, a sudden decrease near the peak load was not observed, and the b-value decreased gradually until failure, at which point it attained its minimum value. More AE related to shear cracking was observed in the case of SFRC specimens. This was due to interlocking between steel fibers, cement matrix, and coarse aggregates. AE testing is useful for studying the material characterization of SFRC, and is beneficial for assessing damage in structures constructed with SFRC. © 2021 American Society of Civil Engineers.Item Experimental study on failure and fracturing attributes of granite after thermal treatments with different cooling conditions(Elsevier B.V., 2022) Srinivasan, V.; Hasainar, H.; Singh, T.N.Thermal damage is one of the fundamental mechanisms affecting the stability of rocks encountered in many deep geo-engineering ventures such as nuclear waste isolation, geothermal extraction etc. In the present study, the findings on influence of heating and subsequent cooling conditions on the fracturing and mechanical behaviour of an Indian granite are discussed. The granite samples from Jalore region of India were heated from room temperature to 600 °C followed by slow cooling and water quenching treatments. It was observed that rapid cooling through quenching had a greater impact on strength, elastic properties than slow cooling rate. Moreover, a drastic shift in terms of fracturing thresholds was witnessed, as a function of both temperature and sudden thermal shock experienced by rock at higher cooling rate. The simultaneous AE monitoring results suggested an early crack damage at higher thermal regimes. With help of microscopic observations, it was observed that inter-granular crack boundaries widened with increasing thermal damage experienced by minerals under both cooling conditions. However, the fracturing process was intense under rapid cooling treatment due to the invasion of water due to quenching which accelerated severe intra-crack growths, especially at higher thermal stress because of the rapid cooling rate than the slow cooling. The increased intensity of thermal cracks with temperatures and with variation in cooling rate was inferred as the primary reason for decay of rock characteristics. This was very well supplemented by decay in strength properties and changes in fracturing attributes of the tested granite as inferred from acoustic monitoring. © 2022