Faculty Publications

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    Thermal effects on acoustic emission based PD in transformer oil: A study
    (2012) Bhavani Shanker, T.; Nagamani, H.N.; Punekar, G.S.
    Transformers operate at different service conditions in the field resulting in operating temperatures of oil and winding, much above ambient temperature. Acoustic emissions due to partial discharge activity in transformer insulation system, including transformer oil, have been investigated by a few researchers at temperatures ranging from 25°C to 40°C. It is more realistic to consider the study at service temperature which could be around 50°C to 70°C; depending on the service conditions and type of insulation employed. The paper deals with acoustic partial discharge behaviour in transformer oil at temperatures ranging from 30°C to 75°C along with some of the properties of transformer oil. © 2012 IEEE.
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    A critical review on estimation of rock properties using sound levels produced during rotary drilling
    (CAFET INNOVA Technical Society cafetinnova@gmail.com 1-2-18/103, Mohini Mansion, Gagan Mahal Road, Domalguda, Hyderabad 500029, 2012) Masood; Vardhan, H.; Mangalpady, M.; Rajesh Kumar, B.
    This paper summarizes the critical review on estimation of rock properties using sound levels produced during rotary drilling. In this paper an overall emphasis has been made to summarize the importance of sound level produced during drilling by considering various parameters like drill bit speed, penetration rate, drill bit diameter, type of drill bit and equivalent sound level produced during drilling for the estimation of rock properties. Further an attempt has also made to include the application of ANN modeling and acoustic emission in estimating rock properties. © 2012 CAFET-INNOVA TECHNICAL SOCIETY.
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    An experimental study on rock damage and its influence in rock stress memory in a metamorphic rock
    (Springer, 2020) Srinivasan, V.; Gupta, T.; Ansari, T.A.; Singh, T.N.
    Rock stress memory, often referred as Kaiser effect, in rocks can be an effective tool to estimate the in situ stress conditions, if the uncertainties in rock damage and its behavior during loading conditions are properly understood. In view of this, the present study is an attempt to investigate the variations in rock stress memory, i.e., the Kaiser effect in a metamorphic rock under multi-stage uniaxial compression. The khondalite rock samples from Eastern Ghats Mobile Belt (EGMB) belonging to southeastern part of Indian subcontinent having complex geological history are examined. The effects of multi-stage compression on the damage evolution and subsequent variations in rock stress memory are investigated. The samples were categorized into different levels of rock stress memory, depending on the stress the rock was able to withhold after loading stages. The damage evolution in the tested rocks was predominantly controlled either by initial loading or failure stress. Higher damage imparted by initial loading and intense fracturing could be the possible reason for poor stress memory function in the investigated rock. Felicity ratio, an indicative of rock damage with stages of loading, supported the observation that rock damage was dominant during initial loading stage. Rock heterogeneity has played a dominant role in decay of Kaiser effect, with intense fracturing during subsequent loading stages in the investigated rocks. To summarize, Kaiser effect can be used to infer rock damage and stress conditions, provided the geological history of the region is also taken into consideration. With rocks from complex geological conditions, Kaiser effect or rock stress memory should be supported by other tools to infer in situ stress, but the method can be effectively used to understand the stress changes and damage mechanism of multiple loading. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
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    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.
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    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