Faculty Publications
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Publications by NITK Faculty
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Item Implementation of Acoustic Emission Testing to Study the Type of Cracking in Reinforced Concrete Beams(Springer Science and Business Media Deutschland GmbH, 2021) Ghosh, S.; Agrawal, R.; Vidya Sagar, R.In this experimental study, crack classification in reinforced concrete (RC) beams was carried out using acoustic emission (AE) testing. Two types of under reinforced RC beams were tested in laboratory subjected to four-point bending, and monotonically increased load was applied. The first type of RC beam had shear reinforcement (steel stirrups), and the second type of RC beam had no shear reinforcement. The generated AE during the fracture process in the tested RC beams were used for the crack classification analysis. Gaussian mixture modeling (GMM) of acoustic emission signals was performed. It was observed that the RC beam without shear reinforcement failed suddenly (brittle nature). However, the RC beam with shear reinforcement failed gradually thereby exhibiting ductile nature. In both the RC beams, considerable AE related to shear cracking appeared at a 20–30% peak load. In the case of the RC beam with shear reinforcement, initially, tensile cracks were developed at the bottom of the beam and slowly started widening upward. Diagonal shear cracks started forming near to the supports when the test specimen reaching to collapse. In the case of the RC beam with no shear stirrups, tensile cracks originated at the bottom of the beam. But in this case, the influence of shear cracks developed near to the supports was more pronounced as it propagated rapidly. By comparing the different AE parameters, a steady increase in the number of hits till failure was observed in the case of the RC beam with shear reinforcement. But on the other hand, an abrupt increase in the number of hits was observed after 50% of peak load in the case of the RC beam with no shear reinforcement. The results are useful to study the sensitivity of AE to the shear reinforcement present in the RC beams. © 2021, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.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 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 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 Internal damage growth in quasi-brittle fibre-reinforced cementitious materials under cyclic compressive loading(Structural Engineering Research Centre, 2023) Vidya Sagar, R.; Basu, D.J.; Suhas Reddy, K.V.; Prathap, Y.; Bhuvaneswari, G.; Sai Keerthi, P.This article reports a comparison between the internal damage growth in cementitious materials without fibres and with fibres subjected to elevated amplitude cyclic compressive loading. The damage progression was assessed using ultrasonic testing method and Acoustic Emission (AE) testing. The intricate fracture mechanism in the test specimens causes rise to a higher harmonic generation, which was used as an indicator to the internal damage. The decrement in wave peak amplitude with higher harmonic generation may be regarded as a ‘internal damge growth’ in the deformable solid. The complexity in the fracture mechanism in fibrous cementitious matrix influenced the heterogeneity of the specimen, which is reflected by the steep decrement in the slope of the line plotted using normalized higher harmonic ratio and load. It was observed that the ‘magnitude of the total damage’ developed in plain concrete at the last loading phase was relatively lower than brass coated steel fibre reinforced concrete. This was supported by the damage parameter based on generated AE, where final failure of the specimens preceded an AE avalanche. Therefore, the utilization of a combination of nondestructive testing techniques such as AE and nonlinear ultrasonic testing can offer a more comprehensive understanding of the progression of damage in quasi-brittle cementitious materials. © 2023, Structural Engineering Research Centre. All rights reserved.