Dokument-ID Dokumenttyp Autoren/innen Persönliche Herausgeber/innen Haupttitel Abstract Auflage Verlagsort Verlag Herausgeber (Institution) Erscheinungsjahr Titel des übergeordneten Werkes Jahrgang/Band ISBN Veranstaltung Veranstaltungsort Beginndatum der Veranstaltung Enddatum der Veranstaltung Ausgabe/Heft Erste Seite Letzte Seite URN DOI Lizenz Datum der Freischaltung OPUS4-27631 Zeitschriftenartikel Prasad M, K.; Wiggenhauser, Herbert; Balasubramaniam, Krishnan Detection of honeycomb defects in reinforced concrete structures using acoustic pulse-echo methods and wavelet transforms Honeycombs/compaction faults occur in the concrete structures due to improper solidification of the concrete, which may reduce the strength of the concrete and also act as a passage for the water/acids that further corrodes the reinforcements. This paper explores about the acoustic pulse-echo techniques for the detection of honeycomb defects in a laboratory specimen located at the Federal Institute for Materials Research and Testing (BAM), Berlin. Since concrete is an inhomogeneous medium, the defect Signals are masked by the material noise due to large amount of scattering/ reflections of acoustic waves. A filtering method using the discrete wavelet transforms is applied on the ultrasonic time Signals for the better localization of defects. Chennai ISNT Indian Society for Non-Destructive Testing 2011 Journal of non-destructive testing & evaluation 10 3 53 59 2016-02-20 OPUS4-32240 Zeitschriftenartikel Kolkoori, Sanjeevareddy; Venkata, K.C.; Balasubramaniam, Krishnan Quantitative simulation of ultrasonic time of flight diffraction technique in 2D geometries using Huygens-Fresnel diffraction model: Theory and experimental comparison This article presents an analytical approach for simulation of ultrasonic diffracted wave signals from cracks in two-dimensional geometries based on a novel Huygens-Fresnel Diffraction Model (HFDM). The model employs the frequency domain far-field displacement expressions derived by Miller and Pursey in 2D for a line source located on the free surface boundary of a semi-infinite elastic medium. At each frequency in the bandwidth of a pulsed excitation, the complex diffracted field is obtained by summation of displacements due to the unblocked virtual sources located in the section containing a vertical crack. The time-domain diffracted wave signal amplitudes in a general isotropic solid are obtained by standard Fast Fourier Transform (FFT) procedures. The wedge based finite aperture transducer refracted beam profiles were modelled by treating the finite dimension transducer as an array of line sources. The proposed model is able to evaluate back-wall signal amplitude and lateral wave signal amplitude, quantitatively. The model predicted range-dependent diffracted amplitudes from the edge of a bottom surface-breaking crack in the isotropic steel specimen were compared with Geometrical Theory of Diffraction (GTD) results. The good agreement confirms the validity of the HFDM method. The simulated ultrasonic time-of-flight diffraction (TOFD) A-scan signals for surface-breaking crack lengths 2 mm and 4 mm in a 10 mm thick aluminium specimen were compared quantitatively with the experimental results. Finally, important applications of HFDM method to the ultrasonic quantitative non-destructive evaluation are discussed. Amsterdam Elsevier B.V. 2015 Ultrasonics 55 33 41 10.1016/j.ultras.2014.08.016 2016-02-20 OPUS4-38915 Zeitschriftenartikel Unnikrishnakurup, Sreedhar; Kidangan, R. T.; P. Vengara, N.; Balasubramaniam, Krishnan; Rajagopal, P.; Phani Prabhakar, K. V.; Padmanabham, G. Application of infrared thermography technique for the monitoring of cold metal transfer (CMT) joining of aluminium to galvanized steel In this study, the feasibility of using non-contact Infrared thermography as a potential tool to monitor the CMT welding process is explored. The presence of internal defects such as porosity, lack of filler material deposition and formation of improper weld bead produce perturbations in the surface temperature which can be identified using an Infrared thermography technique. We present recent results obtained from online monitoring of the the dissimilar joining using CMT weld brazing of Aluminum and Steel using a transmission mode measurement approach. The effect of loss of zinc coating on the weldability of the cold metal transfer joining of aluminum to galvanised steel was investigated. A correlation between measured online thermal indications with the weld anomalies is successfully attempted and the results are compared with the conventional post-weld NDT inspection methods. Kirchwald NDT.net 2016 The e-journal of nondestructive testing & ultrasonics 21 19th World Conference on Non-Destructive Testing (WCNDT 2016) Munich, Germany 13 June 2016 17 June 2016 7 1 8 urn:nbn:de:kobv:b43-389155 http://creativecommons.org/licenses/by-nd/3.0/de/ 2017-01-09 OPUS4-38916 Zeitschriftenartikel Unnikrishnakurup, Sreedhar; Myrach, Philipp; Polomski, Benjamin; Le Claire, Elisabeth; Vengara, N.; Balasubramaniam, Krishnan; Ziegler, Mathias Thermographic crack detection in hot steel surfaces The detection and characterization of surface cracks in steel specimens prior to damage is a technologically and economically highly significant task and is of utmost importance when it comes to safety-relevant structures. In steel production where steel billets at high temperatures have to be inspected while moving a number of well-established NDT methods cannot be applied. Laser thermography however is a promising candidate to serve as a fast, non-contact and remote tool in this case. We present a study that shows that the crack detection capabilities of laser thermography can be extended also to specimens at high temperature. A combination of inductive and laser heating allows to systematically study the contrast formation as well as the optimization of the important measurement parameters. The experiments are accompanied by FEM simulations that provide a better insight of the physical correlations and support the experimental developments. The aim of these studies is to develop a system with high inspection speed and detection performance to be in-line operated under the hostile environment of steel production lines. Kirchwald NDT.net 2016 The e-journal of nondestructive testing & ultrasonics 21 19th World Conference on Non-Destructive Testing (WCNDT 2016) Munich, Germany 13.06.2016 17.06.2016 7 1 8 urn:nbn:de:kobv:b43-389161 http://creativecommons.org/licenses/by/3.0/de/deed.de 2017-01-10 OPUS4-38910 Zeitschriftenartikel Kidangan, R. T.; Unnikrishnakurup, Sreedhar; P. Vengara, N.; Balasubramaniam, Krishnan; Rajagopal, P.; Phani Prabhakar, K. V.; Padmanabham, G.; Riedel, F.; Puschmann, M. Online monitoring of cold metal transfer (CMT) process using infrared thermography Online (passive) thermographic inspection of overlap joints of aluminium and zinc coated steel sheets made by cold metal Transfer weld brazing process was explored. Different experimental Trials were conducted for demonstrating the feasibility of thermographic inspection to detect the porosities, improper weld bead and to differentiate the pre weld temperature. The whole process was monitored using infrared cameras in different wavelength region. Image analysis algorithms were developed to reconstruct the thermal images that contain the signatures of the weld defects and to extract the pre weld temperature and ist evolution with distance from the centre of the weld torch. Post-weld radiography lends strong Support to the observations. Taylor & Francis 2016 Quantitative Infrared Thermography Journal 14 1 68 78 10.1080/17686733.2016.1229330 2017-01-09 OPUS4-39078 Beitrag zu einem Tagungsband Unnikrishnakurup, Sreedhar; Thomas, R.; Balasubramaniam, Krishnan; Narayanan, L.; Phanikumar, G. Dissimilar metal joint quality measurement using infrared thermography: Experimental and numerical approach for the application to CMT welding Joining of dissimilar material has become highly popular research subject in the automobile industry due to the reduced weight and thereby increasing the fuel efficiency. Infrared thermography can be used as a natural tool to measure the temperature near the welding region and correlate the distribution of temperature to the weld quality. In the present work the quality of the dissimilar welded sample is identified using the temperature distribution in the vicinity of the weld pool region. A numerical model for CMT continues welding process has been modeled and simulated for the first time and compared with the experimental measurement. Gdansk Gdansk University of Technology QIRT Council 2016 Proceedings of the 13th International Conference on Quantitative Infrared Thermography - QIRT 2016 The 13th International Conference on Quantitative Infrared Thermography - QIRT 2016 Gdansk, Poland 04.07.2016 08.07.2016 389 390 10.21611/qirt.2016.056 2017-02-06 OPUS4-39105 Beitrag zu einem Tagungsband Puthiyaveettil, N.; Krishna, S.; Kidangan, R.; Unnikrishnakurup, Sreedhar; Krishnamurthy, C. V.; Ziegler, Mathias; Myrach, Philipp; Balasubramaniam, Krishnan In-line laser thermography for crack detection at elevated temperature: A Numerical modeling study The detection and characterization of cracks prior to damage is a technologically and economically highly significant task and is of very importance when it comes to safety-relevant structures. The evaluation of a components life is closely related to the presence of cracks in it. Laser thermography has already high capability for the detection of surface cracks and for the characterization of the geometry of artificial surface flaws in metallic samples. Crack detection in metallic samples at high temperature is highly significant in present manufacturing scenario. During the casting process of billets, surface cracks form, due to the suboptimal cooling rates. These cracks reduce value of the billet and must be removed using machining process after cooling. This secondary process increases cost of manufacturing. In this work we developed a heat transfer model for laser thermography to study the thermal contrast variation with increase in surface temperature using finite element method (FEM). Here we are mainly concentrating the capability of the scanning laser thermography in crack detection which are in elevated temperature and numerical modeling study of thermal contrast variation of crack with respect increase in metal surface temperature. This study is important to prove the capability of laser thermography for crack detection in elevated temperature. Since we are using High power CW Laser to local heating of the metal surface which can give relatively high thermal contrast even at elevated temperature compare to other heating source. Here we are modeled and simulated 2D laser scanning across a surface breaking crack and developed an algorithm to produce the vicinity of crack. The algorithm we developed applied for various surface temperature data. And validated the credibility of the algorithm with experimental data. QIRT 2016 Proceedings 2016 QIRT 2016 2016 13th Quantitative Infrared Thermography Conference 2016 Gdansk, Poland 04.07.2016 08.07.2016 588 596 10.21611/qirt.2016.092 2017-02-07 OPUS4-35743 Zeitschriftenartikel Unnikrishnakurup, Sreedhar; Krishnamurthy, C. V.; Balasubramaniam, Krishnan Monitoring TIG welding using Infrared Thermography - Simulations and Experiments In the current work a 3D model has been developed to predict the thermal cycles during the Tungsten Inert Gas welding of Aluminum 2219. This paper describes the step by step procedure adopted to get the actual cooling rate during the TIG welding process both experimentally and numerically. The model was developed in the COMSOL Finite Element Package and considered a Gaussian heat distribution. The developed model then validated using the experimental data collected in field experiments on actual large propellant tanks. Temperature measurements were performed using Infrared Camera. Results show a close comparison between model and experiment. 2016 Przeglad Elektrotechniczny 4/2016 6 9 10.15199/48.2016.04.02 2016-04-19 OPUS4-39387 Beitrag zu einem Tagungsband Krishna, S. K. P.; Puthiyaveetil, N.; Kidangan, R.; Unnikrishnakurup, Sreedhar; Ziegler, Mathias; Myrach, Philipp; Balasubramaniam, Krishnan; Purushothaman, B. Raw data based image processing algorithm for fast detection of surface breaking cracks The aim of this work is to illustrate the contribution of signal processing techniques in the field of Non-Destructive Evaluation. A component's life evaluation is inevitably related to the presence of flaws in it. The detection and characterization of cracks prior to damage is a technologically and economically significant task and is of very importance when it comes to safety-relevant measures. The Laser Thermography is the most effective and advanced thermography method for Non-Destructive Evaluation. High capability for the detection of surface cracks and for the characterization of the geometry of artificial surface flaws in metallic samples of laser thermography is particularly encouraging. This is one of the non- contacting, fast and real time detection method. The presence of a vertical surface breaking crack will disturb the thermal footprint. The data processing method plays vital role in fast detection of the surface and sub-surface cracks. Currently in laser thermographic inspection lacks a compromising data processing algorithm which is necessary for the fast crack detection and also the analysis of data is done as part of post processing. In this work we introduced a raw data based image processing algorithm which results precise, better and fast crack detection. The algorithm we developed gives better results in both experimental and modeling data. By applying this algorithm we carried out a detailed investigation Variation of thermal contrast with crack parameters like depth and width. The algorithm we developed is applied for various surface temperature data from the 2D scanning model and also validated credibility of algorithm with experimental data. New York AIP Publishing 2017 QNDE conference 2016 - Review of progress in quantitative nondestructive evaluation 1806 978-0-7354-1474-7 QNDE conference 2016 - Review of progress in quantitative nondestructive evaluation Atlanta, GA, USA 18.07.2016 22.07.2016 1 UNSP 140008, 1 9 10.1063/1.4974723 2017-03-15