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Prabhu Rajagopal

Bio: Prabhu Rajagopal is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Ultrasonic sensor & Guided wave testing. The author has an hindex of 18, co-authored 129 publications receiving 1035 citations. Previous affiliations of Prabhu Rajagopal include Imperial College London & Indian Institutes of Technology.


Papers
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Journal ArticleDOI
TL;DR: In this article, the authors address methods to dramatically enhance computational efficiency by only meshing a local region of the material surrounding the defect; this reduction requires some kind of boundary, or boundary condition, which absorbs, rather than reflects, any waves arriving at the exterior of the modeled domain.
Abstract: Finite Element models for simulating wave propagation and scattering from defects are vital for ultrasonic methods in NDE. This article addresses methods to dramatically enhance computational efficiency by only meshing a local region of the material surrounding the defect; this reduction requires some kind of boundary, or boundary condition, which absorbs, rather than reflects, any waves arriving at the exterior of the modelled domain. A variety of approaches exist and we take two approaches, Perfectly Matched Layers (PML) and Absorbing Regions, selected specifically as they are readily implemented in commercially available Finite Element packages without requiring the source code. We illustrate both bulk and guided waves, and analysis is used to guide the performance, and thus to plan the use, of each of them. Finally, application examples illustrate the gains yielded by absorbing layer methods in terms of reducing both model size and unwanted reflections.

163 citations

Journal ArticleDOI
TL;DR: The feasibility of detection of delamination is experimentally demonstrated, whose size is comparable to the ultrasonic wavelength with probability of detection better than 90% using <1% of the total number of samples required for conventional imaging, even under conditions wherein the SNR is as low as 5 dB.

75 citations

Journal ArticleDOI
TL;DR: The interaction of the fundamental shear horizontal (SH0) guided mode with part-thickness cracks in an isotropic plate is studied as an extension within the context and general framework of previous work and theoretical analysis is used to understand the physical basis for such behavior.
Abstract: The interaction of the fundamental shear horizontal (SH0) guided mode with part-thickness cracks in an isotropic plate is studied as an extension within the context and general framework of previous work [“Short range scattering of the fundamental shear horizontal guided wave mode normally incident at a through thickness crack in an isotropic plate,” J. Acoust Soc. Am. 122, 1527–1538 (2007); “Angular influence on scattering when the fundamental shear horizontal guided wave mode is incident at a through-thickness crack in an isotropic plate,” J. Acoust. Soc. Am. 124, 2021–2030 (2008)] by the authors with through-cracks. The symmetric incidence case where the principal direction of the incident beam bisects the crack face at 90° is studied using finite element simulations validated by experiments and analysis, and conclusions are inferred for general incidence angles using insights obtained with the through-thickness studies. The influence of the crack length and the monitoring distance on the specular refl...

73 citations

Journal ArticleDOI
TL;DR: In this article , a baseline-free statistical approach for the identification and localization of delamination using sparse sampling and density-based spatial clustering of applications with noise (DBSCAN) technique is proposed.
Abstract: Delamination in composite structures is characterized by a resonant cavity wherein a fraction of an ultrasonic guided wave may be trapped. Based on this wave trapping phenomenon, we propose a baseline-free statistical approach for the identification and localization of delamination using sparse sampling and density-based spatial clustering of applications with noise (DBSCAN) technique. The proposed technique can be deployed for rapid inspection with minimal human intervention. The Performance of the proposed technique in terms of its ability to determine the precise location of such defects is quantified through the probability of detection measurements. The robustness of the proposed technique is tested through extensive simulations consisting of different random locations of defects on flat plate structures with different sizes and orientation as well as different values of signal to noise ratio of the simulated data. The simulation results are also validated using experimental data and the results are found to be in good agreement.

67 citations

Journal ArticleDOI
TL;DR: The results demonstrate laser ultrasonic testing (LUT) as a promising method for the non-contact inspection of additive manufactured components and the results were validated using X-ray computed tomography and ultrasonic immersion testing.
Abstract: Additively manufactured components are gaining popularity in aerospace, automotive and medical engineering applications. Additive manufacturing (AM) offers tremendous cost advantages over traditional manufacturing methods. However, inter- and intra-layer defects are observed in AM components. Moreover, the lack of appropriate testing methods for assessing the integrity of AM components deters its use, despite the several functional advantages it has to offer. Non-destructive testing (NDT) forms the most common and convenient way of inspecting parts. In this paper, a laser ultrasonic technique for the inspection of AM components is proposed. The results demonstrate laser ultrasonic testing (LUT) as a promising method for the non-contact inspection of additive manufactured components. Furthermore, the results were validated using X-ray computed tomography (CT) and ultrasonic immersion testing (UIT). The sample used in this study was manufactured through selective laser melting (SLM) AM process with built-in holes representing defects.

62 citations


Cited by
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Journal ArticleDOI
01 Apr 1956-Nature
TL;DR: The Foundations of Statistics By Prof. Leonard J. Savage as mentioned in this paper, p. 48s. (Wiley Publications in Statistics.) Pp. xv + 294. (New York; John Wiley and Sons, Inc., London: Chapman and Hall, Ltd., 1954).
Abstract: The Foundations of Statistics By Prof. Leonard J. Savage. (Wiley Publications in Statistics.) Pp. xv + 294. (New York; John Wiley and Sons, Inc.; London: Chapman and Hall, Ltd., 1954.) 48s. net.

844 citations

Journal ArticleDOI
TL;DR: In this article, the use of X-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts.
Abstract: In this review, the use of x-ray computed tomography (XCT) is examined, identifying the requirement for volumetric dimensional measurements in industrial verification of additively manufactured (AM) parts. The XCT technology and AM processes are summarised, and their historical use is documented. The use of XCT and AM as tools for medical reverse engineering is discussed, and the transition of XCT from a tool used solely for imaging to a vital metrological instrument is documented. The current states of the combined technologies are then examined in detail, separated into porosity measurements and general dimensional measurements. In the conclusions of this review, the limitation of resolution on improvement of porosity measurements and the lack of research regarding the measurement of surface texture are identified as the primary barriers to ongoing adoption of XCT in AM. The limitations of both AM and XCT regarding slow speeds and high costs, when compared to other manufacturing and measurement techniques, are also noted as general barriers to continued adoption of XCT and AM.

330 citations