Improved Imaging of Fatigue Crack Profile in Thick Cruciform Samples Using Ultrasonic Phased Array Models
01 Feb 2010-Journal of Pressure Vessel Technology-transactions of The Asme (American Society of Mechanical Engineers)-Vol. 132, Iss: 1, pp 011501
TL;DR: In this article, a semi-elliptical surface starter notch of 2 mm width and more than 400 mm length was created by conducting fatigue fracture test on two mild steel cruciform specimens of 135 mm thickness: one under room temperature and the other under subzero temperature ( -70°C).
Abstract: The determination of depth profile of vertical fatigue cracks generated in thick cruciform samples using an ultrasonic phased array is investigated in this paper. The cracks were formed by conducting fatigue fracture test on two mild steel cruciform specimens of 135 mm thickness: one under room temperature and the other under subzero temperature ( -70°C). A semi-elliptical surface starter notch of 2 mm width and more than 400 mm length was initially created in the specimens. Alternating current potential drop technique and phased array ultrasonic technique were attempted in order to determine the depth profiles of the starter notch as well as that of the crack. Virtual experiments carried out with a finite-difference time domain based numerical model were found to be advantageous in reducing actual experimental trials, facilitate an understanding of the echo signatures, and help assess the crack depth. The profiles of the crack and the notch were verified through destructive assay of the samples and subsequent dye penetrant assisted physical measurements.
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TL;DR: In this paper, the transmissibility analysis on the ultrasonic scan data was used to detect cracks or cracks or crack-like flaws, solely from the relative magnitude of the A-scan data in intact materials and in materials with a crack.
22 citations
21 Jun 2011
TL;DR: In this article, the role of the depth of focus and the focal spot size on the performance of TIVAS were studied semi-analytically and through FDTD simulations.
Abstract: A new phased array inspection scheme, called Technique to Image using Virtual Array Sources (TIVAS), is proposed to image defects at deeper locations with good lateral resolution. An array of virtual focal spots using electronic beam forming and the expanded aperture through electronic linear scanning was employed to achieve significant increase in the focal depths, with improved SNR, when compared to single element array imaging or the conventional phased array focusing technique. The image reconstruction was performed using the well known synthetic focusing approach. In this paper, the role of the depth of focus and the focal spot size on the performance of TIVAS were studied semi‐analytically and through FDTD simulations. It was observed smaller virtual focal spot size provides improved lateral resolution and there is an optimum depth of focus for the smallest focal spot size achievable for a array transducer. Experiments were carried out to validate these findings.
7 citations
TL;DR: In this paper, the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media.
Abstract: The present article addresses the development at Centre for Non-destructive Evaluation, Indian Institute of Technology Madras, of three different numerical methods, namely finite element, ray tracing and finite-difference time-domain methods for investigating the propagation of ultrasonic waves through polycrystalline media. These methods are believed to aid in better understanding of ultrasonic wave interaction in materials exhibiting both simple and complex grain morphologies. The understanding is expected to provide an improved non-destructive assessment of material and defect characterisation.
7 citations
3 citations
TL;DR: In this paper, the results of imaging a slit in a Ni-based weld metal, commercially available as Inconel alloy 600, were compared in an experiment and in simulations using the analytical solution of group velocity or the finite-difference time-domain (FDTD) method.
Abstract: An ultrasonic phased array (PA) does not work well in some weld metals owing to the strong acoustic anisotropy. However, the analysis of anisotropy for the compensation of the shift of the defect image in the PA has not been performed. In this study, we compared the results of imaging a slit in a Ni-based weld metal, commercially available as Inconel alloy 600, in an experiment and in simulations using the analytical solution of group velocity or the finite-difference time-domain (FDTD) method. As a result, we succeeded in reproducing the shift and broadening of the defect image obtained in an experiment by the simulations.
1 citations
References
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TL;DR: The use of ultrasonic arrays for non-destructive evaluation has been extensively studied in the literature as mentioned in this paper, where the main advantages of arrays are their increased flexibility over traditional single element transducers, and their ability to produce immediate images of the test structure.
Abstract: An ultrasonic array is a single transducer that contains a number of individually connected elements. Recent years have seen a dramatic increase in the use of ultrasonic arrays for non-destructive evaluation. Arrays offer great potential to increase inspection quality and reduce inspection time. Their main advantages are their increased flexibility over traditional single element transducer methods, meaning that one array can be used to perform a number of different inspections, and their ability to produce immediate images of the test structure. These advantages have led to the rapid uptake of arrays by the engineering industry. These industrial applications are underpinned by a wide range of published research which describes new piezoelectric materials, array geometries, modelling methods and inspection modalities. The aim of this paper is to bring together the most relevant published work on arrays for non-destructive evaluation applications, comment on the state-of the art and discuss future directions. There is also a significant body of published literature referring to use of arrays in the medical and sonar fields and the most relevant papers from these related areas are also reviewed. However, although there is much common ground, the use of arrays in non-destructive evaluation offers some distinctly different challenges to these other disciplines.
818 citations
TL;DR: In this article, the authors used a commercial finite element (FE) code to study the propagation characteristics of ultrasonic waves in annular structures and demonstrated the potential of the FE method for problems when an analytical solution is not possible because of complicated component geometry.
Abstract: This paper reports on the application of guided waves techniques to nondestructively determine the structural integrity of engineering components. Specifically, this research uses a commercial finite element (FE) code to study the propagation characteristics of ultrasonic waves in annular structures. In order to demonstrate the accuracy of the proposed FE technique, the propagation of guided waves in a flat plate is examined first. Next, the propagation of guided waves in thick ring structures is investigated. Finally, these FE results are compared to analytical and experimental results. The results of this study clearly illustrate the effectiveness of using the FE method to model guided wave propagation problems and demonstrate the potential of the FE method for problems when an analytical solution is not possible because of “complicated” component geometry.
553 citations
TL;DR: Peng and Toksoz as mentioned in this paper presented a method for application of the perfectly matched layer absorbing boundary condition (ABC) to the P•SV velocity-stress finite-difference method.
Abstract: A method is presented for application of the perfectly matched layer (PML) absorbing boundary condition (ABC) to the P‐SV velocity–stress finite‐difference method The PML consists of a nonphysical material, containing both passive loss and dependent sources, that provides ‘‘active’’ absorption of fields It has been used in electromagnetic applications where it has provided excellent results for a wide range of angles and frequencies In this work, numerical simulations are used to compare the PML and an ‘‘optimal’’ second‐order elastic ABC [Peng and Toksoz, J Acoust Soc Am 95, 733–745 (1994)] Reflection factors are used to compare angular performance for continuous wave illumination; snapshots of potentials are used to compare performance for broadband illumination These comparisons clearly demonstrate the superiority of the PML formulation Within the PML there is a 60% increase in the number of unknowns per grid cell relative to the velocity–stress formulation However, the high quality of the PML ABC allows the use of a smaller grid, which can result in a lower overall computational cost
316 citations
TL;DR: In this paper, a 256-channel array system has been developed for the inspection of weldment of BWR internal components such as core shrouds and the TOFD crack sizing technique also can be applied using this system.
77 citations
TL;DR: In this paper, the non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported.
Abstract: The non-dispersive propagation of ultrasonic guided wave higher order modes cluster (HOMC) traveling along the circumferential direction in a hollow cylinder and its interaction with defects in pipe support regions is reported. These circumferential guided waves were generated in mild steel (MS) pipe specimens containing artificially created axial notches (simulating axial cracks) and pinholes (simulating pinhole-like defects) of different sizes in order to simulate conditions such as cracking and corrosion under pipe supports. The characteristics of these guided waves were also studied as a function of parameters related to how they were generated; namely, using: (a) 2.25 MHz linear phased array transducer, (b) 2.25 MHz conventional circular transducer and (c) 1 MHz conventional circular transducer. These higher frequency modes were explored for their ability to detect and size defects. Because of access limitations to the pipe support region in actual field testing, the transducer was always placed at a fixed circumferential position and moved axially along the length of the pipe. The defect position along the circumference was ascertained from the time of flight while the defect size was estimated using the amplitude data. The signals obtained for all three transducer configurations are compared for their ability to locate, detect and size the above-mentioned defects. It was shown that at these relatively higher frequencies, the guided wave modes exhibit small dispersion and have the ability to provide improved imaging of small size defects throughout the cross-section of the pipe.
69 citations