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https://lib.dr.iastate.edu/qnde/1985/allcontent
Recent Events in All Papersen-usThu, 29 Apr 2021 15:14:20 PDT3600An Eddy-Current Model and Inversion Algorithms for Three-Dimensional Flaw Reconstruction
https://lib.dr.iastate.edu/qnde/1985/allcontent/70
https://lib.dr.iastate.edu/qnde/1985/allcontent/70Tue, 01 Jan 1985 00:00:00 PST
We have developed a reconstruction algorithm based on a rigorous electromagnetic model. This model and its associated algorithm assume that the flaw or ‘anomalous region’ lies within a cylinder whose properties are known, and for which we can easily compute a Green’s function. Figure 1 shows a cross-section of the physical system. We have normalized the system equations so that if a voxel is completely covered by a flaw, its conductivity is −1, if a voxel is completely without a flaw, its conductivity is 0, and if a voxel is partially covered by a flaw, its conductivity is between −1 and 0. Our objective is to produce a conductivity map for the mathematical mesh. This approach shows excellent promise as a basis for quantitative nondestructive evaluation.
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L. David Sabbagh et al.Improved Probe-Flaw Interaction Modeling, Inversion Processing, and Surface Roughness Clutter
https://lib.dr.iastate.edu/qnde/1985/allcontent/69
https://lib.dr.iastate.edu/qnde/1985/allcontent/69Tue, 01 Jan 1985 00:00:00 PST
In Reference 1 a first comparison was made of measured eddy current signals with calculations based on nonuniform probe-field interaction theory. These calculations followed the basic analysis developed in Reference 2. They used interrogating field distributions calculated by Dodd and Deeds theory for the air core coils of Reference 3. (Note that Fig. 6 in Reference 1 and Fig. 7 in Reference 3 should be interchanged). In Reference 1 theoretical and experimental plots of the flaw profile curve (a plot of △Z versus distance along the mouth of a surface breaking flaw) were found to be in good agreement, with regard to shape, for several selected EDM notch samples in aluminum. An iterative procedure was also developed for systematically varying the length, depth, and opening width to obtain a best fit to the experimental data.4 In the present paper a full inversion procedure is developed and illustrated for approximately rectangular-shaped EDM notches. The mathematical structure of the inversion problem is first examined and a solution is proposed. Physical reasoning, based on the form of the flaw profile curves, is then used to simplify the approach and to provide guidance in selection of the most suitable probe geometry. Other topics briefly addressed include, possible improvements in the theory for the region with a/§ close to unity and for more realistic flaw shapes (i.e., semi-elliptical, rather than rectangular), inaccuracies due to errors in the probe scan path, and background clutter due to surface roughness, machining marks, and micro-structure.
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B. A. Auld et al.Status of Implementation of the Inverse Born Sizing Algorithm
https://lib.dr.iastate.edu/qnde/1985/allcontent/68
https://lib.dr.iastate.edu/qnde/1985/allcontent/68Tue, 01 Jan 1985 00:00:00 PST
The inverse Born approximation algorithm (IBA) for flaw sizing was proposed theoretically by Rose and Krumhansl in 1977 (1,2). Since that time, it has been experimentally evaluated at a number of laboratories, both in the U.S. and abroad. This paper summarizes the results of those evaluations and describes the status of efforts to develop a fully automatic version of the algorithm.
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R. Bruce ThompsonResonant Scattering and Crack Sizing
https://lib.dr.iastate.edu/qnde/1985/allcontent/67
https://lib.dr.iastate.edu/qnde/1985/allcontent/67Tue, 01 Jan 1985 00:00:00 PST
Theoretical consideration of ultrasonic scattering from interior cracks has received considerable attention in recent years. These studies have led to scattering amplitude computations for ultrasonic backscatter from circular cracks by the method of optimal truncation (MOOT) (1, 2) and by T-matrix techniques (3). A key observation in these results is that a peak in the magnitude of the scattering amplitude is found to occur at approximately ka = 1, where k is the longitudinal wave number and a the crack radius, which is independent of the scattering direction. Up to the present, however, adequate experimental verification of these findings have been impossible due to a lack of suitable laboratory samples.
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Timothy A. Gray et al.Identifying Spherical Voids and Inclusions by Matching the Power Spectra
https://lib.dr.iastate.edu/qnde/1985/allcontent/66
https://lib.dr.iastate.edu/qnde/1985/allcontent/66Tue, 01 Jan 1985 00:00:00 PST
An algorithm is developed to characterize the type and size of a flaw by matching the power spectrum of the flaw with those of the known ones. The algorithm is based on the inversion method developed by Fertig and Richardson for ellipsoidal flaws at low and intermediate frequencies. The present algorithm assumes spherical flaws, but has no restriction in frequency range. The general procedure is to send a wide band ultrasonic pulse upon the flaw and record the reflected waveform. Assuming small acoustic signal level so that linearity holds, the scattering cross-section of the flaw in the direction of the receiver transducer can be obtained by deconvolution with a back wall waveform. For each of the possible flaw types, the most probable radius is estimated by minimizing the “distance” between the measured scattering cross-section and the calculated scattering, cross-sections of that flaw type. The probability for each flaw type is estimated using the values of the minimum “distances” and their second derivatives at the most probable radii of the possible flaw types on the assumption of Gaussian probability distribution.
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K. C. Tam et al.Signal Processing for Underclad Crack Sizing
https://lib.dr.iastate.edu/qnde/1985/allcontent/65
https://lib.dr.iastate.edu/qnde/1985/allcontent/65Tue, 01 Jan 1985 00:00:00 PST
Underclad cracks in the beltline welds of some pressurized water reactors have been implicated by analysis as a potential safety issue. This issue is known as Pressurized Thermal Shock (PTS) in which a complex sequence of events can, in a very limited number of vessels, cause a small underclad crack (6 mm minimum calculated depth) grow to an unacceptable size. A cost effective countermeasure to the PTS issue is the development of a highly reliable inspection technique for underclad cracks.
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R. Shankar et al.Surface Flaw Characterization Using Ultrasonic Backscattered Satellite Pulse Technique
https://lib.dr.iastate.edu/qnde/1985/allcontent/64
https://lib.dr.iastate.edu/qnde/1985/allcontent/64Tue, 01 Jan 1985 00:00:00 PST
Conventionally, part lives of aircraft engine components are determined by empirical and statistical analyses based on fracture mechanics or fatigue crack propagation. Advanced engine design for energy efficiency and improved performance have dictated stringent quality control of components. Small flaws can be critical to the flight safety and service life of those components. It is thus extremely important to characterize the flaw and monitor its growth for better part life management. Eddy current and fluorescent penetrant nondestructive evaluation (NDE) techniques are limited to the detection and sizing of surface cracks. Ultrasonic methods are most commonly used for detection and characterization of subsurface defects; however, some newly developed ultrasonic techniques are gaining popularity for surface flaw detection and sizing.
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Engmin J. ChernDetection and Characterization of Surface Cracks Using Leaky Rayleigh Waves
https://lib.dr.iastate.edu/qnde/1985/allcontent/63
https://lib.dr.iastate.edu/qnde/1985/allcontent/63Tue, 01 Jan 1985 00:00:00 PST
A number of ceramics such as silicon nitride, and zirconia are being considered for high temperature structural applications. The primary problem with these ceramics is their wide fracture strength variability. In consequence, non-destructive evaluation techniques are required to ensure their reliable use. The brittle nature of ceramics inhibits the strain energy release at flaws by plastic deformation. As a result, critical flaw size in these materials is small. For example, flaws in the size range of 20–100 µm are considered as “critical” in silicon nitride for engine applications. Surface cracks are particularly important since they are the major source of failure in ceramics (1). These cracks are generated during machining operations and usually consist of arrays of semi-elliptical cracks with random inclination to the surface, but a preferred alignment parallel to the direction of motion of the abrading particles (2).
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A. Fahr et al.The Effects of Noise and Bandlimiting on a One Dimensional Time Dependent Inverse Scattering Technique
https://lib.dr.iastate.edu/qnde/1985/allcontent/62
https://lib.dr.iastate.edu/qnde/1985/allcontent/62Tue, 01 Jan 1985 00:00:00 PST
In realistic settings data used as input to any inverse scattering algorithm is bandlimited and corrupted by noise. At present there is no satisfactory way to determine the extent to which reconstructions using imperfect data are degraded due to noise and bandlimiting. In this paper, this problem is considered from the point of view of the sensitivity matrix of the mapping that transforms, via an inverse scattering algorithm outlined below,1 reflection data to information about material profiles of media.
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J. P. Corones et al.An Efficient Numerical Method for Determination of Shapes, Sizes and Orientations of Flaws for Nondestructive Evaluation
https://lib.dr.iastate.edu/qnde/1985/allcontent/61
https://lib.dr.iastate.edu/qnde/1985/allcontent/61Tue, 01 Jan 1985 00:00:00 PST
The generalized pulse-spectrum technique (GPST)1 is a versatile and effcient iterative numerical algorithm for solving inverse problems (to determine the unknown coefficients, initial-boundary values, sources, and geometries of the space domain from the additionally measured data in the space-time domain or the space-complex frequency domain) of a system of nonlinear partial differential equations. Mathematically, inverse problems of partial differential equations can be formulated as ill-posed nonlinear operator equations. It is important to point out that the GPST is not a single narrowly defined iterative numerical algorithm but a broad class of iterative numerical algorithms based on the concept that either the nonlinear operator equation is first linearized by any one of the Newton-like iteration methods and then each iterate is solved by using a stabilizing method, e.g., the Tikhonov’s regularization method2, or the stabilizing method is first applied to the nonlinear operator equation and then the regularized nonlinear problem is solved by using a Newton-like iteration method. Hence different choices of various Newton-like iteration methods and stabilizing methods lead to different special forms of GPST, and the efficiency of GPST will then depend upon the particular choices of them and how efficiently one can treat every minute step in the numerical algorithm.
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Y. M. Chen et al.