Showing papers by "Tetsuya Uchimoto published in 2003"
TL;DR: In this paper, an arrayed multi-coil probe was developed for the testing and crack sizing of steam generator tubes by eddy current testing (ECT), which has a high detection speed around the whole tube, without the need for rotation.
Abstract: This paper describes an arrayed multi-coil probe, newly developed for the testing and crack sizing of steam generator tubes by eddy current testing (ECT). The testing speed, the high sensitivity to shallow cracks and the crack sizing are the present requirements in ECT. Because of the multi-coil arrangement, the arrayed probe has a high detection speed around the whole tube, without the need for rotation. It is realized from former studies that knowing the number of cracks, their directions, and their positions beforehand is of great help in crack sizing. Thus, not only the sensitivities but also the spatial resolutions are important. Numerical simulations are applied to help the design of the probe from the viewpoint of the crack sizing of steam generator tubes. Experiments show that the present probe provides both a high detectability and a remarkable capability of reconstructing the shallow cracks of a tube.
58 citations
TL;DR: In this paper, a method for the evaluation of matrix structures of cast irons by means of eddy current (EC) evaluation was proposed, which is sensitive to the difference of matrix structure obtained by microstructure observations.
56 citations
TL;DR: An inversion algorithm for the reconstruction of cracks from eddy current signals is developed in this article and applied to the profile evaluation of natural stress corrosion cracks that were found in steam generator tubes of a nuclear power plant.
Abstract: An inversion algorithm for the reconstruction of cracks from eddy current signals is developed in this study and applied to the profile evaluation of natural stress corrosion cracks that were found in steam generator tubes of a nuclear power plant. A crack is modeled as an assembly of small regions having conductivities inside so that eddy currents that flow across the cracks are considered. The conductivity of each region, which is assumed to be a discrete value, is reconstructed by means of the algorithm. Since the algorithm is based upon a tabu search that usually requires a large number of evaluating solution candidates, simulations are carried out on a supercomputer with the use of parallel computation using up to 128 CPUs so as to reconstruct the crack profiles within a reasonable computational time. It is demonstrated that the algorithm can estimate the profiles of the natural cracks with sufficient accuracy. The simulations also show that the algorithm is highly compatible with parallel computation. Additional simulations using other models of natural cracks are performed. Reconstructed profiles of the natural cracks, as a notch with zero conductivity, are very different from the true profiles, even though the reconstructed signals agree well with the measured values. This reveals that it is necessary to take the internal conductivity into consideration when dealing with natural cracks.
51 citations
TL;DR: In this paper, a machinable metallic ceramic titanium silicon carbide, Ti 3 SiC 2, was successfully used as a substrate for CVD diamond coating, which was synthesized from a mixed powder of Ti, Si and TiC.
25 citations
TL;DR: In this article, the magnetization reversal was observed in nickel (II) formate dihydrate Ni(HCOO)2·2H2O, where the observed weak magnetic moment increases initially below TN=15.5 K, equals zero at T*=8.5 k, and increases again at lowering temperature.
17 citations
TL;DR: The method developed here, that can be used to treat ferromagnetics, is an extension of the precomputed database approach based on the magnetic vector potential method that provides a forward simulator that is about 80 times faster than the conventional one without loss of accuracy, even in the case of ferromagnetic materials.
Abstract: Eddy current testing (ECT) is a nondestructive testing method for metal materials Numerical methods are applied to predict the ECT signals, to aid in the design of ECT probes, and to reconstruct crack shapes from their ECT signals For the testing of nonferromagnetic materials, the high accuracy of some numerical simulation techniques has been demonstrated and several fast computational methods have been presented However, the numerical calculation of electromagnetic fields in ferromagnetic materials remains a difficult and time-consuming task Representing cracks in ferromagnetic materials with secondary electric and magnetic sources leads to a fast method for predicting ECT signals as presented in this article The method developed here, that can be used to treat ferromagnetics, is an extension of the precomputed database approach based on the magnetic vector potential method With the aid of precomputed databases, ECT signals of different cracks can be computed from changes in the secondary sources in a small region, without considering the geometries of the whole conductor This results in fewer degrees of freedom than those of typical finite element approaches, and the method provides a forward simulator that is about 80 times faster than the conventional one without loss of accuracy, even in the case of ferromagnetic materials
11 citations
09 Apr 2003
TL;DR: In this paper, a 3D fast eddy current testing probe was proposed to detect cracks in non-magnetic metal plates, which used to be difficult because of the skin effect generally.
Abstract: This paper demonstrates the crack detection of thick‐walled non‐magnetic metal plates by eddy current testing, which used to be difficult because of the skin effect generally. For the purpose, this paper proposes a novel eddy current testing probe for cracks in thick‐walled plates and evaluates the capability of the present probe. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of the present probe are strong eddy current on the back of specimens and small decay of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect on INCONEL718 specimen with thickness of 7.0mm and 304 Stainless steel specimen with thickness of 8.0mm.
6 citations
TL;DR: In this article, a new eddy current testing probe for cracks in thick-walled non-magnetic metal plates and crack shapes quantitative evaluation was designed, based on the numerical computation using 3D fast eddycurrent code.
Abstract: This paper demonstrates the crack detection of thick-walled non-magnetic metal plates by eddy current testing, which is difficult because of Kelvin skin effect generally. The purpose of this research is the development of an new eddy current testing probe for cracks in thick-walled plates and crack shapes quantitative evaluation. The probe was designed, based on the numerical computation using 3D fast eddy current code. The advantages of this new probe are strong eddy current on the back of specimens and gentle decrement of eddy current in the thickness direction. Through experiments, we confirmed that this probe can detect the back artificial defect with 0.5 mm thickness on IN-CONEL 718 specimen with 7.0 mm thickness. Reconstruction of crack shapes was performed based on the experimental results with the inverse problem code developed by authors. The length and depth of reconstructed defects approximately agree with those of real crack.
5 citations
01 Jan 2003
TL;DR: In this article, the authors proposed a novel concept of eddy current (EC) camera system, which is more than a package of testing and crack shape reconstruction, that enables fine visualization of flaw at a single scan EC camera consists of arrayed multi-coil, EC instrument, inverse analyzer and focusing mechanism Focusing mechanism is realized by tuning of test frequency via inverse analyses
Abstract: This paper proposes a novel concept of eddy current (EC) camera system, which is more than a package of testing and crack shape reconstruction, that enables fine visualization of flaw at a single scan EC camera consists of arrayed multi-coil, EC instrument, inverse analyzer and focusing mechanism Focusing mechanism is realized by tuning of test frequency via inverse analyses
2 citations
01 Jan 2003
TL;DR: In this paper, a genetic algorithm was used to predict the number and positions of cracks and reconstruct the crack shape from two-dimensional scan data, with a satisfactory degree of accuracy.
Abstract: This paper describes a novel method for identifying the number and positions of cracks and reconstructing the crack shape. Using the ECT signal obtained by two-dimensional scanning as a picture image, a template matching method, with the help of a genetic algorithm is applied to predict the number and positions of the cracks. The present method employs the scaling technique of a signal profile with respect to crack length, which is verified by numerical simulation. The number and positions of the cracks are sufficiently well predicted. Crack shape reconstructions from the predicted data are achieved with a satisfactory degree of accuracy.
2 citations
TL;DR: In this article, a template matching method with help of genetic algorithms is applied to predict the number and positions of cracks using the ECT signal obtained by two-dimensional scanning as a picture image.
Abstract: This paper describes a novel method identifying the number and positions of cracks. Using the ECT signal obtained by two-dimensional scanning as a picture image, a template matching method with help of genetic algorithms is applied to predict the number and positions of cracks. The present method employs a superposition of crack signals and a nonlinear scaling technique of a signal profile on crack length which are verified by numerical simulation. The number and positions of cracks are predicted sufficiently.
TL;DR: In this paper, a novel method for visualizing the multiple cracks from ECT image was proposed, where a template matching method was used to predict the shape of cracks in the ECT images.
Abstract: This paper proposes a novel method for visualizing the multiple cracks from ECT image. Assumed two-dimensional scanned ECT signals to be a picture image, then a template matching method predicts crack shapes. Moreover, comparing ECT image of the unknown multiple cracks and that of the known crack separates into each of the cracks. Genetic algorithm performs faster search algorithm in our template matching. Shape reconstructions are achieved in the multiple cracks at intervals of 2 mm with a satisfactory degree of accuracy.