| ID | 21 |
| Title | Fast simulation of ECT signal due to a conductive crack of arbitrary width |
| Author | Zhenmao Chen, Mihai Rebican, Noritaka Yusa, Kenzo Miya |
| Published in | IEEE transactions on Magnetics, Vol. 42, pp. 683-686 (2006) |
| Keywords | crack width, eddy current testing (ECT), forward, analysis, fast simulation method, inverse analysis, new element |
| Abstract | This paper proposes a strategy for the fast simulation of eddy current testing signals due to a conductive crack of arbitrary width. To cope with a crack of width less than that selected for establishing the database, which is necessary in the fast-forward analysis scheme proposed by authors, a new finite element is introduced to treat the case when the crack boundary is contained in the element. By using such a new element, the fast-forward analysis scheme becomes suitable for the reconstruction of both the shape and width of a planar crack. It is verified that such a multiple material element is efficient for an ECT sensor inducing eddy current parallel with the crack surface. For the case with perpendicular eddy current component, however, the approach is not valid because of a scalar potential jump at the crack surface. Finally, the reason of such a singularity is investigated through numerical simulations. |
| ID | 22 |
| Title | Detection of embedded fatigue cracks in Inconel weld overlay and the evaluation of the minimum thickness of the weld overlay using eddy current signals |
| Author | Noritaka Yusa, Ladislav Janousek, Mihai Rebican, Zhenmao Chen, Kenzo Miya, Naoki Chigusa, and Hajime Ito |
| Published in | Nuclear Engineering and Design, Vol. 236, pp. 1852-1859 (2006) |
| Keywords |
nuclear power plants, non-destructive testing, weld overlays, fatigue cracks, head penetration, sizing |
| Abstract |
This study evaluates the applicability of eddy current testing to the detection and sizing of fatigue cracks embedded in Inconel weld overlays. Welded plate specimens, which model head penetration welds and their weld overlays, are fabricated, and fatigue cracks are artificially introduced into the specimens. Eddy current inspections are performed using a uniform eddy current probe driven with 10 kHz, and all of the fatigue cracks are detected with clear signals. Subsequent numerical inversions estimated that the minimum1 thicknesses of the weld overlays were 1.47, 2.17, and 2.23 mm, whereas true thicknesses revealed through destructive testing were 1.51, 3.25, and 2.10 mm, respectively. Thicknesses were evaluated using potential drop and ultrasonic testing methods; the results demonstrated that eddy current testing is the most efficient of the three methods. |
| ID | 23 |
| Title | Utilization of two-directional AC current distribution for enhancing sizing ability of electromagnetic nondestructive testing methods |
| Author | Ladislav Janousek, Noritaka Yusa, and Kenzo Miya |
| Published in | NDT&E international, Vol. 39, pp. 542-546 (2006) |
| Keywords | nondestructive evaluation; depth evaluation; skin depth; eddy current testing; potential drop testing; suerposition |
| Abstract | This paper proposes a novel method for accurately evaluating the depth of a defect using electromagnetic phenomena. The novel method induces AC currents inside a conductive medium and detects the disturbance of the currents. Whereas the principle itself has been utilized in conventional methods, the uniqueness of this new method lies in realizing a current distribution in which there is a region where currents near the surface and those deeply inside the specimen flow opposite to each other. The novel method provides a clear indication corresponding to the depth of the inspected defect. In addition, it enables one to evaluate the depth of a defect that is much deeper than the depth of penetration. After the physical background of this new method is explained, the results of experimental verifications and subsequent numerical simulations are presented. |
| ID | 24 |
| Title | Controlling AC distribution inside conductive material leads to a novel volumetric examination method —experimental verification. |
| Author | Noritaka Yusa, Ladislav Janousek, and Kenzo Miya |
| Published in | Journal of Japan Society for Non-destructive Inspection, Vol. 55, pp. 531-535 (2006) |
| Keywords | electromagnetic nondestructive evaluation, AC, defect depth evaluation, sizing, phase lag, skin depth |
| Abstract | This paper experimentally demonstrates that controlling AC distribution inside conductive material enables one to perform volumetric examination using electromagnetic phenomena. Several current distributions are superposed to locally realize AC distribution having a phase difference of 180 degrees between currents flowing near the surface and those deeply inside, and having non-exponential decay in depth direction. Experimental results clearly show that measuring the phase of magnetic field outside the material as a function of the ratio of the superposition provides information about the depth of defects quantitatively. In addition, this approach is applicable even though the depth of defects is much deeper than the standard depth of penetration; experimental results show clear differences between signals due to near-side notches 10, 12, 15, and 20 mm deep, when an exciting frequency of 100 kHz is adopted. |
| ID | 25 |
| Title | Eddy current data for characterizing less volumetric stress corrosion cracking in nonmagnetic materials |
| Author | Noritaka Yusa, Stephane Perrin, and Kenzo Miya |
| Published in | Materials Letters, Vol. 61, pp. 827-829 (2007) |
| Keywords |
nondestructive testing, eddy current testing, natural crack, benchmark problem, numerical modeling, austenitic stainless steel |
| Abstract |
The authors gather eddy current signals due to artificial stress corrosion cracking so that the data may be available to other researchers. Three cracks are introduced into an austenitic stainless steel plate, eddy current measurements are performed, and then the plate is destroyed to observe the cross-sectional profiles of the cracks. The authors will offer the data, as well as the true profile of the stress corrosion cracking revealed by destructive tests, to anybody who are interested in utilizing it in their studies. |
| ID | 26 |
| Title | A nondestructive strategy for distinction of natural fatigue and stress corrosion cracks based on signals of the eddy current testing |
| Author | Zhanmao Chen, Ladislav Janousek, Noritaka Yusa, Kenzo Miya |
| Published in | Journal of Pressure Vessel Technology, Vol. 129, pp. 719-728 (2007). |
| Keywords | crack distinction, stress corrosion crack, fatigue crack, eddy current testing, nuclear power plant |
| Abstract | In this paper, a novel nondestructive strategy is proposed for distinguishing between a Stress Corrosion Crack (SCC) and a Fatigue Crack (FC) based on signal features of Eddy Current Testing (ECT). The strategy consists of a measurement procedure with a special ECT probe and crack type judgment scheme based on an index parameter that is defined as the amplitude ratio of the inspected signals. An ECT probe, which can induce eddy current flowing mainly in a selected direction, is proposed and applied to detect crack signals by scanning it along the crack with different probe orientation. It is clarified that the ratio of the amplitudes of signals detected for parallel and perpendicular probe orientation is sensitive to the microstructure of the crack, i.e., the parameter is much bigger for a fatigue crack than that of a SCC. Therefore, whether a crack is a SCC or a FC can be recognized nondestructively by comparing the index parameter with a threshold value that is selected a prior. In order to verify the validity of the proposed strategy, a lot of test-pieces of artificial SCC and FC are fabricated and ECT inspections are performed to measure the corresponding crack signals. Numerical simulations are also conducted to investigate the physical principle of the new methodology. From both the numerical and experimental results, it is demonstrated that the strategy is very promising for the distinction of artificial SCC and FC and shows high possibility in practical application to the natural cracks if the threshold value can be properly determined. |
| ID | 27 |
| Title | Numerical evaluation of the ill-posedness of eddy current problems to size cracks |
| Author | Noritaka Yusa, Haoyu Huang, Kenzo Miya |
| Published in | NDT&E international, vol. 40, pp. 185-191 (2007) |
| Keywords | Eddy current testing, conductivity, sizing, inverse problem, electromagnetic nondestructive evaluation |
| Abstract |
This study evaluates whether or not eddy current testing is applicable to the sizing of cracks that appear in a general structure. Two 10 mm thick specimens with artificial stress corrosion cracking are prepared, eddy current testing is performed to gather eddy current signals that result from cracking, and numerical inversions are performed to evaluate the maximum depths of the cracking. The inversions estimate the depths of the cracks are 0.8 and 1.6 mm. Although the simulated signals agree well with the measured ones, destructive tests reveal that the true depths are 1.27 and 2.58 mm. Another numerical simulation is conducted to discuss the ill-posedness of the inverse problem of sizing crack depths from eddy current signals. The simulation simply models a crack as a rectangular region with a constant length and uniform conductivity inside and calculates the eddy current signals of 1024 cracks having variety of depths, widths, and conductivities. Analyzing the results of the simulation reveal that information contained in conventional single-frequency eddy current tests is not sufficient to size conductive cracks in a general sense. |
| ID | 28 |
| Title | Numerical modeling of general cracks from the viewpoint of eddy current testing |
| Author | Noritaka Yusa, Stephane Perrin, Kazue Mizuno, Kenzo Miya |
| Published in | NDT&E international, Vol. 40, pp. 577-583 (2007). |
| Keywords | electromagnetic nondestructive evaluation, eddy current testing, austenitic stainless steel, finite element simulations, fatigue crack, stress corrosion cracking |
| Abstract | This study discusses numerical modeling of fatigue and stress corrosion cracking in eddy current simulations. Ten fatigue crack specimens and another ten stress corrosion crack specimens are prepared for this purpose. The specimens are made of type 316 stainless steel and measure 10 mm in thickness for a general evaluation of the model. Eddy current inspections of the specimens are performed using a differential type plus point probe; the specimens then undergo destructive tests to confirm the true profiles of the cracks. Subsequent numerical simulations are conducted to evaluate the equivalent conductivity and width of the cracks. The simulations demonstrate that a fatigue crack can be modeled as a nonconductive region and it is not necessary to know exactly how wide the opening of a fatigue crack is. They also revealed, in contrast, that stress corrosion cracking needs to be modeled as a conductive region with a certain width. |
| ID | 29 |
| Title | Development of the estimation and optimization model for executing TBM time intervals in maintenance methods combined TBM and CBM |
| Author | Ling Yuanjing, Koh-ichi Maki, Noritaka Yusa, Kenzo Miya |
| Published in | Transactions of the Atomic Energy Society of Japan, Vol. 6, pp. 312-319 (2007) |
| Keywords | executing TBM time interval, maintenance method, combined TBM and CBM, spurious diagnostic, life time of measuring devices, minimizing maintenance cost, state transition model |
| Abstract | A reduction of the maintenance cost and an improvement of utilization in facilities have been performed by introducing Condition-Based Maintenance (CBM ) to nuclear power plants since the 1980s in USA. In Japan, also, maintenance methods combined with TBM (Time-Based Maintenance ) and CBM have a tendency to be applied. In the present work, an estimation and optimization model for extending TBM time interval is developed considering spurious diagnosis of measuring devices in the maintenance method combined with TBM and CBM. Using the present model, the life time of applied measuring devices can be estimated in order to prolong the time interval of TBM execution and satisfy the required one. Moreover, TBM time interval can be given for minimizing the maintenance cost under the condition of the target safety. From a sensitivity analysis of the parameters including the present model, it is clari?ed that leaving the facilities in an abnormal state has the largest e?ect on the cost of damage for the maintenance. |
| ID | 30 |
| Title | Eddy current inspection of closed fatigue and stress corrosion cracks |
| Author | Noritaka Yusa, Stephane Perrin, Kazue Mizuno, Zhenmao Chen, Kenzo Miya |
| Published in | Measurement Science and Technology, Vol. 129, pp. 719-728 (2007) |
| Keywords | electromagnetic nondestructive evaluation, fatigue crack, stress corrosion cracking, austenitic stainless steel |
| Abstract |
This study evaluates the effect of loading on closed crack openings on eddy current signals caused by the crack. Three plate specimens having a fatigue crack and another three specimens having stress corrosion cracking are prepared. Four-point bending of the specimens is carried out to introduce compressive stress to close the opening of the cracks. Then eddy current signals due to the crack are gathered using a plus point type probe. The bending was conducted with a variable load; the eddy current signals remain almost unchanged regardless of the loading. |
| ID | 31 |
| Title | Multi-probe inspection for enhancing sizing ability in eddy-current non-destructive testing |
| Author | Ladislav Janousek, Klara Capova, Noritaka Yusa, and Kenzo Miya |
| Published in | IEEE transactions on Magnetics 44(6), pp. 1618-1621 (2008) |
| Keywords | Nondestructive testing, Eddy current testing, Multisensor systems, Signal reconstruction |
| Abstract | The paper proposes a unique idea for enhancing sizing ability in eddy-current non-destructive testing. A detected crack is inspected using several probes driven at the same exciting frequency but producing different eddy current distributions. Two probes are utilized for the purpose in the paper. The crack signals obtained with the two probes are linearly superposed and a unique value of the ratio of superposition is extracted from the mixed signals. Numerical investigations and experimental verification reveal that the value provides clear indications of the crackfs depth. In addition, the depth of a notch five times as deep as the standard depth of penetration was well evaluated using the method. |
| ID | 32 |
| Title | Enhancements of eddy current testing techniques for quantitative nondestructive testing of key structural components of nuclear power plants |
| Author | Zhenmao Chen, Noritaka Yusa, and Kenzo Miya |
| Published in | Nuclear Engineering and Design 238, pp. 1651-1656 (2008) |
| Keywords | eddy current testing, NDT, defect detection, defect sizing, in-service inspection, welding defect, stress corrosion crack |
| Abstract |
| ID | 33 |
| Title | Sizing of long stress corrosion crack from 2D ECT signals by using a multisegment inverse analysis strategy |
| Author | Li Wang, Zhenmao Chen, Tian-Jian Lu, Minglong Xu, Noritaka Yusa, and Kenzo Miya |
| Published in | International Journal of Applied Electromagnetics and Mechanics 28 (2008), 155-161. |
| Keywords | |
| Abstract | @ |
| ID | 35 |
| Title | Development of computational inversion techniques to size cracks from eddy current signals |
| Author | Noritaka Yusa |
| Published in | Nondestructive Testing and Evaluation 24 (2009), 39-52. |
| Keywords | eddy current testing, electromagnetic nondestructive evaluation, inverse problem, numerical modeling, sizing, reconstruction |
| Abstract | This paper reviews the recent advance in computational inversion techniques to size defects using eddy current signals. Studies reporting the sizing of artificial slits with the aid of computational inversion techniques are briefly overviewed, and then several recent studies dealing with the sizing of fatigue and stress corrosion cracks are introduced. The results of the studies confirm computational techniques for sizing slits are sufficiently mature, and even though the measured signals are polluted with high noise, the boundary profile of slits can be evaluated from the signals. Furthermore, the studies demonstrate fatigue cracks can be dealt with almost identically to artificial slits from the viewpoint of eddy current testing; fatigue cracks introduced inside weld with a rough surface are well sized using eddy current testing with the aid of computational inversion techniques. In contrast, there is a large discrepancy between artificial slits and stress corrosion cracks, and thus conventional approaches are not always applicable to the sizing of stress corrosion cracks. This paper introduces several recent activities in the authorfs group to overcome this problem |
| ID | 36 |
| Title | Some advances in numerical analysis techniques for quantitaitve electromagnetic nondestructive evaluation |
| Author | Zhenmao Chen, Noritaka Yusa, Kenzo Miya |
| Published in | Nondestructive Testing and Evaluation 24 (2009), 69-102. |
| Keywords | @ |
| Abstract | @ |
| ID | 37 |
| Title | Discussion on the equivalent conductivity and resistance of stress corrosion cracks in eddy current simulations |
| Author | Noritaka Yusa and Kenzo Miya |
| Published in | NDT&E International 42 (2009), 9-15 |
| Keywords | electromagnetic nondestructive evaluation, eddy current testing, finite element method, numerical modeling, stress corrosion cracking |
| Abstract | This study evaluates the numerical modeling of stress corrosion cracks from the viewpoint of eddy current simulations. Five stress corrosion cracks are artificially introduced into austenitic stainless steel plates measuring 25 mm in thickness, and then eddy current inspections are conducted to gather eddy current signals and destructive tests performed to confirm the true profiles of the cracks. The cracks are carefully introduced so as not to cluster, and the data obtained enables discussion of the modeling of a single crack quantitatively. Subsequent numerical simulations model each crack as a rectangular region with a fixed width and uniform conductivity, and evaluate the equivalent width and conductivity suitable for modeling the crack. The evaluation reveals that it is not reasonable to correlate the size of a crack and only its width or conductivity, and larger cracks tend to have greater resistance, which is defined as the width divided by conductivity. Furthermore, the values of width and conductivity depend also on the exciting frequency and probe used; however, the resistance remains almost unchanged by the experimental condition. |
| ID | 38 |
| Title | Numerical evaluation of the effectiveness of colloidal gold as a contrast agent |
| Author | Noritaka Yusa, Meiling Jiang, Kazue Mizuno, Mitsuru Uesaka |
| Published in | Radiological Physics and Technology 2 (2009), 33-39. |
| Keywords | gold nanoparticles, Monte Carlo simulation, radiotherapy, imaging agent, monochromatic X-rays, Compton scattering |
| Abstract | Monte Carlo numerical simulations were conducted for evaluating the effectiveness of colloidal gold as a contrast agent. The simulations were conducted in a simple configuration modeling a phantom for maintaining the generality of the results, and the effect of the mass percentage of gold accumulated inside a tumor and that of the energy of the irradiating X-rays were evaluated, as well as other information such as the energy spectrum of the photons reaching the detector and change in the energy deposited inside the phantom. The contrast of the X-ray image due to the layer is calculated from the total energy of photons transmitted to the back surface of the phantom. The simulation revealed that colloidal gold of a mass percentage of 1.0% provided an image for which the contrast was almost 70% of that for bone of the same thickness when X-rays from conventional X-ray tubes were considered. Monochromatic X-rays of 44, 66, and 88 keV, which simulated the Compton-scattering monochromatic X-ray source being developed, were also evaluated. X-rays at the former two energies did not have a significant advantage over the rays from the X-ray tubes. For colloidal gold with a mass percentage of 1.0%, the 88 keV monochromatic X-ray produced an image contrast that was about 10% higher than the contrast for bone of the same thickness, as suggested by the K-absorption energy of gold. However, the improvement was not large, considering the difficulty in making such a high-energy monochromatic X-ray source available. |
| ID | 39 |
| Title | Evaluation of stress corrosion cracking as a function of its resistance to eddy currents |
| Author | Noritaka Yusa and Hidetoshi Hashizume |
| Published in | Nuclear Engineering and Design 239 (2009), 2713-2718. |
| Keywords | electromagnetic nondestructive evaluation, eddy current testing, finite element method, numerical modeling, stress corrosion cracking |
| Abstract | This study discusses the equivalent conductivity, the equivalent width, and the equivalent resistance of stress corrosion cracks from the viewpoint of eddy current testing. Four artificial stress corrosion cracks were prepared for this study, and their eddy current signals were gathered using two absolute pancake probes and two differential type plus point probes. Then their numerical models were evaluated using finite element simulations on the basis of the measured eddy current signals and their profiles revealed by destructive tests. The results of this study revealed that whereas the equivalent conductivity and the equivalent width depend on the exciting frequency utilized, the equivalent resistance of a crack has much less dependency, which agrees well with an earlier report. This study also revealed that the resistance of a crack depends on probe utilized. Larger probes tend to lead to smaller crack resistance. Pancake type probes tend to lead to larger crack resistance than plus point probes. Analyzing the results together with earlier reports indicates that cracks with a large equivalent conductivity tend to have large equivalent width, and supports the validity of assuming the minimum resistance of a stress corrosion crack whereas considering the conductivity and the width individually would not be viable . |
| ID | 40 |
| Title | A nondestrcuctive strategy to evaluate deep near-side defects from eddy current signals |
| Author | Noritaka Yusa, Ladislav Janousek, and Kenzo Miya |
| Published in | Journal of Japan Society for Mechanical Engineers, Series A 75 (2009), 1454-1459. |
| Keywords | Inverse Problem, Nondestructive Inspection, Finite Element Method, Genetic Algorithm, Material Flaw |
| Abstract |