• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.163-170
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• 2005

A modular Gaussian beam model is developed to simulate some ultrasonic testing configurations where multiple interfaces are involved. A general formulation is given in a modular matrix form to represent the Gaussian beam propagation with multiple interfaces. The ultrasonic transducer fields are modeled by a multi-Gaussian beam model which is formed by superposing 10 single Gaussian beams. The proposed model, referred to as "MMGB" (modular multi-Gaussian beam) model, is then applied to a typical contact and angle beam testing configuration to predict the output signal reflected from the corner of a vertical crack. The resulting expressions given in a modular matrix form are implemented in a personal computer using the MATLAB program. Simulation results are presented and compared with available experimental results.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.451-458
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• 2005

The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for various composite laminates. Reflection and transmission optical microscopy were used to investigate the damage zone of specimens. AE signals were classified through short time Fourier transform(STFT) as different types: AE signals with a high intensity and high frequency band were due to fiber fracture, while weak AE signals with a low frequency band were due to matrix cracking and/or interfacial cracking. Characteristic feature in the rate of hit-events having high amplitudes showed a procedure of fiber breakages, which expressed the characteristic fracture processes of notched fiber-reinforced plastics with different fiber orientations. As a consequence, the behavior of fracture in the continuous composite laminates could be monitored through nondestructive evaluation(NDE) using the AE technique.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.178-188
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• 2005

This paper introduces a structural damage identification method to identify 4he multiple directional damages generated within a cylindrical shell by using the measured frequency response function (FRF). The equations of motion for a damaged cylindrical shell are derived. by using a theory of continuum damage mechanics in which a small material volume containing a directional damage is represented by the effective orthotropic elastic stiffness. In contrast with most existing vibration-based structural damage identification methods which require the modal Parameters measured in both intact and damaged states, the present method requires only the FRF-data measured at damaged state. Numerically simulated damage identification tests are conducted to verify the feasibility of the Proposed structural damage identification method.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.459-466
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• 2005

The scanning laser source (SLS) technique has been proposed recently as an effective way to investigate small surface-breaking defects, By monitoring the amplitude and frequency changes of the ultrasound generated as the SLS scans over a defect, the SLS technique has provided enhanced signal-to-noise performance compared to the traditional pitch-catch or pulse-echo ultrasonic methods, An extension of the SLS approach to map defects in microdevices is proposed by bringing both the generator and the receiver to the near-field scattering region of the defects, To facilitate near-field ultrasound measurement, silicon microcantilever probes are fabricated using microfabrication technique and their acoustical characteristics are investigated, Then, both the laser-generated ultrasonic source and the microcantilever probe are used to monitor near-field scattering by a surface-breaking defect.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.189-200
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• 2005

Ultrasonic inspection methods are widely used for detecting flaws in materials. One of the more popular methods involves the extraction of an appropriate set of features followed by the use of a neural network for the classification of the signals in the feature space. This paper describes an approach which uses LMS method to determine the coordinates of the ultrasonic probe followed by the use of SAFT to estimate the location of the ultrasonic reflector The method is employed for classifying NDE signals from the steam generator tubes in a nuclear power plant. The classification results using this scheme for the ultrasonic signals from cracks and deposits within steam generator tubes are presented.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.201-208
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• 2005

In this paper, absolute and differential eddy current signals from various defects in the steam generator tube are numerically predicted and their signal slope characteristics are investigated. The signal changes due to frequency increase are also observed. After studying signal patterns from various defects and frequencies, the analysis of mixed defect signals affected by the presence of a ferromagnetic support plate is attempted. For the signal prediction, axisymmetric finite element modeling is used and this leads us to the slope angle analysis of the signal. Results show that differential signals are useful for locating the position of a defect under the support plate, while absolute signals are easy to presume and interpret even though the effect of support plate is mixed. Combined use of these two types of signals will help us accomplish a more reliable inspection.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.475-482
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• 2005

The iterative calculation by least square method was used to determine the source location of acoustic emission in rock, as so called "traditional method". The results were compared with source coordinates infered from the application of neural network system for new input data, as so called "new method". Input data of the neural network were based on the time differences of longitudinal waves arrived from acoustic emission events at each transducer, the variation of longitudinal velocities at each stress level, and the coordinates of transducer as in the traditional method. The momentum back propagation neural network system adopted to determine source location, which consists of three layers, and has twenty-seven input processing elements. Applicability of the new method were identified, since the results of source location by the application of two methods were similarly concordant.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.6
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• pp.483-486
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• 2005

The relationship between the EFBH (Equivalent Flat-Bottom Hole) size measured by non-destructive method and the actual size by destructive method in many rotors manufactured at Doosan Heavy Industries & Construction Co. Ltd. was investigated. In this investigation. "the Master Curve" compensating the differences between UT reported sizes and actual sizes of defects in our rotor forgings were obtainable. The applicability of this "Master Curve" as a way of calculating the actual defect size was also investigated. For the evaluation of rotor forgings, it is expected that this "Master Curve" may be used to determine the accurate actual sizes of defects.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.209-214
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• 2005

Spot welding is the most widely used in automotive and aerospace industries. The quality of weld depends upon the size of nugget between the overlapped steel plates. Recently, the thickness of the steel plates is much thinner and hence, it introduces the smaller size of nugget. Therefore, it is necessary not only to develop the criterion to evaluate the quality of weld but also to obtain the optimal welding conditions for the better performance. In this paper, the steel plates, 0.5 mm through 1.5 mm thickness, have been spot welded at different welding conditions and the nugget sizes are examined by ultrasonic technique (C-scan type). The relationships between the nugget sizes and the weldability have been investigated. The result of ultrasonic technique shows the good agreement with that of the tensile test.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.3
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• pp.215-221
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• 2005

It is required to evaluate nondestructively depth of surface-breaking cracks in structures. In this paper, the self-compensated technique by laser-based ultrasound is used to measure the depth of surface-breaking defect. Optical generation of ultrasound produces a well defined pulse with reliable frequency content. It is broad banded and suitable for measurement of attenuation and scattering over a wide frequency range. The self-calibrated signal transmission data of surface wave shows good sensitivity as a practical tool far assessment of surface-breaking defect depth. It is suggested that the relationship between the signal transmission and crack depth can be used to predict the surface-breaking crack depths in structures.