• Journal of the Korean Society for Nondestructive Testing
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• v.30 no.2
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• pp.85-90
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• 2010

The infrared energy is emitted in the infrared wavelength range that corresponds to the surface temperature of a object which has temperature that is over the absolute the temperature(OK). The infrared thermography (IRT) is a non-destrnctive testing method that provides thermal video for the user in real-time by converting the infrared quantity that is detected by the infrared detector into temperature. The pipes of nuclear power plant(NPP) could be thinned by the corrosion and fatigue and the defect could lead to a big accident. For this reason, the effective non-destructive testing method is necessary. In this study, the relationship between the measured temperature and the defect depth or size of NPP pipes were recognized and that was applied to detect the wall thinning defects of NPP pipes.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.54-61
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• 2000

In order to determine the mode I stress intensity factor ($K_I$) by means of the alternating current potential drop(ACPD) technique, the change in potential drop due to load for a paramagnetic material containing a two-dimensional surface crack was examined. The cause of the change in potential drop and the effects of the magnetic flux and the demagnetization on the change in potential drop were clarified by using the measuring systems with and without removing the magnetic flux from the circumference of the specimen. The change in potential drop was linearly decreased with increasing the tensile load and was caused by the change in conductivity near the crack tip. The reason of decreasing the change in potential drop with increasing the tensile load was that the increase of the conductivity near the crack tip due to the tensile load caused the decreases of the resistance and internal inductance of the specimen. The relationship between the change in potential drop and the change in $K_I$ was not affected by demagnetization and was independent of the crack length.

• Journal of the Korean Society for Nondestructive Testing
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• v.29 no.4
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• pp.331-337
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• 2009

Space launch vehicles require highly reliable, lightweight structures. It is thus important to monitor the structural health of these components with nondestructive inspections. In this paper, we studied an example of a nondestructive inspection that was partially applied to the manufacture and inspection of a launch vehicle. Ultrasonic tests, X-rays, tapping, and acoustic emissions comprised the inspection method. A payload fairing, high pressure tank, fastener part, and bonding part were used as hardware to be inspected. We proposed a quantitative standard for debonding inspection of the payload fairing and acoustic emission data for the proof test of the high pressure tank. We analyzed the fracture mode of the sandwich fastener part according to frequency changes. We also proposed a standard specimen for ultrasonic inspection of bonds of different materials. The present analyses and results provide data for evaluation of the launch operation sequence to ensure launch vehicles afford high reliability.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.2
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• pp.87-94
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• 2005

In recent, Lamb wave has been actively studied for non-destructive testing of plate. Among those studios, laser generation method of focused Lamb wave is expected to have high spatial resolution with advantages of non-contact testing. In this method, the laser beam is illuminated on the surface of object by through an arrayed-arc slit, and then the energy of the generated Lamb wave is concentrated at a focus of arc. This focusing effect improves the spatial resolution, which is dependant on the geometries of arrayed-arc slit. In this paper, the relationships between the parameters of arc-shaped slit and the focusing ability of the generated Lamb wave was investigated by the simulation based parametric study The results show that to improve the focusing effect, radius of illuminated laser, angle of arc and number of arcs must be increased, which minimum radius of arc and distance between arcs(=wavelength) must be decreased. These results are expected to be used as a guide to design the proper shape of slit.

• Journal of the Korean Society for Nondestructive Testing
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• v.31 no.5
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• pp.508-515
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• 2011

Bovine incisor was investigated using active infrared thermography(IRT) to visualize crack on bovine teeth. An artificial crack was carefully created in bovine incisor sample by compression load of universal tensile machine. While applying a sinusoidal heat wave to the cracked bovine incisor through halogen lamp, consecutive digital infrared images was captured from the sample surface at a frequency synchronized with heat excitation. Phase information of thermal image was calculated by four-point correlation method and processed to produce the phase image of bovine incisor. This phase image showed clearly the crack on the incisor, which was hardly detected in traditional passive thermography.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.1
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• pp.10-17
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• 2000

In boiler high-temperature pipelines such as main steam pipe, header and steam drum in fossil power plants, conventional measurement techniques(replica method, electric resistance method, and hardness test method) for measuring creep damage have such disadvantages as complex preparation and measurement procedures, too many control parameters. And also, these techniques have low practicality and applied only to component surfaces with good accessibility. It needs to apply a reliable and quantitative ultrasonic nondestructive evaluation method that can be replaced for these equipment. In this study, both artificial creep degradation test using life prediction formula and frequency analysis by ultrasonic tests for crept specimens were carried out for the purpose of nondestructive evaluation for creep damage. As a result of ultrasonic tests for crept specimens, we conformed that the high frequency side spectra decrease and central frequency components shift to low frequency band, and also their bandwidth decreases as increasing creep damage in backwall echos.

• Journal of the Korean Society for Nondestructive Testing
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• v.26 no.5
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• pp.343-352
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• 2006

In the present paper, the nondestructive test method was suggest to establish the bonding status of a motor case assembly composed of a steel motor case, adiabatic rubber layer and an ablative composite tube with strain data, AE(acoustic emission) signals and UT(ultrasonic test) data. And, finite element analysis was conducted to verify quantitatively the bonding status of motor case assembly under inner pressure loading. The bonding status could be judged whether the bonding status is perfect or contact condition by the data correlation study with AE signals and strain data measured from air pressure test. And, to classify the bonding status of motor case and rubber layer among bonding layers, UT method was also applied. From this study, the bonding status could be classified and detected into fourth types for all bonding layers as follows: (1) initial un-bonding, (2) perfect do-bonding during an air pressure test, (3) partially de-bonding during an air pressure test, and (4) perfect bonding.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.545-554
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• 2000

Compton X-ray backscatter technique has been used to quantitatively assess the impact damage in quasi-isotropic laminated composites and to obtain a cross-sectional profile of impact-damaged laminated composites from the density variation of the cross section. An adaptive filter is applied to the Compton backscattering data for the reconstruction and noise reduction from many sources including quantum noise, especially when the SNR(signal-to-noise ratio) of the image is relatively low. A nonlinear reconstruction model is also proposed to overcome distortion of the Compton backscatter image due to attenuation effects, beam hardening, and irregular distributions of the fibers and the matrix in composites. Delaminations masked or distorted by the first few delaminations near the front surface are detected and characterized both in width and location, by application of an error minimization algorithm.

• Journal of the Korean Society for Nondestructive Testing
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• v.25 no.1
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• pp.27-35
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• 2005

Ultrasonic inspection methods are widely used for detecting flaws in materials. The signal analysis step plays a crucial part in the data interpretation process. A number of signal processing methods have been proposed to classify ultrasonic flaw signals. 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 spare. This paper describes an alternative approach which uses the least mean square (LMS) method and exportation maximization (EM) algorithm with the model based deconvolution which is employed for classifying nondestructive evaluation (NDE) signals from steam generator tubes in a nuclear power plant. The signals due to cracks and deposits are not significantly different. These signals must be discriminated to prevent from happening a huge disaster such as contamination of water or explosion. A model based deconvolution has been described to facilitate comparison of classification results. The method uses the space alternating generalized expectation maximiBation (SAGE) algorithm ill conjunction with the Newton-Raphson method which uses the Hessian parameter resulting in fast convergence to estimate the time of flight and the distance between the tube wall and the ultrasonic sensor. Results using these schemes for the classification of ultrasonic signals from cracks and deposits within steam generator tubes are presented and showed a reasonable performances.

• Computational Structural Engineering
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• v.11 no.3
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• pp.187-198
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• 1998

지하구조물의 건전성을 평가하기 위한 비파괴시험으로써 탄성응력파를 이용한 충격반향탐사법을 수치해석적인 방법을 통하여 수행하였다. 즉, 일면만으로 접근 가능한 터널 면에서의 충격가진과 동적응답의 측정으로 이질면을 포함한 내부의 상태를 예측할 수 있다. 연구의 수행은 탄성거동을 하는 매질 내부에서 전파되는 탄성응력파의 특성을 이해하고, 이를 동적 유한요소해석으로 모형화하여 충격반향탐사법을 수치해석적으로 수행한다. 이질재료가 2개의 층을 이루고 있는 경우 표면층의 두께를 쉽게 측정할 수 있었으며, 구조물의 병진운동, 휨운동과 구조물 내에서 다중반사되는 탄성응력파에 의한 복합적인 영향을 받는 터널과 같은 원통형 구조물에서 동적응답의 주파수 특성으로부터 터널라이닝 내부에 형성된 공동의 위치와 크기의 예측이 가능하였다. 수치해석적인 방법과 병행하여 다양한 형태의 경계조건을 가지는 구조물에 대한 충격반향탐사법의 실험을 수행할 경우 실제적인 문제에 적용, 건전성 평가의 지표를 마련할 수 있을 것으로 사료된다.