• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.1
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• pp.8-14
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• 2007

X-ray digital tomosynthesis is widely used in the nondestructive testing and evaluation, especially for the printed circuit boards (PCBs). In this study, we propose a simple method to reduce the blur artefact, frequently claimed in the conventional digital tomosynthesis based on SAA (shift-and-add) algorithm, and thus restore the image sharpness. The proposed method is basically based on the SAA, but has a correction procedure by finding blur artefacts from the forward-and back-projection for the firstly obtained, manipulated backprojection data. The manipulation is the replacement of the original data at the POI (plane-of-interest) by zeros. This method has been compared with the conventional SAA algorithm using the experimental measurements and Monte Carlo simulation for the designed PCB phantom. The comparison showed a much enhancement of sharpness in the images obtained from the proposed method.

• Proceedings of the KIEE Conference
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• 2006.04b
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• pp.405-407
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• 2006

자기누설 탐상시스템은 자성체인 구조물에 서검사 대상 물체를 자화시켜 결함부위에서 자기 누설의 여부를 측정함으로써 구조물의 결함, 부식 등을 탐지하는 시스템이다. 본 논문에서는 소형 비파괴 검사시스템을 설계하고 제작하였다. 또한 3차원 유한요소법을 이용하여 해석하고 측정하여 결과를 비교 분석하였다.

• Journal of the Korean Society for Nondestructive Testing
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• v.20 no.6
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• pp.555-561
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• 2000

The remote field eddy current (RFEC) inspection was performed on the ductile cast iron pipes with nominal outer diameter of 100mm, which were machined with various shapes and sizes of defects. Ductile cast iron pipes which are used as water supply pipe have the non-uniform thickness and asymmetric cross section due to relatively high degree of allowable errors during the manufacturing processes. These characteristics of ductile cast in pipes cause the long range background noises in RFEC signals along the pipe. In this study, tile machined defects in pipes were effectively classified by the moving window average (MWA) method which eliminated the long-range noise. The voltage plane polar plots (VPPP) method was used to quantitatively evaluate the depth and circumferential degree of defects. The VPPP signatures showed that the angle between defect signature and the normalized in-phase component on the VPPP is linear to the depth of defects. The nondestructive RFEC technique proved to be capable of quantitatively evaluating the machined defects of underground water supply pipe.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.179-183
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• 2008

Methods of damage detection are used non-destructive test in concrete structures. These are using various sensors, but the most of damage detections are used a visual angle of human. Problems of crack damage detection are occurred to directions and boundary conditions of steel bars using accelerometer in concrete element. In this study, fundamental studies for estimation using 3 axial type of accelerometer and electric resistance property of thermocouple sensors are discussed estimation to effect of arranged steel bars and damage from low strength when they are oscillated elastic wave in concrete specimen.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.3
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• pp.275-283
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• 2002

To detect the position and depth of buried underground utilities, method of Ground Penetrating Radar(GPR) survey is the most commonly used. However, the skin-depth of GPR is very shallow, and in the places where subsurface materials are not homogeneous and are compose of clays and/or salts and gravels, GPR method has limitations in application and interpretation. The aim of this study is to overcome these limitations of GPR survey. For this purpose the site where the GPR survey is unsuccessful to detect the underground big pipes is selected, and soil tests were conducted to confirm the reason why GPR method was not applicable. Non-destructive high-frequency electromagnetic (HFEM) survey was newly developed and was applied in the study area to prove the effectiveness of this new technique. The frequency ranges $2kHz{\sim}4MHz$ and the skin depth is about 30m. The HFEM measures the electric field and magnetic field perpendicular to each other to get the impedance from which vertical electric resistivity distribution at the measured point can be deduced. By adopting the capacitive coupled electrodes, it can make the measuring time shorter, and can be applied to the places covered by asphalt an and/or concrete. In addition to the above mentioned advantages, noise due to high-voltage power line is much reduced by stacking the signals. As a result, the HFEM was successful in detecting the buried underground objects. Therefore this method is a promising new technique that can be applied in the lots of fields, such as geotechnical and archaeological surveys.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.6
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• pp.630-633
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• 2001

This paper propose electronic speckle pattern interferometry(ESPI) for reliability evaluation of electronic device. Especially, vibration problem in a fan of air conditioner, motor of washing machine and etc. is important factor to design the devices. But, it is difficult to apply previous method, accelerometer to the devices with complex geometry. ESPI, non-contact measurement technique applies a commercial fan of air conditioner to vibration analysis. Vibration mode shapes, natural frequency and the range of the frequency are decided and compared with that of FEM analysis. In mechanical deign of new product, ESPI adds weak point of previous method to supply effective design information.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.165-168
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• 2008

This study performed the 3-dimensional inspection analysis for cavitation by using the ultrasonic pulse velocity method to detect detailed various cavitations in a concrete test material. The internal-void are made of non-void test material and two types of which a regular square type and a rectangle type that produced through the 3-dimensional cavitation to put into a $500{\ast}500{\ast}500mm$ sized non-reinforced concrete test material. The tomography method for the ultrasonic pulse velocity method was used for the non-destructive test. As a result, this study has found that it is possible to visualize the cavitation as an image, and to analyze the internal-void in detail by the non-destructive method.

• Journal of the Korean Society for Nondestructive Testing
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• v.35 no.5
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• pp.341-348
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• 2015

Active infrared thermography methods have been known to possess good fault detection capabilities for the detection of defects in materials compared to the conventional passive thermal infrared imaging techniques. However, the reliability of the technique has been under scrutiny. This paper proposes the lock-in thermography technique for the detection and estimation of artificial subsurface defect size and depth with uncertainty measurement.

• Journal of the Korean Society for Nondestructive Testing
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• v.23 no.4
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• pp.328-333
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• 2003

It has been widely recognized that the residual stress of the weldment affect the integrity of steel structures and cause an initiation of crack in the welded regions. Since the power plants adopt a variety of welding processes, it is necessary to know the distribution and magnitude of residual stresses. This paper has attempted to investigate the validity of the saw cutting method and the indentation method to measure the residual stresses in the steel plates. The residual stresses in the specimens of hot reheater pipes, cold reheater pipes and feed water lines in power plants were determined by the saw cutting method and the indentation method. The data were compared and reviewed for the validity of the methods.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.2
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• pp.103-111
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• 1998

A nondestructive ultrasonic technique is presented for estimating the reinforcement volume fractions of particulate composites. The proposed technique employs a theoretical model which accounts for composite microstructures, together with a measurement of ultrasonic velocity to determine the reinforcement volume fractions. The approach is used for a wide range of SiC particulate reinforced Al matrix ($SiC_p/Al$) composites. The method is considered to be reliable in determining the reinforcement volume fractions. The technique could be adopted in a production unit for the quality assessment of the metal matrix particulate composite extrusions.