• Smart Structures and Systems
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• 제5권4호
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• pp.469-482
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• 2009

The emerging sensor-based structural health monitoring (SHM) technology has a potential for cost-effective maintenance of aging civil infrastructure systems. The author proposes to integrate continuous and global monitoring using on-structure sensors with targeted local non-destructive evaluation (NDE). Significant technical challenges arise, however, from the lack of cost-effective sensors for monitoring spatially large structures, as well as reliable methods for interpreting sensor data into structural health conditions. This paper reviews recent efforts and advances made in addressing these challenges, with example sensor hardware and health monitoring software developed in the author's research center. The hardware includes a novel fiber optic accelerometer, a vision-based displacement sensor, a distributed strain sensor, and a microwave imaging NDE device. The health monitoring software includes a number of system identification methods such as the neural networks, extended Kalman filter, and nonlinear damping identificaiton based on structural dynamic response measurement. These methods have been experimentally validated through seismic shaking table tests of a realistic bridge model and tested in a number of instrumented bridges and buildings.

• Journal of the Korean Wood Science and Technology
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• 제34권2호
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• pp.1-9
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• 2006

The structural wooden members of the ancient building are deteriorated by fungi and termite over time. The deteriorate of the members causes the decrease of the specific gravity and the strength of it, so the stability of the building is threatened. Therefore, in this study, the evaluation of the specific gravity, which is correlated with the strength of the wood, was conducted in the post member using Nondestructive Evaluation (NDE) - Drilling Resistance Test (DRT). For the purpose of it, the specific gravity and drilling resistance of small specimens was measured to obtain the correlation between the specific gravity and the drilling resistance. And then, the drilling resistance test of the post members, which were expected to have the deteriorated parts, was performed. Consequently, the correlation between the specific gravity and the drilling resistance was very high ($R^2=0.89$) and the distributions of the specific gravity were evaluated for the each member. Also, the results were verified by the visual inspection of the cross section of it. Especially, the various variations of the wood member such as the deteriorated parts with termite or fungi and the crack could be detected exactly but the knot couldn't because the drill could pass by or could not penetrate the knot.

• 한국생산제조학회지
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• 제21권2호
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• pp.252-258
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• 2012

A study of terahertz waves was made for the nondestructive evaluation of FRP (Fiber reinforced plastics) composite materials. The terahertz systems were consisted of time domain spectroscopy (TDS) and continuous wave (CW). The composite materials investigated include both non-conducting polymeric composites and conducting carbon fiber composites. Terahertz signals in the TDS mode resembles that of ultrasound; however, unlike ultrasound, a terahertz pulse was not able to detect a material with conductivity. The CFRP (Carbon fiber reinforced plastics) laminates were utilized for confirming the experimentation in the terahertz NDE. In carbon composites the penetration of terahertz waves is quite limited and the detection of flaws is strongly affected by the angle between the electric field direction of the terahertz waves and the intervening fiber directions. A refractive index (n) was defined as one of mechanical properties; so a method was obtained in order solve the "n" in the material with non-conductivity. The usefulness and limitations of terahertz radiation are investigated for the NDE of FRP composites.

• 열처리공학회지
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• 제14권2호
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• pp.110-117
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• 2001

Artificial aging was performed to simulate the microstructural degradation in 2.25CrMo steel arising from long time exposure at $540^{\circ}C$. It was found that the carbides became coarser and spheroidized as aging time increased. An attempt was made to evaluate the microstructural degradation in artificially aging heat treated 2.25CrMo steel by the ultrasonic attenuation and velocity measurements. Ultrasonic velocity was found essentially insensitive to the microstructural changes resulting from aging heat treatment. However, the ultrasonic attenuation was observed to increase with increasing aging time. Also, it was noticed that the change of ultrasonic attenuation with aging time was more sensitive at high frequency regions.

• 비파괴검사학회지
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• 제20권3호
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• pp.221-230
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• 2000

콘크리트 비파괴검사법인 충격공진법의 유용성과 적용 한계를 살펴보기 위하여 실험 및 이론적 연구를 수행하였다. 실험적 연구를 위하여, 다양한 개재물이 포함된 콘크리트 슬래브 공시체를 제작한 후 충격공진법을 적용하여 개재물의 존재 및 매실 위치를 찾아보았다. 공시체들 중 몇 경우에는 개재물의 위치를 정확하게 검출할 수 있었으나, 나머지의 경우에는 검출하지 못하였다. 후자의 경우에 있어서 그 실패 원인을 규명하고, 나아가 본 기법의 유용성을 결정하는 주요 인자들을 알아보기 위하여 유한요소 해석을 수행하였다. 본 연구는 충격공진법의 물리적 이해 증진과 향후 발전에 기여할 것이다.

• Journal of Welding and Joining
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• 제12권3호
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• pp.109-117
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• 1994

Spot welding has wide used with a high work efficiency in the automotive and aerospace industries. Up to the present, the technique mainly used to test spot welds on production lines has been entirely depended upon destructive chisel or peel testing. Therefore, it's being very important assignment to secure the NDE technique which can be evaluate spot weld quality with more efficiency and high reliability. This paper discusses the feasibility of UNDE techniques to evaluate spot weld quality. For the sake of the approach to the quantitative measurement of nugget diameter and the discrimination of a the corona bond from nugget, ultrasonic c-scan image and distribution of reflective echo amplitude was measured by immersion method with the mechanical and the electronic scanning of point-focussed ultrasonic beam(25 MHz). As the results of this study, corona bond which is the most dangerous types of interface defects can be successfully detected, as well as expulsion and voids. Ultrasonic testing results were confirmed and compared by optical microscope and SAM(Scanning Acoustic Microscope) observation of the spot-weld cross section. The results show that the nugget diameter can be successfully measured with the accuracy of 0.8 mm.

• 한국안전학회지
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• 제18권4호
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• pp.98-104
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• 2003

Various nondestructive evaluation (NDE) techniques have been studied to locate steel rebars of dowel, and to detect invisible damage such as voids and cracks inside concrete and debonding between rebars and concrete caused by corrosions and earthquakes. In this study, the aurhors developed 3-dimensional (3D) electromagnetic (EM) imaging technology to detect such damage and to identify exact location of steel rebars of dowel. The authors have developed sub-surface two-dimensional (2D) imaging technique using tomographic antenna array in previous works. In this study, extending the earlier analytical and experimental works on 2D image reconstruction, a 3D microwave imaging system using tomographic antenna array was developed, and multi-frequency technique was applied to improve quality of the reconstructed image and to reduce background noises. This paper presents the analytical expressions of numerical focusing procedures for 3D image reconstruction and numerical simulation to study the resolution of the system and the effectiveness of multi-frequency technique. Also, the design of 4?4 antenna array with switching devices is introduced as a preliminary study for the final design of whole array.

• Advances in Computational Design
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• 제8권3호
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• pp.219-236
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• 2023

In this paper, finite element modeling of the laser ultrasonics (LU) process in ablation regime is of interest. The momentum resulting from the removal of material from the specimen surface by the laser beam radiation in ablation regime is modeled as a pressure pulse. To model this pressure pulse, two equations are required: one for the spatial distribution and one for the temporal distribution of the pulse. Previous researchers have proposed various equations for the spatial and temporal distributions of the pressure pulse in different laser applications. All available equations are examined and the best combination of the temporal and spatial distributions of the pressure pulse that provides the most accurate results is identified. This combination of temporal and spatial distributions has never been used for modeling laser ultrasonics before. Then by using this new model, the effects of variations in pulse duration and laser spot radius on the shape, amplitude, and frequency spectrum of ultrasonic waves are studied. Furthermore, the LU in thermoelastic regime is simulated by this model and compared with LU in ablation regime. The interaction of ultrasonic waves with a defect is also investigated in the LU process in ablation regime. Good agreement of the results obtained from the new finite element model and available experimental data confirms the accuracy of the proposed model.

• 비파괴검사학회지
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• 제8권1호
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• pp.30-37
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• 1988

Interfaces, both grain boundaries and phase boundaries, play a very important role in the mechanical behavior of structural materials. The problemis particularly intense in composite materials where interfaces play a primary role in the meehanical response of the composites. This paper will concentrate on the approaches to perform nondestructive evaluation of the interfaces in a man nor in which some measure of the mechanical behavior of the interface can be established. Some of the possible approaches that may have potential for the nondestructive evaluation of interfaces are optical, electronic/ electrical, and acoustic approaches.

• 농업생명과학연구
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• 제46권1호
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• pp.35-41
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• 2012

공진주파수 모드를 이용하는 비파괴 평가기술법을 닥나무를 소성온도별(600, 800, 1000, $1200^{\circ}C$)로 제조한 우드세라믹에 적용하였다. 공진주파수 및 동적 탄성계수는 소성온도가 증가할수록 증가하였다. 동적 탄성계수 및 정적 휨 탄성계수와 휨강도사이에는 밀접한 상관관계가 나타났다. 따라서 공진 주파수 모드를 사용하는 동적 탄성계수측정은 소성온도에 따라 제조된 우드세라믹의 휨강도를 예측하는 비파괴 평가 방법으로 유용할 것으로 판단된다.