• Journal of the Korean Wood Science and Technology
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• 제31권2호
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• pp.31-37
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• 2003

목재의 결함을 탐지하는 비파괴 진단법 중에서 초음파를 이용한 비파괴 시험법은 그 경제성과 사용에서 큰 장점을 지니고 있어, 그 활용과 관련된 연구가 활발히 진행 중이다. 그러나 현재까지의 연구는 입목 또는 원목 등과 같이 비파괴 평가를 위한 측정이 비교적 적은 경우에 국한되어 있어, 목조 문화재 등을 비롯한 구조물의 부재와 같이 부재의 일부 면만을 측정할 수 있는 경우에 대한 연구가 미비한 실정이다. 따라서 본 연구에는 이러한 초음파 시험기의 측정방법의 제한을 극복하는 방법을 모색하고자 그 첫 번째 단계로 결함을 갖는 목재 내에서 초음파 전달 경로를 구명하고자 하였다. 다양한 전달 경로 모델을 가정하고 실제 실험과 비교를 통해 초음파 전달의 가장 적합한 모델을 제시하고자 한다. 실험 시편에 인위적인 결함을 만들어 실험한 결과 초음파가 직접 전달될 수 없는 부분의 경우 그 결함을 피해서 전달되고 전달 경로는 탐촉자의 반대 측면에서 일차반사를 통해 전달되는 것으로 판단되었다.

• Computers and Concrete
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• 제33권5호
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• pp.621-630
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• 2024

This study presents novel electromagnetic wave-based methods for evaluating the integrity of cement-based structures using time domain reflectometry (TDR). Two cement-based plates with embedded rebars are prepared under sound and defective conditions. TDR tests are carried out using transmission lines with various numbers of artificial joints, and electromagnetic waves are measured to assess the integrity of the plates. The experimental results show that the travel time of electromagnetic waves is consistently longer in sound plates than in defective ones, and an increase in the reflection coefficients is observed in the defect zone of the defective plates. Electromagnetic wave velocities are higher in the defective plates, especially when connectors are present in the transmission line. A novel approach based on the area of the reflection coefficient provides larger areas in the defective plates, and the attenuation effect of the electromagnetic waves induces a difference in the areas of the reflection coefficient between the two defect conditions. An alternative method using the centroid of the defect zone slightly overestimates the location of the defect zone. The length of the defect zone is estimated using the defect ratio and wave velocities of cement, air, and plate. The length of the defect zone can also be calculated using the travel times within the plate, total measured length of the plate, and wave velocities in the cement and air. Therefore, the electromagnetic wave-based methods proposed in this study may be useful for estimating the location and length of defect zones by considering attenuation effects.

• 제어로봇시스템학회논문지
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• 제15권11호
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• pp.1076-1079
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• 2009

This article deals with an optical image stabilizer which moves an image sensor in the direction of cancelling the vibration caused by hand shaking to prevent a photographed image from blurring. The ball-guide way method adopted as a transfer device of the image sensor is easy to be manufactured because of its simple structure and is suitable to minimize the friction between mechanisms, but has weakness of a chance of physical defect such as groove and rising. In case that the movement of the transfer device equipped with the image sensor is blunted because a ball is stuck in defects of guide way, the performance of the image stabilizer falls down drastically. We propose a method to prevent the transfer device from blunting by applying artificial vibration. At this time, the artificial vibration should be designed under consideration of dynamic characteristics and specifications of the system to be discriminated from the vibration caused by hand shaking.

• Maxillofacial Plastic and Reconstructive Surgery
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• 제28권2호
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• pp.118-126
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• 2006

In oral and maxillofacial surgery, bone graft is very important procedure for functional and esthetic reconstruction. So, many researcher studied about bone graft material like autogenous bone, allograft bone and artificial bone materials. The purpose of this study is to evaluate the quantity of bone generation induced by $Grafton^{(R)}$ graft, human allogenic demineralized bone matrix. Total 24 sites of artificial bony defects prepared using trephin bur(diameter 8 mm) on parietal bone of six adult New Zealand White rabbits. Experimental group had six defect sites which grafted $Grafton^{(R)}$(0.1 cc). Active control group had nine defect sites, into which fresh autogenous bone harvested from own parietal bone was grafted and passive control group had nine defect sites without bone graft. After six weeks postoperatively, the rabbits were sacrificed. The defects and surrounding tissue were harvested and decalcified in 10% EDTA, 10% foamic-acid. Specimens were stained with H&E. New bone area percentage in whole defect area was measured by IMT(VT) image analysis program. Quantity of bone by $Grafton^{(R)}$ graft was smaller than that of autograft and larger than that of empty defects. In histologic view $Grafton^{(R)}$ graft site and autograft site showed similar healing progress but it was observed that newly formed bone in active control group was more mature. In empty defect, quantity and thickness of new bone formation was smaller than in $Grafton^{(R)}$-grafted defect. $Grafton^{(R)}$ is supposed to be a useful bone graft material instead of autogenous bone if proper maintenance for graft material stability and enough healing time were obtained.

• 비파괴검사학회지
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• 제9권1호
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• pp.22-29
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• 1989

The important point of MPI is the analysis of leakage field in the defective regions. The analysis of leakage field depends on many factors such like geometry and character of defect. In general the calculation of magnetic leakage fields arising from such defects presents an extremely complicated mathematical problem and is practically insoluable, since the inhomogeneities have complex geometrical shapes and may differ in physical nature. Therefore, this paper describes Hall probe measurements of residual leakage field around artificial flaws in alloy steel bar, and shows how the results to recent developments in 2D dipole and analytic models of the magnetic field defect interaction.

• 동력기계공학회지
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• 제8권3호
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• pp.52-57
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• 2004

A new non-destructive inspection technique has been developed. One characteristic of the technique is that defects are visualized by laser ray. Magnetic domains and domain walls of a magneto-optical sensor(MO sensor) are varied by the magnetic flux leaked by defects, and the variations are observed by the reflected light of the laser ray. The information of defect can remotely be inspected by this technique in a real time. This paper describes the results estimated on the 2-dimensional surface defects and opposite-side defects in a ferromagnetic material and the natural surface defect in a clutch disk wheel. The light region of a visible image and the magnitude of a reflected light increases as the input current of the magnetizer increases. The natural surface defect, that has not the width of crack's open mouth, can be also visualized like as 2-dimensional artificial defects.

• Journal of Welding and Joining
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• 제19권6호
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• pp.608-613
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• 2001

In this study, the rotary bending fatigue test was carried out with two kinds of base metal, martensite stainless steel STR3 and austenite stainless steel STR35 and the dissimilar friction welded material with them. To compare the fatigue fifes according to the notch positions, the small circular defect was worked on the bonded line, 1.0mm and 0.5mm distance form the bonded line. The fatigue limits of the STR3 and STR35 base metal were 429.0MPa and 409.4MPa respectably. In comparison with fatigue life at the same notch positions, the STR35 specimens showed about 190% for base metal, 82% for 1.0mm distance notched specimens higher than that of the STR3. But the fatigue life of the 0.5mm distance notched STR35 specimen showed about 35% lower than that of the STR3 specimen. And the bonded line notched specimen was much lower fatigue life than the other specimens because of separation of the bonded line.

• Journal of Chest Surgery
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• 제23권4호
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• pp.654-658
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• 1990

Between January of 1980 and December of 1989, we are encountered 121 cases of Down syndrome here at Yonsei University Medical Center. of these being endocardial cushion defect, ventricular septal defect, tetralogy of Fallot, atrial septal defect, patent ductus arteriosus and complicated anomalies. The mean age was 1 month 2 years with the sexual division at 31 males and 29 females. Among these 60 patients, 10 of them were treated trough surgical management, 8 of them being open heart surgeries, the 8 open heart surgeries are broken down as follow: 4 total correction of ECD, 2 patch repair of VSD, 1 total correction of TOF, 1 patch repair of ASD secundum. Another 2 operative management are ligation of PDA and modified Blalock - Taussig shunt of TOF. Postoperatively all patients were weaned and extubated on an artificial ventilator without any respiratory complications, and were discharged without incident.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권12호
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• pp.4763-4775
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• 2020

This research aims to develop a deep learning-based method that automatically detects and segments the defects on railroad surfaces to reduce the cost of visual inspection of the railroad. We developed our segmentation model by modifying a fully convolutional network model [1], a well-known segmentation model used for machine learning, to detect and segment railroad surface defects. The data used in this research are images of the railroad surface with one or more defect regions. Railroad images were cropped to a suitable size, considering the long height and relatively narrow width of the images. They were also normalized based on the variance and mean of the data images. Using these images, the suggested model was trained to segment the defect regions. The proposed method showed promising results in the segmentation of defects. We consider that the proposed method can facilitate decision-making about railroad maintenance, and potentially be applied for other analyses.

• 한국정보통신학회논문지
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• 제25권9호
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• pp.1144-1151
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• 2021

프레스 공정은 가열 또는 가열하지 않은 상태의 재료에 힘을 가해 원하는 형태로 변형시켜 제품을 만드는 압축 가공 과정이다. 짧은 시간의 연속 압축을 통해 제품을 생산하는 프레스 장비의 특성상 제품 불량은 연속적으로 발생하며 이러한 문제를 해결하기 위한 시스템은 다양한 기술을 이용하여 개발되고 있다. 본 논문은 불량을 탐지하는 인공지능 알고리즘을 기반으로 실시간 불량탐지 시스템을 제안한다. 프레스 장치에 각종 센서를 부착하여 장비의 상태와 불량과의 관계를 빅데이터 플랫폼을 기반으로 정의하고 수집한다. 수집된 데이터를 기반으로 인공지능 알고리즘을 개발하고 개발된 알고리즘을 임베디드 보드를 이용하여 구현함으로써 실제 현장에 적용하여 시스템의 실용성을 보이겠다.