• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.3 s.55
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• pp.173-180
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• 2009

Very-early strength latex-modified concrete(below ; VES-LMC) was developed for possible early-opening-to-traffic after overlay of bridge deck concrete. The purpose of this study is to analyze the cause of map, transverse and longitudinal cracking in VES-LMC and to provide a control method for minimizing occurrence of cracking. The proposed prevention method against map and transverse cracking was verified by field data. VES cement was modified as the unit cement content was reduced from 390kg/$m^3$ to 360kg/$m^3$. The maximum size of coarse aggregate was increased from 13mm to 19mm. The wire mesh and steel fiber were adopted in concrete mixture. From the results, the proposed prevention method against map and transverse cracking was verified since structural cracking was not occurred until 3 years after overlay.

• Journal of Power System Engineering
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• v.16 no.4
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• pp.66-73
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• 2012

본 연구는 횡방향 TIG 용접된 Al6013-T4 알루미늄 합금 용접부의 피로균열전파거동에 미치는 용접후열처리(PWHT)의 영향을 조사하는 것이 주목적이다. 기초적으로 인장시험, 경도 및 미세조직이 조사되었으며, 피로균열전파거동을 고찰하기 위한 피로 시험은 모두 중앙균열인장(CCT) 시험편에 대하여 수행되었다. T82열처리에 있어서 시효시간은 피로균열전파율, 인장강도 및 경도에 대단히 민감함을 나타내었으며, 모재와 열영향부재의 경우가 용접재보다 기계적 성질이 우수하였다. 횡방향 TIG 용접한 Al6013-T4 시험재의 용접후열처리 조건에 따라서 피로균열전파 저항에는 차이가 나타났으며, 본 실험의 조건하에서 24시간 인공시효 PWHT-82 시험편이 피로균열전파 저항이 가장 우수한 결과를 나타내었다.

• Journal of the Microelectronics and Packaging Society
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• v.8 no.3
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• pp.25-30
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• 2001

The stress intensity factors for edge cracks located at the bonding interface between the semiconductor chip and the adhesive layer subjected to a uniform transverse tensile strain are investigated. Such cracks might be generated due to a stress singularity in the vicinity of the free surface. The boundary element method (BEM) is employed to investigate the behavior of interface stresses. The amplitude of complex stress intensity factor depends on the crack length, but it has a constant value at large crack lengths. The rapid propagation of interface crack is expected if the transverse tensile strain reaches a critical value.

• Journal of Korea Multimedia Society
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• v.10 no.8
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• pp.1068-1077
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• 2007

This paper proposes a method that extracts characteristics of cracks such as length, thickness and direction from a concrete slab surface image with image processing techniques. These techniques extract the cracks from the concrete surface image in variable conditions including bad image conditions) using the ART2-based RBF network to recognize the dominant directions -45 degree, 45 degree, horizontal and vertical) of the extracted cracks from the automatically calculated specifications like the lengths, directions and widths of the cracks. Our proposed extraction algorithms and analysis of the concrete cracks used a Robert operation to emphasize the cracks, and a Multiple operation to increase the difference in brightness between the cracks and background. After these treatments, the cracks can be extracted from the image by using an iterated binarization technique. Noise reduction techniques are used three separate times on this binarized image, and the specifications of the cracks are extracted form this noiseless image. The dominant directions can be recognized by using the ART2-based RBF network. In this method, the ART2 is used between the input layer and the middle layer to learn, and the Delta learning method is used between the middle layer and the output layer. The experiments using real concrete images showed that the cracks were effectively extracted, and the Proposed ART2-based RBF network effectively recognized the directions of the extracted cracks.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• v.9 no.2
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• pp.360-365
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• 2005

본 논문에서는 콘크리트 표면 균열 영상에서 균열을 효율적으로 추출하기 위한 화상처리 기법과 ART1 기반 RBF 네트워크를 제안하여 균열의 방향성을 인식한다. 본 논문에서 사용된 화상처리 기법으로는 균열 영상의 빛을 보정하기 위한 모폴로지 기법인 채움(Closing)연산을 적용하고 Sobel 마스크를 적용하여 균열 영상의 에지를 추출한 후 반복 이진화를 적용하여 균열 영상을 이진화한다. 이진화 된 영상에 두 차례에 걸쳐 잡음제거를 수행하여 콘크리트 표면 균열 영상으로부터 균열을 추출한다. 본 논문에서는 추출된 균열을 ART1 기반 RBF 네트워크에 적용하여 균열의 방향성(횡방향, 종방향, $-45^{\circ}$방향, $45^{\circ}$방향)을 자동으로 인식할 수 있는 방법을 제안한다. 제안된 ART1 기반 RBF 네트워크는 입력층과 중간층으로의 학습은 ART1을 적용하고 중간층과 출력층 간의 학습은 Delta 학습 방법을 적용한다. 실제 콘크리트 균열 영상을 적용하여 실험한 결과, 콘크리트 표면 균열 영상에서 효율적으로 균열을 추출할 수 있었고 제안된 ART1 기반 RBF 네트워크가 추출된 균열의 방향성 인식에 효율적인 것을 확인하였다.

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.102-108
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• 2016

The purpose of this study is to examine the reduction effect of shrinkage reducing agent for drying shrinkage induced cracking and suggest the method of controlling the cracking in concrete box culvert for power transmission. Based on drying shrinkage cracking mechanism, it is necessary to perform the numerical analysis, which involves shrinkage reducing effect of shrinkage reducing agent. From the numerical results, it is found that cracking behavior for longitudinal direction and transverse direction due to differential drying shrinkage of box culvert can occur and the experimental observation of concrete cracks support the numerical predictions. The shrinkage reducing agent reduced the concrete cracking by 40~50%, which shows the methodology of controlling of drying shrinkage cracks in box culverts in real construction site.

• Journal of Ocean Engineering and Technology
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• v.12 no.3 s.29
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• pp.42-48
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• 1998

구형 관입시험에 의한 얼음의 균열을 연구 하였다. $-10^{circ}C$에서 S2 기둥얼음의 시편(152mm X 152mm X 152mm)에 stainless 강으로 된 구(지름 25.4mm)로 하중을 가하였다. 구형indentor는 얼음 시편의 장축인 기둥방향에 수직으로 하중을 가하였으며 이때 변위율은 0.038mm/s로 하여 단조증가 하중 시험을 하였다. 하중을 가하기 시작하면 indentor 하부에서 crushing 이 발생하고, 하중이 증가함에 따라서 방사선 균열 또는 횡균열이 성장하여 splitting 또는 spallation이 발생하였다. 단조증가 하중 때와 동일한 indentor를 사용하여 하중 및 비하중율 0.5KN/s로 맥박하중을 가할 때 이들 방사선 균열 및 횡 균열이 발생 성장하였다. 첫 맥박 하중의 크기는 1KN으로 하고 그 뒤 계속 이어지는 시험은 맥박 하중의 크기를 증가시킨 뒤 행하였으며 균열 길이는 맥박과 맥박 사이에서 계측 하였다. 기타 취성고체에서 관찰 되었던 것과 같이 방사선 균열 및 측면균열의 길이는 impression 반지름과 하나의 지수법칙이 성립함을 보여주었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.5
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• pp.1417-1425
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• 1991

본 연구에서는 파괴역학적 개념을 도입하여 수평 회전체에 존재하는 횡방향 개폐균열의 모형을 설명하고 균열거동을 분석하였으며, 균열의 깊이, 회전속도 및 회 전방향에 따른 균열선단에서의 응력확대 계수를 계산하고 그 특성을 분석하였다.

• International Journal of Highway Engineering
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• v.9 no.2 s.32
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• pp.39-49
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• 2007

The objective of this study was to investigate features of transverse crack occurrence and propagation in continuously reinforced concrete pavement(CRCP) when subjected to environmental loading. The finite element model of CRCP was developed and the element removal method was implemented to predict the crack propagation process. To investigate the effect of the type of environmental loading on the CRCP behavior and cracking aspects, the following three different cases were considered: (1) the temperature gradient between top and bottom of the slab does not vary and the constant temperature drop throughout the depth occurs; (2) the temperature at the slab bottom does not vary and the temperature gradient increases; and (3) the temperature between the mid-depth and the bottom of the slab is the same and does not vary and the temperature at the top decreases. The analysis results showed that the crack occurrence and propagation through the depth of the slab in CRCP were significantly affected by the type of environmental loading. The changes in stress distribution and displacements during the crack occurrence and propagation process could also be investigated.

• Journal of Korean Society of Steel Construction
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• v.11 no.4 s.41
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• pp.339-350
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• 1999

In this study, blowholes, a kind of solid defects, were intentionally introduced in transverse butt-welded joints which are widely used for the connection of main members in steel structures to evaluate the fatigue characteristics of these joints with blowholes according to the difference of the size and shape of blowholes, and a series of tests were performed. Static test results proved that the static strength of these joints with blowholes was not affected by their size and shape. From the fatigue test results on these joints with blowholes, the size and shape of blowholes inside the weld metals were strongly affected in fatigue strength, and we suggested the relationship between fatigue strength and their size and shape quantitatively. Also, Using the relationship of fatigue crack growth rate and stress intensity factor range, the fatigue life of transverse butt-welded joints with blowholes can be estimated properly.