• Title, Summary, Keyword: 표면균열

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An Experimental Study on Fatigue Fracture Behaviour of Surface Crack in Finite Plates and Fillet Welded T-joint (유한평판 및 T-joint 필렛 용접부에 있어서 3차원 표면균열의 피로 파괴거동에 관한 실험적 연구)

  • M.S. Han;J.D. Kim;H.S. Lee
    • Journal of the Society of Naval Architects of Korea
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    • v.28 no.2
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    • pp.275-284
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    • 1991
  • Fatigure crack growth from surface defects is one of the most important subjects for the evaluation and the assurance of safety in pressure vessels, piping systems, ship hulls and other various structures. This paper attempts to analysis some practical or general problems such as the estimation of crack growth life to penetrate the plate thickness, based on fatigure crack growth from a single surface flaw and the interaction of multiple flaws. An experiment on the coalescence of multiple undercuts was carried out under cyclic tension condition as a attempt to the analysis of multiple crack problems. It is noted that the fracture strength is characterized by the analogy to that in a single crack growth.

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질소 이온빔을 이용한 인코넬690의 기계적 특성 변화 연구

  • 홍인석;황용석
    • Proceedings of the Korean Nuclear Society Conference
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    • pp.118-122
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    • 1997
  • 차세대 원자력발전소 증기발생기 전열관 재료로 채택된 니켈기저합금으로 기존 전열관 재료인 인코넬600에 비해 고온 고압 조건에서 응력부식균열에 강한 장점을 가진 합금인 인코넬690 시료에 최대 에너지 120 keV의 질소 이온빔을 조사하여 이 재료의 기계적 특성 변화를 관측하였다. 특성 시험으로는 표면 경화를 관찰하기 위한 미세 경도 시험을 수행하여 미세 경도 증가를 확인하였다 아울러 표면 경화가 피로 특성에 미치는 영향을 관찰하기 위해 피로 균열 전파 시험을 수행하여 이온 주입으로 인한 표면 경화가 피로 균열 전파를 촉진시킴을 관찰하였다.

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Finite Element Simulation of Laser-Generated Ultrasound and Interaction with Surface Breaking Cracks (유한요소법을 이용한 레이저 유도 초음파와 표면 균열과의 상호작용 모델링)

  • Jeong, Hyun-Jo;Park, Moon-Cheol
    • Journal of the Korean Society for Nondestructive Testing
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    • v.24 no.3
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    • pp.259-267
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    • 2004
  • A finite element method is used to simulate interaction of laser-based ultrasounds with surface breaking tracks in elastic media. The laser line source focused on the surface of semi-infinite medium is modeled as a shear dipole in 2-D plane strain finite elements. The shear dipole-finite clement model is found to give correct directivity patterns for generated longitudinal and shear waves. The interaction of surface waves with surface breaking cracks (2-D machined slot) is considered in two ways. Both the source and receiver are fixed with respect to the cracks in the first case, while the source is moving in another case. It is shown that the crack depth tested in the range of 0.3-5.0mm $({\lambda}_R/d=0.21{\sim}3.45)$ can be measured using the corner reflected waves produced by the fixed laser source. The moving laser source is found to cause a large amplitude change of reflected waves near crack, and the crack whose depth is one order lower than the wavelength ran be detected from this change.

Evaluation of Crack-Repairing Performance in Concrete Using Surface Waves (표면탄성파를 활용한 콘크리트 균열 보수 성능 평가 기법)

  • Ahn, Eunjong;Kim, Hyunjun;Gwon, Seongwoo;Sim, Sung-Han;Lee, Kwang Myong;Shin, Myoungsu
    • Journal of the Korean Recycled Construction Resources Institute
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    • v.5 no.4
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    • pp.496-502
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    • 2017
  • The purpose of this study is to investigate the applicability of surface-wave techniques for the evaluation of the crack-repairing performance of an epoxy injection method in concrete. In this study, box-shaped concrete specimens with four different crack depths were made with identical mix proportions. The specimens with different crack depths were completely repaired using the same epoxy injection method. The spectral energy transmission ratio of surface waves is used as an index to differentiate the effects of crack depth and crack-repairing performance. The decrease of spectral energy transmission ratio in accordance with the increase of crack depth was identified before repairing. Furthermore, the spectral energy transmission ratio increased after the crack-repairing process in all specimens. The spectral energy transmission ratio is considered as a great indicator for estimating the crack-repairing performance of the epoxy injection method; the ratio was recovered up to almost 95% of the uncracked condition.

Effect of Coating System to Prevent the Deterioration of Concrete Subjected to Compressive Stress (압축응력이 인가된 콘크리트의 열화제어를 위한 표면도막공법의 효과)

  • Yoon, In-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.16 no.3
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    • pp.23-30
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    • 2012
  • For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

Detection and Sizing of Fatigue Cracks in Thin Aluminum Panel with Rivet Holes (리벳구멍을 가진 알루미늄 패널에서 피로균열의 탐지와 균열길이 측정)

  • Kim, Jung-Chan;Kwon, Oh-Yang
    • Journal of the Korean Society for Nondestructive Testing
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    • v.27 no.1
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    • pp.38-47
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    • 2007
  • The initiation of fatigue cracks in a simulated aircraft structure with a series of rivet holes was detected by acoustic emission(AE), then the crack length was determined by surface acoustic wave(SAW) technique. With the initiation and growth of fatigue cracks, AE events increased intermittently to form a stepwise incremental curve of cumulative AE events whereas the crack length increased more or less monotonically. With the SAW technique employed, the crack sizing for 13 different cracks including some short cracks was performed. With the reference to the measurement by traveling microscope, cracks in the range of $1{\sim}8mm$ long were reliably sized by the SAW technique. Although it was impossible to size the short fatigue cracks in the range shorter than 1 mm, the SAW technique still appeared practically useful for a range of crack lengths often found in aircraft structures.

Extraction and Recognition of Concrete Slab Surface Cracks using ART2-based RBF Network (ART2 기반 RBF 네트워크를 이용한 콘크리트 슬래브 표면의 균열 추출 및 인식)

  • Kim, Kwang-Baek
    • 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.

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Self Healing System for Concrete Surface Crack using Polymer based Coating Agent Incorporating Microencapsulated Healing Agent (마이크로캡슐을 함유한 폴리머 코팅제의 콘크리트 표면균열 자기치유시스템)

  • Shin, Ki-Su;Ryu, Byung-Chul;Wang, Xiao-Yong;Park, Ki-Bong
    • Journal of the Korea Institute of Building Construction
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    • v.15 no.6
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    • pp.579-587
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    • 2015
  • In this paper, microencapsulated healing agent was embedded in the polymer matrix to obtain self healing properties. Microencapsulation of methacrylate using polyurea-formaldehyde as a shell material and studied the effect of agitation rate on capsule characteristics such as size, shell thickness, and surface morphology. The formation of microcapsules was confirmed by FTIR and TGA, and capsule characteristics were studied by optical microscopy and SEM. The self-healing effect was evaluated using permeability measurements and further confirmed by surface analytical tools including optical microscope. According to the experimental results, the microencapsulated healing system has the self-heaing ability for artificial cracks.

Fatigue Behavior of Before-and-After Penetration of Aluminium Plate with Long Surface Crack (긴 균열을 갖는 알루미늄판재의 관통전후 피로거동)

  • Nam Ki-Woo;Lee Jong-Rark;Ahn Seok-Hwan
    • Journal of the Korean Institute of Gas
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    • v.3 no.1
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    • pp.1-7
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    • 1999
  • Fatigue behavior of before-and-after penetration was examined experimentally using surface pre-cracked specimens of aluminium alloy 5083-0. The fatigue crack shape before penetration is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using K values proposed by Newman-Raju. It is found that the crack growth behavior on the back side after penetration is unique and can be divided into three stages. By using a crack propagation rule in case of long surface crack, the change in crack shape after penetration can be evaluated quantitatively.

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A Study on Control of Sealing Robot for Cracks of Concrete Surface (콘크리트 표면 균열 실링을 위한 로봇의 제어 방법에 관한 연구)

  • Cho, Cheol-Joo;Lim, Kye-Young
    • Journal of The Korean Society of Civil Engineers
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    • v.35 no.2
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    • pp.481-491
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    • 2015
  • Since the crack in the surface of the concrete acts as the main reason influencing the life span of the structure, regular inspections and maintenance are required. The sealing required for maintenance of the concrete surface is a method of repairing the crack in the surface in the beginning, and is effective in preventing additional cracks and expansion that occurs with time. However, sealing on large sized structures such as tall buildings or bottom parts of bridges are difficult to ensure safety of the workers due to inadequate working environments. Due to this reason, the importance of the need for sealing automation for the maintenance of large sized concrete structures is emerging. This study proposes two control methods to apply robot systems to the sealing of cracks on the bottom parts of concrete bridges. First is the method of automatically tracking the trajectory of cracks. The robot gets the trajectory of the cracks using video information obtained from cameras. Comparing the previous several points and new point, the next point can be estimated. Thus, the trajectory of the crack can be tracked automatically. The other method is sealing by maintaining steady force to the contacting surface. The concrete surface exposed to an external environment for a long time gets an irregular roughness. If robots are able to carry out sealing while maintaining a steady contact force on these rough surfaces, complete equal sealing can be maintained. In order to maintain this equal force, a force control method using impedance is proposed. This paper introduces two developed control methods to apply to sealing robots, and conducts a Lab Test and Field Test after applying to a robot. Based on the test results, opinions on the possibilities of field application of the robot applied with the control methods are presented.