• Smart Structures and Systems
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• 제20권2호
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• pp.175-180
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• 2017

The load-carrying capacity and structural behavior of concrete-filled steel tube (CFST) structures is highly influenced by the grouting compactness in the steel tube. Due to the invisibility of the grout in the steel tube, monitoring of the grouting progress in such a structure is still a challenge. This paper develops an active sensing approach with combined piezoceramic-based smart aggregates (SA) and piezoceramic patches to monitor the grouting compactness of CFST bridge structure. A small-scale steel specimen was designed and fabricated to simulate CFST bridge structure in this research. Before casting, four SAs and two piezoceramic patches were installed in the pre-determined locations of the specimen. In the active sensing approach, selected SAs were utilized as actuators to generate designed stress waves, which were detected by other SAs or piezoceramic patch sensors. Since concrete functions as a wave conduit, the stress wave response can be only detected when the wave path between the actuator and the sensor is filled with concrete. For the sake of monitoring the grouting progress, the steel tube specimen was grouted in four stages, and each stage held three days for cement drying. Experimental results show that the received sensor signals in time domain clearly indicate the change of the signal amplitude before and after the wave path is filled with concrete. Further, a wavelet packet-based energy index matrix (WPEIM) was developed to compute signal energy of the received signals. The computed signal energies of the sensors shown in the WPEIM demonstrate the feasibility of the proposed method in the monitoring of the grouting progress.

• 한국압력기기공학회 논문집
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• 제10권1호
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• pp.90-95
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• 2014

Local wall thinning is a point of concern in almost all steel structures such as pipe lines covered with a thermal insulator made up of materials with low thermal conductivity(fiberglass or mineral wool); hence, Non Destructive Technique(NDT) methods that are capable of detecting the wall thinning and defects without removing the insulation are necessary. In this study we developed a Pulsed Eddy Current(PEC) system to detect the wall thinning of Ferro magnetic steel pipes covered with fiber glass thermal insulator and shielded with Aluminum plate. The developed system is capable of detecting the wall thickness change through an insulation of thickness 10cm and 0.4mm aluminum shielding. In order to confirm the thickness change due to wall thinning, two different sensors, a hall sensor and coil sensor were used as a detecting element. In both cases, the results show a very good change corresponding to the thickness change of the test specimen. During these experiments a carbon steel tube of diameter 210mm and a length of 620mm, which is covered with insulator of 95mm thickness was used. To simulate the wall thinning, the thickness of the tube is changed for a specified length such as 2.5mm, 5mm and 8 mm from the inner surface of the tube. A 0.4mm thick Aluminum plate was covered on the Test specimen to simulate the shielding of the insulated pipelines. For both hall sensor and coil detection methods Fast Fourier transform(FFT) was calculated using window approach and the results for the test specimen without Aluminum shielding were summarized which shows a clear identification of thickness change in the test specimen by comparing the magnitude spectra. The PEC system can detect the wall thinning under the 95 mm thickness insulation and 0.4 mm Al shielding, and the output signal showed linear relation with tube wall thickness.

• 한국음향학회지
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• 제34권3호
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• pp.192-199
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• 2015

펄스 튜브를 이용하여 시편의 전달 손실 성능을 측정할 경우, 시편 설치를 위해 필연적으로 시편과 펄스 튜브 내벽 사이에 간극이 존재한다. 본 논문에서는 이와 같은 간극이 전달 손실 측정 결과에 미치는 영향에 대해 평가했다. 평면파에 대해 일정 폭 및 길이를 갖는 간극 전과 후 음압의 비를 구하여 전달 계수를 유도하고 측정 대상 시편의 전달 계수와 조합하여 간극이 포함된 시편의 전달 손실을 구했다. 이와 같은 해석 모델을 이론해가 존재하는 10 mm 두께의 스테인리스 스틸 시편에 적용하여 시험 결과와 비교함으로서 해석 모델의 적절성을 보였다. 마지막으로 해석 모델을 통하여 간극크기 및 시편 전달 손실 성능에 따라 전달 손실 측정에 미치는 영향을 분석했다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 추계학술발표대회 논문집
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• pp.123-126
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• 2002

To evaluate the bending collapse behavior of an aluminum square tube, a finite element simulation for the four-point bending test was suggested. Local buckling deformation near the center of an aluminum tube specimen was induced which has been partly inserted by two steel bars. Simulation results showed good agreements with those of experiment.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 1996년도 특별강연 및 춘계학술발표 개요집
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• pp.34-37
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• 1996

The expanding method of tube to tubesheet joint part on neclear steam generators are classified into three classes of roller expanding, explosive expanding and hydraulic expanding. After the expanded Mock-Up specimen are made by the three expanding method. The general properties, microstructure/microvickers hardness, pull-out strength, hydraulic leak pressure, of tube to tubesheet joint part were inspected. and We evaluated the operation efficiency of expansion, reproduction of expanded joint about three expanding method. Through the overall evaluation of tube to tubesheet joint part, The hydraukic expanding and explosive expanding could be certificated more useful expanding method.

• 대한기계학회논문집A
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• 제27권2호
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• pp.231-238
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• 2003

The fuel of light water reactor is used for several years under high temperature and pressure, so it needs to be clad with high corrosion resistance material. The cladding materials must have the characteristics of low absorption of a neutron and high corrosion resistance. Zircaloy-2 in Boiling Water Reactor, Zircaloy-4 in Pressurized Water Reactor have been used as cladding materials and Zirlo has been developed as the material for preventing the corrosion. If the fracture of the cladding tube occurs during operation, it will cause the economic loss to shut down and replace the system. So it is needed to evaluate the integrity of the cladding materials. In this paper, the tensile characteristics of the cladding materials were investigated for the basic research of fracture characteristics. Also the residual stress was analyzed to compare the tube type(original type) specimen and the flattened type specimen.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.489-494
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• 2001

The fuel of light water reactor used far several years at high temperature and pressure, so it needs to clad with high corrosion resistance material. The cladding materials need low absorption of a neutron and high corrosion resistance. Cladding materials used Zircaloy-2 in Boiling Water Reactor, Zircaloy-4 in Pressurized Water Reactor and Zirlo has good for long term corrosion. If fracture of cladding tube occured during operation, it caused disaster. So it is needed to estimate of integrity fur cladding materials. In this paper, tension characteristics of cladding materials are investigate which is basic research far fracture characteristic. Also analysis of residual stress effect between tube type(original type) specimen and flattened type specimen.

• Nuclear Engineering and Technology
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• 제34권2호
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• pp.132-141
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• 2002

The effects of microstructure on fretting wear were investigated in Inconel 690 tube. The microstructure observation indicated that the solution annealing temperature and time affected the grain size of the Inconel 690 tubes. The carbide morphology, along grain boundaries, was mainly affected by thermal treatment time and temperature. The wear test results showed that specimens with larger grain size and with coarse carbides along grain boundaries had better wear resistance. Cracks were found in specimens with carbides along the grain boundary, while few cracks were found in carbide free specimens. It seemed that the carbides on grain boundary assisted crack formation and propagation in carbide containing specimens. On the other hand, the micro-hardness of specimen did not have a major role in fretting wear. It could be inferred from the SEM images of worn surfaces that the main wear mechanism of carbide containing specimen was delamination, while that of carbide free specimen was abrasion.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1995년도 가을 학술발표회 논문집
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• pp.317-322
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• 1995

This study is to examine the usefulness in using precast girder-infilled steel tube column in reinforced concrete structures through the analysis of the test results, in order to develope the new composite structural system using precast girder-Infilled steel tube column, The variables of specimen are strength of concrete, the numble of hoops, the form of beam-column The variables of specimen are strength of concrete, the number of hoops, the form of beam-column joints. By raising strength of concrete and incresing number of hoops in beam-column joint, it becomes clear to take similar structure capacity to monolithic structures.

• 한국도로학회논문집
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• 제15권1호
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• pp.23-36
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• 2013

PURPOSES: The problem under this circumstance is that the erosion not only drops strength of the steel dowel bar but also comes with volume expansion of the steel dowel bar which can reduce load transferring efficiency of the steel dowel bar. To avoid this erosion problem, alternative dowers bars are developed. METHODS: In this study, the bearing stresses between the FRP tube dowel bar and concrete slab are calculated and compared with its allowable bearing stress to check its structural stability in the concrete pavement. These comparisons are conducted with several cross-sections of FRP tube dowel bars. Comprehensive laboratory tests including the shear load-deflection test on a full-scale specimen and the full-scale accelerated joint concrete pavement test are conducted and the results were compared with those from the steel dowel bar. RESULTS: In all cross-sections of FRP tube dowel bars, computed bearing stresses between the FRP tube dowel bar and concrete slab are less than their allowable stress levels. The pultrusion FRP-tube dowel bar show better performance on direct shear tests on full-scale specimen and static compression tests at full-scale concrete pavement joints than prepreg and filament-winding FRP-tube dowel bar. CONCLUSIONS: The FRP tube dowel bars as alternative dowel bar are invulnerable to erosion that may be caused by moisture from masonry joint or bottom of the pavement system. Also, the pultrusion FRP-tube dowel bar performed very well on the laboratory evaluation.