• 한국건설순환자원학회논문집
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• 제1권3호
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• pp.211-218
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• 2013

해양환경 조건 중 건습반복환경인 간만대는 구조물내 철근부식이 가장 빨리 일어나는 것으로 알려져 있다. 때문에 부식촉진시험 방법 중 간만대 환경을 재현한 시험방법이 가장 활발하게 진행되어왔다. 그러나 많은 연구들이 부식임계농도 추정이나 염화물침투해석에 집중되어 있는 상황이다. 본 논문에서는 건습반복조건의 환경을 재현하여 구조물내 철근부식촉진시험과 염화물 침투해석을 실시하였다. 배합에 사용된 재료의 종류를 변수로 시험을 실시하였으며, 철근부식모니터링 방법으로 갈바닉 전위측정법과 반전지전위법을 사용하여 철근부식의 유무를 판단하였다. 부식촉진시험결과 각 배합별로 부식기간이 차이가 났으며, 순서는 OPC > FA > BS > 고강도 순으로 나타났다. 부식촉진시험과 동일한 조건으로 FEM 내구성 해석 프로그램인 DuCOM, RCPT 시험을 실시하여 실험결과 값에 대한 타당성을 입증하였다.

• Smart Structures and Systems
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• 제19권3호
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• pp.335-340
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• 2017

Fiber Bragg grating (FBG) sensors are applied to structural health monitoring (SHM) in many areas due to their unique advantages such as ease of multiplexing and capability of absolute measurement. However, they are exposed to cyclic thermal load, generally in the temperature range of $-20^{\circ}C$ to $60^{\circ}C$, in railways during a long-term SHM and the cyclic thermal load can affect the mechanical strength of FBGs. In this paper, the effects of both cyclic thermal load and the reflectivity of FBGs on the mechanical strength are investigated though tension tests of FBG specimens after they are aged in a thermal chamber with temperature changes in a range from $-20^{\circ}C$ to $60^{\circ}C$ for 300 cycles. Results from tension tests reveal that the mechanical strength of FBGs decreases about 8% as the thermal cycle increases to 100 cycles; the mechanical strength then remains steady until 300 cycles. Otherwise, the mechanical strength of FBGs with reflectivity of 6dB (70%) and 10dB (90%) exhibits degradation values of about 6% and 12%, respectively, compared to that with reflectivity of 3dB (50%) at 300 cycles. SEM photos of the Bragg grating parts also show defects that cause their strength degradation. Consequently, it should be considered that mechanical strength of FBGs can be degraded by both thermal cycles and the reflectivity if the FBGs are exposed to repetitive thermal load during a long-term SHM.

• 한국농공학회지
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• 제34권1호
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• pp.41-48
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• 1992

Various soil behaviors usually occurring in the geotechnical problems, such as, cutting and embankments, stability of slope, seepage, consolidations, shearing failures and liquefaction, should be predicted and analyzed in any way. An approach of these predictions may be followed by the development of the constitutive equations as first and subsequently solved by numerical methods. The purpose of this paper is develop the constitutive equation of sands uder monotonic or cyclic loadings. The constitutive equation which is based on elasto-plastic theory, modified anisotropic consolidated stress parameter by Sekiguchi et al and Pender's theory is derived. And the equation is included a new stress parameter, hardening function, Bauschinger's effects and Pender's theory. The model is later evaluated and confirmed the validity by the test data of Ottawa sand, Banwol sand Hongseong sand. The following conclustions may be drawn: 1. The consititutive equation which is based on elasto-plastic theory, modified anisotropic consolidated stress parpameter by Sekiguchi et al and Pender's theory is derived. The equation in included a new stress parameter, hardening function, Bauschinger's effect and Pender's theory. 2. For Ottawa sand, the result of the constitutive equation shows a better agreement than that of Oka et al. The result of axial strain agrees well with the tested data. However, the result of horizontal strain is little bit off for the cyclic loadings or large stress. It is thought that the deviation may be improved by considering Poisson's ratio and precise measurement of shear modulus. 3. Banwol sand is used for the strain and stress tests with different relative densitites and confining pressures. The predeicted result shows a good agreement with the tested data because the required material parameters were directly measurd and determined form this laboratory. 4. For Hongseong sand, the tests under same amplitude of cyclic deviatoric stress shows a similar result with the tested data in absolute strain. It shows the acute shape of turning point because the sine wave of input is used in the test but the serrated wave in prediction.

• 비파괴검사학회지
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• 제36권3호
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• pp.225-230
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• 2016

광섬유 브래그 격자센서(FBG)는 다중화가 용이하고 절대측정이 가능한 고유의 장점으로 다양한 구조물의 구조건전성 모니터링(SHM)에 활용도를 넓혀가고 있다. 하지만, 구조건전성 모니터링을 위해 FBG 센서를 온도 변화 환경에서 장기간 사용할 경우 FBG 센서는 계절적 요인에 의한 큰 폭의 주기적 온도 변화 환경에 노출되므로 센서의 신뢰성 확보를 위해 신호 특성에 대한 검토가 필요하다. 본 연구에서는 패키징된 FBG 센서의 제작에 많이 활용되는 각각 2가지의 모재 및 접착제를 대상으로 시편을 제작한 후 항온항습기 내에서 -$20^{\circ}C{\sim}60^{\circ}C$의 온도 조건에서 300사이클의 반복 열하중시험을 수행하였다. 시험 결과, FBG 센서에 주기적인 반복 열하중이 가해질 경우 일정량의 압축변형이 작용하며 이는 센서로 사용 시 측정 오차로 작용하므로 장기 구조건전성 모니터링을 위해 FBG 센서의 사용 전 안정화 과정을 통한 사전보정이 필요함을 확인하였다.

• 방사성폐기물학회지
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• 제8권3호
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• pp.247-260
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• 2010

한국원자력연구원 처분시스템개발과제에서는 처분용기 재료로 개발중인 저온분사코팅 구리에 대한 틈새부식(Crevice Corrosion) 시험을 실시하였다. 본 시험을 통하여 틈새에서의 부식의 발생여부와 발생되는 시점인 재부동태 전위(Repassivation Potential)를 측정하고자 하였다. 틈새부식 시험 방법으로 (1) ASTM G61-86 : Cyclic Potentiodynamic Polarization Measurements, (2) SWRI의 Potentiodynamic Polarization plus intermediate Potentiostatic Hold method, 그리고 (3) ASTM G192-08 (THE method) :Potentiodynamic- Galvanostatic -Potentiostatic Method 등의 3가지 방법을 소개하였다. 실제 저온분사 코팅구리의 부식시험에서는 ASTM G61-86에 따라서 틈새부식장치를 설치하고, 저온분사코팅구리가 KURT 지하수를 모사한 용액에서 어떻게 틈새부식이 일어나는지 살펴보았다. 전기적 부식조건으로는 Cyclic Polarization Test, Potentiostatic Polarization Test, 및 Electrochemical Impedance Spectroscopy 등을 사용하였다. 그리고 부식이 된 시편에 대해 Profilometer Measurement를 통해 실제 부식표면의 높낮이를 조사하여 틈새부식 유무를 관찰하였다. 최종적인 결론에서는 저온분사코팅구리는 틈새부식을 나타나지 않는다는 것을 확인할 수 있었다. 그리고 시험에 사용된 세종류의 구리에 대한 상대적인 부식평가를 한 결과, 부식전위를 나타내는 개방회로(Open Cell)에서의 전위는 구리의 제조방식과 상관없이 구리의 순도가 높을수록 높은 값을 보이는 것을 확인할 수 있었다. 결론적으로 KURT 심층지하수 조건에서는 구리는 틈새부식이 발생되지 않는다고 결론지었다.

• Smart Structures and Systems
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• 제25권2호
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• pp.135-153
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• 2020

There has been a sustained interest towards the non-contact structural displacement measurement by means of videogrammetric technique. On the way forward, one of the major concerns is the spurious image drift induced by temperature variation. This study therefore carries out an investigation into the temperature effect of videogrammetric technique, focusing on the exploration of the mechanism behind the temperature effect and the elimination of the temperature-caused measurement error. 2D videogrammetric measurement tests under monotonic or cyclic temperature variation are first performed. Features of measurement error and the casual relationship between temperature variation and measurement error are then studied. The variation of the temperature of digital camera is identified as the main cause of measurement error. An excellent linear relationship between them is revealed. After that, camera parameters are extracted from the mapping between world coordinates and pixels coordinates of the calibration targets. The coordinates of principle point and focal lengths show variations well correlated with temperature variation. The measurement error is thought to be an outcome mainly attributed to the variation of the coordinates of principle point. An approach for eliminating temperature-caused measurement error is finally proposed. Correlation models between camera parameters and temperature are formulated. Thereby, camera parameters under different temperature conditions can be predicted and the camera projective matrix can be updated accordingly. By reconstructing the world coordinates with the updated camera projective matrix, the temperature-caused measurement error is eliminated. A satisfactory performance has been achieved by the proposed approach in eliminating the temperature-caused measurement error.

• 구강회복응용과학지
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• 제28권1호
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• pp.57-66
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• 2012

본 연구는 ProTaper Universal에 의도적으로 부여한 내부 응력이 피로 파절에 미치는 영향을 평가하였다. 25 mm 길이의 S1, S2, F1, F2, F3, F4 그리고 F5 파일을 내부 응력을 부여하기 위해서 Endo-Training-Bloc (Dentsply Maillefer)에 auto-stop 될 때까지 속도 300 rpm, 토크 1.0 Ncm의 값으로 밀어 넣었다. 부여한 내부 응력의 횟수에 따라 각각 Stress 0 군(대조군), Stress 1 군, Stress 2 군 그리고 Stress 3 군으로 분류하였다. 경사진 유리판을 사용하였고 파일 파절 시간을 측정하였다. 모든 파일에서는 Stress 3 군은 대조군에 비해 Ni-Ti 파일의 파절 시간이 감소하였고 F2와 F3에서 모든 실험군은 대조군에 비해 파절 시간이 감소하였다. F4와 F5에서 Stress 2 군과 Stress 3 군이 대조군에 비해 파절 시간이 감소하였다. ProTaper Universal의 피로 파절은 파일에 축적된 내부 응력에 의해 영향을 받는다.

• 대한전기학회논문지:전기물성ㆍ응용부문C
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• 제49권3호
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• pp.186-195
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• 2000

In this paper, partial discharge (PD) measurement was performed to evaluate the quality of the cable joint and termination constructions. The resistive coupling technique for PD detection using resistivity of semiconducting layer of the cable in the accessories, such as joints and terminations. With high frequency PD (HEPD) measurement, an excellent sensitivity below 20pC could be achieved under unshielded condition. The localization of the defects in the accessories could be identified. During heating cycle, PDs were monitored and analyzed. At that time, the PDs were dependent on the temperature of the heating cycle and showed cyclic behaviors, which were attributed to local delamination of the interfaces, between epoxy unit and stress relief cone(SRC) and between SRC and cable, due to the difference of thermal expansion. As a conclusion, HFPD measurement technique was proven to be an effective diagnostic method for qualification of extra high voltage (EHV) cable accessories. With this technique, the optimal design of the components of the accessories could be verified not only in an early stage but also under operating condition. This technique would result in the improvement of the reliability of the EHV cable accessories.

• 한국안전학회지
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• 제8권4호
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• pp.16-20
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• 1993

The combined effect of increased pressure/temperature and the reduced material thicknesses act to increase the stress on the radiator componets. The design life of the radiator is influenced by the cyclic stresses and corrosion, which act to weaken the materials, radiator mechanical failure occurs when a tube or solder Joint ruptures, causing coolant loss or insufficient heat rejection. Therefore, in this study, through strain measurement of the tubes in copper/brass radiator, the strain distribution of the tubes in radiator as function of temperature and pressure is obtained.

• 한국자동차공학회논문집
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• 제6권5호
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• pp.153-161
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• 1998

The knock in a spark ignition engine has been investigated to avoid the damage to the engine and unpleasant feeling caused by the pressure waves propagating across the combustion chamber. Knock intensity and knock onset angle were used as physical parameters to quantify the knock characteristics. The knock intensity is defined as a peak to peak value of the bank pass filtered combustion pressure signal and the knock onset angle is determined as the crank angle at which this signal exceeded the threshold level on each cycle. The cyclic variation of knock in four valve single cylinder engine was investigated with these two parameters. The location of autoignition was also examined by ion probes in the cylinder head gasket and squish region in the combustion chamber. For this measurement, a single cylinder engine was modified to accept the pressure transducer, 18 ion probes in the squish region and 8 ion probes in the specially designed PCB (Printed \ulcornerCircuit Board) cylinder head gasket.