• 한국건설순환자원학회논문집
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• 제5권2호
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• pp.113-120
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• 2017

HCP 측정법은 철근부식을 판단하는 비파괴 시험으로 현장에서 효과적으로 사용되고 있다. 본 연구는 실내실험을 통하여 촉진부식실험을 수행하고 건조 상태에서 측정된 HCP 측정값과 부식량의 상관성을 분석하는 연구이다. 이를 위해 4가지 피복두께와 3가지 물-시멘트비를 가진 시멘트 모르타르 시편을 제조하여 6시간, 18시간, 42시간동안 20V의 전압을 가하여 ICM에 의한 촉진실험을 수행하였다. 분석결과 피복두께의 감소, 물-시멘트비의 증가, 촉진부식시간의 증가에 따라 부식량이 증가하였으며, 측정된 HCP 값과는 선형적인 관계를 나타내었다. HCP를 사용하여 부식량을 평가하기 위해서는 전체 부식량을 비교하는 것보다, 일정수준의 HCP 값을 선정하고 이에 따라 부식량을 평가하는 것이 높은 결정계수를 얻는 합리적인 방법으로 평가되었다.

• 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.

• Smart Structures and Systems
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• 제10권3호
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• pp.229-251
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• 2012

Guided waves have shown a great potential for structural health monitoring (SHM) applications. In contrast to traditional non-destructive testing (NDT) methodologies, a key element of SHM approaches is the high process of automation. The monitoring system should decide autonomously whether the host structure is intact or not. A basic requirement for the realization of such a system is that the sensors are permanently installed on the host structure. Thus, baseline measurements become available that can be used for diagnostic purposes, i.e., damage detection, localization, etc. This paper contributes to guided wave-based inspection in anisotropic materials for SHM purposes. Therefore, computational strategies are described for both, the solution of the complex equations for wave propagation analysis in composite materials based on exact elasticity theory and the popular global matrix method, as well as the underlying equations of two active damage localization algorithms for anisotropic structures. The result of the global matrix method is an angular and frequency dependent wave velocity characteristic that is used subsequently in the localization procedures. Numerical simulations and experimental investigations through time-delay measurements are carried out in order to validate the proposed theoretical model. An exemplary case study including the calculation of dispersion curves and damage localization is conducted on an exemplary unidirectional composite structure where the ultrasonic signals processed in the localization step are simulated with the spectral element method. The proposed study demonstrates the capabilities of the proposed algorithms for accurate damage localization in anisotropic structures.

• 한국토양비료학회지
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• 제36권2호
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• pp.92-103
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• 2003

Research and technological advances in the field of remote sensing have greatly enhanced the ability to detect and quantify physical and biological stresses that affect the productivity of agricultural crops. Reflectance in specific visible and near-infrared regions of the electromagnetic spectrum have proved useful in detection of nutrient deficiencies. Especially crop canopy sensors as a ground remote sensing measure the amount of light reflected from nearby surfaces such as leaf tissue or soil and is in contrast to aircraft or satellite platforms that generate photographs or various types of digital images. Multi-spectral vegetation indices derived from crop canopy reflectance in relatively wide wave band can be used to monitor the growth response of plants in relation to environmental factors. The normalized difference vegetation index (NDVI), where NDVI = (NIR-Red)/(NIR+Red), was originally proposed as a means of estimating green biomass. The basis of this relationship is the strong absorption (low reflectance) of red light by chlorophyll and low absorption (high reflectance and transmittance) in the near infrared (NIR) by green leaves. Thereafter many researchers have proposed the other indices for assessing crop vegetation due to confounding soil background effects in the measurement. The green normalized difference vegetation index (GNDVI), where the green band is substituted for the red band in the NDVI equation, was proved to be more useful for assessing canopy variation in green crop biomass related to nitrogen fertility in soils. Consequently ground remote sensing as a non destructive real-time assessment of nitrogen status in plant was thought to be useful tool for site specific crop nitrogen management providing both spatial and temporal information.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.31-36
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• 2000

High temperature and pressure materials in power plant are degraded by creep damage, if they are exposed to constant loads for long times, which occurs in the load bearing structures of pressurized components operating at elevated temperatures. Many conventional measurement techniques such as replica method, electric resistance method, and hardness test method for measuring creep damage have been used. So far, the replica method is mainly used for the Inspection of High temperature and pressure components. This technique is, however, restricted to applications at the surface of the testpieces and cannot be used to material inside. In this paper, ultrasonic evaluation for the detection of creep damage in the form of cavaties on grain boundaries or integranular microcracks are carried out. And the absolute measuring method of quantitative ultrasonic velocity technique for Cr-Mo material degradation is analyzed. As a result of ultrasonic tests for crept specimens, we find that the sound velocity is decreased as the increase of creep life fraction$({\Phi}_c)$ and also, confirmed that hardness is decreased as the increase of creep life fraction$({\Phi}_c)$ but the coefficient of ultrasonic attenuation is increased as the increase of creep life fraction$({\Phi}_c)$. Finally based on the result in this paper, it can be recognized that the ultrasonic techniques using velocities and attenuation coefficient factor are very useful non-destructive methods to evaluate the degree of material degradation in fossile power plants.

• 한국구조물진단유지관리공학회 논문집
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• 제14권6호
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• pp.179-187
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• 2010

콘크리트 내부에 매설된 철근의 부식은 철근콘크리트구조물의 조기 성능저하와 붕괴의 주요원인이 되고 있다. 철근콘크리트 구조물에 발생하는 열화현상 중에서 철근부식에 의해 발생되는 염해는 그 피해가 다른 열화 현상보다 심하고 구조물의 보수 및 시공 측면에서도 막대한 경비가 요구되고 보수시기 또한 정하기 힘들다. 따라서 철근의 부식상태에 대한 조기발견은 관리자의 효율적인 보수 및 보강계획 수립을 위해 매우 중요하다. 한편 철근 부식을 평가하는 방법 중 비파괴측정이 많이 사용되고 있다. 특히 CM-II(corrosion meter) 측정기는 자연전위와 분극저항 및 콘크리트 비저항을 측정할 수 있어서 많이 사용되지만 몇 가지 단점을 가지고 있다. 이러한 단점을 극복하기 위해 매립형 미니센서가 개발되어져 왔다. 이 미니센서를 이용하여 철근 부식을 측정한 후 CM-II(corrosion meter)의 측정결과와 비교분석하여 개발된 미니센서의 타당성을 검증하였다.

• 한국전기전자재료학회논문지
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• 제33권3호
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• pp.231-238
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• 2020

This paper investigates the soundness of porcelain insulators associated with the acoustic emission (AE) technique. The AE technique is a popular non-destructive method that measures and analyzes the burst energy that occurs mainly when a crack occurs in a high-frequency region. Typical AE methods require continuous monitoring with frequent sensor calibration. However, in this study, the AE technique excites a porcelain insulator using only an impact hammer, and it applies a high-pass filter to the signal frequency range measured only in the AE sensor by comparing the AE and the acceleration sensors. Next, the extracted time-domain signal is analyzed for the damage assessment. In normal signals, the duration is about 2ms, the area of the envelope is about 1,000, and the number of counts is about 20. In the damage signal, the duration exceeds 5ms, the area of the envelope is about 2,000, and the number of counts exceeds 40. In addition, various characteristics in the time and frequency domain for normal and damage cases are analyzed using the short-time Fourier transform (STFT). Based on the results of the STFT analysis, the maximum energy of a normal specimen is less than 0.02, while in the case of the damage specimen, it exceeds 0.02. The extracted high-frequency components can present dynamic behavior of crack regions and eigenmodes of the isolated insulator parts, but the presence, size, and distribution of cracks can be predicted indirectly. In this regard, the characteristics of the surface crack region were derived in this study.

• 대한기계학회논문집
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• 제16권3호
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• pp.598-607
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• 1992

본 연구에서는 고온중 장시간 사용중에 일어나는 야금학적 성질의 변화의 추 원인인 특정 탄화물을 비파괴적으로 검출하기 위해, 최근에 연구 되고 있는 전기화학 적 방법을 응용하기 위한 기초연구이다. 한편으로는 비파괴적 방법의 실험실적 연구 를 현장에 응용시키기 위한 시도를 행하고, 본 연구 결과를 이용한 향후 설비 진단 시 스템의 개요를 고찰해 보인다.

• Structural Monitoring and Maintenance
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• 제5권4호
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• pp.463-488
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• 2018

In the last decades, research efforts have been spent to investigate the effect of prestressing on the dynamic behaviour of prestressed concrete (PSC) beams. Whereas no agreement has been reached among the achievements obtained by different Researchers and among the theoretical and the experimental results for simply supported beams, very few researches have addressed this problem in continuous PSC beams. This topic is, indeed, worthy of consideration bearing in mind that many relevant bridges and viaducts in the road and railway networks have been designed and constructed with this structural scheme. In this paper the attention is, thus, focused on the dynamic features of continuous PSC bridges taking into account the effect of prestressing. This latter, in fact, contributes to the modification of the distribution of the bending stress along the beam, also by means of the secondary moments, and influences the flexural stiffness of the beam itself. The dynamic properties of a continuous, two spans bridge connected by a nonlinear spring have been extracted by solving an eigenvalue problem in different linearized configurations corresponding to different values of the prestress force. The stiffness of the nonlinear spring has been calculated considering the mechanical behaviour of the PSC beam in the uncracked and in the cracked stage. The application of the proposed methodology to several case studies indicates that the shift from the uncracked to the cracked stage due to an excessive prestress loss is clearly detectable looking at the variation of the dynamic properties of the beam. In service conditions, this shift happens for low values of the prestress losses (up to 20%) for structure with a high value of the ratio between the permanent load and the total load, as happens for instance in long span, continuous box bridges. In such conditions, the detection of the dynamic properties can provide meaningful information regarding the structural state of the PSC beam.

• 한국구조물진단유지관리공학회 논문집
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• 제24권6호
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• pp.146-152
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• 2020

본 연구는 강교량의 폐합부재 등 시각적으로 탐지하기 어려운 부위의 강재에 대한 손상을 탐지하기 위한 방법을 개발하기 위한 목적의 기초연구이다. 여러 비파괴 방법들 중에서 초음파 속도법을 활용하여 두께가 다른 시편에 대해서 초음파 속도법을 실시하여, 평균 매질내 전파속도를 도출하였고, 이를 활용하여 강재 부재에 대한 회귀분석을 실시하였다. 동일한 재료일 경우 회귀분석의 결과를 활용하면 다른 부재의 두께를 도출할 수 있을 것으로 예상된다. 또한, 광범위한 범위를 스캐닝하기 위해 200 mm/s로 이동하는 연속스캐닝 기법을 검토하였고, 두께가 변화는 부재의 두께를 효과적으로 예측할 수 있었다.