• Smart Structures and Systems
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• 제12권3_4호
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• pp.465-482
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• 2013

Recently, a novel stress sensor, which utilizes the elasto-magnetic (EM) effect of ferromagnetic materials, has been developed to measure stress in steel cables and wires. In this study, the effectiveness of this EM based stress sensors for monitoring of the cable tension force of a real scale cable-stayed bridge was investigated. Two EM stress sensors were installed on two selected multi-strand cables in Hwa-Myung Bridge, Busan, South Korea. Conventional lift-off test was conducted to obtain reference cable tension forces of two test cables. The reference forces were used to calibrate and validate cable tension force measurements from the EM sensors. Tension force variations of two test cables during the second tensioning work on Hwa-Myung Bridge were monitored using the EM sensors. Numerical simulations were conducted to compare and verify the monitoring results. Based on the results, the effectiveness of EM sensors for accurate field monitoring of the cable tension force of cable-stayed bridge is discussed.

• 한국표면공학회지
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• 제38권1호
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• pp.14-20
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• 2005

The control of internal stress is extremely important in electroforming because of the deliberately low adhesion between the electro form and the mandrel. Excessive tensile or compressive stress can cause distortion, separation problem, curling, peeling or separation of electroform prematurely from the mandrel, buckling and blistering. Nickel sulfamate bath has been widely used in electroforming because of its low internal stress and moderate hardness. In this study, real-time stress sensor has been used for stress control in chloride-free nickel sulfamate bath for 400 mm x 300 mm x 500 ㎛ nickel electroform. It was found that compressive stress found at low current density indicated the contamination of electrolyte, which is very useful in procuring buckling and peeling of electroform. No compressive stress is allowed for plate electroform. The real-time stress can also be used for accurate stress control of nickel electroform. The tensile stress was found to be increased slightly with increase in nickel electroform thickness, i.e., from initial 1.47 ksi to 2.02 ksi at 320 ㎛.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.766-777
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• 2008

Currently in increasing number of urban tunnels with small overburden are excavated according to the principle of the New Austrian Tunneling Method (NATM). Successful design, construction and maintenance of NATM tunnel demands prediction, control and monitoring of ground displacement and support stress high accuracy. A magnetic anisotropy sensor is used for nondestructive measurement of stress on surfaces of a ferromagnetic material, such as steel. The sensor is built on the principle of the magneto-strictive effect in which changes in magnetic permeability due to deformation of a ferromagnetic material is measured in a nondestructive manner, which then can be translated into the absolute values of stresses existing on the surface of the material. This technique was applied to measure stresses of H-beams, used as tunnel support structures, to confirm expected measurement accuracy with reading error of about 10 to 20 MPa, which was confirmed by monitoring strains released during cutting tests The results show that this method could be one of the promising technologies for non-destructive stress measurement for safe construction and maintenance of underground rock structures encountered in civil and mining engineering.

• 대한공업교육학회지
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• 제35권2호
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• pp.224-237
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• 2010

수중 운동체가 가동할 때 돔 앞쪽에 설치된 센서에 유기되는 진동파 소음은 구조를 통해 전달된다. 구조를 통해 전달되는 소음과 진동이 음향 센서의 성능을 저하시키는 요인이 되지 않도록 구조물로 타고 들어오는 진동파를 효과적으로 차단하기 위하여 본 연구에서는 CRP(Carbon Reinforced Plastic)와 SNORE링(Self-NOise REduction Ring)를 설치하고 주파수에 따른 변위와 응력의 변화를 관찰하였다. 곡면 구조물의 재질은 알루미늄이며 최대 외경 530mm, 길이 215mm 정도이다. 곡면 구조물의 전면부는 직경이 270mm이며 평면형상으로 되어 있다. 주파수에 따른 CRP와 SNORE 링 부착 전후에서의 응력 감소율을 시뮬레이션 하였으며 12kHz와 15kHz 주변에서는 95% 이상의 감소율을 보였다. 음향 센서의 부착 위치에 따른 응력의 변화를 계산하였으며 중심부에서 가장 높게 나타났고 20mm, 40mm 떨어진 곳으로 이동할수록 응력의 크기가 낮게 나타났다. 본 연구의 결과는 음향센서의 감도를 높이는데 기초자료로 활용할 수 있을 것이다.

• 아시안잔디학회지
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• 제20권2호
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• pp.213-221
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• 2006

본 연구는 토양 수분함량을 즉시 파악할 수 있는 Time Domain Radiometer(TDR)과 식물의 광합성 시 잎에서 반사되는 Reflectance를 통하여 식물의 상태를 파악할 수 있는 Multi-spectral radiometer(MSR)를 사용하여 난지형 잔디인 'Sea Isle 1' Seashore paspalum 과 'Floratam' St. Augustinegrass를 대상으로 토양수분함량과 Reflectance와의 상관관계를 파악하고자 시작하였다. 본 연구를 통해 토양 수분함량이 660, 694 wavelengths와 NDVI, LAI, stress index에서 높은 상관관계를 가지고 있음을 알 수 있었다. 이는 Sensor-based technology가 잔디의 수분요구 시점을 미리 파악할 수 있는 기술의 기초 자료로서 활용될 수 있으며 여러 다른 Sensor-based technology를 이용한 연구로 확대될 수 있을 것이다.

• 한국전산구조공학회논문집
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• 제36권4호
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• pp.251-257
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• 2023

본 연구는 현재 가설되어 가용 중인 프리스트레스트 구조물에 대해서 긴장 응력을 계측하는 방법에 관한 연구를 위해 외부 자화를 이용한 PSC 텐던의 긴장 응력 계측에 관한 연구를 진행하였다. 이에 유한요소해석을 이용하여 PSC 거더에 외부 자화 시 잔존 긴장 응력을 검출하기 위해 PSC 거더 내부의 PS 텐던까지 영향을 줄 수 있는 코일 배치 및 크기 등을 고려하여 최적의 센서를 설계하였다. 또한, 유한요소해석을 이용하여 설계한 센서와 동일한 수치 및 재질 데이터를 이용해 이론적 검증을 진행하였으며 타겟 위치에서 자화의 세기를 계산하였을 때, 유한요소해석 결과와 동일한 결과를 얻어낼 수 있었다. 이를 통해 설계한 센서의 검증 및 비 접촉 외부 자화 EM 센서를 활용하여 PSC I형 거더 내부 텐던의 자화가 가능함을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 전기설비
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• pp.82-84
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• 2005

In a transformer, thermal stress is the most influential parameter affecting the aging behavior of insulation system. The aging behavior of insulation system in transformer is determined mainly by the thermal conditions inside the transformer. The thermal stress on the insulation system may occur from operation in a high temperature caused by overloading or local overheating. Thus, this paper investigated the condition monitoring of insulation condition in thermally accelerated aged transformer oils by in-situ sensor. The condition of aged samples was investigated by measurements of relative permittivity i.e. capacitance change by capacitive sensor. Results from the experiments are presented in this paper.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2006년도 정기 학술대회 논문집
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• pp.159-166
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• 2006

Although the strain distribution along the length of a beam in buildings or infrastructures is non-uniform, most fiber optic sensors are point sensors that can measure the strain only at a local point of a beam. Long gage fiber optic sensors that measure integrated strain over a relatively long length can consider strain variation. This type of sensor was found to be efficient and useful for monitoring large-scale structures. On the other hand, the maximum strain or stress in a beam can not be measured with long gage optic sensors. However, for the assessment of the safety of multi-span steel beams subjected to various vertical loads, the maximum strain or stress measured during monitoring is required for comparison with the allowable stress of the beam calculated by a design code. Therefore, in this paper, mathematical models are presented for determination of the maximum values of strains in more three-span steel beams based on the average strains measured by long gage optic sensors.

• Journal of Welding and Joining
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• 제29권3호
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• pp.76-81
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• 2011

Recently, the structural failures due to fatigue occur frequently with the increase of size of ships and offshore structures. In this respect, the assessment of fatigue life and the residual strength are very important. Currently, the smart materials technology has demonstrated a variety of possibilities for a diagnosis of structural strength and structural health condition for large structures. The benefits and feature of the MFC sensor are more flexible, durable and reliable than conventional smart material. In this study, Micro Fiber Composite (MFC) sensor for the measurement of stress intensity factor (SIF) of two dimensional cracks induced in a structure is developed. Two MFC sensors are placed in the vicinity of the crack tip close to each other with the crack tip in between them. The SIFs of Mode I($K_I$) as well as of Mode II($K_{II}$) based on the piezoelectric constitutive law and fracture mechanics are calculated. In this study, the SIF values measured by MFC sensors are compared with the theoretical results and measured value.

• 제어로봇시스템학회논문지
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• 제17권3호
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• pp.218-222
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• 2011

This paper proposes a single-joint optical torque sensor with one body structure. Conventional optical torque sensors consist of three parts, two plates and an elastic structure. They have slightly slipping problem between plates and elastic structure due to the manufacturing tolerance. Since the order of measurement range of optical sensor is about ten micrometers, the slipping problem causes large measurement error, especially in the case of vibrational or high speed plant. This problem does not occur in the proposed design due to the one body structure. The proposed sensor has advantage of low cost, light weight, and small size. And it is easy to design and manufacture. Simulation works that analysis of stress and strain are performed accurately. To demonstrate the performance of proposed sensor, experiments were implemented to compare with a commercial force/torque sensor (ATI Mini45).