• 한국항공우주학회지
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• 제31권10호
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• pp.21-26
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• 2003

본 논문에서는 광섬유 센서를 사용하여 우주환경하에 노출된 그래파이트/에폭시 복합재 적층판의 열팽창계수의 변화를 측정하였다. 열변형률과 온도를 동시에 측정하기 위해서 두개의 FBG 센서를 사용하였다. 또한 열-진공 챔버를 사용하여 고진공, 자외선, 열적 사이클 등의 인자를 가지는 저궤도(LEO) 우주환경을 모사하였다. 예비실험으로써, 본 실험에서 사용되는 온도범위에 대해 FBG 온도센서를 기준온도계로부터 보정하였고 알루미늄 시편에 부착된 FBG 변형률 센서와 변형률 게이지(ESG)의 비교실험을 통해 FBG 변형률 센서의 사용가능성을 검증하였다. 검증된 FBG센서가 삽입된 그래파이트/에폭시 복합재 평판을 모사된 우주환경에 노출하여 일정한 노화간격마다 열팽창계수 변화를 실시간으로 측정하였다. 실험결과 1000 사이클 노화후의 열팽창계수는 노화전에 비해 대체적으로 큰 변화는 없었지만 전 온도구간에서 약간 감소하는 경향을 보였다. 이러한 현상은 가스방출(outgassing), 수분방출, 모재균열 등에 기인한다.

• 한국기계가공학회지
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• 제17권2호
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• pp.137-144
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• 2018

This study describes the 3D design and analysis of a composite insulation boom of an aerial work platform for electric work. Structural analysis of the composite insulation boom was performed using ANSYS and the total deformation, equivalent stress, and normal elasticity were investigated at 150 mm, 500 mm, 1,000 mm, and 1,500 mm using a mounted strain gauge. The results of the analysis and test were similar in a linearly increasing slope and the difference in the strain value was about 10%. This difference depends on the compressive force in the manufacturing process.

• 센서학회지
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• 제27권2호
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• pp.105-111
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• 2018

In this paper, a torque sensor is designed and fabricated to measure the knee joint torque of a walking assist robot for stroke patients. The torque sensor sensing part was modeled on the link of the part connected to the knee joint motor. The torque capacity of the knee joint was calculated by simulation and the size of the torque sensor sensing part was designed using the finite element method. The torque sensor was fabricated by attaching a strain gauge to the sensing part. Characteristic experiments were conducted to characterize the torque sensor, and the torque sensor was calibrated to utilize it for the control of the walking assist robot. As a result of the characteristics test, the reproducibility error and the nonlinearity error of the torque sensor were 0.03% and 0.04%, respectively. Therefore, it is considered that the developed torque sensor can be used to measure the torque applied to the knee joint when walking on a walking assist robot.

• 대한용접접합학회:학술대회논문집
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• 대한용접접합학회 2002년도 Proceedings of the International Welding/Joining Conference-Korea
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• pp.372-377
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• International Journal of Korean Welding Society
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• 제2권1호
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• pp.40-44
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• 2002

Residual stress by welding should be reduced because that decreases the reliability on strength of welded structure. The reason is that the total stiffness of structure decreases by non-linear behavior of weldment under external load. The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure for steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. This simulation model should be established on the based of variable and accurate measurement data. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test under variable load was performed and the proper degree of stress relaxation was measured by sectioning technique using strain gauge.

• 대한의용생체공학회:의공학회지
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• 제34권1호
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• pp.1-7
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• 2013

According to the frequent use of mobile devices, risk of repetitive strain injury for the finger joints was increasing recently. The purpose of this study was to investigate the difference of muscular endurance limit of the thumb between adults and children. A total of thirty subjects (15 adults: $41.0{\pm}7.9$ years and 15 children: $9.5{\pm}2.7$ years) was recruited for this experiment. Maximum voluntary contraction (MVC) of the thumb was measured for 100 trials for each subject by using a push-pull gauge. From the maximum peak value obtained, three main factors (MVC, endurance limit, and fatigue index) were defined to quantify fatigue characteristics of the thumb flexor muscle. The experimental results showed that the mean of MVC, endurance limit, and fatigue index of the children were approximately 50% compared to the adults (p < 0.001). From the results of Pearson correlation test, the endurance limit was highly correlated with weight, age, hand length rather than height. Based on this study, children are more vulnerable to repetitive task using the thumb such as text/SNS messaging, gaming, and scrolling.

• 방사성폐기물학회지
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• 제19권2호
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• pp.197-204
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• 2021

In this study, the well-known non-destructive acoustic emission (AE) and electrical resistivity methods were employed to predict quantitative damage in the silo structure of the Wolsong Low and Intermediate Level Radioactive Waste Disposal Center (WLDC), Gyeongju, South Korea. Brazilian tensile test was conducted with a fully saturated specimen with a composition identical to that of the WLDC silo concrete. Bi-axial strain gauges, AE sensors, and electrodes were attached to the surface of the specimen to monitor changes. Both the AE hit and electrical resistance values helped in the anticipation of imminent specimen failure, which was further confirmed using a strain gauge. The quantitative damage (or damage variable) was defined according to the AE hits and electrical resistance and analyzed with stress ratio variations. Approximately 75% of the damage occurred when the stress ratio exceeded 0.5. Quantitative damage from AE hits and electrical resistance showed a good correlation (R = 0.988, RMSE = 0.044). This implies that AE and electrical resistivity can be complementarily used for damage assessment of the structure. In future, damage to dry and heated specimens will be examined using AE hits and electrical resistance, and the results will be compared with those from this study.

• 한국군사과학기술학회지
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• 제19권4호
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• pp.476-482
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• 2016

In this study, a method using single Wheatstone bridge flexure has been presented to measure hinge moment acting on control surfaces of wind tunnel models. The structural simplicity of the flexure reduces difficulty regarding gauging and wire-routing, and also makes it feasible to install flexures even inside thin wings. Some flexures were designed and fabricated under typical aerodynamic loads in wind tunnel test, and the strains on the flexure according to applied loads were compared with the result of the analysis by finite element method. The relation between applied loads and output signals showed good linearity, and the standard deviation on the residual errors from linear equation obtained by least square method was within 1.0 % of the maximum design moments. In addition, the FEM analysis on the thickness of load-connecting part of the flexure showed that the sensitivity was improved as the thickness became thin as much as desired to avoid buckling.

• 비파괴검사학회지
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• 제2권2호
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• pp.9-16
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• 1983

There are two weak points in a high pressure vessel, one is a corner, the other is a crack on the base. In order to evaluate safety of a department of a corner and a crack like a starfish on the base in a high pressure vessel (working pressure: $130kg/cm^{2}$), which was made by Marison's Process, we analyzed stress by strain gauge, measured thickness and hardness by ultrasonic testing, and were able to test pressure by water pressure from nondestructive testing. Also destructive testings were applied to measure thickness and to observe microstructure and chemical composition of a corner on the base. From the results of the experiment, values of experiment were satisfied with a condition of application. But, it is considered that a crack on the base is to be investigated with more by Fracture Mechanics.

• 한국환경과학회지
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• 제10권5호
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• pp.323-327
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• 2001

A new method is developed to estimate the evaporation of water from a surface with high accuracy and resolution. The principle of new method is to detect a weight change of buoyant weight according to a change in water level of Class A Pan mesured by the use of a strain-gauge load cell. Field test of evaporation recording new instrument was carried out at Suwon for 10 days July 1999. It is possible in field observation to measure hourly evaporation amount by newly developed evaporation recording instrument in Class A Pan against strong solar radiation. Present study provide a possibility of domestic high accuracy instrument development below than 0.1mm water level measurement accuracy. If there is low humidity and high wind speed conditions which is possible to evaporate from water surface during night time. And it needs continuous study to understand between meteorological elements and latent heat effect at ground level by field observation study using high accuracy evaporation recording instrument.