센서-구조 일체형 복합재료 구조물 제작 방법

한대현 ( Dae Hyun Han ),강래형 ( Lae Hyong Kang ),( Jordan Thayer ),( Chales Farrar ) 한국복합재료학회 2015 Composites research Vol.28 No.4

본 연구는 복합재료 구조물에 전기-기계 변환 기능을 융합한 센서-구조 일체형 복합재료 구조물 제작 방법에 관한 것으로 복합재료 구조물 자체가 센서 역할을 수행할 수 있도록 하여 구조 스스로 충격이나 진동 신호를 감지하고 손상 위치 또는 손상 정도를 실시간으로 모니터링 할 수 있는 다기능 복합 구조물에 관한 연구이다. 복합재 구조물에 전기-기계 변환 기능을 부여하기 위해 복합재 제작에 사용되는 에폭시 수지 대신 전기-기계 변환기능을 갖는 Pb(Ni1/3Nb2/3)O3-Pb(Zr, Ti)O2 (PNN-PZT) 분말과 에폭시 수지를 1:30 wt% 혼합하여 제작된 스마트 수지를 사용하였다. Hand Lay-up 공법과, VARTM(Vacuum Assisted Resin Transfer Molding) 성형 방법을 이용하여 유리섬유에 스마트 수지를 함침시켜 센서-구조 일체형 복합재료 구조물을 제작하였다. 구조물을 센서로 사용하기위해 시편의 윗면과 아랫면에 전도성 도료를 사용하여 전극을 제작하였고, 고전압 앰프를 이용하여 상온에서 30분간 4kV/mm의 전계로 분극 처리를 수행하였다. 이후 충격망치를 사용하여 시편에 충격을 가했을 때 출력되는 전기 신호와 충격망치 신호를 비교하여 충격 신호 감응 및 감도를 측정하고 그 결과를 기술하였다. A composite structure was fabricated with embedded impact detection capabilities for applications in Structural Health Monitoring (SHM). By embedding sensor functionality in the composite, the structure can successfully perform impact localization in real time. Smart resin, composed of Pb(Ni1/3Nb2/3)O3-Pb(Zr, Ti)O2 (PNNPZT) powder and epoxy resin with 1:30 wt%, was used instead of conventional epoxy resin in order to activate the sensor function in the composite structure. The embedded impact sensor in the composite was fabricated using Hand Lay-up and Vacuum Assisted Resin Transfer Molding(VARTM) methods to inject the smart resin into the glass-fiber fabric. The electrodes were fabricated using silver paste on both the upper and bottom sides of the specimen, then poling treatment was conducted to activate the sensor function using a high voltage amplifier at 4 kV/mm for 30 min at room temperature. The composite’s piezoelectric sensitivity was measured to be 35.13 mV/N by comparing the impact force signals from an impact hammer with the corresponding output voltage from the sensor. Because impact sensor functionality was successfully embedded in the composite structure, various applications of this technique in the SHM industry are anticipated. In particular, impact localization on large-scale composite structures with complex geometries is feasible using this composite embedded impact sensor.

드론 탑재 복합센서의 매핑 정확도 분석: 데이터 취득 환경에 따른 사전 캘리브레이션 여부를 중심으로

전일서 ( Ilseo Jeon ),함상우 ( Sangwoo Ham ),이임평 ( Impyeong Lee ) 대한원격탐사학회 2021 大韓遠隔探査學會誌 Vol.37 No.3

드론 매핑 시스템은 재난 피해 조사, 국토 환경 모니터링, 건설 공정 모니터링 등 여러 분야에 응용 가능하다. 드론에 장착된 다양한 개별 센서를 통합하여 활용하려면 시간동기화 등 여러가지 절차가 필요했다. 최근, 영상 센서와 GPS/INS가 함께 내장된 복합센서가 다수 출시되었다. 복합센서는 여러 가지 센서 데이터를 내부적으로 통합하여, 위치/자세를 영상 파일에 바로 태깅하여 제공한다. 이러한 복합센서를 드론 매핑 시스템에 활용하려면 매핑 정확도를 확인해 볼 필요가 있다. 이에 본 연구에서는 다양한 데이터 취득 환경과 사전 캘리브레이션 여부를 중심으로 복합센서의 매핑 정확도를 확인하였다. 첫째, 매핑 정확도가 지상기준점의 개수에 따라 어떻게 변하는지 살펴보았다. 지상기준점 개수가 2개일 때부터 총 RMSE가 1 m 이상에서 약 60 cm로 40 cm가량 줄어드는 것을 확인할 수 있었다. 둘째, 데이터 취득 상황과 사전 캘리브레이션 여부에 따른 매핑정확도를 확인하였다. 지상기준점이 있는 경우에는 개수가 적을지라도 사전 캘리브레이션의 영향이 크지 않은 것을 확인할 수 있었다. 영상의 중복도가 충분하지 않을 때는 사전 캘리브레이션 하는 것이 정확도 개선에 영향을 주는 것을 확인할 수 있었다. 지상기준점이 없는 경우에는 카메라, 탑재체 모두 사전 캘리브레이션 하는 것이 정확도를 개선시키는데 영향이 있음을 확인하였다. 본 연구를 기반으로, 향후 복합센서를 이용한 드론 매핑 수행 시 데이터 취득 조건에 따라 지상기준점 측량과 캘리브레이션 과정을 효율화 하는데 기여할 것으로 기대한다. Drone mapping systems can be applied to many fields such as disaster damage investigation, environmental monitoring, and construction process monitoring. To integrate individual sensors attached to a drone, it was essential to undergo complicated procedures including time synchronization. Recently, a variety of composite sensors are released which consist of visual sensors and GPS/INS. Composite sensors integrate multi-sensory data internally, and they provide geotagged image files to users. Therefore, to use composite sensors in drone mapping systems, mapping accuracies from composite sensors should be examined. In this study, we analyzed the mapping accuracies of a composite sensor, focusing on the data acquisition area and pre-calibration effect. In the first experiment, we analyzed how mapping accuracy varies with the number of ground control points. When 2 GCPs were used for mapping, the total RMSE has been reduced by 40 cm from more than 1 m to about 60 cm. In the second experiment, we assessed mapping accuracies based on whether pre-calibration is conducted or not. Using a few ground control points showed the pre-calibration does not affect mapping accuracies. The formation of weak geometry of the image sequences has resulted that pre-calibration can be essential to decrease possible mapping errors. In the absence of ground control points, pre-calibration also can improve mapping errors. Based on this study, we expect future drone mapping systems using composite sensors will contribute to streamlining a survey and calibration process depending on the data acquisition circumstances.

Active Vibration Control of Composite Shell Structure using Modal Sensor/Actuator System

Seung Jo Kim,Joon Seok Hwang,Jiwon Mok 한국항공우주학회 2006 International Journal of Aeronautical and Space Sc Vol.7 No.1

The active vibration control of composite shell structure has been performed with the optimized sensor/actuator system. For the design of sensor/actuator system, a method based on finite element technique is developed. The nine-node Mindlin shell element has been used for modeling the integrated system of laminated composite shell with PVDF sensor/actuator. The distributed selective modal sensor/actuator system is established to prevent the effect of spillover. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Continuous electrode patterns are discretized according to finite element mesh, and orientation angle is encoded into discrete values using binary string. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator for the first and the second mode vibration control of singly curved cantilevered composite shell structure are designed with the method developed on the finite element method and optimization. For verification, the experimental test of the active vibration control is performed for the composite shell structure. Discrete LQG method is used as a control law.

Vibration and impact monitoring of a composite-wing model using piezoelectric paint

The Korean Society for Composite Materials 2014 Advanced composite materials Vol.23 No.1

This study investigates a piezoelectric paint sensor for large area sensing applications, and its sensing characteristics under dynamic loading conditions such as impact and vibration. The piezoelectiric paint is composed of the <TEX>$Pb(Nb,Ni)O_3-Pb(Zr,Ti)O_3$</TEX> (PNN-PZT) powder and epoxy resin. The PNN-PZT is a kind of soft piezoelectric material that offers many advantages such as high piezoelectric properties, easy poling, and so on. The PNN-PZT/epoxy paint sensor can be easily applied to various engineering structures, even to those having a complex geometry or curved shapes because of its flexibility. In this study, the PNN-PZT/epoxy paint was coated on a composite-wing model. One electrode was made on the upper surface of the piezoelectric paint, while the graphite/epoxy composite structure itself was used as the other electrode. Then poling was conducted at room temperature (<TEX>$20^{\circ}C$</TEX>) under a 4 kV/mm electric field for 10 min. When the composite-wing model was subjected to tree-vibration, its vibration response was monitored by measuring the output voltage of the piezoelectric paint sensor; when the composite-wing model was impacted by an impact hammer, its impact signal was also measured by the piezoelectric paint sensor. The vibration and impact test results showed that the PNN-PZT/epoxy paint sensor captured the dynamic responses of the composite-wing structure very well. We believe that the piezoelectric paint sensor can be useful in many engineering applications such as real-time vibration and impact monitoring, damage detection, nondestructive structural health monitoring, and so on.

광섬유 브래그 격자 센서를 이용한 고온용 복합재료의 물성 측정

강동훈 ( Kang Dong Hun ),박상욱 ( Park Sang Ug ),김수현 ( Kim Su Hyeon ),김천곤 ( Kim Cheon Gon ),홍창선 ( Hong Chang Seon ) 한국복합재료학회 2003 Composites research Vol.16 No.6

복합재료는 비강성, 비강도가 높고 열팽창 계수가 낮으며 우수한 내열특성 등 기계적, 열적 특성이 좋아 항공기, 인공위성을 비롯하여 여러 다른 구조물에 폭넓게 사용되고 있다. 하지만, 복합재료를 고온 환경에 사용하기 위해서는 고온 환경에서의 물성에 대한 검증이 필요하다. 본 연구에서는 FBG 센서가 삽입된 T700/Epoxy 복합재료 시편에 대해 온도에 따른 물성을 측정하였다. 실험은 열챔버 내에서 수행하였고 온도 범위는 상온, 100℃, 200℃, 300℃, 400℃이다. 삽입된 광섬유의 예비 시험을 통해, 광섬유 센서의 삽입이 물성값에 미치는 영향을 확인하였다. 시험에는 [0/{0}/0]_(T), [90₂/{0}/90₂]_(T)와 같은 적충각을 갖는 두 종류의 시편을 사용하였다. 실험 결과로부터, 온도에 따른 복합재료의 물성 변화를 성공적으로 측정하였으며 FBG 센서가 고온 환경의 변형률 측정 센서로 매우 적합함을 확인하였다. Composites are widely used for aircraft, satellite and other structures due to its good mechanical and thermal characteristics such as low coefficient of thermal expansion(CTE), heat-resistance, high specific stiffness and specific strength. In order to use composites under condition of high temperature, however, material properties of composites at high temperatures must be measured and verified. In this paper, material properties of T700/Epoxy were measured through tension tests of composite specimens with an embedded FBG sensor in the thermal chamber at the temperatures of RT, l00℃, 200℃, 300 C, 400 C. Through the pretest of an embedded optical fiber, we confirmed the embedding effects of an optical fiber on material properties of the composites. Two kinds of specimens of which stacking sequences are [0/{0}/0]_(T) and [90₂/(0)/90₂]_(T) were fabricated. From the experimental results, material property changes of composites were successfully shown according to temperatures and we confirmed that fiber Bragg grating sensor is very appropriate to strain measurement of composites under high temperature.

Optimization and gas sensing mechanism of n-SnO₂-p-Co₃O₄ composite nanofibers

Kim, Jae-Hun,Lee, Jae-Hyoung,Mirzaei, Ali,Kim, Hyoun Woo,Kim, Sang Sub Elsevier 2017 Sensors and actuators. B, Chemical Vol.248 No.-

<P><B>Abstract</B></P> <P>Although the employment of n-p heterojunctions is among the most popular strategies to increase the performance of gas sensors, there have been a few systematic studies to determine the optimal composition in n-p heterojunctions. This paper reports the results of a systematic study of (n) xSnO<SUB>2</SUB>-(p) (1-x) Co<SUB>3</SUB>O<SUB>4</SUB> composite nanofibers (NFs) for gas sensing applications. Composite NFs were synthesized by the electrospinning method followed by annealing at 600°C. For gas sensing studies, several gases at optimal working temperature (350°C) were tested. Depending on the nominal composition, the sensors showed either n-or p-type behavior as well as different responses to the target gases. Furthermore, for all gases tested, the 0·5SnO<SUB>2</SUB>-0·5Co<SUB>3</SUB>O<SUB>4</SUB> sensor (nominal composition) showed the best gas sensing characteristics. The underlying gas sensing mechanism was examined in detail. The highest response observed in the 0·5SnO<SUB>2</SUB>-0·5Co<SUB>3</SUB>O<SUB>4</SUB> NFs sensor was primarily attributed to the major role of the p-Co<SUB>3</SUB>O<SUB>4</SUB> nanograins as electron reservoir. In addition, the possible substitution of Co<SUP>+2</SUP>/Co<SUP>+3</SUP> in Sn<SUP>+4</SUP> sites, the catalytic effect of Co<SUB>3</SUB>O<SUB>4</SUB> and generation of defects were likely to be the secondary reasons. This highlights the importance of the optimal composition for achieving the maximum gas-sensing performance in n-p composite NFs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Systematic study on SnO<SUB>2</SUB> (n) −Co<SUB>3</SUB>O<SUB>4</SUB> (p) electrospun composite NFs sensors. </LI> <LI> Transition from p-type to n-type semiconducting behavior by change of composition. </LI> <LI> Among various compositions, 0.5SnO<SUB>2</SUB>-0.5Co<SUB>3</SUB>O<SUB>4</SUB> showed the optimal composition. </LI> <LI> High response to low concentrations of C<SUB>6</SUB>H<SUB>6</SUB>. </LI> <LI> The main reasons for sensing enhancement were heterojunctions and catalytic effect. </LI> </UL> </P>

Active Vibration Control of Composite Shell Structure using Modal Sensor/Actuator System

Kim, Seung Jo,Hwang, Joon Seok,Mok, Ji Wo,Ko, Hyun Moo 서울대학교 항공우주신기술연구소 2001 항공우주신기술연구소 연구보고 Vol.2 No.2

The active vibration control of composite shell structure has been performed with the optimized sensor/actuator system, For the design of sensor/actuator system, a method based on finite element technique is developed. The nine-node Mindlin shell element has been used for modeling the integrated system of laminated composite shell with PVDF sensor/actuator. The distributed selective model sensor/actuator system is established to prevent the effect of spilover. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Continuous electrode patterns are discretized according to finite element mesh, and orientation angle is encoded into discrete values using binary string. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator for the first and thd second mode vibration control of singly curved cantilevered composite shell structure are designed with the method developed on the finite element method and optimization. For verification, the experimental test of the active vibration control is performed for thd composite shell structure. Discrete LQG method is used as a control law.

Active Vibration Control of Composite Shell Structure using Modal Sensor/Actuator System

Kim, Seung-Jo,Hwang, Joon-Seok,Mok, Ji-Won 한국항공우주학회 2006 International Journal of Aeronautical and Space Sc Vol.7 No.1

The active vibration control of composite shell structure has been performed with the optimized sensor/actuator system. For the design of sensor/actuator system, a method based on finite element technique is developed. The nine-node Mindlin shell element has been used for modeling the integrated system of laminated composite shell with PVDF sensor/actuator. The distributed selective modal sensor/actuator system is established to prevent the effect of spillover. Electrode patterns and lamination angles of sensor/actuator are optimized using genetic algorithm. Continuous electrode patterns are discretized according to finite element mesh, and orientation angle is encoded into discrete values using binary string. Sensor is designed to minimize the observation spillover, and actuator is designed to minimize the system energy of the control modes under a given initial condition. Modal sensor/actuator for the first and the second mode vibration control of singly curved cantilevered composite shell structure are designed with the method developed on the finite element method and optimization. For verification, the experimental test of the active vibration control is performed for the composite shell structure. Discrete LQG method is used as a control law.

기준신호 데이터를 이용한 보강된 복합재 구조물에서의 저속 충격위치 탐색

김윤영 ( Yoon Young Kim ),김진혁 ( Jin Hyuk Kim ),박유림 ( Yu Rim Park ),( Pratik Shrestha ),권희중 ( Hee Jung Kwon ),김천곤 ( Chun Gon Kim ) 한국복합재료학회 2016 Composites research Vol.29 No.1

본 연구에서는 4개의 FBG 센서가 설치된 보강된 복합재 구조물을 시편으로 사용하여, 충격해머로 가해진 저속 충격 위치를 탐색하였다. 100 kHz의 데이터 샘플링 속도를 가진 FBG 인터로게이터를 사용하였으며, 제안된 알고리즘을 통해 예상 충격위치를 계산하였다. 복합재 시편은 주 스파(Spar)와 몇 개의 스트링거(Stringer)를 포함하며 전체 면적은 0.8 × 1.2m이다. 247개의 격자점과 36개의 보강재 지점에 대한 기준신호 데이터를 얻었으며,이는 임의의 충격신호에 대한 비교대상이 되었다. 제안된 알고리즘은 normalized cross-correlation을 사용하여 두신호의 상호 유사성을 판독하는 방식으로 작동한다. 각각의 센서 신호로부터 얻어진 correlation 결과는 서로 곱연산되어 상호 보상적인 방법으로 사용되었다. 성능평가를 위해 대상 영역에 대한 20개의 임의의 충격시험을 수행하였다. 시험결과 성공적으로 충격위치를 탐색할 수 있었으며, 4개 센서신호를 사용하여 최대 오차 43.4 mm와 평균 오차 17.0 mm의 성능을 얻었다. 같은 시험에 대하여 사용된 센서의 개수를 변화시켜 가며 그 성능의 변화를 알아보았다. 두 개의 센서를 사용하였을 때 상호 보상적 효과가 최대가 됨을 확인하였으며, 2개의 센서(1, 2번 센서)의 조합으로 최대 오차 42.5 mm와 평균 오차 17.4 mm의 성능을 얻을 수 있었다. Low-speed impact was localized on a stiffened composite structure, using 4 FBG sensors with 100 kHzsampling rate interrogator and devised localization algorithm. The composite specimen consists of a main spar and several stringers, and the overall size of the specimen’s surface is about 0.8 × 1.2 m. Pre-stored reference data for 247 grid locations and 36 stiffener locations are gathered and used as comparison target for a random impact signal. The proposed algorithm uses the normalized cross-correlation method to compare the similarities of the two signals; the correlation results for each sensor’s signal are multiplied by others, enabling mutual compensation. 20 verification points were successfully localized with a maximum error of 43.4 mm and an average error of 17.0 mm. For the same experimental setup, the performance of the proposed method is evaluated by reducing the number of sensors. It is revealed that the mutual compensation between the sensors is most effective in the case of a two sensor combination. For the sensor combination of FBG #1 and #2, the maximum localization error was 42.5 mm, with average error of17.4 mm.

압전세라믹 센서와 광섬유 센서를 이용한 복합재 구조물의 건전성 모니터링

김천곤,성대운,김대현,방형준 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.5

구조건전성 모니터링은 복합재 구조물이 운용되는 단계에서 뿐만 아니라 설계 및 제자단계에서도 중요한 관심사가 되고 있다. 과도한 하중이나 저속충격은 모재균열이나 층간분리와 같은 복합재 파손의 원인이 될 수 있으며 이러한 손상은 구조물의 하중지지성능을 저하시키게 된다. 지능형 복합재 구조물에서의 구조건전성 모니터링 기술의 개발은 항공기와 같은 복합재 구조물의 안전성 향상에 도움이 될 수 있다. 본 연구에서는 압전세라믹 센서 및 광섬유 센서를 복합재 구조물의 건전성 모니터 링에 적용하였으며 파손신호의 특징파악 및 충격위치 검출을 위한 신호처리 방법을 제안하였다. Health monitoring is a major concern not only in the design and manufacturing but also in service stages for composite laminated structures. Excessive loads or low velocity impact can cause matrix cracks and delaminations that nay severely degrade the load carrying capability of the composite laminated structures. To develop the health monitoring techniques providing on-line diagnostics of smart composite structures can be helpful in keeping the composite structures sound during their service. In this study, we discuss the signal processing techniques and some applications for health monitoring of composite structures using piezoceramic sensors and fiber optic sensors.