• Steel and Composite Structures
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• 제27권6호
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• pp.691-702
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• 2018

This paper presents experimental and analytical results of fiber reinforced polymer (FRP) confined steel tubular columns under transverse impact loads. Influences of applied impact energy, thickness of FRP jacket and impact position were discussed in detail, and then the impact responses of FRP confined steel tubes were compared with bare steel tubes. The test results revealed that the FRP jacket contributes to prevent outward buckling deformation of steel at the clamped end and inward buckling of steel at the impact position. For the given applied impact energy, specimens wrapped with one layer and three layers of FRP have the lower peak impact loads than those of the bare steel tubes, whereas specimens wrapped with five layers of FRP exhibit the higher peak impact loads. All the FRP confined steel tubular specimens displayed a longer duration time than the bare steel tubes under the same magnitude of impact energy, and the specimen wrapped with one layer of FRP had the longest duration time. In addition, increasing the applied impact energy leads to the increase of peak impact load and duration time, whereas increasing the distance of impact position from the clamped end results in the decrease of peak impact load and the increase of duration time. The dynamic analysis software Abaqus Explicit was used to simulate the mechanical behavior of FRP confined steel tubular columns, and the numerical results agreed well with the test data. Analytical solution for lateral displacement of an equivalent cantilever beam model subjected to impact load was derived out. Comparison of analytical and experimental results shows that the maximum displacement can be precisely predicted by the present theoretical model.

• 항공우주기술
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• 제12권1호
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• pp.1-9
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• 2013

태양전지 및 전기동력을 이용한 장기 체공 무인기의 체공 효율을 증가시키기 위해서는 구조 경량화가 필수적이다. 본 논문에서는 24시간 장기체공 전기동력 무인항공기인 EAV-2H의 주익 경량화 및 구조 건전성 확보를 위하여 Mylar Film과 섬유강화 복합재료로 구성된 주익을 설계하였다. 보이론 해석을 이용하여 주익 Spar의 형상 선정 및 구조 사이징을 수행하였다. EAV-2H 임무를 고려하여 하중해석을 수행하고 주익의 주요 구성품에 대해 유한요소해석을 수행하였다. 마지막으로 주익의 정적구조시험을 통해 주익의 구조 건전성을 확인하였다. 본 연구를 통하여 개발된 EAV-2H 주익은 이전 모델인 EAV-2에 비교하여 Span 기준 42%의 중량이 감소되었으며, 설계극한하중을 부가하는 정적구조시험을 통과하였다.

• Smart Structures and Systems
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• 제17권1호
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• pp.91-105
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• 2016

One of the most commonly used techniques to strengthen steel reinforced concrete structures is the application of externally bonded patches in the form of carbon fiber reinforced polymers (CFRP) or recently, textile reinforced cements (TRC). These external patches undertake the tensile stress of bending constraining concrete cracking. Development of full-field inspection methodologies for fracture monitoring are important since the reinforcing layers are not transparent, hindering visual observation of the material condition underneath. In the present study acoustic emission (AE) and digital image correlation (DIC) are applied during four-point bending tests of large beams to follow the damage accumulation. AE helps to determine the onset of fracture as well as the different damage mechanisms through the registered shifts in AE rate, location of active sources and change in waveform parameters. The effect of wave propagation distance, which in large components and in-situ can well mask the original information as emitted by the fracture incidents is also discussed. Simultaneously, crucial information is supplied by DIC concerning the moments of stress release of the patches due to debonding, benchmarking the trends monitored by AE. From the point of view of mechanics, conclusions on the reinforcing contribution of the different repair methodologies are also drawn.

• Steel and Composite Structures
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• 제18권3호
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• pp.583-601
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• 2015

In the present study, the combined effects of thermal and mechanical loadings on the interlaminar shear stresses of both moderately thin and thick composite laminated beams are numerically analyzed. The finite element modelling of laminated composite beams and analysis of interlaminar stresses are performed using the commercially available software package MSC NASTRAN/PATRAN. The validity of the finite element analysis (FEA) is demonstrated by comparing the experimental test results obtained due to mechanical loadings under the influence of thermal environment with those derived using the present FEA. Various parametric studies are also performed to investigate the effect of thermal loading on interlaminar stresses generated in symmetric, anti-symmetric, asymmetric, unidirectional, cross-ply, and balanced composite laminated beams of different stacking sequences with identical mechanical loadings and various boundary conditions. It is shown that the elevated thermal environment lead to higher interlaminar shear stresses varying with the stacking sequence, length to thickness ratio, ply orientations under identical mechanical loading and boundary conditions of the composite laminated beams. It is realized that the magnitude of the interlaminar stresses along xz plane is always much higher than those of along yz plane irrespective of the ply-orientation, length to thickness ratios and boundary conditions of the composite laminated beams. It is also observed that the effect of thermal environment on the interlaminar shear stresses in carbon-epoxy fiber reinforced composite laminated beams are increasing in the order of symmetric cross-ply laminate, unidirectional laminate, asymmetric cross-ply laminate and anti-symmetric laminate. The interlaminar shear stresses are higher in thinner composite laminated beams compared to that in thicker composite laminated beams under all environmental temperatures irrespective of the laminate stacking sequence, ply-orientation and boundary conditions.

• Macromolecular Research
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• 제12권1호
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• pp.119-126
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• 2004

In this study, the influence of silane coupling agents, featuring different organo-functional groups on the interlaminar and thermal properties of woven glass fabric-reinforced nylon 6 composites, has been by means of short-beam shear tests, dynamic mechanical analysis, scanning electron microscopy, and thermogravimetric analysis. The results indicate that the fiber-matrix interfacial characteristics obtained using the different analytical methods agree well with each other. The interlaminar shear strengths (ILSS) of glass fabric/nylon 6 composites sized with various silane coupling agents are significantly improved in comparison with that of the composite sized commercially. ILSS of the composites increases in the order: Z-6076 with chloropropyl groups in the silanes > Z-6030 with methacrylate groups> Z-6020 with diamine groups; this trend is similar to that of results found in an earlier study of interfacial shear strength. The dynamic mechanical properties, the fracture surface observations, and the thermal stability also support the interfacial results. The improvement of the interfacial properties may be ascribed to the different chemical reactivities of the reactive amino end groups of nylon 6 and the organo-functional groups located at the ends of the silane chains, which results from the increased chemical reactivity in order chloropropyl > methacrylate > diamine.

• 한국구조물진단유지관리공학회 논문집
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• 제22권6호
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• pp.30-36
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• 2018

기존 콘크리트 구조물의 노후화 또는 지진과 같은 외부 하중에 의하여 구조물의 구조 성능이 저하되기 때문에, 기존 건물의 보수 및 보강 연구는 중요하다. 외부부착 탄소섬유 보강 공법과 같은 효율적인 보수 공법을 사용하면 경제적으로 콘크리트 구조물의 구조 성능을 높일 수 있다. 따라서 외부부착 탄소섬유를 사용한 콘크리트 부재의 실험 연구는 많이 진행되었다. 특히, 콘크리트 보를 사용한 전단 보강에 관한 연구는 탄소섬유의 양, 부착 각도, 스트립의 폭, 그리고 재료간의 상호작용에 관한 것이었다. 하지만 선행된 연구에 비하여 탄소섬유의 이 방향 레이아웃에 관한 다양한 변수 연구는 부족한 상황이다. 따라서 이 연구에서는 이 방향 레이아웃 외부부착 탄소섬유 공법을 사용하여 콘크리트 보의 전단보강 효과를 검증하였다. 이 방향 레이아웃의 보강 효과는 스터럽과의 전단 기여도, 실험체의 전단 거동과 보강 시점에 따른 최대 내력의 비교를 통하여 이루어졌다.

• 한국군사과학기술학회지
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• 제15권6호
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• pp.812-819
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• 2012

Interference and jamming are becoming increasing concern to a radar system nowdays. AESA(Active Electronically Steered Array) antennas and adaptive beamforming(ABF), in which antenna beam patterns can be modified to reject the interference, offer a potential solution to overcome the problems encountered. In this paper, we've developed a planar active phased array radar system, in which ABF, target detection and tracking algorithm operate in real-time. For the high output power and the low noise figure of the antenna, we've designed the S-band TRMs based on GaN HEMT. For real-time processing, we've used wavelenth division multiplexing technique on fiber optic communication which enables rapid data communication between the antenna and the signal processor. Also, we've implemented the HW and SW architecture of Real-time Signal Processor(RSP) for adaptive beamforming that uses SMI(Sample Matrix Inversion) technique based on MVDR(Minimum Variance Distortionless Response). The performance of this radar system has been verified by near-field and far-field tests.

• 한국군사과학기술학회지
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• 제17권1호
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• pp.90-95
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• 2014

The system design and the system performance analysis of 3D imaging laser radar system for the mapping purpose is addressed in this article. For the mapping, a push-bloom scanning method is utilized. The pulsed fiber laser with high pulse energy and high pulse repetition rate is used for the light source of laser radar system. The high sensitive linear mode InGaAs avalanche photo-diode is used for the laser receiver module. The time-of-flight of laser pulse from the laser to the receiver is calculated by using high speed FPGA based signal processing board. To reduce the walk error of laser pulse regardless of the intensity differences between pulses, the time of flight is measured from peak to peak of laser pulses. To get 3D image with a single pixel detector, Risley scanner which stirs the laser beam in an ellipsoidal pattern is used. The system laser energy budget characteristics is modeled using LADAR equation, from which the system performances such as the pulse detection probability, false alarm and etc. are analyzed and predicted. The test results of the system performances are acquired and compared with the predicted system performance. According to test results, all the system requirements are satisfied. The 3D image which was acquired by using the laser radar system is also presented in this article.

• 한국광학회지
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• 제14권3호
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• pp.306-311
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• 2003

본 논문에서는 광전송시스템에서 파장분할다중화 광소자로 사용되는 박막필터형 광소자의 특성 분석 및 평가를 위해 입력광원을 모델링 하였으며 광경로에 대해 광선추적법을 사용하여 전산모의 한 광특성을 실험과 비교, 분석하였다. 그 결과 입력광원에 대한 cell 방식의 모델링이 결합효율의 정확도 및 가우시안 강도분포에 접근성을 볼 때 마이크로 옵틱스형 광소자 분석함에 있어 적합함을 알 수 있다. 박막필터형 광소자에 대한 최적 전산모의 결과 광섬유와 GRIN 렌즈 사이 거리가 0.24mm이며 GRIN 렌즈와 박막필터 사이 거리가 0.25mm일 때 최대 결합효율은 -0.11 ㏈이었으며 동일한 조건에의 실험결과 -0.35 ㏈의 최대 결합효율을 얻었다. 이것은 단심 및 이심페룰, GRIN 렌즈 등과 같은 구성품의 불완전성과 박막필터에 의한 손실을 고려할 때, 전산모의 결과와 매우 일치하는 것으로서 본 연구에서 제안한 입력광원의 모델링을 적용한 전산모의가 박막필터형 광소자의 특성을 예측할 수 있음을 보였다.

• Structural Engineering and Mechanics
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• 제70권6호
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• pp.703-710
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• 2019

While fiber-reinforced plastic (FRP) materials have been largely used in the retrofitting of concrete buildings, its application has been limited because of some problems such as de-bonding of FRP layers from the concrete surface. This paper is the part of a wide experimental and analytical investigation about flexural retrofitting of reinforced concrete (RC) columns using FRP and mechanical fasteners (MF). A new generation of MF is proposed, which is applicable for retrofitting of RC columns. Furthermore, generally, to evaluate a retrofitted structure the nonlinear static and dynamic analyses are the most accurate methods to estimate the performance of a structure. In the nonlinear analysis of a structure, accurate modeling of structural elements is necessary for estimation the reasonable results. So for nonlinear analysis of a structure, modeling parameters for beams, columns, and beam-column joints are essential. According to the concentrated hinge method, which is one of the most popular nonlinear modeling methods, structural members shall be modeled using concentrated or distributed plastic hinge models using modeling parameters. The nonlinear models of members should be capable of representing the inelastic response of the component. On the other hand, in performance based design to make a decision about a structure or design a new one, numerical acceptance should be determined. Modeling parameters and numerical acceptance criteria are different for buildings of different types and for different performance levels. In this paper, a new method was proposed for FRP retrofitted columns to avoid FRP debonding. For this purpose, mechanical fasteners were used to achieve the composite behavior of FRP and concrete columns. The experimental results showed that the use of the new method proposed in this paper increased the flexural strength and lateral load capacity of the columns significantly, and a good composition of FRP and RC column was achieved. Moreover, the modeling parameters and acceptance criteria were presented, which were derived from the experimental study in order to use in nonlinear analysis and performance-based design approach.