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특성 길이를 이용한 평직 복합재 볼트 체결부의 강도 예측
박승범,변준형,안국찬 한국안전학회 2003 한국안전학회지 Vol.18 No.4
A study on predicting the joint strength of mechanically fastened woven glass/epoxy composite has been performed. An experimental and numerical study were carried out to determine the characteristic length and joint strength of composite joint. The characteristic lengths for tension and compression were determined from the tensile and compressive test with a hole respectively. The characteristic lengths were evaluated by applying the point stress failure criterion to a specimen containing a hole at the center subjected to tensile loading and a specimen containing a half circular notch at the center subjected to compressive load. The joint strength was evaluated by the Tsai-Wu and Yamada-Sun failure criterion on the characteristic curve. The predicted results of the joint strength were compared with experimental results.
전도성 고분자 센서 어레이를 이용한 휘발성 유기 화합물 가스 인식
이경문,주병수,유준부,황하룡,이병수,이덕동,변형기,허증수 한국센서학회 2002 센서학회지 Vol.11 No.5
휘발성 유기 화합물 가스(Volatile Organic Compounds)를 인식하고 분석하기 위하여 전도성 고분자 센서어레이를 이용한 시스템을 제작하였다. Polypyrrole와 Polyaniline을 화학중합법으로 센서에 전도성고분자막을 형성하였고 이를 통해 VOC 검지용 센서 어레이를 제작하였다. 센서어레이로부터 측정되는 다차원 데이터는 주성분분석법(PCA)과 RBF(Radial Basis Function Network)을 이용하였다. 제안된 시스템으로 VOCs 가스를 인식하는데 있어서 RBF Network이 PCA방식보다 더욱 효율적인 것으로 판단되었다. We fabricated gas recognition system using conducting polymer sensor array for recognizing and analyzing VOCs(Volatile Organic Compounds) gases. The polypyrrole and polyaniline thin film sensors which were made by chemical polymerization were employed to detect VOCs. The multi-dimensional sensor signals obtained from the sensor array were analyzed using PCA(principal component analysis) technique and RBF(radial basis function) Network. Throughout the experimental trails, we confirmed that RBF Network is effective than PCA technique in identifying VOCs.
Paper : Stitching Effect on Flexural and Interlaminar Properties of MWK Textile Composites
( Joon Hyung Byun ),( Yi Qi Wang ),( Moon Kwang Um ),( Sang Kwan Lee ),( Jung Il Song ),( Byung Sun Kim ) 한국복합재료학회 2015 Composites research Vol.28 No.3
The stitching process has been widely utilized for the improvement of through-thickness property of the conventional laminated composites. This paper reports the effects of stitching on the flexural and interlaminar shear properties of multi-axial warp knitted (MWK) composites in order to identify the mechanical property improvements. In order to minimize the geometric uncertainties associated with the stacking pattern of fabrics, the regular lay-up was considered in the examination of the stitching effect. The key parameters are as follows: the stitch spacings, the stitching types, the stitching location, and the location of compression fixture nose. These parameters have little effect on the flexural and interlaminar shear properties, except for the case of stitching location. However, the geometry variations caused by the stitching resulted in minor changes to the mechanical properties consistently. Stitching on the 0o fibers showed the lowest flexural strength and modulus (12% reduction for both properties). The stitch spacing of 5 mm resulted in 8% reduction for the case of interlaminar strength compared with that of 10 mm spacing.
Twisted Yarn 복합재료의 물성치 시험 및 탄성계수 예측
변중형 ( Joon Hyung Byun ),이상관 ( Sang Kwan Lee ),엄문광 ( Moon Kwang Um ),김태원 ( Tae Won Kim ),배성우 ( Sung Woo Bae ) 한국복합재료학회 2002 Composites research Vol.15 No.6
꼰 섬유(twisted yarn)로 이루어진 복합재료의 탄성계수를 예측하기 위한 강성모델을 제시하였다. 이 모델은 단위 셀 구조를 바탕으로 하여 좌표변환과 구성 재료의 연성 상수를 체적 평균함으로써 복합재료의 탄성계수를 예측하는 방법이다. 해석적인 결과와 실험치와의 비료를 위하여 두 종류의 꼬임 각을 가지는 섬유로 구성된 복합재료에 대한 시험을 하였으며 인장, 압축, 탄성계수를 구하였다. 이 시험편은 유리섬유 및 에폭시 수지를 사용한 RTM, 성형법으로 제조하였다. 탄성계수에 대한 비교 결과 예측치와 실험치는 비교적 잘 일치하였다. 이 모델에 의해 구해진 3차원적인 탄성계수 값은, 꼬인 섬유로 이루어진 직조형 복합재료 구조물의 구조해석을 위한 기본 물성치 입력값으로 사용될 수 있다. A stiffness model has been proposed to predict elastic constants of twisted yarn composites. The model is based upon the unit cell structure, the coordinate transformation, and the volume averaging of compliance constants for constituent materials. For the correlation of analytic result with experiments, composite samples of various yarn twist angles were tested, and strength and Young`s modulus under tensile, compressive, and shear loading have been obtained. The sample was fabricated by the RTM process using glass yarns and epoxy resin. The correlations of elastic constants showed relatively good agreements. The model provides the predictions of the three-dimensional engineering constants, which are valuable input data for the analytic characterization of textile composites made of twisted yarn.
격자 볼츠만 방법을 이용한 난류 경계층에서의 오염물질 확산에 대한 수치적 연구
김준형(Joon-Hyung Kim),윤준용(Joon-Yong Yoon),변성준(Sung-Joon Byun),신명섭(Myung-Seob Shin) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
The purpose of this study is a numerical simulation of pollutant-laden flow in a boundary layer. The pollutant source is divided Ground-Level Source (GLS) and Elevated source (ES). Air velocity and pollutant particle concentration profile is compared with the experiments in a turbulent boundary layer flow. The code for this research uses Large-Eddy Simulation (LES) model by using Lattice Boltzmann Method (LBM). The Lattice Boltzmann subgrid model predicts more exact solution than previous Reynolds-Averaged Navier-Stokes (RANS) model.
하영준(Young-Joon Ha),이승준(Seung-Joon Lee),이준현(Joon-Hyun Lee),변준형(Joon-Hyung Byun) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.6
Carbon fibre reinforced plastics (CFRP) should be inspected in fabrication process in order to enhance quality by prevent defects such as delamination and void. Generally, ultrasonic technique is widely used to evaluate FRP. In conventional ultrasonic technique, transducer should be contacted on FRP. However, conventional contacting method could not be applied in fabrication process and novel non-contact evaluating technique was required. Technique using air-coupled transducer can make non-contacting ultrasonic technique available in evaluation of FRP. Therefore, in this study, generation technique of laser-based ultrasound using Nd:YAG pulse laser(532㎚, 32mJ) system and reception technique using air-coupled transducer are applied for the non-destructive and non-contact evaluation of delamination in CFRP. Wave propagating through artificial delamination region was received using pitch-catch arrangement. Signal characteristics due to defects were analyzed to find a factor for detecting defects. PZT sensor was used to get a trend of waveform and fundamental database. The high frequency component of 1.1 ㎒ of laser-generated guided wave received with piezoelectric sensor disappeared after propagating through delamination region. However, it could not be received this high frequency guided wave by using air-coupled transducer and linear slit array. In a frequency spectrum of laser-generated guided wave received by air-coulped transducer, the first peak of frequency spectrum under 100㎑ received in the defect region showed higher than in the sound region. The peak of frequency spectrum represented approvable parameter to detect delamination in CFRP. By using this feature, line scanning data was acquired in fully non-contacting pitch-catch method and was proved as useful technique for detecting delamination in CFRP.
레이저 유도 초음파를 이용한 복합재료 층간 결함의 비접촉 비파괴 평가
이승준(Seung-Joon Lee),하영준(Young-Joon Ha),이준현(Joon-Hyun Lee),변준형(Joon-Hyung Byun) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The objective of this research is to develop non-contact and real time inspection technique based on laser generated ultrasound to evaluate delamination in CFRP composite fabricated from recently developed 3-dimensional fiber placement system. In this study, a hybrid laser generation/air-coupled detection ultrasonic system is presented. Fiberized Nd:YAG pulse laser with line array slit is used to generate ultrasonic guided wave in unidirectional CFRP specimen with artificial delamination. In order to investigate the reception ability of ultrasonic guided wave propagated through the area of delamination air-coupled transducer is used as reception of guided wave. The characteristic of time domain waveform and frequency spectrum of guided wave received from air-coupled transducer based on non-contact scheme is discussed. By scanning over the surface beneath which a delamination lies, it is possible to achieve 2-dimensional image and measure the size of delamination.