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댐퍼를 갖는 복합구조 외팔보의 비틀림진동해석을 통한 접합부의 구조성능 평가
유형원,최낙삼 漢陽大學校 工學技術硏究所 1999 工學技術論文集 Vol.8 No.1
자동차의 크랭크축계 및 댐퍼풀리를 연구대상 모델로하여 댐퍼를 갖는 외팔보 복합구조물에 대한 자유 비틀림 진동특성을 검토하고 모델실험, 모달해석, 유한요소해석을 실시했다. 실험모델 구조물로는 금속 단일구조물, 금속/고무 복합구조물을 제작 사용했다. 결론적으로, 충격햄머를 이용한 자유진동실험을 통해 용접부와 기계적 체결부, 고무접착부의 강성과 감쇠계수를 1자유도법, 2자유도법, 3자유도법으로 평가할 수 있었다. Torsional free-vibration characteristics of a cantilever beam with damper have been studied using the theoretical and experimental modal analyses and a finite-element method. The torsional beam was made as a model of the crankshaft system with a damper pulley for motor car. Two kinds of model beams were used: simple metal beam and metal/rubber composite structure beam. Consequently, Stiffness and damping factor for weld, mechanical joint and adhered rubber layer could be evaluated using one-degree, two-degree, three-degree of freedom analyses through and impact hammer test.
김정현,우성충,최낙삼 한국비파괴검사학회 2003 한국비파괴검사학회지 Vol.23 No.5
본 연구에서는 연속형 일방향 및 수자직 유리섬유강화 복합재료로 인장 시험편을 만들어 AE 특성에 대한 섬유배향 효과를 살펴보았다. AE 신호들을 STFT 처리하여 특성별로 분류하였으며, 반사식 및 투과식 편광현미경을 이용하여 시험편의 손상영역을 관찰하였다. 저주파수 대역의 약한 AE 신호들은 모재 및 계면에서의 손상으로 나타났으며, 높은 진폭의 고주파수 대역 AE 신호들은 섬유 파단에 기인하였다. 섬유 파단 과정에서 발생하는 고진폭의 AE 사상률을 기본 특성 데이터로 하여 다른 섬유배향과 노치방향을 가진 복합재에서의 파괴과정을 특징지을 수 있었다. 결론적으로, AE법은 연속형 유리섬유 강화 복합재의 파괴거동을 탐지하는데 있어 유용함을 알 수 있었다. The effects of fiber orientation on acoustic emission(AE) characteristics have been studied for the unidirectional and satin-weave, continuous glass-fiber reinforced plastic(UD-CFRP and SW-CFRP) tensile specimens. Reflection and transmission optical microscopy was used for investigation of the damage zone of specimens. AE signals were classified as different types by using short time Fourier transform(STFT) : AE signals with high intensity and high frequency band were due to fiber fracture, while weak AE signals with low frequency band were due to matrix and interfacial cracking. The feature in the rate of hit-events having high amplitudes showed a process of fiber breakages, which expressed the characteristic fracture processes of individual fiber-reinforced plastics with different fiber orientations and with different notching directions. As a consequence, the fracture behavior of the continuous GFRP could be monitored as nondestructive evaluation(NDE) through the AE technique.
복합 적층 박판의 열응력 파손에 대한 진동 활용 비파괴평가
이성혁,이정기,최낙삼 韓國非破壞檢査學會 1999 한국비파괴검사학회지 Vol.19 No.5
두께 1mm의 얇은 복합적층판의 자유경계단부에서 열응력으로 인해 발생하는 미세손상을 진동거동과 관련된 비파괴평가의 가능성을 연구하였다. 유한요소 열응력해석을 통해 예상되는 손상발생영역을 초음파 C-스캔과 광학현미경을 이용하여 관찰하였다. 사인 스윕시험을 이용한 적층보 시험편의 횡진동 해석결과, 미세한 내부손상으로 인해 고유주파수가 확실히 감소하였으며 감쇠비도 상당히 증가하였다. 길이가 짧은 적층보 시험편과 2차 모드의 공진주파수를 이용하여 얇은 적층판에서 열응력으로 유기된 미세손상을 매우 민감하게 평가할 수 있음을 알았다. A feasibility investigation on vibration-based nondestructive evaluation of thermal stress-induced micro failure in the free edge region of thin composite laminates(1mm thick) has been carried out. The failure occurrence and damage zone, which were predicted by the three-dimensional finite-element thermal stress analysis, were observed using the ultrasonic C-scan and optical microscopy. Analysis of the vibration spectrum measured from the laminate beam specimens by the vibration sweep test exhibited that the obvious decrease in resonancy frequency and some considerable increase in damping factor were associated with the micro-failure formation. The vibration technique utilizing short beam and high resonant frequency was found to be very sensitive to the thermal stress-induced damage in the thin laminates.
열하중을 받는 복합재료 적층판의 손상에 대한 열-음향방출해석
김영복,민대홍,이덕보,최낙삼 한국비파괴검사학회 2001 한국비파괴검사학회지 Vol.21 No.3
열-음향방출(thermo-AE) 기법을 이용하여 두께 3㎜, [+456/-456]S 복합재료 적층판의 열응력 유기 손상에 대해 비파괴평가의 유효성을 연구하였다. 반복적인 열부하 사이클에 의해서 thermo-AE 사상수가 감소하는 경향이 뚜렷하게 나타나서 열부하에 따른 카이저효과가 관찰되었다. 열부하사이클중의 thermo-AE 거동을 분석하여 복합재료의 응력자유온도를 결정할 수 있었다. 초음파 C스캔, 광학현미경, 주사형 전자현미경을 통해 섬유파단과 모재파손이 관찰되었으며, 이들 파손 인자는 thermo-AE 신호의 단시간 퓨리에 변환처리에 의해 생성된 3종류의 서로 다른 시간-주파수 특성과 대응하였다. 이 특성을 이용하여 복합재료의 냉각열처리 및 반복 열부하사이클시의 손상발생과정 및 내부 마찰 거동 내역을 추적할 수 있었다.
알루미늄/CFRP 복합재의 접착강도 향상을 위한 경화방법에 관한 연구
이경엽(Kyong Yop Rhee),양준호(Jun Ho Yang),최낙삼(Nak Sam Choi) 한국자동차공학회 2002 한국 자동차공학회논문집 Vol.10 No.3
This study investigates the effect of curing method on the bonding strength of aluminum/CFRP composites. The surface of aluminum panel was treated by DC plasma. Lap shear tests and T-peel tests were performed based on the procedure of ASTM 906-94a and ASTM D 1876-95, respectively. Test samples were fabricated by using the co-curing method and the secondary curing method. The results showed that the shear strength of test samples made by the co-curing method was 2.5 times greater than that of test samples made by the secondary curing method. The T -peel strength of the co-curing method case was almost 2 times greater than that of the secondary curing method case.
Quasi-Disk Type Microbond Pull-Out Test for Evaluating Fiber/Matrix Adhesion in Composites
Choi, Nak-Sam,Park, Joo-Eon,Kang, Soo-Keun SAGE Publications 2009 Journal of composite materials Vol.43 No.16
<P>Adhesion strength between epoxy resin and carbon fiber was analyzed using various microbond types adhered onto a single carbon fiber. Experimental pull-out tests were performed for a quasi-disk type, a hemispherical type and a droplet type microbond specimen. The quasi-disk type microbond specimen showed high regression coefficient and low standard deviation in the measurement of interfacial shear strength data as compared with the droplet and hemispherical ones. Average value of interfacial shear strength for quasi-disk type was about 55% as large as those for the other types. Finite element analysis showed that the stress distributions along the interface in the quasi-disk type specimen did not have such drastic stress concentrations susceptible to variations in the specimen geometry as revealed in the cases of droplet and hemispherical types. The experimental data were different according to the kinds of loading device such as the microvise-tip and the pin-holed plate. The use of a pin-holed steel section was useful for testing the quasi-disk type microbond specimens to give low scattering in the measurement of strength data.</P>
최낙삼(Nak-Sam Choi),이성혁(Sung-Hyuk Lee) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
Local buckling behaviors of aluminum square tube beams reinforced by aluminum plates under three point bending loads have been analyzed using experimental tests combined with theoretical and finite element analyses. For this analysis true stresses were determined from applied loads and cross-sectional area records of a tensile specimen with a rectangular cross-section by real-time photographing. True strains were also obtained from in-situ local elongation measurements of the specimen gage portion by the multi-point scanning laser extensometer. Six kinds of aluminum tube beam specimens reinforced by aluminum plates were employed for the bending test. The bending deformation behaviors up to the maximum load analyzed by the numerical simulation agreed well with experimental ones. After passing the maximum load, reinforcing plate hindering the local buckling of the tube beam was debonded from the aluminum tube beam. An aluminum tube beam strengthened by aluminum plate on the upper web showed the most excellent bending capacity, which could be explained on the basis of the neutral axis shift and the local buckling deformation range.