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탄소섬유/에폭시 복합재료의 층간파괴인성에 미치는 균열진전각도의 영향
황진호,황운봉,Hwang, Jin-Ho,Hwang, Woon-Bong 대한기계학회 1999 大韓機械學會論文集A Vol.23 No.6
Interlaminar fracture toughness of carbon/epoxy composite materials has been studied under tensile and flexural loading by the use of width tapered double cantilever beam(WTDCB) and end notched flexure(ENF) specimens. This study has significantly examined the effect of various interfacial ply orientation, ${\alpha}(0^{\circ},\;45^{\circ}\;and\;90^{\circ})$ and crack propagation direction, ${\theta}(0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;45^{\circ})$ in terms of critical strain energy release rate through experiments. Twelve differently layered laminates were investigated. The data reduction for evaluating the fracture energy is based on compliance method and beam theory. Beam theory is used to analyze the effect of crack propagation direction. The geometry and lay-up sequence of specimens are considered various conditions such as skewness parameter, beam volume, and so on. The results show that the fiber bridging occurred due to the non-midplane crack propagation and causes the difference of fracture energy evaluated by both methods. For safer and more reliable composite structures, we obtain the optimal stacking sequence from initial fracture energy in each mode.
변형률 감지기를 이용한 복합재료 지능구조물의 변형형상예측
윤영복,조영수,이동건,황운봉,하성규,Yoon, Young-Bok,Cho, Young-Soo,Lee, Dong-Gun,Hwang, Woon-Bong,Ha, Sung-Kyu 대한기계학회 1998 大韓機械學會論文集A Vol.22 No.1
A shape estimation is needed to control actively a smart structure. A method is, hence, proposed to predict the deformed shape of the structure subjected to unknown external load using the signal from sensors attached to the structure. The shape estimation is based on the relationship between the deformation of the structure and the signal from the sensors. The matrix containing the relationship between the deformation and signal is obtained using fictitious force or eigenvector of global stiffness matrix. Then the deformed shape can be predicted using the linear matrix and signal from sensors attached to the structure. To verify this method, experiment and FEM were performed and it was shown that the shape estimation method based on the fictitious force predicts deflections well and more accurately than that based on eigenvector.
압하력, 장력에 따른 조질 압연에서의 소재 변형률 예측에 관한 연구
정종현(Jong Hyeon Jeong),고성현(Seong Hyun Ko),김미정(Mi-Jeong Kim),황운봉(Woon Bong Hwang),박현철(Hyun Chul Park) 대한기계학회 2020 大韓機械學會論文集A Vol.44 No.4
조질 압연은 소재의 잔류 응력 및 표면 평탄도 등의 제품 문제를 해결하기 위한 하나의 중요한 공정이다. 유한요소 해석을 기반으로 하는 기존의 연구들은 하나의 스탠드에서의 압연 상황만을 고려하였으며, 소재에 작용하는 장력에 의한 영향에 관하여 수행되지 않았다. 이에 본 연구에서는 2D 유한요소 모델을 통하여 압하력과 장력이 소재 압하에 어떠한 영향을 미치는지에 관한 분석을 수행하였으며, 임의의 해석 조건을 통하여 분석 결과를 검증하였다. 또한 3D 해석 모델을 통하여 소재 폭 방향에 대하여 압연 시 소재가 어떻게 변형하는지에 관한 분석을 수행하였다. Skin pass rolling is an important process to resolve product problems such as strip wave or residual stress. Previous research based on finite element method (FEM) has only considered one stand without the effects of back tension. In this study, the relationships between roll force, back tension, and strain of the workpiece are proposed, and they are verified using randomly selected FEM conditions based on a 2D FEM model composed of two stands and a tension reel. Simulation based on a 3D FEM model is also performed to account for the width directional strain, and the reliability is verified by comparing these results to those of the 2D model.