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Analysis of Wrinkling Behavior in Thin Sheets with Damage
Woo, Kyeongsik,Jenkins, Christopher H. American Institute of Aeronautics and Astronautics 2014 Journal of spacecraft and rockets Vol.51 No.2
In this paper, the wrinkling behavior of corner loaded damaged thin sheets was studied using global/local analysis. In the global analysis, corner loaded square sheet configurations with a single cut or a hole located at the center were analyzed. The wrinkling deformation was obtained explicitly by geometrically nonlinear shell element postbuckling analysis. The effect of the orientation of the cut on the initiation and growth of wrinkles was systematically investigated. It was found that the global wrinkle formation amplified the stress singularity at the cut tip. The wrinkle growth behavior of square sheets with hole-type damage resulted in larger slack areas than the cut-type damage. The J integral at the cut tip was calculated by the local analysis (performed only for the small region around the cut tip). The effect of wrinkle deformation on the amplification of stress singularity was studied by examining the variation of the J integral versus the applied load. The stress intensity factor was found to increase as the cut angle increased.
Numerical Simulation of High Velocity Impact of Circular Composite Laminates
Kyeongsik Woo,In-Gul Kim,Jong Heon Kim,Douglas S. Cairns 한국항공우주학회 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2
In this study, the high-velocity impact penetration behavior of [45/0/-45/90]㎱ carbon/epoxy composite laminates was studied. The considered configuration includes a spherical steel ball impacting clamped circular laminates with various thicknesses and diameters. First, the impact experiment was performed to measure residual velocity and extent of damage. Next, the impact experiment was numerically simulated through finite element analysis using LS-dyna. Three-dimensional solid elements were used to model each ply of the laminates discretely, and progressive material failure was modeled using MAT162. The result indicated that the finite element simulation yielded residual velocities and damage modes well-matched with those obtained from the experiment. It was found that fiber damage was localized near the impactor penetration path, while matrix and delamination damage were much more spread out with the damage mode showing a dependency on the orientation angles and ply locations. The ballistic-limit velocities obtained by fitting the residual velocities increased almost linearly versus the laminate diameter, but the amount of increase was small, showing that the impact energy was absorbed mostly by the localized impact damage and that the influence of the laminate size was not significant at high-velocity impact.
Delamination behavior of L-shaped composite beam with manufacturing defects
Kyeongsik Woo,Biruk F. Nega,Douglas S. Cairns,Jim Lua 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.9
Composite structures are more susceptible to manufacturing defects than conventional materials. Fiber misalignment, cracks, and voids are typical types of manufacturing defects in laminated composites. Defects can greatly reduce structural integrity and load carrying capacity, so their effects on material and structural strengths must be understood. In this paper, the effect of manufacturing defects on the progressive delamination behavior was studied for carbon/epoxy composite laminated L-beam under four-point bending test conditions. The defects of wavy plies and pure resin that had flowed out were characterized from surface photography and then transformed into finite element modeling using semi-automatic approach to which pre-delamination and void were included. Next, progressive failure analyses were performed with the interface delamination and matrix direction failure accounted for by cohesive zone modeling. Numerical results were examined focusing on the effects of defects on the peak load reduction and the variation of delamination pattern. The stacking sequence effect was also investigated.
Numerical Simulation of High Velocity Impact of Circular Composite Laminates
Woo, Kyeongsik,Kim, In-Gul,Kim, Jong Heon,Cairns, Douglas S. The Korean Society for Aeronautical and Space Scie 2017 International Journal of Aeronautical and Space Sc Vol.18 No.2
In this study, the high-velocity impact penetration behavior of $[45/0/-45/90]_{ns}$ carbon/epoxy composite laminates was studied. The considered configuration includes a spherical steel ball impacting clamped circular laminates with various thicknesses and diameters. First, the impact experiment was performed to measure residual velocity and extent of damage. Next, the impact experiment was numerically simulated through finite element analysis using LS-dyna. Three-dimensional solid elements were used to model each ply of the laminates discretely, and progressive material failure was modeled using MAT162. The result indicated that the finite element simulation yielded residual velocities and damage modes well-matched with those obtained from the experiment. It was found that fiber damage was localized near the impactor penetration path, while matrix and delamination damage were much more spread out with the damage mode showing a dependency on the orientation angles and ply locations. The ballistic-limit velocities obtained by fitting the residual velocities increased almost linearly versus the laminate diameter, but the amount of increase was small, showing that the impact energy was absorbed mostly by the localized impact damage and that the influence of the laminate size was not significant at high-velocity impact.
접힌자국이 있는 멤브레인에서 두께에 따른 주름거동의 변화
우경식(Kyeongsik Woo) 한국항공우주학회 2010 韓國航空宇宙學會誌 Vol.38 No.5
본 논문에서는 코너에서 대각선방향으로 인장하중을 받고 있는 접힌자국이 있는 사각형 멤브레인에서 두께가 주름 거동에 미치는 영향을 기하학적 비선형 후좌굴 유한요소해석을 통하여 연구하였다. 멤브레인은 쉘 요소로 모델링 하였고 좌굴을 발생시키기 위하여 면외방향으로 미소의 무작위성 기하학적 결함을 메쉬에 가하였다. 해석은 접히지 않은 원 멤브레인과 수직방향으로 접힌 멤브레인에 대해 수행하였고 그 결과를 비교하였다. 해석 결과 멤브레인의 두께가 감소함에 따라 주름의 발생과 성장을 크게 촉진함을 알 수 있었다. 또한 접힌 자국의 초기 전개각이 증가할수록 국부주름의 낮은 하중에서 발생하였으나 전역주름으로의 성장은 지연되는 경향을 보였다. In this paper, the thickness effect on the wrinkle-crease interaction behavior of corner-loaded creased square membranes was studied using geometrically nonlinear post-buckling analysis. The membranes were modeled using shell elements, and the meshes were seeded with semi-random geometrical imperfection to instigate the buckling deformation. Results indicated that the wrinkle-crease interaction behavior was significantly dependent on the membrane thickness. Both the global and local wrinkles developed earlier as the thickness decreased. It was also found that the wrinkling behavior depended on the initial deployment angle in which the local wrinkle initiation occurred earlier, while the global wrinkle formation was delayed as the angle increased.