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응집영역 모델링 기법을 사용한 노치가 있는 적층복합재료의 파괴해석
우경식 ( Kyeongsik Woo ),더글라스케언스 ( Douglas S. Cairns ) 한국복합재료학회 2017 Composites research Vol.30 No.2
본 논문에서는 응집영역 모델링 기법을 사용하여 노치가 있는 적층복합재료의 파괴거동을 연구하였다. 먼저 노치가 있는 적층복합재료 시편형상에 대해 일반 3차원 고체요소로 모델링 한 후 요소들 사이에 섬유파괴, 기지파괴 및 층간분리 파괴를 담당하는 응집요소를 삽입하여 유한요소 메쉬를 제작하였다. 다음으로 일축인장 시험을 모사하는 하중 및 경계조건을 가하여 점진적 파괴해석을 수행하고 해석결과를 참고문헌의 실험결과와 비교하여 해석의 타당성을 검증하였다. 수치해석 결과로부터 노치가 있는 적층복합재료 인장시편의 파괴시작 및 진전거동을 분석하였으며 파괴모드의 진전을 체계적으로 조사하였다. In this paper, fracture behavior of laminated composites with notch was studied by cohesive zone modeling approach. The numerical modeling proceeded by first generating 3 dimensional solid element meshes for notched laminated composite coupon configurations. Then cohesive elements representing failure modes of fiber fracture, matrix cracking and delamination were inserted between bulk elements in all regions where the corresponding failures were likely to occur. Next, progressive failure analyses were performed simulating uniaxial tensile tests. The numerical results were compared to those by experiment available in the literature for verification of the analysis approach. Finally, notched laminated composite configurations with selected stacking sequences were analyzed and the failure behavior was carefully examined focusing on the failure initiation and progression and the dominating failure modes.
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Failure behavior of inclined thick adhesive joints with manufacturing defect
Tsinuel Nurilligne Geleta,우경식,Douglas S. Cairns,Daniel Samborsky 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.5
In this paper, numerical model of thick adhesive inclined joints has been prepared and validated against experimental test to study the effect of manufacturing defect on the joint strength. The inclined joint was made up of two laminate webs attached to a wedge by a layer of adhesive. Tensile tests were conducted on many thick adhesive joint specimens with two different geometries. One half of the symmetric test specimen was then modeled using finite element analysis in which cohesive zone modeling (CZM) was used to simulate the initiation and propagation of joint fracture. The progressive fracture through the adhesive layer and along adhesive-laminate interface was carefully examined. Based on inspection of the experimental test specimen, potential manufacturing defect types and locations were incorporated in the finite element model. The reduction in strength due to these manufacturing defects was used to predict the most critical flaw type in thick inclined joints. The differences between the “flawless” numerical model and the experimental test specimen was explained when these manufacturing defects were incorporated. The results were found to be consistent with the experimental tests.
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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.
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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.
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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.
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