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류한선,김지훈,이명규,김돈건,이형림,정관수,윤재륜,강태진,Ryou Hansun,Kim Ji Hoon,Lee Myoung-Gyu,Kim Dongun,Lee Hyung Rim,Chung Kwangsoo,Youn Jae Ryoun,Kang Tae Jin The Korean Fiber Society 2005 한국섬유공학회지 Vol.42 No.5
In order to describe the mechanical behavior of highly anisotropic and asymmetric materials such as fiber reinforced composites, the elastic-plastic constitutive equations were used based on the recently developed yield criterion and hardening laws. As for the yield criterion, modified Drucker-Prager yield surface was used to represent the orthotropic and bi-modular (asymmetric) properties of composite materials, while the anisotropic evolution of back-stress was used to account for the hardening behavior. Experimental procedures to obtain the material parameters of the hardening laws and yield surface are presented for 3D braided glass fiber reinforced composites. For verification purposes, finite element simulation results based on the proposed constitutive laws have been compared with measurements for the three point bending tests.
UV-Nanoimprinted Photonic-Crystal Structure for Organic Light-Emitting Diodes
심종엽(Jongyoup Shim),전소희(Sohee Jeon),윤재륜(Jae-Ryoun Youn),강재욱(Jaewook Kang),김장주(Jang-Joo Kim),김세헌(Se-Heon Kim),정준호(Jun-ho Jeong),최대근(Dae-Geun Choi),김기돈(Ki-Don Kim),알리알툰(Ali Ozhan Altun),최준혁(Junhyuk Choi) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
A conventional OLED has only about 20 % light extraction efficiency. When a photonic crystal layer is put in between the anodic layer and the substrate, the light can be extracted to the air by the optical diffraction phenomena. In this article we form a photonic crystal layer (nano-patterned array) directly on the transparent substrate by the UV-nanoimprinting method with a polymer resin. By the FDTD simulation the enhancement of the light extraction is assessed. And the fabrication process details including UV-nanoimprint, SixNy interlayer and OLED layers are presented in this article. The experiment shows that with the imprinted photonic crystal structure the light extraction efficiency is increased by ~50% comparing with the conventional OLED and therefore this nanoimprinted photonic crystal OLED is a promising technology for the future OLED display and illuminator applications.
김성륜 ( Seong Yun Kim ),김형민 ( Hyung Min Kim ),이두진 ( Doo Jin Lee ),윤재륜 ( Jae Ryoun Youn ),이성희 ( Sung Hee Lee ) 한국복합재료학회 2012 Composites research Vol.25 No.4
필름 삽입 사출 시편의 휨은 비대칭적인 잔류응력 분포에 기인한다. 비대칭적 잔류응력과 온도 분포는 삽입된 필름 표면의 수직방향으로 지연되는 열 전달에 의해 발생한다. 사출 공정조건 최적화를 통해 필름 삽입 사출 시편의 휨을 억제할 수 없었기 때문에, 필름 삽입 사출 시편의 휨을 최소화하기 위해서 유리 섬유가 강화된 복합재료를 기판으로 사용하였다. 유리 단섬유의 분포를 마이크로 CT 장비를 이용하여 평가하였다. 복합재료로 구성된 기판을 이용한 필름 삽입 사출 시편의 배향 텐서와 휨을 계산하기 위해서는 적절한 마이크로 역학, 이방적 열팽창계수 및 닫힌 어림법 모델이 선택되어야만 한다. 여섯 종류의 마이크로 역학모델, 세 종류의 열 팽창 계수 모델 및 다섯 종류의 닫힌 어림법 모델을 고려한 후, Mori-Tanaka 모델, Rosen and Hashin 모델 및 third orthotropic 닫힌 어림법 모델을 선택하였다. 수치적으로 계산된 섬유 배향 텐서와 휨에 관한 결과들은 실험결과와 잘 일치하였고, 유리 섬유의 보강효과가 필름 삽입 사출 복합 재료 시편의 휨에 미치는 영향을 파악하였다. Warpage of the film insert molded (FIM) part is caused by an asymmetric residual stress distribution. Asymmetric residual stress and temperature distribution is generated by the retarded heat transfer in the perpendicular direction to the attached film surface. Since warpage was not prevented by controlling injection molding conditions, glass fiber (GF) filled composites were employed as substrates for film insert molding to minimize the warpage. Distribution of short GFs was evaluated by using micro-CT equipment. Proper models for micro mechanics, anisotropic thermal expansion coefficients, and closure approximation should be selected in order to calculate fiber orientation tensor and warpage of the FIM part with the composite substrate. After six kinds of micro mechanics models, three models of the thermal expansion coefficient and five models of the closure approximation had been considered, the Mori-Tanaka model, the Rosen and Hashin model, and the third orthotropic closure approximation were selected in this study. The numerically predicted results on fiber orientation tensor and warpage were in good agreement with experimental results and effects of GF reinforcement on warpage of the FIM composite specimen were identified by the numerical results.