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윤재륜,Seung Hwan Lee,Sheong Hyun Choi,최진일,Jae Rock Lee 한국화학공학회 2010 Korean Journal of Chemical Engineering Vol.27 No.2
Poly(amide-co-imide) (PAI)/multi-walled carbon nanotube (MWCNTs) composites were prepared by using solution mixing with ultrasonication excitation in order to investigate effects of MWCNTs on rheological properties and thermal curing behavior. Steady shear viscosity of the composite showed bell shaped curves with three characteristic patterns: shear thickening, shear thinning, and Newtonian plateau behavior. Both storage modulus and complex viscosity were increased due to higher molecular interaction than that of the pure PAI resin. Especially, hydrogen peroxide treated MWCNT/PAI composites had the highest storage modulus and complex viscosity. Glass transition temperature of the PAI/MWCNT composite was increased with increasing MWCNT content and thermal curing time since the mobility of PAI molecules was reduced as more constraints were generated in PAI molecular chains. It was found that thermal curing conditions of PAI/MWCNT composites are determined by considering effects of weight fraction and surface modification of MWCNTs on internal structure and thermal properties.
사출성형의 충전시 고분자용융액의 압축성이 유동장과 단섬유 배향에 미치는 영향
이상찬,고진,윤재륜,Lee, S.C.,Ko, J,Youn, J.R. 한국유변학회 1998 Korea-Australia rheology journal Vol.10 No.4
단섬유 강화 고분자의 사출성형시 고분자 수지의 유동에 의하여 섬유배향이 필연적으로 일어나며, 섬유배향에 의한 이방성 (anisotropy)은 최종성형물의 품질과 기계적인 특성 등에 많은 영향을 미친다. 사출공정 중에서 충전과정(filling stage)은 섬유배향에 지배적인 역할을 하므로, 충전과정의 유동장을 정확하게 해석하는 것은 매우 중요하다. 형상이 복잡한 캐비티(cavity)와 다중 캐비티에서는 먼저 충전이 완료되어 현탁액(suspension)이 압축을 받고 있는 영역들이 존재하게 된다. 기존의 방법처럼 사출성형의 충전과정을 비압축성 유동으로 가정하면 정확한 유동장을 계산할 수 없다. 본 연구에서는 충전과정에서 압축성을 고려한 혼합 유한요소법/유한차분법을 이용하여 유동장을 계산하였다. 충전이 완료되는 순간에서, 이차배향텐서에 대한 배향변화방정식을 4차 Runge-Kutta 방법을 이용하여 해석함으로써 3차원 섬유배향장을 예측하였다. 충전시간이 다른 4개의 캐비티를 갖는 금형을 제작하여 충전과정에서 압축성 효과를 고려한 수치해석 결과가 실험과 잘 일치함을 보였다. 또한, 압축성과 비압축성 유동장에서 이론적으로 계산된 섬유배향의 차이를 정성적 및 정량적으로 비교하였다. The anisotropy caused by the fiber orientation, which is inevitably generated by the flow during injection molding of short fiber reinforced polymers, greatly influences dimensional accuracy, mechanical properties, and other quality of the final product. Since the filling stage of the injection molding process plays a vital role in determining fiber orientation, an accurate analysis of flow field for the filling stage is needed. Unbalanced filling occurs when a complex or a multi-cavity mold is used leading to development of regions where the fiber suspension is under compression. It is impossible to make an accurate calculation of the flow field during filling with the analysis assuming incompressible fluid. A mold with four cavities with different filling times was produced to compare the numerical analysis results with the experimental data. There was a good agreement between the experimental and theoretical results when the compressibility of the polymer melt was considered for the numerical simulation. The fiber orientation states for compressible and incompressible fluids were also compared qualitatively as well as quantitatively in this study.
박근,이상찬,정준호,양동열,윤재륜,Park, K.,Lee, S.C.,Jung, J.H.,Yang, D.Y.,Yoon, J.R. 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.5
Rapid prototyping is a new prototyping technology which produces three dimensional part models directrly from CAD data and has been extensively applied to various manufacturing processes. There are many types of rapid prototyping systems due to their building principles and materials. In this work, Stereolithography Appaaratus(SLA) which is the most widely-used rapid prototyping system is introduced to achieve die/mold technology innovation. For the purpose, the prototyping technology using SLA is developed such that patterns of which shapes are quite complicated are successfully produced with high accuracy. Using these patterns, prototype die/molds are efficientrly manufactured; a turbocharger rotor, a fan and a wheel patterns, prototype die/molds are efficienterly manufactured ; a turbochager rotor, a fan and a wheel pattern are made, and the molds of the investment casting, the injection molding and the die casting are manufactured respectively. The casting products are produced using these molds and it turns out that these methods are quitre effective for manufacturing products of complicated geometry from the viewpoint of efficiency and productivity.
이두진,김명욱,김성륜,Seung Hwan Lee,윤재륜 한국유변학회 2010 Korea-Australia rheology journal Vol.22 No.2
Fiber orientation and micromechanics should be understood for exact prediction of physical properties and deformation of anisotropic composite parts which are generally treated as homogeneous materials for flow simulation and transversely isotropic materials for structural analyses. Fiber orientation has a significant effect on the mechanical properties and final shape of injection-molded parts. Fiber orientations in glass fiber (GF) reinforced PBT composites were observed by using a microtomography (Micro-CT) and the three dimensional CT results agreed with the prediction. Mechanical properties of the anisotropic composites were estimated by coupled three dimensional flow and structural analyses in which the micromechanics and the fiber orientation were considered spontaneously. In order to verify the coupled FE simulation results a theoretical model and a simple Representative Volume Element (RVE) model were employed. The coupled 3D analyses were in good agreement with the experimental data and the simple RVE model predicted higher stiffness than the experiments but lower stiffness than theoretical upper bound.