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고선택성 폴리이미드 소재의 합성 및 분자동력학 연구를 통한 기체투과도의 비교
이정무,김득주,정문기,이명건,박치훈,남상용,Lee, Jung Moo,Kim, Deuk Ju,Jeong, Moon Ki,Lee, Myung Gun,Park, Chi Hoon,Nam, Sang Yong 한국막학회 2015 멤브레인 Vol.25 No.2
In this study, gas permeability of polyimide materials having a various amine group was measured and molecular dynamics was used to analyze the dynamic characteristics of the gas molecules in the polyimide by calculating the position and velocity of the gas molecules with change of the time. The gas permeability of polyimide membrane having substitution site which increase free volume in the polymer was increased. However, polyimide with rigid structure showed decreased gas permeability. As a result of analyzing the change in the gas permeation behavior using molecular dynamics simulations, we confirmed that the results show the same tendency with actual measurements of the gas permeability. 본 연구에서는 다양한 아민기를 가지는 폴리이미드 소재 및 분리막을 제조하여 그들의 구조의 변화에 따른 기체 투과도를 측정하였으며 동력학(Molecular dynamics; MD) 기술을 이용하여 해당 기체의 시간의 변화에 따른 위치와 속도를 계산하여, 기체분자의 동적 특성을 분석하는데 활용하였다. 투과도 측정결과 합성된 고분자 소재의 경우 고분자 내의 free volume을 증가시키는 치환기를 도입시켰을 경우 기체투과도가 증가되었으나 rigid한 구조가 도입된 폴리이미드는 투과도가 감소되는 경향을 확인하였다. 또한 분자동력학 시뮬레이션을 이용하여 기체투과거동 변화를 분석한 결과 실제 기체투과도 측정결과와 유사한 결과를 나타냄을 확인할 수 있었다.
이정무(Jeong-Moo Lee),송삼홍(Sam-Hong Song) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.4
This paper reviewed characteristics of fatigue crack behavior observed by changing various shapes of initial crack and magnitudes of loading in compact tension shear(CTS) specimen subjected to shear loading. In the high-loading condition, fatigue crack under shear loading propagated branching from the pre-crack tip. Meanwhile, the secondary fatigue crack in the low-loading condition which was created in the notch root due to friction on the pre-crack face grew to a main crack. Influenced by the mode II loading condition, fatigue crack propagation retardation appeared in the initial propagation region due to the reduction of crack driving force and friction on crack face. In both cases, however, fatigue cracks grew in tensile mode type. Propagation path of fatigue crack under the shear loading was 70 degree angle from the initial crack regardless of its shape and load magnitude.
이정무(Jeong-Moo Lee),송삼홍(Sam-Hong Song) 대한기계학회 2004 대한기계학회 춘추학술대회 Vol.2004 No.11
In this study, experiments were tried on the mixed-mode I+II single overloading model which changes the loading mode of overload and fatigue load. Aspects of deformation field in front of the crack which is formed by mixed-mode I+II single overloading were experimentally studied. Then the shape and size of mixed-mode plastic zone were approximately calculated. The propagation behavior of fatigue crack was examined under the test conditions combined by changing the loading mode. The behavior of fatigue cracks were greatly affected by shapes of plastic deformation field and applying mode of fatigue load. Accuracy of prediction and evaluation for fatigue life may be improved by considering all aspects of deformation and behavior of fatigue cracks.
유리섬유 보강 EP 소재의 피로거동에 미치는 Hole Notch의 영향
이정무(Jeong-Moo Lee),서기정(Ki-Jeong Seo),이은동(Eun-Dong Lee),김태진(Tae-Jin Kim),이언석(Eon-Seok Lee) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
This paper reports on an investigation into the effect of hole notches on the injection molded specimens. In order to evaluate the effects of stress concentration and interaction on fatigue behavior, holes were introduced as notch to simple specimen. The material was used in mPPO. Fatigue tests were conducted at 1-hole notch and 2-hole notch specimens. Also, the FEMFAT was used to predict the fatigue life of different hole notch type conditions. The increase of diameter and quantity of hole notch reduced the fatigue strength and fatigue life. As the distance and angle between two holes increase, the fatigue life of the specimen increases. The prediction of FEMFAT gives valid results by considering the various factors of fatigue effect.
모드 II 하중을 받는 CTS 시험편의 피로균열 전파거동에 관한 실험적 연구
송삼홍,이정무,Song, Sam-Hong,Lee, Jeong-Moo 대한기계학회 2003 大韓機械學會論文集A Vol.27 No.7
The purpose of this paper is to investigate fatigue crack behavior under shear(Mode II) loading. Various specimens and devices have been used in order to produce Mode II loading in fatigue experiments for shear crack propagation. But, there is not sufficient comparisons of experimental results between Mode II and others loading modes, because of characteristics of applied loads and specimens. So, compact tension shear(CTS) specimens were used in this paper to investigate the propagation behavior of Mode II by comparing the experimental results between loading modes. We firstly observed the characteristics which was showed in Mode II experiment using CTS specimens. The experimental results under Mode II loading were compared with fatigue crack behavior under Mode I and Mixed-mode I+II loading. The characteristics for initiation and propagation behavior under Mode II loading was investigated by such comparisons.
송삼홍,최지훈,이정무,Song, Sam-Hong,Choi, Ji-Hoon,Lee, Jeong-Moo 대한기계학회 2002 大韓機械學會論文集A Vol.26 No.11
Most cracks in the structure occur under mixed mode loading and those fatigue crack propagation behavior heavily depends on the stress ratio. So, it is necessary to study the fatigue behavior under mixed mode loading as the stress ratio changes. In this paper, the fatigue crack propagation behavior was respectively investigated at stress ratio 0.1, 0.3, 0.5, 0.7 and we changed the loading application angle into 0$^{\circ}$, 30$^{\circ}$, 60$^{\circ}$ to apply various loading mode. The mode I and II stress intensity factor of CTS specimen used in this study was calculated by the displacement extrapolation method using FEM (ABAQUS). Using both the experiment and FEM analysis, we have concluded the relationship between crack propagation rate and stress intensity factor range at each loading mode due to the variation of stress ratio. Also, when the crack propagated under given stress ratio and loading mode condition, we have concluded the dominant factors of the crack propagation rate at each case.