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The Aging Effect of $Avimid^(R)$ K3B/1M7 Laminates in $80^{\circ}C$ Water
김형원,Kim Hyung-Won 한국추진공학회 2005 한국추진공학회지 Vol.9 No.4
미세균열이 생기기 전 $80^{\circ}C$ 물속에서 침수시간에 따른 $Avimid^(R)$ K3B/IM7 복합재의 습기노화 현상에 관하여 연구하였다. $80^{\circ}C$ 물속에서 복합재의 파괴인성을 저하시키는 요인으로는 수지 파괴인성의 저하나 잔류응력의 변화 그리고 섬유와 수지 사이의 계면 손상이다. $80^{\circ}C$ 물속에서 수지에 습기가 포화되는 시간은 500 시간이며 K3B/IM7복합재에 습기가 포화되는 시간은 100 시간이다. 수지가 500 시간 가속노화한 후 DSC 시험을 한 결과 $T_g$는 1% 이내 증가하였으며, 무게는 $7\times10^{-6}m/s^2$ 확산속도로 1.55% 증가하였다. K3B/IM7복합재에 관하여 물속에서 100시간 지난 후 무게는 $1\times10^{-6}m/s^2$ 확산속도로 0.41% 증가했다. 500 시간 노화한 후 수지의 파괴인성은 41% 저하하였으며 100 시간 노화한 후 ${[+45/0/-45/90]}_s$ K3B/IM7 복합재의 미세균열 파괴인성은 43.8% 감소하였다. 그러므로 $80^{\circ}C$ 수분노화 시험에서 복합재 적층의 파괴인성을 감소시키는 주요 원인은 수지 파괴인성의 저하라고 할 수 있다. The Hygrothermal aging of the laminates of $Avimid^(R)$ K3B/IM7 in $80^{\circ}C$ water was studied as a function of immersion time prior to forming microcracks. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, the change in residual stresses or the interfacial damage between the fiber and the matrix. The times to saturation in $80^{\circ}C$ water for the laminates and for the neat resin were 100 hours and 500 hours. After 500 hours aging of the neat resin, the glass transition temperature was changed less than 1% by DSC test, and the weight gain was 1.55% increase with the diffusion coefficient $7\times10^{-6}m/s^2$ and the fracture toughness was decreased about 41%. After 100 hours fully saturated aging of the ${[+45/0/-45/90]}_s$ K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was 0.41% increase with the diffusion coefficient $1\times10^{-6}m/s^2$. In 100 hours, the loss of the fracture toughness of the laminates was 43.8% of the original toughness by the microcracking fracture toughness criterion. Therefore, the main factor to degrade the microcracking toughness of the laminates could be the degradation of the matrix fracture toughness.
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The effects of matrix aging and residual stress changes on $Avimid^{(R)}$ K3B/IM7 laminates
김형원,Kim, Hyung-Won The Korea Institute of Military Science and Techno 2005 한국군사과학기술학회지 Vol.8 No.3
In this paper, the effects of matrix hygrothermal aging and residual stress changes on $Avimid^{(R)}$ K3B/IM7 laminates in $80^{\circ}C$ water were studied. The factors causing the $80^{\circ}C$ water to degradation of the laminates could be the degradation of the matrix toughness, the change in residual stresses. After 500 hours fully saturated aging of the neat resin, the weight gain was 1.55% increase with the diffusion coefficient $7{\times}10^{-6}m^2/s$ and the fracture toughness was decreased about 41%. After 100 hours fully saturated aging of the $[+45/0/-45/90]_s$ K3B/IM7 laminates in $80^{\circ}C$ water, the weight gain was 0.41% increase with the diffusion coefficient $1{\times}10^{-6}m^2/s$ and the loss of the microcracking fracture toughness was 43.8% of the original toughness. To see whether the residual stress influenced the fracture toughness, two ply $[90^{\circ}/0^{\circ}]$ laminates were put in $80^{\circ}C$ water from 2 hours to 8 hours. The changes in residual stress in 8 hours are less than 3MPa. Because the 3MPa change is not sufficient to degrade the laminates, the main factor to degrade the microcracking fracture toughness was the degradation of the matrix fracture toughness.
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김형원 ( Kim Hyung Won ),고호경 ( Ko Ho Kyoung ) 한국수학교육학회 2021 수학교육 Vol.60 No.2
본 연구는 다문화 학생들의 수학학업성취도 변화의 양상을 파악하고 예측하기 위하여 성장혼합모형의 잠재성장모형분석을 하였다. 연구 결과는 다수의 다문화 학생들이 학년이 높아갈수록 성취도가 하향하고 있음과 성취도의 변화가 부모의 소득수준이나 교육수준과 연관이 없는 것으로 분석되었으며, 특히 여학생이 남학생보다 초기 성취도가 낮고 시간이 지남에 따라 급격히 감소할 가능성이 높은 것으로 나타났다. 이러한 결과는 공교육적 차원에서의 다문화 학생지원을 강화할 필요성을 보여주고 있다. Recently, the number of multicultural families has significantly increased in Korea, and this trend creates a need to understand how successfully students from multicultural families achieve their mathematics learning. To understand and predict the changes in mathematics learning achievement of these students over time, we conducted in this study a latent growth mixture model analysis. The study findings show that the majority (92%) of the students from multicultural families experience a decrease in their mathematics achievement over time as their grade level goes up. It was found, in particular, that female students are likely to have lower initial achievements and rapid decline over time more than male students and that the decline over time was more severe for female students than their male counterparts. The findings of this study convey several implications on the how to support the students from multicultural families. First, the result of this study was different from the outcomes of previous studies that presented the income of the household and the education level of the students’ parents as major factors that determine the academic achievement of the students from multicultural families. Furthermore, the study indicates the need for more research to identify variables related to the mathematical achievements of the students from multicultural families and the need to use these research findings to develop public support plans for the students from multicultural families.
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김형원(Hyung-Won Kim),오종윤(Jong_Yun Oh) 한국추진공학회 2009 한국추진공학회 학술대회논문집 Vol.2009 No.5
A design of a subscale solid propellant rocket motor was conducted to do the similitude experiments for the large scale rocket motor. One of the main factor to subscale was the mach number of the solid propellant flume through a nozzle exit The analysis of the flume flow was done to obtain the mach number for the large and subscale rocket motor. The flume shapes on the non dimensional axises by the nozzle exit diameter was matched each other. The propellant grain of a subscale solid rocket motor was designed by the profile of pressure vs time obtained by the mach number of the flume shape. Some analyses of the theoretical solution were compared with the results of the ground static test.
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B 형 간염백신의 면역성에 관한 3 년간 추적 관찰 - 소아와 성인의 면역성을 중심으로 -
김형원(Hyung Won Kim),김현수(Hyun Soo Kim),양동온(Dong On Yang),김세종(Sei Jong Kim) 대한내과학회 1990 대한내과학회지 Vol.39 No.2
N/A This study was performed to assess the effects of HB vaccination and the time of secondary boosting in adults and children. Anti-HBs persistence and boosting responses of plasma derived HB vaccine were estimated for a consecutive three years-follow-up in 12 adults (over 16 years old) and 16 children (under 15 years old) who were negative for five HBV markers with normal transaminase levels hefore immunization, The vaccinations were done at O, lst, and the 6th month for anti-HBs negative persons. The serum transaminases were checked with enzyme kinetic method, The HBs Ag and anti-HBs were checked with EIA technique (mIU/ml) quantitatively at the 1st, 3rd, 6th, 9th, 12th, 24th, and 36th month after primary immunization. The positivities of anti-HBs (over 10 mIU/ml) were 149 at 1st month, 43% at 3rd month, 71%. at 6th month, 93% at 9th month, 93%at 12th month and 79% at 24th month, respectively, The serum levels of anti-HBs showed a progressively decreasing tendency over the course of time. All six anti-HBs negative cases at the 24th month were adults. After secondary boosting immunization for these six cases at the 24th month, the positivities of anti-HBs were remarkably increased to 9395 at the 36th month. In the adult group, The positivities of serum anti-HBs were 17% at the 1st month, 33% at the 3rd month, 50% at the 6th month, 83% at the 9th month, 83% at the 12th month and 50% at the 24th month. After secondary boosting immunization for six cases, the positivity of anti-HBs was 83% (5/6), and the overall positivity of anti-HBs was 92% at the 36th month. In the children group, the positivities of anti-HBs were 1396 at the 1st month, 50% at the 3rd month, 88% at the 6th month, 10% at the 9th month, 100% at the 12th month, 100% at the 24th month and 94% at the 36th month, respectively. The serum anti-HBs was negative only in one case at the 36th month.
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