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고온환경하에서 지르코니아/니켈 소결재의 기계적 특성평가
김연직,Kim, Yeon-Jik 한국재료학회 1996 한국재료학회지 Vol.6 No.9
본 논문에서는 1673K에서 소결한 PSZ/Ni 복합재에 대한 종 탄성계수, 파괴강도, 파괴에너지 등의 기계적 특성을 평가하기 위해, 개량형 소형펀치시험을 행한 결과에 대해 논의한다. 또한 파면관찰과 AE법을 통해 이들 재료의 고온환경에서의 미시파괴과정도 조사하였다. 시험온도는 293K, 1073K, 1273K, 1473K의 4종류로 하였으며, PSZ/Ni 복합재료의 체적 조성비도 80/20, 60/40, 40/60, 20/80의 4종류이다. 이들 실험결과로부터, 1073K이상의 고온에서 Ni 함량이 60%인 PSZ/Ni 복합재가 파괴강도 및 파괴에너지가 가장 우수한 것을 알았다. 파면관찰에 의하면 이 재료의 조성비에서 파고거동이 취성으로부터 연성으로 천이하는 것을 확인할 수 있었다.
김연직,임재규 대한기계학회 1993 대한기계학회논문집 Vol.17 No.6
본 연구에서는 수적법(hand lay up : HLU)을 이용하여 단 섬유포(chopped strand mat : CSM)형태의 유리섬유를 불포화 폴리에스테르 수지에 강화시킨 복합 적층 판을 대상으로 해수중에서 굽힘·피로시험을 실시하여 피로균열 성장거동을 관찰하고 파면관찰을 통하여 GERP의 피로특성을 검토하였다. The fatigue behavior of GFRP composites is affected by environmental parameters. Therefore, we have to study on effect of sea water on fatigue behavior of GFRP composites as to maintain the safety and confidence in design of ocean structure of GFRP. In this paper, we investigated the fatigue properties of chopped strand glass mat/polyester composite in synthetic sea water. (pH 8.2) In case of the glass fiber (CSM type) reinforced polyester composite materials, the fatigue crack in the both dry and wet specimens tested in air or synthetic sea water occurred at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The transition point occurred during the crack propagation shifted to high ${\Delta}K$ value as load increase but its point is not changed regardless of immersion or test environment under a constant load. The synthetic sea water degrades the bond strength between fiber and matrix, thereby the tendency of rapid deceleration and acceleration of the crack growth was appeared.
E-Glass/Polyester 적층복합재료의 인장특성에 미치는 인공해수 및 변형율속도의 영향
김연직,임재규,Kim, Yeon-Jik,Im, Jae-Gyu 한국재료학회 1992 한국재료학회지 Vol.2 No.2
E-glass/Polyester 적층복합재료의 인공해수중에서의 인장특성을 알아보기 위해 PH를 각각 6.0, 8.2, 10.0으로 조절한 가운데 저 변형율 인장시험($1{\times}10^{-4}~1{\times}10^{-7}sec^{-1}$)을 행하였다. 대기와 인공해수중에서 인장하중을 받은 시험된 복합재료는 strain rate가 감소할수록 인장특성이 저하되며 $1{\times}10^{-7}sec^{-1}$의 strain rate에서 약간의 강성저하가 관찰되었다. 한편 인공해수중의 인장특성은 PH값에 따라 약간의 변화를 보였다. The slow strain-rate test($1{\times}10^{-4}~1{\times}10^{-7}sec^{-1}$) was performed to understand the tensile properties of chopped strand glass mat/polyester composite in air and synthetic sea water. (pH 6.0, 8.2, 10.0) For the tested composite subjected to tensile loading in air and synthetic sea water (ph 6.0, 8.2, 10.0), the tensile properties are a little decreased as strain rate decrease and a little decrease in stiffness is observed in $1{\times}10^{-7}sec^{-1}$. The tensile properties were some changed in case the pH value in synthetic sea water is varied.
SiC 휘스커 강화 Al<sub>2</sub>O<sub>3</sub> 복합재료의 고인화
김연직,송준희,Kim Yon Jig,Song Jun Hee 한국재료학회 2004 한국재료학회지 Vol.14 No.9
In this paper, the fracture toughness and mechanisms of failure in a random SiC-whisker/$Al_{2}O_3$ ceramic composite were investigated using in situ observations during mode I(opening) loading. $SiC_{w}/Al_{2}O_3$ composite was obtained by hot press sintering of $Al_{2}O_3$ powder and SiC whisker as the matrix and reinforcement, respectively. The whisker and powder were mixed using a turbo mill. The composite was produced at SiC whisker volume fraction of $0.3\%$. Compared with monolithic $Al_{2}O_3$, fracture toughness enhancement was observed in $SiC_{w}/Al_{2}O_3$ composite. This improved fracture toughness was attributed to SiC whisker bridging and crack deflection. $SiC_{w}/Al_{2}O_3$ composite exhibited typically brittle fracture behavior, but a fracture process zone was observed in this composite. This means that the load versus load-line displacement curve of $SiC_{w}/Al_{2}O_3$ composite from a fracture test may involve a small non-linear region near the peak load.
E-Glass/Polyester 복합재료의 피로균열성장거동에 미치는 흡습의 영향
김연직,권일현,임재규,정세희,Kim, Yon-Jig,Kweon, Il-Hyun,Lim, Jae-Kyoo,Jeong, Se-Hui 한국재료학회 1993 한국재료학회지 Vol.3 No.1
GFRP복합재료의 피로거동은 하중형식, 재질 및 섬유의 강화구조, 환경적인 인자들의 영향을 크게 받는것으로 알려져 있다. 본 연구에서는GFRP의 피로거동에 미치는 증류수 흡습의 영향을 알아보기 위해 chopped strand glass mat강화 불포화 polyester수지 복합재료의피로특성을 조사하였다. 피로균열은 건조재와 흡습재 모두 피로 cycle초기에 발생하며 그 후 균열성장이 점차 둔화되는 영역과 가속되는 영역으로 나뉘어졌다. 또한 증류수의 흡습은 섬유와 기지재 사이의 결합력을 저하시키며 그로 인해 균영성장방향에 수직인곳에서의 fiber pull-out 발생과 균열성장방향에 있는 섬유들에서의 debonding이 증가하여 피로강도가 저하하였다. This paper deals with the fatigue properties of chopped strand glass mat/polyester composite to understand the effect of water absorption on fatigue behavior of GFRP. The fatigue crack in the both no water and a water absorption materials initiated at the initial of cycle. Thereafter, it was divided with two regions that one decreased with the crack extension and the other increased with the crack extension. The absorption of distilled water degrades the bond strength between fiber and matrix, there, by the tendency of fiber pull-out is increased in perpendicular to crack growth deirection and the debonding of fibers increased to the place which is parallel to crack growth direction. Therefore, the reduction of fatigue strength was caused by these factors.
지르코니아 /NiCrAlY 계 플라즈마 용사피막의 고온 파괴거동에 관한 연구
김연직,임재규,Kim, Yeon-Jik,Im, Jae-Gyu 대한기계학회 1996 大韓機械學會論文集A Vol.20 No.10
This paper describes experimental results of modified small punch( MSP) test conducted to evaluate the fracure characteristics and mechanical properties of plasma sparayed zirconia ($ZrO_2$ stabilized with 8wt. % $Y_20_3$ : YSZ) NiCrAlY composite. The mixing ratios of YSZ/NiCrAlY were 0/100, 25/75, 50/50, 100/0 v.%. Test temperatures ranged from 293K to 1473K. This study is directed at development of thermal barrrier coating(TBC) system with superior heat resistance and mechanical properties. The microstructure and fracture process of the composite were examined by SEM and AE method. The mechanical properties of 100% YSZ were nearly independent of the temperatures tested in this study. In contrast, the NiCrAlY-containing composites showed a significant decrease of the mechanical properties above 1273K, showing a ductile- brittle transition behavior up to the temperature. Furthermore, it can seen that 25% YSZ/75% NiCrAlY composite gave the highest fracure strength and fracture energy among the mixing ratio tested over the temperature range.
김연직(Yonjig Kim) 대한기계학회 2008 大韓機械學會論文集A Vol.32 No.9
To understand the tensile behaviors of GFRP at low temperature, three types of specimen have been used in this study. Tensile properties and fracture mechanisms for three orthogonal orientations of plain weave glass fabric reinforced epoxy resin laminate were investigated at temperature range of about -30 to 15℃. The tensile properties of axial and edge type specimen decrease slightly with decreasing temperature to -20℃. However, at -30℃ the decreases in the tensile properties increased considerably. Below -20℃, thickness type specimen showed a marked decreases in the tensile properties. It was obvious that the fracture manner of thickness type specimen was adhesive failure at above -10℃ and a mixed adhesive and cohesive failure at below -20℃.