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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.
VARTM 법으로 제작한 탄소-유리/에폭시 하이브리드 적층재의 인장 특성
김연직 ( Yon Jig Kim ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.10
This paper presents a study of the tensile behavior of carbon and glass fiber reinforced epoxy hybrid laminates manufactured by vacuum assisted resin transfer molding (VARTM). The objective of this study was to develop and characterize carbon fiber reinforced plastic hybrid composite material that is low cost and light-weight and that possesses adequate strength and stiffness. The effect of position and content of the glass fabric layer on the tensile properties of the hybrid laminates was examined. The strength and stiffness of the hybrid laminates showed a steady decrease with an increase of the glass fabric content this decrease was almost linear. Fracture strain of these laminates showed a slight increasing trend when glass fabric content was increased up to 3 layers, but at a glass fabric content > 3 layers the strain was almost constant. When glass fabric layers were at both outer surfaces, the hybrid laminate exhibited a slightly higher tensile strength and elastic modulus due to the small amount of glass yarn pull-out.
Mechanical properties of biodegradable coconut fibre reinforced polylactic acid composite
Kim Yon Jig(김연직),Phan Quoc Thai(판꾹타이),Renliang Wang(왕렌리앙),Jun Yong Choi(최준용),Ruihua Hu(후루이화),Jae Kyoo Lim(임재규) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
In the recent years, the use of natural fiber as reinforcements in polymer composites for replacing synthetic fiber is rapidly increased. Coconut is growing in some tropical countries such as Vietnam, Thailand, India... especially, it is very cheap and infinite resource. Polylactic acid (PLA) is a biodegradable thermoplastic polymer, which was used extensively in recent years because the biodegradable composites are friendly with environment. This study is concerned with the mechanical properties of coconut fiber (coir) reinforced PLA composite. The coconut fiber reinforced PLA composite was manufactured by heating compression mold with different contents of coconut fiber. The tensile test and bending test will be carried out to verify the mechanical properties of composite and the effect of coconut contents to them.
CAE 해석을 이용한 FRP시험편의 사출금형설계에 대한 최적화 연구
김종우(Jong Woo Kim),정도연(Do Yeon Jung),김진호(Jin Ho Kim),김철인(Chul In Kim),최태종(Tae Jong Choi),김연직(Yon Jig Kim),임재규(Jae Kyoo Lim) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
In this paper, CAE analysis and manufacturing of plastic injection molding using fiber reinforced plastics(FRP) were performed for tensile test specimen. ASTM for plastic tensile specimen was applied to design and prevent an injection mold from external impact damage. Injection molding experiments with variations of injection speed, temperature, pressure and weld line were performed and then carbon fiber reinforced polycarbonate specimens was also performed. as a result, how to optimize mold design and connect systematically all of processes from mold design to manufacturing through the efficient use of CAE analysis in development process.
유리-현무암/에폭시 층간 하이브리드 복합재료의 인장특성
김지훈 ( Ji Hoon Kim ),김연직 ( Yon Jig Kim ) 대한금속재료학회(구 대한금속학회) 2014 대한금속·재료학회지 Vol.52 No.1
This study investigates the tensile properties of a glass-basalt/epoxy interply hybrid composite. The objective of this work is to develop an environmentally friendly hybrid composite material that has good strength and stiffness. These composites were fabricated through a vacuum-assisted resin transfer molding process. The glass/epoxy and basalt/epoxy composite were also prepared to compare the properties. The tensile strength of the hybrid composite improved as the basalt fiber content increased. However, we did not find a variation in the elastic modulus defined as the initial slope of the stress-strain curve for the hybrid composite under tensile loading. When the basalt fiber content of the total reinforcement became 40%, the fracture strain of the hybrid composite was higher than that of the glass/epoxy composite. From the test result, we knew that there is almost no difference between the tensile properties of the hybrid composites with different stacking sequences.
탄소-유리/에폭시 하이브리드 복합재의 저온 인장 특성에 미치는 수분의 영향
정하나 ( Ha Na Jung ),김연직 ( Yon Jig Kim ) 대한금속재료학회(구 대한금속학회) 2012 대한금속·재료학회지 Vol.50 No.10
This study investigated the effect of water absorption on the tensile properties of carbon-glass/ epoxy hybrid composites at room temperature and -30℃. To investigate the effect of the position of glass fabric in the hybrid composite on the tensile properties, the stacking pattern of the fiber fabrics for reinforcing was created in three different ways: (a) glass fabrics sandwiched between carbon fabrics, (b) carbon fabrics sandwiched between glass fabrics and (c) alternative layers of carbon and glass fabrics. They were manufactured by a vacuum-assisted resin transfer molding (VARTM) process. The results showed that there was surprisingly little difference in tensile strength at the two different temperatures with dry and wet conditions. However, the water absorption into the hybrid system affected the tensile properties of the hybrid composites at RT and -30℃. When the glass fabrics were at the outermost layers, the hybrid composite had the lowest tensile properties. This is attributed to the fact that the composite had a relatively high water absorption rate.
문상돈(Mun Sang Don),김연직(Kim Yon-jig),임익태(Im Ik-Tae),박찬우(Park Chan Woo) 한국생산제조학회 2008 한국생산제조시스템학회 학술발표대회 논문집 Vol.2008 No.5
As a technology to machine the 3-dimensional shapes of general metal material more flexibly, machining technologies such as metal cutting, grinding, etc have been steadily improved in their accuracy as well. However, the working method using machining technologies are restricted in terms of surface roughness, metal working accuracy and working hours, if a workpiece has an irregular 3-dimensional shape. Magnetic abrasive finishing process is also one of the super-precision machining technologies which proceed with the finishing metal working of precision working piece using the action of magnetic field and the mixed type magnetic abrasive. However, such studies only focus on the improvement of machining accuracy but are still incomplete in investigating the roundness. This study aims to realize the high accuracy finishing machining focusing on the roundness after magnetic abrasive finishing process of circular workpiece and the surface roughness of precision machining surface.