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하성록(Sung Rok Ha),정협재(Hyup Jae Chung),이경엽(Kyong Yop Rhee) Korean Society for Precision Engineering 2006 한국정밀공학회지 Vol.23 No.11
It is well-known that the mechanical properties of MMT (montmorillonite) nanocomposites are better than those of conventional composites. In this study, tensile tests were performed to determine the effect of silane modification of MMT and its weight ratio on the tensile properties of MMT/epoxy nanocomposites. It was found that the tensile strength and the elastic modulus of MMT/epoxy nanocomposites increased with increasing weight ratio of MMT. The elastic modulus of silane-modified MMT/epoxy nanocomposites was higher than that of untreated MMT/epoxy nanocomposites, irrespective of weight ratio.
정수압 조건에서 변형률 변화가 섬유강화 복합재의 층간분리인성에 미치는 영향에 대한 연구
하성록(Sung Rok Ha),이경엽(Kyong Yop Rhee),김현주(Hyeon Ju Kim),정동호(Dong Ho Jung) Korean Society for Precision Engineering 2005 한국정밀공학회지 Vol.22 No.11
It is generally accepted that fracture toughness of fiber-reinforced polymer composites is affected by strain rate in an atmospheric pressure condition. For a present study, the strain rate effect on the fracture toughness of fiber-reinforced laminated composites in the hydrostatic pressure condition was investigated. For this purpose, fracture tests have been conducted using graphite/epoxy laminated composites applying three steps of the strain rate at 270 MPa hydrostatic pressure condition. The strain rates applied were 0.05 %/sec, 0.25 %/sec, and 0.55 %/sec. Fracture toughness was determined from the work factor approach as a function of applied strain rate. The result showed that fracture toughness decreased as the strain rate increased. Specifically, the fracture toughness decreased 12% as the strain rate increased from 0.05 %/sec to 0.55 %/sec.
하성록(Sung Rok Ha),조기대(Ki Dae Cho),강광희(Kwang Hee Kang),양성철(Sung Chul Yang),허기영(Gi Young Hur) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
A naval radar system mounted in ships is exposed to a variety of natural and man-made environments during its operational life. All of all of these events need to be considered in the design of the radar. Specially, a shock wave initiated by detonation of explosive device has a bad influence on life expectancy. Therefore the radar is required to survive in the shock and return to an operational state after the shock has occurred. In this paper, the shock response is analyzed by the dynamic design analysis method (DDAM) and design margin of the radar is evaluated from the results of DDAM.
해수흡수된 두께가 두꺼운 카본/에폭시 복합재의 정수압 증가에 따른 파괴인성에 대한 실험적 연구
하성록(Ha, Sung-Rok),이경엽(Rhee, Kyong-Yop) 한국해안해양공학회 2006 한국해안해양공학회 논문집 Vol.18 No.1
해저환경에서 PMC(고분자기지 복합재)는 금속재 구조물에 비해 부식성이 우수한 것으로 알려져 있다. 해저환경에서 고분자기지 복합재의 파괴특성에 대한 이해는 증가하는 해저구조물 제조에 반드시 필요하다. 본 연구에서, 파괴시험은 해수흡수 된 카본/에폭시 복합재에 대해 정수압을 네단계(0.1 MPa, 100 MPa, 200 MPa and 270 MPa)로 증가시켜 수행하였다. 파괴인성은 정수압에서의 일인자방법을 적용하였다. 파괴거동은 모든 정수압에서 선형적이었고 파괴인성은 정수압이 증가할수록 증가하였다. It is well-known that the corrosive behavior of PMC (polymer matrix composite) structure is much better than the metal structure in the marine environment. The understanding of fracture behavior of PMC in the deep-sea environment is essential to expand its use in the marine industry. For a present study, fracture tests have been performed under low different pressure levels such as 0.1 MPa, 100 MPa, 200 MPa, and 270 MPa using the seawater-absorbed carbon/epoxy composite samples. Fracture toughness was determined from the work factor approach as a function of hydrostatic pressure. It was found that fracture behavior was a linear elastic far all pressure levels. The fracture toughness increased with increasing pressure.
Study on the Compressive Properties of Sandwich Composite Structure for Launching Bridges
하성록(Sung Rok Ha),이대희(Dae Hee Lee),배재만(Jae Man Bae) Korean Society for Precision Engineering 2017 한국정밀공학회지 Vol.34 No.11
It is generally accepted that mechanical properties of sandwich composite are affected by curing pressure variation. For the present study, the effects of curing pressure variation on the compressive properties of balsa wood sandwich composite were investigated. For this purpose, a compressive test was conducted using balsa wood and honeycomb core sandwich composite, applying 40 psi and 60 psi curing pressure conditions. The results showed that compressive load of balsa wood sandwich composite applying 60 psi curing pressure condition is higher than applying a 40-psi curing condition. This phenomenon is due to an increase in the adhesive strength of the balsa wood sandwich composite as the curing pressure increases, thereby improving the compressive strength. Deboning and local buckling were observed on fracture surfaces of all balsa wood sandwich composite, but only global buckling was observed at honeycomb core sandwich composite.
CFRP/Al 하니콤 샌드위치 복합재 T-Joint 구조물의 기계적 물성에 대한 실험적 연구
조기대(Ki Dae Cho),하성록(Sung Rok Ha),강광희(Kwang Hee Kang),김지억(Jie Eok Kim),양성철(Sung Chul Yang) Korean Society for Precision Engineering 2012 한국정밀공학회지 Vol.29 No.3
Application of composite structures on naval ships strongly depends on the mechanical strength and collapse behavior of the T-joints of the whole structure. Because of the weight advantages over single skin composite and bolt fastening joining, three types of T-joints using both honeycomb sandwich composite and adhesive bonding were suggested to determine the effect of T-joint configuration. It was found that joining with a urethane foam block and overlaminates using the secondary co-bonding technique improves T-joint strength.
하성록,이경엽 한국공작기계학회 2008 한국공작기계학회 추계학술대회논문집 Vol.2008 No.-
Clay/epoxy nanocomposites were prepared using clay containing 6 wt%.. Tensile tests were performed using pure epoxy, and clay/epoxy nanocomposites at -30℃, 25℃(room temperature), 40℃, and 70℃(above the glass transition temperature). Tensile strength and elastic modulus at -30℃ were higher than those at room temperature for all cases. However, tensile properties were decreased with the increase of temperature. In particular, at 70℃, tensile properties were lower than 10% of their original values at room temperature, independent of adding of the clay. The reason why tensile properties of clay/epoxy nanocomposites were increased at -30℃ was attributed to the reinforcing effect by adding of clay in the epoxy. However, at 70℃, which is above glass transition temperature of epoxy used in this study, epoxy was softened and had characteristics of rubber. The weakening effect of epoxy was greater than the reinforcing effect by clay.