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Rai, Alok Kumar,Gim, Jihyeon,Thi, Trang Vu,Ahn, Docheon,Cho, Sung June,Kim, Jaekook American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.21
<P>A facile and cost-effective urea-assisted autocombustion strategy has been designed for the fabrication of Co<SUB>3</SUB>O<SUB>4</SUB>/CoFe<SUB>2</SUB>O<SUB>4</SUB> nanocomposite and pure CoFe<SUB>2</SUB>O<SUB>4</SUB> anode materials followed by annealing at 700 and 900 °C for 6 h, respectively. To confirm the exact structure, Rietiveld analysis was performed on the Synchrotron XRD pattern of both the CoFe<SUB>2</SUB>O<SUB>4</SUB> samples annealed at 700 and 900 °C. The results clearly depicts the formation of two phases (Co<SUB>3</SUB>O<SUB>4</SUB>:CoFe<SUB>2</SUB>O<SUB>4</SUB>) with the ratio of [76.3(5):23.6(3)%] in the sample annealed at 700 °C sample, while single phase CoFe<SUB>2</SUB>O<SUB>4</SUB> formation was observed for the sample annealed at 900 °C. It has also been found that the designed nanocomposite sample is composed of small nanoparticles (50–100 nm), while the size of pure CoFe<SUB>2</SUB>O<SUB>4</SUB> particles is in the range from 600 nm to 1 μm. When applied as an anode material, the obtained Co<SUB>3</SUB>O<SUB>4</SUB>/CoFe<SUB>2</SUB>O<SUB>4</SUB> nanocomposite electrode exhibits high reversible capacity as well as excellent cycling stability and better rate capability in comparison to a pure CoFe<SUB>2</SUB>O<SUB>4</SUB> electrode. The enhanced electrochemical performance of the nanocomposite can be attributed to the intimate interconnection between Co<SUB>3</SUB>O<SUB>4</SUB> and CoFe<SUB>2</SUB>O<SUB>4</SUB>, along with the nanosize range of particles and high surface area, which not only favor fast kinetic properties facilitating electron transportation and Li<SUP>+</SUP> ion insertion/deinsertion but also relieve the stress caused by volume changes during the numerous charge/discharge cycles and suppress the degradation of the material.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-21/jp502004c/production/images/medium/jp-2014-02004c_0009.gif'></P>
Sang-Rai Cho,Teguh Muttaqie,Quang Thang Do,Sinho Kim,Seung Min Kim,Doo-Hwan Han 대한조선학회 2018 International Journal of Naval Architecture and Oc Vol.10 No.6
This paper reports on the experimental investigations on the failure modes of ring-stiffened cylinder models subjected to external hydrostatic pressure. Nine models were welded from general structural steel. The shells were initially formed by cold-rolling, and flat-bar ring frames were welded to the shell. The hydrostatic pressure tests were conducted by using water as the medium in pressure chambers. The details of the preparation and main test were briefly explained. The investigation identified the consequence of the structural failure modes, including: shell yielding, local shell buckling between ring stiffeners, overall buckling of the shell together with the stiffeners, and interactive buckling mode combining local and overall buckling. In addition, the ultimate strengths were predicted by using existing design codes. Non-linear numerical computations were also conducted by employing the actual imperfection coordinates. Finally, accuracy and reliability of the predictions of design formulae and numerical were substantiated with the test results.
충격 압력을 받는 판 구조의 영구 처짐에 대한 소성경화의 영향
Sang-Rai Cho,Min-Kyu Park,Won-Seok Heo,Woo-Ram Lim 대한조선학회 2012 대한조선학회 학술대회자료집 Vol.2012 No.5
Behavior of ships and offshore structures under impact loads is highly dependent on material properties. In this paper, mathematical representations of strain hardening are reviewed. The relationship between ultimate tensile strength and yield strength were examined and a formula was derived using mill test certificate data. Regarding this relationship, effects of strain hardening on behavior of plates under impulsive pressure loading is studied. Finally a simple formula was derived for prediction of damage extents in unstiffened plates under impulsive pressure loading using the results obtained from numerical calculations.
Experimental Investigations on the Plastic Damage of Plates due to Lateral Collisions
Cho, Sang-Rai,Kim, Il-Woong,Lee, Sang-Bock The Society of Naval Architects of Korea 2002 Journal of ship and ocean technology Vol.6 No.3
In this paper the results are reported of sixty-nine lateral collision tests, which were performed to investigate the collision resistance of plates. For the tests a collision testing machine of spring-roller conveyer type was designed and fabricated. Using this machine, various plates were tested with different masses and velocities and various headers of the striker. A simple analytical method has also been developed to predict the extent of damage of struck plates due to lateral collision. In the method, it is assumed that the kinetic energy of the striker can be dissipated by the formation of yield lines and membrane tensions in the impacted plate. The calculated predictions of extent of damage using the developed method have been substantiated with the test results, which shows reasonably acceptable correlations.
Cho, Sang-Rai,Le, Dinh Ngoc Can,Jeong, Jang-Hyun,Frieze, Paul A.,Shin, Hyun-Kyoung Pergamon Press 2017 Ocean engineering Vol.142 No.-
<P><B>Abstract</B></P> <P>Protection structures for FPSO (Floating Production Storage and Offloading) caissons should be sufficiently strong so as not to contact caisson pipes even when the protection structure is damaged by an impact by attendant vessels. In the present structural design process, non-linear commercial packages are employed for collision analyses. However, non-linear collision analyses using commercial packages are time-consuming and expensive to operate, especially in the initial design stage. In this study, substantiation of the adopted commercial package was first performed using collision test results on single pipes and H-shape pipes. Then, a rigorous parametric study was conducted by changing the design variables. A simple analytical expression was derived assuming that the kinetic energy of the striking vessel was dissipated by the plastic elongation of pipes and rotation of plastic hinges. Using the parametric study results, design equations to predict the maximum deflection and overall bending damage were obtained by which the effects of local denting and dynamic behaviour could be considered. Additionally, an equation to predict the extent of local denting damage was also derived. The developed procedure was numerically substantiated using the predicted extent of damage to an actual protection structure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Collision damage of FPSO caisson protection structures is developed in this study. </LI> <LI> Numerical analysis method was substantiated using the collision tests results. </LI> <LI> Simple design equations were derived using the parametric study results. </LI> <LI> Maximum deflection, maximum overall bending and local denting damage are predicted. </LI> <LI> A calculation example is also provided for the developed procedure. </LI> </UL> </P>
Cho, Sang-Rai,Muttaqie, Teguh,Do, Quang Thang,Kim, Sinho,Kim, Seung Min,Han, Doo-Hwan The Society of Naval Architects of Korea 2018 International Journal of Naval Architecture and Oc Vol.10 No.6
This paper reports on the experimental investigations on the failure modes of ring-stiffened cylinder models subjected to external hydrostatic pressure. Nine models were welded from general structural steel. The shells were initially formed by cold-rolling, and flat-bar ring frames were welded to the shell. The hydrostatic pressure tests were conducted by using water as the medium in pressure chambers. The details of the preparation and main test were briefly explained. The investigation identified the consequence of the structural failure modes, including: shell yielding, local shell buckling between ring stiffeners, overall buckling of the shell together with the stiffeners, and interactive buckling mode combining local and overall buckling. In addition, the ultimate strengths were predicted by using existing design codes. Non-linear numerical computations were also conducted by employing the actual imperfection coordinates. Finally, accuracy and reliability of the predictions of design formulae and numerical were substantiated with the test results.
충격 압력을 받는 판 구조의 영구 처짐에 대한 소성경화의 영향
Sang-Rai Cho,Min-Kyu Park,Won-Seok Heo,Woo-Ram Lim 한국해양환경·에너지학회 2012 한국해양환경공학회 학술대회논문집 Vol.2012 No.5
Behavior of ships and offshore structures under impact loads is highly dependent on material properties. In this paper, mathematical representations of strain hardening are reviewed. The relationship between ultimate tensile strength and yield strength were examined and a formula was derived using mill test certificate data. Regarding this relationship, effects of strain hardening on behavior of plates under impulsive pressure loading is studied. Finally a simple formula was derived for prediction of damage extents in unstiffened plates under impulsive pressure loading using the results obtained from numerical calculations.
Cho, Sang-Rai,Song, Ick-Cho The Society of Naval Architects of Korea 2003 Journal of ship and ocean technology Vol.7 No.1
Stiffened plates are among the most popular structural elements for marine structures like ships or offshore platforms. Many researchers have performed and reported the results of structural tests on stiffened plates in the open literature. However, the behaviour of stiffened plates in post-ultimate regime has not been fully reported. This paper reports the results of twenty-one axial compression tests including the initial imperfections and material properties of the test models. In aiming to investigate the post-ultimate behaviour of stiffened panels, the axial shortenings were increased up to far beyond the ultimate state. The results obtained from these tests can be utilized in substantiating design formulae in predicting the post-ultimate behaviour of stiffened plates.