• Proceedings of the KSME Conference
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• 2001.06a
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• pp.26-36
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• 2001

Smart sensors and actuators have recently been developed. In this study, first, small-diameter fiber Bragg grating (FBG) sensors developed by the author, whose cladding and polyimide coating diameters were 40 and $52{\mu}m$, respectively, were embedded inside a laminate without resin-rich regions around sensors and the deterioration of mechanical properties of the composite laminate. The small-diameter FBG sensor was embedded in $0^{\circ}$ ply of a CFRP laminate for the detection of transverse cracks in $90^{\circ}$ ply of the laminate. The reflection spectra from the FBG sensor were measured at various tensile stresses. The spectrum became broad and had some peaks with an increase of the transverse crack density. Furthermore, the theoretical calculation reproduced the change in the spectrum very well. These results show that the small-diameter FBG sensors have a potential to detect the occurrence of transverse cracks through the change in the form of the spectrum, and to evaluate the transverse crack density quantitatively by the spectrum width. On the other hand, shape memory alloy (SMA) films were used to suppress the initiation and growth of transverse cracks in CFRP laminates. Pre-strained SMA films were embedded between laminas in CFRP laminates and then heated to introduce the recovery stress in SMA films and compressive stresses in the weakest plies ($90^{\circ}$ ply). The effects of recovery stresses are demonstrated in the experiments and well predicted using the shear-lag analysis and the nonlinear constitutive equation of SMA films.

• Journal of Korean Society of Environmental Engineers
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• v.33 no.1
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• pp.47-53
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• 2011

$SF_6$ (Sulfur hexafluoride) possesses high GWP (Global Warming Potential) as sepcified by the IPCC (Intergonvernmental Panel of Climate Change). Recently, the recovery-separtion of $SF_6$ research area, including permeation properties studies using various membrane's materials and the practical operation of recovery-separtion using membrane of waste $SF_6$ gas is in the initial state. The separation efficiency of a single $SF_6$ and waste $SF_6$ mixture was evaluated using a PSF (polysulfone), PC (tetra-bromo polycarbonate) and PI (polyimide) hollow fiber membranes. According to the results of single gases permeation properties, PI membrane has the highest permselectivity of $N_2$ gas in $N_2/SF_6$ gas. Under the condition of P=0.5 MPa, the highest concentration of recovered $SF_6$ is 95.6 vol % in the separation experiment of $SF_6/N_2$ mixture gas by PC membrane. Under the operation pressure of P=0.3 MPa at a fixed retentate flow rate fixed of 150 cc/min, the maximum recovery efficiency of $SF_6$ is up to 97.8% by PSF membrane. From the results above, it is thought that the separation and recovery technique of $SF_6$ gas using membrane will be used as the representative eco-technology in the $SF_6$ gas treatment in the future.

• The Journal of Korea Robotics Society
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• v.8 no.2
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• pp.136-142
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• 2013

In nature, many small insects are using jumping as a survival strategy. Among them, fleas jump in a unique method. They use an elastomer, 'Resilin', an extensor muscle and a trigger muscle. By contracting the extensor muscle, the elastic energy, that makes a flea to jump, is stored in the resilin. After storing energy, the trigger muscle begins contracting and pulling the extensor muscle. When the extensor muscle crosses the rotational joint, direction of torque generated from the extensor muscle reverses, 'torque reversal mechanism'. Simultaneously, the elastic energy stored in the resilin releases rapidly and is converted into the kinetic energy. It makes a flea to jump 150 times its body length. In this paper, miniaturized jumping robot using flea-inspired catapult mechanism is presented. This mechanism is based on the 4-bar linkage and the reversal joint and is actuated by Shape Memory Alloy (SMA) coiled springs describing the flea's muscle. The robot prototype is fabricated by SCM process using glass fiber prepregs and a sheet of polyimide film. The prototype is 20mm link length, 34mm width and 2.0g weight and can jump 103cm.

• Applied Chemistry for Engineering
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• v.17 no.3
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• pp.331-334
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• 2006

In this study, the ultra-fine fibers (UFs) having an alignment were prepared by electrospinning process, using different collectors made from various materials and collecting methods. A spinning solution was prepared by dissolving poly(amide-co-imide) (PAI) in NMP. The UFs were prepared by using various collectors and collecting methods, and the fibrous shapes were observed by SEM. As a result, a sort of materials of collectors and the collecting methods had not influenced on the average diameters of fibers but the forms of them. The just accumulated UFs on the collectors formed net structures, which had no alignment. On the contrary, the continuously collected UFs formed long fibers with alignment. It was found that the water collector played the roles of the fiber haul, temporary collector, moving path of fibers, and caused some friction between fibers and water, attributed to the formation of continuous UFs at a suitable collecting speed.

• Membrane Journal
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• v.20 no.3
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• pp.249-258
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• 2010

In this study, we tried to observe the permeation on the single $O_2$, $CF_4$ and $SF_6$ gas using a PSF (polysulfone), PC (tetra-bromo polycarbonate) and PI (polyimide) hollow fiber membranes. We also observed the permselectivity on the $O_2/SF_6$ and $CF_4/SF_6$. According to the results of single gases permeation for different pressures, PSF membrane has the highest $O_2$ permeation of 37.5 GPU and PC membrane has the highest $SF_6$ permeation of 2.7 GPU and the highest $CF_4$ permeation of 2.5 GPU at 1.1 MPa. According to the results of single gases permeation for different temperatures, PSF membrane has the highest permeation of $O_2$ at $45^{\circ}C$ and PC membrane has the highest permeation of $SF_6$ and $CF_4$ at $25^{\circ}C$. From the result of $O_2/SF_6$ and $CF_4/SF_6$ permselectivity for different pressures and temperature, the highest permeation and the lowest permselectivity were observed in the PSF and PC membrane. On the contrary, the lowest permeation and the highest permselectivity was observed in the PI membrane.

• Polymer(Korea)
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• v.30 no.1
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• pp.56-63
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• 2006

We have synthesized two types of diamine monomers containing various chain length to prepare polyimides with layered structure. By using these diamines, homo-polyimides and co-polyimides having hydrophobic and hydrophilic segment of flexible side chain were synthesized. The segregated layered structures were formed by repulsive force with main chain as the side chains reach a critical length because the rigid main chains are packed into layered structure with the flexible side chains occupying the space between layers. As a result, the gallery space of each homo-polyimide was increased at spacing of $32.7\~48{\AA}\;or\;7\~10.5{\AA}$ as the increased hydrophobic or hydrophilic side chain length through X-ray diffraction. The gallery space of co-polyimides was also showed similar phenomenon by repulsive force of side chains with different properties. We have also confirmed that gallery space and molar volume were significantly depended on length of flexible side chain via molecular modeling.