• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.11
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• pp.1265-1272
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• 2014

This study performed the progressive failure analysis of adhesive joints of a composite pressure vessel with a separated dome by using a cohesive zone model. In order to determine the input parameters of a cohesive element for numerical analysis, the interlaminar fracture toughness values in modes I and II and in the mixed mode for the adhesive joints of the composite pressure vessel were obtained by a material test. All specimens were manufactured by the filament winding method. A mechanical test was performed on adhesively bonded double-lap joints to determine the shear strength of the adhesive joints and verify the reliability of the cohesive zone model for progressive failure analysis. The test results showed that the shear strength of the adhesive joints was 32MPa; the experiment and analysis results had an error of about 4.4%, indicating their relatively good agreement. The progressive failure analysis of a composite pressure vessel with an adhesively bonded dome performed using the cohesive zone model showed that only 5.8% of the total adhesive length was debonded and this debonded length did not affect the structural integrity of the vessel.

• The Korean Journal of Pain
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• v.20 no.2
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• pp.100-105
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• 2007

Background: Ginseng has been used to manage various types of pain in folk medicine. This study characterized the effect of treatment with intrathecal ginsenosides, the active components of ginseng in a postoperative pain model. Methods: Male Sprague-Dawley rats were implanted with lumbar intrathecal catheters. An incision was made in the plantar surface of the hindpaw. Withdrawal thresholds following the application of a von Frey filament to the wound site were measured. To determine the role of the opioid or GABA receptors following treatment with the ginsenosides, naloxone, bicuculline (a $GABA_A$ receptor antagonist), and saclofen (a $GABA_B$ receptor antagonist) were administered intrathecally 10 min before the delivery of the ginsenosides and the changes of the withdrawal thresholds after application of the von Frey filament were Observed. Results: Treatment with the intrathecal ginsenosides increased the withdrawal threshold in a dose dependent manner. Pre-treatment with intrathecal naloxone reversed the antinociceptive effect of the ginsenosides. However, pre-treatment with intrathecal bicuculline and saclofen failed to have an effect on the activity of the ginsenosides. Conclusions: These results suggest that ginsenosides are effective to alleviate the postoperative pain evoked by paw incision. The opioid receptor, but not GABA receptors, may be involved in the antinociceptive action of the ginsenosides at the spinal level.

• Journal of the Korean Society for Nondestructive Testing
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• v.18 no.2
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• pp.92-102
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• 1998

Prediction of failure behavior in filament-wound composite motor cases is one of the important issues for their reliable application. Acoustic emission during hydroproof testing of the cases is used to solve this problem. Based on the acoustic emission behavior, failure sites can be located successfully. The identification of failure modes is also possible using the distribution of acoustic emission amplitude. Due to the limitation in the number of samples, it is not possible to predict the final burst pressure of motor cases and the effect of impact damage on the final burst pressure.

• Progress in Superconductivity
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• v.13 no.2
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• pp.111-116
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• 2011

Since superconducting wires have no resistance, electromagnets based on the superconducting wires produce no resistive heating with DC current as long as the current does not exceed the critical current of the wire. However, unlike resistive wires, superconducting wires exhibit AC heat loss. Embedding fine superconducting filaments inside copper matrix can reduce this AC loss to an acceptable level and opens the way to AC-capable superconducting coils. Here, we introduce an easy and accurate method to measure AC heat loss from sample superconducting coils by measuring changes in the rate of gas helium outflow from the liquid helium dewar in which the sample coil is placed. This method provides accurate information on total heat loss of a superconducting coil without any size limit, as long as the coil can fit inside the liquid helium dewar. With this method, we have evaluated AC heat loss of two superconducting solenoids, a 180-turn solid NbTi wire with 0.127 mm diameter (NbTi coil) and a 100-turn filamented wire with 1.4 mm diameter where 7 NbTi filaments were embedded in a copper matrix with copper to NbTi ratio of 6.7:1 (NbTi-Cu coil). Both coils were wound on 15 mm-diameter G-10 epoxy tubes. The AC heat losses of the NbTi and NbTi-Cu coils were evaluated as $53{\pm}4.7\;{\mu}W/A^2Hzcm^3$ and $0.67{\pm}0.16\;{\mu}W/A^2Hzcm^3$, respectively.

• Journal of the Korean Society of Propulsion Engineers
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• v.21 no.2
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• pp.32-40
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• 2017

In this study, the procedures for quantitative measurement of void contents of carbon fiber/epoxy composites were suggested. Two types of the composites were considered: autoclave cured composite and filament wound composite. Void contents of the composites were evaluated by the density of the composites and their constituents, which was determined from weights in the air and water, and the weight fraction and volume fraction of the constituents obtained from the digestion method and combustion method. The surfaces of filtered carbon fibers were examined by FE-SEM in order to investigate the validity of resin removal from the composites. According to the results, the resin in the composites could be fully removed by the digestion method and combustion method. Therefore, the weight fraction and volume fraction of the constituents, and void content of the composites could be quantitatively obtained by the suggested procedures.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.169-172
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• 2005

A flywheel system is an electromechanical energy storage device that stores energy by rotating a rotor. The rotating part, supported by magnetic bearings, consists of the metallic shaft, composite rims of fiber-reinforced materials, and a hub that connects the rotor to the shaft. The delamination in the fiber wound composite rotor often lowered the performance of the flywheel energy storage system. In this work, an advanced hybrid composite rotor with a split hub was designed to both overcome the delamination problem in composite rim and prevent separation between composite rim and metallic shaft within all range of rotational speed. It was analyzed using a three-dimensional finite clement method. In order to demonstrate the predominant perfom1ance of the hybrid composite rotor with a split hub, a high spin test was performed up to 40,000 rpm. Four radial strains and another four circumferential strains were measured using a wireless telemetry system. These measured strains were in excellent agreement with the FE analysis. Most importantly, the radial strains were reduced using the hybrid composite rotor with a split hub, and all of them were compressive. As a conclusion, a compressive pressure on the inner surface of the proposed flywheel rotor was achieved, and it can lower the radial stresses within the composite rotor, enhancing the performance of the flywheel rotor.

• Journal of the Earthquake Engineering Society of Korea
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• v.7 no.1
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• pp.1-7
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• 2003

The carbon composite tube can play an important role in replacing or complementing longitudinal and transverse reinforcing steels by providing ductility and strength for conventional columns. In this study, both the experimental and analytical investigations of axial behavior of large-scale square concrete columns confined by carbon composite tube are presented. The specimens are filament-wound carbon composite with 90$^{\circ}$+30$^{\circ}$, 90$^{\circ}$+45$^{\circ}$ winding angle respect to longitudinal axis of tube. The instrumented large-scale concrete-filled composite tubes(CFCT) are subjected to monotonic axial loads exerted by 10,000kN UTM. The influence of winding angle, thickness of tube on stress-strain relationships of the confined columns is identified and discussed. Proposed equations to predict both the strength and ductility of confined columns by carbon composite tube demonstrate good correlation with test data obtained from large-scale specimens.

• Composites Research
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• v.28 no.4
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• pp.143-147
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• 2015

This paper proposes laser ultrasonic technique for the impact damage inspection of hydrogen fuel tank and proves that the impact damage can be visualized using an ultrasonic wave propagation imager with an easy detachable sensor head as an impact damage inspection tool for hydrogen fuel tanks. Also the performances of the proposed ultrasonic propagation imager support it can be implemented in real-world technology when the hydrogen car becomes popular.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.288-292
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• 2008

Dome shape design method of filament wound (FW) composite pressure vessel, which can create various dome shape with fixed boss opening, was suggested. And, the performance indices (PV/W) for composite pressure vessel with same boss opening but different dome shape were investigated by finite element analysis (FEA) and hydro-test. The FEA showed good agreement with test results for burst pressure. Generally, as the dome shape of pressure vessel was changed to flat dome, the inner volume is increased and the burst pressure is decreased. In the case of above ${\rho}_o$=0.54, the performance index showed decreased value due to the low burst pressure. However, at ${\rho}_o$=0.35, the dome shape change brings not significant reduction of burst pressure and performance index.

• Composites Research
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• v.18 no.1
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• pp.45-54
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• 2005

The delamination in the filament-wound composite flywheel rotor often lowers the performance of the flywheel energy storage system. A conventional ring type hub usually causes tensile stresses on the inner surface of the composite rotor, resulting in lowering the maximum rotational speed of the rotor. In this work, the stress and strain distributions within a hybrid composite rotor were derived from the two-dimensional governing equation with the specified boundary conditions, and an optimum pressure at the inner surface of the rotor was proposed to minimize the strength ratio and maximize the storage energy. A split type hub was introduced to apply the calculated optimum pressure at the inner surface, and a spin test was performed up to 40,000 rpm to demonstrate the performance of the split type hub with radial and circumferential strains measured using a wireless telemetry system. From the analysis and the test, it was found that the split type hub successfully generates a compressive pressure on the inner surface of the rotor, which can enhance the performance of the composite rotor by lowering the strength ratio within the rotor.