• Analytical Science and Technology
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• v.24 no.5
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• pp.336-344
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• 2011

The study attempted to find out any effect to prevent photo aging of epoxy resin used for conservation by way of adding UV stabilizer, one of plastic additives. Specimens were made by adding HALS and UVA UV stabilizer as each concentration to 3 kinds of epoxy resin, which are most frequently used for artifacts joining and restoration process, and aging effects were investigated through Color change, SEM, contact angle, FTIR analysis during UV aging experiments. Last, usage suitability was checked when UV stabilizer was added through Universal Tensile strength tester. In result, it is impossible to prevent decomposition of chemical structure in spite of adding UV stabilizer but in the case of epoxy A and R, it is believed that photo aging such as yellowing or crack can be minimized without giving a big influence to adhesive strength of epoxy resin through adding less than 0.1% of UVA. It is expected that above will solve photo aging problem of epoxy resin used for joining and restoration of artifacts and will extend its life as joining and restoration materials.

• Tunnel and Underground Space
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• v.13 no.6
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• pp.444-454
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• 2003

Rock fragmentation technique by cutter penetration has widely been used in the mechanical tunnel excavation. Microcracks propagate and interact because of locally concentrated high stress induced by cutter penetration. which is caused by heterogeneity of rocks. In this study Weibull distribution function and degradation index are used to consider the strength heterogeneity of a rock and the degradation of rock properties after failure. Through the numerical analyses, it is shown that the lateral pressure has an important influence on the rock fragmentation. In the single cutter penetration, large chips are formed as lateral pressure increase. The cutter spacing is also an important factor that affects the rock fragmentation in the double cutter penetration. The fragmentation efficiency of the double cutter penetration is better when cutter spacing is 70 mm than 40 mm and 100 mm. From the results, it is expected that this study can be applied to a TBM tunnel design by understanding of chipping process and mechanism of rock due to cutter penetration.

• Tunnel and Underground Space
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• v.21 no.3
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• pp.164-173
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• 2011

In the present study, the stability of a compressed air energy storage cavern was numerically assessed by concrete plug shapes in order to investigate the optimal shape of concrete plug. The concrete plugs were cylindrical, embedded cylindrical, tapered, and wedged in shape. The stability assessment was carried out based on factor of safety through a strength reduction method and a volume ratio which refers to the ratio of the volume of yield regions in concrete induced by internal pressure to all concrete volume. The results from the present study indicated that the embedded cylindrical and taper shaped plugs were mechanically more stable than the cylindrical and wedge shaped plugs. However, from a comparison of stress distributions in rock mass between the embedded cylindrical and taper shaped plugs, the taper shaped plug was found to be more optimal than the embedded cylindrical plug, since the embedded cylindrical plug caused more stress concentration in the interface between the plug and rock mass than the taper shaped plug.

• Composites Research
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• v.23 no.1
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• pp.44-50
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• 2010

In this paper, two different experiments, namely, salt water spray and salt water immersion, were performed to reproduce the contact of composites with the seawater for three kinds of woven fabric composite material systems which would be used for the WIG(wing in ground effect)craft. After aging 140 days in the salt water environment, material properties of carbon/epoxy and glass/epoxy composite such as tensile, compressive and shear stiffness and strength, and inter-laminar shear strength (ILSS) were measured. By comparing baseline material properties with degraded ones, the effects of the salt water environment on the composite mechanical properties were evaluated. From the experiments, it was confirmed that the difference in aging conditions had very small influence on composite properties. And it was found that tensile strength of carbon/epoxy composites showed little degradation, but much more degradation was observed in glass/epoxy composites. And large degradations on matrix dominant properties were observed. The salt water could damage the fiber-matrix interface, matrix properties and the glass fiber.

• Membrane Journal
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• v.18 no.1
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• pp.75-83
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• 2008

In this research, the research for enhancing the stability at the mechanical strength and thermal stability and high power through the Direct Fluorination of the Polyethylene (PE, Asahi) for secondary battery was conducted. The surface of according to the fluorine gas exposure time and constructional change were observed through the scanning electron microscope image, and the contact angle. The mechanical property was confirmed through the tensile strength and surface hydrophilic property experiment. Charge and discharge experiment, the lifetime property, and the overcharge test were performed in order to confirm the electrochemical characteristic of produced and we confirmed at the high power that the stability about a temperature was improved.

• Composites Research
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• v.26 no.3
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• pp.170-174
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• 2013

Atmospheric glow plasma polymerization was applied to wood powder before fabricating polypropylene (PP) matrix composites. Seven different types of monomers (Oxygen, Benzene, CH4, Acrylic-acid, Hexafluoroethane, Trifluorotolune, Hexamethyl-disiloxane) were analyzed to determine the most suitable precursor for plasma polymerization. The surface energy was calculated from measured contact angle about each monomer on PP. Hexamethyl-disiloxane (HMDSO) had a highest surface energy and is selected as the most suitable monomer. Wood powder and polypropylene were mixed as pellets by twin screw extruder and then 50 wt% wood powder/PP composites were produced by an injection machine. Tensile strength and Flexural strength have improved by 7.59% and 12.43% at the maximum respectively. SEM (Scanning Electron Microscope) observation on the fracture surface revealed that the plasma polymerization have improved the interfacial bonding and the mechanical properties of the composites.

• Computational Structural Engineering
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• v.7 no.3
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• pp.133-141
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• 1994

When a bolt is tightened up to the range of plastic deformation, yielding may be governed by the combined stresses due to the axial force developed in the bolt and the frictional torque induced on the thread by the contact with the nut. Consideration is taken account of the fact that the unengaged portion of the thread has least sectional area, being subject to initial yielding. Once yielding has taken place some strain hardening effect may result. Incremental stress-strain relations are used to treat the continued yielding, which is equivalent to treat continued yielding as if summing up the effects of thin walled cylinders subject to plastic deformation. M10 bolts of fine threads are used for both computational and experimental purposes. Variation of axial forces and frictional torques vs. the frictional coefficients are presented together with other plots showing some characterist of bolt under plastic deformation. Finally, a design and control aid for the tightening(i.e., kind of nomograph) is presented, showing the relationships among the torque factor and frictional coefficients for that particular bolt used in the experiment.

• Speech Sciences
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• v.14 no.2
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• pp.23-33
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• 2007

This study examined the aerodynamic functions (mean airflow rate MFR, subglottal pressure Psub) and closed quotients (CQs) in the fixed pitch (C3, E3, G3, C4) with the variable loudness (70 and 80 dB) as well as in the fixed loudness at 70 dB and 80 dB with the variable pitch (C3, E3, G3, C4) in five classic male singers (Baritone). Results showed that MFR significantly increased at C3, E3, and G3 and Psub significantly increased at C4 when the loudness increased from 70 to 80 dB. At 70 dB, MFR and Psub significantly increased and CQ significantly decreased when the pitch increased from C3 to C4. At 80 dB, MFR significantly decreased when the pitch increased from C3 to G3. However, Psub showed the significant decrease with the pitch increased at 80 dB. In conclusion, as the loudness increases, the aerodynamic loss is getting higher and vocal efficiency becomes lower at low pitch than at higher pitch. At a low loudness level, the main mechanism to control loudness is the amount of medial compression of the vocal folds rather than the aerodynamic function. In addition, the aerodynamic function and medial compression of the vocal folds have a significant role in increasing the loudness level.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.25-33
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• 2003

The failure load and mode of the unidirectional and fabric hybrid composite laminate joints are studied by test and finite element analysis. Test is conducted for the specimens with nine various geometries under pin loading. Finite element analysis is performed considering the contact and friction effects between the pin and laminate by MSC/NASTRAN. Failure is estimated by Tsai-Wu and Yamada-Sun criteria on the characteristic curve. While the failure of the specimens with the small width and edge length are much affected by the joint geometry, the geometry effects are negligible in the specimens with large width and edge length. Finite element analysis based on the characteristic length method reasonably predicts the failure load and mode of the joints.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.8-17
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• 2003

The butt lap joint structures which are usually designed by the concept of slow crack growth damage tolerance, show frequently the behaviors of multiple site fatigue crack growth around the fastener hole edges due to the fretting between the two jointed parts. In this paper, experimental tests of fatigue crack growth have been performed of a bolted butt lap joint structure having an initial corner crack at the fastener hole edge, with different fretting conditions under a flight load spectrum. The obtained test results were reviewed to investigate the effects of fretting fatigue cracks on the damage tolerance crack growth life. Computations of corner crack growth were also carried out using an existed model to compare with test results.