• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1179-1185
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• 2011

Cold and hot-rolled carbon steel sheets are commonly used in railroad cars or commercial vehicles such as the automobile. The sheets used in these applications are mainly fabricated by spot welding, which is a type of electric resistance welding. However, the fatigue strength of a spot-welded joint is lower than that of the base metal because of high stress concentration at the nugget edge of the spot-welded part. In particular, the fatigue strength of the joint is influenced by not only geometrical and mechanical factors but also the welding conditions for the spot-welded joint. Therefore, there is a need for establishing a reasonable criterion for a long-life design for spot-welded structures. In this thesis, ${\Delta}P-N_f$ relation curves have been used to determine a long-life fatigue-design criterion for thin-sheet structures. However, as these curves vary under the influence of welding conditions, mechanical conditions, geometrical factors, etc. It is very difficult to systematically determine a fatigue-design criterion on the basis of these curves. Therefore, in order to eliminate such problems, the welding residual stresses generated during welding and the stress distributions around the weld generated by external forces were numerically and experimentally analyzed on the basis of the results, reassessed fatigue strength of gas welded joints.

• Journal of the Korean Wood Science and Technology
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• v.43 no.6
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• pp.868-875
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• 2015

In order to replace existing slit type steel plate on the wooden structure joint, the FRP-reinforced laminated plates were produced. Four types of FRP-reinforced laminated plates were produced according to the type of reinforcement and adhesive, and before applying to the joint, the adhesion performance test according to KSF 3021 and KSF 2160 and the Compact Tension (CT) type fracture toughness test specified in ASTM D5045-99 were carried out. As a result of adhesion performance test, all GFRP textile, GFRP sheet, and GFRP Textile-Sheet type FRP-reinforced laminated plates satisfied the requirement of soaking delamination percentage with smaller than 5% based on KS standard. However, aramid type specimen satisfied the standard as the soaking delamination percentage of 4.8% but it did not satisfied the standard as the water proof soaking delamination percentage of 70%. As a result of fracture toughness test, the volume ratio of reinforcement to timber became 23% so that the strength of FRP-reinforced laminated plates increased by two to four times in comparison to the control specimen. It was confirmed that the GFRP Textile-Sheet type specimen was most resistant to the fracture most since the ratio of stress intensity factor compared with that of the control increased to 61% owing to the parallel arrangement of glass fiber to the load. As a result of tensile shear strength test using FRP-reinforced laminated plates and nonmetal dowels, it is about 12% lower than metal connectors.

• Journal of Korean Medicine Rehabilitation
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• v.25 no.2
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• pp.15-35
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• 2015

Objectives This study was performed to investigate the effects of Bujasasim-tang ethanol extract (BST) on oxidative stress, inflammation and osteoarthritic rat model. Methods To ensure safety of BST, heavy metal levels were measured and cytotoxicity test was done. In vitro, To evaluate antioxidative effects of BST, total phenolic contents, 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) scavenging activity, reactive oxygen species (ROS) levels were measured. Also, to evaluate anti-inflammatory effects of BST treated group, total nitric oxide (NO) and pro-inflammatory cytokines (IL-$1{\beta}$, IL-6, TNF-${\alpha}$) levels were measured in lipopolysaccharide (LPS)-stimulated RAW 264.7 cells. In vivo, We injected MIA $50{\mu}l$ (60 mg/ml) into knee joints of rats to induce osteoarthritis. Rats were divided into total 3 groups (normal, control, BST treated group, each n=7). Normal group was not treated at all without inducing osteoarthritis and taken normal diet. Control group was induced osteoarthritis by MIA and taken with 2 ml of distilled water once a day for 4 weeks. BST treated group was induced osteoarthritis by MIA and taken BST 2 ml (200 mg/kg/mouse) once a day for 4 weeks. We evaluated dynamic weight bearing with the Incapacitance Test Meter. At the end of experiment, the rats were sacrificed to observe the functions of liver and kidney, changes of WBC, neutrophil, lymphocyte, monocyte levels in blood, to evaluate the levels of pro-inflammatory cytokines, tissue inhibitor of metallopreteinases-1 (TIMP-1), matrix metalloproteinase-9 (MMP-9), prostaglandin $E_2$ ($PGE_2$), leukotriene $B_4$ ($LTB_4$) within serum. We observed change of articular structures by Hematoxylin & Eosin (H&E), safranin-O staining method and measured amount of cartilage by micro CT-arthrography. Statistical analysis was done by unpaired student's t-test with significance level at p<0.05 in SPSS 11.0 for windows. Results 1. Safety of the BST was identified. 2. AST, ALT, BUN, creatinine levels of BST treated group were within normal limit. In vitro, 1. DPPH and ABTS free radical scavenging activities of BST showed dose-dependent increase. 2. ROS production were significantly decreased. 3. Total nitric oxide (NO) and IL-$1{\beta}$ production were decreased. 4. IL-6 and TNF-${\alpha}$ production were significantly decreased. In vivo, 1. Weight bearing ability was significantly increased. 2. WBC, neutrophil, lymphocyte, monocyte levels in blood were decreased. 3. IL-$1{\beta}$ and TNF-${\alpha}$ levels in serum were significantly decreased. and the IL-6 level was decreased. 4. TIMP-1, MMP-9, $LTB_4$, $PGE_2$ levels in serum were significantly decreased. 5. Cartilage volume of BST treated group was significantly increased. Also changes of cartilage, synovial membrane, fibrous tissue were suppressed. Conclusions The results obtained in this study Bujasasim-tang have effects of antioxidative, anti-inflammatory, relieve pain and protection of cartilage. Therefore we expect that Bujasasim-tang is effective treatment for osteoarthritis.

• Journal of the Korean Wood Science and Technology
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• v.42 no.3
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• pp.258-265
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• 2014

By replacing the previous metal connector on the joints of timber structure, the GFRP reinforced laminated wooden pin was produced using a wooden material and Glass fiber reinforced plastic(GFRP) composite laminate. In addition, using the reinforced wooden pin, the tensile type shear strength test was conducted. Based on the result of the bending strength test of the reinforced laminated wooden pin according to the GFRP arrangement, a specimen(Type-A) with a single insertion of GFRP for each layer have shown the most favorable performance. Also, it was verified that densified specimen hot pressed for an hour at the temperature of $150^{\circ}C$ and with the oppression pressure $1.96N/mm^2$ have shown the improved performance of 1.57 times than the specimen without the densification. And in the bending strength test considering the load direction, edgewise have shown a higher performance of 3.51 times than the flatwise. A shear strength test was conducted using the Type-A reinforced laminated wooden pin which have shown a moderate performance on the test. Based on the test conducted by differentiating the type of the joint plate and the connector, compared to the specimen(Type-DS) applied with the drift pin and steel plate, the specimen( Type-WL) applied with the GFRP reinforced laminated wooden pin and GFRP reinforced wooden laminated plate have shown 1.12 times higher shear strength and also have shown an excellent toughness even after the maximum load.

• Journal of Welding and Joining
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• v.29 no.6
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• pp.56-64
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• 2011

Friction stir spot welding between 5454 aluminum alloy sheets with the different thicknesses of 1.4 and 1.0 mm was performed. In the welding process, the tool for welding was rotated ranging from 500 to 2500, and plunged to the depth of 1.8 mm under a constant tool plunge speed of 100 mm/min. And then, the rotating tool was maintained at the plunge depth during the dwell time ranging from 0 to 7 sec. The pull-out speed of the rotating tool was 100 mm/min. The increase of tool rotation speed resulted in the change of the macrostructure of friction-stir-spot-welded zone, especially the geometry of welding interface. The results of the tensile shear test showed that the total displacement and toughness of the welds were increased with the increase of the tool rotation speed, although the maximum tensile shear load was decreased. However, the change in the dwell time at the plunge depth of the tool did not produce the remarkable variation in the macrostructure and mechanical properties of the welds. In all cases, the average hardness in friction-stir-spot-welded zone was higher than that of the base metal zone. By the friction stir spot welding technique, the welds with the excellent mechanical properties than the mechanically-clinched joints could be obtained.

• Journal of the Korean Society for Railway
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• v.19 no.4
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• pp.417-426
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• 2016

In this study, the optimal welding condition of an extruded AZ61 magnesium alloy plate was investigated through evaluation of the mechanical properties and microstructure in the friction stir welding zones. The friction stir welding conditions considered in this study were the tool rotation speeds of 400, 600, and 800rpm and the welding speeds of 200, 300, and 400mm/min. To evaluate the welding strength, tensile and hardness tests were carried out. Microstructures of the welded regions were examined using optical microscopes. Under a tool rotation speed of 800rpm and welding speed of 200mm/min, the joint showed the best joining properties. The UTS, yield strength, and elongation of the welded region showed values of 79.0%, 65.4%, and 30.1%, respectively, of those of the base metal.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.5
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• pp.605-611
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• 2019

The fuel sloshing due to the rapid manoeuvre of the aircraft causes significant loads on internal components, which may break components or piping. In particular, a significant load is applied to the joint of the external fuel tank by sloshing movement, which may affect the safety of the aircraft when the joint of the external fuel tank is damaged. Therefore, in order to improve the survivability of aircraft and crew members, the design of external fuel tanks, and joints should be performed after evaluating the sloshing load through a numerical analysis of the fuel sloshing conditions. In this paper, a numerical analysis was performed on the sloshing test of the external fuel tank for rotorcraft. ALE (Arbitrary Lagrangian Eulerian) technique was used, and the test conditions specified in the U.S. Military Specification (MIL-DTL-27422D) was applied as the conditions for numerical analysis. As a result of the numerical analysis, the load on the joint of the external fuel tank was calculated. Moreover, the effects of sloshing movement on structural soundness were assessed through analysis of stress levels and margin of safety on metal fittings and composite containers.

• Conservation Science in Museum
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• v.26
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• pp.83-182
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• 2021

This study summarized the results of the conservation treatment and investigation on the production method of the golden crown (Treasure No. 339) excavated from Tomb No. 129 (also known as Seobongchong Tomb) in Noseo-dong, Gyeongju-si, Gyeongsangbuk-do Province. The golden crown from Seobongchong Tomb was discovered during the excavations conducted by the Museum of the Government-General of Korea in 1926 during the Japanese colonial era. It is currently in the collection of the National Museum of Korea. A total of six Silla golden crowns have survived in Korea, among which the crown from Seobongchong Tomb is the only example with a dome-shaped hemispherical decoration attached with a bird ornament while otherwise showing the typical features of Silla crowns. The crown had been repaired following its excavation using metallic materials and adhesives, but due to the partial deformation and damage brought about by the repair materials, it required further conservation treatment. This article describes in detail the overall process of the conservation treatment and the restoration of the original form of the golden crown from Seobongchong Tomb, particularly the method of reinforcing the joints to secure the stability of the crown. It presents the characteristics of the crown's production as revealed in the investigation during the conservation treatment, and further analyzes the relationship of this crown from Seobongchong Tomb with other Silla crowns through a comparison of their production techniques. The investigation revealed that the crown was primarily decorated with golden sequins at the time of its production. At a later point some of the sequins in the upright ornament were replaced with comma-shaped jade beads and additional comma-shaped jade beads were added to the headband. In order to determine if such modifications to the decoration had occurred with other Silla crowns, the decoration of the six extant Silla golden crowns were investigated. The crown from Cheonmachong Tomb features traces of this same modification to the decoration and possesses other similarities with the crown from Seobongchong Tomb.

• Korean Journal of Heritage: History & Science
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• v.56 no.4
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• pp.24-37
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• 2023

This study analyzes the materials and external characteristics of the Angbu-ilgu, a kind of scaphe sundial, which was newly designated as a Korean Treasure in 2022. The Angbu-ilgu Treasure is owned by three institutions - the National Palace Museum Of Korea, Gyeongju National Museum, and Sungshin Women's University Museum - and is similar as a twin in its material, size, outward appearance, as well as production techniques that include casting, silver inlays, and metal joints. The Three-Treasure Angbu-ilgu is made of brass in the ratio of 90.6: 6.0: 1.8 with Cu: Zn: Pb. This composition clearly differs from Treasure No. 845, an Angbuilgu which has a composition ratio of 82.2: 3.7: 11.8 with Cu: Zn: Pb. In this new Angbu-ilgu Treasure, the hemisphere's stand has four vertical pillars sculpted in a dragon pattern and bilateral wings carved in a cloud pattern on the pillars, which are joined to the hemisphere's horizontal ring with rivets and silver solders, respectively. The dragon-in-clouds pillar (雲龍柱) shows the most outstanding formative beauty of the various Angbu-ilgu pillars produced in the late Joseon Dynasty. It can be seen that the altitude of the north pole engraved on the Angbu-ilgu was made after 1713. Production is, however, actually estimated to have occurred close to the 19th century, the era of the Jinju Kang family, who were professional Angbuilgu makers. Hopefully, this study will lead to a historical science and technology review with modern scientific instruments analyzing the materials and external characteristics of the three Angbu-ilgus designated as a Korean Treasure in 2022.

• The Journal of the Petrological Society of Korea
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• v.9 no.1
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• pp.13-28
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• 2000

Chojeong area is mainly composed of the Ogcheon Group which consists of regionally metamorphosed, age-unknown sedimentary rocks. In the northwestern parts, the Group is intruded by the Jurassic Daebo granite and Cretaceous felsic and mafic dykes. The lowermost, Midongsan Formation which consists of milky white impure quartzite, crops out along the anticline axes with N40E trend. Ungyori quartzite Formation is intercalated with quartzite and slate. Miwon Formation is most widely exposed in the area and consists mainly of phyllitic sandy rocks with a thin crystalline limestone bed. Hwajeonri Formation is divided into two parts, pelitic lower and calcareous upper parts, composed with phyllite and slate. Changri and Hwanggangri Formations are typical members of Ogcheon Group, the former bearing coally graphite seams consists mainly of black slate and phyllite with intercalated greenish grey phyllite, the latter is pebble bearing phyllite formation of which matrix and pebbles are variable in compositions and size. Biotite granite, porphyritic granite and two mica granite belong to Jurassic so-called Dabo granite. They intruded the Ogcheon Group forming vast contact metarnophic zone. Quartz porphyry, mafic dyke and felsite intruded along the marginal zone of porphyritic granite batholith and fracture of NS trend. Main structural lineaments in Ogcheon Group shows N25-45E, NS and N30-45W trends. The N25-45E trends are mainly from general ductile deformation during regional metamorphism, showing isoclinal folding, Fl foliations and lithological erosional characters. Some of these trends are due to normal faults. The NS and N30-45W trends represent brittle deformation including faults and joints. In the area of granitic batholith, NS to N30- 45 trends are from the direction of dykes. In the soils of the area, average contents of heavy metal elements such as Cd, Cr, Cu, Pb, and Zn are 0.2, 50.6, 35.5, 27.9, and 93.4 ppm respectively, which are not higher than the average values of natural soils, under the tolerable level. Enrichment Index does not show any heavy metal pollution in the area. Average depths of weathering(5m vs. 2m), porosities(43.94 vs. 51.80), densities(l.29 vs. 1.15), and permeabilities(2.52 vs. 8.07) are comparable in granite areas and in the phyllite areas of Ogcheon Group.