• Journal of Conservation Science
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• v.35 no.5
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• pp.440-452
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• 2019

This research has analyzed SI, the traditional steel, and SIHS(SI + HS), SICS(SI + CS), and SINiS(SI + NiS), the materials that were produced through welding and reprocessing three modern steel- HS, CS, and NiS- that have different carbon content. The purpose of the analyzation was to improve the definition of the multi-layered pattern that appears in the forging process. In observing modified structures on the commissures of three modern steel that have different carbon component to the SI, SINiS produced the most significant multi-layered pattern as well as the excellent welding quality. The excellent welding quality was due to the content of nickel which helped the forge welding process with other materials. There was no significant difference in crystal grain per materials, and SICS showed the highest hardness. At the measurement of EPMA for commissures of the materials, SINiS showed the highest definition of the multi-layered pattern due to the nickel and carbon content. The results above showed that the carbon steel with nickel content is the best material for the most definite multi-layered pattern, expressed from the multi-layered structure which is a characteristic of traditional forge welding technology. It is expected that the result of this research can be utilized as the technical data in further researches regarding the relics excavated from ancient welding process and their multi-layered structure and patterns.

• Journal of the Institute of Convergence Signal Processing
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• v.19 no.2
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• pp.61-67
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• 2018

Welding preheating means that the surface of the base material to which the metal is welded before the main welding is heated to a constant temperature. It prevents the cracks of the adjacent influences such as reduction of material hardening degree by controlling the cooling rate, suppression of segregation of impurities, prevention of thermal deformation, and moisture removal. For this reason, it is a necessary operation for high quality welding. Induction heating is an efficient heating method that converts electric energy into heat energy by applying electromagnetic induction phenomenon. Compared with combustion heat generated by gas and liquid, it is clean, stable, and economical as well as rapid heating. It can be heated regardless of the shape, depth and material of the heating body by modifying the shape of the frequency and the coil with a simple structure. In this paper, we implemented a low frequency welding preheating system using induction heating technique and observed the temperature changes of coil resistance, inductance and automotive transmission parts according to the height of each transmission in winding coil for three kinds of automotive transmission parts. We confirmed that the change of current is a very important factor in the low frequency heating.

• Journal of the Korea Concrete Institute
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• v.20 no.2
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• pp.231-237
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• 2008

This study was performed to evaluate joint behavior of prestressed concrete(PSC)-steel mixed girders through the flexural test of 14 beams according to embedded length, amount of reinforcing steel, stud arrangement, and prestressing force. All test beams were failed by turns of desertion of reinforcing steel, stud, and steel plate. From test results, prestressing force was more effective on performance of connection than stud arrangement and reinforcing steel. And the spacing of stud is also more effective than embedding length. This paper also presented 3D nonlinear analysis considering the slip of composite section as well as the static load tests of PSC-steel mixed girders. According to the slip modulus, the nonlinear analysis showed that the behavior of hybrid girders could be divided into three parts as full-composite, partial-composite and non-composite. However, the experimental results showed that the PSC-steel hybrid girders with shear connectors took the part of partial composite action in ultimate load stage. In addition, it was founded that stud shear connectors and welded reinforcements were contributed to improve the ultimate strength of hybrid girders for about 20%.

• Journal of Welding and Joining
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• v.18 no.2
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• pp.213-213
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• 2000

This study was performed to investigate types and formation mechanism of cracks in two Al alloy welds, A5083 and A7NO1 spot-welded by pulse Nd: YAG laser, using SEM, EPMA and Micro-XRD. In the weld zone, three types of crack were observed: center line crack($C_{C}$), diagonal crack($C_{D}$), and U shape crack($C_{U}$). Also, HAZ crack($C_{H}$), was observed in the HAZ region, furthermore, mixing crack($C_{M}$), consisting of diagonal crack and HAZ crack was observed.White film was formed at the hot crack region in the fractured surface after it was immersed to 10%NaOH water. In the case of A5083 alloy, white films in C crack and $C_D crack region were composed of low melting phases, Fe₂Si$Al_8$ and eutectic phases, Mg₂Al₃ and Mg₂Si. Such films observed near HAZ crack were also consist of eutectic Mg₂Al₃. In the case of A7N01 alloy, eutectic phases of CuAl₂, $Mg_{32}$ (Al,Zn) ₃, MgZn₂, Al₂CuMg and Mg₂Si were observed in the whitely etched films near $C_{C}$ crack and $C_{D}$ crack regions. The formation of liquid films was due to the segregation of Mg, Si, Fe in the case of A5083 alloy and Zn, Mg, Cu, Si in the case of A7N01 aooly, respectively.The $C_{D}$ and $C_{C}$ cracks were regarded as a result of the occurrence of tensile strain during the welding process. The formation of $C_{M}$ crack is likely to be due to the presence of liquid film at the grain boundary near the fusion line in the base metal as well as in the weld fusion zone during solidification. The $C_{U}$ crack is considered a result of the collapsed keyhole through incomplete closure during rapid solidification. (Received October 7, 1999)

• Journal of Conservation Science
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• v.38 no.4
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• pp.289-300
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• 2022

In the 6^th and 7^th centuries, 5 iron artifacts excavated form the Baekje Stone Tomb in Guryong-ri site, Ungcheon, Boryeong, were studied. The sample were metal microscopic observation, SEM-EDS analysis and Raman micro-spectroscopy analysis were conducted to understand the metallurgical characteristics. The microstructure observation showed the presence of ferrite and pearlite throughout, and differences in carbon content existed depending on the direction. Non-metallic inclusions were in the form of long lines, and most of them were wüstite, fayalite. It is indicated that the artifacts were forge welded using hypoeutectoid steel, with signs of carburizing and decarburizing processes. Some crystals with high P₂O₅, TiO₂, CaO content were identified as sarcopside, ulvöspinel, and perovskite, respectively, through Raman spectroscopy. A comparison of the results with previous studies on the sites of Bujang-ri site in Seosan and Bongseon-ri site in Seocheon, which are adjacent sites in the coastal area, revealed that, while heat treatment technology was available, the artifacts were not heat-treated considering the purpose for use for these artifacts. The chemical composition of the non-metallic inclusions P₂O₅, TiO₂, CaO were plotted in proportions to SiO₂ and compared with adjacent sites. Considering that the P₂O₅/SiO₂ ratio was widely distributed, the refining technology was not uniform. In addition, the TiO₂/SiO₂ ratio was found to be higher than that of other sites, meaning that a titanium-containing ore was used to manufacture the artifacts, unlike in surrounding sites, but it is not detected in all artifacts, so it may have been affected by various factors such as furnace walls in addition to raw materials. Although slag formers were used, considering the CaO/SiO₂ ratio and the (Al₂O₃/SiO₂)/(CaO/SiO₂) ratio, which appear to be similar to the surrounding sites, but it is possible that CaO containing raw ore was used because it is also affected by the components of raw ore. As a result of the study, it is highly likely that ore different from that of the surrounding sites was used for production, but a more comprehensive comparative study with the surrounding sites is needed in the future.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.907-913
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• 1994

The design of railroad bridges differs from road bridges because of the interface between track structure and bridge structure. The track generally consists of Continuous Welded Rail(CWR) which is fixed by fasteners to the sleepers embedded in the ballast. The ballast provides the interface between the track structure and the bridge structure. Large longitudinal forces can develop from the temperature variation in rail and bridge structure. These longitudinal forces are specially important for long bridges because the bridge layout for span length, pier dimensions and arrangement and type of bearings can be governed by these forces. This report provides a comparison of longitudinal track forces determined by analysis and actual measured track forces. In recent practice the longitudinal track force for European railways is analyzed using a finite element analysis method. This method is very time-consuming and requires the detail design of the bridge to be complete. Redesign is required if the design criteria for longitudinal track forces are not satisfied. There is a need to develop a simple analysis method considering the large number of bridge structures and a relatively short design time on the Korean High Speed Rail Project. The analysis results presented herein, based on a simplified analysis, show good agreement with those obtained by finite element analysis, as well as with those measured on an actual track. The proposed analysis method is particularly useful for the preliminary design of bridge structures.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.39 no.3
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• pp.319-325
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• 2015

High-strength steel has replaced mild steel as the material of choice for truck decks or frames, owing to the growing demand for lightweight vehicles. Although studies on the weld fatigue characteristics of mild steel are available, studies on high-strength steels have been seldom conducted. In this study, firstly, we surveyed a chosen number of approaches and selected the Radaj method, which uses the notch factor approach, as the one suitable for evaluating the fatigue life of commercial vehicles. Secondly, we obtained the S-N curves of HARDOX and ATOS60 steel welds, and the F-N curves of the T-weld and overlapped-weld structures. Thirdly, we acquired a general S-N curve of welded structures made of high-strength steel from the F-N curve, using the notch factor approach. Fourthly, we extracted the weld fatigue characteristics of high-strength steel and incorporated the results in the database of a commercial fatigue program. Finally, we compared the results of the fatigue test and the CAE prediction of the example case, which demonstrated sufficiently good agreement.

• Journal of the Korean Society for Nondestructive Testing
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• v.32 no.2
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• pp.162-169
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• 2012

This study detected SCC defects of dissimilar metal welded(STS304 and SA106 Gr. b) pipes using the ultrasonic infrared thermography method and the lock-in image treatment method among infrared thermography method. The infrared excitement equipment has 250 Watt of output and 20 kHz of frequency. By using the ultrasound infrared thermography method, the internal defects of dissimilar metal weld joints of pipes used at nuclear power plants could get detected. By an actual PT test, it was observed that the cracks inside the pipe existed not as a single crack but rather as a multiple cracks within a certain area and generated a hot spot image of a broad area on the thermography image. In addition, UT technology could not easily defects detected by the width of $10\;{\mu}m$ fine hair cracks. but, ultrasound infrared thermography technique was defect detected.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.3
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• pp.52-60
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• 2018

In the automobile industry, in order to increase the fuel efficiency and conform to the safety regulations, it is necessary to make the vehicles as light as possible. Therefore, it is crucial to manufacture dual phase steels, complex phases steels, MS steels, TRIP steels, and TWIP from high strength steels with a tensile strength of 700Mpa or more. In order to apply ultra-high tensile strength steel to the body, the welding process is essential. Resistance spot welding, which is advantageous in terms of its cost, is used in more than 80% of cases in body welding. It is generally accepted that ultra-high tensile strength steel has poor weldability, because its alloy element content is increased to improve its strength. In the case of the resistance spot welding of ultra-high tensile steel, it has been reported that the proper welding condition area is reduced and interfacial fracture and partial interfacial fracture occur in the weld zone. Therefore, research into the welding quality judgment that can predict the defect and quality in real time is being actively conducted. In this study, the dynamic resistance of the weld was monitored using the secondary circuit process variables detected during resistance spot welding, and the factors necessary for the determination of the welding quality were extracted from the dynamic resistance pattern. The correlations between the extracted factors and the weld quality were analyzed and a regression analysis was carried out using highly correlated pendulums. Based on this research, a regression model that can be applied to the field was proposed.

• Journal of the Korean Institute of Gas
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• v.21 no.5
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• pp.70-76
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• 2017

The standards related to the "Urban Gas Business Act" and the "Safety Control and Business Regulation of Liquefied Petroleum Gas Act" prescribe the separation distance between gas piping joint excluding welded joints and electric equipments(electric switch, watt meter, breaker, connector, etc). The "Korea Electro technical Regulation" also prescribes the distance between gas piping joints and electric equipments in accordance with the gas related standards. In case of the standards related to the "Urban Gas Business Act", the distance criteria stipulated in the standard of supplying facilities are different from those stipulated in the standard of using facilities. In this study, we have conducted pilot test on the possible ignition distance from the piping joint when LP gas is leaked from the point. We have also examined the adequacy of current standards on the separation distance between gas piping joint and electric equipments. As a result of the tests, we have found that ignition is able to occur at a distance of 30 cm as stipulated in the current standards or more when LP gas is leaked from the joint of the pipe. Therefore, we have made a decision that the criteria for separation distance between gas piping joint and electric equipment specified in the current standards related to the "Urban Gas Business Act" and the "Safety Control and Business Regulation of Liquefied Petroleum Gas Act" is appropriate.