• Journal of the Korean Society for Precision Engineering
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• v.33 no.4
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• pp.257-264
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• 2016

Solid state joining techniques are increasingly applied in a wide range of industrial applications. Friction welding is a solid state welding technique that is used to join similar or dissimilar materials. In this study, friction welding was applied to rotor shaft composed of a disk and a shaft. The disk and shaft were manufactured by hot forging and rolling, respectively. The aim of the study was to predict the structural characteristics during hot forging and friction welding process for rotor shaft of turbo charger. The structural characteristics were determined by heat input and heat affected zone (HAZ) during a short cycle time. Thus, transient FE analysis for hot forging and friction welding was based on heat transfer. The results were used to predict structural characteristics during hot forging and friction welding processes. The prototype of rotor shaft was manufactured by the result-based process parameters.

• Journal of Advanced Marine Engineering and Technology
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• v.11 no.2
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• pp.71-81
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• 1987

Nowadays, the high development of industrial technique demands the optimal design of marine structures to be welded under the water, because the underwater welding of the ship hull and marine structures can decrease manpower and cost of production. However there is not available at present any report on fatigue behavior about underwater welded joints. In this paper under tention- tension repeated fatigue stress with frequency of 10 cycles per second by local controlled system, the fatigue strength properties of underwater welded joints of SM41A-2 Plate-to-Plate of 10 mm thickness were experimentally examined. The results obtained were as follows : 1) The fatigue strength of underwater welded joints of SM41A-2 was peaked at the heat input of about 1, 400 joule/mm(180 A, 36 V), while, at the heat input of more than about 1, 100 joule/mm (160 A, 33 V) that of the underwater welds at the higher than cycle of life rather than the lower cycle was higher than that of the base metal but lower than that of the atmosphere welds on account of both cooling and notch effects. 2) The fatigue limit of underwater welds increased with an increase of heat input resulting in a peak of that at the heat input of about 1, 400 joule/mm and then decreased gradually. 3) The fatigue strength at N cycles was peaked between the heat input of about 1, 400 and 1, 700 joule/mm where the strain was rapidly increased. 4) It was confirmed that the optimal zone of heat input condition for obtaining the underwater welds fatigue strength higher than that of the base metal exists, and if out of this zone, the fatigue strength of the underwater welds was lower than that of the base metal because of lack weld penetration, inclusion of slag, voids, etc. 5) By the fatigue test, the underwater welds fractured brittly without visual deformation, so the strain was remarkably less than of the atmosphere welds. 6) The fatigue life factor was peaked at the heat input of about 1, 600 joule/mm (200 A, 36 V) at which the mean strain is a little higher than that of the base metal but quite lower than those of the atmosphere welds, resulting in good underwater welds because both fatigue strength and ductility of the underwater welds are higher than those of the base metal at such heat input.

• Tunnel and Underground Space
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• v.22 no.3
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• pp.221-225
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• 2012

Magnesium is one of the light weight materials, which can improve fuel economy and reduce emissions in automotive industry. Recently, magnesium alloys have gained considerable attention due to good mechanical properties. In this work, we have performed an explosive welding using the magnesium alloys (AZ31) and stainless steel (SUS 304). As a result, SUS304/AZ31 were successfully combined each other; however, a resolidified interlayer was observed at the point of welded layer. To reduce the resolidified interlayer, we have changed the thickness (0.5 mm and 1 mm) of stainless steel, distance (45 mm and 60 mm) between explosive and the center of materials and initial angle ($20^{\circ}$ and $30^{\circ}$) of explosive. In the case of the thickness 0.5 mm and angle of $30^{\circ}$, the resolidfied interlayer was not observed due to the increase of distance from the explosive. To accurately estimate the resolidified interlayer, electron probe micro-analyzer (EPMA) method and hardness were used. For the EPMA analysis, mixed materials were confirmed at the resolidified interlayer, and the measurement exhibited the middle value compared with the AZ31 and SUS304.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1116-1120
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• 2004

In the nuclear power plant, there are several cylindrical vessels such as reactor vessel, pressuriser and so on. The vessels are usually constructed by welding large rolled plates, forged sections or nozzle pipes together. In order to assure the integrity of the vessel, these welds should be periodically inspected using sensors such as ultrasonic transducer or visual cameras. This inspection is usually conducted under water to minimize exposure to the radioactively contaminated vessel walls. The inspections have been performed by using a conventional inspection machine with a big structural sturdy column, however, it is so huge and heavy that maintenance and handling of the machine are extremely difficult. It requires much effort to transport the system to the site and also requires continuous use of the utility's polar crane to move the manipulator into the building and then onto the vessel. Setup beside the vessel requires a large volume of work preparation area and several shifts to complete. In order to resolve these problems, we have developed an underwater mobile robot guided by the laser pointer, and performed a series of experiments both in the mockup and in the real reactor vessel. This paper introduces our robotic inspection system and the laser guidance of the mobile robot as well as the results of the functional test.

• Journal of Ship and Ocean Technology
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• v.1 no.1
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• pp.26-34
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• 1997

Under water wet welding is an economically alternative for the repair of offshore structures. In this paper investigations on the fatigue strength of a wet welded pipe structural member have been reported. For the connection a special sleeve patch design has been developed. The joint was fatigue tested. The evaluation of the test was carried out by means of the hot-spot approach with regard to several extrapolation rules of the hot-spot stress. Obtained results have been compared to actual classfication rules and recommendations.

• Journal of Ocean Engineering and Technology
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• v.5 no.1
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• pp.81-87
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• 1991

In this paper, an attempt has been taken for improving the weldability of wer welds of TMCP steel plate by shielding around weld arc surroundings. The principal results of this experimental investigation can be summarized as follows: 1) The cooling rates resulting from wet wlds with the developed electrode on TMCP steel plate could be lower than that of the non-shieled wet welds. 2) The metallurgical characteristics in umderwater wet welds of TMCP steel plate and the developed electrode could be improved by shielding around weld arc surroundings.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2001.05a
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• pp.139-143
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• 2001

Ring-stiffened cylinders are widely used as the pressure hull of submarines and underwater vehicles. For large ring-stiffened cylinders cylindrical shells are fbricated by cold rolling of flat plates and then welding of curved shells. After forming cylinders ring-stiffeners are welded on th the cylinders. Due to these cold roiling and welding initial shape imperfections and residual stresses exists in fabricated ring-stiffened cylinders. It is well known that the initial shape and material imperfections affect the ultimate strength of ring-stiffened cylinders significantly. In this paper previous researches on the effects of initial shape imperfections and residual stresses are briefly reviewed Recently a numerical analysis computer program was developed to predict the ultimate strength of ring-stiffened cylinders subjected to hydrostatic pressure, which is based on the Dynamic Relaxation technique. This program was employed to numerically investigate those effects. The numerical predictions were substantiated with relevant experimental results.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.281-284
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• 2006

After building a ship in a shipyard, there are so many repeated inspection of welding seam defects and painting status before delivering to the ship's owner. An inspection on the bottom part of a ship in commercial service should be done in every two years for the purpose of safety and for the prevention of ship speed deterioration. conventional welding seam inspection systems are rely on the visual inspection by human or the ultrasonic inspection for the selective part of a ship. This paper suggests a remote controlled inspection system for the examination of large ships or steel structures. The proposed system moves in contact with the ship under inspection and have a CCD camera to provide visual-guidance information to a remotely located human worker. Additionally this system utilizes a weld line tracking algorithm for an optimal position control. We verified the effectiveness of the inspection system by experimental data.

• Journal of the Korea institute for structural maintenance and inspection
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• v.23 no.2
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• pp.44-50
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• 2019

The underwater structures of landing pier are not easy to access and it is difficult to check the damage. Lately, typhoons and earthquakes have occurred frequently, which may cause damage to underwater structures of landing pier. In this study, to prevent collapse of underwater structures and to maintain systematically, the application method of FBG sensors and safety evaluation methods were studied. In order to confirm the application of the FBG sensor to the circular steel pipe used as a pile on the landing pier, we conducted laboratory tests and confirmed that the FBG sensor should be applied by welding. As a result of structural analysis of the landing pier structure, the optimal position of FBG sensor confirmed. The stresses on the dead load were calculated by structural analysis, the stresses on the live load were calculated by using the data obtained from the FBG sensor, and then the stress acting on the pile was calculated by adding the two stresses. The calculated stress was compared with the allowable stress to evaluate the safety of the pile. This study was carried out as a basic study to find a way to evaluate the safety of the landing pier in real time.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.3-5
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• 2005

Explosion Bulge Test has been carried out in order to evaluate base metal and weldment of high strength steels which used for submarine and aircraft carrier. High strength steels such as DS80/100/130 and PFS80/100 were developed by ADD and POSCO. In future, these materials will be used for the construction of larger submarine and aircraft carrier, and EBT is necessary to certificate hull materials for these. EBT methode in air and underwater was developed by ADD, and this report described the test procedure of EBT and the results of EBT for high strength steels.