• Journal of Welding and Joining
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• v.33 no.1
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• pp.87-93
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• 2015

This study was performed to develop repair technology for J-Groove dissimilar metal weld of pressurizer heater sleeve in nuclear power plants. Pad, J-Groove automatic welding and mechanical machining equipments to develop repair technology using 'Half Nozzle Repair' were designed and manufactured. To obtain the optimum welding process parameters during Pad temperbead overlay welding, several welding experiments using Taguchi method were conducted. Weldability of Pad overlay weld specimens was estimated by PT/RT test, FE-SEM, EDS and Vickers hardness test. Also, J-Groove welding to adjust weld shape conditions requiring in ASME Code was carried out and its integrity of weld specimens was evaluated through PT/RT test and optical microscope. Consequently, it was revealed that Pad and J-Groove overlay welding for dissimilar metal weld of pressurizer heater sleeve could be possible to meet Code standard without weld defect.

• Journal of Welding and Joining
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• v.29 no.5
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• pp.63-71
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• 2011

Three-dimensional finite element analysis is performed to study the temperature distribution phenomenon of TIG assisted friction stir welding (TAFSW) between dissimilar plates (Al 6061-T6 and stainless steel 304). TAFSW is a solid-state welding process that integrates TIG (Tungsten Inert Gas) into a friction stir welding (FSW), to preheat the harder material ahead of FSW tool during welding. In order to facilitate the industrial application of welding, 3D numerical modeling of heat transfer has been carried out applying Finite Element Method (FEM). The temperature distribution due to heat generation during TAFSW on dissimilar materials joint is analysed using in-house solver. Moving heat source along with frictional heat between the work specimens and tool surface is considered to calculate the heat input. The analytical model used predicts successfully the maximum welding temperatures that occur on the dissimilar materials during TAFSW. Comparison with the infra red camera and thermocouple measurement results shows that the results from the current numerical simulation have good agreement with the measured data.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.64-71
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• 2011

In this paper, crack propagation analyses in the inner diameter (ID) repair weld of the dissimilar metal weldment of a nozzle were performed using a finite element alternating method (FEAM). To calculate the theoretical solution for the crack tip stress intensity factor, a weak type singular integral equation consisted of crack surface traction and dislocation density function was constructed and solved in conjunction with the FEAM. A two-dimensional axisymmetric finite element nozzle model was prepared and ID repair welding was simulated. An initial crack, 10% depth of weld thickness, was assumed and crack propagation trajectory from the initial crack to the 75% depth of thickness was calculated using the FEAM. Crack growth versus time curve was also calculated and compared with the curves obtained from ASME code method. With the method constructed in this paper, crack propagation trajectory and crack growth time were calculated automatically and effectively.

• Journal of Welding and Joining
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• v.35 no.2
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• pp.35-42
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• 2017

The GMA welding process involves large number of interdependent variables which may affect product quality, productivity and cost effectiveness. The relationships between process parameters for a vertical weldment and mechanical properties are complex because a number of process parameters are involved. To make the vertical-position welding, a method that predicts bead geometry and accomplishes the desired mechanical properties of the weldment should be developed. In addition, a reliable welding process and conditions must be implemented to reduce weld structure failure. In this study, the welding process analysis of investigates the interaction between the heat input and welding parameter(Welding current, Arc voltage, Welding speed) for predicting the weldment hardness.

• Journal of Ocean Engineering and Technology
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• v.19 no.1 s.62
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• pp.44-48
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• 2005

The shock absorbers for marine vehicles are very important components to absorbing the shock resulting from driving. Depending on the kinds of vehicles, these essential components, piston and piston rod, must be made of S25C, S45C, and SCM440, must be precisely machined, and assembled by the bolts. Other materials used have been difficult to weld, and could be unstable in quality, by the conventional arc welding. Also, they have been associated with a lot of technical problems in manufacturing. However, using the friction welding technique, such problems will be avoided. These factors have necessitated the domestic development of the marine shock absorber using a friction welding, as well as stimulating a new approach to the study of real-time weld quality evaluation by AE techniques.

• Journal of Power System Engineering
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• v.6 no.1
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• pp.68-73
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• 2002

An opportunity to use the elevated temperature has been recently increasing in various elements of heat facilities or machines such as heat exchanger tubes, pressure vessels, engines of aircraft, boilers and turbines in power plants, and nuclear reactor components, etc. as machinery industry develops. Thus, the development of such elevated-temperature heat-resisting materials and the studies on their elevated-temperature materials friction welding, creep design and analysis have been considered as an important and needful fact. In this paper, friction welding optimization for 1Cr0.5Mo to STS304 and AE applications for the weld quality evaluation were investigated. The important results of this study are as follows : The techniques for dissimilar friction welding optimization of the elevated temperature materials 1Cr0.5Mo and STS304 and its real-time weld quality evaluation by AE were developed, considering on both strength and toughness. Quantitative relationship was identified among welding condition, weld quality and cumulative AE counts.

• 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.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.73-78
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• 2008

The paper presents the characteristics of mechanical properties within the heat affected zone (HAZ) of dissimilar metal weld between SA508 Gr.1a and F316 stainless steel (SS) with Alloy 82/182 filler metal. Tensile tests were performed using small-size specimens taken from the HAZ regions close to both fusion lines of weld, and the micro-structures were examined using optical microscope (OM) and transmission microscope (TEM). The results showed that significant gradients of the yield stress (YS), ultimate tensile stress (UTS), and elongations were observed within the HAZ of SA508 Gr.1a. This was attributed to the different microstructures within the HAZ. In the HAZ of F316 SS, however, the welding effect dominated the YS and elongation rather than UTS, and TEM micrographs conformed the strengthening in the HAZ of F316 SS was associated with a dislocation-induced strain hardening.

• Journal of Welding and Joining
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• v.18 no.1
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• pp.59-69
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• 2000

The purpose of the present study was to investigate weld metallurgical phenomena such as primary solidification mode, microstructural evolution and hot cracking susceptibility in nitrogen-bearing austenitic stainless steel GTA welds. Eight experimental heats varying nitrogen content from 0.007 to 0.23 wt.% were used in this study. Autogenous GTA welding was performed on weld coupons and the primary solidification mode and their microstructural characteristics were investigated from the fusion welds. Varestraint test was employed to evaluate the solidification cracking susceptibility of the heats and TCL(Total Crack Length) was used as cracking susceptibility index. The solidification mode shifted from primary ferrite to primary austenite with an increase in nitrogen content. Retained delta ferrite exhibited a variety of morphology as nitrogen content varied. The weld fusion zone exhibited duplex structure(austenite+ferrite) at nitrogen contents less than 0.10 wt.% but fully austenitic structure at nitrogen contents more than 0.20 wt.%. The weld fusion zone in alloys with about 0.15 wt.% nitrogen experienced primary austenite + primary ferrite solidification (mode AF) and contained delta ferrite less than 1% at room temperature. Regarding to solidification cracking susceptibility, the welds with fully austenitic structure exhibited high cracking susceptibility while those with duplex structure low susceptibility. The cracking susceptibility increased slowly with an increase in nitrogen content up to 0.20 wt.% but sharply as nitrogen content exceeded 0.20 wt.%, which was attributed to solidification mode shift fro primary ferrite to primary austenite single phase solidification.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.1
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• pp.22-28
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• 2013

Robotic GMA (Gas Metal Arc) welding process is one of widely acceptable metal joining process. The heat and mass inputs are coupled and transferred by the weld arc to the molten weld pool and by the molten metal that is being transferred to the weld pool. The amount and distribution of the input energy are basically controlled by the obvious and careful choices of welding process parameters in order to accomplish the optimal bead geometry and the desired quality of the weldment. To make effective use of automated and robotic GMA welding, it is imperative to predict online faults for bead geometry and welding quality with respect to welding parameters, applicable to all welding positions and covering a wide range of material thickness. MD (Mahalanobis Distance) technique was employed for investigating and modeling the GMA welding process and significance test techniques were applied for the interpretation of the experimental data. To successfully accomplish this objective, two sets of experiment were performed with different welding parameters; the welded samples from SM 490A steel flats. First, a set of weldments without any faults were generated in a number of repeated sessions in order to be used as references. The experimental results of current and voltage waveforms were used to predict the magnitude of bead geometry and welding quality, and to establish the relationships between weld process parameters and online welding faults. Statistical models developed from experimental results which can be used to quantify the welding quality with respect to process parameters in order to achieve the desired bead geometry based on weld quality criteria.