• Journal of Welding and Joining
• /
• v.10 no.2
• /
• pp.51-62
• /
• 1992

A torch was designed and fabricated in order to develope the technology of "locally drying underwater welding" by water curtain method. The condition for the formation of the possible local cavity, the mechanical properties and the thermal cycle of welds were investigated in the developed welding equipment compared with in-air welding. The possibility of highly reliable and practical underwater welding was found. The proper local cavity was formed above the water flowrate of 30l/min and CO$_{2}$ gas flowrate of 100l/min. The bead width and penetration depth were increased with increasing welding current. The hardness of weldments is about 160Hv in air welding, but about 210Hv in underwater welding. The elongation and the impact value of underwater weldments are 15% and 6Kg/cm$^{2}$ respectively, which are only half as much as the values of in-air welding. The cooling time in the temperature range from 800.deg.C to 500.deg.C affecting the structure and the hardness of weldments is about 22sec. in air welding while about 10sec. in underwater welding.r welding.

• Proceedings of the KWS Conference
• /
• 2003.11a
• /
• pp.150-152
• /
• 2003

This simulation was carried out to estimate the process time and to improve the operation efficiency. The subassembly process consists of piece arrangement, tack welding, robot welding, manual welding and the robot welding of them was the focus of the simulation. Robot welding stage was analyzed by UML and IDEFø method, and then it was represented as the three-dimensional model(simulator) based on the analysis. The output of this simulation was the cycle time for one day's work. The cycle time for the different torch and the different piece arrangement was investigated by the 3-dimensional simulation.

• Journal of Welding and Joining
• /
• v.28 no.4
• /
• pp.18-25
• /
• 2010

Super-duplex stainless steels (SDSS) have a good balance of mechanical property and corrosion resistance when they consist of approximately equal amount of austenite and ferrite. The SDSS needs to avoid the detrimental phases such as sigma(${\sigma}$), chi(${\chi}$), secondary austenite(${\gamma}2$), chromium carbide & nitride and to maintain the ratio of ferrite & austenite phase as well known. However, the effects of the subsequent weld thermal cycle were seldom experimentally studied on the micro-structural variation of weldment & pitting corrosion property. Therefore, the present study investigated the effect of the subsequent thermal cycle on the change of weld microstructure and pitting corrosion property at $40^{\circ}C$. The thermal history of root side was measured experimentally and the change of microstructure of weld root & the weight loss by pitting corrosion test were observed as a function of the thermal cycle of each weld layer. The ferrite contents of root weld were reduced with the subsequent weld thermal cycles. The pitting corrosion was occurred in the weld root region in case of the all pitted specimen & in the middle weld layer in some cases. And the weight loss by pitting corrosion was increased in proportional to the time exposed at high temperature of the root weld and also by the decrease of ferrite content. The subsequent weld thermal cycles destroy the phase balance of ferrite & austenite at the root weld. Conclusively, It is thought that as the more subsequent welds were added, the more the phase balance of ferrite & austenite was deviated from equality, therefore the pitting corrosion property was deteriorated by galvanic effect of the two phases and the increase of 2nd phases & grain boundary energy.

• Nuclear Engineering and Technology
• /
• v.52 no.8
• /
• pp.1724-1731
• /
• 2020

Low cycle fatigue tests on the hydrogenated welding seam of Zr-Sn-Nb alloy at room temperature and 360 ℃ had been carried out by using the funnel-shaped flat specimens. The relationships between nominal stress & strain directly measured across the funnel and local stress & strain at the root of the funnel are given by considering cyclic plasticity correction. The results show that the fatigue resistance of welding seam at room temperature is only slightly better than that at 360 ℃. Probabilistic fatigue life curves are obtained by using a two-parameter power function.

• Journal of Welding and Joining
• /
• v.21 no.5
• /
• pp.561-567
• /
• 2003

For construction of I-beam steel structures, a fillet welding is one of the main manufacturing process. However, this welding process cause some problems associated with welding residual stress and welding deformation that are harmful to the safety of structures. Accordingly, this study clarified the creation mechanism of the welding deformation on I-beam steel structure from the experimental results given by the FEM method. To prevent or minimize the longitudinal bending deformation, first of all, a field supervision is necessary to observe the optimal groove design. Secondly, the welding order for cooling weld zone is needed.

• Journal of the Korean Society of Safety
• /
• v.8 no.1
• /
• pp.59-63
• /
• 1993

It is very difficult to find not only optimized welding condition but also fatigue characteristics of the dissimilar weld. In this study. Low carbon steel (SS41) and austenitic stainless steel (STS304) were welded by GTAW welding with STS309 stainless wire rod and Single Edge Notch specimens were used for the examination of fatigue behavior on welding heat cycle. The fatigue crack growth rate in HAZ of SS41 was the highest. The second was in STS304 bond line and the lowest was in HAS of STS304.

• Journal of the Korean Society for Heat Treatment
• /
• v.16 no.3
• /
• pp.141-147
• /
• 2003

The effects of heat treatment on the fatigue life and welding residual stress of welded plates were investigated in this study. The plates were welded by flux cored arc welding process, and post weld heat treated at $600^{\circ}C$ for 1 hour. The residual stresses of welded plates before and after post weld heat treatment were measured by hole drilling method. To measure the fatigue life of welded plates, low cycle fatigue tests under strain control and high cycle fatigue tests under load control were performed respectively, by using cylindrical specimens containing weld metal and heat affected zone. The obtained result shows that the post weld heat treatment reduces the residual stress, and resultantly changes the fatigue life of welded plate. Goodman diagrammatic analysis has also been performed to study the effect of post weld heat treatment on the high cycle fatigue life.

• Progress in Superconductivity and Cryogenics
• /
• v.25 no.4
• /
• pp.28-31
• /
• 2023

This study presents a comprehensive procedure for the low cycle fatigue test of ultrasonically welded (UW) coated conductor (CC) lap-joints. The entire process is examined in detail, from the robust fabrication of the UW REBCO CC joints to the reliability testing under a low number of repeated cycle fatigue conditions. A continuous I_c measurement system enables real-time monitoring of I_c variations throughout the fatigue tests. The study aims to provide a step-by-step procedure that involves joint fabrication, electromechanical property (EMP) tests under uniaxial tension for stress level determination, and subsequent low-cycle fatigue tests. The joints are fabricated using a hybrid method that combines UW with adding In-Sn soldering, achieving a flux-free hybrid welding approach (UW-HW flux-free). The selected conditions for the low cycle fatigue tests include a stress ratio of R=0.1 and a frequency of 0.02 Hz. The results reveal some insights into the fatigue behavior, irreversible changes, and cumulative damage in the CC joints.

• Transactions of the Korean Society of Machine Tool Engineers
• /
• v.12 no.1
• /
• pp.32-37
• /
• 2003

Evaluation of fatigue strength on the spot welded part is very important for strength design of spot welded steel structures. In this paper, we could get the life cycle of the spot welded part using the lethargy coefficient obtained through the quasi-static tensile shear test for the specimen welded by current 10kA. The reliability evaluation of the life cycle is completed by comparing the life cycle calculated under the constant loading rate with the life cycle obtained by dynamic fatigue test. And then the result calculated by the lethargy coefficient is verified through the lift cycle calculated using the dynamic final tensile stress formula under the increased loading speed. This way can make save the time and cost in processing of predicting the life cycle of a structure.

• Journal of Welding and Joining
• /
• v.8 no.4
• /
• pp.46-57
• /
• 1990

TMCP steel manufactured by controlled rolling followed by accelerated cooling process is known to have extra-ordinary mechanical properties such as tensile strength and toughness. However, there is much uncertainty about the fatigue fracture characteristics, especially, in the welded state of this steel. In case of this steel, the softening zone by welding is generated in heat affected zone in contrast with the case of conventional normalized high strength steel. This softening zone is considered to play significant roles in low cycle fatigue fracture of the welded part of this steel. In this paper, the low cycle fatigue behaviors of TMCP steel were inspected in as-received and welded state using the smooth specimen. The fatigue life-time was seperately investigated on the basis of failure of the specimen and crack initiation which is detected by differential strain method. Moreover, the low cycle fatigue characteristics of TMCP steel were quantitatively compared with those of the conventional normalized steel of same strength level.