• Proceedings of the KSME Conference
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• 2004.04a
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• pp.72-77
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• 2004

In a primary reactor cooling system(RCS), a dissimilar weld zone exists between cast stainless steel(CF8M) in a pipe and low-alloy steel(SA508 cl.3) in a nozzle. Thermal aging is observed in CF8M as the RCS is exposed for a long period of time to a reactor operating temperature between 290 and $330^{\circ}C$, while no effect is observed in SA508 cl.3. The specimens are prepared by an artificially accelerated aging technique maintained for 300, 1800 and 3600 hrs at $430^{\circ}C$, respectively. The specimens for elastic-plastic fracture toughness tests are prepared one type, which notch is created in the heat affected zone(HAZ) of CF8M. And, the specimens for fatigue crack growth tests are prepared in three classes, which notches are created at the center of deposited zone, the HAZ of CF8M, and the HAZ of SA508 cl.3. From the experiments, the J-integral values with the increase of aging time decrease, and the differences of the fatigue crack growth behaviors are relatively small in the three classes specimens.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1109-1116
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• 2013

This study aims to investigate the spatial randomness of fatigue crack growth rate for the friction stir welded (FSWed) 7075-T651 aluminum alloy joints. Our previous fatigue crack growth test data are adopted in this investigation. To clearly understand the spatial randomness of fatigue crack growth rate, fatigue crack growth tests were conducted under constant stress intensity factor range (SIFR) control testing. The experimental data were analyzed for two different materials-base metal (BM) and weld metal (WM)-to investigate the effects of spatial randomness of fatigue crack growth rate and material properties, the friction stir welded (FSWed) 7075-T651 aluminum alloy joints, namely weld metal (WM) and base metal (BM). The results showed that the variability, as evaluated by Weibull statistical analysis, of the WM is higher than that of the BM.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.9
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• pp.1159-1168
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• 2013

In pressurized water nuclear reactors (PWRs), the reactor pressure vessel (RPV) upper head contains penetration nozzles that use a control rod drive mechanism (CRDM). The penetration nozzle uses J-groove weld geometry. Recently, the occurrence of cracking in alloy 600 CRDM penetration nozzle has increased. This is attributable to primary water stress corrosion cracking (PWSCC). PWSCC is known to be susceptible to the welding residual stress and operational stress. Generally, the tensile residual stress is the main factor contributing to crack growth. Therefore, this study investigates the effect on weld residual stress through different analysis methods for normal operating conditions using finite element analysis. In addition, this study also considers the effect of repeated normal operating condition cycles on the weld residual stress. Based on the analysis result, this paper presents a normal operating condition analysis method.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.12
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• pp.1317-1323
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• 2014

The aim of this paper is to investigate the effects of crack orientation on fatigue crack growth behavior in friction stir welded (FSWed) Al 7075-T651. Fatigue crack growth testing was conducted on compact tension (CT) specimens machined from the friction stir welds and the base metal under constant stress intensity factor range control. Tests were performed with the crack propagating nominally perpendicular to the weld line (termed the TL specimen) and the crack propagating in a parallel direction of the weld line (termed the LT specimen), and with three different constant stress intensity factor ranges. Both these specimen orientations were found to have a considerable effect on the fatigue crack growth behavior. Paris's law was adopted for the analysis of experimental results; the exponent m of the WM-LT specimen was determined to be 3.56, which was the largest value in this experimental conditions.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.10a
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• pp.263-268
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• 2001

The constant .DELTA. K fatigue tests are performed in SS41 and its weldment. The LASER ISDG method is used in determination of crack opening ratio. This method is more precise than indirect measurement method, faster and easier than other direct measurement method. And obtained results are followed 1) Crack opening ratio U is proportional to fatigue crack growth rate da/dN at constant .DELTA. K 2) Fatigue crack growth rate da/dN in weldment increases in weld metal and heat affected zone, decreases in base metal as crack grows.

• Journal of Welding and Joining
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• v.16 no.4
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• pp.47-54
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• 1998

Various equipments in plants are welded with two different materials and it is required to investigate the effects of fatigue crack propagation on the neighborhood of a welded portion. The characteristics of fatigue crack growth in the base metal of carbon and stainless steel, in the carbon and stainless steel sides located in the neighborhood of welded portion (carbon/stainless steel), respectively and welded portion, are investigated. The results show that the crack growth in the welded portion (carbon/stainless steel) is an average value of the crack growths in the carbon and stainless steel respectively located in the neighborhood of the welded portion. It is found that the crack growth in the welded portion is not significantly different from those in the carbon and stainless steel sides. Hence it can be concluded that the structure welded with two different materials wold not impede the integrity based on the fatigue crack growth.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1317-1321
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• 2007

Aluminized steel sheet that Al coated on low carbon steel has a excellent heat resistance, thermal reflection and corrosion resistance. It has applied to fuel tank, automotive exhaust systems, etc. Laser weldability of the aluminized steel for the full penetration welding will be described in this paper. We focused on the effect of Al coating conditions on weld strength. For these objectives, aluminized steel sheets that has various thickness and coating weight were prepared for laser welding. And then, tensile-shear and hardness test were carried out. At that same time, Al content mixed in weld after laser welding was evaluated and investigated a correlation between the mixed Al and mechanical properties. Besides, as removing partially coating layer, weldability has been investigated according to position of coating layer. As a result of this study, as increasing Al content in weld, tensile-shear strength was decreased. Also it was identified that Al of coating layer caused grain growth.

• Journal of Ocean Engineering and Technology
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• v.26 no.1
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• pp.64-69
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• 2012

Dissimilar friction welds were produced using 15-mm diameter solid bars of chrome molybdenum steel (KS SCM440) and carbon steel (KS SM20C) to investigate their mechanical properties. The main friction welding parameters were selected to ensure good quality welds on the basis of visual examination, tensile tests, Vickers hardness surveys of the bond area and HAZ, and macro-structure investigations. The specimens were tested as-welded and post-weld heat treated (PWHT). The tensile strength of the friction welded steel bars was increased to 100% of the SM20C base metal under the condition of a heating time of more than four seconds. Optimal welding conditions were n = 2,000 (rpm), HP = 60 (MPa), UP = 100 (MPa), HT = 5 (s),and UT = 5 (s), when the total upset length was 7.8 (mm). The hardness distribution peak of the friction welded joints could be eliminated using PWHT. The two different kinds of materials were strongly mixed to show a well-combined structure of macro-particles, with no molten material, particle growth, or defects.

• Journal of Welding and Joining
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• v.14 no.4
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• pp.33-42
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• 1996

In recent years there has been a significant growth in the use of the automated and/or robotic welding system, carried out as a means of improving productivity and quality, reducing product costs and removing the operator from tedious and potentially hazardous environments. One of the major difficulties with the automated and/or robotic welding process is the inherent lack of mathematical models for determination of suitable welding process parameters. Partial-penetration, single-pass bead-on-plate welds were fabricated in 12mm AS 1204 mild steel flats employing five different welding process parameters. The experimental results were used to develop three empirical equations: curvilinear; polynomial; and linear equations. The results were also employed to find the best mathematical equation under weld bend width to assist in the process control algorithms for the Gas Metal Arc Welding(GMAW) process and to correlate welding process parameters with weld bead width of bead-on-plates deposited. With the help of a standard statistical package program. SAS, multipe regression analysis was undertaken for investigating and modeling the GMAW process, and significance test techniques were applied for the interpretation of the experimental data.

• Journal of Welding and Joining
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• v.7 no.1
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• pp.42-50
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• 1989

The application of fracture mechanics is being increased gradually to assess the safety of welded structures containing crack. Fatigue crack propagation behavior and elastic-plastic fracture toughness J$_{IC}$ of home made flux cored wire(1.22mm) CO$_{2}$ weldments was discussed. Especially fatigue crack propagation test was carried out by .DELTA.K control instead of load control and elastic-plastic fracture toughness J$_{IC}$ was obtained by ASTM-R curve method on C.T.specimen in transverse direction of weldments. The results obtained are as follows; (1) Weld metal presented an almost complete similarity to base metal on fatigue crack propagation rate in transverse direction. (2) Weld metal was more than base metal on J$_{IC}$ value in transverse direction. (3) F.C.W. CO$_{2}$ weldments had an excellent characteristic of fatigue crack propagation rate and J$_{IC}$ in less than 50kg/mm$^{2}$ steel grade, this would result from that weld metal had good static strength.trength.