• Proceedings of the KSME Conference
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• 2004.11a
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• pp.348-352
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• 2004

In finite element analysis of mechanical behavior of weld, typical process is first to obtain a finite element model containing residual stress by conducting welding analysis and then to examine the computational specimen for various external loading. The numerical specimen with residual stress has irregular boundary lines since one usually begins the welding analysis from a body having regular straight boundary lines and large thermal contraction takes place during cooling of weld metal. We notice that these numerical weld specimens are different from the real weld specimens as the real specimens are usually cut from a bigger weld part and consequently have straight boundaries neglecting elastic relaxation associated with the cutting. In this paper, an iterative finite element method is described to obtain a weld specimen which is bounded by straight lines. The stress distributions of two types of weld specimen, one with regular and the other with irregular boundaries, are compared to check the effect of the boundary shape. Results show that the stress distribution can be different when large plastic deformation is induced by the application of external loading. In case of elastic small deformation, the difference turns out almost negligible.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.10a
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• pp.668-671
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• 1995

In this study, the fatigue charateristics of weld specimen was studied experimentally by using the various specimen types. The specimen type were tensile shesr(TS) specimen, cross tension(CT) specimen, and T typr (TT) specimen. Tensile test and fatigue test were carried out and microstucture was investigated. Finite element method was used to investigate stress distribution near nugget edge. Finally fracture mechanics approach was tried to the various specimen types.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.485-488
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• 2000

In this study, the fatigue characteristic of spot weld specimen was studied by using the various specimen. The specimen types were tensile shear specimen welded one spot and two spot, and cross tension. The tensile tests and fatigue tests were executed to know the mechanical properties under static and fatigue load condition. In addition, the relationship was illustrated by finite element method.

• Korean Journal of Metals and Materials
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• v.50 no.4
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• pp.280-284
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• 2012

In this study, we prepared a sample of AISI 409L weld metals using automotive exhaust manifolds and evaluated their corrosion properties by conducting an anodic polarization test after 10 minute of heat treatment at $900^{\circ}C$. The specimens of AISI 409L transformed fully ferrite. Weld metal was refined more than base metal. Specimen of heat treatment at $900^{\circ}C$ and as weld specimen was formed precipitation. However heat treatment specimen was bulkly formed and coarser than the as weld specimen. The strength measured by 10 Hv highly at heat treatment specimens in comparison with as weld. The increase in strength is attributed to the precipitation of Ti. The result of heat treatment suggest that there was a decrease of current density and high corrosion potential. Following heat treatment process produced Ti precipitation and for this reason, it can restrain Cr-carbide so that steel will have more corrosion resistance.

• Proceedings of the KWS Conference
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• 2003.05a
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• pp.263-265
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• 2003

The transverse crack, a type of cold crack, occurs perpendicular to the axis of the weld interface, longitudinal residual stresses ($\sigma$k direction) are more important in transverse crack occurrence from my own experience. Specimens were fabricated and welded under actual construction conditions, and then residual stresses of longitudinal stresses were measured for different welding conditions with SAW and FCAW process. The residual stress values for the specimen welded Interpass temperature below 30$^{\circ}C$ was higher than the specimen welded interpass temperature of 100～120$^{\circ}C$. And also the residual stress values for a specimen measured at weld surface, as welded condition, was higher than that of longitudinal residual stresses that was measured from a small test piece, due to the residual stress was relieved in the process of the cutting and machining. Transverse weld cracks were detected in the area of the maximum residual stresses both SAW and FCAW process.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.67-72
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• 2008

The objective of this study is to design a laboratory specimen for simulating residual stress of circumferential butt welding of pipe. Specimen type and method for residual stress generation were proposed based on the review of prior studies and parametric finite element simulation. To prove the proposed specimen type and loading method, the residual stress was generated using the designed specimen by applying proposed method and was measured. The measured residual stress using X-ray diffraction reasonably agreed with the results of finite element simulation considered in the specimen design. Comparison of residual strains measured at several locations of specimen and given by finite element simulation also showed good agreement. Therefore, it is indicated that the designed specimen can reasonably simulate the residual stress of circumferential butt welding of pipe.

• Journal of the Korean Society of Safety
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• v.24 no.1
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• pp.7-13
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• 2009

The objective of this study is to design a laboratory specimen for simulating residual stress of circumferential butt welding between pipes. Specimen type and method to generate residual stress were proposed based on the review of prior studies and parametric finite element analysis. To prove the proposed specimen type and loading method, the residual stress was generated using the designed specimen by applying proposed method and was measured. The measured residual stress using X-ray diffraction reasonably agreed with the results of finite element analysis considered in the specimen design. Comparison of residual strains measured at several locations on the specimen and given by finite element simulation also showed good agreement. Therefore, it is indicated that the designed specimen in this study can reasonably simulate the axial residual stress of a circumferential butt welding of pipe.

• Journal of the Korean Society for Railway
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• v.7 no.4
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• pp.345-349
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• 2004

This study investigates the fatigue lives of SM490A material(base metal) specimens and fillet weld specimens, which are made same material and weld method for the railway vehicle. These fatigue lives have a difference, the fatigue lives of weld specimen are shorter than those of base metal. We measured the strains on the weld positions of the specimens during the fatigue test for investigation of crack initiation and crack growth. In these result, we could find the information of the crack initiation position on weld bead and the history of crack growth. Also we knew that the fatigue crack initiation cycles and the changes of the strain which were affected the fractured surface roughness and morphology.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.71-77
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• 2010

This paper was studied on microstructure, mechanical properties and corrosion characteristics of 316L stainless steel pipe welds was fabricated by orbital welding process. S-Ar specimen was fabricated by using Ar purge gas and S-$N_2$ specimen was fabricated by using $N_2$ purge gas. Ferrite was not detected in weld metal of S-$N_2$ specimen but the order of 0.13 Ferrite number(FN) was detected in weld metal of S-Ar specimen. Oxygen and Nitrogen concentration of S-$N_2$ specimen was higher than S-Ar specimen on HAZ and inner bead. The welds microstructural characteristics of S-Ar and S-$N_2$ specimens are similar. The microvickers hardness values of S-Ar and S-$N_2$ specimens welds were similar and average values of each regions were in the range of 174~194. The microstructures of S-Ar and S-$N_2$ weld metal were full austenite by primary austenite solidification. The Solidification structures of S-Ar and S-$N_2$ weld metal were formed directional dendrite toward bead center. The potentiodynamic polarization curve of STS 316L pipe welds exhibited typical active, passive, transpassive behaviour. Corrosion current density$(I_{corr.})$ and corrosion rate values of S-Ar specimen in 0.1M HCl solution were $0.95{\mu}A/cm^2$ and $0.31{\mu}A$/year respectively. The values of S-$N_2$ specimen were $1.4{\mu}A/cm^2$ and $0.45{\mu}m$/year.

• Proceedings of the KSME Conference
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• 2005.11a
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• pp.124.2-124.2
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• 2005