• Journal of Power System Engineering
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• v.11 no.3
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• pp.41-46
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• 2007

The microstructure and electrochemical analysis of welds of electric resistance welding(ERW) pipe were investigated. The direction of metal flow line in HAZ of ERW pipe shifted to the inner(or outer) surface of pipe by plastic deformation during welding. The lowest heat input welds of ERW pipe was showed crack by liquid penetrant testing. Accelerated corrosion test by constant current density of 20mA/$cm^{2}$ developed groove at the welds of ERW pipe and the measured grooving factors were about $1.2{\sim}1.5$. Corrosion potential of base metal obtained by cyclic polarization in artificial sea water(3.5wt.% NaCl solution) was 100mV higher than that of weld metal of ERW pipe.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.10 no.1
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• pp.94-100
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• 2001

Distortion is a potential problem with all welded fabrication and should be caused dimensional changes and mismatch of joints during welding fabrication. Correction unacceptable weld distortion is extremely costly and in some case impossible. The aim of the present work is to verify the variation of the compressive force, tensile force and distortion during plastic deformation under Tungsten-inert-gas(TIG) welding, on type 304 stainless steel. Experimental results show that possibili-ty if measuring deformation during welding and good correlation was found between analytical and experimental result ad finite element methods have been used to model temperature analysis.

• Proceedings of the Korean Society of Laser Processing Conference
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• 1999.05a
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• pp.29-32
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• 1999

The material properties of laser welding zone such as strength coefficient, work-hardening exponent, and plastic anisotropic ratio are analytically obtained from those of base metals based on the tensile tests. . The finite element formulation is developed for predicting strain distributions and weld line movements in the forming processes of laser welded blank. The welding zone(WZ) is modelled with the several, narrow finite elements whose material characteristics are based on the experimental results and the analytical equations. In order to show an application of the developed weld element the stamping process of auto-body door inner panel is simulated. FEM predictions are compared and showed good agreements with experimental observations.

• Journal of Welding and Joining
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• v.22 no.2
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• pp.51-58
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• 2004

Residual stresses, which can be produced during the welding process, play an important role in an industrial field. Welding residual stresses are exerting negative effect on the fatigue behavior and integrity of structure. In this study, as a result of the thermal elasto-plastic finite element analysis for the welds of a nuclear component, the residual stress distributions are estimated for as-welded condition. Also, finite element techniques are developed to simulate the relaxation of the residual stresses according to the various mechanical stress relieving(MSR) loads such as hydrostatic pressure loading, tensile pipe-end loading, and mechanical stress improvement process(MSIP) loading. Finally, the results of residual stress redistributions for various loading conditions are compared and reviewed qualitatively and quantitatively to find an optimum loading condition.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2009.05a
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• pp.242-243
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• 2009

Friction stir welding and friction stir processing is a new solid state processing technique for ioining and micro..structural modification in metallic materials. It has been applied not only joining for light metals but also modification of the microstructure to enhance mechanical properties. In thin study, we investigated the mechanical properties for applied friction stir welding and processing under various parameters such as probe diameter, probe type, traveling speed and rotating speed for 5456-H116 AI allov. As a result of experiments, optimum condition of friction stir welding is traveling speed of 15mm/min, rotating speed of 500RPM at 6mm diameter probe. Moreover, in the case of friction stir processing, the optimum condition is traveling speed of 15mm/min, rotating speed of 250RPM at full screw probe. As above mentioned, the mechanical characteristics enhanced with the decreasing of traveling speed and the increasing of friction areas because of plastic flow due to high friction heat. These result can be used as reference data for ship repairment.

• Journal of Welding and Joining
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• v.11 no.1
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• pp.42-51
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• 1993

In this study, investigations were conducted in calculating parameters of elastic-plastic fracture mechanics using single specimen. The validity of these testing methods was judged by the confirmation of multiple specimen method of stop block test. The results were as follows: In order to measure a fracture toughness using the instrumented impact test, two general requirement must be considered; One, setting up proper impact velocity considered the effect of loading and the other, the necessity of low blow test for obtaining true energy by the compliance correction. It was possible to detect a crack initiation point by calculating the compliance changing rate from a load-defection curve. Criterion of a stable crack growth, $T_{mat}$ could be estimated by using key-curve method for a base metal. and combining Kaiser's rebound compliance with Paris-Hutchison's $T_{appl}$ equation for the brittled zone of welding heat affected.at affected.d.

• Proceedings of the KWS Conference
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• 2009.11a
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• pp.99-99
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• 2009

마그네슘은 지구상에서 존재하는 금속 중 가장 가벼운 실용화 금속이다. 따라서 최근 산업 전반적으로 대두되는 경량화에 대응하는 데 중요한 소재로 각광받고 있으며 그 활용이 활발하게 추진되고 있다. 본 연구에서는 이러한 동향에 대응하는 일환으로 POSCO에서 생산되고 있는 압연 마그네슘판재를 적용하였다. 적용 대상은 철도 분야의 경량화를 위한 전장품을 선정하고, 실물 크기로 제작하였다. 제작은 두께 3.5 mm 의 판재를 사용하였으며 용접은 Friction Stir Welding 및 GTAW 를 사용하였다. 그림1에 제작이 완료된 형상을 나타낸다. 그리고 제작중의 용접과정에 대하여 3차원 열탄소성 해석을 수행하여 변형 과정에 대한 검토를 수행하였다. 그림2에 해석과정의 한 예를 나타낸다.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.7 no.3
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• pp.68-78
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• 1998

Welding structure contains residual stress due to thermal-plastic strain during welding process, and its magnitude and distribution depend on welding conditions. Cracks initiate from various defects of the weldment, propagate and lead to final fracture, The crack initiation and propagation processes are affected by the magnitude and distribution. Therefore, the magnitude and distribution of weldment residual stress should be considered for safety design and service of welding structures. Also it is very important that more accurate assessment method of fatigue crack growth must take into account the redistributing the residual stress quantitively. because the residual stress in weldment has characteristics of its redistribution with loading magnitude, number of cycles and fatigue crack propagation. In this study fatigue crack behavior of STS-304 weldment was investigated during crack propagation into tensile residual stress region or compressive residual stress region. Crack growth rates were predicted and compared with experimental results.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.805-816
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• 2015

In the present study, external restraints imposed normal to the plate during the cooling stage were determined to be effective for reduction of the angular distortion of butt-welded or fillet-welded plate. A welding analysis model under external force during the cooling stage was idealized as a prismatic member subjected to pure bending. The external restraint was represented by vertical force on both sides of the work piece and bending stress forms in the transverse direction. The additional bending stress distribution across the plate thickness was reflected in the improved inherent strain model, and a set of inherent strain charts with different levels of bending stress were newly calculated. From an elastic linear FE analysis using the inherent strain values taken from the chart and comparing them with those from a 3D thermal elasto-plastic FE analysis, welding deformation can be calculated.

• Journal of Ocean Engineering and Technology
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• v.13 no.2 s.32
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• pp.66-73
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• 1999

This paper presents the experimental examinations and statistical quantitative analysis of the correlation between the cumulative counts of acoustic emission(AE) during plastic deformation periods of the welding and the tensile strength and other properties of the tube-to-tube welded joints of O.D. 30mm (I.D 18mm) nozzle steel. This is a new approach which attempts finally to develop real-time quality monitoring system for friction welding. And this study results in practical possiblility of real-time quality control more than 100% joint efficiency showing good weld no micro structural defects.