• Journal of Welding and Joining
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• v.21 no.1
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• pp.66-71
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• 2003

The release of residual stress by mechanical loading and unloading is often performed in the fabrication of box structure fur steel bridge. The proper degree of loading and unloading is significant at release method of residual stress by mechanical loading because that degree is changed by material and geometric shape of welded structure. Therefore, the simulation model that could exactly analyze the release of residual stress by mechanical loading is to be necessary. In this study, the non-linear behavior of weldments under external loading and unloading, such as the decrease and increase of structure stiffness, was investigated by monitoring of nominal stress and strain. Tensile loading and unloading test and the proper degree of stress relaxation was measured by sectioning technique using strain gauge. Analysis model that is indispensable for the effective application of MSR method was established on the basis of test and measurement result.

• Journal of Welding and Joining
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• v.19 no.6
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• pp.652-657
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• 2001

To analyze and predict crack initiation position and propagation directions on the spot welded area are very important for strength design of the automobile body structure. It is necessary to test by method considering random loads with variable amplitude for strength design of vehicle body structure, because driving cars are actually subjected to random loads with variable amplitude in the road. Although this condition, nearly all tests haute been performed under constant load conditions in the laboratory because it is impossible to replay like an actual conditions. In this study, using in-plane bending type specimens, the overload factor affecting on the fatigue strength, crack initiation and propagation directions of spot-welded specimens have been studied.

• Journal of Welding and Joining
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• v.29 no.3
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• pp.70-75
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• 2011

Welding process generates distortion and residual stress in the weldment due to rapid heating and cooling. Welding distortion and residual stress in the welded structure result in many troubles such as dimensional inaccuracies in assembling and safety problem during service. The accurate prediction of welding residual stress is thus very important to improve the quality of weldment and find the way to reduce itself. This paper presents the simulation of welding-induced residual stress analysis to examine the cause of cracking in the SUS-overlay welding specimen at FPSO Moon Pool structure.

• Journal of Welding and Joining
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• v.8 no.3
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• pp.79-88
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• 1990

Welded joint often contains soft or softened regions such as the HAZ of TMCP steel welded with high heat input. In this study, the equivalent yield strength of plate structure containing softened region was predicted by FEM analysis, and its incremental behavior was explained with the results of the analysis. The calculated results of yield strength indicated the following for the plate structures. 1) As the softened region starts to yield, shear stress begins to build up along the boundary between base metal and softened region. This results in multi-axial stress condition which gives restraint on the softened region. 2) Restraint effect has a significant influence on the distribution of the shear stress, the nominal stress, and the strain. 3) The yielding behavior of softened region becomes the same as that of base metal when both ratios of length to width and thickness to width of softened region are larger than 30 and 13 respectively.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.58-63
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• 2010

The purpose of this study is to develop improved boom structures with reliable fatigue strength of weldment and lower production cost. For that purpose, multibody dynamic analysis was performed to evaluate forces acting on arm & boom cylinders and joints of boom structure during operation of an excavator for three working postures, then stress analysis was made to investigate stress distribution around diaphragms at the bottom plate of boom structures which was known to be susceptible to fatigue failures of welded joints, and finally boom structure with optimum arrangement of diaphragms was proposed. This work basically consists of the following two parts: part 1 focuses on multibody dynamic analysis of excavators during operation and part 2 includes evaluations of fatigue strength of welded joints for modified boom structures.

• Journal of Welding and Joining
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• v.17 no.6
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• pp.78-83
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• 1999

Solder joint is the weakest part which connects in mechanically and electronically between package body and PCB(Printed Circuit Board). Recently, the reliability of solder joint become the most critical issue in surface mounted technology. The solder joint interconnection between plastic package and PCB is susceptible to shear stress during thermal storage due to the mismatch in coefficient of thermal expansion between plastic package and PCB. A general computational approach to determine the effect of solder joint shape on the fatigue life presented. The thermal fatigue life was estimated from the engelmaier equation which was obtained from the temperature cycling loading($-65^{\circ}C$ to $150^{\circ}C$). As result of the simulation, TSOP structure has the shortest thermal fatigue life and the same structure Copper lead has 2.5 times as much fatigue life as Alloy 42 lead. In BGA structure, fatigue life time extended 80 times when underfill material exists.

• Journal of Welding and Joining
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• v.20 no.3
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• pp.98-104
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• 2002

A study on microstructures of welds for Zircaloy-4 sheath end closure by the resistance upset welding methods was carried out. Two upset welding process variations such as magnetic farce and multi-impulse resistance welding were used. Grain size and microhardness across welds were analysed in terms of welding parameters. Magnetic farce resistance weld with one cycle of unbalanced mode has smaller upset length and $\alpha-grain$ size in heat affected zone than those of multi-impulse resistance weld because of lower heat input and shorter welding time. Heat affected zone formed by two upset resistance welding variations revealed fine Widmanstatten structure or martensitic ${\alpha}'$ structure due to the high heating rate and foster cooling rate. Magnetic force resistance welds showed recrystallized grains before grain growth, whereas multi-impulse resistance welds showed full grain growth.

• Journal of Welding and Joining
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• v.14 no.4
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• pp.79-88
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• 1996

For improvement in productivity and weld quality, weld seam tracking and welding parameter control are very essential in the welding of a structure which can not be cxactly fit-up due to mismatch, discontinous gap, deflection, etc.. In this study, an automatic weld seam tracking system is developed for I-butt joint structure, and the system consists of XYZ working table, vision sensor and user interface program. In the developed vision sensor system, an image projection algorithm for weld-line detection and an adaptive current control algorithm for gap variation were implemented. The user interface program developed in this study by basing on the objct oriented concept could provide very convenient way to utilize the tracking system with the pull-down menu driven structure. The developed system showed a good seam tracking and weld quality control capability corresponding to deflected weld lines and gap variations.

• Journal of Welding and Joining
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• v.29 no.2
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• pp.40-45
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• 2011

The purpose of this study is to establish the optimum line heating condition to straighten the excessive bending distortion of a thin plate welded structure. For it, the extensive FEA and experiments were performed to evaluate the effect of heat source, heating speed and position on the straightening of a thin plate welded structure. In accordance with the results obtained by FEA and experiments, the straightening effect of line heating was strongly depends on the variables used in this study. With the results, the optimum line heating condition was established by using the response surface method and verified through comparing it with the numerical analysis result.

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.274-277
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• 1998