• Proceedings of the KWS Conference
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• 2009.11a
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• pp.24-24
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• 2009

현재 조선소를 비롯하여 각종 산업 전반적으로 기존의 SCR 용접기를 대체하여 용접품질이 우수한 인버터 용접기가 널리 사용되고 있는 실정이다. 그러나 기존 인버터 용접기의 전원은 Mono 타입으로 이루어져 있어 대용량 인버터 용접기의 경우 대용량 스위칭 소자가 요구되어 제조원가가 높다. 그리고 문제 발생 시 용접기의 사용이 불가능하게 된다. 개발된 단위모듈을 병렬로 연결하여 대용량 용접기를 구성하게 되면 제조원가를 절감할 수 있으며 병렬로 연결되어 단위 모듈에 문제가 발생하여도 계속적인 사용이 가능하고, 주 회로를 작은 용량으로 분산시켜 전력을 제어하므로 높은 에너지 효율을 가지게 된다. 또한 인버터 용접기의 가장 중요한 성능인 스위칭 주파수에 있어서도 기존의 인버터 용접기는 20kHz의 스위칭 주파수를 가지지만 본 기술은 낮은 전력을 병렬로 연결하여 대용량을 동시에 제어가능 하므로 약 70kHz의 고속제어가 가능하다. 본 연구에서는 개발된 용량 170A단위모듈을 병렬로 연결하여 단위모듈 집적형 인버터 아크용접기 510A, 680A급의 부하테스트 실시 및 기본출력특성에 대하여 실험하였으며, GMAW에서 ${\Phi}1.6$ 솔리드 와이어를 이용하여 두께 20t의 후판 맞대기 용접에 적용실험을 실시하였다. 그 결과 모든 전류영역에서의 부하특성 및 출력특성이 양호하게 나타났으며, 후판 맞대기 용접에서는 SAW에 버금가는 생산성과 용접특성을 얻을 수 있었다.

• Journal of Korean Society of Steel Construction
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• v.23 no.2
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• pp.137-146
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• 2011

In the fabrication of steel bridges, blast cleaning prior to painting is carried out on the steel members to clean the forged surface and to increase the adhesive property of the applied painting systems. The effect of blast cleaning on the fatigue strength improvement of the weld joints, however, is not clear. In this study, Almen strips and steel specimens were blast-treated, conforming to ten types of blast-cleaning conditions deducted from the blast-cleaning conditions of seven steel structure fabrication companies. The arc height, roughness, hardness, and compressive residual stress were measured before and after the implementation of the ten blast-cleaning methods, and the relationship between the blast conditions and the measured values was studied. The geometry of the weld toe and the compressive residual stress near the weld toe were also measured before and after the blast cleaning of the butt-welded joints, and fatigue tests were carried out on the butt weld joints. The test results showed that blast cleaning significantly increases the fatigue strength and limit.

• Journal of Korean Society of Steel Construction
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• v.10 no.3 s.36
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• pp.423-435
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• 1998

In this paper fatigue strength reduction of butt weld with penetration defect, which can be seen frequently in the steel bridge, was assessed quantitatively. S-N curves were derived and investigated through the constant amplitude fatigue test of fully or partially penetrated welded specimen made of SWS490 steel. The fracture mechanical method was applied in order to calculate the remaining fatigue life of the partially penetrated butt welds. The fatigue limit of the fully penetrated butt welds was higher than that of category A in AASHTO's fatigue design curves, and the slope of S-N curves with 5.57 was stiffer than that of other result for welded part generally accepted as 3. The fatigue strength of the partially Penetrated butt weld was strongly influenced by the size of lack of penetration, D. It decreased drastically with increasing D from 3.9 to 14.7mm. Fracture behaviour of the partially penetrated butt weld is able to be explained obviously from the beach mark test that a semi-elliptical surface crack with small a/c ratio initiates at a internal weld root and propagates through the weld metal. To estimate the fatigue life of the partially penetrated butt weld with fracture mechanics, stress intensity factors K of 3-dimensional semi-elliptical crack were calculated by appling finite elements method and fracture mechanics parameters such as C and m were derived through the fatigue test of CT-specimen. As a result, the fatigue lives obtained by using the fracture mechanical method agreed well with the experimental results. The results were applied to Sung-Su bridge collapsed due to penetration defects in butt weld of vertical member.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.461-466
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• 2013

This paper examines the characteristics of butt welding joint shrinkage for shipbuilding and marine structures main plate. The shrinkage strain of butt welding joint which is caused by the process of heat input and cooling, results in the difference between dimensions of the actual parent metal and the dimensions of design. This, in turn, leads to poor quality in the production of ship blocks and reworking through period of correction brings about impediment on improvement of productivity. Through experiments on butt welding joint's shrinkage strain on large structures main plate, the deformation of welding residual stress in the form of I, Y, V was obtained. In addition, the results of experiments indicate that there is limited range of shrinkage in the range of 1 ~ 2 mm in 11t ~ 21.5t thickness and the effect of heat transfer of weld appears to be limited within 1000mm based on one side of seam line so there was limited impact of weight of parent metal on the shrinkage. Finally, it has been learned that Shrinkage margin needs to be applied differently based on groove phenomenon in the design phase in order to minimize shrinkage.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.1
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• pp.47-54
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• 2013

This study investigates the crack growth behavior due to primary water stress corrosion cracking (PWSCC) in the dissimilar metal butt weld of a reactor piping using Alloy 82/182. First, detailed finite element stress analyses were performed to predict the stress distribution of the dissimilar metal butt weld in which the hydrostatic and the normal operating loads as well as the weld residual stresses were considered to evaluate the stress redistribution due to mechanical loadings. Based on the stress distributions along the wall thickness of the dissimilar metal butt weld, the crack growth behavior of the postulated axial and circumferential cracks were predicted, from which the crack growth diagram due to PWSCC was proposed. The present results can be applied to predict the crack growth rate in the dissimilar metal butt weld of reactor piping due to PWSCC.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.1091-1092
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• 2013

• Proceedings of the KWS Conference
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• 2000.04a
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• pp.139-143
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• 2000

Laser beam weldability of Zircaloy-4 was investigated using a pulsed Nd:YAG laser of 550W average power. Mechanical properties and microstructure of laser butt welded Zircaloy-4 test specimens were examined. The influence of laser generated during laser welding was analyzed and optimum laser welding parameters were investigated.

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.20-22
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• 2006

• Proceedings of the KWS Conference
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• 2006.10a
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• pp.98-100
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• 2006

• Proceedings of the KWS Conference
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• 2003.11a
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• pp.200-203
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• 2003

The purpose of this paper is to investigate the influence of weld bead profiles on stress concentration factors (K$\sub$t/). We evaluated K$\sub$t/ by varying three parameters such as toe radii, flank angles and bead heights. The three parameters have similar effects on K$\sub$t/.